Removal of uranium from aqueous solution by a permeable reactive barrier loaded with hydroxyapatite-coated quartz sand: Implication for groundwater remediation

Uranium (U) contamination has been widely found in groundwater and greatly threatens human health. The present study investigated U removal from aqueous solution using a permeable reactive barrier (PRB) with hydroxyapatite as a reactive material under appropriate conditions. Different-size hydroxyapatites were loaded to quartz sand and the mineral composition of the composite materials was identified by XRD before being applied to column experiments and after adsorption U. Results showed that U removal processes were influenced by sorbent particle size, initial U concentration and hydraulic loading, and initial U concentration exerted the greatest effect on U removal efficiency. Uranium sorption data were fitted to Thomas and Yoon-Nelson models. The fitting results indicated that Thomas model was better than Yoon-Nelson model for description of U sorption characteristics in this study, which had higher correlation coefficients (> 0.97). Adsorbed U formed plate-like crystals and occurred widely on the surface of hydroxyapatite, as visualized by SEM. Determination of XPS and EDS in samples with high U concentration implied that U adsorption was achieved via either dissolution-precipitation reactions involving low-solubility U-bearing minerals or surface complexation with reactive function groups on the surface of hydroxyapatite, which was supported by U speciation calculated at equilibrium atmospheric CO2 and U solid phases. The findings suggest that the hydroxyapatite-based PRB can serve as an effective treatment technique for remediation of U contaminated groundwater.