Minerals and Metals in Ancient India v1.c26.s7.9

v1.c26.s7.9

(8) Freestone *et al.* (1985a: 239) estimated that 8 lakh tons of debris at Zawar contains 6 lakh tons of spent retorts. Each retort weighs about 3 kg and might have produced 500 g of zinc. On this basis one lakh tons of zinc might have been produced during the thirteenth-seventeenth century AD. Our estimate is more conservative. Possibly 40 to 50 thousand tons of metallic zinc were produced. 6 lakh tons of spent retorts contain 2 lakh tons of residues within, assaying about 3 per cent zinc. Therefore some six thousand tons of zinc metal remain within the retort residue and another thousand tons in the lead slag. We have shown that most of this zinc can be recovered from the siliceous slag by a special ‘fast leaching’ process. (Biswas *et al.*, 1986)