NON-TRADITIONAL TECHNOLOGIES OF EXTRACTION OF PRECIOUS METALS FROM INDUSTRIAL TECHNOGENIC WASTE

ABSTRACT

In this article discusses the possibility of combining the products of enrichment of waste from metallurgical production and the chemical technology for the extraction of platinum and palladium from ChMA concentrates obtained after processing industrial technogenic wastes from the Chodak Mining Administration. In this research work is determined the effectiveness of methods for the selective leaching of platinum and palladium, and also pays attention to the methods of dissolution, reduction of platinum metals and methods for their purification from various impurities.

АННОТАЦИЯ

В данной статье рассматривается возможность объединения продуктов обогащение отходов металлургического производства и химическая технология извлечения платины и палладия из концентратов ЧРУ полученных после переработки техногенных отходов Чодакского Рудоуправлении. В работе определена эффективность методов селективного выщелачивание платины и палладия, а также уделено внимание способам растворения, восстановления платиновых металлов и методам их очистки из различных примесей.

Keywords: tailings, gravity separation, mineralogical composition, platinum, electron microscope, leaching.

Ключевые слова: отходы обогащения, гравитационное обогащение, минералогический состав, платина, электронный микроскоп, выщелачивание.

Today, in the conditions of Uzbekistan, there is no integrated technology for processing industrial technogenic wastes and extracting rare and precious metals in the conditions of AGMK JSC with small amounts of rare metals. The presence of technogenic waste containing platinum, palladium and rhodium at JSC AGMK indicates that the plant can manage the manufacturing industry by processing wastes for several years without processing ore [1].

The total amount of enrichment wastes of the Chodak mine administration is 1.844 million tons. The average content of gold ranges from 0.5 g/t to 0.67 g/t, the silver contents in average is 8.27 g/t, and significant contents of platinum group metals, in particular platinum and palladium, were also found. As a result of gravitational enrichment of technogenic wastes of the Chodak Mining Administration (ChMA), a gravity concentrate is obtained with a gold content of 5.65 g / t, silver 38.76 g / t, platinum 1.5-2 g / t, palladium 5-7 g / t [2,3].

The mineralogical composition and structure of the concentrate obtained as a result of the enrichment of technogenic waste from ChMA were studied under a JSM-IT200 scanning electron microscope. As a result of the analysis, it was founded that platinum is denser, that is parts of the sample reflecting light more brightly and it is more associated with palladium and oxygen, and the amount of platinum in the studied sample is 0.25% (See Figure 1.). Further experiments are aimed at the development of chemical technologies for the extraction of individual noble metals from platinoids. For this purpose, the initial sulfuric acid leaching of ChMA concentrates was chosen to remove impurity metals such as copper, iron and zinc, which are further directed to leaching, the gradual extraction of gold and silver, and by the end of the processes it is planned to extract platinum and palladium using aqua regia and selective precipitation [4].

Figure 1. Electron microscopy images of ChMA concentrate

According to the described technology, an experimental flowsheet for the processing of ChMA concentrates was developed in the conditions of the refinery of JSC "AGMK" and the series of experiments were carried out for the integrated extraction of noble and plane metals (see Fig. 2.). [5].

The process of processing of concentrates begins with the treatment of sulfuric acid solutions to transfer non-ferrous metals into the composition of the solution.

In this case, precious metals remain in the insoluble residue and are sent to refining processes.

The sulfates of non-ferrous metals are returned to the main copper production. For reliable solubility of impurity non-ferrous metals, the concentrate is often subjected to roasting before the leaching process [6].

MeS + 4H₂SО₄ →MeSO₄ + 4Н₂О + 4SО₂                                               (1)

MeO + H₂SО₄ → MeSО₄ + H₂О                                                          (2)

Me + 2H₂SО₄ → MeSО₄ + 2H₂О + SО₂                                                (3)

At the same time, the metal occurs in the form of a compound of Cu, Zn, Fe, Co, and other non-ferrous metals, thus purifying the concentrate from non-ferrous metals. The remaining insoluble cake is dissolved in two ways to test the effectiveness of the solvent.

