RU2096507C1 - Method of processing chloride slag containing precious metals - Google Patents

Abstract

FIELD: precious metal recovery. SUBSTANCE: chloride slag is mixed with fluxes and melted followed by separation of silver-gold alloy from slag and processing it to isolate gold and silver. Prior to be melted, chloride slag is mixed with sodium hydroxide and sodium carbonate, fired, and resulting cake is leached in water. Non-dissolved residue is melted with fluxes to form silver-gold alloy. EFFECT: facilitated silver and gold recovery. 2 cl, 4 tbl

Description

 The invention relates to the field of metallurgy of precious metals, in particular to the refining of gold and silver.

In the process of refining gold-silver alloys by chlorination in a melt, chloride slag is formed. This intermediate product contains up to 5% gold, mainly in the form of small metal inclusions, 55-70% silver chloride, 5-30% base metal chlorides, mainly copper and iron, 10-20% silicon oxides, boron, sodium, since the chlorination process at a temperature of 1150 ^o C on the surface of the molten metal is loaded with drill and quartz sand. Chloride slag is processed to extract precious metals.

 A known method of processing chloride slag, which is taken as a prototype, as the closest to the claimed technical solution.

Полученный серебряно-золотой сплав направляют на хлорирование вместе с новой партией сырья. Обеззолоченный вторичный хлоридный шлак гранулируют выливанием в воду и обрабатывают подогретым солянокислым раствором в присутствии окислителя (NaClO₃). В результате обработки в раствор переходят медь, железо и другие цветные металлы. Осадок очищенного хлорида серебра восстанавливают металлическим цинком в пульпе. Цементное серебро отфильтровывают, плавят на аноды и направляют на электролитическое рафинирование.According to the known method, the primary chloride slag (PCS) is remelted with the addition of 4% sodium carbonate. In this case, about a fifth of silver is reduced by reaction (1) and, descending into the bottom of the melt, collects most of the gold in the chlorides

The resulting silver-gold alloy is sent for chlorination together with a new batch of raw materials. The de-malted secondary chloride slag is granulated by pouring into water and treated with a heated hydrochloric acid solution in the presence of an oxidizing agent (NaClO ₃ ). As a result of processing, copper, iron and other non-ferrous metals pass into the solution. The precipitate of purified silver chloride is reduced with metallic zinc in the pulp. Cement silver is filtered off, melted on anodes and sent to electrolytic refining.

 The disadvantages of this method of processing chloride slag are significant costs and not high enough recovery of precious metals in the target products. These shortcomings are due to the multioperational technology, a significant consumption of reagents, relatively high losses of precious metals with solutions and dust.

 The problem to which the invention is directed, is to increase the efficiency of processing primary chloride slag by reducing the loss of precious metals with industrial products and waste.

 The problem is solved by achieving a technical result, which consists in simplifying the technological scheme for the processing of chloride slag.

The specified technical result is achieved by the fact that in the known method of processing chloride slag containing precious metals, including melting chloride slag with the addition of sodium carbonate, separating the target silver-gold alloy from the slag, processing the silver-gold alloy to produce gold and silver, according to the invention before Sodium hydroxide is added to the mixture of chloride slag with sodium carbonate by melting, the mixture is calcined at a temperature of 500-600 ^o C, and the resulting cake is subjected to aqueous leaching. While sodium hydroxide, sodium carbonate and chloride slag are mixed in the following ratio of components, wt.

Sodium hydroxide 15-30
Sodium Carbonate 10-20
Chlorine Slag Else
Reduced firing of chloride slag makes it possible to convert silver from chloride to a metal form, and base metals copper, iron from chlorides to oxides. Water leaching separates the water-soluble components of the cake of sodium chloride and excessively introduced carbonate and sodium hydroxide from metallic silver. Concentration melting of insoluble cake of sinter provides obtaining silver-gold alloy and slag. In this case, almost all base elements present in the starting material are concentrated in the slag.

Специальными исследованиями установлено, что реакция (2) интенсивно протекает уже при температуре 320^oC, после расплавления щелочи. Полная металлизация серебра достигается при температуре 500-600^oC. Определено, что продуктом реакции 2 кроме частиц дисперсного металлического серебра является легкоплавкая смесь хлорида натрия и гидроксида натрия, так как для полной металлизации серебра гидроксид натрия вводится с избытком 15-20% от стехиометрии. При температуре 500^oC данная солевая фаза системы NaCl-NaOH находится частично в расплавленном состоянии, что вызывает оплавление спека, прилипание его к частям обжиговых устройств. В результате затрудняется процесс обработки спека, разрушаются детали обжиговых устройств.The physicochemical nature of the proposed method is based on the process of thermal reduction of silver chloride with a mixture of sodium hydroxide and sodium carbonate at temperatures no higher than 600 ^o C. The interaction of silver chloride with sodium hydroxide proceeds according to reaction 2:

