RU2802924C1 - Method for processing gold-containing concentrates - Google Patents

Abstract

FIELD: metallurgy of precious metals.

SUBSTANCE: invention is related to processing of gold-bearing concentrates of double hardness. The method for processing sulfide gold-bearing concentrates includes acid treatment of the concentrate, thickening, feeding the thickened pulp into the autoclave, autoclave oxidation of the concentrate under oxygen pressure, cooling the leached pulp by self-evaporation, conditioning the autoclave pulp, its dehydration and washing, and further extraction of gold by sorption cyanidation of the autoclave residue. At the same time, a sodium dichromate solution with a concentration of 2.0 to 2.2 kg/L and a flow rate of 143 to 200 liters per 1 ton of the initial gold-bearing concentrate is fed into the autoclave pulp, and autoclave oxidation is carried out at a temperature of 210 to 250°C.

EFFECT: increase of degree of extraction of gold from gold-bearing concentrates of double refractoriness.

1 cl, 6 tbl

Description

The invention relates to the metallurgy of precious metals, in particular to the processing of refractory gold-containing concentrates.

There is a known method for processing refractory gold-containing concentrates using autoclave oxidative leaching (AOL) (US patent No. 4610724, published 09.09.1986). The concentrate is subjected to acid treatment to destroy carbonates (decarbonization) and leached in an autoclave at a temperature of 135 - 250 ° C under an oxygen pressure of 0.5 - 5.0 MPa. During the AOB process, gold-containing sulfides are oxidized, and the stubborn fine gold contained in them is released. The leached pulp is cooled in a self-evaporator and sent to a continuous countercurrent decantation system, where the solid residue is washed from acid and soluble compounds of iron and arsenic formed during autoclave oxidation. Gold is extracted from the washed residue using one of the traditional cyanidation methods (CIL, CIP, RIL, RIP).

The main disadvantage of this method is the low gold recovery when processing double-resistivity concentrates, since this method does not provide sufficient removal of organic carbon responsible for the preg-robbing mechanism, i.e. absorption or sorption of gold dissolved during autoclave oxidation on the carbon surface. With the AOB parameters described in patent No. 4610724, the degree of oxidation of organic carbon does not exceed 10-15%, thus, the remaining organic carbon continues to actively absorb gold, thereby reducing the final recovery.

There is a known method for processing double-refractory raw materials (US patent No. 5851499, published on December 22, 1998), according to which gold-bearing material (ore or concentrate) is supplied to autoclave leaching, in which the weight ratio of sulfide sulfur to carbonate ion (S/CO ₃ ) should be between 4:1 and 0.5:1. This ratio is achieved by adding limestone or mixing source materials with different contents of sulfides and carbonates. The resulting mixture is further ground to a particle size of P80 = 75 – 38 microns and subjected to autoclave leaching at a temperature not exceeding 215 °C for no more than 45 minutes. The liquid phase of the leached pulp must contain from 7 to 25 g/l of free sulfuric acid and have an oxidation-reduction potential (ORP) of no more than 700 mV (relative to a standard hydrogen electrode (SHE)). This method makes it possible to process double-resistant raw materials with acceptable gold recovery. However, for many concentrates, especially those with a high content of organic carbon, the method gives unsatisfactory results.

The main disadvantages of the method are low gold recovery when processing gold-containing concentrates of double resistance, the formation of gypsum deposits on the internal parts of autoclaves and a decrease in the degree of oxygen use due to the release of carbon dioxide in the autoclave and the need to remove it by discharging exhaust gas.

There is a known method for processing gold-containing concentrates of double resistance using AOB (RF patent No. 2514900, published 10/05/2014), including acid treatment (decarbonization) of the crushed concentrate, washing the resulting acidic pulp from chlorides, AOB of the washed concentrate pulp, cooling the oxidized pulp by self-evaporation, conditioning of the pulp, its dehydration and washing and further extraction of gold by sorption cyanidation of the autoclave residue. According to this method, the acidic pulp of the gold-containing concentrate is washed from chlorides on a filter or by countercurrent decantation, the autoclave oxidation process is carried out at a temperature of 225 - 235 ° C and is completed when the redox potential of the pulp is reached in the range of 700 - 730 mV, relative to a standard hydrogen electrode (SHE). ). This method allows the processing of gold-containing concentrates of double resistance with high gold recovery.

