RU2228381C1 - Hydrometallurgical method for developing persistent copper-gold sulfide concentrates - Google Patents

Abstract

FIELD: mining industry. SUBSTANCE: invention concerns recovering precious metals whose recovery using common leaching reagents is not efficient. Method of invention comprises adding 80-93% sulfuric acid to concentrate, stirring and heating resulting pulp to 200-250 C followed by stirring for further 5-6 h and leaching soluble sulfates. In the process, weight ratio of concentrate to sulfuric acid ranges from 1:3 to 1:5. Leaching of sulfates is accomplished by adding, at constant agitation, water to achieve pulp-to-water weight ratio 1:(3-5). After developing copper-gold concentrates according to present invention, concentration of copper in solid residues is lowered from 16% to 0.15- 0.20% and gold concentration from 183 g/t to 280-450 g/t. EFFECT: increased persistent concentrate development efficiency. 4 tbl

Description

The invention relates to hydrometallurgy of precious and non-ferrous metals, in particular to the hydrometallurgical processing of ore concentrate for the extraction of precious metals that are difficult to recover using conventional leaching reagents.

The pyrometallurgical method for processing copper-gold concentrates is known, according to which copper-gold concentrate is mixed with concentrates of copper ores and melted in thermal ore furnaces at a temperature of 1400-1600 ° C. Noble metals in the smelting process go into copper matte. Matte is then either refined with blister copper smelting or decomposed with a sulfuric acid solution of oxidized iron with the transfer of copper into solution. Noble metals in both cases are extracted from solid residues by a known method of cyanidation [I.N. Maslyanitsky, L.V. Chuguev, V.F. Borbat, M.V. Nikitin, L.S. Haircut. Metallurgy of precious metals. - M .: Metallurgy, 1987, p. 68].

The main disadvantages of the pyrometallurgical method include the complexity of the technological scheme of processing at high energy costs, especially at the stages of concentrate melting and matte refining, the relatively high losses of precious metals with melting slag in the form of small kings, shielded by slag components.

In the hydrometallurgical method, before cyanidation, ores and concentrates are subjected to oxidative treatment in order to destroy the sulfide matrix of minerals. Nitric acid is often used as an oxidizing agent.

The known method [US Patent No. 5236492. The extraction of precious metals from refractory ores], in which the ore is ground to a value of 10 mm, treated with strong mineral acid (preferably sulfuric) at pH <2 to convert acid-absorbing minerals to water-soluble sulfate salts, then the ore is treated with nitric acid in an amount 5-200% higher than stoichiometrically necessary, and the released nitrogen oxides are disposed of. A nitric acid-resistant binder can be added to form a stronger ore sinter, which is leached with a nitric acid solution fed continuously or intermittently.

In another similar method [US Patent No. 5425800, IPC ⁵ C 22 B 11/00, 06/20/95. Extraction of precious metals from refractory ores. - RZ "Metallurgy", 1996, 11G 148P] ore, crushed to 6.4 mm, is treated at 45-85 ° C in a closed vessel for 1-12 hours with a solution of nitric acid HNO ₃ to dissolve sulfide minerals. The nitric oxide released in this case is regenerated into nitric acid. The concentration of the used solution of 20-70% nitric acid, the amount of 100-300% of the stoichiometric. Washed with water, the ore is treated with some alkali to pH> 10 and subjected to heap leaching with cyanide solutions.

In one of the other known methods [US Patent No. 4647307, IPC C 01 G 49/00, 1987], the pyrite or arsenopyrite ore concentrate is oxidized with nitric acid in an autoclave at a temperature of 80 ° C in the presence of oxygen and continuous mechanical stirring. After decomposition of pyrite or arsenopyrite from the solid residue, noble metals such as gold can be recovered by conventional methods: cyanidation, thiourea treatment, etc.

Another known method [US Patent No. 3793429, IPC C 22 B 3/00, 1974] involves pretreatment with nitric acid of sulfide copper ores and concentrates containing about 28% copper, 25% iron, silver 145.8 g and gold 16, 7 g per 1 ton of concentrate.

