Solvent extraction of platinum using amine based extractants in different solutions: A review

Platinum is one of the platinum group metals that are found in nature in small quantities along with other metals in various ores. In order to meet its increasing demand, it is necessary to harvest platinum by processing and recycling secondary materials that have been generated due to their end-of-service life. Usually, the pyro/hydrometallurgical processes that consist of a heat treatment, leaching followed by a solvent extraction are employed to recover the metallic valuables from such primary and secondary materials. The solvent extraction process is an important technique that is employed to extract the metallic valuables from the leach solution using organic extractants. To develop efficient and eco-friendly processes, R & D studies are being conducted for the extraction of platinum from the leach solutions using various organic reagents viz., anionic, cationic and solvating extractants. Because the amine based extractants have been extensively employed for the extraction of Pt under different conditions, the present paper critically reviews Pt recovery in the presence of metallic and non-metallic species in the solutions obtained by processing primary/secondary materials. The selection of extractant depends on the various conditions viz. material, media and impurities but in most of the cases the amine based extractants such as Alamine/Aliquat were found to be suitable for Pt recovery. The diluted nitric acid, aqueous thiocyanate and thiourea in the presence of HCl and sodium bisulfite were found effective stripping agents. The results on the extraction of Pt, its mechanism and complex formations, scrubbing of impurities and selective stripping have been used to obtain a purified solution that could be subsequently processed to produce pure metallic valuables from such solutions by precipitation/crystallization. The piece of comparative and summarized review will be useful for researchers to develop various processes for Pt recovery in various conditions.