RU2370555C1 - Method of processing concentrate of refineries dust - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: method consists in leaching of source product in solution of caustic soda, in separation of non soluble residue from alkali solution, and in melting of non soluble residue with additives. After melting melt is settled and cooled to solidification, then hardened metal is divided along borders of phase division to slag and bottom heavy melt. Further, bottom heavy melt is crumbled into powder and processed as concentrate of refinery production, then leached in solution of hydrochloric acid wherein gaseous chlorine is supplied. Additives not containing selenium, tellurium or their compounds are used at melting of non soluble residue. Upon crumbling bottom heavy melt produced at melting is treated with solution of nitric acid; nitric acid solution containing lead and silver is separated from non soluble residue processed as concentrate of refineries. ^ EFFECT: additional extraction of lead from source product. ^ 1 tbl, 1 ex

Description

The invention relates to the metallurgy of noble metals (BM) and can be used in the technology of refining metals of the platinum group (PGM).

Various inappropriate products and wastes inevitably arise at refineries, containing PGM, silver, gold, in particular, such as dust collectors and water-insoluble residues of dust extracts, obtained by cleaning the dust and gas tunnel and electrostatic precipitators (the so-called dust concentrate of refining production).

A characteristic feature of both dust flares and refining dust concentrate (CAP) is that their base is represented by a large number of different chemical elements and their compounds, mainly volatile non-precious metal chalcogenides, lead, ammonium and silver chlorides, and carbon black. This intermediate product contains (0.5-3)% PGM (in total), (0.00-0.3)% gold, (3-15)% silver, (10-25)% lead, (4-8) % selenium, (4-10)% tellurium, (2-4)% arsenic. The processing of dust shelters or KAPA presents significant difficulties and is associated with large material and labor costs.

From generally available literature it is known that the processing of dust can be carried out by the pyrometallurgical method - by melting a mixture containing soda, borax, glass and, in some cases, coal as fluxes, and copper is used as a collector of precious metals [Fundamentals of Metallurgy. T.5, M., Metallurgy, 1968, p. 316].

The disadvantages of this analogue method when it is used for processing dust concentrate of refining production (CAPP), which contains, along with BM, significant amounts of base metal chalcogenides, include the formation of large quantities of secondary dust pulverizers enriched in volatile chalcogenides, lead and arsenic containing BM and in need of processing.

A known method of processing refining products containing chalcogenides, lead, platinum group metals, gold and silver, including dust concentrate of refining production (CAPA), including leaching the initial product in a solution of caustic soda, separating the insoluble residue from the alkaline solution, melting insoluble residue with additives, sedimentation and cooling of the melt until solidification, separation of the hardened product at the phase boundaries into slag and bottom heavy alloy, grinding heavy alloy bottom into powder and its processing as a concentrate of refining production using leaching in a solution of hydrochloric acid with the supply of chlorine gas [RF Patent No. 2291212, Efimov VN, Temerov SA, Moskalev AV, Churkin V .A., Gubin M.V. - BI No. 1, 2007]. This method is the closest in technical essence to the claimed method and adopted as a prototype.

The use of the prototype method for processing dust concentrate of refining production (KAPA) along with a number of positive features is associated with the following negative consequences.

When KAPA is leached in a solution of caustic soda, it is possible to extract most of the chalcogenes (Te, Se) and arsenic from the initial product in an alkaline solution. However, another harmful impurity - lead from KPAP in an alkaline solution is practically not removed and is concentrated in the insoluble residue. In the subsequent smelting of this material with additives, which (in accordance with the prototype) use intermediate products obtained during cementation or hydrolytic processing of refining solutions and containing, in addition to copper and iron, tellurium and selenium in appreciable quantities, lead goes mainly into heavy BM heavy alloy in the form of chemically stable chalcogenides, which seriously complicates subsequent refining. In addition, lead partially passes during smelting into dust sublimates, where it gradually accumulates.