The main disadvantage of this method is that it ensures the elimination of only one component of autoclave preg-robbing – the chloride ion – due to its washing. Carbonaceous matter during and after AOB often remains active towards soluble gold complexes and can potentially remain a cause of loss of precious metal. Also, washing the acid treatment pulp does not always ensure the removal of significant amounts of chloride ion before the autoclave, since chlorine can enter the crystal lattice of minerals that do not decompose during the decarbonization process and be inaccessible for washing.

There is a known method for processing gold ores and double-resistance concentrates at elevated AOB temperatures (Eurasian patent No. 035804, published on August 13, 2020), including acid treatment of crushed concentrate to produce acidic pulp, autoclave oxidation of the resulting pulp at elevated temperature and pressure in the presence of oxygen, cooling leached pulp, conditioning of the pulp and further extraction of gold by sorption cyanidation of the conditioned pulp, characterized in that before the AOB, an additive of chlorides of alkali or alkaline earth metals is introduced into the liquid phase of the pulp in a concentration of 10-50 mg/l, autoclave oxidation is carried out at a temperature of 235-250 °C for the time required to oxidize 60-90% of natural carbon-containing gold sorbents in the range of 6 to 8 hours at an oxygen partial pressure of 2-6 bar, and the oxidation of gold-bearing minerals containing pyrite and arsenopyrite present in the concentrates is completed within first hour.

The main disadvantages of this method are: high capital costs, increased energy consumption, increased requirements for structural strength and corrosion resistance of the materials used, increased likelihood of the formation of a large number of deposits on the internal walls of the equipment of this technology, which leads to increased equipment downtime.

There is a known method for processing gold-containing concentrates of double resistance using AOB, adopted as the closest prototype analogue (RF patent No. 2732819, published on September 22, 2020), including acid treatment of the concentrate, thickening to produce pulp, feeding the pulp into an autoclave, autoclave oxidative leaching of the pulp under oxygen pressure, cooling of the leached pulp by auto-evaporation, its conditioning, dehydration and washing with further extraction of gold by sorption cyanidation of the autoclave residue, while autoclave oxidative leaching is carried out at a temperature of 190-240 ° C and feeding 25-100 kg/t of nitric acid or 30 -100 kg/t nitrate salt.

The main disadvantages of the method are the high risk of release of toxic nitrogen-containing gases and active corrosion of hardware not made of inert materials.

The technical result is to increase the degree of gold recovery from gold-containing concentrates of double refractoriness.

The technical result is achieved by feeding a sodium dichromate solution into the autoclave pulp with a concentration of 2.0 to 2.2 kg/l and a flow rate of 143 to 200 liters per 1 ton of initial gold-containing concentrate, while autoclave oxidation is carried out at a temperature of 210 to 250°C.

The method is carried out as follows. The initial gold-containing concentrate, containing from 40 to 85 g/t of gold, is ground in a mill to a particle size of 0.10 to 0.45 microns, 90% of the desired grade. Grinding occurs in wet mode, the solid content of the crushed pulp should be no more than 50%.

Next, the resulting pulp is sent for acid treatment to destroy the carbonates included in the original concentrate. Acid treatment is carried out using concentrated sulfuric acid in reactors with constant stirring, the process temperature ranges from 60 to 70°C for a duration of 30 to 60 minutes. The pH of the pulp after acid treatment is in the range from 1.6 to 1.8, which corresponds to the almost complete removal of acid-soluble carbonates.

Then the resulting pulp is sent for thickening to a radial thickener. As a result of thickening, two products are obtained: the upper overflow, which is an acidic solution, and the lower overflow, which is a pulp of carbon-free gold-containing concentrate.

The top drain of the thickener is sent for neutralization. Neutralization is carried out using crushed limestone in reactors with constant stirring. The process temperature ranges from 60 to 80°C with a duration of 30 to 60 minutes. The pulp obtained during neutralization is filtered on a filter press. As a result of filtration, two products are obtained: filtrate, which is process water, which can be returned to the operating cycle of the technology, and filtration cake, consisting of gypsum. Filtration cake is a waste product and is sent to the sludge storage facility.

The bottom drain of the thickener is sent to autoclave oxidative leaching (AOL).

