RU2514900C2 - Processing of gold-bearing concentrates of two-fold hardness - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: process can be used in hydrometallurgy for processing of gold-bearing two-fold hardness concentrates, that is, stock containing gold dispersed in sulphides and organic carbonaceous substance. Prior to feeding the concentrate acid pulp produced by pre-treatment of concentrate with acid into autoclave is cleaned of chlorides. Autoclave leaching is conducted at 225-235°C and terminated at reaching the pulp redox potential in the range of +700 - 730 mV relative to standard hydrogen electrode. For cleaning the pulp of chlorides at filter or at continuous return flow decantation hot condensate or natural water and/or desalinised water may be used. To maintain preset temperature at autoclave leaching cold fresh and/or reused water is fed to every section of autoclave.

EFFECT: higher gold yield.

4 cl, 7 dwg, 3 tbl, 2 ex

Description

The invention relates to the metallurgy of non-ferrous metals, in particular to the processing of refractory gold-bearing concentrates.

The most common reason for the persistence of gold-bearing raw materials (ores and concentrates) is the fine dispersion of gold in sulfides, usually in pyrite and arsenopyrite. Some refractory gold-bearing ores and concentrates also contain an organic carbonaceous substance that has sorption activity with respect to the gold cyanide complex (pregrobbing phenomenon), which gives the raw material additional persistence. Therefore, such raw materials are often called double stubborn raw materials. The present invention is intended for the processing of refractory gold-bearing concentrates and in particular for the processing of concentrates of double persistence.

A known method of processing refractory gold-bearing concentrates using autoclave oxidative leaching (US patent No. 4610724). The concentrate is subjected to acid treatment for the destruction of 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 autoclave leaching, gold sulfides are oxidized and the refractory refined 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 from acid and soluble iron and arsenic compounds formed during autoclave oxidation are washed. Gold is extracted from the washed autoclave residue using one of the traditional cyanidation methods (CIL, CIP, RIL, RIP). The method is environmentally friendly and, for refractory gold-bearing concentrates that do not contain organic carbonaceous matter, provides high gold recovery.

However, for refractory gold-bearing concentrates, this method in many cases gives a low gold recovery, which is its main disadvantage.

As studies have shown, during autoclave oxidation of refractory gold-bearing concentrates, not only the opening of finely dispersed gold occurs, but also the suppression of the sorption activity of carbonaceous matter (pregrobbing). This is due to the fact that during autoclave oxidation, partial oxidation of carbonaceous organic matter occurs; The resulting oxidation products passivate the remaining non-oxidized carbonaceous substance and sharply reduce its sorption activity. It turned out, however, that despite the almost complete decomposition of sulfides and the suppression of pregrobbing, gold recovery in some cases remains low.

Additional studies have shown that the reason for this is the presence of chlorides in the autoclave pulp. Hereinafter, chlorides are understood as Cl ^- ions, which can enter the autoclave pulp with fresh water, circulating solutions, and also leach out of the chloride-containing minerals of the feedstock. The negative effect of chlorides is manifested even at their concentration in the liquid phase at the level of 1-5 mg / l. With an increase in the concentration of chlorides, the recovery of gold decreases significantly, while the negative effect increases with an increase in the content of organic carbon in concentrates.

The mechanism of the negative effect of chlorides is not finally established. It is assumed that the gold released during the oxidation of sulfides at high (over 170 ° C) temperature is oxidized by Fe ³⁺ ions and is bound by chloride to water-soluble complexes:

Gold that has passed into solution is sorbed by a carbonaceous substance and, upon cooling of the autoclave pulp, is reduced to metal:

The metallic gold formed in coal is inaccessible to the action of cyanide.

A known method of processing gold-bearing concentrates of double persistence containing chlorides (US patent No. 5851499), adopted as the closest analogue (prototype). In accordance with this method, a gold-containing concentrate enters the autoclave leach, in which the weight ratio of sulfide sulfur to carbonate ion (S / CO ₃ ) should be from 4: 1 to 0.5: 1. This ratio is achieved by adding limestone or by mixing the starting materials with different contents of sulfides and carbonates. The resulting mixture is ground to a particle size of P ₈₀ = 75 ÷ 38 μm and is subjected to autoclave leaching at a temperature of no higher than 215 ° C for no more than 45 minutes. The leached pulp liquid phase should contain from 7 to 25 g / l of free sulfuric acid and have a redox potential (ORP) of not more than +700 mV (relative to the standard hydrogen electrode (SVE). To increase gold recovery, it is recommended to use additives of metal binding compounds chlorides into strong complexes (Cu, Pb, Zn, Co, Bi) or sparingly soluble compounds (Ag, Pb, Hg, Bi). Gold is extracted from the autoclave residue by cyanidation.

