Removal of Cd²⁺, Ni²⁺ and PO₄ ³⁻ from aqueous solution by hydroxyapatite-bentonite clay-nanocellulose composite

A novel hydroxyapatite-bentonite clay-nanocellulose (CHA-BENT-NCC) composite material was successfully prepared as adsorbent for the removal of Ni²⁺, Cd²⁺ and PO₄ ³⁻ from aqueous solutions. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive analysis of X-rays (EDAX), X-ray diffraction analysis (XRD) and Fourier-transform infrared spectroscopy (FTIR) were used for characterization of the adsorbent. The effect of pH, contact time, temperature, and initial adsorbate concentration were studied for optimization purpose. The adsorption behavior of the investigated ions were well described by the Freundlich adsorption model, and the maximum adsorption capacity for Ni²⁺, Cd²⁺ and PO₄ ³⁻ was estimated to be 29.46 mmol/g, 10.34 mmol/g and 4.90 mmol/g, respectively. Desorption efficiency was achieved by treatment with 0.01 M HNO₃ for metals and 0.10 M NaOH for PO₄ ³⁻. Five adsorption–desorption cycles were performed without significant decrease in adsorption capacities. The CHA-BENT-NCC material proved to be a very effective adsorption material for the treatment of mining water also from a copper mine in Finland.