RU2116365C1 - Charge for producing platinum group metals - Google Patents

Abstract

FIELD: precious metal technology. SUBSTANCE: charge is intended for pyrometallurgical processing of concentrates and middlings from platinum metal finishing. Charge contains silicate glass, carbon-containing reducing agent, original concentrate or finishing middlings, and, additionally, sodium sulfate and calcium fluoride. EFFECT: increased recovery of platinum group metals into desired product, reduced loss of metals with slag, and reduced expenses on subsequent processing of platinum metals in finishing cycle. 3 tbl

Description

 The invention relates to the field of metallurgy of precious metals, in particular to the pyrometallurgical processing of concentrates and intermediate products of the refining of platinum metals.

 In the raw materials balance of production of platinum group metals (PGMs), a significant share is made up of concentrates of secondary raw materials and intermediate products of their primary processing. This group of materials includes, in particular, coal-based ash of palladium catalysts and concentrates for the reduction treatment of chloride solutions from the dissolution of scrap metal containing precious metals. These concentrates are characterized by a high, up to 80%, content of slag-forming components - oxides of silicon, iron, aluminum, sodium and others, and a relatively low content of PGM, in the amount from 5 to 30%. A feature of these materials is the almost complete absence of an internal collector in them - base elements that form compounds with low melting points with PGM.

 The simplest method for processing such concentrates is enrichment smelting to produce the target alloy of PGM and slag. In this case, the initial concentrate mixed with various fluxes is used as a charge.

Known mixture for melting concentrates of precious metals, including soda, borax, quartz sand and fluorspar [1]. The disadvantage of the analogue is the low extraction of platinum metals in the target alloy at a melting temperature of ≈ 1300 - 1350 ^o C due to the low content or absence in the charge of the collector of platinum metals.

 Known mixture for melting concentrates containing platinum metals, which is taken as a prototype, as the closest to the proposed technical solution [2]. Known charge includes copper oxide, soda, borax, silicate glass, starch and PGM refining concentrate.

The disadvantages of the charge of the prototype are the low content of PGM in the resulting target alloy on a copper collector and, accordingly, the increased cost of processing alloys in the refining cycle. These disadvantages are due to the fact that copper with platinum metals forms a predominantly continuous series of solid solutions with a smooth decrease in the melting temperature. Therefore, for the complete collection of PGMs at a temperature of 1300-1350 ^o C, copper is required by mass 1.5-2.0 times more than that contained in the charge of platinum metals.

 The problem to which the invention is directed, is to increase the efficiency of processing concentrates of refining platinum metals.

 The problem is solved by achieving a technical result, which consists in increasing the content of platinum metals in the target alloy due to the formation, in the process of melting of the charge, MPN sulfides with a high content of platinum metals and a relatively low melting point.

The specified technical result is achieved by the fact that sodium sulfate (Na ₂ SO ₄ ) and calcium fluoride (CaF ₂ ) in the following ratio of components, wt.%:
Silicate glass - 25 - 45
Calcium Fluoride - 3 - 6
Sodium Sulfate - 5 - 15
Carbon-containing reducing agent - 2 - 5
Refining concentrate or intermediate product containing platinum metals and base elements - Else
The purpose of fluxes and additives in the proposed mixture is as follows.

 Silicate glass is introduced to slag the slag-forming components of PGM concentrates and as a source of silica for platinum sulphidation reactions if silicon oxide is absent in the concentrates. Calcium fluoride (fluorite or fluorspar) is used as a flux, which reduces the viscosity of the slag and increases the interfacial tension at the slag-metal interface, which contributes to the coalescence of drops of the PGM alloy and their separation from the slag phase. It was found that the necessary and sufficient ratio in the charge between ordinary silicate glass - bottle, window, and the addition of calcium fluoride should be about 8. Sodium sulfate is used as a platinum metal sulfidizer. Carbon is a reducing agent in the sulfidation reactions of platinum metals. It was determined that for the completeness of the sulfidation reaction, the necessary and sufficient ratio in the charge between sodium sulfate and a carbon-containing reducing agent should be 2.5-3.0.

The physicochemical nature of the process realized during heating and smelting of the proposed mixture consists in reactions with the release of elemental sulfur as an intermediate product, according to reactions 1-3:
Na ₂ SO ₄ + 2C ⇄ Na ₂ S + 2CO ₂ ≈ 620 ^o C (1)
Na ₂ SO ₄ + Na ₂ S + ₂ SiO ₂ ⇄ ₂ Na ₂ SiO ₃ + SO ₂ + S ≈ 865 ^o C (2)
SO ₂ + C ⇄ S + CO ₂ ≈ 865 ^o C (3)
Sulfur released in the entire volume of the semi-molten charge interacts vigorously with dispersed particles of platinum metals, forming stable PGM sulfides by type 4 reactions:
Pt + S ⇄ PtS ≈ 900 ^o C (4)
PGM sulfides having a melting point of 800-1000 ^o C, in the form of liquid droplets fall into the lower part of the melt, forming the phase of the target alloy of platinum metals.

The mass fraction of sulfur in PGM sulfides usually does not exceed 16-18%, the rest is platinum metals. This is due to the fact that the amount of sulfur in PGM sulfides averages from 20 at.% (Pd ₄ S) to 50 at.% (PtS) and that the atomic weight of sulfur is almost 3-6 times less than that of platinum metals. As a result, the target alloys obtained by smelting PGM concentrates according to the proposed charge are characterized by a high content of platinum metals.

