An effective utilization of the slag from acid leaching of coal-waste: Preparation of water glass with a low-temperature co-melting reaction

摘要

This paper presents an effective utilization of slag from acid leaching of coal-waste with a novel approach, namely low-temperature co-melting method, for preparation of sodium silicate (Na_2O•nSiO_2) using slag from acid leaching of coal-waste as feedstock. It is very interesting that the co-melting reaction temperature of the mixture of Na_2CO_3 and the feedstock (50～100 μm) was as low as 850 ℃, which was significantly lower than the temperature used in traditional sodium silicate production (1400 ℃). The optimum SiO_2/Na_2O ratio was identified as 7:3 according to the results of thermogravimetry-differential scanning calorimetry (TGA-DSC), ICP-AES, and X-ray diffraction (XRD) analyses. In this condition, the main product was sodium disilicate (Na_2O•2SiO_2), with water solubility of 85.0%. More importantly, the impurities such as aluminum in the feedstock, which had adverse effect on subsequent treatment, were concentrated almost completely in the filter residue as insoluble sodium alumunosilicates, i.e., Na(Si_2Al)O_6•H_2O. The lower co-melting temperature of this process demonstrates a significant energy-saving opportunity and thus a promising approach for highly effective utilization of coal-waste.