Process for selectively extracting gold by thiosulfate method

Abstract

The invention discloses a selective gold extraction process by a thiosulfate method, which comprises the following steps of: adding gold ore and anion exchange resin into an aqueous solution of a leaching agent, and stirring and leaching to obtain ore pulp containing gold-loaded resin; the leaching agent comprises thiosulfate, copper salt and ammonia water; separating the gold-loaded resin from the ore pulp, and desorbing the gold-loaded resin by adopting a desorption agent to obtain a gold-rich desorption solution; and adding dithionite into the gold-rich desorption solution for reduction to obtain an elemental gold product. According to the process disclosed by the invention, resin adsorption and recovery are synchronously realized during gold leaching, and coadsorption of copper is avoided, so that gold can be enriched by adopting the gold-loaded resin through one-section desorption, and the gold extraction process flow is greatly simplified. In addition, the process is high in gold leaching rate, short in leaching time, low in agent consumption and low in leaching cost. In addition, the resin can be directly and circularly used for gold leaching without regeneration, the reduction barren solution can be circularly used for desorption of the gold-loaded resin by supplementing a small amount of desorption agent, and the recovery cost is low.

Description

Technical Field

[0001] The invention belongs to the field of hydrometallurgy, and in particular relates to a thiosulfate method selective gold extraction process. Background Art

[0002] Cyanide extraction has long been the mainstream gold extraction technology due to its simple process, low production costs, and high leaching rates. However, cyanide is highly toxic, and its use poses significant environmental risks. Therefore, the development of clean gold extraction technologies is crucial for the green and sustainable development of the gold industry. Currently, the most widely reported methods include the halogen method, thiourea method, thiocyanate method, lime sulfur method, glycine method, and thiosulfate method. In comparison, the thiosulfate method offers advantages such as a non-toxic and inexpensive leaching agent, gold extraction in an alkaline medium, and excellent leaching performance for ores difficult to treat with cyanide, such as those containing carbon and copper. Therefore, it is widely considered the most promising gold extraction process.

[0003] The thiosulfate gold leaching reaction is shown in formula (1-1). In the absence of a catalyst, the reaction rate is very slow. Usually, Cu(II) and NH3 are introduced to catalyze the leaching. Thus, the thiosulfate method forms a mixture of Cu(II), NH3, S2O3 2– However, S2O3 2– Unstable, the decomposition produces sulfur oxygen impurity ions such as S3O6 2– 、S4O6 2– The ions will be adsorbed or deposited on the gold surface, passivating the gold surface and hindering further dissolution of the gold, making it difficult for the gold leaching rate of this method to reach the level of the cyanide method. This is one of the key factors restricting the industrial application of the thiosulfate method.

[0004] 4Au + 8S2O3 2– + O2+ 2H2O → 4Au(S2O3)2 3– + 4OH – (1-1) The complex process and high cost of gold recovery in the leachate are another problem that restricts the promotion and application of the thiosulfate method. Gold can be directly recovered from the solution by methods such as replacement and electrodeposition. However, since the copper concentration in the leachate can be as high as hundreds or even thousands of times that of gold, copper will be replaced / deposited together with gold during recovery, resulting in a large consumption of replacement metal and low current efficiency, resulting in high gold recovery costs, and low gold product grade, which still requires further separation and purification, and a long process flow. Therefore, it is necessary to separate copper and gold in advance and achieve gold enrichment. Methods such as adding activated carbon, resin, etc. to the leachate for adsorption are expected to achieve the above purpose. However, activated carbon has a low affinity for Au(S2O3)2 3– The affinity of the resin is very weak and cannot effectively adsorb gold. Strong alkaline anion resin can effectively adsorb gold. However, a large amount of copper (in the form of Cu(S2O3)3 5–In this form, they are also adsorbed simultaneously. Therefore, a two-stage complex desorption process of first desorbing copper and then desorbing gold is required for the loaded resin to achieve the separation and enrichment of copper and gold. Moreover, due to the high copper content, a large amount of desorbent is used, resulting in high desorption costs.

[0005] In summary, due to the passivation effect of the sulfur-oxygen impurity ions generated by the oxidation and decomposition of S2O3 2– on the gold leaching, the gold leaching rate is low. In addition, the serious interference of the copper introduced during leaching on the gold recovery makes the gold recovery process complex and costly, which causes difficulties in the popularization and application of the gold extraction method by thiosulfate. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the above-mentioned deficiencies and defects in the background technology, and provide a selective gold extraction process by thiosulfate method with a high gold leaching rate, a short process, and low costs.

[0007] To solve the above technical problem, the technical solution proposed by the present invention is as follows: A selective gold extraction process by thiosulfate method includes the following steps: (1) Add gold ore and anion exchange resin to an aqueous solution of the leaching agent, and carry out stirring leaching under the condition of a pH value of 9 - 10 to obtain a pulp containing gold-loaded resin; the leaching agent includes thiosulfate, copper salt, and ammonia water; the concentration of thiosulfate is 0.05 - 0.1 mol / L, the concentration of copper salt is 1.5 - 5 mmol / L, and the concentration of ammonia water is 0.1 - 0.5 mol / L; (2) Separate the gold-loaded resin from the pulp, and use a desorbent to desorb the gold-loaded resin to obtain a gold-rich desorbing solution; the desorbent is a mixed solution containing chloride salt and sulfite; (3) Add sodium dithionite to the gold-rich desorbing solution for reduction to obtain elemental gold products.

