Multistep non-cyanide leach processing for metal recovery

Abstract

A process of leaching precious metal from a feed source in a multi-step process contacts comminuted ore with a diluted solution of a chloride source and soaks for at least 10 minutes; adds a second source of chloride to the solution, preferably by dissolution of a chloride source, for a contact time of at least 1 hour; adds a reducing agent, preferably an acid source such as HCl, to initiate a leaching process; holds for a contact time of at least 1 hour, preferably between 1 to 24 hours; adds an indifferent salt to complete the leaching process; and recovers a metal. The process is optionally cyanide and arsenic free. Such processes are suitable for large scale operations with high solids loading in the liquid-solids separation operations.

Description

PatentAttorney Docket No. 134465-5028-WOMULTISTEP NON-CYANIDE LEACH PROCESSING FOR METAL RECOVERYCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based on and claims the benefit of priority to U.S. Provisional Application No. 63 / 679,387, filed August 5, 2024, the entire disclosure of which is hereby incorporated by reference.TECHNICAL FIELD

[0002] The present disclosure relates to recovering one or more metals from rock, ore, waste materials, etc. by leaching comminuted or crushed feed materials with leaching reagents in a continuous and integrated multistep leaching and metal recovery process in which oxidantreduction agents are combined to have a more efficient and economic metal recovery process. In the first steps, the oxidant leaching solution prepared using one or more chloride sources is mixed with the ore and then the reduction leaching solution is added to the slurry to complete the metal extraction process. Then an indifferent salt, preferably a chloride salt, which improves leach performance through improved dissolution as well as recovery of a pregnant solution from the leach residue solids is added. The process is cyanide free and / or arsenic free. The leaching solutions create an oxidation-reduction environment capable of recovering a broad spectrum of metals, including precious metals like gold, silver, platinum, and palladium, rare earth elements, such as cerium, dysprosium, erbium, europium, gadolinium, holmium, lanthanum, lutetium, neodymium, praseodymium, promethium, samarium, scandium, terbium, thulium, ytterbium, and yttrium, as well as base metals such as copper, nickel, cobalt, tin, and lead. Additionally, other valuable metals such as lithium, aluminum, antimony, magnesium, and manganese can be leached using this method. The disclosed processes can be implemented to treat various feed materials including, for example tailings from, mining and resources extraction, mining waste, industrial waste such as coal ash, dredging spoils, etc.DB1 / 161304616.2 1PatentAttorney Docket No. 134465-5028-WOBACKGROUND

[0003] For decades, the mining industry has relied on cyanide leaching as the standard method for extracting precious metals, including gold, silver, and platinum group metals (PGMs) - platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), and osmium (Os) - from mineral ores. This process has proven highly effective for simple oxide minerals, which can be readily processed through basic cyanidation techniques. However, the landscape of metal extraction has become increasingly challenging as ore bodies grow more complex. In particular, when precious metals are found in association with sulfide minerals such as pyrite and arsenopyrite, the efficiency of cyanide leaching drops dramatically. This decrease in effectiveness is primarily due to the refractory nature of these sulfide minerals, which resist conventional leaching methods. As a result, gold recovery rates from sulfide ores or concentrates often fall below 40%, rendering the cyanidation process economically unviable for these types of gold- bearing materials. This limitation has spurred the search for alternative extraction methods better suited to complex, refractory ores.

[0004] The cyanide consumption increases when the refractoriness of the gold ore is increased. A refractory gold ore is a gold-containing ore that is resistant to recovery by direct cyanidation. Other minerals and metals are also dissolved in the alkaline cyanide solution, and they usually consume cyanide and oxygen and thus reduce

[0005] Problems which occur during the cyanidation of ore to recover gold and silver include locking of precious metals so that cyanide solutions cannot penetrate and dissolve the precious metals; the existence, or formation during leaching, of strongly adherent films on the surface of native gold and silver, inhibiting or preventing further dissolution of the metals; high cyanide consumption which is often accompanied by high lime consumption; long leach times required because of very slow reaction of precious metal minerals with cyanide; leach solution fouling, rendering it inactive for precious metal dissolution and often causing difficulties in metal precipitation from pregnant solution; readsorption or reprecipitation of precious metal from solution after initial dissolution; and toxic arsine gas formation on precipitating precious metal from pregnant solution.

[0006] The cyanide leaching process is further constrained by significant environmental and safety concerns. A major issue is the potential formation of hydrogen cyanide, an extremelyDB1 / 161304616.2 2PatentAttorney Docket No. 134465-5028-WO toxic gas that poses severe risks to human health and the environment. This danger necessitates stringent safety protocols and specialized handling procedures. Moreover, the acidic treatment of solid residues from cyanide leaching is generally avoided due to the risk of generating additional hydrogen cyanide. Despite efforts to implement recycling and other mitigation strategies, cyanide- based extraction inevitably produces substantial quantities of toxic solid waste and contaminated liquids. The safe disposal of these hazardous byproducts presents a considerable challenge, requiring complex and costly measures to ensure environmental compliance. These factors not only increase operational expenses but also raise serious environmental and ethical concerns, prompting the industry to seek more sustainable and less hazardous alternatives for metal extraction.

[0007] The search for viable alternatives to cyanide in gold leaching has intensified in recent years, driven by the pressing need to address the severe toxicity and environmental hazards associated with cyanide-based processes. This quest has led to significant advancements in the field of hydrometallurgy, with several promising alternative lixiviants emerging as potential replacements. Notable among these reported leaching reagents are thiosulfate, thiocyanite, thiourea, and chloride in combination with an oxidizing agent like HN03, H2O2 and hypochlorite.

[0008] In the quest for more environmentally friendly and efficient metal extraction processes, researchers have investigated various alternative leaching methods. Among these, thiosulfate leaching has emerged as a promising candidate. This technique offers several advantages over traditional cyanide leaching. Thiosulfate exhibits significantly lower toxicity compared to cyanide, addressing one of the primary concerns associated with conventional leaching methods. The process demonstrates improved selectivity for Platinum Group Metals (PGMs), potentially leading to more efficient recovery of these valuable elements. Thiosulfate leaching can be conducted under less extreme conditions than cyanide leaching, potentially reducing energy requirements and equipment wear. For certain types of refractory ores that resist conventional cyanide leaching, thiosulfate has shown enhanced effectiveness, potentially expanding the range of economically viable ore bodies.

[0009] These characteristics make thiosulfate leaching an attractive option for the mining industry, particularly in scenarios where environmental concerns are paramount or when dealing with complex, refractory ores that yield poor results with traditional methods. However, it isDB1 / 161304616.2 3PatentAttorney Docket No. 134465-5028-WO important to note that while promising, this technique may still have limitations and its applicability can vary depending on the specific mineralogy of the ore being processed.

[0010] Oxidative pre-treatment has been explored such as Roasting: Converting sulfides to oxides before leaching can improve metal recovery and Pressure oxidation: Using autoclaves to oxidize sulfides under high pressure and temperature.

[0011] Roasting is a process that involves heating the ore to high temperatures in the presence of air or oxygen. The primary objective is to convert sulfide minerals into more readily leachable oxide forms. The typical temperature range: 500-700°C is looking for the conversion of sulfides to oxides, which are generally more amenable to leaching. Potential for simultaneous removal of other impurities (e g., arsenic, antimony). Can significantly improve gold recovery from refractory ores. Considerations include energy costs and potential environmental impacts from sulphur dioxide emissions.

[0012] Pressure Oxidation utilizes autoclaves to create a high-temperature, high-pressure environment for oxidizing sulfide minerals. Typical conditions: 180-225°C, 1500-3200 kPa oxygen overpressure, under that operating conditions the methodology shows a highly effective at breaking down sulfide mineral structures. Can achieve near-complete oxidation of sulfides, resulting in excellent metal liberation. Pressure oxidation operates in a closed system, potentially offering better control over emissions compared to roasting. Generally, more capital-intensive but can be more environmentally friendly than roasting.

[0013] Both methods aim to overcome the limitations of conventional leaching by altering the ores mineralogy to make valuable metals more accessible. The choice between roasting and pressure oxidation depends on various factors, including ore composition, economic considerations, and environmental regulations. These pre-treatment techniques, when combined with appropriate leaching methods, can significantly enhance metal recovery from complex, refractory ores that are otherwise resistant to conventional extraction processes.

[0014] In the ongoing quest to improve metal extraction from complex ores, researchers and industry experts have investigated multifaceted approaches that combine different techniques. These integrated methods aim to leverage the strengths of various processes to achieve superior metal recovery. The two more relevant are the two-stage leaching and the Roast-Leach process.DB1 / 161304616.2 4PatentAttorney Docket No. 134465-5028-WO

[0015] Two-stage Leaching involves a sequential application of different leaching agents to maximize metal extraction. A typical example includes a first stage where the ore is treated with dilute sulfuric acid to dissolve easily leachable components. Another objective of the first step is help remove interfering elements or gangue minerals. In the second stage, a strong oxidative leaching using hydrochloric acid (HC1) is carried out. The targets are the more resistant mineral phases utilize the oxidizing power of chloride systems to enhance metal dissolution. Benefits of this approach include: a) Improved overall metal recovery, b) Potential for selective extraction of different metals in each stage, c) Reduction of reagent consumption compared to single-stage processes.

[0016] Roast-leach procedures combine an approach that integrates thermal pre-treatment with subsequent hydrometallurgical extraction. Thermal pre-treatment (roasting) is typically conducted at temperatures between 500-700°C to convert sulfides and other refractory minerals to more leachable forms and also eliminate volatile impurities. After that, the material is leached using the appropriate lixiviants based on the roasted ore characteristics, which can be conventional or novel leaching agents. Advantages of this method include a) Enhanced metal liberation and recovery, especially for refractory ores, b) Potential for improved selectivity in metal extraction, and c) Reduction in reagent consumption during the leaching stage.

[0017] These combined approaches demonstrate the industry's move towards more sophisticated, tailored processes for metal extraction. By integrating multiple techniques, these methods can address the complexities of various ore types, potentially improving both the economic viability and environmental sustainability of metal recovery operations. However, the specific combination and parameters must be determined for each ore type to ensure maximum effectiveness and efficiency.

[0018] Chloride-based leaching has emerged as another promising alternative in metal extraction processes, offering a versatile approach to recovering a diverse array of metals. This method has demonstrated effectiveness in leaching both precious and base metals, making it a valuable tool in the field of hydrometallurgy. Unlike some more selective leaching methods, chloride-based systems can effectively dissolve and extract a wide range of metals. This includes precious metals such as gold, silver, and platinum group metals (PGMs), as well as base metals like copper, nickel, and zinc. Under desirable conditions, chloride leaching can achieve highDB1 / 161304616.2 5PatentAttorney Docket No. 134465-5028-WO dissolution rates for many metals, potentially leading to improved overall recovery rates. The presence of chloride ions can enhance the solubility of certain metal complexes, facilitating their extraction from ore matrices. Chloride-based leach solutions are often well-suited for subsequent electrowinning processes, allowing for efficient metal recovery from the solution. The chloride- baes leaching requires carefully controlling parameters such as chloride concentration, pH, and redox potential, it may be possible to selectively leach certain metals over others.

[0019] Chlorine oxidation of ore, while effective for precious metal extraction, presents several significant challenges. For instance, in the presence of high sulfide content, chlorine consumption increases. Sulfide oxidation produces sulfuric acid, necessitating lime for neutralization, which results in increased overall reagent costs. Chlorine's non-selective nature dissolves various ore constituents, leading to contamination of the leach solution and complicating subsequent precious metal precipitation processes. Additionally, chlorine dissolves base metals present in the ore. These dissolved base metals can precipitate during zinc cementation, interfering with the recovery process and affecting product purity. The presence of co-extracted base metals in the precipitate can potentially impact the final product's quality and value. While this method can be effective, especially for certain refractory ores, these challenges necessitate careful process design and control to ensure both efficiency and economic viability. Modem hydrometallurgical approaches have since evolved to address some of these issues, but the fundamental challenges remain relevant considerations in process development for complex ores.

[0020] However, it is important to note that chloride-based leaching also presents certain challenges, including potential corrosion issues with processing equipment and the need for careful control of process conditions. Despite these considerations, the versatility and effectiveness of chloride-based leaching make it a significant area of interest for researchers and industry professionals seeking to improve metal extraction processes, particularly for complex or low-grade ores.

[0021] These developments reflect the industry's commitment to innovation in the face of evolving challenges. By pursuing more sustainable, efficient, and economically viable extraction methods, the sector aims to meet the growing global demand for metals while minimizing environmental impact and maximizing resource utilization. This ongoing research andDB1 / 161304616.2 6PatentAttorney Docket No. 134465-5028-WO development effort is needed for the future of the mining and metallurgical industries, particularly as they grapple with lower-grade ores and more complex mineralogies.

[0022] The metal extraction industry is significantly transforming, driven by several key factors. A growing imperative is to develop and implement more environmentally benign leaching methods. This shift is motivated by: a) Stricter environmental regulations, b) Corporate sustainability goals and c) Public pressure for greener mining practices. These eco-friendly approaches aim to reduce toxic emissions, minimize water consumption, and decrease the overall environmental footprint of metal extraction processes.

[0023] Most of the companies are looking for emerging technologies. The sector is witnessing a surge in research and development activities focused on innovative leaching methods and pre-treatment processes, looking to improve metal recovery from refractory ores by developing more selective leaching agents and reducing the energy consumption in extraction processes minimizing waste generation and improving waste management.

