Separation of palladium from waste electronic card leaching solutions by solvent extraction using a tertiary amine

In this research, waste electronic cards were processed to recover precious metals, presenting new challenges for the efficient extraction of metals of interest. After a pretreatment that removed base metals (Cu, Fe, Zn, and Ni), via pressure leaching with sulfuric acid and oxygen, precious metals were leached in a chloride medium, resulting in an aqueous solution containing Ag, Au, Pt, and Pd chlorides. Palladium was recovered from this solution using a solvent extraction process, which concentrated the chloride solution with a tertiary amine extractant. The process achieved over 95% extraction efficiency for palladium at a pH of 1.5 and a phase ratio of 1.2:1. Extraction isotherms indicated a higher loading capacity with a 12% tertiary amine concentration diluted in kerosene. A McCabe-Thiele diagram showed that three theoretical stages were needed for effective extraction. To determine best re-extraction conditions, thiourea (CS(NH₂)₂) in 0.5 M HCl was used, and the aqueous phase ratios were varied. A stripping efficiency of over 98% for palladium was achieved using 1Mthiourea at a phase ratio of 5:1 and ambient temperature (25 °C). Thus, palladium can be selectively extracted from a chloride solution using solvent extraction with a tertiary amine, yielding a concentrated solution.