Kinetic and thermodynamic studies of the Adsorption of cr (vi) onto some selected local Adsorbents

Abstract

Adsorption is one of the most widely applied techniques for environmental remediation of Cr (VI). Waste effluent containing Cr (VI) causes a serious environmental problem. Commercially available activated carbon adsorbents are the one that usually applied for the removal of Cr (VI). However; these adsorbents are expensive materials and need to be replaced by cheaper but effective adsorbents. In this study, locally available biomasses obtained from avocado kernel seeds, juniperus procera sawdust and papaya peels were investigated as adsorbents for the removal of Cr (VI). The study employed batch method to investigate the efficiency of the adsorbents. Parameters that influence adsorption such as: effects of pH, adsorbents dose, initial concentration, contact time, and temperature were optimized (pH: 1 for all of untreated and activated carbon of juniperus procera sawdust adsorbents, 2 and 3 for activated carbon of avocado kernel seeds and papaya peels found optimal respectively, adsorbents dose: 0.5 g, [Cr (VI)]: 5 mg/L, contact time: 160 min and temperature: 40 oC). To understand the adsorption isotherm, the Langmuir and Freundlich adsorption isotherm models were investigated and the data was found best fit to Freundlich isotherm model indicating that the heterogeneity of the adsorbents surface. Kinetic studies were made and the pseudo-second order kinetic model was found to be more suitable for describing the experimental data. Thermodynamic parameters (ΔGo , ΔHo and ΔSo ) have also been calculated and found that the adsorption process as feasible, spontaneous and exothermic in nature. The positive values of the entropy change suggest that the increased randomness at solid-liquid interfaces during the adsorption. Finally, the efficiencies of the adsorbents towards the removal of chromium from tannery wastewater were also examined and it was found as they have capacity to remove chromium from wastewater solution. Keywords: Adsorption; adsorbents; chromium (VI); isotherms; Adsorption kinetic; thermodynamic of adsorption.