[0024] Some mining companies are focusing on refractory ores mainly due to the easily accessible ore deposits becoming depleted, there is an increasing emphasis on extracting metals from complex, refractory ores.

[0025] These developments reflect the industry's commitment to innovation in the face of evolving challenges. By pursuing more sustainable, efficient, and economically viable extraction methods, the sector aims to meet the growing global demand for metals while minimizing environmental impact and maximizing resource utilization. This ongoing research and development effort is needed for the future of the mining and metallurgical industries, particularly as they grapple with lower-grade ores and more complex mineralogies.

[0026] The metal-containing materials are typically comminuted or crushed before leaching to increase surface area and improve metal recovery.

[0027] Alternative lixiviants to cyanide were discussed by M. G. Aylmore at the World Gold Conference in Montreal in 2011, as part of the Conference of Metallurgists. The alternatives include halide-based systems such as chlorine, bromine, and iodine. The combination of 5M hydrochloric acid with oxidizing agents (chlorine or chloride electrolyte) was also considered, though information on leaching with regenerated hydrochloric acid was limited. Other oxidants explored included oxygen, nitric acid, and ferric chloride, mainly for high-grade concentrates andDB1 / 161304616.2 7PatentAttorney Docket No. 134465-5028-WO often as pre-treatment before cyanide leaching. However, these alternatives lacked suitable recovery processes compared to cyanide extraction. Thiosulfate leaching has been effective for copper-gold and carbonaceous ores, where cyanide yields poor gold recoveries. While these alternative methods show promise in addressing specific challenges in gold extraction, especially for ores that respond poorly to conventional cyanide leaching, their widespread adoption has been hindered by limitations in recovery processes and the need for further development to match the efficiency of cyanide-based methods.

[0028] Chloride / hypochlorite solutions are an alternative leaching reagent to cyanide for gold extraction. These solutions can dissolve gold across a wide pH range, making them more versatile than cyanide. The solution's pH determines the dominant oxidizing species:• pH > 7.5: Hypochlorite ion (OC1-) is predominant.• pH 3.5-7.5: Hypochlorous acid (HOC1) is the main oxidizing agent.• pH < 3.5: Molecular chlorine (CI2) evolves at low pH.Among these species, hypochlorous acid (HOC1) is identified as the most effective for gold leaching. HOC1 facilitates the formation of the gold chloride complex [AuCh]-. It is potentially less toxic than cyanide, effective across a broader pH range, and may be suitable for ores that respond poorly to cyanide leaching. However, the effectiveness may vary depending on ore mineralogy. Proper pH control is used to maintain the desired oxidizing species. Chloride-based systems can be corrosive, requiring appropriate materials for processing equipment. They may be particularly useful for refractory ores or those with high copper content and could be an option for environmentally sensitive areas where cyanide use is restricted. While promising, more research is needed to improve the process for various ore types. Scale-up and industrial implementation studies are necessary to assess its viability as a widespread cyanide alternative. This chloride / hypochlorite leaching system represents one of several promising alternatives to cyanide in gold extraction. Its ability to operate effectively across a wide pH range and its potentially lower toxicity makes it an interesting option for further development in the field of hydrometallurgy.

[0029] In some embodiments, the process may include electrolysis of a saline source to generate the chloride-based leaching solution that contains hypochlorous acid (HOC1). During electrolysis, chlorine gas (CI2) evolves at the anode (bubbles form), hydrogen gas (H2) evolves at the cathode (bubbles form), and HOG forms in the solution when the pH is controlled betweenDB1 / 161304616.2 8PatentAttorney Docket No. 134465-5028-WO5.5-6.5. Hydrochloric acid or sodium hydroxide may be used to control the pH to the desired range. An example of the electrolytic process is illustrated in FIG. 5. The saline source may include filtered seawater (natural or artificial), a made-up solution that includes sodium chloride, or a rejected stream from a desalination process or a combination of such saline sources.

[0030] In some embodiments, the saline source includes a rejected stream from a desalination process. The rejected stream is the portion of the incoming feedwater that is not converted into fresh water and is instead discharged because it contains elevated concentrations of salts and other impurities than the original feedwater. In some embodiments, the rejected stream may include sodium chloride at a concentration of 70 g / L to 300 g / L. Repurposing the rejected stream may reduce the volume of waste to be discharged, making final disposal more manageable and environmentally friendly. For example, electrolysis of the rejected stream may generate the chloride-based leaching solution and / or active chloride species for leaching.

[0031] Despite considerable efforts to replace cyanide, none of the reported leaching reagents have been used in the industrialization of gold production due to drawbacks such as (i) high reagent consumption, (ii) complex chemistry, (iii) lack of industrial techniques for gold recovery from resulting solutions, and (iv) lower gold recovery rates compared to cyanide. Other issues include toxicity, cost, long reaction times, and poor selectivity. Therefore, developing more effective leachants with higher efficiency and / or lower toxicity is desirable from both an environmental and economic perspective.

[0032] Although cyanide remains the primary leaching reagent for gold recovery in the mining industry, it has several drawbacks, including high toxicity, slow leaching kinetics, and low gold extraction for refractory ores. Considerable efforts have been made to find alternatives to cyanide. There is a growing trend toward more environmentally friendly leaching methods, and it is clear that the economic viability of a process depends on metal prices, recovery rates, and processing costs. The industry is seeking emerging technologies focusing on new leaching methods and pre-treatment processes to improve recovery from refractory ores. While cyanide leaching remains important, the industry is actively developing and implementing alternative methods to address the challenges posed by complex, refractory sulfide ores. The choice of method depends on specific ore characteristics, economic considerations, and environmental regulationsDB1 / 161304616.2 9PatentAttorney Docket No. 134465-5028-WOSUMMARY OF THE DISCLOSURE

[0033] A continuous and integrated multistep leaching and metal recovery process is disclosed, in which oxidant-reduction agents are combined to have a more efficient and economic metal recovery process. In the first steps, the oxidant leaching solution prepared using one or more chloride sources is mixed with the ore and then the reduction leaching solution is added to the slurry to complete the metal extraction process. Then an indifferent salt, preferably a chloride salt, which improves leach performance through improved dissolution as well as recovery of a pregnant solution from the leach residue solids is added. The process is cyanide free and / or arsenic free.

[0034] The invention involves a two-step interchangeable leaching process that combines an oxidizing agent and a reducing agent to extract gold, silver, and other precious metals from ores.

[0035] The present invention outlines a continuous and integrated multistep leaching and metal recovery process, combining oxidizing and reducing agents to achieve a more efficient and economical metal recovery process.

[0036] The sequence in which the oxidizing and reducing agents are combined will minimize reagent consumption and allow for more stable control of operational parameters.

[0037] The method employs a unique chloride source or a combination of various chloride sources to create a primary leaching solution. This disclosure pertains to a method for recovering one or more metals using a unique chloride source or a combination of different chloride sources within an acidic environment

[0038] Accordingly, the present application describes a method for leaching and extracting gold, silver, and / or palladium from a substance containing these metals. The process involves a mixture with an aqueous phase that includes an oxidizing agent and an acid agent

[0039] In the first stage of this process, a primary oxidative leaching solution is mixed with the ore in two separate steps to maximize the oxidation process. A specific time is allowed between the first and second addition of the oxidative leaching solution.

[0040] In the second step of this continuous process, an acid trigger is added to the slurry undergoing leaching. The acid initiates chemical reactions to break down various ores to release the trapped gold. The process does not function efficiently without small yet effective amounts of acid in the hypochlorite leach solution.DB1 / 161304616.2 10PatentAttorney Docket No. 134465-5028-WO

[0041] The advantage of the present disclosure is the combined improvement of both the leach dissolution and subsequent pregnant solution recovery from the residue solids.

[0042] The advantages of the present disclosure result in increased leach rates due to increased ionic activity in the leach. These and other advantages are satisfied, at least in part, by a process of leaching a metal in a leach medium including a leaching reagent and indifferent salt to increase the leach rate.

[0043] Chloride-based leaching solutions are a well-established technique in hydrometallurgy, particularly effective for certain metals when used with reducing agents. Creating an oxidation-reduction environment is essential for efficient metal recovery, enhancing the solubility and extraction of various metals, especially in the case of sulfide ores or complex materials

[0044] Lixiviants, extractants, and other materials used in the process can be recovered and recycled. This gold leaching and recovery process does not involve cyanidation, thereby avoiding the environmental and other hazards associated with cyanide use. High levels of gold extraction and recovery can be achieved by enhancing the solid-liquid separation steps.

[0045] This invention successfully eliminates the use of cyanide compounds for gold leaching from ore. The improved method is highly effective at temperatures below the boiling point of water and requires the ore to be in contact with the leach solution for only relatively short periods.

[0046] Fine grinding of the ore is desirable as it promotes rapid interaction between the precious metal compounds within the ore matrix and the chemicals in the leach solution.

[0047] To simultaneously extract gold, silver, and other precious metals from ores, the process conditions are adjusted to ensure that comminuted ore is first contacted with a primary leach solution and then with an acidic secondary leach solution

[0048] In the present invention, various methods were employed to supply a potent oxidizing agent, using chloride sources to prepare the oxidative leaching solution.

[0049] One or two sources of chloride such as sodium chloride (NaCl), calcium hypochlorite (Ca(OCl)2), a source of sodium hypochlorite (NaClO), such as commercial bleach, sodium dichloro-s-triazinetrione dihydrate (ChH-iCLNsNaOs), anhydrous sodium dichloro-s-DB1 / 161304616.2 11PatentAttorney Docket No. 134465-5028-WO triazinetrione (C CENiNaCF), trichloro-s-triazinetrione (C3CI3N3O3), and FeCI are combined to create an oxidative leaching solution.

[0050] The selected chloride source can be dissolved in water to provide the required chloride concentration in the primary leaching solution and then the leaching solution is contacted with ore to obtain a slurry with a solid concentration from 8 to 50 %, preferably 10 to 35 %.

[0051] Optional the selected chloride sources can be added directly to the slurry with ore to obtain a solid slurry concentration from 8 to 50 %, preferably 10 to 35 %.

[0052] The oxidant for the leaching process can be generated by several methods, including industrial electrolysis of salt solutions or brines from a natural body of water such as seawater. These methods allow chlorine to be generated efficiently, even from seawater sources, which are readily available in many coastal areas. The most common method of producing chlorine involves the electrolysis of aqueous solutions (e.g., brine) containing sodium chloride (NaCl). In an electrolysis cell, chlorine gas (CI2) is produced at the anode, while hydrogen gas (H2) and sodium hydroxide (NaOH) are produced at the cathode. Impurities in seawater such as magnesium and calcium can interfere with the electrolysis process and may require purification steps. Before electrolysis, the brine (seawater, or saltwater solution) may be purified to remove impurities that may interfere with the electrolysis process. Purification may involve: (i) filtration: removes insoluble particles (sand, dirt, etc.) from the brine, (ii) precipitation of impurities: calcium and magnesium ions in seawater can form insoluble salts, so they are removed by chemical precipitation (for example, lime (CaO) can be added to remove calcium as calcium carbonate (CaCOs), (iii) ion exchange (one preferred purification method in this application): an ionexchange process may be used to remove specific ions from the brine, particularly in seawater processing, and (iv) membrane filtration - membranes such as microfiltration (MF), ultrafiltration (UF), or nanofiltration (NF) can be employed to remove fine particles, organic matter, and divalent ions like calcium and magnesium.

[0053] In the first part of the process, the oxidant leaching solution is in contact with comminuted ore. The oxidative leach solutions also preferably contain a secondary source of chloride, such as water soluble salt. Enough of a base, such as sodium chloride, is added to the primary leach solution.DB1 / 161304616.2 12PatentAttorney Docket No. 134465-5028-WO

[0054] In aqueous solution, the hypochlorite ion (CIO ) is unstable and tends to undergo disproportionation into chloride (CP) and chlorate (CICh ) ions, especially when heated. Due to this instability, it may be advantageous to use alternative oxidizing agents in the leach solution. Water-soluble oxidants such as metal chlorates (e.g., sodium chlorate), chlorites, or chlorine dioxide can be added directly to provide similar oxidative potential. These compounds can serve as effective substitutes for hypochlorite, delivering equivalent redox chemistry in situ without relying on unstable hypochlorite solutions.

[0055] In this first step, the secondary supplementary chloride source containing the same key chemical components as the primary leach solution is a base and preferably has a pH of 7-12.

[0056] The order of the addition of the chloride source as part of the initial leaching solution can be changed without impacting the leaching process

[0057] After the ore and oxidant leaching solution have been in contact for 0.5 to 3 hours the secondary reductive leaching solution is added directly to the slurry.

[0058] The acid leaching solution is added to the slurry, acting as a catalyst to initiate the reaction between the leach solution and the ore. The preferred catalyst is hydrochloric acid, though hypochlorous, chloric, and other oxy-acids of chlorine can also be used, as well as sulfurous and hydrosulfuric acids. Hydrogen sulfide can also be utilized because it reacts with chlorides to form hydrochloric acid in situ.

[0059] As earlier noted, the primary leach solution is basic and preferably has a pH in the range of 7-11. To reduce the pH of the leach solution to the range of 4-7, hydrochloric acid, or any other acid may be utilized which does not precipitate metal from the solution.