Autoclave oxidative leaching is carried out in a horizontal, continuously operating autoclave with five sections, each of which is equipped with a mixing device. Oxygen and sharp water are supplied under each mixing device for cooling. The thickener bottom discharge pulp enters the first section of the autoclave, where it begins to be oxidized by oxygen, as a result of which the sulfides included in the original concentrate are oxidized to sulfates. At the final stage of sulfide oxidation, a solution of sodium dichromate salt with a concentration of 2.0 to 2.2 kg/l and a flow rate of 143 to 200 liters per 1 ton of initial gold-containing concentrate is supplied to the autoclave, in the fourth section. In the process of autoclave oxidative leaching, sodium dichromate acts as a secondary oxidizing agent and preferentially interacts with organic carbon, oxidizing it to carbon dioxide. Autoclave oxidation is carried out at temperatures from 210 to 250°C and an increased oxidation time from 20 to 60 minutes. The partial pressure of oxygen is between 3 and 7 bar. As a result of autoclave oxidation with the addition of sodium dichromate in the fourth section of the autoclave, autoclave oxidation pulp is obtained.

The autoclave oxidation pulp is sent to a self-evaporator for cooling. As a result of cooling, steam and cooled autoclave oxidation pulp are obtained. The steam is released into the atmosphere through a gas cleaning system.

The cooled autoclave oxidation pulp is sent to a conditioning operation to dissolve the basic sulfates formed during the autoclave oxidation process. Conditioning occurs in reactors with constant stirring, the process temperature is from 80 to 95 ° C, the duration is from 60 to 240 minutes.

The pulp obtained as a result of conditioning is sent for thickening to a radial thickener. As a result of thickening, two products are obtained: the top drain, which is an acidic solution containing mainly ferric sulfate, and the bottom drain, which is a conditioned oxidized pulp in which gold is concentrated.

The top drain of the thickener is sent for neutralization. Neutralization is carried out using crushed limestone in reactors with constant stirring and a temperature of 60 to 80 ° C for 30 to 60 minutes. The pulp obtained during neutralization is filtered on a filter press. As a result of filtration, two products are obtained: filtrate, which is process water, which can be returned to the operating cycle of the technology, and filtration cake, consisting of gypsum, hematite and scorodite. Filtration cake is a waste product and is sent to the sludge storage facility.

The bottom discharge of the thickener is sent to sorption cyanidation or RIP process. Cyanidation is carried out in reactors with constant stirring using a solution of potassium or sodium cyanide, crushed lime to maintain the pH in the range from 10.0 to 10.5, and an ion exchange resin that absorbs the gold dissolved during cyanidation. As a result of sorption cyanidation, a mixture is obtained consisting of cyanidation pulp and resin saturated with gold. The resulting mixture is sent to a vibrating screen to separate the resin and cyanidation pulp. Screening produces two products, cyanidation pulp and gold-rich resin.

The cyanidation pulp is sent for neutralization and then to a sludge storage facility.

The resin saturated with gold is sent for desorption. Desorption is carried out in sorption columns using a solution of potassium or sodium cyanide. As a result of desorption, two products are obtained, a regenerated resin and a gold-saturated cyanide solution.

The regenerated resin is returned back for sorption cyanidation.

The cyanide solution saturated with gold is sent for electrolysis, where the gold from the solution is reduced to metal.

The method is illustrated by the following examples.

Example 1. A flotation gold concentrate, the chemical composition of which is given in Table 1, was processed.

Table 1 – Chemical composition of the concentrate

Content of components, % Au (g/t) C _total C _org As Fe _{Stotal SSO4} Sb Si Al K 83.0 3.2 3.1 9.1 19.5 17.5 0.08 0.09 14.6 4.5 1.46

The concentrate was crushed in a planetary mill to a particle size of 0.10 to 0.45 microns, 90% of the required class, in wet grinding mode. Next, the resulting crushed concentrate pulp was diluted with distilled water to a solid content of 20%. The resulting pulp was subjected to acid treatment using concentrated sulfuric acid to remove carbonates for 60 minutes at 60°C and a final pulp pH of 1.6 to 1.8.

The resulting acidic pulp was transferred to a 1.2 liter titanium autoclave, where it was diluted with distilled water to a solid content of 16%.

Then the autoclave was heated to temperatures from 210 to 250°C, after reaching the set temperature, the supply of oxygen began to a partial pressure of 5 bar and stirring was turned on. This moment was considered the beginning of the experiment. During the experiment, oxygen consumption was continuously measured. The temperature and pressure in the autoclave were maintained automatically at a given level.