This method allows the processing of double-strength concentrates containing chlorides with acceptable gold recovery. However, the method has serious disadvantages:

1. Calcium sulfate formed during decomposition of carbonates contained in concentrates of double persistence or added with the addition of limestone contributes to the formation of gypsum deposits (deposits) on the internal parts of the autoclave (walls, partitions, mixers, etc.); the autoclave must often be stopped for cleaning, which reduces its productivity and contributes to the premature destruction of an expensive lining.

2. Gaseous carbon dioxide is released during the decomposition of carbonates. The accumulation of carbon dioxide in the gas phase of the autoclave leads to a decrease in the partial pressure of oxygen and, as a consequence, to a decrease in the rate of oxidation of sulfides and a decrease in productivity. To prevent the accumulation of carbon dioxide, the gas phase must be renewed by releasing exhaust gas. This leads to a decrease in the degree of use of oxygen, since oxygen leaves together with the gas. This leads to a significant (10-30%) increase in the consumption of this gas, respectively, the capital and operating costs for the autoclave redistribution increase.

3. The limitation of the operating temperature of the process (not higher than 215 ° C) significantly (1.5-2 times) reduces the rate of oxidation of sulfides and, accordingly, the productivity of the process. An increase in temperature is impossible, since in the presence of chlorides, reactions 1–2 intensify and gold recovery decreases.

4 Recommended additives are expensive and environmentally unsafe.

The task of the invention is to eliminate the noted disadvantages of the closest analogue.

The claimed technical result is achieved by the fact that in the method of processing gold-bearing concentrates of double tenacity, including acid treatment of the crushed concentrate to produce acidic pulp, autoclave leaching of the concentrate at elevated temperature and oxygen pressure, cooling the leached pulp by self-evaporation, conditioning the pulp, dehydrating and washing it, and further gold recovery by sorption cyanidation of the autoclave residue, in contrast to the closest analogue, before the autoclave by leaching, the acidic pulp is washed from the chlorides and fed to the autoclave leaching, which is carried out at a temperature of 225-235 ° C and is completed upon reaching the redox potential of the pulp in the range + 700-730 mV (relative to the standard hydrogen electrode).

Chlorides can be washed on a filter or by continuous countercurrent decantation.

For washing from chlorides, it is possible to use hot condensate obtained by condensation of a self-evaporator vapor, or natural and / or demineralized water with a chloride concentration of not more than 2 mg / l.

To maintain the set temperature during autoclave leaching, cold fresh and / or circulating water with a chloride content of not more than 2 mg / l is possible in each section of the autoclave.

The concentrate ground to a particle size of 90-95% -44 μm is subjected to acid treatment. This operation is intended not only for the decomposition of carbonates, but also for the transfer of a readily soluble part of the chlorides into the solution. The resulting acidic pulp enters the thickener system, where it is washed by continuous countercurrent decantation from chlorides to a concentration of less than 2.0-3.0 mg / L. Washing is carried out with natural and / or circulating water with a chloride content of not more than 2 mg / l. Hot condensate obtained by condensing a pair of self-evaporators can also be used for washing. The washed concentrate in the form of pulp is pumped by a high pressure pump to the first compartment of a multi-section (4-7 sections) horizontal autoclave. Autoclave leaching is carried out at a temperature of 225-235 ° C. At this temperature, significantly higher than the prototype temperature (215 ° C), pregrobbing is more completely suppressed, but due to the low chloride concentration in the solution, the negative effect of reactions 1-3 on gold recovery is minimized. Obviously, increasing the process temperature to 225-235 ° C is possible only with the preliminary washing from chlorides. Under these conditions, almost complete oxidation of sulfides (more than 98%) is achieved with a pulp residence time in the autoclave of not more than 30-35 minutes. An increase in temperature above 235 ° C is impractical, since in this case, due to the exponential increase in water vapor pressure, the total pressure in the autoclave increases significantly. This leads to an increase in capital and operating costs for the autoclave redistribution.

