Alkaline powder formulation for the formation of stable tetraiodo-gold(III) complex in alkaline medium using a triple buffer system and stepwise oxidants

Abstract

This invention provides a novel powder and method for its use for the extraction and complexation of gold from sources containing this metal. The powder comprises an optimized combination of borax, sodium bicarbonate, and glycine as a triple buffer system, iodide ion as a leaching agent, a complementary combination of potassium persulfate and potassium monopersulfate (Oxone®) as an oxidant, and a copper salt as a catalyst for the oxidation-reduction cycle. In the proposed method, the powder is contacted with a solid gold-containing feed under mild alkaline conditions and ambient temperature to form a stable iodide-gold complex. This complex can be recovered to pure metallic gold through chemical or electrochemical reduction, and the leaching solution can be reused after recovery without loss of yield.

Description

Description of the invention Title of the invention Alkaline powder formulation for the formation of stable tetraiodo-gold(III) complex in alkaline medium using a triple buffer system and stepwise oxidants Technical background of the relevant invention This invention is in the field of mineral chemistry and hydrometallurgical processes and is specifically related to technologies for the extraction, recovery and purification of gold from mineral resources and electronic waste under alkaline conditions. Technical problem and stating the objectives of the invention Currently, common industrial processes for gold dissolution and complexation (especially halide and iodine / iodide methods) are mainly carried out under strongly acidic conditions (pH < 3). These approaches are associated with a set of serious challenges: 1. Severe equipment corrosion: A concentrated acidic environment causes rapid corrosion of tanks, pipes, and pumps, requiring the use of special alloys or acid-resistant coatings such as PTFE or tantalum, which significantly increases the investment cost. 2. Emission of toxic vapors and gases: In iodine / iodide processes, free iodine (I₂) is emitted as toxic and corrosive vapors, which not only pose safety and health risks, but also require complex absorption and filtration systems. 3. Uncontrollability of the iodide oxidation process: In many methods, strong oxidizers (such as chlorine, bromine, or persulfate in an acidic environment) cause excessive oxidation of I⁻ to IO₃⁻, which reduces the efficiency of the process and increases the cost of iodide consumption. 4. Low stability of the gold complex: AuI₄⁻ complexes formed in acidic or semi-acidic environments decompose rapidly and produce gold precipitates or unstable iodine compounds. 5. High energy consumption: Many existing processes require temperatures above 60–80°C to maintain reaction rates, which leads to significant energy consumption and increased operating costs. The precious metals extraction, e-waste recycling, and laboratory processes industries require technologies that: Work in milder conditions (pH close to neutral or slightly alkaline). Have precise control over the iodide oxidation process and active iodine production. Produce AuI₄⁻ complexes with long-term stability (> 72 hours). Have higher safety and lower emissions of hazardous substances. Significantly reduce investment and operating costs. Considering the aforementioned problems, this invention is designed with the following objectives: 1. Create a mildly alkaline environment (pH ≈ 8) using a multicomponent buffer system (borax + sodium bicarbonate + glycine) that minimizes pH changes during the reaction. 2. In situ and controlled production of active iodine oxidants using two oxidants with different reaction rates (potassium persulfate and potassium hydrogen monopersulfate) to prevent excessive oxidation of I⁻. 3. Improving the stability of the AuI₄⁻ complex by using glycine as a stabilizer and amino acid buffer. 4. Reducing energy consumption by allowing the reaction to be carried out at room temperature (25-40°C) 5. Increase safety and reduce environmental pollution by eliminating strong acids and preventing the release of toxic free iodine vapors. 6. Reduce operational and investment costs by eliminating the need for acid-resistant equipment and reducing the consumption of expensive chemicals. A description of the state of the prior art and the history of developments related to the claimed invention. The oldest industrial non-cyanide approach to gold dissolution is the iodine-iodide system, patented since the 1970s and 1980s. In patents US3957505A and US4557759, gold is converted to soluble gold-iodine complexes in the presence of molecular iodine and an iodide salt, and then the gold is precipitated with a reducing agent; the solution is regenerated with an oxidizing agent. The kinetics of gold dissolution in iodine / iodide mixtures are strongly dependent on iodide, iodine, and pH concentrations, according to Davis and Tran (1991); increasing iodide and controlling pH improve dissolution rates, but the high cost of iodine and issues of stability of I₂ / I₃⁻ species and re-oxidizing management remain challenges. The use of iodine / iodide in recycling