Hydrometallurgical processing of pyrite concentrates from Yoshlik deposits

. The work aimed to develop a rational technology for processing ore from the Yoshlik deposit, taking into account the solution of issues of the integrated use of mineral raw materials and environmental protection, and the development of a technological scheme. To enrich the ore of the Yoshlik deposit, a combined gravity-flotation technological scheme was recommended, followed by sorption cyanidation of the pyrite concentrate. According to the results of research on the results of sample the ore of the Yoshlik deposit, it was revealed that pyrite flotation is required to enrich the ore. Without pyrite flotation, gold recovery is low from 52 to 68%, with the use of pyrite flotation, the recovery increase is up to 24%. The specified purpose of the work follows the need to solve the following problems: compilation of a literature review on the current state of enrichment of copper ores; study of the material composition of ore samples from the Yoshlik deposit; experimental substantiation of the influence of various factors on the concentration of ore. In the ore sample of the Yoshlik deposit, gold is unevenly distributed by size classes, the precious metal is concentrated mainly in sludge classes.


Introduction
Uzbekistan has significant reserves of non-ferrous metals -copper, lead, zinc, tungsten and other metals of this group. A characteristic feature is that the extraction of ore is carried out mainly in an open way, which ensures the profitability of the mines [1].
Non-ferrous metal ore reserves are mainly concentrated in the Almalyk ore field. The Kalmakyr deposit is unique, and significantly surpasses foreign analogues in the extraction of copper-molybdenum ores. On the territory of Uzbekistan, copper-molybdenum ores are processed, in which the content of copper and pyrite sulfides prevails. At present, the Almalyk Mining and Metallurgical Plant is a major producer of copper in our republic, and the copper industry is one of the leading branches of non-ferrous metallurgy, and the task of creating and developing a rational and integrated technology for processing copper ores is very relevant [2].
Copper and its alloys were used in ancient times before the advent of writing and were important for the development of the material culture of human society. Currently, copper ore is considered a fossil rock, which contains approximately 0.5% copper. When enriching the ore, concentrates are obtained, in which the copper content in comparison with its content in the ore increases tenfold. If for the smelting of 1 ton of copper, it is necessary to directly smelt 120-160 tons of poor ore, then only 3-6 tons of concentrates need to be smelted [3].

Materials and methods
The method of processing ore and concentrates must be carefully justified for each type of raw material. The choice of method is preceded by research work in a laboratory, semiindustrial and preferably on an industrial scale. At the same time, the following most important indicators are compared: the complexity of the use of raw materials or the completeness of the extraction of metals; operating costs; consumption of basic materials, electricity and fuel, production costs; the cost of received and sold products and possible profit; the volume of capital costs for the construction of a workshop or plant and the payback period of capital investments. The selected technological scheme of enrichment should provide high technological performance at minimum economic costs.
The purpose of this work is to study the material composition and develop a technology for the hydrometallurgical processing of pyrite concentrate since the task of creating and developing a rational and integrated technology for the processing of pyrite concentrates is very relevant [4].
The pyrite concentrate obtained during the enrichment of porphyry copper ore from the Yoshlik deposit was chosen as the object of study. The ore of the deposit is characterized by copper-porphyry gold-molybdenum-containing ore type. The mass fraction of copper in ore samples from the Yoshlik deposit, according to sieve analysis, is 0.49 and 0.34%, respectively. The bulk of the precious metal is concentrated in the categories of practically closed and completely closed intergrowths, accounting for 60.30%. Partially open gold particles in intergrowths of medium quality are noted in the amount of 20%. According to the results of phase analysis, the main part of the gold in the ore samples of the Yoshlik deposit is in the cyanidated form -88.39%. At the same time, the share of free gold is 26.62%, and that of open-growth gold is 64.63%. The persistence of gold is mainly due to its association with sulfides and, to a lesser extent, with minerals insoluble in aqua regia [5][6][7][8].
A sieve analysis was performed for the pyrite concentrate obtained during the beneficiation of the ore from the Yoshlik deposit. According to the results of the analysis, the fineness of the material was P 80 -0.071 mm. When performing the analysis in each class, the content and distribution of gold, silver, copper, and molybdenum were determined. The granulometric composition of the sample is shown in Table 1. According to the sieve analysis, the material is distributed unevenly by size classes and is represented mainly by the sludge class (-0.020 mm), its yield reaches 56.92%. In other size classes, the material is distributed in waves with slight fluctuations in outputs [9][10][11][12][13].
The gold content in the concentrate according to sieve analysis is 3.67 g/t with fluctuations in size classes from 2.76 to 8.54 g/t. The distribution of the valuable component by size classes is uneven. For gold in the sample, the one-modal nature of the opening is traced. In the +0.106 mm class, a modal peak in the gold content is recorded, it accounts for 22.46% of the valuable component. The degree of gold concentration in this class reaches 2.32 conventional units. In the interval -0.106 + 0.020 mm, the metal is distributed in proportion to the outputs of the classes. In the slime class, the gold is finely disseminated, and the metal opening is not observed.

