Process for efficient metal recovery from ore using a novel hydrometallurgical technique

Abstract

A method for extracting and recovering metals from ore, the method comprising: crushing and / or grinding the ore to a target grind size; conducting an acidic pre-leaching stage on ore or ore concentrate to destroy acid consuming gangue minerals and extract acid soluble zinc and / or manganese; conducting a reductive leaching stage using sulphur dioxide gas to reduce manganese dioxide minerals within the ore to Mn2+ oxidation state and extract zinc and other metals; conducting a dithionate destruction stage to decompose dithionate into manganese sulfate and sulfur dioxide gas when dithionate levels exceed a predefined limit; conducting an iron precipitation stage to remove iron and aluminum impurities; conducting a zinc recovery stage via solvent extraction and crystallization; conducting a sulphide polishing precipitation stage to remove one or more of residual unrecovered zinc, copper, nickel, cobalt, cadmium, arsenic, or other base metals; conducting a manganese solvent extraction stage to selectively extract manganese away from calcium, sodium, magnesium and potassium; and conducting a manganese crystallization stage to produce high purity manganese sulphate monohydrate (HPMSM).

Description

PROCESS FOR EFFICIENT METAL RECOVERY FROM ORE USING A NOVEL HYDROMETALLURGICAL TECHNIQUEFIELD OF THE DISCLOSURE

[0001] The present disclosure generally relates to the field of hydrometallurgical processing, and more specifically, to a novel process for the efficient extraction and recovery of metals, particularly manganese and zinc, from ore.BACKGROUND

[0002] Hydrometallurgical processing is a well-established method for the extraction and recovery of metals from ores. This method involves the use of aqueous chemistry for the recovery of metals from ores, concentrates, and recycled or residual materials. Processing techniques that are commonly used include leaching, solvent extraction, and electrowinning.In the context of metal extraction, leaching is a process where a solute is extracted from its parent material by way of a solvent. This process is often used to extract metals from ores, where part or all of the ore is broken down into its constituent elements through the use of an acid or base. The leachate (solution that has been leached) can then be further processed to extract the desired metal.

[0003] Solvent extraction, also known as liquid-liquid extraction, is a method to separate one or more components based on their relative solubilities in two different immiscible liquids, usually water and an organic solvent. In the field of metal recovery, solvent extraction is often used to separate metals ions from the leachate.Electrowinning is an electrochemical process used to reduce metal ions in solution tometal on a cathode. The metal ions are reduced to metal atoms at the cathode while oxidation occurs at the anode. This process is often used in conjunction with leaching and solvent extraction to recover the desired metal. Manganese and zinc are two metals that are often extracted and recovered using hydrometallurgical processes. Manganese is a chemical element that is not found as a free element in nature; it is often found in oxide minerals and in combination with iron, calcium, and silicon. Zinc is a slightly brittle metal at room temperature and has a blue-silvery appearance when oxidation is removed. The extraction and recovery of these metals from ores require precise control of various factors such as particle size, acidity, temperature, and the availability of reducing agents. The optimization of these factors is paramount to maximize the extraction efficiency and the purity of the recovered metals.SUMMARY

[0004] According to an aspect of the present disclosure, a method for extracting and recovering metals from ore includes crushing and / or grinding the ore to a target grind size, conducting an acidic pre-leaching stage on ore or ore concentrate to destroy acid consuming gangue minerals and extract acid soluble zinc and / or manganese, and conducting a reductive leaching stage using sulphur dioxide gas to reduce manganese dioxide minerals within the ore to Mn2+oxidation state and extract zinc and other metals. The method also includes conducting a dithionate destruction stage to decompose dithionate into manganese sulfate and sulfur dioxide gas when dithionate levels exceed a predefined limit, conducting an iron precipitation stage to remove iron and aluminum impurities, conducting a zinc recovery stage via solvent extraction and crystallization, conducting a sulphide polishing precipitation stage to remove one ormore of residual unrecovered zinc, copper, nickel, cobalt, cadmium, arsenic, or other base metals, conducting a manganese solvent extraction stage to selectively extract manganese away from calcium, sodium, magnesium and potassium, and conducting a manganese crystallization stage to produce high purity manganese sulphate monohydrate (HPMSM).

[0005] According to other aspects of the present disclosure, the method may include precipitating manganese from a crystallizer bleed as manganese carbonate to be recycled as a neutralizing agent, or precipitating manganese from the solvent extraction raffinate as manganese carbonate to be recycled as a neutralizing agent. The method may also include conducting a crystallization of one or more of the potassium, sodium, dithionate in the raffinate to produce a mixed salt sulphate, producing process water to be recycled. The target grind size may be between 75 pm to 500 pm, the reductive leaching stage may be conducted with a retention time between 2 and 48 hours, and the iron precipitation stage may be conducted using lime and / or manganese carbonate in a series of agitated tanks. The zinc recovery stage may include cooling the solution to less than 40°C prior to zinc solvent extraction, the manganese solvent extraction stage may include a scrubbing stage to remove impurities from the organic phase, and the manganese crystallization stage may include adjusting the pH of the manganese strip liquor using manganese carbonate prior to crystallization.

