Sustainable application of coal fly ash: One-step hydrothermal cleaner production of silicon-potassium mineral fertilizer synergistic alumina extraction

Abstract

Coal fly ash (CFA) is the main solid waste discharged from coal-fired power plants, a new method for preparing silicon-potassium mineral fertilizer using KOH hydrothermal treatment CFA was proposed to improve its comprehensive utilization rate and reduce its threat to ecological environment security. In this paper, the characteristics of CFA raw material and transformation residue were studied, the agricultural applicability of the process was verified by pakchoi planting experiments, and the effects of the silicon-potassium mineral fertilizer on soil physical-chemical characteristics were investigated. The results show that increasing the leaching temperature and time can improve the extraction rate of alumina from CFA, and the reaction rate is controlled by the mixing of interfacial chemical reaction and solid product layer diffusion. The CFA raw material was hydrothermally leached at 280 g/L K2O 200 °C for 1 h, in which the Al2O3 extraction rate was 27.46%. The main component of the transformation residue was potassium aluminum silicate hydrate, which is the main component of the silicon-potassium mineral fertilizer, and the effective K2O and SiO2 content is 25.07% and 34.56%. The application of CFA residue can effectively improve the fertility and productivity of the soil, providing nutrients for the growth of pakchoi and improving the soil quality. This research provides theoretical guidance for the preparation of silicon-potassium mineral fertilizer using CFA and has the potential for practical production, which is important for the resourceful use of CFA and its application in agriculture.