[0008] As a further improvement, the thiosulfate in step (1) is one or more of sodium thiosulfate, ammonium thiosulfate, and calcium thiosulfate.

[0009] As a further improvement, the copper salt in step (1) is copper sulfate.

[0010] As a further improvement, the anion exchange resin in step (1) is a strongly basic chlorine-type anion exchange resin.

[0011] As a further improvement, the concentration of the anion exchange resin in step (1) is 5 - 20 kg / m 3 .

[0012] As a further improvement, the conditions for the leaching in step (1) are: the temperature is 25 - 45 °C, the stirring rate is 400 - 800 r / min, and the time is 4 - 12 h.

[0013] As a further improvement, the chloride salt in step (2) is sodium chloride, and the sulfite is sodium sulfite.

[0014] As a further improvement, the conditions for the desorption in step (2) are: the concentration of sodium chloride is 0.5 - 1 mol / L, the concentration of sodium sulfite is 0.01 - 0.05 mol / L, the dosage of the desorbent is 5 - 10 times the resin bed volume, and the flow rate of the desorbent is 1 - 5 resin bed volumes per hour.

[0015] As a further improvement, the dithionite in step (3) is sodium dithionite.

[0016] As a further improvement, the conditions for the reduction in step (3) are: the dosage of sodium dithionite is 1.5 - 2 times the theoretical dosage, and the reduction time is 5 - 20 min.

[0017] The object of the present invention is to eliminate the passivation of gold leaching caused by the thio-oxygen impurity ions generated by the oxidative decomposition of S2O3 2– to improve the gold leaching rate, and at the same time avoid the adverse effects of high-concentration impurity copper on gold recovery to simplify the recovery process and reduce the recovery cost. By solving the above two major problems, the industrial application process of the green non-cyanide gold extraction method of the thiosulfate method is promoted.

[0018] The mechanism of the present invention is as follows: The copper-ammonia-catalyzed thiosulfate gold leaching reaction is shown in equations (1)-(2). The oxidant Cu(NH3)4 2+ causes Au to lose electrons and be oxidized to Au + , Au + coordinates with S2O3 2– to form Au(S2O3)2 3– , realizing the leaching of gold. At the same time, Cu(NH3)4 2+ obtains the electrons lost by Au and is reduced to Cu(S2O3)3 5– , which is oxidized to Cu(NH3)4 again under the oxidation of dissolved oxygen 2+ (which will not be adsorbed by the anion exchange resin), realizing the regeneration of Cu(NH3)4 2+ . When a strongly basic chlorine-type anion resin is added during leaching, its reaction to adsorb the leached gold (Au(S2O3)2 3– ) and the copper in the pulp (Cu(S2O3)3 5– ) is shown in equations (3)-(4). Due to the S3O6 generated by the oxidative decomposition of S2O3 2– ​2− 、S4O6 2− The affinity with resin is significantly stronger than Cu(S2O3)3 5– But weaker than Au(S2O3)2 3− Therefore, the Cu(S2O3)3 adsorbed by the resin in the initial leaching 5– It is easy to be S3O6 2− 、S4O6 2− The gold-loaded resin is desorbed by a mixed solution of sodium chloride and sodium sulfite, and the reaction is shown in equation (7). SO3 2– First, with the adsorbed Au(S2O3)2 3– The reaction generates Cl with a higher affinity to the resin – Weak Au(S2O3)(SO3) 3– Then the complex ion is Cl – Replaced by Au(S2O3)(SO3) 3– Diffusion into the solution, to achieve the desorption of gold on the loaded resin. Sodium dithionite is used to reduce and recover the gold in the desorption solution. The reaction is shown in equation (8). Au(S2O3)(SO3) 3– The gold in the solution is reduced to elemental gold, S2O4 2- Oxidized to SO3 2– Among them, |-NR3 + Cl − The “|” in the column represents the main structure of the chloride-type anion resin, -NR3 + It is a quaternary ammonium group.

[0019]

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) High gold leaching rate, short leaching time, low reagent consumption and low leaching cost. The dissolved gold can be immediately adsorbed by the resin, and the gold concentration in the slurry is extremely low, which improves the leaching kinetics of gold. At the same time, S2O3 2– The sulfur and oxygen impurity ions produced by oxidation and decomposition can also be immediately adsorbed by the resin, eliminating their passivation effect on gold leaching, greatly facilitating gold leaching. Due to the above two reasons, an ideal gold leaching rate can be achieved, and the leaching time is shortened, thereby significantly reducing reagent consumption and gold leaching costs.

[0021] (2) The gold-loaded resin desorption process is simple, with less reagent consumption, high efficiency, and low cost. Compared with recovery methods such as displacement and electrodeposition, in the present invention, the leaching of gold and the resin adsorption and recovery of gold are carried out simultaneously, eliminating steps such as solid-liquid separation of pulp, solution clarification, and deoxidation, and the operation is simple. Compared with traditional resin adsorption and recovery, since the resin in the present invention does not adsorb copper, the gold-loaded resin can be enriched with gold by one-stage desorption, and the desorbent dosage is low, so the desorption process is simple and the cost is low.

