Assessment of the Adsorption Capacities of Fired Clay Soils From Jimma (Ethiopia) For the Removal of Cr (VI) from Aqueous Solution

Abstract

The abilities of three thermally treated clay soils, S1, S2 and S3, which differed in textural compositions, to remove Cr (VI) from aqueous solutions were evaluated. Removal efficiencies of the clays were found to be influenced by textural composition, pH, initial Cr(VI) concentration, shaking time and adsorbent dose. An increase in the clay content of a clay-based soil by 1 % was found to result in an increase of about 0.5% in Cr(VI) removal. The adsorption of Cr(VI) by the clay-based soils was highest at pH 1 and 2 and, decreased above pH 2. For the lower initial concentrations (5 – 50 mg/L) of Cr(VI), adsorption was observed to increase sharply. A slower increase was observed up to about 75 mg/L and adsorption density remain nearly constant above 75 mg/L. The Cr(VI) adsorption process was better represented by the Langmuir model than by the Freundlich, with correlation coefficients (r2) ranging 0.97 to 0.99. The adsorption capacities (qm) of S3, S2 and S1 calculated by using the Langmuir model were 8.77 mg/g, 4.81 mg/g, and 4.74 mg/g, respectively. The kinetics of Cr(VI) adsorption followed the pseudo-second-order model as determined by the stronger correlation (r2 ranging from 0.971 to 0.992) and higher agreement between qe and qexp. Keywords: adsorption; clay soils; texture; adsorption kinetics; adsorption isotherm.