Experiment No. 1 was carried out in modes close to the AOB modes of analogue patents, i.e. autoclave oxidation with the duration required for complete oxidation of sulfides, the AOB temperature was 230°C, the excess oxygen pressure was 5 bar. In this case, the experiment ended when oxygen stopped being consumed. This experience was a reference; comparisons were made based on its indicators.

Experiments No. 2, 3, 4, 5 and 6 were carried out with the addition of sodium dichromate as a secondary oxidizing agent after complete oxygen consumption and an increased residence time of the pulp in the autoclave. Sodium dichromate salt was added to the autoclave using a piston pump in the form of a solution with a concentration of 2.1 kg/l in quantities ranging from 47 to 238 l/t of the original concentrate. The pulp peroxidation time was 30 minutes, the AOB temperature was 230°C.

Experiments No. 7, 8, 9 and 10 were carried out with the addition of sodium dichromate as a secondary oxidizing agent after complete oxygen consumption and an increased residence time of the pulp in the autoclave. Sodium dichromate salt was added to the autoclave using a piston pump in the form of a solution with a concentration of 2.1 kg/l in an amount of 190 l/t of the original concentrate. The pulp peroxidation time varied from 10 to 80 minutes, the AOB temperature was 230°C.

Experiments No. 11, 12, 13, 14 and 15 were carried out with the addition of sodium dichromate as a secondary oxidizing agent after complete oxygen consumption and an increased residence time of the pulp in the autoclave. Sodium dichromate salt was added to the autoclave using a piston pump in the form of a solution with a concentration of 2.1 kg/l in an amount of 190 l/t of the original concentrate. The pulp peroxidation time was 30 minutes, the AOB temperature varied from 190 to 260°C.

Experiments No. 16, 17, 18 and 19 were carried out with the addition of sodium dichromate as a secondary oxidizing agent after complete oxygen consumption and an increased residence time of the pulp in the autoclave. Sodium dichromate salt was added to the autoclave using a piston pump in the form of solutions with concentrations ranging from 1 to 2.2 kg/L in quantities ranging from 182 to 400 L/t of the original concentrate. The pulp peroxidation time was 30 minutes, the AOB temperature was 230°C.

The end of all experiments was the same: the autoclaved pulp, regardless of the method of its preparation, was cooled to a temperature of 95°C and conditioned at this temperature for 2 hours directly in the autoclave.

The pulp was then filtered, resulting in two products, a filtration cake and a solution, which was sent for disposal. The cake was washed with water and subjected to sorption cyanidation (RIP), which was carried out at a pulp solids content of 20%, cyanide concentration of 0.1%, pH from 10.0 to 10.5, Purogold resin concentration of 5% by volume for 24 hours.

Next, the gold content in the sorption cyanidation cakes was determined using the fire assay method. Gold recovery was calculated based on the initial grade in the concentrate and the final grade in the cyanidation tailings. The results obtained are shown in Table 2.

Table 2 - Experimental results

Experience no. Duration of oxidation stages, min T, °C Conc. Na ₂ Cr ₂ O ₇ solution,
kg/l Consumption of Na ₂ Cr ₂ O ₇ solution, l/t of initial concentrate Oxidation degree Torg, % Gold recovery, % Stage 1 Stage 2 General 1 19 - 19 230 2.1 - 5.6 90.0 2 20 thirty 50 230 2.1 47 37.5 95.8 3 21 thirty 51 230 2.1 95 48.6 96.4 4 21 thirty 51 230 2.1 143 68.8 98.4 5 20 thirty 50 230 2.1 190 68.6 98.3 6 19 thirty 49 230 2.1 238 69.0 98.4 7 20 10 thirty 230 2.1 143 5.3 87.9 8 21 20 41 230 2.1 143 11.5 91.5 9 19 50 69 230 2.1 143 69.0 98.3 10 19 80 99 230 2.1 143 68.9 98.4 eleven 37 thirty 67 190 2.1 143 31.6 93.1 12 26 thirty 56 210 2.1 143 35.6 94.9 13 16 thirty 46 240 2.1 143 69.1 98.5 14 9 thirty 39 250 2.1 143 73.1 99.7 15 7 thirty 37 260 2.1 143 73.5 99.8 16 20 thirty 50 230 1.0 400 68.3 98.2 17 21 thirty 51 230 1.5 267 69.0 98.3 18 19 thirty 49 230 2.0 200 68.1 98.1 19 20 thirty 50 230 2.2* 182 68.7 98.4

* - maximum solubility of sodium dichromate in water at 20°C.

