Response surface method optimization of preparation fly ash based polysilicate aluminum chloride coagulant: performance and microstructure characterization
LAO De-ping1, DING Shu-qiang2, NI Wen1, LI Xiao-guang2, LI Jia-jie1, GAO Guang-hui2
1. School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing 100083, China;
2. National Institute of Clean and Low Carbon Energy, Beijing 102211, China
This paper investigates the factors that influence the preparation of polysilicate aluminum chloride coagulant using coal fly ash and their performance and microstructure. Four factors(basicity, n(Si):n(Al), polymerization temperature and reaction time) and three levels of response surface experiments were carried out, which regarded the transmittance of Kaolin simulated wastewater as the evaluation index. Results show that the optimum scheme when the basicity was 1.18, the n(Si):n(Al) was 5.64, the polymerization temperature was 47.40℃, and the reaction time was 2.48 hours. At the optimum theme, the predicted value of transmittance reaches 86.58%, the relative error of all the verification experiments was 0.18%, and the correlation coefficient of the model is 0.9984, which indicated the RSM optimization model is reliable. The performance of coagulant increases continuously with the increase of dosage, and tends to be stable eventually. With the increase of pH of wastewater, it increases first and then decreases. X-ray diffraction test indicates the formation of sodium chloride and new amorphous polymers which through the polymerization reaction of fly ash leachate and polysilicic acid. The infrared tests illustrates that a large amount of nonionic complex state (such as metal-hydroxyl groups) occurs between polysilicate acid and Al3+ and it's hydrolysate. The SEM micrograph shows that the product presents a three-dimensional reticular structure, with high level of aggregation and branches.
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