DEVELOPMENT AND IMPROVEMENT OF TECHNOLOGY FOR EXTRACTION OF PRECIOUS METALS FROM TECHNOGENIC RAW MATERIALS

ABSTRACT

In this work, the effectiveness of methods for the selective extraction of platinum, palladium and rhodium is determined, and attention is also paid attention to the methods of dissolution, reduction of platinum metals and methods of their purification from various impurities. Based on the study of this topic and the analysis of the results of the research, the authors have developed a comprehensive method for extracting platinum, palladium and rhodium using selective methods in combination with hydro- and pyrometallurgy technologies.

АННОТАЦИЯ

В работе определена эффективность методов селективного извлечения платины, палладия и родия, а также уделено внимание способам растворения, восстановления платиновых металлов и методы их очистки из различных примесов. На основе изучения данной тематики и анализа результатов проведенных исследований, авторы разработали комплексный способ извлечения платины, палладия и родия с применениеми селективных методов в сочетании с технологиями гидро- и пирометаллургии.

Keywords: platinum metals, waste electrolyte solution, selective precipitation, aqua regia dissolution, washing, calcination.

Ключевые слова: платиновые металлы, сбросной электролитный раствор, селективная осаждения, царское-водочное растворение, промывка, прокалка.

Introduction. The Republic of Uzbekistan possesses a reliable raw material base for the extraction and production of a number of noble, rare and trace metals. Some of them are concentrated in independent deposits, such as copper and molybdenum, others can be extracted as associated components from deposits of copper, uranium polymetals and other minerals. In Uzbekistan, the main reserves of platinum, palladium, rhodium and the radiogenic isotope of osmium - 187 are found in the porphyry copper deposits of the Almalyk ore region. In the Chatkal-Kuramin region, manifestations of gabbroid magmatism and associated MPG (most often palladium, platinum and rhodium) are known. [1].

Research methods and results. Waste electrolyte from the gold and silver refining shop of the copper-smelting plant of JSC "AMMK", obtained from copper-electrolyte sludge, was selected as the object of the study. When smelting copper and nickel sulphide raw materials, platinum metals are concentrated in the anodes, which, during further electrolysis, transforms into red mud, where their content, depending on the composition of the initial sulfide ores, varies widely, from tenths to several percent [2]. Chemical analysis of samples was carried out by atomic emission spectroscopy of red mud obtained by processing copper ores, rich in PGM, are given in table 1.

Experimental studies are carried out in a laboratory reactor with a stirrer. All hydrometallurgical processes royal vodka dissolution, precipitation, reduction and purification processes of palinodes are carried out in a titanium reactor [3].

Table 1.

Results of chemical analysis of copper sludge, %

Tank equipment is designed to accumulate solutions obtained during the production of platinum, palladium and rhodium powder. The tank equipment (reactor) is made of VT-1 (R - II) titanium V = 2m³. For filtration processes, it is used in laboratory suction filters, and for drying, firing and calcination processes, laboratory muffle furnaces with the Snol 1400 brand are used.

The study of spent electrolytes with the aim of obtaining palinodes, in particular, platinum, palladium and rhodium, was carried out by the JSC "AMMK", as a result of which it was necessary to examine many processes intended for the complex extraction of platinum metals from electrolyte solutions. Among them, the optimal operations are of the following order:

- accumulation of platinum-palladium solutions after electrolysis of gold, the content of platinum and palladium in solution is more than> 100 mg/dm³ and they are in chloride compounds: PtCl₂ and PdCl₂; - waste electrolyte solutions after electrolysis of gold with a platinum concentration of 10-80 mg/dm³ are oxidized with hydrogen peroxide, while PtCl₂ passes over to PtCl₄;

- precipitation of palladium thiourea complex in thiourea solution, product filtration, cake roasting at 500-600⁰C. In this case, the firing time was 2-3 hours, where the resulting product is subjected to reduction with a hydrazine solution. The recovered product is sent for washing with distilled water, after which it is dried at a temperature of 100-120⁰C and dissolved in aqua regia.

With an increase in duration, the degree of solubility of metals increases, since aqua-aqua leaching of Pd and Pt is associated with the kinetics of solubility. It can be seen from the diagram (Fig.1) that the degree of dissolution of Pd is higher than the degree of solubility of Pt. This explains that the overall recovery of palladium is higher than that of platinum. Also, the main influencing parameter on the solubility is the concentration of the solution, the consumption of aqua regia and the duration of the dissolution process. It was experimentally determined that with an increase in the time of aqua-vodka dissolution, the consumption of the solution increases, as a result of which the concentration of palladium in the solution increases accordingly and is equal to 200 g/dm³ at 120 minutes of the process duration with the consumption of reagent 2l per 100 g palladium product. The obtained result determined the optimal regime of aqua-vodka dissolution of the palladium product and described in the curve graph shows the growth of solubility of metals of the platinoids group, in particular, platinum and palladium [4].

Figure 1. Dependence of the degree of PGM solubility on the duration of the process

The dried palladium product is poured in small portions into a heated container V–0,05m³ with a mixture of concentrated nitric and hydrochloric acid, the consumption of aqua regai is 2 liters per 100 g of Pd product. Dissolution is carried out with constant heating for 1-2 hours. The research results are shown in Fig. 1.

We extract platinum from the solution by selective methods. For this purpose, the selective precipitating reagent of ammonium chloride was chosen, which precipitates only platinum from solution, while palladium remains in solution. The solution is treated with a small amount of ammonium chloride and the process is carried out in a reactor with mechanical stirring. The results of these experiments - the basis for industrial implementation shows that tetrachloropalladium acid is a solution, ammonium hexachloroplatinate (IV) becomes a precipitate, which, without much effort, accurately separates palladium from platinum [5].

After filtration and washing, the chloropalladosamine is ignited. At 600-900°C, complex decomposes to metallic palladium. For complete purification of metallic powder, palladium is treated with formic and citric acid, then it is thoroughly washed with distilled water and the product is dried. In this case, Pd powder is formed with a purity of 99,5–99,9%. As a result of the experiments, a technological scheme for extracting precious metals from industrial waste was developed (Fig. 2).

Conclusions. As a result of extensive research, including a number of experiments and experiments, a new technological scheme was developed, consisting of 20 operations with a cycle time of 24-26 hours. At the same time, the cost-effective extraction of PGMs from solutions with a platinoid content of 50 mg per 1 liter reaches more than 84%. The result is refined platinum powder with a mass fraction of 98,0-99,0% and palladium in powder 99,5-99,94% (Table 2 and table 3).

Table 2.

 Results of chemical analysis of the obtained platinum powder

Figure 2. Technological scheme for obtaining refined platinum and palladium powder from industrial waste

The method is also suitable from an environmental point of view, since the resulting acidic filtrates are neutralized with an alkali solution or alkaline filtrates obtained during the reduction of palladium to metal with formic acid or hydrochloric acid hydrazine.

Table 3.

Results of chemical analysis of the obtained palladium powder

The introduction of this technology undoubtedly gives a positive economic effect due to the production of precious platinum and palladium, as well as the additional extraction of rhodium and improves the ecological situation in the places of accumulation of industrial waste [6].

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