Phosphate Adsorption onto Granular-Acid-Activated-Neutralized Red Mud: Parameter Optimization, Kinetics, Isotherms, and Mechanism Analysis
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Powdered-acid-activated-neutralized red mud (Aan-RM), the chemico-physically modified product of red mud, was for the first time employed with hydroxypropyl methylcellulose and powdered straw as the main ingredients for granular Aan-RM production for phosphate removal. In order to better understand the phosphate adsorption characteristics of granular Aan-RM, the influence of operational parameters on the performance of granular Aan-RM and the possible adsorption mechanisms involved were investigated. The results demonstrated that the adsorbent dosage, adsorption temperature, and initial solution pH influenced the adsorption performance of granular Aan-RM significantly. The maximum phosphate adsorption capacity of granular Aan-RM reached 153.227 mg/g with the granular Aan-RM dosage of 3.0 g/L, adsorption temperature of 40 °C, and initial solution pH of 6.0. The whole adsorption process was well described by nth-order kinetic model and Langmuir–Freundlich isotherm. Meanwhile, X-ray photoelectron spectroscopy (XPS) analysis of P 2p peak on granular Aan-RM after phosphate adsorption demonstrated that 79.01 % of the phosphate was adsorbed through precipitation and ion exchange mechanisms with strong chemical bonds, and 20.99 % of the phosphate was adsorbed through surface deposition mechanism with weak chemical bonds.
KeywordsRed mud Granule Phosphate adsorption Precipitation Surface deposition
The authors are thankful to the China Scholarship Council (CSC), the National Natural Science Foundation of China (51178047, 51378190, 51039001), and Furong Scholar of Hunan Province for support.
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