[0022] (3) The lean resin can be directly returned to leaching without regeneration, with simple operation and low cost. While gold is desorbed from the resin, the counter ions on the resin are converted into chloride ions (a small amount of sulfite ions will be adsorbed), and the resin returns to its initial form (see Equation (7)), that is, gold desorption and resin regeneration are completed synchronously. Therefore, the lean resin can be directly returned to the leaching stage for gold extraction again without regeneration, eliminating the resin regeneration step, simplifying the gold extraction process, and effectively reducing the gold extraction cost. Moreover, when the chloride ions and a small amount of sulfite ions adsorbed on the resin are returned to leaching, since the resin has a very weak affinity for these two ions, they are easily replaced by Au(S2O3)2 3− 、S3O6 2− 、S4O6 2− etc., without affecting the resin adsorption effect, and a small amount of chloride ions and sulfite ions can also promote gold leaching.

[0023] (4) The reduction and recovery effect of gold in the desorption solution is good, with low cost, and the reduced lean solution is easy to recycle. The gold in the desorption solution is reduced by the strong reducing agent sodium dithionite, with less reagent consumption, short reduction time, high gold recovery rate, and low cost. After the gold in the desorption solution is reduced, the dithionite is oxidized to sulfite, which happens to be the main component of the desorbent. Therefore, this process not only does not introduce foreign impurity ions, but also can supplement the sulfite lost due to oxidation during the desorption process, which is beneficial to the recycling of the desorption lean solution.

[0024] In summary, the process of the present invention realizes the resin adsorption and recovery of gold synchronously during gold leaching, and avoids the co-adsorption of copper. Therefore, the gold-loaded resin can be enriched with gold by one-stage desorption, and the gold extraction process flow is greatly simplified. Moreover, this process has a high gold leaching rate, short leaching time, less reagent consumption, and low leaching cost. In addition, the resin can be directly recycled for gold leaching without regeneration, and the reduced lean solution can be recycled for the desorption of the gold-loaded resin by adding a small amount of desorbent, with low recovery cost.

[0025] The present invention has an essential difference from adding resin during the leaching process in the cyanidation method for gold extraction, which is described in detail as follows: The purposes of adding resin in the gold extraction process by cyanidation method include: (1) Compared with adding resin to the leaching solution for adsorption and gold recovery after filtering the pulp, adding resin during the leaching process to conduct leaching and adsorption simultaneously can complete the leaching and gold adsorption in one step, eliminating the need for steps such as solid-liquid separation, washing, and clarification of the solution of the pulp, thus simplifying the gold extraction process; (2) The leaching speed of the cyanidation method is slow, usually requiring more than 24 hours, so the production cycle is long. Since resin is added during leaching, gold is immediately and effectively adsorbed by the resin after being dissolved, and the gold concentration in the pulp is extremely low, improving the kinetic conditions for gold leaching, promoting the dissolution of gold, shortening the leaching time, and increasing production efficiency.

[0026] In contrast, the starting point and ultimate goal of adding resin during the leaching process in the present invention are not to omit conventional processes such as solid-liquid separation, washing, and clarification of the solution of the pulp and shorten the leaching time like the cyanidation method (the leaching speed of the thiosulfate gold leaching method itself is much faster than that of the cyanidation method, usually only requiring 8 - 12 hours), but to remove impurities, that is, to comprehensively eliminate the adverse effects of impurity ions on the leaching and recovery of gold, improve the gold extraction effect, reduce production costs, solve the two major problems restricting the industrial application of the thiosulfate method, and thus achieve its complete replacement of the cyanidation method.

[0027] Specifically, the analysis of the reasons for the lower gold leaching rate of the thiosulfate method than that of the cyanidation method in the present invention and the ideas for solving this problem are described in detail as follows: S2O3 2– is a metastable substance and is prone to decomposition under the condition of the existence of Cu(NH3)4 2+ to generate thio-oxygen impurity ions such as S3O6 2− and S4O6 2− that have obvious passivating effects on gold leaching. As the leaching progresses, they gradually accumulate, and the passivation of gold leaching becomes more and more serious, resulting in weak dissolution of gold in the later stage of leaching. Therefore, although the leaching rate of this method is relatively fast, the gold leaching rate is difficult to catch up with that of the cyanidation method. To solve this problem, the present invention creatively adopts the method of adding strongly basic anion exchange resin during the leaching process. At the moment when thio-oxygen impurity ions such as S3O6 2− and S4O6 2− are generated, since the resin has a very strong affinity for them, the impurity ions are immediately adsorbed by the resin before reaching the gold surface, so they cannot passivate the gold surface, and thus the gold leaching rate is greatly increased.

[0028] Specifically, the analysis of the reasons for the adverse effects of the catalyst copper introduced during the leaching process on gold recovery in the present invention and the ideas for solving this problem are described in detail as follows: The gold concentration in the thiosulfate leaching solution is usually only 1 - 10 mg / L, while the copper concentration can be as high as 100 - 2000 mg / L. For a leaching solution with such a low gold concentration and a copper impurity concentration much higher than that of gold, it is obviously uneconomical to directly recover gold by electroplating / copper powder replacement. It is necessary to separate and enrich gold and copper before recovery. However, activated carbon has a certain adsorption effect on Au(S2O3)23– It cannot be adsorbed, so it is not feasible for gold recovery. When using resin adsorption, copper will be adsorbed together with gold, and a two-stage desorption process of first desorbing copper and then desorbing gold is required to separate and enrich gold. Moreover, due to the high copper loading, a large amount of desorbent is used, resulting in high desorption costs. To solve the above problems, co-adsorption of copper needs to be avoided. For this purpose, the present invention adopts the method of adding resin during leaching. At the beginning of leaching, part of the copper is adsorbed by the resin in the form of Cu(S2O3)3 5– , and as leaching proceeds, S2O3 2– gradually decomposes, continuously generating S3O6 2 − , S4O6 2− and other ions. The resin has a significantly stronger affinity for these ions than for Cu(S2O3)3 5– but weaker than for Au(S2O3)2 3− . Based on this property difference, the present invention cleverly uses the decomposition products of S2O3 2– to gradually replace the Cu(S2O3)3 5– adsorbed on the resin. At the end of leaching, the gold-loaded resin obtained contains almost no copper. Therefore, the gold-loaded resin can be separated and enriched by a simple one-stage desorption, significantly simplifying the gold recovery process. Moreover, since the copper desorption process is omitted, the desorption cost is greatly reduced.

