Microwave-Assisted Acid Leaching for Recovery of Silicon from Diamond-Wire Cutting Waste Slurry

The recovery of crystalline silicon from diamond-wire cutting waste with microwave-assisted hydrochloric acid leaching was studied. The experimental results indicated that the optimum conditions for the hydrochloric acid concentration, liquid-solid ratio, leaching time, leaching temperature and particle size were 2 mol/l, 6:1 ml/g, 10 min, 100 degrees C and 98 nm, respectively. Under optimal conditions, the purity of silicon could reach 99.57% because the polar molecule hydrochloric acid has a temperature effect, orientation effect and molecular rotation effect in microwave electromagnetic fields. For metal oxides with variable valences showing strong absorption of microwave irradiation, the leaching efficiencies of Al and Ca are not nearly as good as that of Fe. The kinetic experiment showed that the leaching of metal impurities (Al, Fe,Ca) in hydrochloric acid was controlled by the solid product layer diffusion, with apparent activation energies calculated to be 21.16 kJ/mol, 13.31 kJ/mol and 16.63 kJ/mol for Al, Fe and Ca, respectively.