Selective phosphate removal of oxygen vacancy-rich magnesium oxide microrods: Performance and mechanism
HU Qi-li1,2, PANG Shu-yue2
1. School of Chemical and Environmental Engineering, Sichuan University of Science & Engineering, Zigong 643000, China; 2. College of Ecology and Environment, Chengdu University of Technology, Chengdu 610059, China
Abstract：Oxygen vacancy-rich magnesium oxide (OV-MgO) microrods were prepared through the combination of chemical precipitation method with high-temperature calcination. The effects of adsorbent dosage, pH values of the solution, coexisting ions and humic acid on the phosphate removal performance were explored. The adsorption kinetic and isotherm models were used to analyze the mass transfer process and the equilibrium characteristics of phosphate adsorption. X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR), electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) were adopted to reveal the phosphate adsorption mechanisms. The results indicated that OV-MgO microrod was a mesoporous material with a total pore volume of 0.18cm3/g, and had a good acid resistance. The phosphate adsorption was influenced by SO42− and HCO3− ions, but its adsorption capacity only decreased by 5.18% and 4.67%, respectively, exhibiting an extremely high selectivity. NH4+ and Ca2+ ions present in the solution contributed to the phosphate adsorption based on the formation of struvite crystals and calcium phosphate precipitates. The adsorption of phosphate on OV MgO nanorods followed the fractal-like pseudo-first-order kinetic model (Adj. R2=0.9979 and RMSE=3.25). The fitting result of the Vermeulen model indicated that the intraparticle diffusion was the rate-controlling step. The maximum adsorption capacity predicted by the Langmuir isotherm model was 267.1mg/g (as PO43−-P). The adsorption mechanisms of phosphate mainly included ligand exchange, surface precipitation and oxygen vacancy capture.
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