[0029] In summary, it is fundamentally different from the purpose of adding resin in the cyanide system. The present invention simultaneously solves the adverse effects of impurity ions on gold leaching and recovery by adding resin during the leaching process, thereby significantly improving the gold extraction effect, effectively simplifying the gold extraction process, and significantly reducing the gold extraction cost, producing a very obvious effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0031] Figure 1 is the process flow diagram of the selective gold extraction process by the thiosulfate method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] To facilitate the understanding of the present invention, the following will describe the present invention more comprehensively and in detail in combination with the drawings of the specification and the preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0033] Unless otherwise defined, all technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of the present invention.

[0034] Unless otherwise specified, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through the market or prepared by existing methods.

[0035] As Figure 1 shown, the thiosulfate process for selective gold extraction in some specific embodiments of the present invention includes the following steps: (1) Add gold ore and anion exchange resin to an aqueous solution of the leaching agent and stir for leaching to obtain a pulp containing gold-loaded resin. The leaching agent includes thiosulfate, copper salt, and ammonia water.

[0036] In some embodiments, the thiosulfate is one or more of sodium thiosulfate, ammonium thiosulfate, and calcium thiosulfate. The copper salt can be copper sulfate, etc.

[0037] In some embodiments, the anion exchange resin is a strongly basic chlorine-type anion exchange resin, such as 201×7 resin, Amberlite IRA-400 resin, etc.

[0038] In some embodiments, the leaching conditions are as follows: the thiosulfate concentration is 0.05 - 0.1 mol / L (preferably 0.07 - 0.08 mol / L), the copper salt concentration is 1.5 - 5 mmol / L (preferably 1.8 - 2.5 mmol / L, more preferably 2 mmol / L); the ammonia water concentration is 0.1 - 0.5 mol / L (preferably 0.2 - 0.3 mol / L); the anion exchange resin concentration is 5 - 20 kg / m 3 ; the gold ore pulp concentration is 20 - 50 wt%, the pulp pH value is 9 - 10; the temperature is 25 - 45 °C, and the time is 4 - 12 h. The pulp concentration refers to the mass of the added gold ore / the total mass of the leaching system × 100%.

[0039] The realization of the present invention depends on generating sufficient S3O6 2− and S4O6 2− so as to replace Cu(S2O3)3 5– . The higher the concentration of the copper salt as the oxidant, the greater the consumption of thiosulfate, and the more S3O6 2− and S4O6 2− are generated. The higher the concentration of ammonia water as the copper salt stabilizer, the more stable the copper salt, the lower the consumption of thiosulfate, and the less S3O6 2− and S4O6 2−The less, and at the same time the above pH also ensures the generation of sufficient S3O6 2− and S4O6 2− If the pH is lower than or higher than the above range, it is difficult to generate sufficient S3O6 2− and S4O6 2− . In the above concentration ranges of thiosulfate, ammonia water and copper salt and at the above pH, the Cu(S2O3)3 initially adsorbed by the resin 5– is basically replaced by the S3O6 2− and S4O6 2− generated in the system, and finally copper (Cu(S2O3)3 5− ) is hardly adsorbed by the resin. Specifically, at the above copper salt, ammonia water concentration and pH, the initial concentration of thiosulfate is 50 - 100 mmol / L, and the total concentration of the intermediate products S3O6 2− and S4O6 2− generated by its decomposition is about 15 - 30 mmol / L. The initial concentration of copper salt is 1.5 - 5 mmol / L, and about 1 / 3 exists in the form of Cu(S2O3)3 5− , that is, 0.5 - 1.7 mmol / L is adsorbed by the resin, and 15 - 30 mmol / L of S3O6 2− and S4O6 2− is sufficient to replace all the Cu(S2O3)3 5− adsorbed by the resin at 0.5 - 1.7 mmol / L.

[0040] In some embodiments, the stirring rate of stirring leaching is 400 - 800 r / min. At this stirring speed, Cu(S2O3)3 5– can be converted into Cu(NH3)4 2+ , the concentration of Cu(S2O3)3 5– in the solution decreases, and the adsorption of copper is further reduced.

[0041] (2) Separate the gold-loaded resin from the pulp, and use a desorbent to desorb the gold-loaded resin to obtain a gold-rich desorbing solution. The desorbent is a mixed solution containing a chloride salt and a sulfite.

[0042] In some embodiments, the chloride salt can be sodium chloride, etc., and the sulfite can be sodium sulfite, etc.