Special studies have established that reaction (2) proceeds intensively even at a temperature of 320 ^o C, after melting of the alkali. Complete silver metallization is achieved at a temperature of 500-600 ^o C. It is determined that the reaction product 2, in addition to dispersed silver metal particles, is a low-melting mixture of sodium chloride and sodium hydroxide, since sodium hydroxide is introduced in excess of 15-20% of stoichiometry to completely silver metallize. At a temperature of 500 ^o C, this salt phase of the NaCl-NaOH system is partially in the molten state, which causes the fusion of the cake, its adhesion to parts of the firing devices. As a result, the process of processing the cake is complicated, the details of the calcining devices are destroyed.

To prevent intense melting of cake, sodium carbonate is introduced in addition to sodium hydroxide in the reaction mixture of reductive calcination of chloride slag. Under conditions of heat treatment of the mixture, sodium carbonate reduces part of silver chloride by reaction 1 and increases the melting point of the NaCl-NaOH-Na ₂ CO ₃ salt system, since the melting point of sodium carbonate is 852 ^o C. In this case, the effect of complete silver metallization is achieved and intensive reflow spec. It was found that the necessary and sufficient ratio between hydroxide and sodium carbonate in the mixture, in which there is no intense melting of cake, is 1.5-2.0.

Base metal chlorides present in chloride slag interact with sodium hydroxide during heat treatment of the mixture according to type 3 reactions:
2CuCl + 2NaOH ⇄ Cu ₂ O + 2NaCl + H ₂ O (3)
In the inventive method, it is allowed to use solid sodium hydroxide in the form of granules or an aqueous solution of sodium hydroxide with a standard concentration of 45% NaOH, which is produced by the industry, in the process of preparing the reaction mixture. To a certain extent, the use of sodium hydroxide in the form of an aqueous solution is preferable, since the dust emission during the preparation of the mixture decreases, and the contact of the reacting substances improves.

The temperature range for firing a mixture of chloride slag with hydroxide and sodium carbonate is selected from the conditions for the maximum degree of silver reduction, process efficiency, and performance of the sinter leaching operation. When the firing temperature is lower than 500 ^o C, the degree of silver metallization decreases and, accordingly, the silver content in the aqueous salt solution from the leaching of cake and in the slag during melting of the insoluble cake is increased. As a result, silver recovery in the target alloy is reduced. Raising the firing temperature above 600 ^o C no longer affects the degree of metallization of silver, but is accompanied by an excessive consumption of electricity, leads to fusion of cake, complicates the operation of firing equipment.

 The lower and upper limits of the content of sodium hydroxide and carbonate in the mixture provide, when firing chloride slag, respectively, with a low and high content of silver and base metals, the complete metallization of silver and the formation of oxides of copper, iron and other base metals. A decrease in the content in the mixture of sodium hydroxide less than 15% and sodium carbonate less than 10% leads to a decrease in silver recovery in the target alloy, due to its incomplete metallization. An increase in the content of sodium hydroxide in the mixture above 30% and sodium carbonate more than 20% is impractical, since it does not improve the performance of chloride slag, but leads to an excessive consumption of reagents, complicates the operation of the roasting equipment.

 An example of using the proposed method.

 For experimental verification of the proposed method used primary chloride slag (PCH) crushed to a particle size of less than 1.0 mm, the compositions of which are given in table. one.

 For the preparation of mixtures for the reheating of PCh, reagents of the grade “KH” were used sodium hydroxide in granules and anhydrous sodium carbonate. Nine mixtures were prepared, each weighing 100 g, seven of which corresponded to the claimed, and two exorbitant composition. Each mixture was loaded into a porcelain crucible. To qualitatively average and contact the reacting substances, 35 ml of water were poured into each crucible with the mixture and the mixture was stirred until pasty.

Each crucible with the mixture was kept in an electric furnace at a given temperature for 90 minutes. Then the crucible was unloaded, cooled and placed in a glass of water. After separating the cake from the crucible, the precipitate was leached in water with stirring, filtered and dried. Aqueous solutions from cake leaching were analyzed for the content of gold, silver and copper by atomic absorption method. The insoluble cake was weighed and mixed with fluxes for concentrating smelting. In experiments 1 to 9 the charge for melting contained, in wt. 52 insoluble cake, 30 borax, 14 quartz sand, 4 calcium oxide. The mixture was loaded into chamotte crucibles, melted and kept at a temperature of 1250 ^o C for 60 min in a crucible furnace with silica heaters. The cooled products slag and silver-gold alloy were knocked out of the crucible, separated and weighed. A sample from the alloys was taken with chips by drilling an ingot at three points, the slag was pulverized and analyzed for metal content by assay and atomic absorption methods of analysis.