[0060] The present invention asserts that the balance of different chloride species affects the amount of chloride consumed during leaching. Leaching can be performed as a co-current, countercurrent, or alternative process, and is most conveniently conducted at atmospheric pressure — pressurization is not necessary. The leaching process is carried out at temperatures ranging from ambient up to the boiling point of the leaching solution, with a preferred range of 25- 40°C. The oxidation-reduction potential (ORP) should be at least 900 mV, p between 1020-1100 mV. The chloride concentration in the solution is preferably at least 100 g / L, with a typical range of 200-300 g / L, and can vary within specific ranges as needed. Hydrochloric acid in the lixiviant should not exceed a 20% mass ratio, with a preferred concentration of at least 10% and preferablyDB1 / 161304616.2 13PatentAttorney Docket No. 134465-5028-WO14-18% mass ratio, such as 2-4M. The chloride concentration in the lixiviant is most effective in the 1-400 g / L range, preferably 100-400 g / L range, particularly 200-300 g / L.

[0061] Some embodiments of the present disclosure relate to enhancing metal leaching by adjusting certain ratios. A first ratio (Rl) is the acid-to-ore ratio, expressed as a mass percentage (m / m), which may be within a range of 0.1 to 2.0, 0.2 to 1.9, 0.3 to 1.8, 0.4 to 1.7, 0.5 to 1.6, or preferably 1 to 1.8 or 1 to 1.5. A second ratio (R2) is the chloride salt-to-ore ratio, also expressed as a mass percentage (m / m), which may be within a range of 0.1 to 4.0, 0.2 to 3.8, 0.4 to 3.6, 0.6 to 3.4, 0.8 to 3.5, 1 to 3.3, 1.5 to 3.1, or preferably 0.75 to 2.5 or 2 to 3. The inventors found that maintaining a ratio of Rl to R2 between 0.15 and 1, 0.2 to 0.9, 0.25 to 0.8, or preferably 0.3 to 0.6, achieved a pH range of 4-7 and an oxidation-reduction potential (ORP) of 900-1100 mV. The first ratio (Rl) and the second ratio (R2) can be adjusted to the noted ranges separately or collectively as a group. Leaching can be performed in a single-stage or multi-stage process, with co-current or countercurrent steps as needed.

[0062] An additional advantage of the present disclosure is that the leaching reagent, as well as the other constituents used in the metal recovery process, are cyanide-free and arsenic-free, which results in a metal recovery process that has reduced handling safety requirements, has reduced worker exposure concerns and is more environmentally friendly than processes that employ cyanide and / or arsenic.

[0063] A still further advantage of the present disclosure is the reduction in dissolution of minerals introducing impurities to the pregnant solution.

[0064] Additional advantages of the present disclosure include improved liquid-solids separation such as increased efficiency in an amount of liquid-solids separation at a constant feed solids concentration and throughput or at a higher specific throughput rate at constant feed solids concentration and thickener and filter separation performance. Such improvements translate to smaller apparatus requirements and lower operating costs. Further, such processes are suitable for large scale operations with high solids loading in the liquid-solids separation operations.

[0065] Further advantages entail requiring less feed dilution and mixing of the leach slurry to achieve acceptable flocculation, which translates to a smaller thickener or elimination of thickeners from the process.DB1 / 161304616.2 14PatentAttorney Docket No. 134465-5028-WO

[0066] These and other advantages are satisfied, at least in part, by a process of leaching metal from a feed source by combining the feed source with a leaching reagent comprising, consisting essentially of, or consisting of a solution of sodium hypochlorite, and an indifferent salt including, consisting essentially of, or consisting of a chloride salt, preferably a sodium chloride salt in a leaching medium to form a feed slurry; leaching a metal or salt thereof from the feed slurry to form a leach slurry containing a pregnant leach liquor having metal salts dissolved therein and leach solids residue; separating the pregnant leach liquor from the leach solids residue; recovering metal salts from the pregnant leach liquor and forming a residual leach solution having a concentration of the indifferent salt dissolved therein of at least about 0.4 wt%; and recycling the residual leach solution to form additional feed slurry.

[0067] The processes of the present disclosure are suitable for large-scale operations such as in the mining industry and can form feed slurry at a rate of at least two metric tonnes in a 24 hour period, e.g., feed slurry is formed at a rate of at least 1-2 metric tonnes in a 10 hour period such as at a rate of least 1-2 metric tonnes in 5 hours, or 1 hour period. The processes of the present disclosure are also suitable for liquid-solids separation operations (thickener and / or fdtration) in which a slurry has a high solids concentration, e.g., greater than 10 wt% solids, such as greater than 15 wt% solids and greater than 20 wt%, 25 wt% and even higher than 50 wt% of solids during the liquid-solids separation operation.

[0068] Such leaching operations can be used with high clay content ore or rock such as sedimentary rock that is composed primarily of clay-sized particles, e.g., claystone, mudstone, etc. In an aspect of the present disclosure, the process includes leaching a clay rich material, e.g., an ore or rock having more than 30% clay sized particles of less than 10 microns.

[0069] Ores are often leached at solids concentrations not unlike that of a thickener underflow. An advantage of the present disclosure is an effective flocculation at an elevated solids concentration (e.g., greater than 10 wt% solids, such as greater than 15 wt% solids and greater than 20 wt%, 25 wt% and even higher than 50 wt% of solids), thus making possible additional dewatering of the leach slurry by gravity or mechanical separation after flocculation without the extensive dilution conventionally required for flocculation.

[0070] An additional advantage of the present disclosure is accelerated dewatering under compression. The increased dewatering rate under compression applies to membrane pressDB1 / 161304616.2 15PatentAttorney Docket No. 134465-5028-WO pressure filtration with pressures up to 25 bar, and also for the consolidation in tailings storage facilities under self-weight compression.

[0071] Another advantage of processes of the present disclosure is that the residual leach solution includes a high concentration of the indifferent salt and can be recycled back to the leach system operation to form additional leach slurry which significantly improves the economics of the process.

[0072] Embodiments include one or more of the following features individually or combined. For example, in some aspects, the feed source including a metal or metal salt can comprise rock, ore or a waste material such as from spent electronic equipment such as spent batteries, or spent circuit boards, which can contain precious metals such as gold, silver, platinum, palladium, etc. and other valuable metals such as lithium, copper, nickel, cobalt, tin, lead, aluminum, antimony, magnesium, manganese, etc. In other embodiments, the leach medium is at a temperature of at least 30 °C. The feed source can also comprise, or alternatively comprise, tailings from mining and resource extraction, mining waste, industrial residues such as coal ash, or other waste or spoils, such as dredging spoils. In further embodiments, water for the leach medium or the leach medium is heated by a natural source.

[0073] Additional advantages of the disclosed leaching solution, leaching process, and methods for recovering one or more metals will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment is shown and described, simply by way of illustration of the best mode contemplated of carrying out the inventions. As will be realized, other and different embodiments are contemplated and / or are possible, and the several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent similar elements throughout.

[0075] FIG. 1 is a schematic illustration of a leaching flowsheet that can be used in practicing certain aspects of the present disclosure.DB1 / 161304616.2 16PatentAttorney Docket No. 134465-5028-WO

[0076] FIG. 2 is another schematic illustration of a leaching flowsheet that can be used in practicing certain aspects of the present disclosure.

[0077] FIGS. 3 and 4 are results from analysis on extracted ore and show the impact on gold recovery for ratio R1 (the acid-to-ore ratio) and ratio R2 (the chloride salt-to-ore ratio), both expressed as mass percentages (m / m), for a first set of salt chloride (FIG. 3) and a second set of salt chloride (FIG. 4).

[0078] FIG. 5 is a schematic illustration of an electrolysis flowsheet that can be used in practicing certain aspects of the present disclosure.DETAILED DESCRIPTION OF THE DISCLOSURE

[0079] The invention features a two-step interchangeable leaching process that uses both an oxidizing agent and a reducing agent to extract gold, silver, and other precious metals from ores. Additionally, the present invention describes a continuous and integrated multistep leaching and metal recovery process that, in addition to combining oxidizing and reducing agents, incorporates an indifferent salt to enhance metal recovery by improving the solid-liquid separation step.

[0080] More specifically, the present invention offers a method for extracting precious metals from ore by mixing the ore with a salt brine containing at least one chloride source, followed by acidifying the slurried ore.

[0081] The balance of the ratio between oxidizing and reducing agents maintains the solution's oxidation-reduction potential (ORP). Without this balance, the ORP drops below 600 mV, preventing gold extraction from sulfidic ores. Maintaining this ratio is an important operational parameter to sustain the reaction and avoid excessive reagent consumption.

[0082] In the method of the present invention, the ore is introduced into a leaching step where it is contacted and leached with a lixiviant oxidant solution containing various oxidant sources. Such oxidants include alkali metal peroxides, alkali metal perchlorates, ammonium perchlorate, magnesium perchlorate, alkali metal chlorates, magnesium chlorate, alkali metal hypochlorites, chlorine, hydrogen peroxide, and other non-sulfur-containing oxidants, as well as their mixtures. Examples of alkali metal peroxides are sodium peroxide and potassium peroxide. Examples of alkali metal perchlorates include sodium perchlorate and potassium perchlorate.DB1 / 161304616.2 17PatentAttorney Docket No. 134465-5028-WOAmmonium perchlorate, magnesium perchlorate, and magnesium chlorate can also be used. Alkali metal chlorates include sodium chlorate and potassium chlorate, while sodium hypochlorite is an example of an alkali metal hypochlorite. Other oxidants should be free of sulfur, with chlorine and sodium chlorate being preferred.

[0083] The reducing leaching solution acts as a catalyst to initiate the reaction between the leach solution and the ore. The preferred catalyst is hydrochloric acid, although hypochlorous acid, chloric acid, and other oxy-acids of chlorine, as well as sulfurous and hydrosulfuric acids, can also be used. Besides eliminating the carbonates that might be present in the ore, this acidic addition displaces the equilibrium of the hypochlorite / water system towards the liberation of free chlorine,

[0084] Hydrogen sulfide is another option as it reacts with chlorides to form hydrochloric acid in situ. While the concentration of hydrochloric acid can vary, the preferred concentration is no more than about 20% (mass ratio). This concentration can be achieved through azeotropic distillation, solvent extraction, membrane technologies, extractive rectification, or a combination of these methods. This low concentration of hydrochloric acid offers process advantages, including benefits in recycling steps and reduced effluent disposal requirements

[0085] A further aspect of the present invention involves a method for leaching a material, which includes the following steps: (i) Preparing a slurry by mixing the ore with water and dissolving salt brine, (ii) Adding an oxidant source, such as hypochlorite, to the solution from step (i) to create an oxidant leaching solution with a pH ranging from 7 to 12 and an oxidation-reduction potential (ORP) between 400 and 600 mV. (iii) Introducing a reducing agent, preferably hydrochloric acid (HC1), to the solution from step (ii) to initiate the leaching process, adjusting the pH to between 4 and 7 and raising the ORP to at least 900 mV. (iv) Recovering the metal.

[0086] According to another aspect of the invention, the leaching is conducted at an elevated temperature, specifically above room temperature, in the range of 20°C to 35°C.

[0087] According to a further aspect of the invention, the acid leaching process is carried out with a retention time of approximately 0.5 to 10 hours, preferably between 1 and 4 hours.

[0088] An indifferent salt, such as sodium chloride, also can be used as an augmenting reagent in a chloride leach system. For example, addition of sodium chloride is known to increase the chloride activity, thereby improving chloride leach.DB1 / 161304616.2 18PatentAttorney Docket No. 134465-5028-WO

[0089] It is worth noting that while the process appears promising, its effectiveness would depend on various factors such as the specific composition of the source materials, the exact formulation of the chloride leaching solution, and the process conditions (temperature, pH, redox potential, etc.). Additionally, the downstream separation and purification of the leached metals influence the overall success of the process. The method involves controlling the pH of the slurried ore in the range between 4-7, and adding oxidative and / or reductive in an amount sufficient to keep the oxidation-reduction potential to a range between approximately 700 and 1200 mV versus an Ag / AgCl reference electrode

[0090] As used herein an indifferent salt is a salt that is highly soluble in water, disassociating in to one or more cations and anions, and remains dissolved in an aqueous phase of the leaching process without precipitating from a slurry throughout the process and remains dissolved in any recycled aqueous liquid. The disassociated cations or anions of the indifferent salt further do not chemically react to form coagulates or chemically react with components of a slurry such as polymer flocculant during the process or undergo oxidation or reduction reactions during the process. Such indifferent salts are advantageous since they remain dissolved in the aqueous phase of compositions and can be substantially recovered in an aqueous phase and thus subsequently used to treat additional ore or slurry.

[0091] Leaching metal -based ore includes mechanical destabilizing the ore, e.g. crushing, followed by extracting the metal with a leaching agent, typically in an aqueous medium, to convert the target metal into soluble salts that can be separated from unwanted solids. Leaching agents include chlorides source, acids, such as sulfuric acid, hydrochloric (HC1) acid, etc. In certain aspects of the present disclosure, an indifferent salt is used as an augmenting reagent in a leach system, particularly in an acidic leach system. Certain indifferent salts are known to increase dissolution rates of metals from ore. Further, indifferent salts can improve solid-liquid separation of slurries formed during the leaching process and thus improve the efficiency of the metal recovery process.

