Institute of Chemistry of the Far-Eastern Branch of Russian Academy of Sciences, Vladivostok, Russia:

M. A. Medkov, Head of Laboratory of Mineral Raw Materials Processing, e-mail: medkov@ich.dvo.ru
S. I. Ivannikov, Junior Researcher of Sorption Processes Laboratory, e-mail: fyajkfqn@mail.ru
A. A. Yudakov, Deputy Director on Scientific Work and Innovations, Engineering-Technological Center1, e-mail: etcih@mail.ru

Far Eastern Federal University, Vladivostok, Russia:

A. V. Taskin, Chief Specialist of Department of Industrial Cooperation Development and Technology Transfer, e-mail: taskin@yandex.ru

Our paper shows the results of investigations of technogenic wastes from gold placer Kedrovka (Krasnoarmeisky district in Primorsky region). Screen and mineral analyses show the prevalence of powder-like gold in the samples (~80%), ~ 3% of individual gold particles (0.2–0.3 mm size), ~5% of gold with the size 0.1–0.2 mm, and about 15% of nanogold bound with sulfide minerals. Gold particles in the investigated samples are lozenge-shaped with canted edges, and occur in the intergrowths with quartz. Lamellar, powderlike and “running” gold is also found. The possible causes for gold losses during the technogenic placers mining are shown. We show the scheme of dividing the initial technological samples into fractions, and the possibility of gold concentration in the heavy minerals' non-magnetic fraction concentrate which can be used as raw material for the subsequent hydrometallurgical extraction of gold. We investigated the possibilities of thin and ultra-thin gold extraction from technogenic deposit slimes and sludges using the environmentally safe methods of hydrometallurgy (in particular ammonium thiosulfate and thiourea leaching). The optimal conditions, allowing a high degree of efficiency to extract gold from technogenic objects, were established in laboratory conditions. The thiourea leaching solution (30 g/l of thiourea, 10 g/l of sulphuric acid, 2 g/l of ferric chloride or 20 g/l of ammonium peroxodisulfate), allows to extract up to 90% of gold into solution from the technogenic gold-bearing samples heavy fraction minerals concentrate. Ammonium thiosulfate leaching solution (37.5 g/l Na₂S₂O₃, 25.0 g/l NH₄, 3.8 g/l CuSO₄), allows to extract up to 95% of gold into solution from the technogenic gold-bearing samples heavy fraction minerals concentrate. The advantages and limitations of each method are shown together with the possibility of reducing the cost of ammonia-thiosulfate leaching due to the reuse of anion exchange resins. The possibility of effective gold deposition from solution leaching is also shown.
This work was carried out with the financial support of the Ministry of Education and Science of Russian Federation (agreement No. 14.578.21.0015 on 05.06.2014; unique ID: RFMEFI57814X0015).

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