Leaching of manganese nodules at elevated temperature and pressure in the presence of oxygen

Abstract

Indian Ocean polymetallic nodules were leached with dilute sulphuric acid at elevated temperature and pressure in the presence of oxygen. Conditions were established for treating the nodules for the extraction of three metals, i.e. copper, nickel and cobalt, with minimum iron and manganese contamination of the leach solution. By leaching the nodules for 4 h at 423 K using 0.46 g of H₂SO₄ per g of nodule and keeping the oxygen partial pressure at 0.55 MPs, almost all the copper and nickel and 88% of the cobalt could be extracted. Under these leaching conditions 28% manganese and 5.7% iron were also leached. To achieve the extraction of four metals, i.e. copper, nickel, cobalt and manganese, charcoal was used as the reductant for reducing the manganese dioxide and rendering it soluble as manganese sulphate. The extraction of copper, nickel, cobalt and manganese were 77, 99.8, 88 and 99.8% respectively under the following leaching conditions: time 4 h, temperature 423 K, H₂SO₄ 0.66 g of nodule and oxygen partial pressure 0.55 MPa. The studies showed that the conditions employed for leaching copper, nickel and cobalt could be extended to the extraction of manganese too, simply by increasing the acid concentration from 0.46 g to 0.66 g per g of nodule and with the addition of 0.05 g of charcoal per g of nodule to the initial slurry.