from electronic waste has also been reported by Lucheva et al. (2016); with 25 g / L iodine and 100 g / L potassium iodide (KI) at room temperature, very fast recovery (≈97.5% in 1 min) was reported, although unwanted CuI precipitation and iodine cost were cited as limitations. New innovations use inorganic oxidants to produce “active iodine” in situ, rather than directly consuming large amounts of iodine. Chinese patent CN109943718A describes “Gold extraction with halide + persulfate oxidant” which uses persulfate (K₂S₂O₈ / Na₂S₂O₈ / NH₄) and halide salts including (KI / NaI); but sets the operating environment to pH≤7 and uses carbon in pulp (CIP) for leaching. Pathways based on the oxidation of iodide to I₂ / I₃⁻ (or even to iodate) in the fields of electrochemistry and materials have also been reviewed by Prehal et al. (2020), showing that precise control of iodine species (I⁻ / I₃⁻ / I₂ / IO₃⁻) is key to the stability and regenerability of the system. Alkaline glycine leaching has been one of the major research areas of the last decade. In this system, usually at pH (9–11) with oxidants such as H₂O₂ or other oxidants, gold is converted to aminodicarboxylate complexes; patent WO2015031943A1 and its US version show the process of recovering precious metals (including gold) in a glycine environment. Studies by Oraby et al. (2020) on glycine show that choosing the right oxidant (e.g., permanganate) can enhance recovery, but the complexation chemistry and mechanisms are different from halides and do not rely on iodide ion. Many classical iodine / iodide processes are designed to operate in acidic or near-neutral environments and often require molecular iodine injection or costly regeneration cycles to maintain “active iodine”; corrosion control, iodine vapor toxicity, and management of side-deposits such as (CuI) are also problematic. Persulfate-based halide methods reported in the patent literature largely maintain process pH ≤7 and rely on classical carbon / cellulose adsorption (CIP / CIL) frameworks; evidence of the use of mildly alkaline multicomponent buffer systems for long-term stabilization of gold iodide (AuI₄⁻) complexes with step oxidants is very limited. On the other hand, the alkaline glycine route, although it operates at high pH, ​​is fundamentally different in the nature of the complex and its optimal oxidant from the iodide system and cannot be a direct replacement for halide-based chemistry. Thus, the literature gap is evident in the simultaneous combination of a mild multicomponent alkaline buffer for stabilization (pH ≈ 8) and control of iodine species) with stepwise oxidants (to maintain “active iodine” without injecting too much iodine) in the presence of a dilute metal catalyst and directly targeting the stability of the AuI₄⁻ complex. This is exactly the claimed distinction of the invention compared to the existing files. (Especially in comparison to the classical iodine / iodide patents and persulfate-based halide patents at pH ≤ 7) The simultaneous combination of a ternary buffer system (borax + sodium bicarbonate + glycine) with two different oxidants (K₂S₂O₈) and (KHSO₅) and copper catalyst at low concentration, for the production and stability of the tetraiodo-gold complex in alkaline medium has not been reported so far. Providing a solution to an existing technical problem along with an accurate, sufficient, and integrated description of the invention This invention provides a formulation for the formation of a stable tetraiodo-gold complex in a mildly alkaline environment (pH ≈ 8). The formulation is designed using a triple buffer system (borax + sodium bicarbonate + glycine), two-step oxidants (potassium persulfate and potassium monopersulfate) and a low-consumption metal catalyst (copper sulfate pentahydrate). The aim of this design is to precisely control the pH, gradually produce active iodine in situ, prevent excessive iodide oxidation and stabilize the AuI₄⁻ complex for a long time. The composition of the formulation (wt%) is available in Table 1 of the map file. The following is a scientific explanation of the components and their role in the formulation: Borax: High capacity primary buffer at pH (8–9) whose weight percentage is 30-40% according to Table 1 in the map file and is added in the first stage to form a triple buffer according to Figure 1. Preventing pH fluctuations even in the presence of acidogenic reactions. Preventing unwanted metal precipitation through the formation of weak complexes. Basic reaction process: Borax reacts with water in an aqueous medium to form boric acid and hydroxide ions. This process causes a slight increase in the alkalinity of the solution and, due to its constant dissociation close to the mildly alkaline pH range, creates a high buffering capacity. In addition, the resulting boric acid can be converted to borate ion in the presence of water, which itself creates an effective buffering equilibrium in the pH range close to 9. This property allows borax to withstand sudden changes in acidity or alkalinity and to keep the pH of the environment constant within the desired range. Sodium bicarbonate: A reinforcing buffer is added next to borax, the weight percentage of which is 4-8% according