[0006] According to another aspect of the present disclosure, a method for extracting and recovering manganese and zinc from ore includes crushing and / or grinding the ore to a target grind size, conducting an acidic pre-leaching stage to destroy acid consuming gangue minerals and extract acid soluble zinc and manganese, conductinga reductive leaching stage using sulphur dioxide gas to reduce manganese dioxide minerals within the ore to Mn2+oxidation state and extract zinc and other metals, conducting a dithionate destruction stage to decompose dithionate into manganese sulfate and sulfur dioxide gas, conducting an iron precipitation stage to remove iron and aluminum impurities, conducting a zinc recovery stage via solvent extraction and crystallization, conducting a sulphide polishing precipitation stage to remove residual unrecovered zinc, copper, nickel and other base metals and impurities, conducting a manganese solvent extraction stage to selectively extract manganese away from calcium, sodium, magnesium and potassium, conducting a manganese crystallization stage to produce high purity manganese sulphate monohydrate (HPMSM), conducting a drying and packaging stage to prepare the HPMSM for shipment, and conducting a manganese and ammonia recovery stage to recover residual un-extracted manganese and ammonia.

[0007] According to other aspects of the present disclosure, the method may include conducting a manganese precipitation stage on the raffinate to produce manganese carbonate, conducting an ammonia recovery stage on the raffinate to produce an ammonia solution that is recycled, or conducting a crystallization stage on the raffinate to remove one or more of potassium, sodium, dithionate, and calcium, as a sulphate or dithionate salt. The target grind size may be between 75 pm to 500 pm, the reductive leaching stage may be conducted with a retention time between 2 and 48 hours, the iron precipitation stage may be conducted using lime and / or manganese carbonate in a series of agitated tanks, the zinc recovery stage may include cooling the solution to less than 40°C prior to zinc solvent extraction, the manganese solvent extraction stage mayinclude a scrubbing stage to remove impurities from the organic phase, and the manganese crystallization stage may include adjusting the pH of the manganese strip liquor using manganese carbonate prior to crystallization.

[0008] The foregoing general description of the illustrative embodiments and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure and are not restrictive.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 illustrates an example process flow of a method for extracting and recovering metals from ore, in accordance with one or more implementations.

[0010] FIG. 2 illustrates an example flow sheet block flow diagram for extracting and recovering manganese and zinc from ore, in accordance with one or more implementations.DETAILED DESCRIPTION

[0011] Methods for extracting and recovering metals from ore are disclosed. The following description sets forth exemplary aspects of the present disclosure. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure. Rather, the description also encompasses combinations and modifications to those exemplary aspects described herein.

[0012] The present disclosure relates to a method 100 (as shown in Fig. 1 of the drawings) for extracting and recovering metals from ore, particularly manganese and zinc. In some aspects, the method involves a series of stages including crushing and / orgrinding the ore, conducting an acidic pre-leaching stage, a reductive leaching stage, a dithionate destruction stage, an iron precipitation stage, a zinc recovery stage, a sulphide polishing precipitation stage, a manganese solvent extraction stage, and a manganese crystallization stage. These stages are be designed to effectively extract and recover valuable metals from the ore, while also managing and minimizing the presence of impurities. An example of a flow sheet block flow diagram for extracting and recovering manganese and zinc from ore, in accordance with one or more implementations, is shown at Fig.2 of the drawings. However, it should be appreciated that other flow sheet implementations may also be possible within the scope of the present invention.

[0013] In some aspects, the method 100 begins with a comminution process 102, which involves crushing and / or grinding the ore. Manganese containing rock is reduced in size to prepare it for metal extraction. The rock is crushed to a P80 of around 30 to 400 mm then wet milled to a target grind size, with a P80 between 150 pm to 500 pm, producing a milled slurry containing 30-40% solids by weight. The slurry is thickened to increase the solids content up to 60 % solids by weight before acid pre-leaching circuit.

[0014] This process is designed to reduce the size of the ore to a target grind size, which can facilitate the subsequent extraction and recovery of metals. The target grind size may vary depending on the specific characteristics of the ore and the desired efficiency of the extraction and recovery process.

