Electrolytic Zinc production at Vizag Smelter

Hindustan Zinc Limited operates 30,000 MTPA capacity Zinc Smelter at Visakh apatnam. Zinc is produced by hydrometallurgical route. Sulphidic zinc conce ntrate is blended and roasted in Fluosolid Roaster to produce calcine (Zinc Oxide) and SO2 gas which is converted to sulphuric acid by Contact process . Calcine is leached with return spent acid in two stages - Neutral Leaching and Acid Leaching. Slurry is thickened for solid - liquid separation. Resul ting neutral overflow solution is subjected to three step purification to g et pure zinc sulphate solution. Purified neutral solution is electrolysed in conventional Cell House consis ting of 360 cells. Electrolytic zinc deposits on aluminium cathode sheets, stripping of zinc i s carried out after 24 hours. Zinc cathodes are melted and cast into ingots . Zinc dress is recycled. Zinc ferrite residue is processed by pyrometallur gical route in waelz kiln to improve zinc recovery and to produce environme ntally inert slag, cadmium metal and Silver concentrate are recovered. Liqu id effluents an treated in a modern Effluent Treatment plant to remove heav y metals. Gaseous emissions are controlled.