Results and discussion
The mass fraction of copper according to sieve analysis is 1.10% with variations in size classes from 0.75 to 1.32%. The copper content is evenly distributed by size classes and increases sharply in the slime class -0.020 mm to 1.32%. Copper is characterized by a unimodal distribution by size classes. The modal peak falls on the size class -0.020 mm. The degree of concentration of copper in the sludge class is 1.20 conventional units.
The chemical composition of the pyrite concentrate obtained during the enrichment of the ore from the Yoshlik deposit was determined using optical emission, atomic absorption, gravimetric, IR spectroscopic, titrimetric and photometric methods of analysis. The content of gold and silver is determined by the method of assay analysis. The chemical composition of the concentrate is presented in Table 2.
According to the data presented in the table above, it was found that the chemical composition of the pyrite concentrate sample is 24.06% represented by lithophile components. The main one is silica, which accounts for 15.42% of the total mass of the sample. The share of alumina is at the level of 4.35%. The total proportion of oxides of alkali and alkaline earth metals in the sample is 3.24%. The amount of potassium oxide is at the level of 1.33%, and calcium and magnesium oxides -0.73 and 1.18%, respectively. The proportion of sodium oxide is below the detection limit. The carbon content in the sample is 0.21%. All carbon is part of carbonates.
The ore-forming elements in the concentrated sample are represented by iron and sulfur. The amount of iron in the sample reaches 32.0%. The mass fraction of sulfur in the sample is 37.6%, the overwhelming mass of sulfur is included in the composition of sulfide minerals. The proportion of sulfate sulfur is 0.26%.
Non-ferrous metals include copper, zinc and lead. The amount of copper in the concentrate reaches 1.71%, and zinc and lead are fixed in the amount of 0.171 and 0.139%, respectively. Table 3 shows their phase analysis. As shown in the table above, all metals are presented mainly in the sulfide form: the proportion of copper, which is part of the sulfides, is 97.5% of the total mass of the element; the proportion of zinc in the sulfide form is 76% of the total mass of the metal. The ratio of sulfide and oxidized lead is fixed by a less pronounced predominance of the element in the sulfide form -56.1%.
To determine the mineral composition of the pyrite concentrate obtained during the enrichment of the ore of the Yoshlik deposit, diffractometric and quantitative mineralogical analyzes were performed. The diffractometric analysis makes it possible to determine the composition of the concentrate by the main minerals, the proportion of which in the sample is more than 1%. The mineral composition of the sample is presented in Table 4. According to the data presented in Table 4, it was found that the mineral composition of the concentrate is 26.8% represented by rock-forming minerals. Quartz prevails among them, the share of which in the sample is at the level of 11%. The share of mica is 7%, and chloriteis 4%. Feldspars are noted in the amount of 3%. The sample contains carbonates represented by calcite and dolomite, the total amount of which is 1.8%.
Ore mineralization in the concentrate is represented by sulfides, among which pyrite predominates. Its number is 68%. The total share of sulfide minerals is 73.2%. Chalcopyrite and other copper sulfides are present in an amount of 4.8%. Sphalerite and galena are each in an amount of 0.2%. Molybdenite, arsenopyrite and silver minerals are noted in the number of single characters.
To clarify the forms of gold occurrence, and the nature of its relationship with ore and rock-forming minerals, a phase analysis (rational) of gold in pyrite concentrate was performed.
The following forms of gold occurrence were determined: free, with a clean surface (recoverable by amalgamation), free, in oxide films (recoverable by amalgamation after treatment with hydrochloric acid), in the form of open intergrowths, recoverable by cyanidation and resistant to cyanidation. The results of the phase analysis are presented in Table 5. The total gold content according to the results of phase analysis was 3.68 g/t. After treatment of the sample with hydrochloric acid, an additional 9.24% of the noble metal was revealed. The total amount of free gold in concentrate was 11.14%. The share of gold in open aggregates in the concentrate sample accounts for 63.86%. In total, 75% of the noble metal is present in the form available for direct cyanidation.
Without pyrite flotation, gold recovery is low from 52 to 68%, when using pyrite flotation increase in recovery is up to 24%. The need to use pyrite flotation depends on the material composition of the ores and is because part of the gold in the ore is associated with pyrite. This type of ore is recommended to be processed according to a combined gravity-flotation scheme followed by sorption cyanidation.