[0043] In some embodiments, the resin and the pulp are separated by a sieve. The desorbing conditions for the gold-loaded resin are: the concentration of sodium chloride is 0.5 - 1 mol / L, the concentration of sodium sulfite is 0.01 - 0.05 mol / L, the dosage of the desorbent is 5 - 10 times the resin bed volume, and the flow rate of the desorbent is 1 - 5 resin bed volumes per hour.

[0044] Since the gold-loaded resin obtained at the end of leaching contains almost no copper (mainly (|-NR3)3Au(S2O3)2 3– , (|-NR3)2 + S3O6 2− , (|-NR3)2 + S4O6 2− ), the gold-rich desorbing solution basically contains only gold (Au(S2O3)(SO3) 3– ).

[0045] The lean resin after desorption can be directly returned to leaching without regeneration.

[0046] The separated pulp is filtered to obtain leaching residues and leaching solution, and the leaching solution can be returned to the gold leaching in step (1).

[0047] (3) Add dithionite to the gold-rich desorbing solution for reduction to obtain elemental gold products.

[0048] In some embodiments, the dithionite can be sodium dithionite or the like.

[0049] In some embodiments, the conditions for reducing and recovering gold are as follows: the dosage of sodium dithionite is 1.5 - 2 times the theoretical dosage, and the reduction time is 5 - 20 min.

[0050] A small amount of desorbent is added to the reduced lean solution for recycling and used for desorbing the gold-loaded resin.

[0051] The chemical composition of a gold-bearing oxidized ore is shown in Table 1. The following examples and comparative examples of gold leaching experiments were all carried out using this gold ore for research.

[0052] Table 1 Chemical element analysis of gold-bearing oxidized ore

[0053] Note: The unit of Au is g / t, and the units of the other elements are wt%.

[0054] Comparative Example 1 First, add water to the reactor, then add the leaching agent (sodium thiosulfate, copper sulfate, ammonia water), and finally add the gold ore (the particle size after grinding, the proportion of -200 mesh is 81.5%) and adjust the pH of the pulp to the set value with sodium hydroxide and sulfuric acid, and then carry out stirring leaching (the stirring rate is 500 r / min). The specific leaching conditions are as follows: the concentration of sodium thiosulfate is 0.075 mol / L, the concentration of copper sulfate is 2 mmol / L, the ammonia concentration is 0.3 mol / L, the pulp concentration is 33%, the temperature is 25 °C, the pH value of the pulp is 10, and the time is 12 h. The gold leaching rate and sodium thiosulfate consumption at different leaching times are shown in Table 2.

[0055] As can be seen from Table 2, when leaching for 1 h, the gold leaching rate is only 34.5%, and the consumption of sodium thiosulfate is 12.3 kg / t. -矿 . As the leaching time increases, the gold leaching rate gradually rises first. When leaching for 4 h, the gold leaching rate reaches 76.2%, and the consumption of sodium thiosulfate increases to 20.3 kg / t. -矿 . When the leaching time continues to increase, the gold leaching rate basically no longer increases, that is, the dissolution of gold is hindered, while the consumption of sodium thiosulfate continues to increase. This is because S3O6 2− and S4O6 2− produced by the consumption of sodium thiosulfate passivate the gold surface, making it difficult for the dissolution of gold to continue.

[0056] Table 2 Gold leaching rate and sodium thiosulfate consumption at different leaching times

[0057] Filter the above pulp to obtain the leaching solution and leaching residue. Add Amberlite IRA-400 resin to the leaching solution for adsorption, and the resin concentration is 10 kg / m 3 . The changes in the concentrations and adsorption rates of gold and copper in the leaching solution with time are shown in Table 3.

[0058] Table 3 Changes in the concentrations and adsorption rates of gold and copper in the leaching solution with time

[0059] As can be seen from Table 3, before adsorption, the concentrations of gold and copper in the leaching solution are 0.96 mg / L and 63.5 mg / L respectively. The copper concentration is lower than the initial value of 127 mg / L because part of the copper precipitates into the residue during the leaching process. After adsorbing for 10 min, the concentrations of gold and copper drop to 0.62 mg / L and 52.2 mg / L respectively, and the adsorption rates are 35.4% and 17.8% respectively. As the adsorption time increases, the concentrations of gold and copper gradually decrease. After adsorbing for 120 min, the adsorption rates of gold and copper reach 88.5% and 39.2% respectively. The main reason for the low copper adsorption rate is that a considerable part of the copper in the leaching solution exists in the form of Cu(NH3)4 2+ cations, which will not be adsorbed by the strongly basic anion exchange resin, and only the copper existing in the form of Cu(S2O3)3 5– will be adsorbed by the strongly basic anion exchange resin.

[0060] The gold-loaded resin obtained by adsorption for 120 min in Table 3 was packed into a column, and the resin was desorbed in two stages to separate and enrich copper and gold. First, 1 M NH3•H2O + 0.75 M (NH4)2SO4 was used to desorb copper, and then 1 M NaCl + 0.05 M Na2SO3 was used to desorb gold. The dosage of the desorbent was 10 resin bed volumes for both, and the flow rate of the desorbent was 2 resin bed volumes per hour. There was no loss of gold during the copper desorption process. The desorption rates of copper and gold with the change of desorbent dosage are shown in Table 4.