[0092] The feed source including a metal or metal salt can comprise rock or ore. Leaching metal-based rock or ore includes mechanical destabilizing the ore, e.g., crushing, grinding, milling (including high energy milling). The feed source including a metal or metal salt can also comprise a waste material, such as from spent electronic equipment (such as spent batteries, or spent circuitDB1 / 161304616.2 19PatentAttorney Docket No. 134465-5028-WO boards), which can contain precious metals such as gold, silver, platinum, palladium, etc. and other valuable metals such as lithium, copper, nickel, cobalt, tin, lead, aluminum, antimony, magnesium, manganese, etc. A mechanical destabilization process of waste material can include crushing the waste material and separating undesirable solids, e.g., scrap paper, plastics, outer metallic bodies. Whether the feed source originates from rock or ore or from waste material, after mechanical destabilization, the process can include optionally sieving the crushed material to a certain size

[0093] After mechanical destabilization, the processed feed source is processed in a leach system to convert the target metal into soluble salts that can be separated from unwanted solids. The leach system extracts metal with a leaching reagent, typically in an aqueous medium, to form a pregnant solution. The pregnant solution is then further processed to precipitate solids and then separate the solids from the liquid. The separated solids are then further processed, such as by concentrating, to recover the one or more metals while the residual leach solution can be recycled back to the leach system.

[0094] Leaching reagents for the leach system also include acids, such as sulfuric acid, hydrochloric (HC1) acid, etc. Use of chlorides, e.g., including HC1 acid, for leaching metals such as gold is known but has not found significant commercial use because of problems associated with corrosion due to high chloride concentrations in leach solutions, among other issues. However, chloride leach systems have a few advantages: The chloride chemistry is well understood; and The chemistry is clean in that outcomes can be readily predicted, and the chemistry readily controlled. The main chemical advantages of the chloride leach system are: (1) Higher ionic activities are possible and therefore also higher reaction rates which results in smaller leach equipment; (2) The solubilities of many metals are higher because of complexing, resulting in higher leach recoveries and also in higher concentrations in the leach product solution which in turn results in higher metal recoveries in the recovery step; (3) The chloride leach system allows selective metal separation; (4) Often the lixiviant regeneration is more straightforward; and (5) The energy consumption for subsequent electrolysis if used is lower due to the higher electrolyte solution conductivity. The chloride low pH leach is typically only used for materials with few acid-consuming minerals, thus limiting the acid consumption. The chloride leach can be either low-pH oxidative or low-pH non-oxidative (e.g., reductive).DB1 / 161304616.2 20PatentAttorney Docket No. 134465-5028-WO

[0095] In certain aspects of the present disclosure, an indifferent salt is used as an augmenting reagent in a leach system, particularly in an acidic leach system. Certain indifferent salts are known to increase dissolution rates of metals from ore. Further, indifferent salts can improve liquid-solids separation of the leach slurry and thus further improve the efficiency of the metal recovery process.

[0096] As used herein an indifferent salt is a salt that is highly soluble in water, disassociating in to one or more cations and anions, and remains dissolved in an aqueous phase of the leaching process without precipitating from a slurry throughout the process and remains dissolved in any recycled aqueous liquid. The disassociated cations or anions of the indifferent salt further do not chemically react to form coagulates or chemically react with components of a slurry such as polymer flocculant during the process or undergo oxidation or reduction reactions during the process. Such indifferent salts are advantageous since they remain dissolved in the aqueous phase of compositions and can be substantially recovered in an aqueous phase and thus subsequently used to treat additional ore or slurry. As used herein, “highly soluble” means a highly soluble salt is an ionic compound that easily dissolves in water, forming a homogeneous solution with a high concentration of dissolved ions.

[0097] An indifferent salt, such as sodium chloride, also can be used as an augmenting reagent in a chloride leach system. For example, addition of sodium chloride is known to increase the chloride activity, thereby improving a chloride leach.

[0098] The objective of leaching rock and ore is to liberate and dissolve one or more target metals (or salts thereof) such as precious metals, such as gold and silver, base metals, platinum group metals, rare earth elements, heavy metals, alkali metals such as lithium, and alkaline metals, etc. At times, additional complexing agents are used for precious metal extraction and are added to leach process to ensure that the liberated metals remain in solution, typically called a pregnant solution. For example, organosulfur compounds such as thiourea can be used.

[0099] It has also been conventional to use cyanide as a complexing agent for precious metal extraction. However, for various health and environmental reasons, it is beneficial to minimize or eliminate the use of cyanide from the process. Thus, the disclosed leaching process does not use cyanide, i.e., is a cyanide-free process, and the resulting pregnant solution is cyanide- free.DB1 / 161304616.2 21PatentAttorney Docket No. 134465-5028-WO

[0100] Similarly, other hazardous reagents, such as arsenic, are also not used in the disclosed leaching process, i.e., the leaching process is arsenic-free, and the resulting pregnant solution is arsenic-free.

[0101] Once target metals are in solution, the pregnant solution is processed to separate the solution from the unwanted remaining solids, which is an effective method for both separation and often simultaneous upgrading of the solids. The metals are selectively removed from the pregnant solution by a variety of methods such as for example precipitation, cementation, electrolysis, or carbon or resin loading. This selective removal upgrades the metal content further.

[0102] In one specific application, refractory gold or silver ores are extracted from the host mineral using a chloride leach process, where sodium chloride is employed to enhance leach kinetics. The electrochemical potential (Eh) of the system can be further controlled by using reagents such as ferrous chloride, hydrochloric acid, or sulfuric acid to enhance the leaching system's performance. At specific pH values and with an electrochemical potential controlling reagent, chloride acts as a complexing ligand to keep gold and silver in solution. This approach eliminates the need for cyanide or other complexing agents like thiourea, allowing the precious metals to remain in solution for separation from the non-leached gangue solids through solid-liquid separation methods, such as thickening or filtration, including filtration with a filter cake wash.

[0103] The gold and silver are readily precipitated from the pregnant solution and once precipitated can be recovered again by liquid-solids separation as a concentrate from the remaining barren solution.

[0104] In the case of lithium extraction, processes of the present disclosure can improve the economics of recovering the lithium from lithium-hosted, lithium-rich clays or clay-rich lithium minerals. The presence of lithium in clays can be as impurities, as inclusions, in lattice cavities, by adsorption on particle surfaces or edges or by isomorphous substitution. These clays present a challenge in the dewatering of the leach residue and the efficient recovery of the pregnant solution from the leach residue consisting of clays.

[0105] However, processes of the present disclosure are suitable for high clay content ores such as sedimentary rock that is composed primarily of clay-sized particles, e.g., claystone, mudstone, etc. In an aspect of the present disclosure, the process includes leaching a clay rich ore, e.g., an ore having more than 30%, 40%, 50% of clay sized particles of less than 10 microns.DBl / 161304616.2 22PatentAttorney Docket No. 134465-5028-WO

[0106] In another aspect of the present process, lithium can be leached from sedimentary rock, such as claystone found in Nevada, USA, by treating such rock with a leach medium that includes a high concentration of an indifferent salt (without an acid or chloride source).

[0107] A total dissolved indifferent salt concentration of the indifferent salt should preferably be (on solution basis) at least of at least 0.5 wt% and preferably no less than about 0.75 wt%, such as at least about 1 wt%, 1.5 wt%, 2 wt% and even at least about 2.5 wt% 3 wt%, 4 wt%, 5 wt%, 10 wt% etc. In addition, the leach medium is preferably at a temperature of at least about 20 °C, such as at least about 25 °C, 30 °C, 32 °C (about 90 °F), 33 °C, 35 °C, 37 °C (about 99 °F), 38 °C (about 100 °F), 40 °C, 42 °C, 45 °C. Advantageously, water used for the leach medium or the leach medium itself can be heated by natural sources, i.e., sources of heat that occur naturally at a leach site, such as by solar radiation, geothermal heating, and / or other natural sources available at the site for a large scale operation to room temperature or to a temperature of at least about 20 °C, such as at least about 25 °C, 30 °C, 32 °C (about 90 °F), 33 °C, 35 °C, 37 °C (about 99 °F), 38 °C (about 100 °F), 40 °C, 42 °C, 45 °C.

[0108] The addition of an indifferent salts such as is the case with sodium chloride to a slurry system can also markedly improve flocculation, floccule aggregation, settling and consolidation of particles from a slurry with a clear release of solution. The flocculation and subsequent dewatering are improved with or without addition of polymer flocculant, although the addition of a nominal amount of polymer flocculant further disproportionally improves liquidsolids separation performance.

[0109] FIGS. 1 and 2 illustrate generalized leaching 100 flowsheets. As illustrated, a feed source is provided to a mechanical destabilizer (110). The feed source can comprise ore, rock etc. including one or more metals of interest. The feed source can also comprise, or alternatively comprise, a waste material such as from spent electronic equipment, e.g., spent batteries, spent circuit boards, etc., which include one or more metals of interest. Metals of interest from such feed sources can include gold, silver, platinum, palladium, etc. and other valuable metals such as lithium, copper, nickel, cobalt, tin, lead, aluminum, antimony, magnesium, manganese, etc.

[0110] Mechanical destabilization (110) grinds, mills, such as with a high energy mill, crushes, etc. the feed source to liberate solid particles and promote the leach process. The mechanically destabilized feed source, i.e., processed feed source, can then be sent to a leachDBl / 161304616.2 23PatentAttorney Docket No. 134465-5028-WO system (112) in which a feed slurry (not shown) is formed by combining the feed source with a leach medium including water with one or more leaching reagents and one or more indifferent salts. In one aspect of the present disclosure, the leaching reagent includes a solution of sodium hypochlorite in which the sodium hypochlorite is in an amount of 3% solution to 12% solution. Augmenting reagents, such as for example ferric chloride, can also be added to the leach system (112). An electrochemical potential controlling reagent, if desired, can also be added to the leach system (112) and can be either be an oxidant such as oxygen or hydrogen peroxide in the case of an oxidative leach, or a reducing agent such as ferrous chloride, alcohol or hydrocarbon required in a non-oxidative leach.

[0111] Most metals are soluble in a chloride leach medium through complexing. For example, depending on the electrochemical potential, gold and silver are complexed by the chloride in the medium and remain soluble. In the case of lithium leach, a chloride leach is especially favorable due to the high solubility of lithium chloride. A number of chloride process leach routes are possible. One such route is the roasting of ore feed in the presence of a chloride source, such as for example potassium chloride. Other chloride sources are also possible. Lithium in a lithium containing ore can be converted in the roast to lithium chloride, which then on contacting with water will leach due to the high solubility of lithium chloride in water. This process route is more applicable for lithium ores refractory to an acid leach and when lithium is present in the clay through isomorphous substitution, as for example in Hectorite.

[0112] Another process route is the direct leach of lithium with acid, of which one possibility is hydrochloric acid formed from the sodium hypochlorite solution. The presence of indifferent salts increases the chloride concentration which improves the leach kinetics. The addition of an indifferent salt can reduce the leach of higher valent ion and therefore unwanted impurities. Further, the indifferent salt together with a polymer flocculant improves liquid-solids separation of high clay ore.

[0113] The target metal or metals are leached from the feed slurry in leach system (112) with the leach medium to form a leach slurry (114) containing a pregnant leach liquor of metal salts and leach solids residue. Advantageously, water used for the leach medium or the leach medium itself can be heated by natural sources to a temperature of at least about 20 °C, such as at least about 25 °C, 30 °C, 32 °C (about 90 °F), 33 °C, 35 °C, 37 °C (about 99 °F), 38 °C (about 100DB1 / 161304616.2 24PatentAttorney Docket No. 134465-5028-WO°F), 40 °C, 42 °C, 45 °C. The pregnant leach liquor and leach solids residue of the leach slurry are then separated.

[0114] Processes of the present disclosure are suitable for large scale operations such as in the mining industry and can form feed slurry at a rate of at least two metric tonnes in a 24 hour period, e.g., feed slurry is formed at a rate of at least 1-2 metric tonnes in a 10 hour period such as at a rate of least 1-2 metric tonnes in a 5 hour period, or 1 hour period. With such large scale operations thickeners are employed to increase the rate of processing the feed material during the operation.

[0115] As illustrated in FIG. 1, leach slurry (114) can undergo a liquid-solids (L / S) separation operation (120) such as by thickening (122) followed by fdtration (124), e.g., bed filtration, to separate the pregnant leach liquor from the leach solids residue. The liquid-solids separation can be implemented using other liquid-solids separation systems such as for example centrifuging, crossflow filtration or counter-current decantation. An advantage of the processes of the present disclosure is that the liquid-solids separation operation (thickening and / or filtration) can be carried out with a leach slurry having a high solids concentration, e.g., greater than 10 wt% solids, such as greater than 15 wt% solids and greater than 20 wt%, 25 wt% and even higher than 50 wt% of solids during the liquid-solids separation operation.

[0116] Typically, the filter cake (leach solids residue) is washed (wash water) to recover as much of the pregnant solution as possible. Filtration is an attractive liquid-solids separation technology as the dilution of the leach solution within the circuit is minimized. Leach residues high in clay are typically difficult to filter, often rendering the whole leach extraction process uneconomical. The presence of clays will also introduce operational issues in terms of cloth blinding and residual sticky cake adhering to the cloth prevents proper filter press closure, causing operational maintenance costs and the loss of valuable online filtration time or loss in throughput. However, it was found that including a sufficiently high concentration of indifferent salt within the leach medium during the leaching operation allows liquid-solids separation by filtration even with feed materials high in clays, e.g., at and above 1.5 %. In addition, filtration of the leach slurry can be carried out at a high solids concentration, e.g., greater than 10 wt% solids, such as greater than 15 wt% solids and greater than 20 wt%, 25 wt% and even higher than 50 wt% of solids during filtration.DB1 / 161304616.2 25PatentAttorney Docket No. 134465-5028-WO

[0117] FIG. 2 shows a liquid-solids separation operation that does not include a thickening step in which leach slurry (114) can undergo a liquid-solid separation directly by filtration (124a). That is, separating the pregnant leach liquor from the leach solids residue can occur directly from the leach slurry (114) by filtration without a prior thickening step even with a high solids loading and in a large scale operations in which feed slurry and / or leach slurry is formed at a rate of at least two metric tonnes in a 24 hour period, e.g., the slurry is formed at a rate of at least 1-2 metric tonnes in a 10 hour period such as at a rate of least 1-2 metric tonnes in a 5 hour period, or 1 hour period. Such a filtration step can be carried out with the leach slurry having a high solids concentration, e.g., greater than 10 wt% solids, such as greater than 15 wt% solids and greater than 20 wt%, 25 wt% and even higher than 50 wt% of solids during filtration.