to Table 1 in the map file and is added in the first stage according to Figure 1. Compensation for pH reduction caused by hydrolysis of persulfates. Creating a dual buffer system to increase overall buffering capacity. Basic Reaction Process: Sodium bicarbonate forms equilibria in aqueous media that make it an effective buffer in the acidic to mildly alkaline range. In one pathway, the bicarbonate ion can lose a proton and become carbonate ion; this reaction occurs in the alkaline pH range and plays an important role in neutralizing weak acids. In the other pathway, the bicarbonate ion can absorb a proton and become carbonic acid, which is unstable in the environment and decomposes into water and carbon dioxide. This two-way equilibrium gives sodium bicarbonate the ability to cope with sudden changes in pH and, as a reinforcing buffer alongside borax, maintains the stability of the reaction medium. Glycine: Amino acid buffer with buffer capacity at physiological pH, which according to Table 1 has a weight percentage of 4-8% and according to Figure 1 in the map file, is added in the first stage and after the addition of borax and sodium bicarbonate. Forming temporary complexes with Au³⁺ and facilitating ligand transfer to I⁻ Antioxidant property to prevent unwanted oxidation of I⁻ by oxygen.  Basic reaction process: Glycine exists in a mild alkaline medium in the form of a stable zwitterion, which provides special capabilities in the complexation process of metals. This compound can first react with trivalent gold ions and form a temporary complex with amino acid ligands. This temporary complex keeps gold in a soluble and active state until, in the next step, iodide ions replace the glycine ligands and a stable tetraiodo-gold complex is formed. This “ligand transfer” mechanism, in addition to facilitating the reaction rate, prevents premature precipitation or hydrolysis of gold. Glycine also has antioxidant properties, preventing unwanted oxidation of iodide ions by dissolved oxygen, which is of great importance for maintaining process efficiency in open systems. Potassium iodide: It is the main complexing agent, which is added in the second stage according to Figure 1, and according to Table 1, its weight percentage is 35-45%. Main source of I⁻ ions for the formation of the AuI₄⁻ complex. Tetraiodide-forming: Formation of I₄⁻ in the presence of I₂. Increasing the iodide concentration shifts the equilibrium towards the formation of a stable complex and prevents the formation of gold oxides. Basic reaction process: Iodide ions play multiple roles in this formulation. In the presence of trivalent gold ions, the complexation process is rapid and the tetraiodo-gold complex is formed with very high thermodynamic stability, the formation of which is highly favorable and spontaneous in terms of free energy. In the presence of monovalent gold ions, iodide ions are able to combine with it and form the diiodo-gold complex, which is also thermodynamically stable. In addition, in the reaction medium, free iodine molecules produced from the gradual oxidation of iodide ions react with the existing iodide ions and form stable polyiodide species. In one of these pathways, the tetraiodide species is obtained, the equilibrium of its formation is strongly shifted towards the products. In the other pathway, the pentaiodide species is formed, which also has a significant stability constant. These side reactions cause the bulk of the free iodine to remain in the form of soluble and stable complexes, preventing unwanted evaporation or precipitation. Potassium persulfate: Strong oxidizer to convert part of the iodide into active iodine (I₂), which has a weight percentage of 10-6% according to Table 1 and is added as the primary iodide oxidizer in the third step according to Figure 1. In-situ and controlled production of I₃⁻ and I₄⁻ species Highly reactive at room temperature and compatible with alkaline pH. Basic Reaction Process: Potassium persulfate in this formulation acts as a strong oxidant and reacts with iodide ions to produce free iodine molecules. This free iodine immediately combines with excess iodide ions to form stable polyiodide species such as triiodide and tetraiodide. This process causes the bulk of the iodine to remain in the form of soluble complexes and prevents unwanted evaporation or precipitation. Electrochemically, persulfate has a very high oxidizing potential, which allows the reaction to be carried out at room temperature and without the need for strong acidic conditions. At the same time, the reaction pathway is designed to control the rate of production of active iodine and prevent its excessive formation or unwanted oxidation to iodate. Potassium monopersulfate: A stepwise oxidizer with a reaction rate lower than potassium persulfate, which has a weight percentage of 2-6% according to Table 1 and is added in the fourth step as shown in the figure. Maintaining I⁻ / I₂ balance over time and preventing excessive oxidation to IO₃⁻ Secondary regulator of the oxidation process. Basic reaction process: Potassium monopersulfate, known as Oxone®, decomposes into active ions in an aqueous medium and acts as a selective oxidant with moderate strength. This compound is able