China Nonferrous Metallurgy

The efficient removal of chloride ion (Cl-) is a bottleneck problem in the field of the recycling of waste acid generated from the nonferrous metallurgy. In recent years, advanced oxidation process has shown great application potential in removal of Cl-. In this paper, the dechlorination efficiency, mechanism, cost and operation management of lead dioxide (PbO₂), sodium bismuthate (NaBiO₃) and potassium peroxymonosulfate (PMS) were compared and analyzed. In order to achieve the residual Cl- concentration of less than 200mg/L for the requirements of waste acid reuse, the dosage of PbO₂ NaBiO₃ and PMS were 4, 1.5 and 1.5 times of the theoretical value, while the required reaction temperature were 50, 20 and 60℃, respectively. The regeneration of PbO₂ and NaBiO₃ were realized by mixing the dechlorination solid products with chlorine gas absorption solution, and the dechlorination efficiency of the regenerated reagents were higher than 90% in five cycles. Highly active intermediate species such as hydroxyl radical (·OH), sulfate radical (·SO^-₄) and chlorine radical (·Cl) were involved in the dechlorination processes of PbO₂ NaBiO₃ and PMS. The contribution of direct oxidation, indirect oxidation of ·OH and indirect oxidation of ·SO^-₄ for dechlorination process of PMS were about 84%, 9% and 7%, respectively. In terms of practical application value, NaBiO₃ has more advantages in cost and energy consumption due to its renewability, high by-product recovery value and low reaction temperature, while PMS is simpler in terms of operation and management because it does not introduce impurities.