Acid-activated Bauxsol was applied to treat wastewater with high phosphate concentration in a batch adsorption system in this paper. The effect of acid activation on the change of Bauxsol structure was systematically investigated. The mineralogical inhomogeneity and intensity of Bauxsol decreased after acid activation, and FeCl3·2H2O and Al(OH)3 became the dominant phases of acid-activated Bauxsol adsorption. Moreover, the BET surface area and total pore volume of Bauxsol increased after acid activation. Interaction of initial solution pH and adsorption temperature on phosphate adsorption onto acid-activated Bauxsol was investigated by using response surface methodology with central composite design. The maximum phosphate adsorption capacity of 192.94 mg g(-1) was achieved with an initial solution pH of 4.19 and an adsorption temperature of 52.18 °C, which increased by 7.61 times compared with that of Bauxsol (22.40 mg g(-1)), and was higher than other adsorbents. Furthermore, the desorption studies demonstrated that the acid-activated Bauxsol was successfully regenerated with 0.5 mol L(-1) HCl solution. The adsorption capacity and desorption efficiency of acid-activated Bauxsol maintained at 80.48% and 93.02% in the fifth adsorption-desorption cycle, respectively, suggesting that the acid-activated Bauxsol could be repeatedly used in wastewater treatment with high phosphate concentration.
Keywords: Activation; Central composite design; Desorption; Red mud; Structure change.
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