Selective removal of chromium (VI) from water by Dowex 1X8: Optimization operating conditions

Abstract

The chromium is a metal that is widely used in industry. This is the so-called hexavalent form which is more problematic because in this form, chromium is very toxic. The removal of chromium (VI) from aqueous solutions by a strong anion exchange resin Dowex 1X8 was investigated in this paper. Batch adsorption studies were conducted to evaluate the effect of various physico-chemical parameters such as initial pH, initial       Cr (VI) concentration, adsorbent dosage, contact time and temperature. In order to optimize the effect of the main parameters and their mutual interaction for the adsorption process, a full factor design of the type 2^k has been used. The adsorbent dose of resin and pH are the most significant parameter affecting chromium (VI) adsorption.

The adsorption isotherms were correlated with the Langmuir, Freundlich, Dubinin-   Redushkevich and Temkin models. The different parameters of each model were calculated.

Various thermodynamic parameters such as standard Gibbs free energy (DG°), standard enthalpy (DH°), and standard entropy (DS°) were also determined. These parameters showed that Cr (VI) adsorption is a spontaneous and exothermic process. The kinetic process was evaluated by first–order, second–order and Elovich kinetic models. Attractively, Dowex 1X8 resin demonstrated a preferable absorption toward Cr (VI) in the presence of competing anions, such as in aqueous solutions.