The results of Run 1 show that organic carbon was only slightly oxidized, resulting in low gold recovery.

The results of experiments 2–6, in which the proposed method was used and the consumption of the secondary oxidizer sodium dichromate was varied, show the effectiveness of the proposed method. At a sodium dichromate consumption of 47 l/t, the degree of gold recovery increased to 95%; an increase in reagent consumption contributed to an increase in gold recovery. The consumption of a sodium dichromate salt solution with a concentration of 2.1 kg/l at 143 l/t can be taken as optimal, since its further increase does not contribute to a significant increase in gold recovery.

The results of experiments 7–10, in which the proposed method was used and the peroxidation time was varied, also show the effectiveness of the proposed method. According to Table 2, it can be seen that the optimal peroxidation time for this material is 30 minutes.

The results of experiments 11–15, in which the proposed method was used and the AOB temperature was varied, also show the effectiveness of the proposed method. Low AOB temperatures up to 230°C are ineffective. Probably, such values are not enough for the effective interaction of sodium dichromate with organic carbon. Increasing the temperature above 250°C is not advisable since it has little effect on gold growth. Thus, the temperature range of the proposed method lies in the range from 220 to 250°C.

The results of experiments 16–19 show that the concentration of the supplied sodium dichromate salt does not affect the main indicators. Technologically, it is most expedient to supply a sodium dichromate salt solution with the maximum permissible concentration to reduce the volume of process equipment. Those. the most optimal concentration lies in the range from 2 to 2.2 kg/l; increasing it is undesirable as it can lead to supersaturation of the solution.

Thus, the proposed method makes it possible to increase the degree of gold recovery by adding a secondary oxidizer, increasing the duration of oxidation and increasing the temperature of the active substance to 250°C.

Example 2. A flotation gold concentrate was processed, the chemical composition of which is given in Table 3.

Table 3 – Chemical composition of the concentrate

Content of components, % Au (g/t) C _total C _org As Fe _{Stotal SSO4} Sb Si Al K 84.8 3.0 2.6 6.5 14.7 12.6 0.16 0.07 16.9 3.8 1.75

The concentrate was crushed in a planetary mill to a particle size of 0.10 to 0.45 microns (90% of the required class) in wet grinding mode. Next, the resulting crushed concentrate pulp was diluted with distilled water to a solid content of 20%. The resulting pulp was subjected to acid treatment using concentrated sulfuric acid to remove carbonates for 60 minutes at 60°C and a final pulp pH of 1.6 to 1.8.

The resulting acidic pulp was transferred to a 1.2-L titanium autoclave, where it was diluted with distilled water to a solid content of 16%.

Then the autoclave was heated to temperatures from 210 to 250°C, after reaching the set temperature, the supply of oxygen began to a partial pressure of 5 bar and stirring was turned on. This moment was considered the beginning of the experiment. During the experiment, oxygen consumption was continuously measured. The temperature and pressure in the autoclave were maintained automatically at a given level.

Experiment No. 1 was carried out in modes close to the AOB modes of analogue patents, i.e. autoclave oxidation with the duration required for complete oxidation of sulfides, the AOB temperature was 230°C, the excess oxygen pressure was 5 bar. In this case, the experiment ended when oxygen stopped being consumed. This experience was a reference; comparisons were made based on its indicators.

Experiments No. 2, 3, 4, 5 and 6 were carried out with the addition of sodium dichromate as a secondary oxidizing agent after complete oxygen consumption and an increased residence time of the pulp in the autoclave. Sodium dichromate salt was added to the autoclave using a piston pump in the form of a solution with a concentration of 2.1 kg/l in quantities ranging from 47 to 238 l/t of the original concentrate. The pulp peroxidation time was 30 minutes, the AOB temperature was 230°C.

Experiments No. 7, 8, 9 and 10 were carried out with the addition of sodium dichromate as a secondary oxidizing agent after complete oxygen consumption and an increased residence time of the pulp in the autoclave. Sodium dichromate salt was added to the autoclave using a piston pump in the form of a solution with a concentration of 2.1 kg/l in an amount of 190 l/t of the original concentrate. The pulp peroxidation time varied from 10 to 80 minutes, the AOB temperature was 230°C.