[0061] Table 4 Variation of Copper and Gold Desorption Rates with Desorbent Dosage

[0062] As can be seen from Table 4, when the desorbent dosage was 1 resin bed volume, the copper desorption rate was only 5.2%. With the increase of the desorbent dosage, the copper desorption rate gradually increased. When the desorbent dosage was 10 resin bed volumes, the copper desorption rate reached 92.5%, and a small amount of copper remained undesorbed. When the desorbent dosage was 1 resin bed volume, the gold desorption rate was only 11.6%. With the increase of the desorbent dosage, the gold desorption rate gradually increased. When the desorbent dosage was 10 resin bed volumes, the gold desorption rate reached 96.7%, and similarly, a small amount of gold remained undesorbed, and it was necessary to increase the desorbent dosage.

[0063] Example 1 First, water was added to the reactor, then the leaching agent (sodium thiosulfate, copper sulfate, ammonia water) was added, and finally the gold ore (the particle size after grinding -200 mesh accounted for 81.5%) and the resin (Amberlite IRA-400) were added. Then, sodium hydroxide and sulfuric acid were used to adjust the pH of the pulp to the set value, and then stirring leaching was carried out (the stirring rate was 500 r / min). The specific leaching conditions were: sodium thiosulfate concentration 0.075 mol / L, copper sulfate concentration 2 mmol / L, ammonia concentration 0.3 mol / L, pulp concentration 33%, resin concentration 10 kg / m 3 , temperature 25 °C, pulp pH value 10, time 12 h. The variations of gold and copper concentrations, gold leaching rate, and sodium thiosulfate consumption with leaching time are shown in Table 5.

[0064] As can be seen from Table 5, at 1 h of leaching, the gold and copper concentrations in the leaching solution were 0.004 mg / L and 24.8 mg / L respectively. Therefore, the dissolved gold was adsorbed by the resin very thoroughly, and a large amount of copper was also adsorbed by the resin. At this time, the gold leaching rate was only 61.2%, and the sodium thiosulfate consumption was only 11.5 kg / t -矿。As the leaching time increases, the concentration of gold in the leaching solution is very low while the concentration of copper gradually increases. This means that the dissolved gold is immediately adsorbed by the resin, while the copper adsorbed by the resin is gradually replaced and enters the solution. This is because the S3O6 2– and S4O6 2− ions generated have a stronger affinity for the resin than Cu(S2O3)3 2− but weaker than Au(S2O3)2 5– . Therefore, they can gradually replace the copper on the resin while the gold remains on the resin, thus achieving the selective adsorption of gold. Moreover, since the resin effectively adsorbs sulfur-oxygen impurity ions such as S3O6 3− and S4O6 2− , it effectively eliminates their passivation effect on gold leaching. Therefore, the gold leaching rate reaches 87.6% at 4 h of leaching, which is higher than the gold leaching rate of 78.6% without resin after 12 h of leaching (see Table 2). At the same time, the copper concentration in the leaching solution at 4 h of reaction is 61.6 mg / L, which is comparable to the copper concentration of 63.5 mg / L in the leaching solution obtained without resin after 12 h of reaction in the comparative example (see Table 3). Therefore, almost all the adsorbed copper is replaced, and the resin hardly adsorbs copper. Moreover, even after 12 h of leaching, the gold leaching rate is still increasing, which further confirms that adding resin during leaching has a significant effect on eliminating the adverse effects of sulfur-oxygen impurity ions on gold leaching. 2−

[0065] Table 5 Concentrations of gold and copper in the leaching solution, gold leaching rate and sodium thiosulfate consumption at different leaching times

[0066] The pulp containing resin after 4 h of leaching in Table 5 was separated using a sieve to obtain the loaded resin and the pulp. The loaded resin was packed into a column. To further verify whether copper is adsorbed by the resin, 1 M NH3•H2O + 0.75 M (NH4)2SO4 was first used to desorb copper. The dosage of the desorbent was 10 resin bed volumes, and the flow rate of the desorbent was 2 resin bed volumes per hour. The change in the copper concentration in the desorbing solution with the dosage of the desorbent is shown in Table 6. As can be seen from the table, when the dosage of the desorbent is 1 resin bed volume, the copper concentration in the desorbing solution is only 0.05 mg / L. As the dosage of the desorbent increases, the copper concentration in the desorbing solution first increases and then decreases. However, the copper concentration is within 0.4 mg / L, so copper is hardly adsorbed by the resin during the leaching process.

[0067] Table 6 Change in copper concentration in the desorbing solution with the dosage of the desorbent

[0068] ​Since the resin contains basically no copper, 1 M NaCl + 0.05 M Na2SO3 was used to directly desorb gold from the resin. The dosage of the desorbent was 10 resin bed volumes. The variation of the gold desorption rate with the dosage of the desorbent is shown in Table 7. As can be seen from the table, when the dosage of the desorbent was 1 resin bed volume, the gold concentration in the desorbing solution was 8.33 mg / L and the gold desorption rate was 22.1%. With the increase of the dosage of the desorbent, the gold concentration and the gold desorption rate in the desorbing solution gradually increased. When the dosage of the desorbent was 3 resin bed volumes, the gold concentration in the desorbing solution reached the maximum value of 13.04 mg / L and then began to decline. When the dosage of the desorbent was 5 resin bed volumes, the gold desorption rate exceeded 90%. With the further increase of the dosage of the desorbent, the rising amplitude of the gold desorption rate slowed down. When the dosage of the desorbent was 10 resin bed volumes, the gold desorption rate reached 99.8%, and the gold desorption was very complete. Compared with Table 4, under the condition of the same dosage of the desorbent, the gold desorption rate in Table 7 was significantly higher. Therefore, the desorption of gold was easier, so the dosage of the desorbent was reduced and the desorption cost decreased. Compared with Table 7, when the desorbent of each resin bed volume flowed through the resin bed layer, the gold concentration in the obtained desorbing solution was much greater than that of copper, indicating that copper was hardly adsorbed by the resin. Therefore, the selective adsorption and recovery of gold was realized by this process.