[0015] In some cases, the target grind size may be between 75 pm to 500 pm. This range may be beneficial in ensuring that the ore is sufficiently reduced in size to allow for effective extraction and recovery of metals, while also minimizing the energyconsumption and potential wear and tear on the crushing and / or grinding equipment. In other cases, the target grind size may be specified to be between 150 pm to 500 pm. This range may be beneficial in situations where a coarser grind size is desired, such as when the ore contains larger particles of valuable metals that can be more effectively extracted and recovered at a coarser grind size.

[0016] In some aspects, the method includes an acidic pre-leaching stage 104. This stage may be conducted on the ore or ore concentrate after the comminution process. The acidic pre-leaching stage is designed to destroy or decompose acid consuming gangue minerals (such as, for example, carbonates) and extract acid soluble zinc and manganese ahead of the reductive leaching circuit 106, allowing for improved operational control in the downstream circuit. The pre-leach stage 104 also extracts acid-soluble zinc and manganese hosted within the ore.

[0017] In some cases, the acidic pre-leaching stage 104 involves the use of sulphuric acid. The sulphuric acid may be dosed into a series of stirred tank reactors, providing a total retention time of 1 to 24 hours. The dosage of sulphuric acid may be controlled to achieve a discharge acidity between pH 0.5 and pH 3. This acidity range may be beneficial in ensuring effective destruction of acid consuming gangue minerals, depression of dithionate formation and extraction of acid soluble zinc and manganese.

[0018] In other cases, the acidic pre-leaching stage may also involve the extraction of metals from minerals containing acid soluble zinc and manganese hosted within the ore. This extraction process may be facilitated by the acidic conditions created by the sulphuric acid, which can dissolve the acid soluble zinc and manganese minerals, allowing them to be extracted into the leach solution. In yet other cases, the acidic pre-leaching stage may also involve the destruction of acid consuming gangue minerals such as carbonate. The destruction of these minerals may be beneficial in improving the operational control in the downstream circuit, as it can reduce the consumption of acid in the subsequent stages of the method.

[0019] After completion of the acidic pre-leaching stage, the acidic slurry may advance to the reductive leaching stage 106. In some aspects, a portion of the advancing acidified slurry may be directed to a thickener, where the slurry is thickened. The overflow from the thickener, containing free acid and dissolved metals, may report to the reductive leaching stage, while the underflow slurry may advance to dithionate destruction via a pre-heater.

[0020] In some aspects, the method includes a reductive leaching stage 106. This stage 106 involves the use of sulphur dioxide gas (at concentrations between 10 % and 99% SO2 by volume), which is be sparged into stirred tank reactors containing the acidified slurry from the acidic pre-leaching stage, creating a chemically reducing environment. Reductive leach retention time is between 1 and 48 hours.

[0021] The sulphur dioxide gas creates a chemically reducing environment within the reactors, which can facilitate the reduction of manganese dioxide minerals within the ore to the Mn2+oxidation state (The manganese dioxide minerals within the rock react with the dissolved sulphur dioxide and are reduced from their native Mn4+and Mn3+valence states to Mn2+oxidation state, enabling dissolution into the aqueous solution). This reduction process enables the manganese to dissolve into the aqueous solution, thereby facilitating its extraction.

[0022] In some cases, the reductive leaching stage may be conducted with aretention time between 3 and 48 hours. SO2 is added up to 120 % stoichiometric demand, based on the reductively soluble metal content within the ore. This range may be beneficial in ensuring sufficient time for the reduction and dissolution of the manganese dioxide minerals, while also allowing for the extraction of other metals such as zinc.

[0023] In other cases, the retention time for the reductive leaching stage may be between 3 and 24 hours. This range may be beneficial in situations where a shorter retention time is desired, such as when the ore contains a high concentration of manganese dioxide minerals that can be quickly reduced and dissolved. In yet other cases, the reductive leaching stage may be conducted with a retention time between 3 and 48 hours. This range may provide a balance between the efficiency of the reduction and dissolution process and the extraction of other metals. Particle size, acidity, temperature and sulphur dioxide gas availability are optimized to maximize manganese extraction. During the leaching process zinc is also extracted as well as other base, alkali and heavy metals found within the ore.

[0024] During the reductive leaching stage, other metals such as zinc, as well as base, alkali, and heavy metals found within the ore, may also be extracted. This extraction process may be facilitated by the chemically reducing environment created by the sulphur dioxide gas, which can dissolve these metals into the aqueous solution.

[0025] In some aspects, the reductive leaching stage also involves the generation of a secondary sulphur species, dithionate (S20e2’ is generated in solution at concentration from 0.05 g / L to 100 g / L), in solution. Higher free acidity entering the reductive leachcircuit depresses the formation of dithionate. The formation of dithionate may be managed through the control of acid addition during the acidic pre-leaching stage, with a free acid concentration up to 40 g / L in the reductive leach feed targeted to depress the formation of dithionate.

