Polar Division of “Norilsk Nickel” MMC, Norilsk, Russia

A. L. Kozhanov, Chief Engineer of Metallurgy Shop

M. A. Litvyak, Deputy Head of Metallurgy Shop, e-mail: litvyak@mz.nk.nornik.ru
S. N. Moiseev, Senior Master of Metallurgy Shop

Cakes of gas cleaning originate from Cu- and Ni-slimes processing circuit in the course of secondary anodes smelting at Polar Division of MMC “Norilsk nickel”, and contains 25% of silver. Under the technology employed the cakes are recycled back to electric smelting. The main form of silver in the cakes is represented by chloride being subject to re-sublimation during anode smelting. The undertaken studies involved development and commercial testing of a process flowsheet comprised of cakes treatment with sodium sulfide solution and subsequent roasting with copper slime. The flowsheet provides recovery of silver as a semiproduct with composition close to a marketable product — crude silver of SChP (СПЧ) grade. The cakes underwent sulfiding under conditions found to be optimal in the laboratory tests. Silver chloride in cakes decreased from 18–20 to 0.3–0.5% corresponding sulfiding level of 97–98%. The given operation made the solution free of sodium sulfide and it was further disposed together with streams from pure selenium production. Sulfided cakes were reported to roasting together with copper slime. This feed mode was determined by the following process reasons: roasting of pure sulfided cake results in undesirable sharp silver increase in leach liquors which induces the need for alteration of downstream process variables. Silver recovery efficiency was evaluated using laboratory tests for leaching calcine, sampled at the outlet of the roasting furnace. The data acquired were compared with results for leaching of pure copper slime calcine of the same batch mixed with cake from gas cleaning. Therefore the implementation of the flowsheet developed for processing of silver-containing cakes from furnace gas-cleaning firstly enables reduction of silver loss by means of elimination of its recycling and secondly increases yield of granulated silver.

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