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

•Activated aluminum oxide (AAO) and lanthanum oxide (LO) had high P removal ability.•P adsorption capacity was 20.88 mg/g for the former and 46.95 mg/g for the latter.•Efficient phosphate removal was achieved at pH <~ 5.0 for AAO and pH <~ 10.5 for LO.•The adsorption by the oxides was interpreted by the ligand exchange mechanism.•Adsorbed P could be recovered by acid treatment or basic treatment.

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 20.88 mg/g and 46.95 mg/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 5.0 mg P/L to < 0.5 mg P/L were determined as 0.08–0.1 g/L for LO and 1.2 g/L for AAO, respectively. The adsorbed phosphate could be completely desorbed by treatment with 0.1 M NaOH for AAO, while for LO both acid treatment (0.5 M HCl) and basic treatment (12.5 M NaOH) were viable.

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