Hydrometallurgical extraction and recovery of silver from silver concentrate generated at the zinc electrowinning plant

Abstract

Hindustan Zinc Limited operates two zinc hydrometallurgical plants in India adopting conventional roast-leach-electrowin process in which silver in the roasted calcine reports in the neutral leach residue. Generally, silver in the leach residue is enriched to obtain silver concentrate through froth flotation process, which is further processed through roast-leach-precipitation-reduction process to obtain high pure silver sponge which is then melted to obtain high pure silver ingot. Lead reports in the leach residue with small amounts of silver during the above process. Since there is an inherent difficulty of water balance in zinc circuit while adopting the above process it was felt necessary to find out a suitable process to recover locked up silver and lead in the leach residue. This paper describes the experimental conditions under which the silver concentrate is leached in brine solution to solubilize silver and lead values and the conditions with which lead and silver are cemented out from the leach solution using aluminium sheet. The solution is recycled 3-4 times to converse the sodium chloride and discharged as effluent, without causing any environmental pollution problems to the Inland discharge to the sea and existing treatment at VZS. The effluent, which is mainly sodium chloride, is free from heavy metals. The process described in this paper is suggested route is innovative, easy to operate, economical and environment friendly. This paper also explains how zinc and remaining lead values are recovered from the brine leach residue through the normal process values at VZS. Based on the results a conceptual flow sheet has been developed and other advantages of the process are presented in the paper.