Processing of Tungsten Preconcentrate from Low Grade ore to Recover Metallic Values

摘要

For the exploitation of a low grade tungsten deposit of Tapaskonda, A.P., India containing 0.1-0.16 percent WO_3, preconcentrate with 13.06 percent WO_3 was produced by physical beneficiation. This concentrate containing ferberite along with small amount of wolframite minerals was treated following two routes viz. soda ash roast-leach and alkali pressure leach processes. The parameters such as time, temperature, concentration of alkali, etc., have been studied to optimise the recovery of tungsten. In the soda roast-leach process about 89 percent tungsten was recovered by roasting the concentrate at 1073 K for 4h under the oxidizing conditions. In the alkali pressure leaching process, tungsten recovery was 94 percent at 463K for 20 bar pressure, 100 g/L sodium hydroxide and 60 minutes time. The leaching kinetics followed diffusion control model with lixiviant reacting the mineral phase through the porous product layer. An activation energy of 31.2 kJ/mole was acquired in the temperature range 428-473 K. The leach liquor was purified with respect to different impurities by a two-stage precipitation process. Tungsten from the purified leach solution was extracted by 10 percent Alamine-336 and 10 percent isodecanol in kerosene. The loaded metal when stripped with NH_4OH produced ammonium paratungstate (APT) solution which was crystallised to get the crystal of APT. The alkali pressure leach - solvent extraction process was thus found attractive for treating such concentrates.