The presented work shows the results of vacuum melting of industrial Zn-Ag-Pb alloy arising from the processing of silver-bearing foam. The tests were carried out in an induction vacuum aggregate in the temperature range 773 - 873 K and pressure 10 - 1 000 Pa. Based on the results obtained, the values of the density of the evaporating stream of zinc and lead were estimated, which were at the level from 3,95×10-4 to 9,53×10-4 gZncm-2 s-1 and from 5,39×10-5 to 30,9×10-5 gPbcm-2 s-1 . In addition, silver losses were estimated in the analysed process. The maximum degree of dezincification of the alloy achieved for the assumed temperature and pressure was 99 %

J. Łabaj

L. Blacha

English

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361METALURGIJA 59 (2020) 3, 361-363J. ŁABAJ, L. BLACHALEAD AND ZINC REMOVAL FROM ALLOY Zn-Ag-Pb UNDER REDUCED PRESSUREReceived – Primljeno: 2019-12-04Accepted – Prihvaćeno: 2020-03-12Preliminary Note – Prethodno priopćenjeJ. Łabaj: jerzy.labaj@polsl.pl, L. Blacha - Silesian University of Tech-nology, Faculty of Materials Science, Katowice, PolandThe presented work shows the results of vacuum melting of industrial Zn-Ag-Pb alloy arising from the processing of silver-bearing foam. The tests were carried out in an induction vacuum aggregate in the temperature range 773 - 873 K and pressure 10 - 1 000 Pa. Based on the results obtained, the values of the density of the evaporating stream of zinc and lead were estimated, which were at the level from 3,9510-4 to 9,5310-4 gZncm-2s-1 and from 5,3910-5 to 30,910-5 gPbcm-2s-1. In addition, silver losses were estimated in the analysed process. The maximum degree of dezin-cification of the alloy achieved for the assumed temperature and pressure was 99 %. Key words: Zn-Ag-Pb alloy, fire refining of lead, silver-bearing foam, vacuum refining, evaporation of metalsINTRODUCTIONSilver is one of the most valuable admixtures found in zinc-lead primary raw materials. During their pyro-metallurgical processing, this metal almost entirely goes to raw lead, from which it is separated in the pro-cess of fire refining. The silver removal technology is based on the formation of intermetallic compounds of the Ag-Zn system by adding zinc to liquid lead. These compounds, due to their low density, accumulate in the form of so-called silver-bearing foam on the surface of the bath, from where they are gradually removed. As a result of melting the foam, a Zn-Ag-Pb alloy is obtained that contains up to 30 % of silver mass and approx. 25 % of lead. This alloy is most often subjected to a smelt-ing process under reduced pressure in order to remove from it, by means of evaporation, both zinc and lead. The amount of metals repelled in this process depends on many factors. The most important of them are tem-perature, pressure [1-4], type of aggregate in which the process is carried out [5-9] and the composition of the alloys [10] and atmosphere in the furnace [11-14]. The presented work shows the results of research on indus-trial melting of a Zn-Ag-Pb alloy resulting from the pro-cessing of silver-bearing foam for the removal of both zinc and lead from it. The tests were carried out in an induction vacuum aggregate[15].RESEARCH METHODOLOGY The research was carried out on an industrial alloy of Zn-Ag-Pb containing 82,06 % mass of Zn; 7,23 %mass of Ag and 5,49 % mass of Pb. All experiments were carried out in an induction vacuum aggregate ISSN 0543-5846METABK 59(3) 361-363 (2020)UDC – UDK 546.47.57.815:66.067-546.815:546.47-661.185:533.5/66.067=111equipped with a rotary pump - diffusion pump system. At the beginning of each experiment, the alloy sample was placed in a graphite crucible with an internal diam-eter of 20 mm, which was introduced into the head with an induction coil. After its closure, the sample was heat-ed to the assumed temperature (this process was carried out in helium atmosphere) and then the pressure in the system was lowered. The tests were carried out in graphite crucibles in the temperature range of 723 - 873 K and at working pressure from 10 to 1 000 Pa. RESEARCH RESULTS AND THEIR ANALYSIS Figure 1 and 2 show as an example changes in the content of zinc, lead and silver in the Zn-Ag-Pb alloy obtained for remelts carried out at a