Studies in reduction-roast leaching ion exchange of copper converter slag from an Indian copper complex, Ghatshila

Abstract

Utilization of industrial waste is of utmost important due to pollution constraints. Large quantities of converter and anode slags are generated in different unit operations for the production of copper in I.C.C. Ghatshila. The converter slag contains about 2.75% copper, 0.9% nickel, 52.0% iron, and 0.6% cobalt and cannot be rejected due to its economic importance. X-ray diffraction (XRD) studies revealed the presence of copper in elemental, oxide, and silicate phases and iron in silicate (feyalite) and oxide (Fe2O3) phases. From the earlier work on leaching by an acetic acid lixiviant up to 55% Copper could be extracted at 250 mL of acetic acid/100 g of slag, 125 degrees C temperature, and 35 atm of oxygen pressure. Low copper recovery was attributed to the presence of copper silicate and sulfide phases which could not be detected by XRD. Therefore, reduction roasting by noncoking coal was done to increase the copper recovery. A coal sample from Talchar which contained 30% fixed carbon, 40% volatile, and 30% ash was used for reduction roasting. Pellets were prepared manually by mixing powdered coal in different proportions with ground slag (-100 mesh). Roasting of the pellets was carried out in the temperature range of 650-800 degrees C. Maximum percent extraction of copper and nickel (97% Cu and 20% Ni) could be achieved at the temperature of 720 degrees C, for 90 min of roasting with 20% reductant. The acetic acid requirement was 130 mL/100 g of reduced pellets, while leaching at the oxygen pressure of 35 atm for 120 min at 120 degrees C. The solid-liquid ratio was maintained at 1:5 in all the experiments. The copper concentration in the leach liquor was 4.5 g/L. Iron dissolution was minimum (max 1%) in all the experiments. The ion-exchange technique was employed to separate copper from acetate solution. Zeolite resin was found to be suitable for the separation of copper from leach liquor. About 92% copper was recovered by geolite. 2.5 N H2SO4 was found to be most effective for the stripping of the copper from resin.