[0118] Typically, the leach solids residue, e.g., filter cake, is washed (wash water) to recover as much of the pregnant solution as possible. As explained for FIG. 1, filtration is an attractive liquid-solids separation technology as the dilution of the leach solution within the circuit is minimized and filtration is enhanced by including a sufficiently high concentration of indifferent salt within the leach medium during the leaching operation.

[0119] Metal salts dissolved in the pregnant solution can be selectively recovered by a variety of methods such as for example precipitation, cementation, electrolysis, or carbon or resin loading. As shown in the examples of FIGS. 1 and 2, metal salts can be recovered from the pregnant leach liquor (132) by adding reagents that precipitate the metal salts in a precipitation operation (140). However, other recovery mechanisms such as for example cementation, electrolysis, carbon or resin loading can be used in place of or in addition to precipitation.

[0120] In the case of precipitation or cementation, the metal or metal salts precipitated as solid form can be removed from the remaining now essentially barren solution (residual leach solution) by another liquid-solid separation system operation (150). In this example, a product slurry is formed by precipitated metal or metal salts in a residual leach solution and the solids are separated from the product slurry.

[0121] Such a liquid-solid separation system operation can include, for example, thickening followed by filtration to form a concentrate (160) of the metal and metal salts and a residual leach solution (170). However, other liquid-solid separation systems can be used in place of or in addition to by thickening followed by filtration such as, for example, centrifuging,DB1 / 161304616.2 26PatentAttorney Docket No. 134465-5028-WO crossflow filtration or counter-current decantation. Depending on the chemistry, a leach solution regeneration step may or may not be required.

[0122] An advantage of the processes of the present disclosure is that leaching with a solution of sodium hypochlorite can occur without the use of cyanide or arsenic, and the processing of product slurry having a high solids concentration can still occur.

[0123] Another advantage of the processes of the present disclosure is that the liquid-solids separation operation (thickening and / or filtration) of the product slurry can be carried out with a product slurry having a high solids concentration, e.g., greater than 10 wt% solids, such as greater than 15 wt% solids and greater than 20 wt%, 25 wt% and even higher than 50 wt% of solids during the liquid-solids separation operation even in a large scale operation. Further, precipitated metal and / or metal salts can be directly filtered from the residual leach solution to form the concentrate (160) without a prior thickening step even in large scale operations. That is, separating metal salts from the pregnant leach liquor in the product slurry can occur directly from the product slurry by filtration without a prior thickening step even with high solids loading and in a large-scale operation.

[0124] Another advantage of processes of the present disclosure is that the residual leach solution (170) includes a high concentration of the indifferent salt, e.g., the same or higher concentration or very close to the same concentration of the indifferent salt, as the concentration of the indifferent salt in the leach medium at the start of the leach system 112 because the indifferent salt remains in solution during the process. There may be some increase in the amount of indifferent salt depending on the feed source or there may be some loss due to various steps in the process. However, in an aspect of processes of the present disclosure, the residual leach solution has a concentration of the indifferent salt dissolved therein of at least about 0.4 wt%, such as at least 0.5 wt% and preferably no less than about 0.70 wt%, such as at least about 1 wt%, etc. and up to and including the amount in the leach medium.

[0125] As shown in FIGS. 1-2, the residual leach solution (170) can be recycled back to the leach system (112) to form additional leach slurry which significantly improves the economics of the process.

[0126] Further, an effective liquid-solids separation improves the overall efficiency of the metal recovery process. Effective liquid-solids separation steps can improve recycling of leachingDB1 / 161304616.2 27PatentAttorney Docket No. 134465-5028-WO reagents thus limiting the cost of replenishing leaching reagent in the circuit, as well as reducing downstream complications where remaining solution is unwanted.

[0127] In an aspect of the present disclosure, the overall efficiency of the leach system can be improved by including an indifferent salt to the system. The indifferent salt can be added with the leaching reagents in the leach system. Alternatively, or in addition, thereto, the indifferent salt can be included at the liquid-solid separation stage of the process. The addition of an indifferent salt at a sufficient concentration in the leaching medium of a slurry can improve the liquid-solid separation process and thus improve the overall process of metal recovery.

[0128] As shown in the example of FIGS. 1 and 2, an indifferent salt is added in the leach system (112). For example, the chloride concentration in a leach system can be increased by the addition of a soluble indifferent chloride salt. Typically, the soluble salt is added at the same time as the other leach components are added. For example, sodium chloride is one such augmenting reagent that can be added to promote the solution ionic activity. The increased ionic activity in turn improves the leach kinetics. Typically, sodium chloride concentrations of greater than 1 % up to 5% or less, alternatively, 3.5 % or less or 3.0 % or less, in the leach medium are sufficient to achieve the enhanced ionic activity. The sodium chloride as ionic additive fits well into the chloride leach system.

[0129] Further, including an indifferent salt can minimize subsequent unwanted precipitation reactions. The addition of an indifferent salt to the leach process improves the subsequent liquid-solids separation step(s) and appears indifferent to the type of system employed for liquid-solids separation, thus improving the overall leaching efficiency. It is advantageous to include indifferent salts that do not interfere with the leach and the recovery steps. In the case of a chloride leach system, it is advantage to utilize indifferent salts of chloride, e.g., sodium chloride which is inexpensive and relatively benign.

[0130] Use of chloride as an augmenting reagent as well as indifferent salts including if / how chloride from indifferent salt has to be balanced against the presence of chloride from the solution of sodium hypochlorite.

[0131] After the feed slurry is leached, unwanted solids are removed from the process. In one aspect of the present disclosure, the aqueous medium in any slurry of the process includes a sufficient concentration of indifferent salt to improve separation of solids from the aqueous phaseDB1 / 161304616.2 28PatentAttorney Docket No. 134465-5028-WO of the slurry. It was found that by adding indifferent salt in a sufficient quantity (>1.5 wt%) to a feed source, efficient aggregation of solid particles and efficient flocculation results. It was further found that this process is considerably more efficient than conventional coagulation methods in that flocculation can be carried out at higher feed solids concentrations, requires less mixing and is effective with minerals such as for example clays that traditionally have been refractory to liquid-solids separation. The floccule aggregates formed are more robust and less prone to shear. The flocculation is more efficient in capturing fine and ultra-fine particles, which results in a cleaner overflow liquid.

[0132] In one aspect of a process of leaching a metal from a feed source, a slurry formed from either a leach slurry or product slurry or other slurries includes the chloride solution from one or more chloride sources. In such a case, the chloride solution can be at a sufficient concentration that the slurry can be directly filtered to remove solids without diluting the slurry and / or without use of a thickener apparatus or thickening step. In another aspect of a process of leaching a metal from a feed source, thickeners are used to facilitate liquid-solids separation.

[0133] Advantageously, the process of the present disclosure results in an increased liquidsolids separation efficiency of at least 25% as compared to slurry without the added indifferent salt. The comparison is done at constant feed solids concentration and throughput.

[0134] When employing a thickener, the processes of the present disclosure can have as increased rate of sedimentation of solids, an increased overflow liquid throughput, and / or an increased percentage by mass of solids of thickener underflow slurry as compared to slurry in the thickener apparatus without the added indifferent salt. Each of the rate of sedimentation of solids, overflow liquid throughput, percentage by mass of solids of thickener underflow slurry can individually be increased by at least 25%, e.g., by at least 50%, 75%, 100%, 125% or higher, as compared to a slurry in the thickener apparatus without the added indifferent salt. Without being bound to theory, the reasons for the separation efficiency improvement lies in the robust nature of the formed floccule aggregates and their increased settling rate in the upper part of the thickener, as well as in the higher hydraulic conductivity and consequent higher dewatering rate of the solids bed in the lower part of the thickener, as well as the improved fines and ultra-fines capture when treating (or combining) the feed source with the indifferent salt.DB1 / 161304616.2 29PatentAttorney Docket No. 134465-5028-WO

[0135] In practicing aspects of the present process, thickening a slurry includes treating the slurry with at least one polymer flocculant or solution thereof. The slurry can be treated in the thickener apparatus with the at least one polymer flocculant concurrent with or subsequent to treating the slurry with the indifferent salt. In some embodiments of the application, the feed source can be combined with the at least one polymer flocculant in the thickener apparatus concurrent with or subsequent to combining the feed source with the indifferent salt. The process can further comprise removing underflow slurry and overflow aqueous liquid from the sediment tank as two distinct streams.

[0136] Further, the solids loading rate for a feed slurry treated according to processes of the present disclosure can be greater than typically achieved in thickeners. Typical solids loading rate for coarse sand is about 1.0 to 1.5 (metric tonne / hour) / meter squared ((t / h) / m2) and for typically feed slurries between about 0.3 and 1.0 (t / h) / m2. Advantageously, the solids loading rate for a feed source to be treated (or combined) with an indifferent salt and optionally polymer flocculant can be greater than 2 (t / h) / m2, such at least about 2.5 (t / h) / m2 and at least about 3, 3.5, 4, 4.5, 5 and 6 (t / h) / m2. The improvement in solids loading rate results in a substantial reduction of thickener cross sectional area, which either translates to smaller diameter thickener or alternative less thickeners, representing a substantial savings in capital costs.

[0137] Further, the solids loading rate for a feed source treated according to processes of the present disclosure can be greater than typically achieved in thickeners. Typical solids loading rate for coarse sand is about 1.0 to 1.5 (metric tonne / hour) / meter squared ((t / h) / m2) and for typically feed slurries between about 0.3 and 1.0 (t / h) / m2. Advantageously, the solids loading rate for a feed source to be treated (or combined) with an indifferent salt and optionally polymer flocculant can be greater than 2 (t / h) / m2, such at least about 2.5 (t / h) / m2 and at least about 3, 3.5, 4, 4.5, 5 and 6 (t / h) / m2. The improvement in solids loading rate results in a substantial reduction of thickener cross sectional area, which either translates to smaller diameter thickener or alternative less thickeners, representing a substantial savings in capital costs.

[0138] In high-rate thickeners, solids contents in the underflow are of the order of 50% by weight, depending on the nature of the feed slurry and conditions of thickener operation (feed rate, etc.) Higher solids concentrations in the underflow slurry can at times be obtained using high- density, high-compression or paste thickeners. These are taller than conventional thickeners toDB1 / 161304616.2 30PatentAttorney Docket No. 134465-5028-WO increase the self-consolidating weight on the solids in the formed bed. They also have steeper floor slopes to enhance the movement of settled slurry to the discharge point. The higher bed solids density of these thickeners relative to high rate thickeners greatly increases the rake torque, requiring a higher rake drive capability. In addition, as the solids density increases near the base of the thickener, hydraulic conductivity decreases, lowering the rate of water release. High density thickeners are more expensive than high rate thickeners and there is a trade-off between cost, the ability to pump thickener underflow and the amount of water recovered.

[0139] An indifferent salt preferably has a solubility in water of greater than 2 g of salt per 100 g of water (i.e., a salt / water solubility of 2g / 100g) at 20 °C. Preferably the indifferent salt has a water solubility of at least about 5 g / 100 g at 20 °C, e.g., at least about 10 g / 100 g of salt / water at 20 °C. Indifferent salts that are useful in practicing processes of the present disclosure include salts having a monovalent cation without multivalent cations, e.g., alkali halide salts such as sodium chloride, potassium chloride; also salts having monovalent cations without multivalent cations such as sodium and potassium nitrate, sodium and potassium phosphates, sodium and potassium sulfates, etc. are useful in practicing processes of the present disclosure. Other indifferent salts having monovalent cations useful in practicing processes of the present disclosure include ammonium-based salts without multivalent cations such as ammonium chloride (NH4CI), ammonium bromide (NH4Br), ammonium carbonate ((NI C^CO ), ammonium bicarbonate (NH4HCO3), ammonium nitrate (NH4NO3), ammonium sulfate ((NH4)2SO4), ammonium hydrogen sulfate (NH4HSO4), ammonium dihydrogen phosphate (NH4H2PO4), ammonium hydrogen phosphate ((NH4)2HPO4), ammonium phosphate ((NH4)3PO4), etc. Mixtures of such salts can also be used.

