Optimizing antimony-tin concentrate production modes

For selective extraction of antimony and tin from the sludge resulting from final filtration of the spent process solutions of the main production sites of JSC “Uralelektromed” a process flowsheet has been developed and implemented to obtain antimony-tin concentrate for further production of antimony-tin alloy for soldering. To improve the process of antimony-tin concentrate precipitation from alkaline-sulfide electrolyte the anodic polarization was investigated and lab experiments including identification of process and economic parameters were performed. The electrode processes were researched using polarization curves method. Regression analysis showed that alkali concentration affects the anode potential 4–5 times stronger than sodium sulfide at current density of 1000 A/dm2. It was concluded that electrolyte should contain at least 70 g/dm3 of sodium hydroxide and 40–80 g/dm3 of sodium sulfide. In this case, anode adverse reactions and increased voltage in the cell are excluded. The experimental results identified adverse influence of electrolyte intensive circulation on formation of cathode deposit and thus the main laboratory tests were performed with stationary electrolyte. Current density and cathode-anode gap were variable parameters. The electroextraction was carried out with depleted electrolyte, i.e. without its replenishing with fresh portion. The initial electrolyte composition g/dm3: antimony — 14.0 to 16.0; tin — 16.1 to 18.16; arsenic — 8.6 to 19.3; sodium hydroxide — 64 to 81; sodium sulfide — 47 to 66. The best process and economic parameters were obtained for one-stage process with residual concentration of antimony and tin of less than 2 g/dm3 and 12 g/dm3 respectively. The antimony-tin concentrate contained 62.0% of antimony and 36.6% of tin. The study shows that the reduction of anode current density increases the current yield while the decrease of inter-electrode space reduces the power consumption. It was concluded that it is unpractical to further extract tin from spent solutions after antimony-tin concentrate precipitation without additional treatment.