[0026] The reductive leach off-gas, consisting primarily of moisture and inerts from the dilute SO2 gas stream, is directed to a wet gas scrubber to remove any residual SO2. The leaching reaction is complete when the target manganese concentration, between 30 g / L to 125 g / L Mn, is achieved in the leach solution.

[0027] Upon completion, the reductive leach discharge slurry is preferably thickened up to 65 % solids and filtered to generate a leach solution of manganese, zinc and lesser amounts of impurities metals and dithionate. The filtered solids may advance to waste (i.e., tails) handling, while the leach solution may advance to subsequent stages of the method 100 for further processing and recovery of the extracted metals. The thickener overflow and filtrate may advance to dithionate destruction 108. If the dithionate concentration is less than the design limit (20 g / L S20e2’), the manganese leach solution will bypass the destruction circuit and advance to iron precipitation 110.

[0028] In some aspects, the method includes a dithionate destruction stage 108. This stage 108 is designed to decompose dithionate, a byproduct of the reductive leaching stage, into manganese sulfate and sulfur dioxide gas. The dithionate destruction stage 108 may be particularly beneficial when the concentration of dithionate in the leach solution exceeds a predefined limit, as it can help manage thepresence and potential impact of dithionate on the extraction and recovery process.

[0029] In some cases, the dithionate destruction stage 108 involves contacting the leach solution, which contains concentrations of the dithionate, with a portion of acidified ore redirected from the acidic pre-leaching stage104. In other words, the filtered leach solution containing concentrations of dithionate between 5 g / L and 100 g / L, produced during the reductive leach, is contacted with the portion of acidified ore redirected from the acid pre-leach circuit.

[0030] The amount of acidified ore redirected to the destruction circuit is controlled based on its contained Mn content and the measured concentration of dithionate within the PLS. This combined dilute slurry is processed through a pressure oxidation autoclave operating at temperatures between 110°C and 220°C with a residence time of 0.5 hours to 4 hours. Dithionate within the PLS is disproportionated into manganese sulfate and sulfur dioxide gas. The MnO2 contained in the acidified ore acts as an oxidant to support this disproportion reaction, and through this mechanism, consumes the released sulphur dioxide through its role as an oxidizing agent.

[0031] In some aspects, the method includes an iron precipitation stage 110. This stage 110 is designed to remove impurities, primarily iron and aluminum, from the acidic Mn-rich leach solution. The iron precipitation stage may be conducted in a series of agitated tanks, which can facilitate the mixing of the leach solution and the precipitation reagents.

[0032] Precipitation conducted is via oxidation with air and neutralisation using lime and / or manganese carbonate in a series of agitated tanks. Air is sparged into the reactors to oxidize any ferrous iron to ferric iron. This oxidation process may befacilitated by the introduction of air and / or manganese dioxide into the agitated tanks. The oxidized iron may then be precipitated from the leach solution using a neutralizing agent. The neutralizing agent may be selected based on its ability to react with the oxidized iron and form a precipitate that can be easily separated from the leach solution.

[0033] The neutralizing agent used in the iron precipitations stage 110 may be lime and / or manganese carbonate slurry is added to raise the solution pH to a set point between pH 1.8 and pH 5.5. The slurry pH setpoint, manganese dioxide and air addition is maintained for a period of up to 24 hours, until all iron has been removed from solution. These reagents may be beneficial in precipitating the iron and aluminum impurities, while also minimizing the potential impact on the pH of the leach solution.The use of lime and / or manganese carbonate may also be beneficial in situations where the leach solution contains a high concentration of iron and aluminum impurities, as these reagents can effectively precipitate these impurities even at high concentrations.

[0034] In some cases, the iron precipitation stage involves the oxidation of ferrous iron to ferric iron. This oxidation process may be facilitated by the introduction of air and / or manganese dioxide into the agitated tanks. The oxidized iron may then be precipitated from the leach solution using a neutralizing agent. The neutralizing agent may be selected based on its ability to react with the oxidized iron and form a precipitate that can be easily separated from the leach solution.

[0035] After the iron precipitation stage 110, the resultant slurry may be thickened and then filtered. The filter cake, consisting of iron removal precipitates, and neutralization residue, may be washed with raw water to recover any entrainedmanganese-rich solution. Once washed, the iron residue may be advanced to a waste handling facility or for further processing. The iron-free manganese-rich leach solution may then advance downstream to subsequent stages (such as, for example, zinc removal) of the method 100 for further processing and recovery of the extracted metals.