[0069]

[0070] Example 2 First, water was added to the reactor, then the leaching agent (sodium thiosulfate, copper sulfate, ammonia water) was added, and finally the gold ore (the particle size after grinding, -200 mesh accounted for 81.5%) and the resin (Amberlite IRA-400) were added. Then, the pH of the pulp was adjusted to the set value with sodium hydroxide and sulfuric acid, and then stirring leaching was carried out (the stirring rate was 500 r / min). The specific leaching conditions were as follows: the concentration of sodium thiosulfate was 0.075 mol / L, the concentration of copper sulfate was 2 mmol / L, the ammonia concentration was 0.3 mol / L, the pulp concentration was 33%, and the resin concentration was 10 kg / m 3 , the temperature was 25 °C, and the time was 12 h. The variations of the gold and copper concentrations, the gold leaching rate, and the consumption of sodium thiosulfate with the leaching time at different pulp pH values are shown in Table 8.

[0071] As can be seen from the table, at pH = 8, the gold leaching rate was 72.5%, and the copper concentration in the leaching solution was as low as 35.6 mg / L. This was because the consumption of sodium thiosulfate was low (12.2 kg / t -矿 ))), and the S3O6 2− and S4O6 2−Less, it is difficult to replace the copper adsorbed on the resin. As the pH increases to 9 and 10, both the gold leaching rate and the consumption of sodium thiosulfate increase significantly, and the copper concentration in the leaching solution increases to over 60 mg / L. However, when the pH increases to 11, although the consumption of sodium thiosulfate further increases, due to the decomposition of S3O6 2− and S4O6 2− being unstable under this condition, it is difficult to replace the copper adsorbed on the resin. Therefore, the copper concentration in the leaching solution decreases, and its catalytic gold leaching effect decreases, resulting in a decrease in the gold leaching rate. When the pH increases to 12, part of the copper will precipitate in the form of hydroxide, passivating the dissolution of gold, so the gold leaching rate further decreases. At the same time, due to the too high pH, S3O6 2− and S4O6 2− decompose due to instability, so it is very difficult to replace the copper adsorbed on the resin, and thus the copper in the leaching solution is very low.

[0072]

[0073] Example 3 First, add water to the reactor, then add the leaching agent (sodium thiosulfate, copper sulfate, ammonia water), and finally add the gold ore (the particle size after grinding, the proportion of -200 mesh is 81.5%) and the resin (Amberlite IRA-400). Then, adjust the pH of the pulp to the set value with sodium hydroxide and sulfuric acid and carry out stirring leaching (the stirring rate is 500 r / min). The specific leaching conditions are as follows: the concentration of sodium thiosulfate is 0.075 mol / L, the concentration of copper sulfate is 2 mmol / L, the ammonia concentration is 0.3 mol / L, the pulp concentration is 33%, the temperature is 25°C, the pH value of the pulp is 10, and the time is 12 h. The gold leaching rate and the consumption of sodium thiosulfate under different resin concentrations are shown in Table 9.

[0074] As can be seen from the table, when the resin concentration is 5 kg / m 3 , the gold leaching rate reaches 90.8%, and the consumption of sodium thiosulfate is 22.1 kg / t -矿 . As the resin concentration increases, the gold leaching rate gradually increases while the consumption of sodium thiosulfate gradually decreases. When the resin concentration is 20 kg / m 3 , the gold leaching rate reaches 95.1%, and the consumption of sodium thiosulfate is 18.8 kg / t -矿 . Therefore, the increase in resin concentration is beneficial to improving the gold leaching rate and reducing the consumption of sodium thiosulfate.

[0075] Table 9 Gold leaching rate and sodium thiosulfate consumption under different resin concentrations

[0076] Example 4 First, water was added to the reactor, then the leaching agent (sodium thiosulfate, copper sulfate, ammonia water) was added, and finally the gold ore (the particle size after grinding, with 81.5% passing through -200 mesh) and the resin (Amberlite IRA-400) were added. Then, sodium hydroxide and sulfuric acid were used to adjust the pH of the pulp to the set value, and then stirring leaching was carried out (the stirring rate was 500 r / min). The specific leaching conditions were as follows: the concentration of sodium thiosulfate was 0.075 mol / L, the concentration of copper sulfate was 2 mmol / L, the ammonia concentration was 0.3 mol / L, the pulp concentration was 33%, and the resin concentration was 10 kg / m 3 , the temperature was 25 °C, the pH value of the pulp was 10, and the time was 12 h. After leaching, the resin was separated from the pulp, and the obtained loaded resin was packed into a column. A mixed solution composed of 1 M NaCl + 0.05 M Na2SO3 with a volume of 10 resin bed volumes was used to desorb the resin, and the flow rate of the desorbing agent was 2 resin bed volumes per hour. After desorption, sodium dithionite was added to the obtained gold-rich desorbing solution for gold reduction and recovery, and the reduction time was 10 min. The gold reduction rates under different dosages of sodium dithionite are shown in Table 10.

