RU2843966C1 - Method of gold-bearing sulphide concentrates processing - Google Patents

Abstract

FIELD: hydrometallurgy.

SUBSTANCE: invention relates to hydrometallurgy and can be used for processing of gold-bearing sulphide concentrates. Method includes preliminary grinding of the concentrate to content of particles of class -45 mcm of 85% or more. Further, method includes atmospheric oxidation of concentrate at temperature 95±5 °C, ratio L:S in pulp 2.5-6.0 m³/t for 6-20 hours in sulphuric medium in presence of ions of trivalent iron and oxygen. At that, as the reagents containing sulphuric acid and oxygen, liquid and gaseous products and process wastes are used – sulphuric autoclave solution containing 20-50 g/l of Fe³⁺ and H₂SO₄ ions, and waste gases of autoclave oxidation with volume fraction of oxygen 80-90%. Solid residue is separated and subjected to autoclave oxidation at temperature 220-230 °C and oxygen partial pressure of 0.3-0.9 MPa to ensure the transfer of sulphide and elementary sulphur to the sulphate form by 97% or more. Obtained pulp is conditioned, gold-bearing solid residue is separated with further extraction of gold by sorption cyanidation.

EFFECT: improving processing efficiency of gold-bearing sulphide concentrates as per autoclave-hydrometallurgical technology providing increasing of through extraction of gold.

3 cl, 2 dwg, 1 tbl, 1 ex

Description

The method relates to the field of hydrometallurgy and can be used to increase the efficiency of autoclave-hydrometallurgical processing of gold-containing sulphide concentrates.

In world practice, the following methods of preliminary oxidation of sulfides have found application for processing refractory gold-bearing ores and concentrates: oxidative roasting, bacterial leaching, atmospheric oxidation during ultrafine grinding of raw materials, and the most widespread - autoclave oxidation. This is explained by the fact that autoclave oxidation has a number of important advantages compared to other methods indicated above: firstly, high speed and depth of oxidation of raw materials, allowing to reduce gold losses with underoxidized sulfides; secondly, lower sensitivity to fluctuations in the composition of concentrates; thirdly, utilization of arsenic in the form of low-hazard stable compounds, which causes minimal impact on the environment.

If there is a need to increase the productivity of an existing autoclave plant, there are several options for achieving the goal:

• increase in the number of autoclaves;

• commissioning of additional capacities of the air separation plant;

• reduction of the content of sulphide minerals in processed raw materials;

• use of internal production reserves.

The first two options are associated with a significant increase in capital and operating costs due to an increase in the fleet of expensive capital equipment. Reducing the sulphide content in the feedstock is difficult, since a significant portion of refractory gold is associated with sulphide minerals. The most promising option is the fourth.

The autoclave technology's own reserve is off-gas - a mixture of gases continuously removed from the autoclave, with which 10-20% of oxygen is usually lost. Oxygen losses are due to the need to maintain a certain level of its partial pressure in the autoclave, but due to the accumulation of gaseous impurities: nitrogen, carbon dioxide, etc. - a constant discharge of a small part of the gas phase is required. Off-gas is unloaded from the autoclave under a pressure of 3.0 MPa and can be sent to reactors for preliminary partial atmospheric oxidation of raw materials.

The sulfuric acid solution from the autoclave discharge after its separation from the gold-containing solid phase can also be considered as a technological reserve. The solution contains sulfuric acid and Fe(III) ions, a significant part of which is usually not used in the technology and can be directed to partial atmospheric oxidation of raw materials as a leaching agent.

The main oxidizers of sulfide minerals in the autoclave are gaseous oxygen and Fe(III) ions; oxidation by oxygen can be described by the main reaction equations (1-6):

A small portion of sulfides can be oxidized in an autoclave by interaction with trivalent iron ions according to reactions (7-10):

The products of sulfide oxidation reactions are iron in the form of Fe(II) and Fe(III), arsenic mainly in the form of As(V), as well as sulfate sulfur S(VI) and elemental sulfur S(0). It is worth noting that when carrying out atmospheric oxidation of sulfide concentrate in a sulfuric acid sulfate medium, up to 30% of sulfide sulfur is converted into elemental sulfur.

