Kinetics modeling in liquid phase sorption of copper ions on brushite di-calcium phosphate di-hydrate CaHPO₄·2H₂O (DCPD)

Abstract

The sorption behavior of copper ions Cu²⁺ from aqueous solution on calcium phosphate DCPD was studied in static conditions, using batch experiments. The reaction process has shown the occurrence of two major steps. During the first interaction minutes, a rapid process occurred and led to removal of over 70% of copper ions by diffusion at the solid–solute interface. In the second step, the equilibrium was reached slowly after 300–400 min of reaction. Using the surface kinetic modeling, the experimental data was found to follow the pseudo-first-order model, which suggests the predominance of the chemisorption-type process, corresponding to a cation-exchange reaction between Cu²⁺ in solution and Ca²⁺ present in the phosphate structure. The sorption isotherm study has shown a well fit of the experimental data with the Sips model, with parameters indicating a single surface layer sorption mechanism and a maximum retention capacity of 309 mg/g when using low concentrations of reactants. At higher concentrations of Cu²⁺, the pH of solutions decreases and the system becomes heterogeneous due to the partial dissolution of calcium phosphate DCPD.

Keywords:

• Calcium phosphate brushite
• Kinetic modeling
• Copper
• Isotherm models

Acknowledgment

The authors are grateful for the financial support of this project by research Grant (SCH04/09) of University of Mohammed V-Agdal, Morocco.