The concentrate is first ground to <0.053 mm and then leached with nitric acid at 90 ° C. After treatment with nitric acid, the pulp is subjected to separation into solid and liquid fractions. The solid residue is treated in intermediate steps to remove sulfur and unreacted sulfides by froth flotation and then treated with cyanide solutions to extract gold and silver into the solution. The liquid fraction of the pulp is subjected to intermediate purification and neutralization before sending it to the stage of electrolytic separation of copper.

The main disadvantage characteristic of the above methods is the use of expensive nitric acid. The insufficient completeness of the decomposition of minerals with nitric acid at atmospheric pressure necessitates the process in an autoclave with stirring, which further complicates the process of extraction of precious metals.

A known hydrometallurgical method of autoclave oxidative leaching of sulfuric acid pyrite concentrate (see. RZ "Metallurgy", 1G173, 1994, No. 1, p. 27. Sulfuric acid pressure oxidation of pyrite concentrate from Vaal Reef East Gold mine / TopKava VA // Proc.Ist .Int.Conf / Mod.Process Miner.And Miner. Process. Beijing, Sept. 22-25, 1992 .-- Beijing, 1992, s. 630-635). In this method, readily available inexpensive sulfuric acid is used. Grinded to 90% <0.075 mm concentrate containing, wt.%: Sulfur S _total 36.6; Fe iron 36.8; silicon oxide SiO ₂ 20.75; aluminum oxide Al ₂ O ₃ 6.0 and gold 8.26 g per 1 ton of concentrate; autoclave is treated with a solution of sulfuric acid H ₂ SO _{4 with a} concentration of 53-64 g / l in the presence of oxygen. Optimal leaching conditions: temperature t = 190 ° С; partial pressure of oxygen 750 kPa; the ratio of solid T and liquid W fraction was T: W = 1: 4; leaching time 3 hours. The pulp formed during leaching is sent from the autoclave to the evaporator for quick cooling to a temperature below 100 ° C and then to the pulp collector, from where it is pumped for filtration to separate the solid and liquid phases. The insoluble residue — the solid fraction — is repulped with water to wash off soluble sulfates and unreacted sulfuric acid.

The extraction of gold from the insoluble residue was carried out in the traditional way - cyanidation in capsule flasks. Consumption of NaCN 2.5 kg / t, alkali 225-363 kg / t. Cyanide temperature - room, duration 24 hours. At the same time, high gold recovery from refractory pyrite concentrate is achieved. This method is selected for the prototype.

The main disadvantages of this method are the complexity of the hardware design of the process, since an autoclave is used, operating under pressure significantly higher than atmospheric, a heat exchanger-self-evaporator for rapid cooling of the pulp, pumps and high-pressure fittings. In addition, to conduct a more complete decomposition of sulfides, it is necessary to use an oxidizing agent - oxygen under a pressure of 750 kPa. This leads to a significant increase in the cost of the process of opening the concentrates.

The objective of the invention is to simplify the method while achieving a higher technical result - increasing the efficiency of opening resistant copper-gold sulfide concentrates.

The technical result is achieved by the method of hydrometallurgical opening of refractory copper-gold sulfide concentrates, including adding sulfuric acid to the concentrate, mixing and heating the resulting pulp, leaching of soluble sulfates, according to the invention, concentrated sulfuric acid with a concentration of 80-93% is used for opening in an amount based on a ratio of 1 : 3 <T: L <1: 5, where T is the mass of the concentrate, L is the mass of concentrated sulfuric acid, the resulting pulp is heated to a temperature of 200-250 ° C and can withstand atmospheric pressure and stirring for 5-6 hours, and leaching of soluble sulphates is carried out by adding water to achieve a ratio of 1: 3 _<1 T: F ₁ <1: 5, where T ₁ - weight of pulp, M ₁ - weight of water, with constant stirring.