to oxidize iodide ions to free iodine, but it does so in a gradual and controlled manner. Under appropriate conditions, part of the iodide ion is converted to free iodine and the other part to soluble polyiodide complexes, without excessive oxidation to iodate. This feature allows the level of active iodine in the solution to remain constant for a long time and the stability of the gold complexes to be maintained. Also, due to the relative stability of monopersulfate in an alkaline medium, the reactions proceed uniformly and without a sudden drop in oxidizing power, which is of great importance in controlling the process and preventing pH fluctuations. Copper sulfate pentahydrate: The catalyst for the oxidation reaction of iodide to active iodine, which has a weight percentage of 0.5-2, is added according to Table 1 and in the fifth step according to Figure 1. Reducing activation energy and increasing the rate of complex formation Use in low concentration to prevent CuI precipitation. (Copper-iodide) Basic Reaction Process: Copper sulfate pentahydrate in this formulation acts as a homogeneous catalyst and provides a cycle of oxidation-reduction reactions to accelerate the formation of active iodine. In the first step, divalent copper ions react with iodide ions to form a temporary precipitate of copper iodide and a small amount of free iodine. Then, this precipitate combines with excess iodide ions in the solution to form a soluble iodide-copper complex. Finally, this complex reacts with the main oxidant of the system to regenerate divalent copper ions, while more free iodine is introduced into the solution. This catalytic cycle allows the iodide oxidation process to proceed more quickly, without significantly consuming copper. Using a low concentration of this compound prevents the formation of stable copper-iodine precipitates and maintains the clarity of the reaction solution. Explanation of shapes, maps and diagrams Table 1: Ingredients in the formulation Figure 1: Flowchart of the steps of the gold extraction and complexation process using an alkaline buffer system and iodine oxidants: Figure 1 shows an overview of the steps of the process. In this method, first a three-component buffer solution is prepared and potassium iodide is added to it. Then the main oxidant (potassium persulfate) and then the auxiliary oxidant (potassium monopersulfate) are introduced into the system in stages to control the level of active iodine. Next, a copper sulfate catalyst is added to the solution. A gold-containing feed (such as shredded electronic waste) is placed in the solution to perform the gold complexation process. Finally, the gold is recovered from the solution and the leaching solution can be reused. A clear and precise statement of the advantages of the claimed invention over prior inventions. Unique triple buffer system: This invention introduces for the first time a multi-stage buffer system that includes a synergistic combination of borax, sodium bicarbonate, and glycine. This system is able to maintain the pH of the solution in the mildly alkaline range of about 8 and offers a very high buffer capacity. This feature minimizes pH changes due to side reactions and provides a stable and optimal environment for the formation and stabilization of gold-iodine complexes. The triple buffer system allows for precise simultaneous operation of the reactions by preventing the medium from becoming too acidic or basic. In situ production of active iodine oxidizers: One of the most important innovations of this invention is the possibility of producing active iodine oxidizing species in situ in solution. In this method, the combination of potassium persulfate with potassium iodide produces active iodine, without the need for the direct use of metallic iodine. The process is described as follows: Potassium persulfate reacts with potassium iodide to produce molecular iodine. This molecular iodine is then converted to various forms, such as potassium triiodide and potassium tetraiodide, in the presence of excess iodide. These species act as strong and controlled oxidizers, allowing for precise control of the extent and rate of gold oxidation. This method not only eliminates the hazards associated with working with metallic iodine, but also increases the safety and controllability of the reaction. Controlled staged oxidation: The invention uses a combination of potassium persulfate and potassium monopersulfate with different reaction rates. This approach allows for a gradual and controlled oxidation of iodide to molecular iodine, preventing excessive conversion of iodide to iodate. The result of this stepwise control is to maintain an optimal balance between the different iodine species and significantly increase the efficiency of gold complex formation. Low-consumption copper catalyst with optimal performance: The use of copper sulfate pentahydrate as a catalyst at very low concentrations (about 1% by weight) increases the reaction rate without interfering with the final product or consuming the catalyst itself. This catalyst reduces the activation energy of the reaction and allows the process to be carried out at room temperature, which has significant economic and environmental