Separation and Recovery of Precious and Base Metals using a Column Packed with Microcapsules Containing an Extractant

Abstract

A fundamental investigation of the separation and recovery of PdCl₄^2-, PtCl₆^2-, HCr₂O₇^-, Cu²⁺, Ni²⁺ and Zn²⁺ from an aqueous solution by using microcapsules containing a metal extractant has been undertaken. As extractants,2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHPNA) and tri-n-octylamine loaded with hydrochloric acid (TOA-HCl) were used. The extractants were successfully encapsulated in microcapsules during the in situ microencapsulation process. The extractabilities of the metals into the microcapsules were estimated from the extraction isotherm of the metal ions. According to the Langmuir model, the saturation amount of metal extracted and the extraction equilibrium constant were determined. The microcapsules containing EHPNA and TOA-HCl were suitable for the extraction of base metal ions and precious metal ions, respectively. Using a reactor in which two columns packed with each microcapsule containing EHPNA and TOA-HCl are connected in series, the separation and recovery of precious metals from base metals was examined. In this way, the mutual separation of precious metals can be successfully achieved by feeding a suitable eluent stepwise into the column.