Phosphate Removal from Aqueous Solution by Aluminum (Hydr)oxide-coated Sand

Abstract

A powder form of aluminum (hydr)oxides is not suitable in wastewater treatment/filtration systems because of low hydraulic conductivity and large sludge production.In this study, aluminum (hydr)oxide-coated sand (AOCS) was used to remove phosphate from aqueous solution.The properties of AOCS were analyzed using a scanning electron microscopy (SEM) combined with an energy dispersive X-ray spectrometer (EDS) and an X-ray diffractometer (XRD).Kinetic batch, equilibrium batch, and closed-loop column experiments were performed to examine the adsorption of phosphate to AOCS.The XRD pattern indicated that the powder form of aluminum (hydr)oxides coated on AOCS was similar to a low crystalline boehmite.Kinetic batch experiments demonstrated that P adsorption to AOCS reached equilibrium after 24 h of reaction time.The kinetic sorption data were described well by the pseudo second-order kinetic sorption model, which determined the amount of P adsorbed at equilibrium (qe = 0.118 mg/g) and the pseudo second-order velocity constant (k = 0.0036 g/mg/h) at initial P concentration of 25 mg/L.The equilibrium batch data were fitted well to the Freundlich isotherm model, which quantified the distribution coefficient (KF = 0.083 L/g), and the Freundlich constant (1/n = 0.339).The closed-loop column experiments showed that the phosphate removal percent decreased from 89.1 to 41.9% with increasing initial pH from 4.82 to 9.53.The adsorption capacity determined from the closed-loop experiment was 0.239 mg/g at initial pH 7.0, which is about two times greater than that (qe = 0.118 mg/g) from the kinetic batch experiment at the same condition.