The use of concentrated (80-93%) sulfuric acid allows the process to be carried out at high temperatures - 200-250 ° C. The upper limit is limited by the boiling point of sulfuric acid of a certain concentration, for example, for 80% it is 210.2 ° C, and for 93% it is 263 ° C [A.G. Ameline. Sulfuric acid production. - M .: "Chemistry", 1967, p.19]. At temperatures above 200 ° C, concentrated sulfuric acid exhibits oxidizing properties, the mechanism of which is considered as the action of oxygen released during the partial decomposition of sulfuric acid sequentially to sulfuric (SO ₃ ) and then sulfur (SO ₂ ) anhydride [Khabashi F. Fundamentals of applied metallurgy. T.II. - M .: Metallurgy, 1975, p.102]. Below 200 ° C these processes occur less intensively.

The ratio of 1: 3 <T: W <1: 5 is selected from the condition of providing an excess of sulfuric acid in the pulp taking into account partial evaporation and its decomposition, as well as achieving the viscosity of the pulp, which provides a sufficient mass transfer rate in the pulp. With a ratio of T: L = 1: 3, the pulp becomes viscous, which negatively affects the rate of mass transfer. Increasing the ratio to 1: 6 leads to an excess consumption of sulfuric acid.

As a result of the action of concentrated sulfuric acid at high temperature and continuous stirring of the pulp, the sulfide minerals of the concentrate decompose with the formation of soluble metal sulfates and the release of sulfur dioxide, and the decomposition of minerals, in contrast to the prototype, is carried out at atmospheric pressure without the use of an autoclave and associated equipment and without additional supply of oxygen. The time of 5-6 hours is selected from the condition of the most complete decomposition of sulfide minerals.

After sulfuric acid treatment, the pulp is leached with soluble sulfates and excess sulfuric acid. In this case, leaching is carried out with constant stirring by adding water to achieve a ratio of 1: 3 <T ₁ : W ₁ <1: 5, where T ₁ is the mass of the pulp, W ₁ is the mass of water. The lower limit is selected from the condition of the most complete quantitative removal of soluble sulfates from the pulp. The upper limit is limited by the rational use of wash water.

The pulp formed during leaching is subjected to forced filtration. The filtrate, after extraction of copper from it by any known method, is electrolysis with an insoluble anode, crystallization of copper sulfate, etc. - and oleum fortifications can be returned to the stage of sulfation of the concentrate. The solid residue from the filter is subjected to repulpation in order to wash soluble sulfates sorbed by the solid residue. Wash water is used to leach soluble sulfates in the previous stages, and from the solid residue, after treatment with alkali, precious metals are recovered in a known manner, for example, cyanidation.

The implementation of the method is illustrated by the following example.

The hydrometallurgical opening was subjected to a copper-gold concentrate composition, wt.%: Copper Cu 16,0; iron Fe _total 5.0; Fe _oxidized 3.5; sulfur S _total 8.0; magnesium oxide MgO 2.5; calcium oxide CaO 21.0; alumina Al ₂ O ₃ 8.0; silica SiO ₂ 36.8; Au gold 183 g / t; Ag silver 238 g / t. The persistence of the concentrate is characterized by a high copper content in the form of sulfide minerals and a thin impregnation of native gold and silver.

A portion of the crushed concentrate with a mass of T = 0.1 kg is placed in an open reaction vessel, sulfuric acid F is added at a concentration of 93.5% based on the selected ratio T: W = 1: 5. The vessel is placed in an electric furnace with automatic temperature control equal to 220 ° C. A stirrer is introduced into the vessel, the electric drive of which is located outside the furnace. With continuous stirring and constant temperature, the vessel with the reaction mass is kept for 5 hours. After that, the electric heating of the furnace is turned off and carefully, in small portions with stirring, pour water (or washing water from the solid residue repulpation) into the vessel at the rate of T ₁ : W ₁ = 1: 5, where T ₁ is the pulp mass, W ₁ is the wash mass water. Then, the mixer is disconnected from the electric drive shaft, the vessel is removed from the furnace, the solid residue and the solution are separated on a suction filter.

