Micro/nanostructured hydroxyapatite structurally enhances the immobilization for Cu and Cd in contaminated soil

The presence of high copper (Cu) and cadmium (Cd) contamination in soils around mining areas has raised serious health concerns. Improving hydroxyapatite (HAP) adsorption capacity for Cu and Cd is important if its application potential in heavily contaminated soils is to expand. The micro/nanostructured HAP (mnHAP) was synthesized using a template-induced method to improve the HAP immobilization of Cu and Cd in contaminated soils. Commercial and synthetic HAPs were evaluated as amendments in Cu and Cd remediation tests with 1.5 and 3.0 % addition level for 90 days, and soils without HAP materials (0.0 %) were designated as the controls; each treatment was repeated three times. The materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N-2 adsorption, and scanning electron microscopy (SEM)-energy-dispersive spectra (EDS) and then quantitatively determined the Cu and Cd contents by inductively coupled plasma (ICP) and inductively coupled plasma mass spectrometry (ICP-MS). The mnHAP was more effective in immobilizing Cu and Cd than the two commercial HAPs. After treatment with mnHAP at the 3.0 % addition level for 90 days, the contaminated soils showed 55.2 and 84.8 % reductions in Cu and Cd concentrations in the toxicity characteristic leaching procedure (TCLP) leaching procedure, respectively. The experimental data indicated that the enhanced Cu and Cd immobilization by mnHAP was due to the increases of surface area and the improvement of structure and newly introduced carboxylate groups on its surface. These findings show that regulating the structure and surface properties of HAP can enhance Cu and Cd immobilization in soils.