LEACHING OF MANGANESE NODULES AT ELEVATED-TEMPERATURE AND PRESSURE IN THE PRESENCE OF OXYGEN

Indian Ocean polymetallic nodules were leached with dilute sulfuric acid at elevated temperature and pressure in the presence of oxygen. Conditions were established for the extraction of copper, nickel and cobalt with minimum iron and manganese contamination of the leach solution. By leaching for 4 h at 423 K using 0. 46 g of H//2SO//4 per g of nodule and keeping the oxygen partial pressure at 0. 55 MPa, almost all the copper and nickel and 88% of the cobalt could be extracted. Under these conditons 28% manganese and 5. 7% iron were also leached. To achieve the extraction of nickel, cobalt and manganese, charcoal was used as the reductant for reducing the manganese dioxide and rendering it soluble as manganese sulfate. The extraction iof 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, H//2SO//4 0. 66 g per g of nodule and oxygen partial pressure 0. 55 MPa. The conditions employed for leaching copper, nickel and cobalt could be extended to the extraction of manganese by increasing the acid concentration from 0. 46 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.