Microwave-enhanced selective leaching of arsenic from copper smelting flue dusts

摘要

Alkaline sulphide leaching processes have been widely used for the arsenic selective removal from metallurgical wastes. However, high consumption of energy and chemicals as well as long extraction time have forced the industries to find more cost-effective and eco-friendly separation techniques. In this work, a feasible microwave-enhanced leaching process was developed for arsenic selective removal from copper smelter dusts, and arsenic leaching efficiency could reach similar to 98 % after leaching for 10 min with 0.5 mol.L-1 alkaline solution, in contrast to 86 % removal for the conventional electrical-heating leaching with even a more intensive alkali content (1.0 mol.L-1) and a longer extract time (1.5 h). Furthermore, energy cost was cut down to one-tenth of the conventional leaching process. Two enhancing mechanisms were proposed: 1) rapid oxidation of As(III) of the dusts occurred under microwave irradiation reduced the energy potential for arsenic dissolving in alkali media; 2) cracks and fissures formed in the dust particles after microwave, coupled with the temporary and localized superheating in the bulk liquid, would dramatically enhance arsenic leaching kinetics and decrease the activation energy value from 42.88 to 35.81 kJ.mol(-1) (40-70 degrees C). This work may have important implications to the development of new technologies to purify arsenic-bearing materials.