Thus, the prolonged use of the prototype method for processing dust concentrate from refining production leads to lead cycling in refining intermediate products, to a gradual increase in its content both in the CAPP and in bottom heavy alloys sent for refining obtained by melting insoluble residues.

The increasing presence of lead in CAP and in bottom heavy alloys obtained by melting significantly complicates and increases the cost of subsequent refining of platinum group metals, gold and silver, and leads to an increase in labor costs and reagent consumption. Attempts at hydrometallurgical leaching of lead from heavy bottom alloys (before launching the latter for chlorination) proved to be ineffective due to the high chemical stability of lead compounds with chalcogenes. So, when nitric acid is used to process ground heavy alloys obtained by the prototype method, it is possible to extract no more than (45-50)% lead in the solution. The rest of the lead is in a chemically resistant form; it is not removed from the alloys into the nitric acid solution and gets into refining, increasing the consumption of reagents and labor costs.

The technical result of the invention is aimed at creating an additional channel for the withdrawal of lead from the technological cycle during the processing of CAPA.

The achievement of the technical result is ensured by the fact that when melting the insoluble residue obtained by leaching the CAPA in a solution of caustic soda, additives are used that do not contain selenium, tellurium or their compounds, and the bottom heavy alloy obtained by melting is treated with a solution of nitric acid and then separated nitric acid solution containing lead and silver from the insoluble residue, the latter is processed as a concentrate of refining production.

The essence of the method lies in the fact that when melting N.O. get a heavy BM alloy containing lead and silver in forms soluble in nitric acid and having brittleness sufficient for grinding. From such an alloy, after grinding and treatment with nitric acid, lead and silver are sufficiently completely extracted into the nitric acid solution without affecting the PGM, which are concentrated in the insoluble residue. After separation of the nitric acid solution from the insoluble residue, the latter practically does not contain lead and is processed as a concentrate of refining production.

The resulting nitric acid solution does not contain PGM and gold, and after precipitation and separation of first silver chloride and then lead sulfate, it can be disposed of.

Thus, in addition to the withdrawal of chalcogenes and arsenic from CAPA to a solution of caustic soda, which provides a prototype method, the proposed method makes it possible to completely extract lead and silver into the nitric acid solution, preventing them from entering the insoluble residue, which is then processed into as a concentrate of refining production.

Using the proposed method can significantly reduce labor costs, reagent consumption and the duration of operations during the processing of KAPA, to ensure the irrevocable withdrawal of lead from the refining cycle.

An example of using the method.

We took 300 g of wet (W = 38.0%) dust concentrate from refining production (CAPA). According to the analysis, the initial product (by dry weight) contained,%: Pt - 0.286; Pd 0.354; Rh 0.06; Ir 0.006; Ru - 0.233; PGM (in total) - 0.939%; Au - no; Ag -13.95; Te - 4.46; Se - 4.52; Sn 7.46; As 2.14; Pb - 20.98; Fe - 4.31.

The initial product was pulverized in water, 175 ml of caustic soda (d = 1.457 g / cm ³ ) was added to the obtained pulp and leached in an alkaline solution with stirring at a temperature of (80-90) ° С for 1 h, after which it was separated by alkaline filtration solution from insoluble residue. In this case, two products were obtained — an alkaline solution in an amount of 760 ml and an insoluble residue. The yield of the latter amounted to 202.5 g (W = 46.0%) or 59% of the starting product launched for leaching (by dry weight). According to the analysis, the content of BM in n.o. amounted to,%: Pt-0.48; Pd - 0.601; Rh is 0.1; Ir - 0.01; Ru - 0.395; Au - no; Ag is 23.7. Thus, the content of PGM and silver (in total) increased and amounted to 25.286%, which is 1.7 times more than in the starting material before leaching.

Base elements passed into the caustic soda solution from the initial product. According to the results of the analysis, their concentration in solution was, g / l: Te - 5.33; Se - 7.65; Sn - 3.77; As - 4.54; Pb - 15.30. Thus, 49% of tellurium, 69% of selenium, 21% of tin, 87% of arsenic, and 29% of lead passed into the solution from the initial product. More than 99.9% of PGM and silver remained in the insoluble residue. In an alkaline solution, 24.0 mg / L of PGM (in total) and 20.0 mg / L of silver were detected.