 In the table. 2 presents the data on the processing of chloride slag of three types depending on the content of sodium hydroxide and carbonate in the mixture for reduction firing (op. 1 5). In the table. 3 shows the results of the processing of chloride slag "B" depending on the firing temperature (op. 6 - 9).

 The data table. 2 show that the burning of chloride slag with hydroxide and sodium carbonate within the claimed limits of the mixture composition and temperature allows, ceteris paribus, to obtain the target silver-gold alloys containing gold and silver, in total, 96.57 99.71% and waste with a minimum content of noble metals. So aqueous saline solutions contain gold 0.51 0.64 mg / l and silver 22.5 35.2 mg / l, and slags respectively contain 0.0019 0.0032% gold and 0.132 0.187% silver.

 Firing of chloride slag at a flow rate of sodium hydroxide and sodium carbonate below the declared limits (op. 4) leads to an increase in the content of gold and silver in the aqueous solution and slag and, accordingly, reduces the extraction of precious metals in the target alloy. An increase in the consumption of reagents for roasting chloride slag of the above-mentioned limits (op. 5) practically does not improve the performance of industrial product processing.

 The results of experiments 6–9 (Table 3) show that reductive firing of the mixture at the temperature of the lower limit (op. 8) leads to a deterioration in the processing of chloride slag, while firing at the temperature of the higher limit (op. 9) does not improve them.

 An example of using the prototype method.

 To compare the performance of the proposed method and the prototype method, an experiment was conducted processing chloride slag "B" in accordance with the operations and modes of the prototype method.

They took 62.0 g of chloride "B" slag with a grain size of less than 1 mm, mixed with 2.5 g of sodium carbonate powder, loaded the mixture into a chamotte crucible and melted in an electric furnace at 1150 ^o C. At the end of the melting, the crucible was unloaded and cooled. The smelting products of silver-gold alloy and desalted chloride slag were separated and weighed. Received 7.3 g of a silver-gold alloy and 57.8 anhydrous chloride slag. Secondary chloride slag was crushed to a particle size of less than 0.315 mm and leached in a solution containing 100 g / l HCl and 50 g / l NaClO ₃ , at T: W = 1: 5, temperature 65 ^o C for 6 h in a laboratory reactor with temperature control . At the end of leaching, the pulp was filtered off, the insoluble precipitate was dried. Thus received 49.3 g of insoluble precipitate and 300 ml of a copper solution.

The insoluble precipitate was pulped in 50 ml of a solution containing 40 g / L HCl and 15 g / L NaClO ₃ , heated to a temperature of 60 ^° C and treated with zinc powder in an amount of 7.8 g for 40 minutes with stirring. At the end of the recovery treatment, the precipitate was washed with a 4% hydrochloric acid solution and dried. Accordingly, 34.3 g of precipitate and 100 ml of zinc solution were obtained.

The precipitate, which is a mixture of dispersed powder of reduced silver and slag-forming components, was mixed with 6.0 g of sodium carbonate and 1.5 g of calcium oxide, the mixture was loaded into a chamotte crucible and melted at 1150 ^o C. After the melting, the crucible was cooled, the products were separated and weighed. Received 24.3 g of silver anode alloy and 14.6 g of slag.

 The alloys, solutions, and slag obtained in the experiment were analyzed for the content of gold, silver, and copper by assay and atomic absorption methods of analysis.

 Data on the composition of the products and the distribution of gold, silver and copper in them are given in table. 4, a comparison of the achieved indicators from the use of the claimed and known method is presented in table.5.

 Thus, the data table. 4, 5 show that the use of the proposed method for processing chloride slag can increase gold extraction by 1.127% in the target alloy, increase the efficiency of the removal of base metals, in particular copper, with conditionally dump slag, and reduce the total specific processing costs by about 1.5 times chloride slag due to a twofold reduction in the number of technological operations, reduction in labor costs, reduction in the amount of spent chemical reagents, electricity and auxiliary materials.

Claims (2)

1. A method of processing chloride slag containing noble metals, including melting, separating the target silver-gold alloy from slag, processing a silver-gold alloy to produce gold and silver, characterized in that before melting, the starting material is mixed with sodium carbonate and sodium hydroxide then the resulting mixture is fired at 500,600 ^{° C.} , the obtained cake is subjected to water leaching, and the insoluble residue from leaching is melted.  2. The method according to claim 1, characterized in that the sodium hydroxide, sodium carbonate and chloride slag are mixed in the following ratio of components, wt. Sodium hydroxide 15 30
Sodium carbonate 10 20
Chloride Slag Else

Images