Due to the heat released during the oxidation of sulfides, the process of autoclave leaching is autogenous. To compensate for the excess heat and maintain the set temperature, cooling water is supplied to each section of the autoclave, the chloride content of which should not exceed 2 mg / l. In the last section of the autoclave, the redox potential (ORP) should be between +700 and +730 mV (relative to the standard hydrogen electrode). Such an ORP value indicates the complete oxidation of sulfides and at the same time guarantees a degree of oxidation of a carbonaceous substance sufficient to suppress pregrobbing. At a lower potential, a decrease in gold recovery due to incomplete oxidation of sulfides is possible; at a higher potential, gold interacts with chloride and precipitates on a carbonaceous substance, which also leads to a decrease in gold recovery.

Compared with the prototype, the proposed method allows to increase the productivity of autoclaves, reduce oxygen consumption, eliminate the need for frequent stops of autoclaves to clean their internal surfaces from gypsum deposits.

EXAMPLES

The above is confirmed, but not limited to examples of the implementation of the proposed method in comparison with the prototype method.

The experimental verification was carried out on flotation gold-containing concentrates with different contents of organic carbon. Concentrates were obtained from ore samples from one of the domestic deposits. The composition of the concentrates is shown in table 1.

Table 1 Try Gold (g / t) Organic carbon (%) Sulfide Sulfur (%) Iron (%) Arsenic (%) BUT 23.8 1,2 23.34 25.7 9.19 B 22.0 0.4 22.8 24.6 7.8

Example 1

This example demonstrates the effect of washing the concentrate before autoclave oxidation and the temperature of autoclave oxidation on the recovery of gold from gold sulfide concentrates containing organic carbon.

A portion of the sample concentrate A was pre-crushed to a particle size of 90-95% -44 μm. In all experiments, distilled water was used. Then, the concentrate was repulped with water to a solids content of 30% and treated with sulfuric acid (decarbonized) for 60 min until a pH of 1.5-2.2 was reached. The acidic pulp was concentrated to a solids content of ~ 60% and washed with decantation with water. The number of washes ranged from 0 (without washing) to 3. For each washing took 4 wt. hours of water per 1 wt. hours solid.

The washed pulp was transferred to a 1.1 L titanium autoclave and diluted with water to a solids content of 13-14%. According to calculations, such a density should have a pulp in an industrial autoclave for carrying out the process in an autogenous mode. The autoclave was heated to a predetermined temperature, oxygen was supplied to a partial pressure of 730 kPa, 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 predetermined level. The process was completed after the cessation of oxygen consumption (according to the flow meter).

The autoclave pulp was conditioned (twisted) at a temperature of 95 ° C for 2 hours. The resulting pulp was filtered in an acidic filtrate using a selective electrode to determine the concentration of chlorides. The cake was washed on the filter with water and subjected to sorption cyanidation (RIL). The process was conducted at a solids content of 20%, cyanide concentration 0.1%, pH 10-11, resin concentration AM-2B 5% (volume) for 24 hours. After cyanidation, sorbent was isolated from the pulp on a sieve, the pulp was filtered, and the solid phase washed and subjected to gold assay.

The results are shown in table 2 and in figures 1 and 2.

In the first series of experiments (experiments 1-5), autoclave oxidation of an unwashed concentrate was carried out at temperatures of 190-235 ° C. Experiments 1-3 were carried out according to the prototype, i.e. at a temperature of less than 215 ° C and without washing from chlorides. The extraction of gold in this case amounted to 82.0-82.5%. The increase in temperature led to a drop in gold extracts, which is consistent with the prototype.

In the second series of experiments (experiments 6-11), the concentrate, which was washed three times, was also subjected to autoclave oxidation at temperatures of 200-235 ° C. It can be seen that in the temperature range 200-220 ° C, the extraction of gold is practically independent of temperature, remaining at the level of 90-91%. However, in the temperature range 225-235 ° C, gold recovery increases by 2-4%. Apparently, this effect is due to the fact that at higher temperatures a more complete oxidation / passivation of the carbonaceous substance occurs, i.e. suppression of pre-robbing. In addition, the process speed and, consequently, the performance of the autoclave increases by a factor of 2-3.

Thus, it can be seen that if the concentrate is not washed, an increase in temperature has a negative effect on the recovery of gold. During autoclave oxidation of the concentrate washed from chlorides, the level of gold recovery is noticeably higher, and an increase in temperature to 225-235 ° C leads to an additional increase in gold recovery.

