Sustainable and clean utilization of coal gangue: activation and preparation of silicon fertilizer

Coal gangue, a by-product produced during the coal processing, has a serious impact on the environment. Using coal gangue as a fertilizer has been proven helpful in potentially reducing its environmental impact and improving its value. In this study, the formation mechanism and influencing factors of coal-gangue-based silicon fertilizer was studied using XRD and FT-IR measurement technologies. The results showed that the layered structure of coal gangue was severely damaged above 600 ℃, where the kaolin began to transform into metakaolin. When CaCO3 alone was added, CaCO3 mainly played a catalytic role, forming only a small amount of calcium silicate with available-Si content below 12.60%. When corn stalk powder alone was added, the oxides of the corn stalk ash participated in the chemical reaction involving coal gangue, forming nepheline (K(Na, K)3Al4Si4O16) and other silicates with available-Si content of 14.56%. When coal gangue, CaCO3, and corn stalk powder were mixed and calcined, the available-Si content was as high as 22.97% under the synergistic effect of CaCO3 and corn stalk powder; the concentration of toxic metals and ions was below 52.87 mg/kg. The prepared silicon fertilizer can reduce the pollution of coal gangue and meet the agricultural needs of China.