Technological innovation in the zinc electrolyte purification process of a hydrometallurgical zinc plant through reduction in zinc dust consumption

Abstract

The Electrolytic Zinc Plant at Debari commenced operation in 1967 with a capacity of 18000 Mt/a. In 1976 this plant was expanded to 45000 Mt/a, thereafter to 49000 Mt/a by incorporating a residue treatment facility. In the beginning, the plant was designed using the cold β-Naphthol purification batch operation. During expansion, a continuous hot purification process was adopted, through the addition of KSb tartrate and zinc dust to remove the impurities. The average zinc dust consumption envisaged in the basic package was 62 kg/Mt of zinc ingot produced, but from 1977 to 1986 zinc dust consumption ranged from 70 kg/Mt to 80 kg/Mt. In 1983–1984, when the residue treatment facility was incorporated, in-house development work was carried out to update the solution purification system commensurate with the intake of impurities from the residue treatment plant solution. Research work was carried out to decide on a suitable purification process to minimise the zinc dust consumption and obtain solution of higher purity. On a laboratory scale, batch and continuous scale experiments were carried out and an optimum process to suit the available plant equipment was worked out. It was found, on the basis of laboratory-scale experiments, that recycled zinc dust is very active for cobalt purification, resulting in low zinc dust consumption and, hence, increased financial gains. Based on these results, batch and continuous trials on a plant scale were conducted. The results were very encouraging and the plant was modified accordingly. Ultimately, two-stage hot antimony purification with recycled zinc dust was adopted in the scheme. Automatic control with a weigh feeder was incorporated. This has resulted in reduced zinc dust consumption in the plant, to 35 kg/Mt of zinc produced. A similar system of purification was implemented in a second plant of Hindustan Zinc Limited at Vizag and there also zinc dust consumption was brought down to 40 kg/Mt of zinc ingot production from 65–70 kg/Mt.