Coal gasification coarse slag based composite ferric aluminum silicate coagulants: Preparation, performance, and mechanism

A novel process of acid leaching neutralization was initiated for the preparation of inorganic polymeric com-posite ferric aluminum silicate coagulant (CFAS) based on the reutilization of solid waste coal gasification coarse slag (CGCS). Firstly, a single-factor experiment was carried out to optimize the preparation process by adjusting pH, polymerization time and maturation temperature. The results proved that the coagulant of CFAS was ach-ieved under the optimal conditions of pH 3.0, polymerization reaction time 120 min and the maturation tem-perature of 80 degrees C. CFAS was further characterized by X-ray Fluorescence Spectrometry (XRF), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscope (SEM). It was found that CFAS was mainly occupied with Si, Fe, Ca, and Al. Secondly, the performance of CFAS was evaluated by domestic sewage, and the results indicated the best removal efficiency of turbidity of 93.8%, ammonia nitrogen (NH4-N) of 94.8%, and chemical oxygen demand (COD) of 63.9% were achieved when the dosage of CFAS was 150.0 mg/L, initial pH of domestic sewage was 3.0, and the initial temperature was 30 degrees C, which were further investigated by response surface methodology (RSM), it was found that the temperature played a greater role in the coagulation process, followed by dosage coagulant and pH. Additionally, the coagulation mechanisms demonstrated that the charge neutralization dominated the coagulation process, affiliated by adsorption bridge, and sedimentation netting based on the microscope image of CFAS, the variation of zeta potential and particle size of flocs.