Recovery of Noble Metals from Spent Catalysts: A Review
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UCTION
PLATINUM group metals incorporate six noble metals, namely platinum (Pt), palladium (Pd), iridium (Ir), osmium (Os), rhodium (Rh) and ruthenium (Ru). All the metals in this group have similar physical and chemical properties. PGMs are chemically inert, highly resistant against corrosion, electrically and thermally stable, and have high mechanical strength.[1–3] Their properties are highly desirable, and > 90 pct of overall PGMs are used by the electricity and catalyst industries. PGMs are limited natural resources with only 66,000 tons available worldwide. Only 2 to 10 g/ton of PGM content is present in natural ores. The recovery of PGM as a co-product or by-product depends on their percentage in the ore. Recent advances in the technologies for the extraction and recovery of PGMs have enhanced their
SAI KRISHNA PADAMATA, ANDREY S. YASINSKIY, PETER V. POLYAKOV, and DMITRIY YU. VARYUKHIN are with the School of nona˜ ferrous metals and materials science, Siberian federal university, Krasnoyarsk, Russia 660025. Contact e-mail: [email protected]. EVGENY A. PAVLOV is with the JSC a˜ Krastsvetmeta˜ , Krasnoyarsk, Russia 660027. Manuscript submitted September 12, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
application in the chemical industry, oil refining, medical practices, vehicle and equipment construction, jewelry making, etc.[4,5] Production of 73 pct of primary PGMs in the world is associated with the Bushveld Complex of South Africa, while the rest of the PGM reserves are mainly concentrated in Russia, Zimbabwe, the USA and Canada.[6] The PGM ores are mainly in the form of sulfide and arsenide materials such as PtAs2, Pt(AsS)2, PtS, (Pt, Pd)S, (Pt, Pd, Ni)S, Pd3Sb and RuS2 along with elemental ruthenium.[7] Fernandez [8] presented comprehensive data related to the amounts of PGMs in different forms. PGMs are recovered from highgrade concentration ores (200 to 2000 g/ton of PGM and 0.3 to 2.5 pct Cr2O3) by the matte-smelting-refining technique. Initially, the PGM ores are crushed and ball-milled into fine particles. This ore in the form of particles is treated in gravity separators and transferred to flotation cells to produce a sulfide-rich PGM concentrate, where reagents such as dithiophosphate and xanthate collectors are used for the flotation process at 7.5 to 9 pH.[9] Smelting is performed on the sulfide-rich PGM concentrates to remove feldspar, plagioclase, pyroxene and biotite gangue materials. The matte is treated in converters where the slag containing SO2 and FeO is removed. The converter matte is transferred to a base metal refinery where Cu,
Ni and other metals are removed. The PGM concentrate with > 65 pct PGM is refined in a precious metal refinery, and high-quality PGMs are recovered (see Figure 1). The demand for PGMs is increasing because of their various applications in industries. Figure 2 shows the demand and recycling of PGM in 2019. The demand for Pt, Pd and Rh is around 660.305 tons, but recycling only provides 189.02 tons. This shows that future acquirement of these metals will dep
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