Kinetic and adsorption behaviour of aqueous cadmium using a 30 nm hydroxyapatite based powder synthesized via a combined ultrasound and microwave based technique

The removal of heavy metals such as cadmium from contaminated waterways and soils is a very important aspect of environmental remediation. This study investigated the kinetic and adsorption performance of a nanometre scale hydroxyapatite (HAP) synthesised from a combined ultrasound and microwave based technique for the removal of cadmium from an aqueous salt solution. Parameters such as contact time, initial pH, initial cadmium concentration and temperature were investigated. The Freundlich isotherm resulted in a more precise modelling of the communicated experimental data. Maximum monolayer adsorption capacity of absorber was found to be 123.45 mg/g at 298 K. Kinetic studies established cadmium adsorption tended to follow a pseudo-second order model and intra-particle diffusion played a significant role in determining the rate. Adsorption was endothermic, spontaneous and resulted in structural changes to the HAP matrix. The structural changes were investigated using both X-ray diffraction and field emission scanning electron microscopy