It is known that the rate of oxidation of sulfides with gaseous oxygen (reactions (1)-(4)) in sulfuric acid media under atmospheric conditions is low. The rate of oxidation with Fe ³⁺ ion (reactions (7)-(10)) is 2-4 orders of magnitude higher. The limiting stage of the process under atmospheric conditions is the oxidation of the formed Fe ²⁺ ions to Fe ³⁺ with gaseous oxygen (reaction (5)), which leads to a decrease in the concentration of Fe ³⁺ ions and the accumulation of elemental sulfur in the solid phase of the pulp. To ensure an acceptable oxidation rate under atmospheric conditions, a high (20-50 g/l) concentration of Fe ³⁺ ions is required, the source of which can be a solution after autoclave oxidation and conditioning of the autoclave pulp. Iron in the liquid phase of the pulp is formed and accumulates during the oxidation of iron-containing sulfide minerals (pyrite and arsenopyrite). During autoclave oxidation, hydrolytic precipitation of Fe ³⁺ occurs with the formation of secondary compounds of various compositions (sulfates, jarosites, hydroxides, etc.). Due to the conditioning of the autoclave pulp, some of the unstable secondary phases pass into solution, while the concentration of Fe ³⁺ ions increases.

Thus, to increase the efficiency and productivity of enterprises processing gold-bearing sulphide concentrates using autoclave-hydrometallurgical technology, it is advisable to use autoclave oxidation products - autoclave off-gas and sulphuric acid solution, they can be used for partial oxidation of sulphide minerals under atmospheric conditions. In this case, Fe ³⁺ ions will directly participate in the oxidation reaction of sulphides, and gaseous oxygen will oxidise Fe ²⁺ ions to Fe ³⁺ , maintaining their concentration at an acceptable level. An important technological advantage of organizing such a process is the absence of the need to use live steam to heat the pulp. Heating of the pulp to a temperature of 95±5°C will be carried out by mixing the initial concentrate pulp with a hot (80±5°C) solution after autoclave oxidation and conditioning and supplying hot exhaust gas from the operating autoclave (~220-230°C at the outlet of the autoclave), containing “spent” oxygen and water vapor.

A method is known (patent WO 2000017407 A1, published 30.03.2000), which provides for the extraction of precious metals from refractory gold-bearing concentrate, including fine grinding of the material to a size of 80% of the class less than 20 μm, leaching in an alkaline medium in the presence of oxygen while maintaining the pH at a level of 5-7 units and a temperature of 60-85°C using limestone and lime as alkaline reagents with oxidation of sulfides, including pyrite up to 95% and further cyanidation of the oxidized material to extract gold and silver.

The disadvantages of this method are:

• high capital and operating costs for ultrafine grinding of concentrate prior to atmospheric oxidation;

• long duration (more than 24 hours) of deep oxidation of sulfides under atmospheric conditions;

• costs of alkaline reagents used to neutralize the released sulfuric acid and maintain the pH at a given level;

• low degree of oxidation of sulfide sulfur (up to 95%) and, as a consequence, insufficient degree of recovery of refractory gold associated with sulfide minerals.

A variant is known (FLSmidth® Rapid Oxidative Leach (ROL) Process), according to which Fe ³⁺ sulfate, which is the main oxidizer of sulfides in sulfuric acid environments under atmospheric conditions, is introduced into the pulp of atmospheric oxidation (80-105°C) in addition to gaseous oxygen. The method was developed for processing copper concentrates in which the main sulfide mineral is chalcopyrite. When oxidizing chalcopyrite with Fe ³⁺ ion and oxygen, copper extraction into the solution reached 97-99% in 6 hours. According to the authors, the process can also be easily adapted for operation at temperatures close to the melting point of elemental sulfur. At present, the ROL process has no practical application due to little study.

The disadvantages of this method are:

• lack of information on the technological applicability of the method for processing refractory gold-bearing concentrates containing mainly pyrite;

• costs for ultrafine grinding of concentrate before atmospheric oxidation;

• the predominant formation of elemental sulfur during the oxidation of sulfide sulfur under atmospheric conditions, the presence of which in the oxidation residue will lead to an increase in the consumption of cyanide during its sorption cyanidation for gold extraction. Measures are necessary to reduce its content in the solid phase.