temperature of 873 K and a pressure of 10 Pa and 1 000 Pa. Based on these changes, the average values of zinc and lead flux den-sity were estimated, which are collected in Table 1 there are presented gained for all experiments estimated mass losses of both lead and zinc from the analyzed alloy. Table 1 Zinc and lead weight loss UPb / %T/Kp/Pa723 773 823 8731 000 8,55 8,85 14,31 17,03100 10,27 14,04 18,01 29,8550 12,62 18,72 20,02 33,8020 14,34 20,03 29,29 38,6010 15,38 22,72 41,41 48,82UZn / %1 000 41,30 55,79 65,43 76,26100 48,34 65,85 75,16 80,9450 52,35 72,43 76,95 81,5420 62,61 80,12 82,93 86,4610 85,80 96,34 98,64 99,53362J. ŁABAJ et al.: LEAD AND ZINC REMOVAL FROM ALLOY Zn-Ag-Pb UNDER REDUCED PRESSURE METALURGIJA 59 (2020) 3, 361-363spectively from 3,9510-4 to 9,5310-4 gcm-2s-1 for zinc and from 5,3910-5 to 30,910-5 gcm-2s-1 for lead.  With the increase in temperature and pressure in the melting aggregate, there was also a decrease in the NZn/NPb ratio, which is illustrated, as an example in the Figure 5. CONCLUSIONSBased on the results of the conducted tests of vacuum melting of the Zn-Ag-Pb alloy it was stated that:• It is possible to remove zinc from the analysed alloy up to 98 and lead up to 49 %• As the temperature increases as well as the working pressure decreases in the measuring system, the silver loss in the alloy increases to 18 %. This phenomenon is unfavourable from the point of view of the idea of the technological process itself. • The obtained values of evaporating zinc and lead streams for the adopted process parameters were within the range from 3,9510-4 to 9,5310-4 gcm-2s-1 for zinc and from 5,3910-5 to 30,910-5 gcm-2s-1 for lead. In Table 2, the average density values of the zinc and lead evaporating from the liquid alloy are collected. Graphic interpretations of the changes in value of these fluxes in the temperature range of 723 – 873 K are pre-sented in Figures 3 and 4.The data presented above shows that the increase in temperature from 723 K to 873 K with a simultaneous decrease in working pressure in the melting system is ac-companied by an increase in the degree of zinc removal from the alloy from 41 to 99 % and lead from 8,5 to 49 %. At the same time, for the same range of basic process parameters (p, T), an increase in the average value of the flux density of the evaporating metals was observed re-Figure 1  Change of lead content in Zn-Ag-Pb alloy during remelting carried out at the temperature of 873 K Figure 2  Change of zinc content in the Zn-Ag-Pb alloy during remelting carried out in the temperature of 873 K Table 2 Zinc and lead flux densitiesNZn×104 /g cm-2s-1T/Kp/Pa 723 773 823 8731 000 3,95 5,34 6,26 7,31100 4,63 6,30 7,20 7,7550 5,01 6,94 7,37 7,8120 6,00 7,68 7,94 8,2810 8,22 9,23 9,45 9,53NPb×105 / g cm-2s-1T/Kp/Pa 723 773 823 8731 000 5,39 5,58 9,02 10,70100 6,49 8,85 11,40 18,4050 7,96 11,80 12,60 21,0020 9,04 12,60 18,50 24,3010 9,70 14,30 26,20 30,90Figure 3 Zinc evaporation flux densityFigure 4 Lead evaporation flux density Figure 5  Change in the NZn/NPb ratio for tests carried out at a pressure of 10 Pa 363J. ŁABAJ et al.: LEAD AND ZINC REMOVAL FROM ALLOY Zn-Ag-Pb UNDER REDUCED PRESSUREMETALURGIJA 59 (2020) 3, 361-363REFERENCES[1] L. Blacha, J. Łabaj. Factors determining the rate of the pro-cess of metal bath components. Metalurgija 51 (2012) 4, 529-533.[2] R.G. Ward. Evaporative losses during vacuum induction melting of steel. Journal of the Iron and Steel Institute (1963) 1, 11-15.[3] R. Kammel, B. Kociok. Vacuum refining of silver skims in an induction furnace. Transactions of the Institutions of Mining and Metallurgy C. 87 (1978), 88-93.[4] J. Piątkowski, B. Gajdzik, T. Matuła. Crystallization and structure of cast A390.0 alloy with melt overheating tem-perature. Metalurgija 51 (2012), 321-324.[5] R. Schwarze, L. Savov, F. Obermeier, D. Janke. A numeri-cal model flow the evaporation process of an electromag-netic stirred iron melt. European Congress on Computa-tional Methods in Applied Sciences and Engineering EC-COMAS, Swansea, 2001, UK, 4-7.[6] S. Golak, R. Przyłucki. 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Lead and zinc removal from alloy Zn-Ag-Pb under reduced pressure

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