[0036] In some aspects, the method includes a zinc recovery stage 112. This stage 112 involves the use of solvent extraction and crystallization to recover zinc from the leach solution. The zinc recovery stage may be designed to effectively extract and recover zinc, while also managing and minimizing the presence of impurities. The manganese rich leach solution free of iron and aluminium is advanced to zinc recovery, consisting of zinc removal via solvent extraction followed by crystallization of the resultant strip solution to produce zinc sulfate heptahydrate.

[0037] Prior to entering zinc solvent extraction stage 112, the solution is subjected to a polishing filter to remove all suspended solids and is cooled to less than 50°C. The polished and cooled solution is contacted with an organic phase containing a zinc selective extractant and a suitable diluent in 1 to 4 extraction mixer-settlers. During extraction, the pH is controlled at the target setpoint between pH 1.5 and 3 using ammonium hydroxide. The organic is loaded to a target Zn concentration of 5 to 20 g / L, generating a raffinate solution with less than 5 g / L residual zinc.

[0038] The zinc loaded organic is stripped using concentrated sulfuric acid generating a concentrated zinc sulfate strip solution with a concentration greater than 100 g / L zinc. This strip solution is advanced to the zinc crystallization circuit, producing zinc sulphate heptahydrate. The crystalline zinc product is dried then packaged.

[0039] In summary, the zinc recovery stage may involve a combination of cooling,solvent extraction, scrubbing, and crystallization processes. These processes may be designed to effectively extract and recover zinc from the leach solution, while also managing and minimizing the presence of impurities. The zinc recovery stage may be particularly beneficial in the extraction and recovery of zinc from ore, and may contribute to the overall efficiency and effectiveness of the method.

[0040] In some aspects, the method 100 includes a sulphide polishing precipitation stage 114. This stage 114 may be designed to remove residual unrecovered zinc, copper, nickel, and other base metals and impurities from the leach solution. Raffinate from zinc solvent extraction is rich in manganese and contains minor concentrations of residual unrecovered zinc, copper, nickel and other base metals and impurities. These base and heavy metals are removed from solution via sulphide precipitation.

[0041] In the sulphide polish, sodium hydrosulphide (NaHS) solution is mixed into the zinc raffinate solution in a series of stirred tank reactors. The dosed NaHS reacts with the target impurity base metal ions in solution, resulting in their precipitation as base metal sulphides. Effective sulphide precipitation is managed through maintained control of NaHS addition. The reagent is dosed at greater than 100% stoichiometric demand based on the non-manganese base-metal concentration in solution. Solution pH is controlled throughout the sulphide precipitation circuit using a base to a setpoint between pH 3 and 6.

[0042] After sulphide precipitation, the discharge solution is filtered to generate the purified manganese rich solution and a base metal sulphide concentrate. The PLS is subjected to polishing filtration, cooled to less than 50°C then advanced to manganesesolvent extraction.

[0043] In some aspects, the method 100 includes a manganese solvent extraction stage 116. This stage 116 is designed to selectively extract manganese away from calcium, sodium, magnesium, and potassium found at varying concentrations in the manganese-rich solution. The manganese solvent extraction stage 116 may produce a high purity manganese sulphate solution, which can be fed to a manganese crystallizer for the production of high purity manganese sulphate monohydrate (HPMSM). Residual dithionate present is also rejected into the raffinate.

[0044] The manganese solvent extract stage 116 comprises three key sub-stages, namely an extraction stage, a scrubbing stage, and a stripping stage. In the initial extraction stage, the polished solvent extraction feed solution is contacted with an organic phase containing a manganese selective extractant (which may include, by way of non-limiting example, an organic acid such as phosphoric and / or phosphinic acid) and a suitable diluent, which has been first saponified using ammonia to 50 and 95% of the total extraction circuit base demand. Manganese extraction is conducted across 2 to 5 extraction stages. The solution pH across in extraction is controlled using an ammonium hydroxide solution. At completion of extraction, the target manganese concentration in the raffinate is less than 10 g / L.

[0045] In the subsequent scrubbing stage, minor amounts of calcium, sodium, potassium, magnesium, and other impurity metals load onto the organic during manganese extraction. To remove these unwanted impurities the loaded organic from extraction is subjected to 1 to 6 stages of scrubbing using acidified demineralized water, with a sulfuric acid concentration of 1-25 g / L. The scrubbed organic proceeds to thestrip stage.

[0046] In the subsequent stripping stage, the loaded and scrubbed organic phase is stripped across 1 to 4 stages of stripping using a strip feed solution containing up to 150-250 g / L sulfuric acid. A pure strip solution with a manganese concentration greater than 80 g / L is generated. Once stripped, the barren organic is recycled back to the saponification mixer. The highly pure manganese sulphate strip liquor leaves the stripping stage and is advanced to the manganese crystallization circuit. The raffinate from the manganese solvent extraction circuit, containing calcium, potassium, magnesium, sodium, ammonium, and residual concentrations of manganese and dithionate is advanced to the ammonia recovery and impurity removal circuit.