[0140] Certain ammonium-based salts are useful for practicing the present disclosure since residual ammonium-based salts on the concentrated solids can be beneficial to plant life. In fact, many of the ammonium-based salts are useful as fertilizers, e.g., ammonium chloride, ammonium nitrate, ammonium sulfate, etc. Many of the monovalent cation sulfate and phosphate salts are also useful as fertilizers. In certain embodiments of the present disclosure, the indifferent salt or salts used in the processes of the present disclosure can preferably be non-toxic and beneficial to plant life to aid in environmental remediation and the restoration of mine sites.DBl / 161304616.2 31PatentAttorney Docket No. 134465-5028-WO

[0141] When a sufficiently high concentration of the indifferent salt is included in treating ore or a feed slurry, the indifferent salt can destabilize and consolidate solids in a slurry. For a relatively short process times with a relatively low energy input, a total dissolved indifferent salt concentration of the indifferent salt should preferably be at least of at least 0.5 wt% and preferably no less than about 0.75 wt%, such as at least about 1 wt%, 1.5 wt%, 2 wt% and even at least about 2.5 wt% 3 wt%, 4 wt%, 5 wt%, 10 wt% etc. Determination of the concentration of the indifferent salt dissolved in the aqueous fraction includes the amount added together with any indifferent salt that may already be part of the aqueous fraction of the feed slurry prior to addition of indifferent salt to the process.

[0142] The indifferent salt(s) can be used to treat feed slurry of the present disclosure as a solid, e.g., combining the salt as a powder with the feed slurry. Alternatively, the salt can be in a solution to treat feed slurry, e.g., by combining an aqueous salt solution with feed slurry in the thickener apparatus. In some aspects of the present disclosure, an aqueous solution of the indifferent salt can be used having a concentration of no less than about 1 wt%, e.g., greater than about 2 wt%, 3 wt%, 5 wt%, 7 wt%, 10 wt%, 20 wt%, 30 wt% and even as great as a 40 wt% or as an aqueous salt slurry. The feed slurry and indifferent salt solution should be mixed at a ratio sufficient to destabilize and consolidate solids in the slurry.

[0143] In some embodiments of the present processes, the leach medium may include a polymer flocculant. A concentration of the polymer flocculant in the leach medium may have a range of not less than zero to up to about 0.005 wt % or up to about 0.01 wt % or up to 0.04 wt % or up to 0.05 wt % or up to 0.1 wt % or up to 0.2 wt % or up to 0.4 wt %.

[0144] In some embodiments of the present processes, it can be more advantageous to use a natural source of the indifferent salt or salts such as in a natural body of water including such salts in sufficiently high concentration such as at least about 2 wt% and even at least about 3 wt% or greater. For example, ocean or seawater can be used as a source of indifferent salts, which can significantly improve the economics of the process under certain conditions. The vast majority of seawater has a salinity of between 31 g / kg and 38 g / kg, that is, 3. 1-3.8%. On average, seawater in the world’s oceans has a salinity of about 3.5% (35 g / L, 599 mM). Seawater includes a mixture of salts, containing not only sodium chloride as sodium cations and chlorine anions (together totaling about 85% of the dissolved salts present), but also sulfate anions and calcium, potassiumDB1 / 161304616.2 32PatentAttorney Docket No. 134465-5028-WO and magnesium cations. There are other ions present (such as bicarbonate), but these are the main components. Another natural source of highly soluble salts that can be used as a source of highly soluble salts includes a hypersaline body of water, e.g., a hypersaline lake, pond, or reservoir. A hypersaline body of water is a body of water that has a high concentration of sodium chloride and other highly soluble salts with saline levels surpassing ocean water, e.g., greater than 3.8 wt% and typically greater than about 10 wt%. Such hypersaline bodies of water are located on the surface of the earth and also subsurface, which can be brought to the surface as a result of ore mining operations.

[0145] In other embodiments of the present processes, it can be advantageous to use a brine produced in desalinization of salt water as a source of an indifferent salt(s). The brine can be used alone as a source of the indifferent salt(s) or in combination with another source of indifferent salt(s) such as seawater.

[0146] In other embodiments of the present processes, it can be advantageous to use artificial seawater as a source of an indifferent salt(s). The artificial seawater can be used alone as a source of the indifferent salt(s) or in combination with another source of indifferent salt(s) such as seawater. The artificial seawater may contain about 3.5% by weight of sodium chloride. Artificial seawater can be prepared by mixing one or more suitable salts with water; suitable salts include sodium chloride (NaCl), magnesium chloride hexahydrate (MgCh 6H2O), sodium sulfate (Na2SC>4), calcium chloride dihydrate (CaCh-2H2O), potassium chloride (KC1), sodium bicarbonate (NaHCCh), potassium bromide (KBr), boric acid (H3BO3), strontium chloride hexahydrate (SrCh 6H2O), and sodium fluoride (NaF).

[0147] Although indifferent salts can destabilize and consolidate solids in a slurry, adding one or more polymer flocculant(s) can reduced the time for sedimentation and increase overflow output. Hence, one or more polymer flocculants(s) can be added concurrent with or subsequent to treating the feed slurry with the indifferent salt in the thickener apparatus.

[0148] Polymers that are useful in practicing the present disclosure include water soluble flocculating polymers such as polyacrylamides or copolymers thereof such as nonionic polyacrylamides and copolymers thereof, an anionic polyacrylamide (APAM) such as a polyacrylamide-co-acrylic acid, and a cationic polyacrylamide (CP AM), which can contain comonomers such as acryloxyethyltrimethyl ammonium chloride, methacryloxyethyltrimethylDB1 / 161304616.2 33PatentAttorney Docket No. 134465-5028-WO ammonium chloride, dimethyldiallyammonium chloride (DMDAAC), etc. Other water-soluble flocculating polymers useful for practicing the present disclosure include a polyamine, such as a polyamine or quaternized form thereof, e.g., polyacrylamide-co-dimethylaminoethylacrylate in quaternized form, a polyethyleneimine, a polydiallyldimethyl ammonium chloride, a polydicyandiamide, or their copolymers, a polyamide-co-amine, polyelectrolytes such as a sulfonated polystyrenes can also be used. Other water-soluble polymers such as polyethylene oxide and its copolymers can also be used. The polymer flocculants can be synthesized in the form of a variety of molecular weights (MW), electric charge types and charge density to suit specific requirements. Advantageously, the flocculating polymer used in practicing processes of the present disclosure do not include use of activated polysaccharides or activated starches, i.e., polysaccharides and starches that have been heat treated, in sufficient amounts to lower the density of the floc to below the density of the tailings water from which they are separated. Such activated polysaccharides and activated starches when used in sufficiently high dosages tend to form low density flocs which rise to the surface of an aqueous composition, which can cloud overflow liquid.

[0149] The amount of polymer(s) used to treat a slurry should preferably be sufficient to flocculate the solids in the feed slurry. The amount of polymer(s) used to treat feed slurry can be characterized as a dosage based on the weight percent of the solids in the feed slurry. In some embodiments of the present disclosure, one or more polymer flocculant(s) can be used to treat feed slurry at a dosage (weight of the flocculant(s) to weight of the solids in the slurry) of no less than zero and up to about 0.005 wt%, e.g., up to about 0.01 wt% and in some implementations up to about 0.015 wt%, 0.020 wt%, 0.025 wt%, 0.03 wt%, 0.04 wt%, even up to about 0.07 wt %, 0.09 wt %, 0.1 wt %, 0.2 wt %, or 0.4 wt%.

[0150] Because indifferent salts and polymer flocculants that are preferably water soluble are used in the process of the present disclosure, the temperature of thickening slurries in a thickener apparatus need not be elevated above ambient temperature to practice the process. In certain embodiments, treating a feed slurry according to the various embodiments herein can be carried out at about ambient temperature or no more about 2 to about 5 °C above ambient temperature.

[0151] In practicing aspects of the present process, thickening slurry includes treating a feed source with an indifferent salt or solution thereof in a thickener apparatus including a sedimentDB1 / 161304616.2 34PatentAttorney Docket No. 134465-5028-WO tank and separating and recovering overflow aqueous liquid, e.g., clarified water, from the sediment tank after treating the feed source. The process can include combining a feed source with a concentration greater than 2 wt% solids, such as greater than 15 wt% and even greater than 20 wt% solids and higher such as 50%, with an indifferent salt in the feed. With sufficient concentration of the indifferent salt in the aqueous phase of the feed slurry, the solids settle to the bottom of the tank under the pull of gravity and can be pushed towards the outlet port by rakes. Advantageously, the solids loading rate for a feed source to be treated (or combined) with an indifferent salt and optionally polymer flocculant can be greater than 1.0 (t / h) / m2, such at least about 2.5 (t / h) / m2 and at least about 3, 3.5, 4, 4.5, 5 and 6 (t / h) / m2. As the result of the possibility to feed the liquid-solids separation unit at a higher solids concentration by using an indifferent salt with polymer and because of the higher solids loading rates achievable, substantially less liquidsolids separation surface will be required, reducing either the size or the number of the units required, thus reducing the capital and operating cost requirement substantially.

[0152] Clarified water can exit a thickener sediment tank through an overflow port or lip of the tank. Conventional overflow clarity is typically in the range of 500 ppm to 5000 ppm. But to achieve such low overflow clarity, the solids loading rate is relatively kept low. An advantage of the present disclosure is that even with a very high solids loading rates (e.g., at least about 4, 5 and 6 (t / h) / m2, the overflow clarity remains lower than 5000 ppm, such as lower than 2500 ppm, 1000 ppm and even lower than 500 ppm or 300 ppm. Such overflow clarity can be determined by a turbidity detector. A reduction in overflow clarity reduces upstream and downstream complications that would have been caused by the presence of suspended solids. The reduction in suspended solids eliminates a build-up of slimes within the process, introducing also a circulating load. Slimes increase the reagent consumption. Slimes also change the rheology of the slurries, thus impacting extraction processes negatively. Downstream slimes can be the cause of impurities being introduced, requiring expensive cleaning process steps. Substantial savings are therefore realized through the production of a clear pregnant solution recovery in the liquid-solids separation step.

[0153] Settling performance and the final solids content of the settled solids (thickener underflow slurry) is enhanced by the indifferent salt at sufficient concentration in the slurry. An advantage of treating (or combining) feed source with an indifferent salt according to aspects ofDB1 / 161304616.2 35PatentAttorney Docket No. 134465-5028-WO the present disclosure is that a rise rate of the feed slurry can be very low even with a high solids loading rate because of being able to process a high feed solids concentration, otherwise not possible. For example, a rise rate of the feed slurry can be less than 3 (meter / hour) (m / h) at a solids loading rate (t / h) / m2 between about 3 to 6 and even less than 2 m / h at a solids loading rate about 1.5 (t / h) / m2. The possibility of feeding the liquid-solids separation units at a high solids concentration results in the use of smaller units thus substantially reducing the capital and operating costs.

[0154] Advantageously, since the indifferent salt is highly water-soluble salt, the indifferent salt remains almost entirely in the aqueous phase of the feed slurry and can be recovered with overflow aqueous liquid, e.g., clarified water, from the sediment tank after treating the feed source. In certain embodiments of the present disclosure, the overflow liquid, e.g., clarified water, recovered from the feed slurry has a concentration of the indifferent salt that is similar to the concentration of the indifferent salt in the feed slurry. Some loss of indifferent salt may be due to loss with removing underflow slurry. However, it is preferable that the directly recovered overflow aqueous liquid has a concentration of the indifferent salt dissolved therein of at least about 0.4 wt%, such as at least 0.5 wt% and preferably no less than about 0.70 wt%, such as at least about 1 wt%, etc. The separated overflow liquid including the dissolved indifferent salt can be used to treat additional tailings in the thickener apparatus. In addition, the separated overflow liquid including the dissolved indifferent salt can be concentrated prior to use to treat additional feed slurry such as by nano filtration, reverse osmosis, combinations thereof, etc.

[0155] Advantageously, the treatment of the leach residue with indifferent salt and polymer improves the consolidation rate in thickening, filtration and later in the filter storage facility.

[0156] EXAMPLES

[0157] A refractory gold sample from a Canadian mine was obtained. The ore contained both oxide and sulfide material, with a gold content of approximately 0.5 to 0.7 g / ton.

[0158] In one example, sixty grams of the unprocessed ore (P80 of 110 microns) was mixed in a stirred reaction vessel at room temperature and atmospheric pressure with a primary oxidant leaching solution containing 100 grams of water and 10 grams of the first chlorine salt source. After 15-45 minutes, the second chlorine salt source was added. The pH of the leachDB1 / 161304616.2 36PatentAttorney Docket No. 134465-5028-WO solution ranged from 7 to 12, depending on the amount of the second chlorine salt added. In this experiment, different quantities of the second salt were tested.

[0159] After 1 to 3 hours of interaction between the ore and oxidative leaching solution, the reductive leaching solution was added to the stirred reaction vessel, and the pH of the leached solution was 4-7 and the ORP was > 900 mV.

[0160] The entire quantity of leach solution was mixed for an additional 1 to 10 hours, maintaining the pH and ORP within the desired range (4-7 and 900-1100 mV) by adjusting the oxidative / reductive ratio. To complete the leaching process, an indifferent salt was added to the mixed leach solution before separating the extracted ore from the pregnant solution (precious metal-rich leach solution).

[0161] The extracted ore was analyzed, and the results are presented in FIGS. 3 and 4. These figures show the impact on gold recovery for ratio R1 (the acid-to-ore ratio) and ratio R2 (the chloride salt-to-ore ratio), both expressed as mass percentages (m / m). The main difference between FIGS. 3 and 4 is the chloride species in FIG. 3 is chloride (CF) and the chloride species in FIG. 4 is hypochlorite (CIO ). However, both figures show the same trend, emphasizing the importance of maintaining the correct ratios and controlling the leaching operational parameters. Adding the leaching reagents in the proper sequential manner is one aspect of this invention.

[0162] In another example, sixty grams of the unprocessed ore (P80 of 110 microns) was mixed in a stirred reaction vessel at room temperature and atmospheric pressure with an oxidative leaching solution containing 100 grams of water and 10 grams of sodium chloride. After 15-45 minutes, the second chlorine salt was added. The pH of the leach solution was in a range of from 4 to 7. An ORP of the leach solution was in a range of 800-1200 mV.

