Alkaline pressure oxidative leaching of bismuth-rich and arsenic-rich lead anode slime

A new alkaline pressure oxidative leaching process (with NaNO₃ as the oxidant and NaOH as the alkaline reagent) is proposed herein to remove arsenic, antimony, and lead from bismuth-rich and arsenic-rich lead anode slime for bismuth, gold, and silver enrichment. The effects of the temperature, liquid-to-solid ratio, leaching time, and reagent concentration on the leaching ratios of arsenic, antimony, and lead were investigated to identify the optimum leaching conditions. The experimental results under optimized conditions indicate that the average leaching ratios of arsenic, antimony and lead are 95.36%, 79.98%, 63.08%, respectively. X-ray diffraction analysis indicated that the leaching residue is composed of Bi, Bi₂O₃, Pb₂Sb₂O₇, and trace amounts of NaSb(OH)₆. Arsenic, antimony, and lead are thus separated from lead anode slime as Na₃AsO₄· 10H₂O and Pb₂Sb₂O₇. Scanning electron microscopy and energy-dispersive spectrometry imaging revealed that the samples undergo appreciable changes in their surface morphology during leaching and that the majority of arsenic, lead, and antimony is removed. X-ray photoelectron spectroscopy was used to demonstrate the variation in the valence states of the arsenic, lead, and antimony. The Pb(IV) and Sb(V) content was found to increase substantially with the addition of NaNO₃.