Removal of Mo(VI) from aqueous solutions using sulfuric acid-modified cinder: kinetic and thermodynamic studies

Abstract

Removal of Mo(VI) from aqueous solutions was investigated using cinder modified by sulfuric acid. Various parameters such as pH, agitation time, Mo(VI) concentration, and temperature have been studied. The maximum adsorption of Mo(VI) occurred at pH between 4.0 and 6.0. Kinetic studies showed that the adsorption generally obeyed a pseudo second-order model. The activation energy was 31.4 kJ mol⁻¹, indicating that the adsorption process was governed mainly by interactions of physical nature. Furthermore, application of Langmuir and Freundlich isotherm models to the adsorption equilibrium data showed that the adsorption behavior obeyed the Langmuir model. The adsorption capacity was found to be 10.8 g Mo(VI) kg⁻¹ adsorbent. Finally, thermodynamic parameters such as ΔH ⁰, ΔS ⁰, and ΔG ⁰ were also evaluated, which showed that the adsorption of Mo(VI) on the treated cinder was endothermic, entropy increasing, and spontaneous. In conclusion, the sulfuric acid-modified cinder was shown to be an inexpensive, effective, and simple adsorbent for the removal of Mo(VI) from water.

Keywords:

• adsorption
• Mo(VI) removal
• cinder
• kinetics
• thermodynamic

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Acknowledgments

The authors thank the anonymous reviewers, as well as the editor in chief, Prof. Hartmut Frank, for their editorial comments and suggestions, which improved the manuscript considerably. We also acknowledge financial support for this research from the National Natural Science Foundation of China (No. 50979012) and the Geping Greenness acid action-123 Project (CEPF 2008-123-1-6). The authors also would like to acknowledge Dr Rui for her collaboration in the production of the manuscript.