[0163] After 3 hours of interaction between the ore and oxidative leaching solution, a polymer flocculant was added to the leach solution and the solid-liquid separation was performed.

[0164] In yet another example, sixty grams of the unprocessed ore (P80 of 110 microns) was mixed in a stirred reaction vessel at room temperature and atmospheric pressure with a primary oxidant leaching solution containing 100 grams of water and 10 grams of sodium chloride. After 15-45 minutes, the second chlorine salt source (hydrochloric acid) was added. The pH of the leach solution was in a range of from 1 to 2. An ORP of the leach solution was in a range of 400 to 600 mV.DB1 / 161304616.2 37PatentAttorney Docket No. 134465-5028-WO

[0165] After 1 to 3 hours of interaction between the ore and oxidative leaching solution, the reductive leaching solution containing FeCh was added to the stirred reaction vessel, and the pH of the resulting leach solution was in a range of 1 to 5 and the ORP was in a range of 300 to 400 mV.

[0166] The entire quantity of leach solution was mixed for an additional 3 hours. To complete the leaching process, an indifferent salt was added to the mixed leach solution before separating the extracted ore from the pregnant solution (precious metal-rich leach solution). A polymer may be added to the mixed leach solution if necessary to further consolidate the solids in the solution.

[0167] Embodiments

[0168] Embodiment 1A: A process of leaching precious metal values from a feed source, comprising the steps of:(a) Contacting the comminuted ore with a diluted solution of a chloride source, and allowing a soaking time of at least 10 minutes, preferably between 10 minutes and 3 hours.(b) Dissolving or adding the second source of chloride to the solution of step (a).(c) Allow a contact time of at least 1 hour for the solution from (b), preferably between 1 to 4 hours.(d) Adding a reducing agent to the solution from step (c), preferably an acid source such as HC1, to trigger the leaching process.(e) Allow a contact time of at least 1 hour for the solution from (d), preferably between 1 to 24 hours.(f) Adding an indifferent salt to the solution from step (e) to complete the leaching process.(g) Recovering metal.

[0169] Embodiment IB: A process of leaching precious metal values from a feed source, comprising the steps of:(a) Contacting the comminuted ore with a diluted solution of a chloride source (e.g., sodium chloride), and allowing a soaking time of at least 10 minutes, preferably between 10 minutes and 3 hours.DB1 / 161304616.2 38PatentAttorney Docket No. 134465-5028-WO(b) Dissolving or adding the second source of chloride (e.g., hydrochloric acid) to the solution of step (a) to form a resultant mixture having a pH of 1-2 and an ORP of 400-600 mV.(c) Allow a contact time of at least 1 hour for the solution from (b), preferably between 1 to 4 hours.(d) Adding a reducing agent (e.g., FeCh) to the solution from step (c) to trigger the leaching process. The mixture at this stage has a pH of 1-5 and an ORP of 300-400 mV.(e) Allow a contact time of at least 1 hour for the solution from (d), preferably between 1 to 24 hours, preferably 3 hours.(f) Adding an indifferent salt to the solution from step (e) separate the solids from the liquids in a solid / liquid separator. If necessary, a polymer flocculant may be added.(g) Recovering metal.(h) Recovering the reagents (e.g., sodium chloride and polymer flocculant, if used) and recycled for use in subsequent leaching processes.

[0170] Embodiment 1C: A process of leaching precious metal values from a feed source, comprising the steps of:(a) Contacting the comminuted ore with a diluted solution of a chloride source (e.g., sodium chloride), and allowing a soaking time of at least 10 minutes, preferably between 10 minutes and 3 hours.(b) Dissolving or adding the second source of chloride (e.g., another chloride salt that is disclosed herein) to the solution of step (a) to form a resultant mixture having a pH of 4-7 and an ORP of 800-1200 mV.(c) Allow a contact time of at least 1 hour for the solution from (b), preferably between 1 to 4 hours, more preferably 3 hours.(d) Adding an indifferent salt and a polymer flocculant to the solution from step (c) to enhance phase separation and to facilitate recovery of the pregnant solution.(g) Recovering metal.(h) Recovering the reagents (e.g., sodium chloride, chloride salt, and polymer flocculant) and recycled for use in subsequent leaching processes.

[0171] Embodiments IB and 1C may be interchangeable.DBl / 161304616.2 39PatentAttorney Docket No. 134465-5028-WO

[0172] Embodiment 2: The material has a pulp density in the range of 8 to 50 %, preferably 10 to 35 %.

[0173] Embodiment 3: An oxidant leaching solution is in contact with comminuted ore. The oxidative leach solutions also preferably contain a primary and secondary source of chloride, such as water soluble salt. Enough of a base, such as sodium chloride, is added to the primary leach solution.

[0174] Embodiment 4: The secondary supplementary chloride source plays a catalytic role in the process. The secondary leach solution, while containing the same key chemical components as the primary leach solution, is a base and preferably has a pH of 7-12 and an oxidation-reduction potential (ORP) of 400 to 800 mV.

[0175] Embodiment 5: The order of the addition of the chloride sources as part of the initial leaching solution can be changed without impacting the leaching process.

[0176] Embodiment 6: A reducing agent is added preferably an acid source such as HC1, the reducing agent acting as a catalyst to initiate the reaction between the leach solution and the ore.

[0177] Embodiment 7A: The reducing agent noted will adjust the pH of the leach solution to the range of 4-7, and the ORP will be at least 900 mV.

[0178] Embodiment 7B: The reducing agent noted will adjust the pH of the leach solution to the range of 1-5 and the ORP will be about 300-400 mV.

[0179] Embodiment 7C: The reducing agent noted will adjust the pH of the leach solution to the range of 1-2 and the ORP will be about 400-600 mV.

[0180] Embodiment 8: A chloride, such as sodium chloride (NaCl), calcium hypochlorite (Ca(OCl)2), a source of sodium hypochlorite (NaClO), such as as commercial bleach, sodium dichloro-s-triazinetrione dihydrate (CsHiChNsNaOs), anhydrous sodium dichloro-s-triazinetrione (CsCENaNaOa), trichloro-s-triazinetrione (C3CI3N3O3), and FeCE are combined to create an oxidative leaching solution.

[0181] Embodiment 9: The preferred reduction agent is hydrochloric acid, though hypochlorous, chloric, and other oxy-acids of chlorine can also be used, as well as sulfurous and hydrosulfuric acids. Hydrogen sulfide may also be utilized because it reacts with chlorides to form hydrochloric acid in situ.DBl / 161304616.2 40PatentAttorney Docket No. 134465-5028-WO

[0182] Embodiment 10: The process is cyanide free.

[0183] Embodiment 11 : The process is arsenic free.

[0184] Embodiment 12: A concentration of the indifferent salt dissolved in the leach medium is 1 wt% to 30 wt%.

[0185] Embodiment 13: The indifferent salt is an alkali halide salt.

[0186] Embodiment 14: The indifferent salt is a chloride-based salt.

[0187] Embodiment 15: The indifferent salt is sodium chloride.

[0188] Embodiment 16: The process further comprises recycling the residual leach solution to form additional feed slurry.

[0189] Embodiment 17: The recovered metal is a precious metal.

[0190] Embodiment 18: The process further comprises recovering the precious metal from the recovered metal salts.

[0191] Embodiment 19: The process further comprises introducing a slurry generated in the process to a thickener apparatus to separate the slurry into an underflow slurry and an overflow liquid with an increase in liquid-solids separation rate and / or efficiency of at least 25% as compared to the slurry in the thickener apparatus without the added indifferent salt.

[0192] Embodiment 20: The feed slurry is formed at a rate of at least two metric tonnes in a 24 hour period and separating the pregnant leach liquor from the leach solids residue occurs directly from the leached slurry by filtration without a prior thickening step.

[0193] Embodiment 21 : The feed slurry is formed at a rate of at least two metric tonnes in a 24 hour period and separating the pregnant leach liquor from the leach solids residue occurs when the leach slurry has a solids concentration of greater than 10 wt% solids.

[0194] Embodiment 22: The feed slurry is formed at a rate of at least two metric tonnes in a 24 hour period and recovering the metal salts from the pregnant leach liquor includes separating the metal salts from the pregnant leach liquor in a product slurry having a solids concentration of greater than 10 wt% solids.

[0195] Embodiment 23: Separating the metal salts from the pregnant leach liquor in the product slurry occurs directly from the product slurry by filtration without a prior thickening step.

[0196] Embodiment 24: feed source includes a lithium containing sedimentary rock.

[0197] Embodiment 25: The leach medium is at a temperature of at least 30 °C.DB1 / 161304616.2 41PatentAttorney Docket No. 134465-5028-WO

[0198] Embodiment 26: The water for the leach medium or the leach medium is heated by a natural source.

[0199] Embodiment 27: The balance of different chloride species affects the amount of chloride consumed during leaching.

[0200] Embodiment 28: The leaching can be performed as a co-current, countercurrent, or alternative process, and is most conveniently conducted at atmospheric pressure — pressurization is not necessary.

[0201] Embodiment 29: The total chloride concentration from both sources in the solution is preferably at least 100 g / L, with a typical range of 200-300 g / L, and can vary within specific ranges as needed.

[0202] Embodiment 30: A reducing agent, such as hydrochloric acid, in the lixiviant should not exceed a 20% mass ratio, with a preferred concentration of at least 10% and ideally 14- 18% mass ratio, such as 2-4M.

[0203] Embodiment 31 : The chloride concentration in the lixiviant is most effective in the 100-400 g / L range, particularly 200-300 g / L.

[0204] Embodiment 32: Metal leaching is enhanced by adjusting two ratios. The first ratio (Rl) is the acid-to-ore ratio, expressed as a mass percentage (m / m), which should be within a range of 0.1 to 2.0, with 1 to 1.8 being preferred. The second ratio (R2) is the chloride salt-to-ore ratio, also expressed as a mass percentage (m / m), which should be within a range of 0.1 to 4.0, 2 to 3, or preferably 0.75 to 2.5.

[0205] Embodiment 33: Maintaining a ratio of Rl to R2 between 0.15 and 1, with 0.3 to 0.6 being preferred, achieves a pH range of 4-7 and an oxidation-reduction potential (ORP) of 900- 1100 mV.

[0206] Embodiment 34: Leaching can be performed in a single-stage or multi-stage process, with co-current or countercurrent steps as needed.

[0207] Embodiment 35: The process may include electrolysis of a saline source to generate the chloride-based leaching solution that contains hypochlorous acid (HOC1). During electrolysis, chlorine gas (CL) evolves at the anode (bubbles form), hydrogen gas (H2) evolves at the cathode (bubbles form), and HOC1 forms in the solution when the pH is controlled between 5.5-6.5. Hydrochloric acid or sodium hydroxide may be used to control the pH to the desired range. AnDB1 / 161304616.2 42PatentAttorney Docket No. 134465-5028-WO example of the electrolytic process is illustrated in FIG. 5. The saline source may include filtered seawater (natural or artificial), a made-up solution that includes sodium chloride, or a rejected stream from a desalination process or a combination thereof.

[0208] Embodiment 36: The process may include a reagent management system (RMS) to (i) recover and recycle reagents (depending on the specific leaching process configuration, different membrane arrangements may be implemented to enable the recycling and recovery of 90% to 95% of the reagent back into the leaching process), (ii) concentrate the leach solution (depending on the type of metal or combination of metals dissolved in the pregnant solution, different membrane arrangements may be employed to concentrate the pregnant solution up to 10X) thereby leading to downstream effects (e.g., reduction in the size of the solutions for the Merrill-Crowe process) and leading to a more efficient process compared to conventional leaching methods, (iii) generate the indifferent salt by, for example, a membrane configuration to produce a stream free of divalent cations and anions, such as Mg and Ca, while separating the monovalent cations and anions into a separate stream to be used in the leaching / extraction process, and (iv) produce species in situ through electrolysis for the leaching process, enabling on-demand reagent production integrated within the process flow. The RMS is designed to align with a zero-discharge policy. It is preferred that all, and at least most, i.e., greater than 95%, materials, reagents, and solutions utilized in the process are fully recovered, recycled, or repurposed within the system, eliminating or substantially eliminating the need for waste disposal. For example, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.25%, at least 99.5%, at least 99.75%, at least 99.9% or each of the materials, reagents, and solutions are recovered recycled, or repurposed within the system. Also for example, no more than 5%, no more than 4%, no more than 3%, no more than 2%, no more than 1%, no more than 0.75%, no more than 0.5%, no more than 0.25% of materials, reagents, and solutions used in the process are waste. Accordingly, the sustainability of the leaching process may improve and environmental impact may be reduced.

[0209] The RMS may include: (i) filters, such as sand filters, cartridge filters, and membrane filters (e.g., filters for ion exchange, reverse osmosis, nanofiltration, ultrafiltration, and / or microfiltration) for purifying seawater or saltwater solution to remove impurities that may interfere with the electrolysis process, (ii) an electrolytic cell to electrolyze the purified seawater or saltwater solution to generate the oxidant for the leaching process, (iii) an evaporator to reduceDB1 / 161304616.2 43PatentAttorney Docket No. 134465-5028-WO a volume of wastewater in tailings and / or the residual leach solution, leaving behind a more concentrated slurry or solids, and (iv) a solid-liquid separator (e.g., a clarifier and / or a filter press) to separate the solids in the slurry from the liquid. The equipment in the RMS are fluidly connected to each other.

