Removal of selenite using ‘waste’ Fe(III)/Cr(III) hydroxide: Adsorption kinetics and isotherms

Abstract

Removal of selenite [Se (IV)] from aqueous solution on to industrial solid ‘waste’ Fe(III)/Cr(III) hydroxide as adsorbent was investigated in the present article. Maximum adsorption was found to be at pH 4.0. Pretreated Fe(III)/Cr(III) hydroxide was found to be more efficient for the removal of selenite compared to untreated adsorbent. Langmuir and Freundlich isotherms have been studied. The Langmuir adsorption capacity (Q ₀) of the pretreated and untreated adsorbents was found to be 15.63 and 6.04 mg g⁻¹, respectively. The adsorption process fit into the second-order kinetics. Thermodynamic parameters show that the adsorption process is spontaneous and endothermic in the temperature range 32 to 60°C. Coexisting anions vanadate and phosphate significantly affect the adsorption of selenite for both the pretreated and untreated adsorbents. Molybdate, thiocyanate, sulphate, nitrate and chloride do not significantly affect the removal of selenite for pretreated adsorbent.

Keywords:

• Selenite
• adsorption
• kinetics
• isotherm
• temperature

Acknowledgements

The authors are grateful to Dr P. Weidler, Institute for Technical Chemistry, Karlsruhe Research Center (Germany) for the analysis of surface area and pore size distribution of the adsorbent. Grateful acknowledgement is due to DAAD, Germany for the equipment grant, which facilitated the experimental work.