advantages. Technical advantages: Works at a mild pH (around 8) instead of the very low acidic pH of traditional methods. High stability of the gold complex. High efficiency under optimal conditions. High reaction speed. No production of toxic gases during the reaction. Economic benefits: Reducing the need for acid-resistant equipment, resulting in reduced capital costs. Reduced energy consumption due to lower operating temperature. Increase process safety and reduce costs associated with employee safety. Reducing waste and costs associated with chemical disposal. Description of at least one implementation method for implementing the invention On an industrial scale, this formulation can be used to extract gold from ore or electronic waste. The prepared solution is applied directly to samples containing gold and after complex formation, the gold is separated and recovered. For illustrative purposes, a semi-industrial scale laboratory implementation of this invention for extracting and complexing gold from electronic waste (printed circuit boards containing gold) is performed as follows: 1. Preparation of triple buffer solution In a stirred tank, the required amount of borax and sodium bicarbonate is dissolved in distilled water until the initial pH reaches about 8.1. Glycine is then added and the solution is continued to be stirred until it becomes uniform. 2. Adding the main complexing agent Potassium iodide is added to the buffer solution and stirred until completely dissolved. This step prepares the environment for gold complexation. 3. Initial oxidation begins Potassium persulfate is added gradually (over 5 minutes) to the solution to initiate controlled oxidation of iodide ions and formation of active iodine. 4. Stepwise oxidation regulation About 10 minutes after the addition of the initial oxidant, potassium monopersulfate is added to the solution to maintain the active iodine level throughout the process. 5. Adding catalyst A dilute solution of copper sulfate pentahydrate (with a final concentration of about 1% by weight) is introduced into the system to increase the rate of the iodide oxidation reaction. 6. Golden food entry The gold-containing PCB chips are placed in a stainless steel mesh basket and immersed in the reaction solution. Gentle stirring and temperature control are carried out in the range of 25 to 40 degrees Celsius. 7. Gold complexation Within 8 to 12 minutes, gold ions released from the feed surface react with iodide ions to form a stable complex AuI₄⁻. This complex remains in solution and produces a characteristic color that indicates the progress of the reaction. 8. End of reaction and separation of solid feed After the reaction is complete, the feed basket is removed from the solution and the solution containing the AuI₄⁻ complex is prepared for the gold recovery step. 9. Gold recovery from solution Depending on the industrial application, gold can be separated from the complex and recovered as pure metal by chemical reducing agents or electrochemical methods. 10. Recycling of leaching solution The remaining solution, after readjusting the iodide and oxidant concentrations, can be reused in subsequent cycles, which reduces material consumption and operating costs. Explicit mention of the industrial application of the invention Applications in gold mining industries: Extraction of gold from ore Recycling gold from electronic waste Refining and purifying raw gold Applications in chemical industries: Production of gold catalysts Synthesis of gold nanoparticles Electrochemical applications Applications in analytical laboratories: Quantitative determination of gold in various samples Separation of gold from interfering metals Standardization of gold solutions Applications in environmental considerations: Reducing pollution Removal of strong corrosive acids No production of toxic gases Dramatic reduction of hazardous chemicals Applications in recycling:  Possibility of recycling raw materials Reduction of chemical waste Compliance with green standards

Claims

Claims What is claimed: Claim 1) A composite powder for the extraction and complexation of gold from sources containing this metal, comprising: borax, sodium bicarbonate and glycine as a triple buffer system with multi-stage pH control, a source of iodide ions as a leaching agent, potassium persulfate and potassium monopersulfate (Oxone®) as supplementary oxidants to create active iodine species, a copper salt as a catalyst for the iodide oxidation-reduction cycle, the components of which are selected to form a stable iodide-gold complex under mild alkaline conditions and ambient temperature. Claim 2) A method for extracting and complexing gold using the powder of claim 1, comprising the steps of: preparing an aqueous solution containing said powder, contacting the solution with a solid feed containing gold under mild alkaline conditions and ambient temperature, forming active iodine species through a controlled reaction of oxidants, creating a stable iodide-gold complex, recovering pure metallic gold by chemical or electrochemical reduction, so that the leaching solution can be used for subsequent cycles without loss of efficiency.

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