A method for extracting precious metals from ores or concentrates is known (patent application WO 2020/165845 A1), which includes, according to one of the proposed schemes, autoclave oxidation of the original ore or concentrate with dehydration of the resulting autoclave pulp (thickening and, if necessary, filtration) and feeding the autoclave cake containing secondary Fe ³⁺ compounds to the stage of atmospheric oxidation of the ore or concentrate. Also, at the stage of atmospheric oxidation, if necessary, an autoclave solution is supplied to maintain an optimal water and acid balance. Oxygen is supplied to autoclave and atmospheric oxidation.

The disadvantages of this method are:

1) Using the solid phase of the pulp after autoclave oxidation as a source of Fe ³⁺ ions is ineffective, since during autoclave oxidation, as a result of hydrolytic precipitation of Fe ³⁺ under different conditions, secondary compounds of various compositions (hematite, hydroxides, basic iron sulfate, jarosites) are formed, which are stable in sulfuric acid environments. When autoclave cake is dissolved in sulfuric and chloride environments, the amount of released Fe ³⁺ ions may be insufficient for deep oxidation of sulfide minerals under atmospheric conditions.

2) At the stage of atmospheric oxidation, for intensive and deep oxidation of sulphide minerals, ultrafine grinding of the material is necessary, which is carried out in specially designed reactors. The use of such reactors is associated with large capital and operating costs.

3) To open up the maximum amount of refractory gold, deep oxidation of sulphide minerals is required, which is achieved in atmospheric conditions over a long period of time (more than 24 hours).

4) Oxidation of sulphide minerals in atmospheric conditions is associated with the formation of noticeable quantities of elemental sulphur. During sorption cyanidation of atmospheric oxidation residues, a high specific consumption of cyanide will be observed due to their non-target interaction.

5) The need to produce additional amounts of oxygen and the low degree of oxygen utilization in atmospheric oxidation reactors. To increase it, it is necessary to use powerful drives for mixing devices and high vertical reactors to create pressure due to the hydrostatic column of pulp.

The closest method adopted as a prototype is the method for processing gold-bearing refractory sulfide concentrates disclosed in PETROV G.V. et al. Comparison of Methods for Enhanced Gold Recovery from Double-Refractory Gold Concentrates in Autoclave Oxidation Technology. iPolytech Journal, 2023, Vol. 27, No. 4, pp. 809-820. A known method for processing gold-bearing refractory sulfide concentrate includes its preliminary grinding to a particle content of -45 μm class of 85% or more, atmospheric oxidation of the concentrate in a sulfuric acid medium, separation of the solid residue, its autoclave oxidation at temperatures of 220-230 °C and a partial oxygen pressure of 0.3-0.9 MPa, conditioning of the resulting pulp, separation of the gold-bearing solid residue, followed by gold extraction from it by sorption cyanidation.

The implementation of a combination of autoclave and atmospheric oxidation methods for gold-bearing concentrates under the conditions described in the prototype method is associated with high capital and operating costs in gold production. A more rational arrangement of the process flow chart is required to ensure acceptable process indicators.

The technical result of the present invention is an increase in the efficiency of processing gold-containing sulphide concentrates using autoclave-hydrometallurgical technology, which provides for an increase in the through extraction of gold.

The claimed result is achieved by the fact that in the method for processing gold-bearing refractory sulphide concentrate, including its preliminary grinding to a particle content of class -45 μm of 85% or more, atmospheric oxidation of the concentrate in a sulfuric acid medium, separation of the solid residue, its autoclave oxidation at a temperature of 220-230 ° C and a partial oxygen pressure of 0.3-0.9 MPa, conditioning of the resulting pulp, separation of the gold-bearing solid residue with subsequent extraction of gold from it by sorption cyanidation, according to the invention, atmospheric oxidation of the concentrate is carried out at a temperature of 95±5 ° C, a L:S ratio in the pulp of 2.5-6.0 m ³ /t for 6-20 hours in a sulfuric acid medium in the presence of ions of trivalent iron and oxygen, while liquid and gaseous products and waste of the technology - sulfuric acid - are used as reagents containing sulfuric acid and oxygen. an autoclave solution containing 20-50 g/l of Fe ³⁺ and H₂SO₄ ions, and autoclave oxidation off-gases with an oxygen volume fraction of 80-90%, with autoclave oxidation of the solid residue being carried out to ensure the conversion of sulfide and elemental sulfur into sulfate form by 97% or more.