Hydrometallurgical studies of the pyrite concentrate of the ore sample from the Yoshlik deposit included the selection of optimal cyanide leaching parameters. As part of the study of the optimal parameters of the process, the following groups of studies were carried out: leaching at different concentrations of NaCN; cyanidation at different solids content in the pulp; cyanidation at various concentrate sizes; studying the dynamics of gold dissolution; study of the possibility of reducing the consumption of NaCN; studies on the extraction of copper from cyanidation solutions; disposal of cyanide tailings.
To select the optimal concentration of sodium cyanide in the leaching of precious metals, studies were carried out using NaCN concentrations of 0.2.0.1.0.05 and 0.03%. The leaching mode, the same for all studies, is presented in Table 6, the results of the studies are in Table 7.  Based on the research results, it was concluded that pyrite concentrate cyanidation should be carried out at a NaCN concentration in the liquid phase of the pulp at the level of 0.2%. Reducing the concentration of sodium cyanide leads to a significant decrease in gold recovery. To select the optimal density of the pulp during the leaching of precious metals, studies were carried out on cyanidation at various solids content of 35, 40, 45 and 50%. Leaching was carried out using a NaCN concentration of 0.2%. Other leaching parameters, the same for all studies, are similar to those presented in Table 6. The results of the studies are shown in Table 8.
From the presented data it follows that the cyanidation of the pyrite concentrate must be carried out at a solid content in the pulp of 40%. A decrease in the solids content in the pulp will lead to an increase in the volume of leaching apparatuses. The increase in pulp density hurts the level of gold recovery.
To select the optimal size of the pyrite concentrate, studies were carried out on its cyanidation at various degrees of grinding: 80% -71 microns (initial), 80% -45 microns, 80% -38 microns and 80% -20 microns. The leaching was carried out at a solids content in the pulp of 40% using a NaCN concentration of 0.2%. Other leaching parameters, the same for all studies, are similar to those presented in Table 6. The results of the studies are shown in Table 9. To select the optimal duration of leaching of precious metals, studies were carried out on cyanidation for 12, 16, 24, 30, 36 and 48 hours.
Leaching was carried out at a fineness of 80% -45 μm with a solids content in the pulp of 40% using a concentration of NaCN at the level of 0.2%. Other leaching parameters, the same for all studies, are similar to those presented in table 6. The results of the studies are shown in table 10. Cyanidation of pyrite concentrate was carried out at a process duration of 24 hours. An increase in the duration of leaching will lead to an increase in the volume of leaching apparatuses. Reducing the duration of leaching leads to incomplete dissolution of the cyanide gold.
The performed studies have shown that gold leaching is accompanied by high consumption of sodium cyanide due to the presence of a large number of sulfides and copper in the pyrite concentrate. To assess the possibility of reducing the consumption of NaCN, three series of studies were carried out: cyanidation with the addition of PbO; pulp pre-treatment before cyanidation; circulation of solutions during cyanidation.
The addition of lead compounds to the cyanidation process should allow the sulfide sulfur in the solution to be converted into insoluble lead sulfide.
As operations for preparing the material for cyanidation, the treatment of the pulp with milk of lime, and the oxidation of the concentrate with air and oxygen in an alkaline medium were used. These operations should make it possible to passivate the surface of sulfide minerals and thereby reduce their activity concerning sodium cyanide.
The circulation of the liquid phase of the pulp in the operation of cyanidation should reduce the number of dissolved impurities due to their accumulation in the solution.
Leaching was carried out at a fineness of 80% -45 μm with a solids content in the pulp of 40% using a NaCN concentration of 0.2% for 24 hours. Other leaching parameters are similar to those presented in table 6. The results of studies aimed at reducing the consumption of sodium cyanide are shown in Table 11.

Conclusion
Thus, the performed hydrometallurgical studies made it possible to determine the optimal mode of pyrite concentrate cyanidation: material size 80% -45 µm; preliminary lime treatment of the pulp for 2 hours at pH 11.0; solution turnover, because this contributes to the reduction of NaCN consumption. During cyanidation of the pyrite concentrate obtained from the ore of the Yoshlik, I deposit with a gold content of 2.15 g/t in the indicated mode, the predicted level of gold extraction into the solution will be 78.14% with a metal content in the cake of 0.47 g/t. The extraction of silver into the cathode deposit will be 40%.