Removal and recovery of phosphate from water by activated aluminum oxide and lanthanum oxide

Abstract

Phosphorus is a non-renewable resource for food production in modern agriculture and a leading cause of eutrophication in water bodies. Both the removal and recovery of phosphorus from water/wastewater are important. The phosphate adsorption performances of activated aluminum oxide (AAO) and lanthanum oxide (LO) have been investigated. Langmuir adsorption capacities for AAO and LO of 20.88mg/g and 46.95mg/g, respectively, were attained. Efficient phosphate removal by AAO could only be achieved under acidic pH conditions (<~5.0), whereas that by LO was not greatly influenced at pH<10.5. The adsorption mechanism is interpreted as a ligand-exchange process, and a surface complex of monodentate nonprotonated species (≡La–OPO3) has been identified by FTIR for LO. The adsorption of phosphate is quite selective, especially for LO. The dosages required to lower a phosphate concentration level of around 5.0mg P/L to <0.5mg P/L were determined as 0.08–0.1g/L for LO and 1.2g/L for AAO, respectively. The adsorbed phosphate could be completely desorbed by treatment with 0.1M NaOH for AAO, while for LO both acid treatment (0.5M HCl) and basic treatment (12.5M NaOH) were viable.