In this case, atmospheric oxidation of the concentrate is carried out in high vertical reactors with a height of up to 20-25 m to increase the oxidation rate and the degree of oxygen utilization as a result of creating pressure in the lower part of the apparatus due to the hydrostatic column of pulp.

Moreover, the pulp is heated before atmospheric oxidation using a steam-gas mixture discharged during cooling of the autoclave pulp in self-evaporators.

The process is organized in high vertical reactors (up to 20-25 m) to ensure high speed, depth of oxidation of sulphide minerals and improved oxygen dissolution as a result of creating pressure in the lower part due to the hydrostatic column of pulp.

The basic technological scheme for processing gold-containing sulphide concentrates using the proposed method is presented in Figure 1.

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

EXAMPLES OF IMPLEMENTATION OF THE PROPOSED METHOD

The preparatory operation before atmospheric oxidation (AtMO) was the regrinding of the flotation concentrate to a content of -45 µm particles of 90-95%.

Atmospheric oxidation of the crushed concentrate was carried out at a temperature of 95-100°C in two variants: the first - at atmospheric pressure in a 2-liter glass beaker; the second - in an autoclave with a volume of 1.1 liters at an excess pressure of 1-2 bar, which was created by feeding oxygen into it. In both variants, gaseous oxygen (99% vol.) was fed into the reactor from a cylinder. The crushed wet concentrate (humidity 20-25%) was repulped in distilled water or a synthetic solution simulating the composition of the liquid phase of the pulp after its autoclave oxidation and conditioning of the autoclave pulp, containing 31.8 g/l Fe, 2.6 g/l Fe ²⁺ , 34.9 g/l S and 49.0 g/l H ₂ SO ₄ . The solid content of the pulp was 14% (the L:S ratio in the pulp was 6:1 ml/g). The duration of atmospheric oxidation was 6 hours.

Autoclave oxidation of the residue after atmospheric oxidation was carried out in a 1.1 l autoclave at 225±3°C and a partial oxygen pressure of 7 bar. The wet residue (20-25% humidity) after atmospheric oxidation was loaded into the autoclave and the calculated amount of distilled water was added to the solid content in the pulp of 17% (the L:S ratio in the pulp was 5:1 ml/g). The autoclave was sealed, the pulp was heated to the operating temperature, after which gaseous oxygen was supplied to the pulp and oxidation of sulfides and elemental sulfur was carried out until oxygen consumption completely ceased. Upon completion of autoclave oxidation, the pulp was cooled, excess pressure was released from the autoclave and the autoclave pulp was conditioned at a temperature of 95±2°C for 2 hours.

The solid autoclave cake after conditioning was subjected to sorption cyanidation under the following parameters: 24 hours, pH 10.0-10.5, L:S ratio in the pulp 4:1 ml/g, potassium cyanide concentration 1-2 g/l, addition of Purogold sorbent 5% vol. The cake after cyanidation was submitted for assay analysis to determine the residual gold content and determine the proportion of cyanidable gold in it (gold recovery).

The chemical composition of the original concentrate is given in Table 1.

The main results of atmospheric oxidation of crushed concentrate are shown in Figure 2. The figure shows the following symbols: βs - degree of oxidation of sulfide sulfur; y(cake) - yield of residue after atmospheric oxidation; C(S) and C(S ⁰ ) - content of sulfide and elemental sulfur in the residue of atmospheric oxidation; АО - autoclave oxidation.

During atmospheric oxidation of the crushed concentrate with gaseous oxygen without adding an autoclave solution at an excess pressure of 2 bar for 6 hours, 10.6% of sulfide sulfur was oxidized, the residual content of which was 25.2%. The yield of the residue was 93.6%. Oxidation of the concentrate with oxygen under atmospheric conditions at a pulp pH of 1.7-1.8 units proceeded slowly.

The oxidation rate of the concentrate with the addition of a solution after autoclave oxidation and conditioning, containing about 30 g/l of Fe ³⁺ ions, proceeded several times faster. With atmospheric oxidation with an excess pressure of 2 bar for 6 hours, 4 times more sulfide sulfur (46.0%) was oxidized, the residual content of which was 19.9%. The yield of the residue decreased to 71.7%.