[0047] In some aspects, the method 100 includes a manganese crystallization stage 118. This stage 118 may be designed to produce high purity manganese sulphate monohydrate (HPMSM) from the manganese strip liquor obtained from the manganese solvent extraction stage. The manganese crystallization stage may involve adjusting the pH of the manganese strip liquor using manganese carbonate prior to crystallization. This pH adjustment may be beneficial in controlling the free acid content in the strip liquor, thereby controlling the acidity of the HPMSM product.

[0048] The manganese strip liquor from solvent extraction is pH adjusted using manganese carbonate to the target crystallizer feed pH, then pumped to the salt crystallization system. The solution is subjected to conventional evaporative crystallization processes.

[0049] In the crystallizer, the recycle rate is controlled by the design increase in temperature across the heater. The crystallizer operates with a 1 to 45 % bleed. Thebleed is split with the majority recycled back to sulphide precipitation circuit to control impurities. A portion of the bleed is used to generate high purity manganese carbonate used for pH control in the strip solution.

[0050] The produced HPMSM slurry from the crystallizer is fed to a centrifuge. The centrifuge dewaters the slurry, producing a wet cake (nominally 5 to 20% w / w moisture) which is discharged to the crystallization dryer. The HPMSM cake is washed during the centrifuge operating cycle.

[0051] In some aspects, the method 100 includes a drying and packaging stage 120. This stage 120 may be designed to prepare the high purity manganese sulphate monohydrate (HPMSM) produced in the manganese crystallization stage for shipment. The drying and packaging stage may involve the use of a dryer to remove the moisture from the moist HPMSM cake produced by the centrifuge. The drying process may be beneficial in reducing the moisture content of the HPMSM cake to a suitable level for packaging and shipment. The final dried product contains a manganese concentration greater than 32 wt%.

[0052] In some aspects, the above method 100 is the first of two separate manganese recovery circuits. The first processes a portion of the manganese crystallizer bleed, generating a high purity manganese carbonate precipitate for use in the crystallizer as a feed solution neutralizing agent. In the second process 122 (and as shown in part in Fig. 2), the full raffinate stream from manganese solvent extraction, to recover residual un-extracted manganese producing a manganese carbonate precipitate which is recycled into the upstream leach and purification. Both manganese precipitation circuits function in the same manner, however the distribution of the circuitproducts and their purity is different. The description below focuses on the second circuit, treating the raffinate prior to ammonia recovery.

[0053] Within the second circuit, and in some aspects, the method further includes a manganese recovery strep by raffinate treatment. The raffinate from manganese solvent extraction advances to the manganese recovery circuit after residual entrained organic is removed.

[0054] Manganese recovery from the raffinate is conducted via precipitation using ammonium bicarbonate and ammonium hydroxide, generating a manganese carbonate precipitate. Ammonium bicarbonate is dosed into a series of stirred tank reactors at a target dosage rate as demanded by the stoichiometric requirement to achieve less than 100 ppm residual manganese in circuit discharge solution. During precipitation, ammonium hydroxide is added stoichiometrically to maintain the desired pH.

[0055] After completion of the manganese precipitation reaction, the manganese carbonate precipitate is thickened, and the underflow advanced to a filter. The MnCOs filter cake is repulped and recycled back to the reductive leach and or iron removal circuit, where the manganese metal is recovered as aqueous manganese sulphate. The thickener overflow and filter filtrate advance to ammonia recovery.

[0056] Within the second circuit, and in some aspects, the method further includes an ammonia recovery and gypsum removal stage. The role of ammonia recovery is to convert then recover the ammonium to ammonia, which entered the process as ammonia dosed to the zinc and manganese solvent extraction circuits for pH control.

[0057] After manganese recovery, the solution containing ammonium sulphate, ismixed with lime. The lime addition is controlled based on measured discharge pH, with a discharge target between pH 10 to pH 11. Lime reacts with the aqueous ammonium sulphate generating ammonia and gypsum. A portion of the gypsum slurry containing ammonia is recycled to the feed of the ammonium conversion process to act as a seed material to increase the particle size of the gypsum precipitates. During the ammonium conversion process, a secondary reaction occurs between the lime and aqueous magnesium sulphate within the raffinate, originating from soluble magnesium within the plant feed; this second reaction precipitates magnesium from solution as solid magnesium hydroxide and a byproduct of gypsum.

[0058] During the conversion process, some amount of ammonia is volatilized as a gas above the slurry within the conversion vessels. Air is swept across the tanks and the ammonia is recovered in an acid scrubber. Scrubber discharge is returned to the ammonia slaker. The slaker process liquid phase products consist of ammonia, potassium sulphate, sodium sulphate. The solid phase consists of gypsum and magnesium hydroxide.