[0077] As can be seen from the table, when the dosage of sodium dithionite was 0.5 times the theoretical dosage, the gold reduction rate was 72.2%, and the purity of the obtained elemental gold product was 98.2%. As the dosage of sodium dithionite increased, the gold reduction rate and the purity of the gold product gradually increased. When the dosage of sodium dithionite was 1.5 times the theoretical dosage, the gold reduction rate reached 98.6%, and the purity of the gold product was 99.6%. When the dosage of sodium dithionite was further increased to 2 times the theoretical dosage, the gold reduction rate increased to 99.9%, the gold in the desorbing solution was completely reduced, and the purity of the gold product also increased to 99.9%. Therefore, high-purity gold products can be obtained by reducing the gold-rich desorbing solution with sodium dithionite.

[0078] Table 10 Gold reduction rates under different dosages of sodium dithionite

[0079] Example 5 First, water was added to the reactor, then the leaching agent (sodium thiosulfate, copper sulfate, ammonia water) was added, and finally the gold ore (the particle size after grinding, with 81.5% passing through -200 mesh) and the resin (Amberlite IRA-400) were added. Then, sodium hydroxide and sulfuric acid were used to adjust the pH of the pulp to the set value, and then stirring leaching was carried out (the stirring rate was 500 r / min). The specific leaching conditions were as follows: the concentration of sodium thiosulfate was 0.075 mol / L, the concentration of copper sulfate was 2 mmol / L, the ammonia concentration was 0.3 mol / L, the pulp concentration was 33%, and the resin concentration was 10 kg / m 3, temperature 25 °C, pulp pH value 10, time 12 h. After leaching, the resin was separated from the pulp, and the loaded resin obtained was packed into a column. A mixed solution composed of 1 M NaCl + 0.05 M Na2SO3 with a volume of 10 resin beds was used to desorb the resin. After desorption, sodium dithionite was added to the obtained gold-rich desorbing solution for the reduction and recovery of gold, and the dosage of sodium dithionite was 1.5 times the theoretical dosage. The gold reduction rates at different reduction times with different dosages of sodium dithionite are shown in Table 11.

[0080] As can be seen from the table, when the reduction time was 5 min, the gold reduction rate was as high as 98.2%, and the gold purity in the obtained elemental gold product was 99.6%. Therefore, the efficiency of sodium dithionite in reducing and recovering gold from the above desorbing solution is very high. With the increase of the reduction time, the gold reduction rate increased slightly. When the reduction time was 20 min, the gold reduction rate reached 99.8%, and the gold product purity increased to 99.9%. Therefore, sodium dithionite can efficiently reduce and recover gold in the gold-rich desorbing solution.

[0081]

[0082] The above are only the preferred embodiments of the present invention and do not impose any formal restrictions on the present invention. Therefore, any simple modifications, equivalent changes, and decorations made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A selective gold extraction process by the thiosulfate method, characterized in that, Including the following steps: (1) Adding gold ore and anion exchange resin into an aqueous solution of a leaching agent, and performing stirring leaching under the condition that the pH value is 9-10 to obtain a pulp containing gold-loaded resin; the leaching agent includes thiosulfate, copper salt and ammonia water; the concentration of the thiosulfate is 0.05-0.1 mol / L, the concentration of the copper salt is 1.5-5 mmol / L, and the concentration of the ammonia water is 0.1-0.5 mol / L; (2) Separating the gold-loaded resin from the pulp, and performing desorption on the gold-loaded resin with a desorbing agent to obtain a gold-rich desorbing solution; the desorbing agent is a mixed solution containing a chloride salt and a sulfite; (3) Adding sodium dithionite into the gold-rich desorbing solution for reduction to obtain a metallic gold product.

2. The thiosulfate process for selective gold extraction according to claim 1, characterized in that, The thiosulfate in step (1) is one or more of sodium thiosulfate, ammonium thiosulfate and calcium thiosulfate.

3. The thiosulfate process for selectively extracting gold according to claim 1 or 2, characterized in that, The copper salt in step (1) is copper sulfate.

4. The thiosulfate process for selective gold extraction according to claim 1, characterized in that The anion exchange resin in step (1) is a strongly basic chlorine-type anion exchange resin.

5. The thiosulfate process for selective gold extraction according to claim 1 or 4, characterized in that, The anion exchange resin concentration in step (1) is 5 to 20 kg / m 3 .

6. The thiosulfate process for selective gold extraction according to claim 5, characterized in that, The conditions of the leaching in step (1) are: the concentration of the gold ore pulp is 20-50 wt%, the temperature is 25-45 °C, the stirring rate is 400-800 r / min, and the time is 4-12 h.

7. The thiosulfate process for selective gold extraction according to claim 1, characterized in that, The chloride salt in step (2) is sodium chloride, and the sulfite is sodium sulfite.

8. The thiosulfate process for selective gold extraction according to claim 7, characterized in that, The conditions of the desorption in step (2) are: the concentration of sodium chloride is 0.5-1 mol / L, the concentration of sodium sulfite is 0.01-0.05 mol / L, the dosage of the desorbing agent is 5-10 times the resin bed volume, and the flow rate of the desorbing agent is 1-5 resin bed volumes per hour.

9. The thiosulfate process for selectively extracting gold according to claim 1, characterized in that, The sodium dithionite in step (3) is sodium dithionite.

10. The thiosulfate process for selective gold extraction according to claim 9, characterized in that, The conditions of the reduction in step (3) are: the dosage of sodium dithionite is 1.5-2 times the theoretical dosage, and the reduction time is 5-20 min.

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