The second product obtained by filtration of the pulp — the insoluble residue — was dried and further processed by the smelting method with the addition of only fluxes containing no selenium, tellurium, or their compounds.

For this, 100.0 g of dry insoluble matter was taken (from the obtained 109.35 g by dry weight, 100.0 g of product was taken for melting, the rest was used for analysis) and mixed with flux additives, which were used as 25.0 g of crushed silicate-sodium glass and 15.0 g of calcium oxide. The total mass of the charge was 140.0 g.

All components of the mixture were mixed and loaded into a chamotte melting crucible. The crucible was placed in a shaft laboratory electric furnace and subjected to isothermal exposure (melting) for 45 minutes at a temperature of 1250 ° C. At the end of the melting, the crucible was unloaded from the furnace.

After cooling the melt, a hardened product was removed from the crucible, which was divided along the formed phase boundary into slag and heavy bottom alloy. Received:

- 58.2 g of a bottom heavy alloy of platinum metals and silver containing (according to the analysis) 42.55% PGM and silver (in total). In addition to BM, the obtained alloy contained,%: Te - 5.50; Se - 2.92; Sn - 14.60; As 0.34; Pb - 29.72; Fe - 2.58.

- 48.3 g of sodium silicate slag that does not contain (according to spectral analysis) platinum group metals.

Table 1. Content and distribution of elements by products in the processing of crushed heavy alloy Names. product m, (g) V, (ml) Content / Distribution (%, g / l) Pt Pd Rh Ir Ru Ag Source alloy 58.2 g

But. 23.5 g

Silver chloride 21.4 g

Lead sulphate 25.0 g

Stock solution 300 ml

Fe Pb Sn Se Te As Source alloy 58.2 g

BUT 23.5 g

Silver chloride 21.4 g

Lead sulphate 25.0 g

Stock solution 300 ml

The heavy BM heavy alloy had satisfactory brittleness, it was crushed into powder and treated with a solution of nitric acid to obtain an ORP = 850 mV (in comparison with a silver chloride electrode). Then, the insoluble residue was separated from the nitric acid solution. In this case, two products were obtained: 23.5 g of an insoluble residue (by dry weight), in which PGM was concentrated, and 300 ml of a nitric acid solution not containing PGM. During leaching, most of the lead and silver went into the nitric acid solution from the alloy.

The insoluble in nitric acid residue (n.o.) contained 6.68% PGM (in total), 30.9% silver. It was processed as a concentrate of refining production using leaching in a solution of hydrochloric acid, with the supply of gaseous chlorine.

From the nitric acid solution, silver was precipitated and separated, first, in the form of silver chloride, and then lead in the form of lead sulfate. Both of these products do not contain PGM and can be processed by existing methods, or shipped to related enterprises.

Table 1 shows the content of the analyzed elements in the crushed heavy alloy, which was aimed at treatment with nitric acid, as well as the mass and composition of the products of its processing with the distribution of BM and base elements over them.

Claims (1)

A method of processing a dust concentrate of refining production containing chalcogenides, lead, platinum group metals, gold and silver, including leaching the initial product in a solution of caustic soda, separating the insoluble residue from the alkaline solution, melting the insoluble residue with additives, settling and cooling the melt to solidify, separation hardened product at the phase boundary into slag and bottom heavy alloy, grinding the bottom heavy alloy into powder and its processing as refining concentrate using leaching in a solution of hydrochloric acid with the supply of chlorine gas, characterized in that when melting the insoluble residue using additives that do not contain selenium, tellurium or their compounds, the melted bottom alloy after grinding is treated with a solution of nitric acid and nitric acid is separated off a solution containing lead and silver from the insoluble residue, which is processed as a concentrate of refining production.