Many efforts to recover precious metals from spent metal complexes catalysts have been developed. The reasons for the necessity in this area are: (1) The abundance of these elements in the earth's crust is<10-3 ppm (~6.6*104 tons worldwide); (2) global demand for platinum group metals is >590 tons; (3) electronics and catalyst industries consume>90 pct of precious metals (about 65 pct of Pd, 45 pct of Pt and 84 pct of Rh are used in catalytic converters); (4) properties of precious metals (resistance to corrosion and oxidation, high melting temperatures, electrical conductivity and catalytic activity) are of great commercial interest[1]. Therefore, effective recovery of precious metals and extraction from spent metal complexes catalysts are environmentally and economically desirable.
Alfa Chemistry can offer the service of precious metals recovery, working towards a sustainable future with our efforts on creating glorious future.
Recycling Processes
The process of recovery of precious metals from catalysts is divided into three main steps: physical corruption, adopt recycling technique and extraction.
Physical corruptionRecycling techniqueExtractionRecycling process
▶ Physical corruption: The spent catalyst should undergo (1) dismantling, (2) size reduction and (3) physical separation before the start of the main process.
▶ Recycling technique: The selection of the recycling technique mainly depends on three factors: (1) type of catalyst supporter, (2) precious metals (loading) content and (3) presence of other base metals.
▶ Extraction: Finally, recycling of spent catalysts to extract precious metals can be divided into five basic steps: sampling/homogenization, pre-concentration, dissolution, enrichment and purification.
Recycling Technique
Several recovery techniques have been introduced over the past 20 years and most of them are already being employed in our laboratory.
▶ Hydrometallurgy: In the hydrometallurgical process, the spent catalysts are dissolved in the aqua regia, cyanide or strong acids such as HNO3, HCl and H2SO4. The leaching efficiency is enhanced by adding oxidizing agents such as O2, H2O2, Cl2 and I2.
▶ Pyrometallurgy: In the pyrometallurgical process, the spent catalyst is transformed physically and chemically by performing a thermal treatment. Calcination, chlorination and precious metals smelting collection are considered the three kinds of pyrometallurgical technologies.
Fig.1 Flowsheet illustrating platinum group metals (PGMs) recovery by the pyrometallurgical process
▶ Physical Separation: In the spent metal complexes catalyst, the catalyst carriers are honey comb-structured items with porous catalyst layers on the surface. precious metals are only present on these porous layers where a simple energy-efficient and inexpensive process like physical separation can be implemented to separate the precious metals or precious metals-containing layer from the carrier would be significant to eliminate the toxic gases usually released from the regular recycling process.
▶ Electrochemical Techniques: High-temperature electrochemical treatment can be applied to extract precious metals from spent metal complexes catalysts. In general, the electrochemical methods are easy to arrange and can be performed with low waste emissions and low energy and reactant consumption.
▶ Other Techniques: Combination of pyrometallurgical treatment and electrolytic, membrane electrode assembly process, combination of pyro- and hydrometallurgical processes, biotechnological recovery and others.
Fig.2 Variety of techniques used for spent catalyst processing and related products. *SCF: supercritical fluid; Me*: Fe, Cu, Pb, Al; SLM: supported liquid membrane; PGMs: platinum group metals
Separation Methods
▶ Solvent Extraction Method: In this method, extractants are added to the pretreated leaching liquor where ideal concentrations of precious metals are available for the separation. The three types of extractants added according to the requirements are basic (amine), neutral and acidic extractants..
▶ Ion-Exchange Method: In the ion-exchange method, the ion exchange resin is added to the leaching solution, sometimes combined with a synthetic solution loaded with precious metals in their complex form.
▶ Precipitation Method: In this method, a suitable precipitating agent is added to the leaching solution containing precious metals ions, where the precious metals interact with the agents and form insoluble substances and are individually separated thereafter.
Why Choose Us?
Alfa Chemistry offers leading-edge refining processes to recover the greatest amount precious metals from a wide range of production material by-products, particularly from catalyst. According to different products, specific techniques will be employed, we guarantee that you will be get highest return from us. Contact our engineers to discuss your precious metal recovery and refining needs and requirements.