[0210] Embodiment 37: The process disclosed herein may further include a step of recovering, by a reagent management system, at least 95% of the indifferent salt from the concentrated leach solution. The concentrating of the leach solution to form a concentrated leach solution and a recovered chloride salt is performed by the reagent management system. The reagent management system recovers at least 95% of the at least one chloride salt to form the recovered chloride salt. The recycling of the recovered chloride salt is performed by the reagent management system, and the reagent management system is configured to recycle at least 95% of the at least one chloride salt.

[0211] Embodiment 38: Combinations of the various embodiments 1-37.

[0212] Only the preferred embodiments of the present invention and examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein. Thus, for example, those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific substances, procedures and arrangements described herein. Such equivalents are considered to be within the scope of this invention, and are covered by the following claims.DB1 / 161304616.2 44

Claims

1. PatentAttorney Docket No. 134465-5028-WOCLAIMSWHAT IS CLAIMED IS:

1. A process of leaching precious metal values from a feed source; the process comprising the steps of: a) contacting a comminuted ore formed from the feed source with a diluted solution of a chloride source for a first residence time of at least 10 minutes, preferably between 10 minutes and 3 hours; b) dissolving or adding a secondary source of chloride to the solution of step (a) to form a primary leach solution that contacts the comminuted ore; c) holding the primary leach solution from (b) for a second residence time of at least 1 hour, preferably between 1 to 4 hours; d) adding a reducing agent to the solution from step (c), preferably an acid source such as HC1, to form a secondary leach solution to effect a leaching process; e) holding the secondary leach solution from (d) for a third residence time of at least 1 hour, preferably between 1 to 24 hours; f) adding an indifferent salt to the solution from step (e) to complete the leaching process; and g) recovering metal from the solution from step (f).

2. The process of claim 1, wherein a slurry generated in the process has a pulp density in the range of 8 to 50 %, preferably 10 to 35 %, and wherein the pulp density refers to (i) a mass of solids present in the slurry based on a total mass of the slurry or (ii) a volume of solids present in the slurry based on a total volume of the slurry.

3. The process according to claims 1 or 2, wherein the primary leach solution contains the chloride source and the secondary source of chloride, wherein the primary leach solution is an oxidative leach solution,DBl / 161304616.2 45PatentAttorney Docket No. 134465-5028-WO wherein the secondary source of chloride includes a water soluble salt, and wherein a base, such as sodium chloride, is added to the primary leach solution.

4. The process as in any one of the preceding claims, wherein the secondary source of chloride plays a catalytic role in the process, wherein the secondary leach solution includes one or more chemical components as in the primary leach solution and a base, and wherein the primary leach solution has a pH of 7-12 and an oxidation-reduction potential (ORP) of 400 to 800 mV.

5. The process as in any one of the preceding claims, wherein the primary leach solution has a pH of 1-2 and an oxidation-reduction potential (ORP) of 400 to 600 mV.

6. The process as in any one of the preceding claims, wherein an order of addition of the chloride source and the secondary source of chloride as part of the primary leaching solution can be changed without impacting the leaching process.

7. The process as in any one of the preceding claims, wherein the reducing agent is added as an acid source, and wherein the reducing agent acts as a catalyst to initiate a reaction between the secondary leach solution and the ore.

8. The process of claim 7, wherein the acid source is HC1.

9. The process as in any one of the preceding claims, wherein the secondary leach solution has a pH of 4-7, and an oxidation-reduction potential (ORP) of at least 900 mV.

10. The process as in any one of the preceding claims, wherein the secondary leach solution has a pH of 1-5, and an oxidation-reduction potential (ORP) of 300-400 mV.DB1 / 161304616.2 46PatentAttorney Docket No. 134465-5028-WO11. The process as in any one of the preceding claims, wherein the primary leaching solution includes the chloride source and the secondary source of chloride, wherein the chloride source and the secondary source of chloride include (i) sodium chloride (NaCl), (ii) calcium hypochlorite (Ca(OCl)2), (iii) sodium hypochlorite (NaClO), (iv) sodium dichloro-s-triazinetrione dihydrate (CiFUChNNaOs), (v) anhydrous sodium dichloro-s- triazinetrione ( ChNsNaCb), (vi) trichloro-s-triazinetrione (C3CI3N3O3), or (vii) a combination of any two or more of (i) to (vi), and wherein the chloride source is combined with FeCh to create the primary leaching solution.

12. The process of claim 11, wherein sodium hypochlorite (NaClO) is from commercial bleach or prepared from electrolysis of a saline source.

13. The process according to claim 12, wherein the indifferent salt is an alkali halide salt.

14. The process according to claim 12, wherein the indifferent salt is a chloride-based salt.

15. The process according to claim 12, wherein the indifferent salt is sodium chloride.

16. The process as in any one of the preceding claims, where the reducing agent does not precipitate metal from the solution.

17. The process as in any one of the preceding claims, wherein the reducing agent is hydrochloric acid.

18. The process as in any one of claims 1-16, wherein the reducing agent is hypochlorous, chloric, or an oxy-acid of chlorine.

19. The process according to any one of the preceding claims, wherein the process is cyanide free.DB1 / 161304616.2 47PatentAttorney Docket No. 134465-5028-WO20. The process according to any one of the preceding claims, wherein the process is arsenic free.

21. The process according to any one of the preceding claims, further comprising, after the step g), forming a residual leach solution, and recycling the residual leach solution to form an additional feed slurry, wherein the recycling of the residual leach solution is performed by a reagent management system, and wherein at least 95% of the residual leach solution is recycled.

22. The process according to any one of the preceding claims, wherein the metal is a precious metal.

23. The process according to claim 22, further comprising recovering the precious metal from the recovered metal.

24. The process according to any one of the preceding claims, wherein the precious metal includes gold, silver, or both.

25. The process according to any one of claims 1 to 21, wherein the metal is a rare earth element.

26. The process according to any one of the preceding claims, further comprising introducing a slurry generated in the process to a thickener apparatus to separate the slurry into an underflow slurry and an overflow liquid with an increase in liquid-solids separation rate and / or efficiency of at least 25% as compared to the slurry in the thickener apparatus without the added indifferent salt.

27. The process according to claim 26, further comprising, prior to the introducing of the slurry, adding a polymer flocculant to the slurry, wherein a concentration of the polymer flocculant in the slurry is up to 0.4 wt%, andDBl / 161304616.2 48PatentAttorney Docket No. 134465-5028-WO wherein a concentration of the indifferent salt dissolved in the leach medium is 1 wt% to 30 wt%.

28. The process according to any one of the preceding claims, wherein in the step a), the contacting of the comminuted ore with the diluted solution of the chloride source forms a feed slurry, wherein the feed slurry is formed at a rate of at least two metric tonnes in a 24 hour period, wherein in the step d), triggering the leaching process forms a leach slurry that contains leach solids residue and a pregnant leach liquor containing the metal, and the process further comprises separating the pregnant leach liquor from the leach solids residue directly from the leach slurry by filtration without a prior thickening step.

29. The process according to claim 28, wherein the feed slurry is formed at a rate of at least two metric tonnes in a 24 hour period and separating the pregnant leach liquor from the leach solids residue occurs when the leach slurry has a solids concentration of greater than 10 wt% solids.

30. The process according to claim 28, wherein the feed slurry is formed at a rate of at least two metric tonnes in a 24 hour period and the metal is recovered from the pregnant leach liquor by separating the metal from the pregnant leach liquor in a product slurry having a solids concentration of greater than 10 wt% solids.

31. The process of claim 30, wherein separating the metal from the pregnant leach liquor in the product slurry occurs directly from the product slurry by filtration without a prior thickening step.

32. The process according to any one of the preceding claims, wherein the feed source further comprises rock, tailings, mining waste, coal ash, dredging spoils, or waste electronic equipment, and preferably the feed source further comprises a lithium containing sedimentary rock.DB1 / 161304616.2 49PatentAttorney Docket No. 134465-5028-WO33. The process according to any one of the preceding claims, wherein the primary leach solution, the secondary leach solution, or both are at a temperature of room temperature, preferably at least 25°C.

34. The process according to any one of the preceding claims, wherein the primary leach solution, the secondary leach solution, or both are at a temperature of room temperature to 45° C.

35. The process according to any one of the preceding claims, wherein water for the primary leach solution, the secondary leach solution, or both is heated by a natural source, or the primary leach solution, the secondary leach solution, or both are heated by the natural source.

36. The process according to any one of the preceding claims, wherein the balance of different chloride species affects the amount of chloride consumed during leaching.

37. The process according to any one of the preceding claims, wherein the leaching process can be performed as a co-current, countercurrent, or alternative process, and occurs at atmospheric pressure.

38. The process according to any one of the preceding claims, wherein a total chloride concentration in the leach solution is 1-400 g / L, alternatively at least 100 g / L, alternatively in a range of 200-300 g / L.

39. The process according to any one of the preceding claims, where a concentration of the reducing agent in the secondary leach solution does not exceed a 20% mass ratio, and the concentration is at least 10% mass ratio, preferably 14-18% mass ratio, more preferably 2-4M.

40. The process according to any one of the preceding claims, where a concentration of chloride in the secondary leach solution is 1-400 g / L, or 100-400 g / L range, preferably 200-300 g / L-DBl / 161304616.2 50PatentAttorney Docket No. 134465-5028-WO41. The process according to any one of the preceding claims, further comprising adjusting a first ratio (Rl) and a second ratio (R2) to increase metal leaching, wherein the first ratio (Rl) is an acid-to-ore ratio, expressed as a mass percentage (m / m), and is in a range of 0.1 to 2.0, preferably 1 to 1.8, and wherein the second ratio (R2) is a chloride salt-to-ore ratio, expressed as a mass percentage (m / m), and is in a range of 0.1 to 4.0, preferably 0.75 to 2.5.

42. The process of claim 41, further comprising maintaining a ratio of Rl to R2 between 0.15 and 1, preferably 0.3 to 0.6.

43. The process of claim 42, wherein a pH range is 4-7 and an oxidation-reduction potential (ORP) is 900-1100 mV.

44. The process of claim 42, wherein the leaching process occurs in a multi-stage process, with co-current or countercurrent steps.

45. The process according to any one of the preceding claims, further comprising generating in situ the primary leach solution via electrolysis of a saline source.

46. The process of claim 45, wherein the saline source includes seawater or a rejected stream from a desalination process or a combination thereof.

47. The process according to any one of the preceding claims, further comprising: recovering, by a reagent management system, at least 95% of the indifferent salt from the solution from the step (g), concentrating, by the reagent management system, the solution from the step (g) to form a concentrated leach solution and a recovered chloride salt, wherein the reagent management system recovers at least 95% of the chloride source to form the recovered chloride salt, and recycling, by the reagent management system, the recovered chloride salt, wherein the reagent management system is configured to recycle at least 95% of the chloride source.DB1 / 161304616.2 51PatentAttorney Docket No. 134465-5028-WO48. The process of claim 47, wherein the reagent management system is configured to recover, recycle, or repurpose at least 95% of materials, reagents, and solutions utilized in the process.

49. A process of leaching a metal from a feed source, the process comprising combining a first portion of the feed source with a primary leach solution to form a feed slurry; adding a reducing agent to the feed slurry to form a secondary leach solution to effect a leaching process that forms a first leach slurry containing leach solids residue and a pregnant leach liquor having the metal; adding an indifferent salt to the first leach slurry; separating the pregnant leach liquor from the leach solids residue; recovering the metal from the pregnant leach liquor and forming a residual leach solution having the indifferent salt dissolved therein; recovering, by a reagent management system, at least 95% of the indifferent salt from the residual leach solution; and adding the recovered indifferent salt to a second leach slurry formed from combining a second portion of the feed source, the primary leach solution, and the secondary leach solution, wherein the primary leach solution includes a chloride source and a secondary source of chloride, wherein the chloride source and the secondary source of chloride each independently includes (i) sodium chloride (NaCl), (ii) calcium hypochlorite (Ca(OCl)2), (iii) sodium hypochlorite (NaClO), (iv) sodium dichloro-s-triazinetrione dihydrate (CsHrChNsNaOs), (v) anhydrous sodium dichloro-s-triazinetrione (CsCLNsNaCh), (vi) trichloro-s-triazinetrione (C3CI3N3O3), or (vii) a combination of any two or more of (i) to (vi), wherein the primary leach solution has a pH of 7-12 and an oxidation-reduction potential (ORP) of 400 to 800 mV, wherein the reducing agent includes HC1, wherein the secondary leach solution has a pH of 4-7, and an oxidation-reduction potential (ORP) of at least 900 mV,DBl / 161304616.2 52PatentAttorney Docket No. 134465-5028-WO wherein an acid-to-ore ratio (Rl) is expressed as a mass percentage (m / m), and is in a range of 0.1 to 2.0, preferably 1 to 1.8, wherein a chloride salt-to-ore ratio (R2) is expressed as a mass percentage (m / m), and is in a range of 0.1 to 4.0, preferably 0.75 to 2.5, and wherein a ratio of Rl to R2 is between 0.15 and 1, preferably 0.3 to 0.6.

50. The process according to claim 49, wherein the feed source comprises rock, tailings, mining waste, coal ash, dredging spoils, or waste electronic equipment, and preferably the feed source further comprises a lithium containing sedimentary rock, and wherein the metal includes (i) gold, (ii) silver, (iii) a rare earth element, or (iv) any combinations of (i) to (iv).DBl / 161304616.2 53

Images