In all experiments shown in Tables 1-4, the filtrate volume after the suction filter was adjusted to 0.5 L and copper concentration in it was measured by chemical and atomic sorption methods [G. Charlot. Methods of analytical chemistry. - M .: Chemistry, 1969], calculate the amount of copper in the filtrate and its degree of extraction from the concentrate.

The solid residue from the separation of the pulp on the suction filter is subjected to repulpation with water, dried at a temperature of 110-115 ° C, and a sample is taken for analysis of the residual content of copper and gold in it. The gold content in solid residues increased from 183 to 450 g / t.

The results of the experiments of opening the concentrate depending on the concentration of sulfuric acid, time, temperature and the T: W ratio are presented in Tables 1-4.

Table 1 shows the effect of the concentration of sulfuric acid on the degree of opening of the concentrate. The conditions of the experiments: T: W = 1: 5; pulp heating temperature - above 200 ° C; sulfatization time 5 hours.

Table 2 shows the effect of sulfatization time on the degree of opening of the concentrate. Test conditions: sulfuric acid concentration of 90%; T: W = 1: 5; pulp heating temperature - over 200 ° С.

Table 3 shows the effect of sulfatization temperature on the degree of opening of the concentrate. Test conditions: sulfuric acid concentration of 90%; T: W = 1: 5; sulfatization time 5 hours.

Table 4 shows the effect of the T: W ratio in the pulp on the degree of opening of the concentrate. Test conditions: sulfuric acid concentration of 90%; pulp heating temperature - over 200 ° С; sulfatization time 5 hours.

From the results given in Tables 1-4, the following conclusions can be drawn:

1. The concentration of sulfuric acid for opening copper-gold concentrates should be close to the “vitriol” oil - 90-93%.

2. The time of the sulfatization process using 90% sulfuric acid is 5-6 hours, when the degree of opening is high, and the copper content in the solid residue is the smallest. An increase in time up to 7 hours does not significantly affect the autopsy process.

3. At a ratio of T: L = 1: 3, the reaction mass becomes viscous, which negatively affects the rate of mass transfer. An increase in the ratio to 1: 6 leads to an excess consumption of sulfuric acid, which does not justify an increase in the degree of opening of the concentrate.

4. The process of sulfation is advisable to be carried out at temperatures of 200 - 250 ° C.

The obtained results of the extraction of precious metals from the solid residues of the hydrometallurgical opening of a copper-gold sulfide concentrate by cyanidation showed that under ordinary cyanidation conditions (sodium cyanide consumption 2.5 kg / t, solid to liquid ratio 1: 2, room temperature, cyanide time 24 hours) the average gold recovery was 95.7%, silver 93.5%. These data also showed that the same result as in the prototype was achieved in a simpler and lower cost way.

Thus, the proposed method, due to the distinguishing features made according to the invention, ensures the transfer of copper of the copper-gold sulfide concentrate into a soluble state, which allows the precious metals to be converted from the solid residue to a solution by cyanation under high conditions with a high degree of recovery, and sulfate solutions, after precipitation electrolytic copper powder and strengthening oleum, reused at the stage of sulfatization.

Claims (1)

The method of hydrometallurgical opening of refractory copper-gold sulfide concentrates, including adding sulfuric acid to the concentrate, mixing and heating the resulting pulp, leaching of soluble sulfates, characterized in that concentrated sulfuric acid with a concentration of 80-93% is used for opening in an amount based on a ratio of 1: 3 <T: W <1: 5, where T is the mass of the concentrate, W is the mass of concentrated sulfuric acid, the resulting pulp is heated to a temperature of 200-250 ° C and kept at atmospheric pressure and mixed SRI for 5-6 h, and the leaching of soluble sulphates is carried out by adding water to achieve a ratio of 1: 3 _<1 T: F ₁ <1: 5, where T ₁ - weight of pulp, M ₁ - weight of water with constant stirring.