Thiosulfate leaching of Au, Ag and Pd from a high Sn, Pb and Sb bearing decopperized anode slime

Abstract

Compared with Au+ and Ag+, Pd2+ is easier to be complexed by S2O32− in ideal situation, based on DFT (density functional theory) calculation. Thermodynamics analysis shows that palladium can also be effectively leached by ammoniacal thiosulfate solution besides gold and silver. The Sn and Sb in a high Au, Ag, Pd, Sn, Pb and Sb bearing decopperized anode slime had no obvious detrimental effect on thiosulfate leaching of the precious metals, but the Pb could cause seriously detrimental impact. Only 37.3% of Au, 69.2% of Ag and 43.8% of Pd in the decopperized anode slime could be extracted by direct thiosulfate leaching. After sodium hydroxide pretreatment where 56.9% of Pb and 13.6% of Sb in the slime were removed, thiosulfate leaching under optimal operating conditions only extracted 68.1% of Au, 81.7% of Ag and 67.6% of Pd in the pretreatment residue. The low extraction is probably because there was a PbO passivation layer on slime particle surfaces. After the carbonate transformation and subsequent acetic acid pretreatment in which 93.8% of Pb in the transforming residue was removed, thiosulfate leaching could extract as much as 88.0% of Au, 93.4% of Ag and 80.7% of Pd in the pretreatment residue. There was no such passivation layer on the surfaces of slime particles during the leaching, attributing to comparatively thorough removal of Pb by the pretreatment.