Behavior and Mechanism of Uranium Removal from Acidic Uranium-Contaminated Groundwater by Sandstone Particle/Hydroxyapatite Composite
Acidic in-situ leaching of sandstone-type uranium deposits leaves residual acid and uranium in groundwater, posing environmental risks. This study investigated the feasibility of loading hydroxyapatite (HAP) onto aquifer sandstone particles for in-situ remediation. Sandstone particles were collected from an aquifer and reacted with a HAP-generating solution for 52 days to produce sandstone/HAP composite. Batch experiments examined the effects of initial pH, initial uranium concentration, composite dosage, and interfering ions on uranium removal. Results showed successful HAP loading on sandstone surfaces. At initial pH 3, uranium concentration 5 mg/L, composite dosage 3 g/L, and 24 h reaction, uranium removal reached 95.6%. Interfering ions suppressed removal in the order Fe3+ > Mn2+ > Ca2+ > Mg2+ > SO4^2-. Removal mechanisms included electrostatic adsorption, ion exchange, and dissolution-reprecipitation, with good stability of immobilized uranium. This work validates the concept of in-situ HAP loading in aquifers and provides a basis for practical application in acidic uranium-contaminated groundwater remediation.