Removal efficiencies of 99.96% for As, 99.98% for Zn, and approximately 100% for Cd were achieved. The HTP-ZC results indicate that As, Cd and Zn are condensed as residues and removed in the condensation stage. To cope with this, a novel high-temperature pyrolysis-zone condensation (HTP-ZC) vacuum purification process is proposed for further As separation.

In contrast to the removal efficiencies of Zn and Cd by LTVD, the removal efficiency of As impurities is only 4%. Correspondingly, the contents of Zn and Cd impurities decreased from 4 ppmw and 1 ppmw to 0.006 ppmw and 0.01 ppmw, respectively. Detailed analysis of the initial and purified lead was performed by glow discharge mass spectrometry (GDMS) to reveal that Cd and Zn were evaporated as volatiles and were removed from the refined lead in a crucible. In this paper, the low-boiling point trace impurities As, Zn and Cd in refined lead are removed by low-temperature vacuum distillation (LTVD).

Environmentally friendly vacuum distillation has been employed to purify refined lead (99.996%), aiming to separate low-boiling point trace impurities of As, Zn and Cd in refined lead and to provide a foundation for the preparation of high-purity lead (5 N) and ultrapure lead (6 N).

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