Recoveries of Ru(III) and Co(II) by Solvent Extraction and Ion Exchange from Tungsten Carbide-Cobalt Scrap through a HCl Leaching Solution

Abstract

The addition of ruthenium to tungsten carbide-cobalt hard metals improves their mechanical properties. Since ruthenium is a platinum group metal, the recovery of ruthenium together with cobalt from the scrap of hard metals is of great importance. In order to develop a recovery process of ruthenium and cobalt, separation experiments were performed from the synthetic HCl leaching solution of the scrap of hard metals. In this work, solvent extraction and ion exchange were employed to investigate the separation behavior of the two metal ions as a function of HCl concentration. Ru(III) was selectively extracted over Co(II) by Aliquat 336 (trioctyl methylammonium chloride) and Alamine 300 (tri-n-octyl amine) when HCl concentration was lower than 5 M. The highest separation factor between Ru(III) and Co(II) was obtained at 3 M HCl. The loaded Ru(III) was stripped from Aliquat 336 by dilute HCl solution. Only Ru(III) was loaded into the anion exchange resins employed in this work in the HCl concentration range from 1 to 9 M. The highest loading percentage of Ru(III) was obtained from 3 M HCl solution. The loading of Ru(III) into anion exchange resins followed Freundlich isotherm and the loading capacity of the resins were determined. The loaded Ru(III) was eluted by the mixture of HCl and thiourea. Compared to solvent extraction, ion exchange was found to be more efficient to separate Ru(III) and Co(II) from the HCl solution in terms of separation factor and the ease of operation.