Reuse of secondary aluminum ash: Study on removal of fluoride from industrial wastewater by mesoporous alumina modified with citric acid

Longitudinal loading of citric acid as modifier onto the surface of other supports as highly efficient fluoride removing adsorbents has received extensive attention. But the loading of acid into mesoporous alumina synthesized using industrial solid waste secondary aluminum ash as raw material is rarely reported. In this study, MA was prepared by secondary aluminum ash reuse to industrial solid waste, and the MA was modified with citric acid for fluoride removal. The structural properties of this adsorbent were characterized by N2 adsorption–desorption isotherm, XRD, FTIR spectroscopy. Meanwhile, the adsorption conditions, such as contact time, initial concentration and pH, were examined to evaluate the effect of fluoride adsorption. The adsorption properties are stable under acidic conditions. Chemisorption is a rate determining step because it complies with the Langmuir model and the pseudo second order model. The adsorption equilibrium was quickly reached in 30 min (117.98 mg g−1). With good cycling performance, 98.20% of the initial adsorption capacity was maintained after 5 cycles. Ion exchange between OH and fluoride is the main process of fluoride adsorption. The introduction of citric acid greatly increased the amount of -OH in the adsorbent. The extent of the influence of coexisting anions on fluoride adsorption is most pronounced for PO43− and CO32−. The results of high fluoride containing industrial wastewater treatment show that citric acid modified MA can solve the environmental pollution problem of industrial solid waste secondary aluminum ash on one hand, and at the same time provide new ideas for fluoride adsorbents.