Evaluation of novel ligand dithiodiglycolamide (DTDGA) for separation and recovery of palladium from simulated spent catalyst dissolver solution

Novel ligand, namely, N,N,N′,N′-tetra-(2-ethylhexyl)-dithiodiglycolamide (DTDGA) has been evaluated for separation and recovery of palladium from simulated spent catalyst dissolver (SSCD) solution. Liquid-liquid batch extraction studies were carried out to understand the influence of various parameters on the extraction behavior of palladium. Extraction equilibrium studies showed near complete extraction of palladium within 5 min. With the increase in hydrochloric acid concentration, the extraction of palladium increased up to 3.0 M HCl and then remained constant on further increase in acidity. Stoichiometry of the extracted species was determined to be PdCl2⋅DTDGA by mole ratio plot. The effect of various diluents on the extraction of palladium was studied and it was found that there is quantitative uptake in n-paraffinic diluents and the extraction decreases with increase in polarity of diluent. More than 99% of palladium was back extracted in single contact using 0.01 M thiourea in 0.1 M HCl. Extraction studies with SSCD solution showed negligible uptake of Fe, Cr, Ni, and Pt, thus showing very high selectivity and extractability of DTDGA for palladium.