Experiments No. 11, 12, 13, 14 and 15 were carried out with the addition of sodium dichromate as a secondary oxidizing agent after complete oxygen consumption and an increased residence time of the pulp in the autoclave. Sodium dichromate salt was added to the autoclave using a piston pump in the form of a solution with a concentration of 2.1 kg/l in an amount of 190 l/t of the original concentrate. The pulp peroxidation time was 30 minutes, the AOB temperature varied from 190 to 260°C.

Experiments No. 16, 17, 18 and 19 were carried out with the addition of sodium dichromate as a secondary oxidizing agent after complete oxygen consumption and an increased residence time of the pulp in the autoclave. Sodium dichromate salt was added to the autoclave using a piston pump in the form of solutions with concentrations ranging from 1 to 2.2 kg/L in quantities ranging from 182 to 400 L/t of the original concentrate. The pulp peroxidation time was 30 minutes, the AOB temperature was 230°C.

The end of all experiments was the same: the autoclaved pulp, regardless of the method of its preparation, was cooled to a temperature of 95°C and conditioned at this temperature for 2 h directly in the autoclave.

The pulp was then filtered, resulting in two products, a filtration cake and a solution, which was sent for disposal. The cake was washed with water and subjected to absorption cyanidation (RIP), which was carried out at a pulp solids content of 20%, cyanide concentration 0.1%, pH 10.0 to 10.5, Purogold resin concentration 5% by volume for 24 hours.

Next, the gold content in the sorption cyanidation cakes was determined using the fire assay method. Gold recovery was calculated based on the initial grade in the concentrate and the final grade in the cyanidation tailings. The experimental results are presented in Table 4.

Table 4 – Experimental results

Experience no. Duration of oxidation stages, min T, °C Conc. Na ₂ Cr ₂ O ₇ solution,
kg/l Consumption of Na ₂ Cr ₂ O ₇ solution, l/t of initial concentrate Oxidation degree Torg, % Gold recovery, % Stage 1 Stage 2 General 1 19 - 19 230 2.1 - 8.5 90.2 2 20 thirty 50 230 2.1 47 40.5 97.0 3 19 thirty 49 230 2.1 95 49.5 97.9 4 20 thirty 50 230 2.1 143 62.4 98.3 5 21 thirty 51 230 2.1 190 70.1 99.1 6 22 thirty 52 230 2.1 238 69.9 99.1 7 19 10 29 230 2.1 190 12.5 89.9 8 19 20 39 230 2.1 190 42.5 97.1 9 20 50 70 230 2.1 190 41.9 97.0 10 21 80 101 230 2.1 190 42.0 97.1 eleven 42 thirty 72 190 2.1 190 29.8 93.7 12 25 thirty 52 210 2.1 190 69.3 97.3 13 13 thirty 43 240 2.1 190 75.3 99.5 14 7 thirty 37 250 2.1 190 78.9 99.9 15 5 thirty 35 260 2.1 190 78.8 99.9 16 20 thirty 50 230 1.0 400 70.0 99.0 17 21 thirty 51 230 1.5 267 70.5 99.2 18 19 thirty 49 230 2.0 200 69.9 99.1 19 20 thirty 50 230 2.2* 182 70.1 99.0

* - maximum solubility of sodium dichromate in water at 20°C.

The results of Run 1 show that organic carbon was only slightly oxidized, resulting in low gold recovery.

The results of experiments 2–6, in which the proposed method was used and the consumption of the secondary oxidizer sodium dichromate was varied, show the effectiveness of the proposed method. At a sodium dichromate solution consumption of 47 l/t, the degree of gold recovery increased to 97%; an increase in reagent consumption contributed to an increase in gold recovery. The consumption of a sodium dichromate salt solution with a concentration of 2.1 kg/l at 190 l/t can be taken as optimal, since its further increase does not contribute to a significant increase in gold recovery.

The results of experiments 7–10, in which the proposed method was used and the peroxidation time was varied, also show the effectiveness of the proposed method. According to Table 4, it can be seen that the optimal peroxidation time for this material is 20 minutes.

The results of experiments 11–15, in which the proposed method was used and the AOB temperature was varied, also show the effectiveness of the proposed method. Low AOB temperatures up to 230°C are ineffective. Probably, such values are not enough for the effective interaction of sodium dichromate with organic carbon. Increasing the temperature above 250°C is not advisable since it has little effect on gold growth. Thus, the temperature range of the proposed method lies in the range from 220 to 250°C.