 The upper and lower limits of the content of silicate glass in the charge during the smelting of concentrates, respectively, with a high and low content of slag-forming components, the formation of stable neutral slag with a relatively low melting point. Going beyond the limit of silicate glass in the charge leads to an increase in the residual content of PGM in the slag at a flow rate below the proposed limit due to its refractoriness. An increase in the glass content in the charge of more than 45% is impractical, since it does not improve the melting indices.

 The upper and lower limit of the content of calcium fluoride in the charge ensures optimum viscosity and surface properties of the slag melt during melting and a relatively low residual content of noble metals in the slag.

 A decrease in the content of calcium fluoride in the charge of less than 3% increases the viscosity of the resulting slag and reduces its surface tension, which leads to an increase in the residual content of PGM in the slag. An increase in the content of calcium fluoride in the charge of more than 6% is impractical, since it does not improve melting indices.

 The upper and lower limits of the content of sodium sulfate in the charge during smelting, respectively, rich and poor in PGM materials, the completeness of sulfidation of platinum metals with the formation of stable sulfides. Going beyond the limit of sodium sulfate in the mixture leads to a deterioration of the process. When the content is below 5%, the residual PGM content in the slag increases due to the incompleteness of sulfidation. Exceeding the content of sodium sulfate for 15% does not increase the extraction of PGMs in the target alloy and is an overrun of the reagent.

 The amount of carbon introduced into the charge of 2-5 wt.%, According to experimental data, ensures the completeness of the processes of sulphidation of PGMs, respectively, with a low and high limit of consumption of sodium sulfate.

 A comparative analysis of the proposed charge with the prototype shows that the proposed composition of the charge differs from the known introduction of components - sodium sulfate and calcium fluoride. Thus, the proposed technical solution meets the criterion of "novelty."

 To prove the compliance of the invention with the criterion of "inventive step", a comparison was made with other technical solutions known from sources included in the "prior art".

 The proposed mixture for producing an alloy of metals of the platinum group meets the requirement of "inventive step", as it provides a high content of PGM in the target alloy during concentrate smelting of concentrates and intermediate products of refining and reduces the cost of subsequent processing of alloys. As a result, the efficiency of processing concentrates and intermediate products of refining of PGMs increases, which does not follow explicitly from the prior art.

 Examples of the use of the proposed mixture.

 For experimental verification of the proposed mixture used crushed silicate window glass, calcium fluoride, sodium sulfate, charcoal and concentrates of platinum metals. Concentrate "A" is an intermediate product obtained during cementation-hydrolytic treatment of solutions with zinc and iron from the dissolution of scrap metal containing PGM. Concentrates "B" and "C" - ash from the burning of spent coal-based palladium catalysts used in the petrochemical industry. The compositions of these concentrates are given in table. one.

Eleven blends were prepared, each weighing 100.0 g, three of which corresponded to the proposed ones, and eight - to transcendental compositions. Each charge was loaded into a chamotte crucible, melted and kept at a temperature of 1350 ^o C for 60 min in a crucible furnace with silica heaters. After melting, the crucibles were removed from the furnace and cooled. The products were cooled - the slag and the PGM alloy were knocked out of the crucible, separated by the natural interface, weighed, ground into powder and analyzed for the content of elements by spectral and chemical analysis methods.

 Data on the composition of the mixture, the yield of smelting products, the content of platinum metals in them, are given in table. 2.

 The data obtained show that the proposed mixture allows to obtain high technological performance in the processing of concentrates smelting PGM. Due to the efficiency of the process of sulphidation of platinum metals and the optimal composition of the slag during melting, the formation of the target sulfide alloy of PGM with a high content of noble metals and high extraction of PGM in this alloy is achieved. As follows from the data of table 2, the proposed mixture provides the target alloys with a platinum content of 70.98-73.42 wt. % and slags according to the results of spectral analysis not containing PGM. The transition from the proposed (op. 1-3) to transcendental (op. 4-11) compositions of the blends leads to a deterioration in the smelting performance either due to irrational overspending of fluxes, or due to an increase in losses of PGM with slags.

 An example of the use of the charge of the prototype.

 To compare the indicators of the proposed charge and charge-prototype conducted the experience of concentrating smelting concentrate "B" on the composition of the prototype charge. The mixture contained 200.0 concentrate "B"; 12.0 copper oxides; 157.0 soda; 58.0 drills; 35.0 glasses; 20.0 starch. Melting, separation and analysis of the products was carried out according to the above method.

 As a result of smelting, 20.4 g of the PGM alloy and 334.5 g of slag were obtained. The target PGM alloy contained, wt.%: 50.49 palladium; 44.11 copper; 2.50 iron. The slag contained respectively, wt.%: 0.09 palladium; 0.18 copper; 9.73 iron.

 Comparison of the achieved indicators from the use of the declared (op. 3) and the known charge are presented in table. 3.

 The data table. 3 show that the use of the proposed charge allows for smelting to increase the extraction of PGM in the target alloy, to reduce the loss of platinum metals with slag. Due to the higher PGM content in alloys, the costs of the subsequent processing of PGM alloys in the refining cycle are significantly reduced.

 To prove the criterion of "industrial use", it should be indicated that the issue of using the proposed charge at the Schelkovo Secondary Precious Metals Plant in 1997 is being studied.

Claims (1)

A mixture for producing an alloy of metals of the platinum group, including silicate glass, a carbon-containing reducing agent, a concentrate or intermediate product of refining containing platinum metals and non-precious elements, characterized in that the mixture additionally contains sodium sulfate and calcium fluoride in the following ratio, wt.%:
Silicate glass - 25 - 45
Calcium Fluoride - 3 - 6
Sodium Sulfate - 5 - 15
Carbon-containing reducing agent - 2 - 5
Refining concentrate or intermediate product containing platinum metals and base elements - Else

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