Analysis of Figure 2 shows that an increase in excess pressure contributed to a regular increase in the degree of oxidation of sulfide sulfur (the residual content of sulfide sulfur decreased) during atmospheric oxidation due to an increase in the concentration of dissolved oxygen in the liquid phase of the pulp. At the same time, the cake yield decreased and the content of elemental sulfur in the solid phase of the pulp increased. The degree of transformation of sulfide sulfur into the elemental form did not depend on excess pressure and amounted to 23-31%.

With the increase of excess pressure, the residual concentration of sulfuric acid in the liquid phase of the pulp decreased (from 44 g/l to 29 g/l), the concentration of Fe ²⁺ ions decreased (from 28 g/l to 15 g/l) and the concentration of Fe ³⁺ ions increased (from 11 g/l to 34 g/l). Thus, excess pressure contributed to more intensive oxidation of Fe ²⁺ ions by oxygen, due to which the concentration of Fe ³⁺ ions was at a sufficient level for deep oxidation of sulfide minerals.

When implementing the proposed method on an industrial scale, it is recommended to use vertical reactors up to 20-25 m high, due to which pressure will be created in the lower part, facilitating the intensification of oxidation of sulfides and Fe ²⁺ ions.

The atmospheric oxidation residue with the maximum content of elemental sulfur (4.9%) was subjected to autoclave oxidation. The rate of autoclave oxidation of the initial concentrate and the residue of its atmospheric oxidation at a temperature of 225°C was approximately the same (19-20 minutes). The presence of elemental sulfur did not affect the rate and depth of oxidation of sulfide minerals. The degree of oxidation of sulfide sulfur was 98%.

According to chemical analysis, the residual content of elemental sulfur in the solid phase of the autoclave pulp did not exceed 0.2%. Thus, elemental sulfur in the autoclave was oxidized by 99%.

The through gold recovery in two oxidation stages under atmospheric and autoclave conditions was 93.7% (residual gold content in cyanidation cake 3.8 g/t), which was approximately 2% higher than autoclave oxidation of the initial concentrate after grinding under the same parameters. During autoclave oxidation of the atmospheric oxidation residue, the through cake yield was 13% lower due to the removal of some iron and arsenic from the concentrate at the atmospheric oxidation stage.

The results of the experiments showed the technological possibility of carrying out preliminary oxidation of refractory gold-bearing concentrates with the addition of a solution after autoclave oxidation and conditioning containing Fe ³⁺ ions for the oxidation of sulfide mineral particles, as well as achieving high technological indicators of subsequent autoclave oxidation of the resulting residues.

Claims (3)

1. A method for processing gold-bearing refractory sulphide concentrate comprising its preliminary grinding to a -45 μm particle content of 85% or more, atmospheric oxidation of the concentrate in a sulphuric acid medium, separation of the solid residue, its autoclave oxidation at a temperature of 220-230°C and a partial oxygen pressure of 0.3-0.9 MPa, conditioning of the resulting pulp, separation of the gold-bearing solid residue, followed by gold extraction from it by sorption cyanidation, characterized in that the atmospheric oxidation of the concentrate is carried out at a temperature of 95±5°C, a L:S ratio in the pulp of 2.5-6.0 ^m3 /t for 6-20 hours in a sulphuric acid medium in the presence of ferric iron ions and oxygen, wherein liquid and gaseous products and waste from the process - autoclave sulphuric acid - are used as reagents containing sulphuric acid and oxygen. a solution containing 20-50 g/l of Fe ³⁺ and H ₂ SO ₄ ions, and autoclave oxidation exhaust gases with an oxygen volume fraction of 80-90%, with autoclave oxidation of the solid residue being carried out to ensure the conversion of sulfide and elemental sulfur into sulfate form by 97% or more. 2. The method according to paragraph 1, characterized in that atmospheric oxidation of the concentrate is carried out in high vertical reactors with a height of up to 20-25 m to increase the oxidation rate and the degree of oxygen utilization as a result of creating pressure in the lower part of the apparatus due to the hydrostatic column of pulp. 3. The method according to paragraph 1, characterized in that the pulp is heated before atmospheric oxidation using a steam-gas mixture discharged during cooling of the autoclave pulp in self-evaporators.