[0059] The gypsum slurry containing ammonia is advanced to the ammonia stripping columns. Within the column the slurry is contacted with steam across a high surface area. The steam strips the ammonia from solution generating a wet ammonia vapor. The mixture of ammonia and water vapor is captured from the column and condensed within a heater exchanger into a solution reporting an ammonia concentration greater than 5 wt%. The discharged slurry from the column contains a residual ammonia concentration less than 0.5 g / L.

[0060] The low ammonia slurry is thickened to a solids concentration greater than 20% by weight. A portion of the thickener underflow is recycled to the gypsum precipitation tanks as seed to be introduced into the ammonia slaker and the remainder routed to the gypsum tailings filter or a second stage of ammonia recovery. The thickener overflow is recycled to the acid leach with excess advanced to calcium precipitation.

[0061] In some aspects, and as a further extension of the method 100 (and as shown, in part, in Fig. 2), the method may include a sodium-potassium removal and water recycling stage. After manganese-ammonia recovery and gypsum removal the solution contains predominantly, potassium, residual calcium, and sodium. These impurities are removed using a combination of reverse osmosis and crystallization, the clean permeate and condensate produced through the removal stages are recycled within the plant as clean process water.

[0062] A first stage of this process involves calcium precipitation and thickening. Prior to reverse osmosis, calcium is removed to prevent scaling. Calcium is precipitated as calcium carbonate using sodium carbonate. The overflow solution from gypsum removal is advanced to calcium precipitation consisting of a series of stirred tank reactors. Within the series of reactors, sodium carbonate solution is dosed at a controlled rate based on the reagent demand to achieve less than 100 ppm Ca in the discharge solution. Through this process, aqueous calcium is precipitated as calcium carbonate.

[0063] The discharge slurry is advanced to the calcium thickener where it is thickened to more than 30 % solids by weight. The thickened underflow is routed to the gypsum tails thickener; the overflow containing potassium, sodium and any residual ammonium is cooled to less than 40°C and advanced to reverse osmosis to concentratethe contained potassium and sodium in solution ahead of crystallisation. The cooled solution is subjected to RO where more than 90% of the water is recovered to permeate for reuse within the process. The high potassium retentate solution is advanced to the zero discharge crystalliser.

[0064] A second stage of the process involves zero discharge crystallization. The upgraded RO retentate is routed to a conventional evaporative crystallizer where the mono-valent sulphates are crystallized producing a mixed sulphate crystal product and a pure water condensate. The crystal product mostly consisting of potassium and sodium sulphate and residual amounts of calcium sulphate, ammonium sulphate and dithionate salts is dried and bagged.

Claims

What is claimed is:1 . A method for extracting and recovering metals from ore, the method comprising: crushing and / or grinding the ore to a target grind size; conducting an acidic pre-leaching stage on ore or ore concentrate to destroy acid consuming gangue minerals and extract acid soluble zinc and / or manganese; conducting a reductive leaching stage using sulphur dioxide gas to reduce manganese dioxide minerals within the ore to Mn2+oxidation state and extract zinc and other metals; conducting a dithionate destruction stage to decompose dithionate into manganese sulfate and sulfur dioxide gas when dithionate levels exceed a predefined limit; conducting an iron precipitation stage to remove iron and aluminum impurities; conducting a zinc recovery stage via solvent extraction and crystallization; conducting a sulphide polishing precipitation stage to remove one or more of residual unrecovered zinc, copper, nickel, cobalt, cadmium, arsenic, or other base metals; conducting a manganese solvent extraction stage to selectively extract manganese away from calcium, sodium, magnesium and potassium; and conducting a manganese crystallization stage to produce high purity manganese sulphate monohydrate (HPMSM).

2. The method of claim 1 , further comprising precipitating manganese from a crystallizer bleed as manganese carbonate to be recycled as a neutralizing agent.

3. The method of claim 1 or claim 2, further comprising precipitating manganese from the solvent extraction raffinate as manganese carbonate to be recycled as a neutralizing agent.

4. The method of any one of claims 1 to 3, further comprising conducting a crystallization of one or more of the potassium, sodium, dithionate in the raffinate to produce a mixed salt sulphate, producing process water to be recycled.

5. The method of claim 1 , wherein the target grind size is between 75pm to 500pm.

6. The method of claim 1 , wherein the reductive leaching stage is conducted with a retention time between 3 and 48 hours.

7. The method of claim 1 , wherein in the iron precipitation stage ferrous iron is first oxidized using air and / or manganese dioxide and then precipitated using a neutralizing agent in a series of agitated tanks.

