Adsorptive removal of copper (II) from aqueous solutions on phosphates: equilibrium, kinetics, and thermodynamics

Abstract

Limit of World Health Organization standard for safe amount Cu(II) in drinking water is 5 mg/L. The large usage of this material is reported to be the cause of various environmental and health hazard. Adsorption process that stands for the most common techniques due to its low cost and relative high efficiency, could perform its removal from wastewater. However, the most common adsorbents remain expensive compared with other potential natural and available adsorbents. In this work, natural and synthetic phosphates are tested for their efficacy to remove Cu(II) from contaminated water solution. Results were compared with those found with activated carbon used as reference. Effect of pH, adsorbent doses, temperature, and initial concentrations on the uptake of Cu ions by the adsorbent were examined based on statistical experimental design. Physical treatment was made to increase adsorption capacity of the tested adsorbents. The thermodynamic parameters such as free energy (ΔG°), enthalpy (ΔH°), and entropy changes (ΔS°) for the adsorption of Cu(II) were computed to predict the nature of adsorption process. Adsorption isotherms were determined and correlated with common isotherm equations such as Langmuir and Freundlich models. Adsorption data related to the two types of phosphate fit well pseudo-order model. Data confirm also net increase in adsorption with pH, adsorbent doses, while it decreases with an increase in initial concentration of copper. Variation of standard enthalpy (∆H°) and entropy (ΔS) were beyond zero. This indicates clear tendency of the adsorption process to randomness in the solid/solution interface and reflects exothermic nature of the process, while the negative value of standard free energy variation indicates spontaneous process. Langmuir model fitted much better than the Freundlich model. These materials were found to be promising as potential adsorbents for the removal of Cu(II) from aqueous solution.

Keywords:

• Activation
• Adsorption
• Copper
• Hydroxyapatite
• Experimental design
• Phosphates

Acknowledgement

We thank the “National Center for Scientific and Technical Research” in Rabat (Morocco) for their support by the Excellence Scholarship.

Notes

Presented at the 7th International Conference on Water Resources in the Mediterranean Basin (WATMED7) 8–11 October 2014, Marrakesh, Morocco