The results of experiments 16–19 show that the concentration of the supplied sodium dichromate salt does not affect the main indicators. Technologically, it is most expedient to supply a sodium dichromate salt solution with the maximum permissible concentration to reduce the volume of process equipment. Those. the most optimal concentration lies in the range from 2 to 2.2 kg/l; increasing it is undesirable as it can lead to supersaturation of the solution.

Example 3. A flotation gold concentrate was processed, the chemical composition of which is given in Table 5.

Table 5 – Chemical composition of the concentrate

Content of components, % Au (g/t) C _total C _org As Fe _{Stotal SSO4} Sb Si Al K 40.9 3.6 3.3 1.9 19.5 19.4 0.09 0.94 13.5 5.6 1.8

The concentrate was crushed in a planetary mill to a particle size of 0.10 to 0.45 microns (90% of the required class) in wet grinding mode. Next, the resulting crushed concentrate pulp was diluted with distilled water to a solid content of 20%. The resulting pulp was subjected to acid treatment using concentrated sulfuric acid to remove carbonates for 60 minutes at 60°C and a final pulp pH of 1.6 to 1.8.

The resulting acidic pulp was transferred to a 1.2 liter titanium autoclave, where it was diluted with distilled water to a solid content of 16%.

Then the autoclave was heated to temperatures from 210 to 250°C, after reaching the set temperature, the supply of oxygen began to a partial pressure of 5 bar and stirring was turned on. This moment was considered the beginning of the experiment. During the experiment, oxygen consumption was continuously measured. The temperature and pressure in the autoclave were maintained automatically at a given level.

Experiment No. 1 was carried out in modes close to the AOB modes of analogue patents, i.e. autoclave oxidation with the duration required for complete oxidation of sulfides, the AOB temperature was 230°C, the excess oxygen pressure was 5 bar. In this case, the experiment ended when oxygen stopped being consumed. This experience was a reference; comparisons were made based on its indicators.

Experiments No. 2, 3, 4, 5 and 6 were carried out with the addition of sodium dichromate as a secondary oxidizing agent after complete oxygen consumption and an increased residence time of the pulp in the autoclave. Sodium dichromate salt was added to the autoclave using a piston pump in the form of a solution with a concentration of 2.1 kg/l in quantities ranging from 47 to 238 l/t of the original concentrate. The pulp peroxidation time was 30 minutes, the AOB temperature was 230°C.

Experiments No. 7, 8, 9 and 10 were carried out with the addition of sodium dichromate as a secondary oxidizing agent after complete oxygen consumption and an increased residence time of the pulp in the autoclave. Sodium dichromate salt was added to the autoclave using a piston pump in the form of a solution with a concentration of 2.1 kg/l in an amount of 190 l/t of the original concentrate. The pulp peroxidation time varied from 10 to 80 minutes, the AOB temperature was 230°C.

Experiments No. 11, 12, 13, 14 and 15 were carried out with the addition of sodium dichromate as a secondary oxidizing agent after complete oxygen consumption and an increased residence time of the pulp in the autoclave. Sodium dichromate salt was added to the autoclave using a piston pump in the form of a solution with a concentration of 2.1 kg/l in an amount of 190 l/t of the original concentrate. The pulp peroxidation time was 30 minutes, the AOB temperature varied from 190 to 260°C.

Experiments No. 16, 17, 18 and 19 were carried out with the addition of sodium dichromate as a secondary oxidizing agent after complete oxygen consumption and an increased residence time of the pulp in the autoclave. Sodium dichromate salt was added to the autoclave using a piston pump in the form of solutions with concentrations ranging from 1 to 2.2 kg/L in quantities ranging from 182 to 400 L/t of the original concentrate. The pulp peroxidation time was 30 minutes, the AOB temperature was 230°C.

The end of all experiments was the same: the autoclaved pulp, regardless of the method of its preparation, was cooled to a temperature of 95°C and conditioned at this temperature for 2 h directly in the autoclave.

The pulp was then filtered, resulting in two products, a filtration cake and a solution, which was sent for disposal. The cake was washed with water and subjected to absorption cyanidation (RIP), which was carried out at a pulp solids content of 20%, cyanide concentration 0.1%, pH 10.0 to 10.5, Purogold resin concentration 5% by volume for 24 hours.

Next, the gold content in the sorption cyanidation cakes was determined using the fire assay method. Gold recovery was calculated based on the initial grade in the concentrate and the final grade in the cyanidation tailings. The experimental results are presented in Table 6.