8. The method of claim 7, wherein the neutralizing agent is an alkali.

9. The method of claim 8, wherein the alkali is one or more of lime, and manganese carbonate.

10. The method of claim 1 , wherein the zinc recovery stage includes cooling thesolution to less than 50°C prior to zinc solvent extraction.

11. The method of claim 1 , wherein the manganese solvent extraction stage includes a scrubbing stage to remove impurities from the organic phase.

12. The method of claim 1 , wherein the manganese solvent extraction stage includes the use of a manganese selective extractant.

13. The method of claim 12, wherein the manganese selective extractant is an organic acid such as phosphoric and / or phosphinic acid.

14. The method of claim 1 , wherein the manganese crystallization stage includes adjusting the pH of the manganese strip liquor using manganese carbonate prior to crystallization.

15. A method for extracting and recovering manganese and zinc from ore, the method comprising: crushing and / or grinding the ore to a target grind size; conducting an acidic pre-leaching stage to destroy acid consuming gangue minerals and extract acid soluble zinc and manganese; conducting a reductive leaching stage using sulphur dioxide gas to reduce manganese dioxide minerals within the ore to Mn2+oxidation state and extract zinc and other metals; conducting a dithionate destruction stage to decompose dithionate into manganese sulfate and sulfur dioxide gas; conducting an iron precipitation stage to remove iron and aluminumimpurities; conducting a zinc recovery stage via solvent extraction and crystallization; conducting a sulphide polishing precipitation stage to remove residual unrecovered zinc, copper, nickel and other base metals and impurities; conducting a manganese solvent extraction stage to selectively extract manganese away from calcium, sodium, magnesium and potassium; conducting a manganese crystallization stage to produce high purity manganese sulphate monohydrate (HPMSM); and conducting a drying and packaging stage to prepare the HPMSM for shipment.

16. The method of claim 15, wherein ammonia is used as the basifying agent within the manganese solvent extraction stage.

17. The method of claim 15 or 16, further comprising conducting a manganese precipitation stage on the raffinate to produce manganese carbonate.

18. The method of any one of claims 15 to 17, further comprising conducting an ammonia recovery stage on the raffinate to produce an ammonia solution that is recycled.

19. The method of any one of claims 15 to 18, further comprising conducting a crystallization stage on the raffinate to remove one or more of potassium, sodium, dithionate, and calcium, as a sulphate.

20. The method of claim 15, wherein the target grind size is between 75pm to500pm.

21. The method of claim 15, wherein the reductive leaching stage is conducted with a retention time between 3 and 48 hours.

22. The method of claim 15, wherein the iron precipitation stage is conducted using lime and / or manganese carbonate in a series of agitated tanks.

23. The method of claim 15, wherein the zinc recovery stage includes cooling the solution to less than 50oCprior to zinc solvent extraction.

24. The method of claim 15, wherein the manganese solvent extraction stage includes a scrubbing stage to remove impurities from the organic phase.

25. The method of claim 15, wherein the manganese crystallization stage includes adjusting the pH of the manganese strip liquor using manganese carbonate prior to crystallization.

26. A method for extracting and recovering manganese and zinc from ore, the method comprising: crushing and / or grinding the ore to a target grind size; conducting an acidic pre-leaching stage to destroy acid consuming gangue minerals and extract acid soluble zinc and manganese; conducting a reductive leaching stage using sulphur dioxide gas to reduce manganese dioxide minerals within the ore to Mn2+oxidation state and extractzinc and other metals; conducting a dithionate destruction stage to decompose dithionate into manganese sulfate and sulfur dioxide gas; conducting an iron precipitation stage to remove iron and aluminum impurities; conducting a zinc recovery stage via solvent extraction and crystallization; conducting a sulphide polishing precipitation stage to remove residual unrecovered zinc, copper, nickel, cobalt, cadmium, arsenic, or other base metals; conducting a manganese solvent extraction stage to selectively extract manganese away from calcium, sodium, magnesium and potassium; conducting a manganese crystallization stage to produce high purity manganese sulphate monohydrate (HPMSM); conducting a drying and packaging stage to prepare the HPMSM for shipment; and conducting a manganese and ammonia recovery stage to recover residual un-extracted manganese and ammonia.

27. The method of claim 26, wherein the target grind size is between 75pm to 500pm.

28. The method of claim 26, wherein the reductive leaching stage is conducted with a retention time between 3 and 48 hours.

29. The method of claim 26, wherein the iron precipitation stage is conducted usinglime and / or manganese carbonate in a series of agitated tanks.

30. The method of claim 26, wherein the zinc recovery stage includes cooling the solution to less than 50oCprior to zinc solvent extraction.

31. The method of claim 26, wherein the manganese solvent extraction stage includes a scrubbing stage to remove impurities from the organic phase.

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