SB-PB-AG ALLOY PROCESSING BY VACUUM DISTILLATION

Abstract

The paper relevance is determined by the need to create an environmentally safe, high-performance and cost-efficient integrated vacuum distillation technology for the processing of lead-containing middling products and wastes, in particular, a Sb-Pb-Ag (SPA) alloy resulting from the recovery of silicate slag from copper anode slime melting to obtain sellable mono-element concentrates of an­timony, lead and silver. Laboratory studies were carried out on SPA alloy processing with the calculations of «T—x» temperature-com­position VLE (vapor liquid equilibrium) diagrams to analyze the behavior of Sb-Pb and Pb-Ag binary alloys during processing, select preliminary system temperature and pressure, and assess component separation efficiency in the following conditions: T = = 900+2100 K, P = 1+133 Pa, т = 8+16 hours. The aim of the study was to investigate the effect of temperature and pressure in the system, the duration of sublimation on the completeness of extraction and the degree of antimony, lead and silver separation from the SPA composition. Activity coefficients of binary alloy components when constructing VLE diagrams were calculated using the MI- VM (molecular interaction volume model). The information is obtained regarding the effect of temperature and vacuum level on the degree of sublimation and separation of metals from Sb—Pb and Pb—Ag compositions of different contents. Saturated vapor pressures were calculated for Sb (p* = 273.664+ 67436.9 Pa), Pb (0.149+485.9), Ag (5.05440 -5 -6.558) at T = 1073+1773 K. It was demonstrat­ed that the high values of the pSb /PPb = 1832.98+138.79, рр ь /pA g = 2948.16+74.09 ratio and lgPsb = 2.099+3.33 and lgPp b = 1.813+ +3.944 separation factor create theoretical prerequisites for a selective isolation of these metals by vacuum distillation, when anti­mony and lead are successively enriched in the gas phase (Ps^ > 1, Pp b > 1), and silver — in the liquid phase. The molar fraction of hard-to-sublimate lead/silver in the gaseous phase ур Ь /уA g = (1.55+982)T0 -3 /(36+772)T0 -3 is increased with rising temperature 894+1601/1399+2099 K, pressure 1.33+133 Pa and metal content in the alloy x Pb /x Ag = 0.9+0.9999/0.9+0.99. The MIVM model was used to calculate the activity factors of antimony Ysb = 0.832+0.999, lead yp b = 0.474+1.0, YA g = 0.331+0.999 for Sb/Pb and Pb/Ag al­loys with the following composition 0.1+0.9/0.9+0.1 in the investigated temperature range. The found dependences of the amount and composition of polymetallic alloy sublimation products on the process parameters are important for practical application due to the development of a principal technology for SPA processing by vacuum distillation.