Institute of Chemistry and Technology of Rare Elements and Mineral Raw materials of KSC RAS, Apatity, Russia:

A. G. Kasikov, Head of Hydrometallurgy sector, e-mail: kasikov@chemy.kolasc.net.ru
A. M. Dvornikova, Senior Researcher
E. S. Kshumaneva, Senior Researcher

JSC “Kola MMC”, Monchegorsk, Russia:
A. P. Tyukin, Head of the Department for Scientific and Technical Development and Environmental Safety

The possibilities of selective palladium recovery by solvent extraction from solutions of hydrochloride leaching of the Kola MMC semiproduct (PGM concentrate, the sediment after filtration of cobalt cake leaching solution) were studied. A brief overview of SX reagents proposed for palladium extraction from different industrial solutions was given. The β-hydroxy oxime type reagent Mextral 84H (LIX 84I analog) was chosen for laboratory scale tests of palladium SX from PGM concentrate leaching solution, which was used as 15–30% solution in hydrogenated kerosene RJ-3. It has been found that the addition of a small additive (1% vol.) of the tertiary amine Alamine 336 to extractant improved the kinetics of palladium extraction, reducing the time to about 60 minutes to reach equilibrium. Nevertheless, an increase of amine concentration in the mixture led to deterioration of extraction properties and an increase in the co-extraction of impurities; hence, it was expedient to use the extractant with minimum content of the amine as kinetic accelerator. From the concomitant impurities, when β-hydroxy oxime mixtures were used, only copper was co-extracted in appreciable degree, which could be effectively removed from the extract by washing with 2 mol/l H₂SO₄. It was also observed that the introduction of the amine into the extraction mixture improves palladium stripping with acid — 6 mol/l HCl, which eliminated the need of complexing agents (thiourea, ammonium thiocyanate etc.) using for this purpose, facilitating further processing of strip solutions. As a result of laboratory tests, the selective recovery of 99.5% palladium was demonstrated while using 30% vol. Mextral 84H with the addition of 1% vol. Alamine 336 from the solution of PGM concentrate hydrochloride leaching, containing 6.5 g/l Pd, having pH = 0.6, at phase ratio O:A = 1 during 60 minutes at 1 step. Stripping with 6 mol/l HCl at the phase ratio O:A = 1:5 during 10 minutes at 3 steps provided by the back-extraction of 87.3% palladium in hydrochloric strip solution.

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