In the third series of experiments (experiments 5, 12, 13, 11), the number of concentrate washes was changed before autoclave oxidation at a temperature of 235 ° C. It can be seen that with autoclave leaching of the concentrate without washing, the gold recovery is only 77.1%, which is explained by the high concentration of chlorides in the autoclave solution - 15.7 mg / l (experiment 5). Washing decarbonized concentrate (experiments 12, 13, 11) allows to reduce the concentration of chlorides several times. So, when washing three times (experiment 11), the chloride concentration decreases to 2.5 mg / l, and the gold recovery during cyanidation rises to 95.0%. It can also be seen that the first washing gives a particularly large increase in extraction. The second and especially the third washes give a lesser effect, therefore, a further increase in the number of washes from an economic point of view is impractical. The effect of chloride washing and autoclave leaching temperatures on gold recovery is shown in Table 2.

table 2 Experience number Number of washes Temperature (° C) Chloride Concentration (mg / L) Gold recovery (%) one* 0 190 13.0 82.1 2 * 0 200 12.8 82.0 3 * 0 210 13.1 82,4 four 0 225 14.6 79.3 5 0 235 15.7 77.1 6 3 200 2.9 90,4 7 3 210 3,1 90.8 8 3 220 2,3 91.0 9 3 225 2.1 93.2 10 3 230 2.9 94.6 eleven 3 235 3.2 95.0 5 0 235 15.7 77.1 12 one 235 6.5 89.8 13 2 235 3.2 93.5 eleven 3 235 2,5 95.0 * Prototype method

Example 2

This example demonstrates the effect of washing the concentrate and purifying cooling water before autoclave oxidation, as well as the residence time and ORP during autoclave oxidation, on the recovery of gold from gold sulfide concentrates containing organic carbon.

Sample B served as the feedstock. Autoclave oxidation was carried out in a pilot plant in a continuous mode. The pilot autoclave is a horizontal titanium apparatus, divided by partitions into 4 sections. Useful capacity of the autoclave (on pulp) 27 l. The first section is twice as large as the next three. Each section is equipped with an impeller mixer (the first section - two). Oxygen is supplied under the mixer to each section. The pulp with a solids content of 50-70% is continuously supplied by a high pressure pump to the first section, the pulp flow is controlled by a flow meter. The leached pulp is also unloaded continuously from the last section. The autoclave has a gas discharge system. At start-up, the autoclave is heated using electric heaters, after entering the heating mode, it is turned off. To remove a large amount of excess heat (heat of exothermic oxidation reactions of sulfides), “sharp” water is supplied to each section. The autoclave is equipped with a control system that allows you to automatically maintain the desired temperature (by changing the supply of "sharp" water to each of the sections) and the pressure in the apparatus, as well as the supply of oxygen under each of the mixers. Each section of the autoclave is equipped with a special sampling device that allows you to take pulp samples during autoclave leaching.

The pilot test procedure was as follows. A sample of the concentrate (at least 150 kg) was pulp in water. Sulfuric acid was added to the pulp with stirring until a final pH of ~ 2-2.5 was reached. The resulting decarbonized pulp was filtered on a suction filter, the cake on the filter was washed with 4 times the amount of water. The washed cake was pulped with water to a solids content of 50-70% and used as a food for the autoclave. For comparison, in some experiments, a decarbonized, but not washed concentrate was used as food.

The autoclave was filled with water and heated to a predetermined temperature. After that, the power was turned on to the autoclave and oxygen supply was started. The exit to stationary mode was considered the beginning of the experiment. During the experiment, pulp samples were periodically taken from each section of the autoclave. For control, samples were also taken from the autoclave unloading. After measuring the ORP, the samples were filtered, the cake was washed with water, a sample was taken for chemical analysis, and the cake was subjected to sorption cyanidation according to the procedure described in Example 1. The chloride concentration was determined in the liquid discharge phase. Sectional testing made it possible to monitor the dynamics of sulfide oxidation during pulp movement along the length of the autoclave. Knowing the performance of the autoclave by concentrate and pulp, the residence time of the pulp in the autoclave at the time of sampling from a particular section was calculated. The degree of decomposition of sulfides was judged by the residual content of sulfide sulfur in sectional samples of the solid phase.