Table 6 - Experimental results

Experience no. Duration of oxidation stages, min T, °C Conc. Na ₂ Cr ₂ O ₇ solution,
kg/l Consumption of Na ₂ Cr ₂ O ₇ solution, l/t of initial concentrate Oxidation degree Torg, % Gold recovery, % Stage 1 Stage 2 General 1 14 - 14 230 2.1 - 9.6 85.2 2 13 thirty 43 230 2.1 47 21.5 87.9 3 15 thirty 45 230 2.1 95 54.5 91.5 4 14 thirty 44 230 2.1 143 69.8 95.9 5 14 thirty 44 230 2.1 190 87.1 97.9 6 15 thirty 45 230 2.1 238 87.3 98.0 7 14 10 44 230 2.1 190 11.5 85.6 8 16 20 36 230 2.1 190 86.9 98.0 9 15 50 65 230 2.1 190 87.5 98.3 10 15 80 95 230 2.1 190 87.3 98.0 eleven 29 thirty 59 190 2.1 190 47.5 89.5 12 21 thirty 46 210 2.1 190 74.1 95.6 13 9 thirty 39 240 2.1 190 88.9 98.5 14 6 thirty 36 250 2.1 190 90.1 99.5 15 4 thirty 34 260 2.1 190 91.0 99.7 16 20 thirty 50 230 1.0 400 87.4 98.0 17 21 thirty 51 230 1.5 267 87.0 97.9 18 19 thirty 49 230 2.0 200 87.1 98.2 19 20 thirty 50 230 2.2* 182 87.5 98.1

* - maximum solubility of sodium dichromate in water at 20°C.

The results of Run 1 show that organic carbon was only slightly oxidized, resulting in low gold recovery.

The results of experiments 2–6, in which the proposed method was used and the consumption of the secondary oxidizer sodium dichromate was varied, show the effectiveness of the proposed method. At a sodium dichromate consumption of 47 l/t, the degree of gold recovery increased to 88%; an increase in reagent consumption contributed to an increase in gold recovery. The consumption of a sodium dichromate salt solution with a concentration of 2.1 kg/l at 190 l/t can be taken as optimal, since its further increase does not contribute to a significant increase in gold recovery.

The results of experiments 7–10, in which the proposed method was used and the peroxidation time was varied, also show the effectiveness of the proposed method. According to Table 5, it can be seen that the optimal peroxidation time for this material is 20 minutes.

The results of experiments 11–15, in which the proposed method was used and the AOB temperature was varied, also show the effectiveness of the proposed method. Low AOB temperatures up to 230°C are ineffective. Probably, such values are not enough for the effective interaction of sodium dichromate with organic carbon. Increasing the temperature above 250°C is not advisable since it has little effect on gold growth. Thus, the temperature range of the proposed method lies in the range from 220 to 250°C.

The results of experiments 16–19 show that the concentration of the supplied sodium dichromate salt does not affect the main indicators. Technologically, it is most expedient to supply a sodium dichromate salt solution with the maximum permissible concentration to reduce the volume of process equipment. Those. the most optimal concentration lies in the range from 2 to 2.2 kg/l; increasing it is undesirable as it can lead to supersaturation of the solution.

Processing of double-refractory gold-containing concentrates using the proposed method can significantly increase the degree of removal of organic carbon in the AOB operation and, thereby, increase the degree of gold extraction from refractory gold-containing concentrates due to the addition of a sodium dichromate salt solution with a concentration of 2.0 to 2.2 kg/l as a secondary oxidizer in an amount from 136 to 200 liters per ton of initial concentrate, increasing the oxidation time on AOB from 20 to 60 minutes, carrying out AOB in the temperature range from 220 to 250°C.

Claims (1)

A method for processing sulfide gold-containing concentrates, including acid treatment of the concentrate, thickening, feeding the thickened pulp into an autoclave, autoclave oxidation of the concentrate under oxygen pressure, cooling the leached pulp by self-evaporation, conditioning the autoclaved pulp, its dehydration and washing and further extraction of gold by sorption cyanidation of the autoclave residue, characterized in that that a sodium dichromate solution with a concentration of 2.0 to 2.2 kg/l and a flow rate of 143 to 200 liters per 1 ton of initial gold-containing concentrate is fed into the autoclave pulp, while autoclave oxidation is carried out at a temperature of 210 to 250°C.