PJSC “MMC “Norilsk Nickel”, Polar Division, Norilsk, Russia:

I. S. Kuzmina, Chief Specialist, Сеnter for Engineering Support of Production, Copper Plant
M. A. Litvyak, Chief Engineer of the Metallurgical Workshop, Copper Plant, e-mail: litvyakma@nornik.ru
K. A. Batsunov, Chief Specialist of the Prospective Development Department, Scientific and Technical Department
A. I. Ryabushkin, Chief Specialist in Precious Metals, Scientific and Technical Department

Prior to 2007, iridium KP-3 grade concentrate of Copper Plant PGM Concentrator was obtained by processing the anodic dissolution liquor and iridium was precipitated in glass-enameled capacitive autoclaves manufactured by Shinko-Pfaudler (Japan). As a result of long service in aggressive conditions at high temperatures the autoclaves went out of order and were dismantled and KP-3 production was suspended. The process was resumed upon installation of a tubular autoclave — a continuous apparatus with unlimited solution throughput per cycle. Design, installation and commissioning were completed in 2011–2014. The full-scale tests provided the optimal iridium precipitation conditions: temperature conditions and sulfur-bearing reductant flowrate. The revealed structural shortcomings of the tubular autoclaves were remedied. The titanium was found to be a major iridium-co-precipitated impurity diluting the concentrates and preventing concentrate from meeting the KP-3 grade requirements. The impurity enters the cake when sulfate solutions autoclaving during its salts decomposition (hydrolysis). Two-stage precipitation in the tubular autoclave was proposed for titanium and iridium separation. The first stage includes precipitation of titanium hydroxide with no reagents added. Following filtration the solution enters the second stage where a sulfur-bearing reagent added causes iridium precipitation. Full-scale tests proved the proposed flowchart to be effective: up to 70–80% of titanium is removed from solution at the first stage, iridium loss in titanium hydroxide precipitate does not exceed 4%, highly selective concentrate contains more than 50% iridium.

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