At the first stage, the cake was dissolved with a nitric acid solution; the results of the dissolution of metals are shown in the table 1. Based on the analysis of nitric acid solutions, the degree of solubility of metals is lower, for these reasons it was no longer checked for nitric acid solution, and the cake was directly subjected to aqua regia dissolution [7]. The chemistry of the processes of aqua regia dissolution is given in reactions 4-7:

Au + HNO₃ + 3HCl = AuCl₃ + NO + 2H₂O                                                   (4)

Ag + HNO₃ + 3HCl = AgCl₂ + NO + 2H₂O                                                   (5)

3Pt + 4HNO₃ + 18HCl = 3H₂[PtCl₆]+ 4NO + 8H₂O                                         (6)

3Pd + 4HNO₃ + 18HCl = 3H₂[PdCl₆]+ 4NO + 8H₂O                                        (7)

In order to remove the undissolved part of the product, a filtration process is carried out, the cake is removed and the valuable components are in solution.

Figure 2. The proposed technological scheme for the processing of ChMA concentrates with the extraction of precious metals

Gold and silver are separately precipitated from the solutions and sent to the refinery department, while the rest platinum and palladium remain in the solution [8]. For the selective separation of platinum, the solution is treated with a small amount of ammonium chloride in order to separate platinum from the palladium-containing solution, the process is carried out in a reactor with mechanical stirring according to the following reaction [9].

3Н₂PtCl₆ + 2NH₄Cl = ↓(NH₄)₂PtCl₆ + 2HCl                                 (8)

The precipitated platinum is separated from the solution through filtration and the precipitate goes for further processing (the platinum complex is calcined, treated with a nitric acid solution, washed and we get the purest platinum powder, see Table 2.) The solution containing palladium goes to neutralize and precipitate the solution from impurities [10].

Table 1.

Results of the chemical analysis of the aqua leaching of the concentrate

№ Samples

aqua regia solution

According to the results which were obtained experimentally, it can be seen that insoluble chlorpalladosamine is precipitated from a solution with hydrochloric acid: HCl consumption is 1 liter per 100 g of palladium powder.

Pd(NH₃)₄Cl₂ + 2HCl = Pd(NH₃)₂Cl₂ + 2NH₄Cl                        (9)

After filtration and washing, chloropalladosamine is calcined at elevated temperatures and decomposed to produce palladium metal. After calcination, the palladium powder is subjected to manual abrasion [11].

Recovery with formic and citric acids, washing and drying: The resulting composition of the powder contains Pb, Sn and other metal impurities in a very small amount. To remove impurities, we treat with citric acid and, after removing impurities, wash the powder with distilled water and dry the product, and a pure Pd powder is formed [12].

Pd(NH₃)₂Cl₂  → Pd + 2HCl↑ + N₂↑ +  2H₂↑                                 (10)

As a result of extensive research work, including a number of experiments, a new technological scheme was developed. The advantages of the recommended technology are: high purity of the derivable palladium and platinum powder with lower energy costs, high productivity, savings in reagents, and a high degree of extraction of precious metals. The method is also applicable in an ecological point of view, since the resulting acidic filtrates are neutralized with an alkali solution or alkaline filtrates obtained by reducing palladium to metal with formic acid or hydrochloric hydrazine [13].

Table 2.

 Results of chemical analysis of the resulting platinum and platinum powder

Pt powder

Under laboratory conditions, several experiments were carried out on the extraction of palladium and platinum powder from ChMA concentrates in the refinery of JSC AGMK. The experiments were carried out in different concentrations of the solvent to determine the optimal mode of the technological cycle [14].

The results of the experiments are presented in Table 1 and the results of the obtained pure metals are shown in Table 2. The introduction of this technology will give an undoubted economic effect due to the additional extraction of valuable components and improve the environmental situation in places where man-made waste accumulates [15].

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