Abstract
Phosphorus removal from wastewater has become urgent because of eutrophication control. Phosphate concentration in control for phosphate removal and recovery by Mg-Fe oxide has been investigated. The results show that the adsorption capacity of phosphate by Mg-Fe oxide calcined at 450°C was 28.3mg/g, and it was kept at wide optimal adsorption pH ranges (4-10). The coexisting ions had influenced phosphate adsorption process and the order is CO32- > SO42- > NO3- > Cl-, with the inhibition rate of CO32- being 43%. Interestingly, phosphate concentration plays an important role in phosphate removal by Mg-Fe oxide. Under higher initial phosphate concentrations (200-800mg/L), Sips model was well fitted. In addition, the adsorption kinetics was well described by the pseudo-second-order kinetic model before 25min and the pseudo-first-order kinetic model after 25min. In contrast, Langmuir model and pseudo-second-order kinetic model were fitted under lower initial phosphate concentrations (20-200mg/L). The results of XRD, XPS, SEM, and TEM characterization show that Mg3(PO4)2 was formed by surface precipitation under 800mg/L phosphate solution, and Mg-Fe layered structure was present via the unique memory effect under 20mg/L phosphate solution. Mg-Fe oxide can be recovered through CO32- ion exchange, and the removal efficiency of phosphate was 56% after seven cycles.
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