The results of pilot autoclave experiments, namely the effect of washing chlorides and temperature in the pilot test mode, are shown in table 3 and in figures 3-7. In experiments 1 (prototype) and 2, the concentrate was not washed, and tap water (chloride content ~ 7-8 mg / l) was used to prepare the initial pulp and as “sharp” water; Autoclave oxidation was carried out at temperatures of 200 ° C (prototype method) and 225 ° C. In experiment 3, the concentrate was not washed either, but distilled water was used to prepare the initial pulp and as “sharp” water. In experiments 4 and 5, the concentrate was washed with distilled water on the filter before being fed into the autoclave (2 mass parts of water per mass part of the concentrate); distilled water was also used to prepare the initial pulp and as “sharp” water; autoclave oxidation was carried out at temperatures of 225 ° C and 223 ° C.

The experiments were carried out with different concentrate performance and, therefore, different pulp residence times in the autoclave.

Table 3. Experience number Randomly
Ditel
Nost
by concent
ratu (kg / h) Temperature (° C) Autoclave section Stay time
vania (min) Concentrate
walkie-talkie of chlorides (mg / l) Ste
sulphide oxidation stump (%) ORP (mV) Extracted. gold
(%) Concentrate - without washing; water - tap (7-8 mg / l of chloride) one 21 on.** 80.6 +658 73,2 2 32 on. 96.7 +698 82.1 one* 7.9 200 3 39 on. 98.9 +713 86.4 four 44 on. 99,2 +720 84.5 Unloading 44 14.8 99.7 +728 83.9 one 21 on. 85.1 +674 76.0 2 thirty on. 98.8 +707 85.1 2 7.6 225 3 37 on. 99.0. +725 82.1 four 42 on. 99.1 +727 79,4 Unloading 42 15,5 99.6 +735 81.5 Concentrate - without washing; distilled water (<1 mg / l chloride) one 32 on. 98.7 +719 91.5 2 48 on. 99.0 +757 89.6 3 5.5 225 3 62 on. 99.5 +801 86.3 four 71 on. 99,2 +816 84.5 Unloading 71 8.4 99.7 +810 82.9 Concentrate - washed; distilled water (<1 mg / l chloride) one eighteen on. 82.3 +678 73.6 2 25 on. 91.4 +699 83.1 four 9,4 225 3 thirty on. 97.8 +710 90.1 four 34 on. 99.5 +716 92.3 Unloading 34 3.0 99.6 +722 93.2 one 19 on. 86.5 +685 75,4 2 26 on. 95.0 +705 86.5 5 9.5 235 3 31 on. 98.8 +714 93.7 four 35 on. 99.5 +720 94.9 Unloading 35 3.4 99.8 +725 93.2 * Prototype method ** on. - not analyzed

In experiment 1 (prototype), autoclave oxidation was carried out at a temperature of 200 ° C. The maximum recovery was 86%. With an increase in the temperature of autoclave oxidation to 225 ° C (experiment 2), the extraction decreased. In these experiments, a high chloride content in the autoclave solution was observed (approximately 15 mg / l).

In experiment 3, where the concentrate was also not washed, but distilled water (<1 mg / L chloride) was used as the “sharp” water, the chloride content decreased to 8.4 mg / L, and the maximum gold recovery increased (to 91, 5%).

The maximum gold recovery (93-95%) was obtained in experiments 4 and 5, carried out by the proposed method, i.e. with washing the concentrate, using distilled water and at a temperature of 225-235 ° C.

It is also seen that, regardless of the temperature and performance of the concentrate, the maximum gold recovery corresponds to an ORP value from +700 to +730 mV. This indicator can be used as an indicator to control the process.

Claims (4)

1. A method of processing gold-bearing concentrates of double persistence, including acid treatment of the crushed concentrate to produce acidic pulp, autoclave leaching of the concentrate at elevated temperature and pressure of oxygen, cooling the leached pulp by self-evaporation, conditioning the pulp, dehydrating and washing it, and further extracting gold by sorption cyanidation of the autoclave residue characterized in that before the autoclave leaching, the acidic pulp is washed from chlorides and fed to vtoklavnoe leaching is conducted at a temperature 225-235ºS and ends upon reaching the slurry redox potential in the range + 700 ÷ 730 mV vs. the standard hydrogen electrode. 2. The method according to claim 1, characterized in that the washing from the chlorides is carried out on a filter or by continuous countercurrent decantation. 3. The method according to claim 2, characterized in that hot condensate obtained by condensing steam while cooling the autoclave pulp in a self-evaporator, or natural and / or demineralized water with a chloride concentration of not more than 2 mg / l is used for washing from chlorides. 4. The method according to claim 1, characterized in that in order to maintain a predetermined temperature during autoclave leaching, cold fresh and / or circulating water with a chloride content of not more than 2 mg / l is supplied to each section of the autoclave.

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