International Research Journal of Pure and Applied Chemistry

This study examines the removal of Cr⁶⁺ from aqueous solutions using unmodified and oxalic acid modified African yam bean (AYB) pod and groundnut (G’NUT) shell as adsorbents. The effects of time, pH, temperature, and metal ion concentration were investigated. The amount of metal ions adsorbed increased as the initial concentration increased; groundnut shell gave a better adsorption capacity. Maximum uptake was recorded at pH of 6.0 whereas uptake level decreased at pH greater than 6.0. Kinetic studies showed that the physisorption reaction rates could be described better by a pseudo-second order model with R² values close to 1. Various thermodynamic parameters such as ∆G^o, ∆S^o, and ∆H^o were calculated. The values obtained for ∆G^o were all negative for both adsorbents; indicating that the sorption processes investigated was spontaneous. Findings showed that an increase in temperature results in a lower metal loading per unit weight of the adsorbents, suggesting exothermic nature of the process. The process was also examined in terms of Freundlich adsorption model which showed R² values between 0.6952 and 0.9956. From the parameters considered, it was revealed that the modification of the adsorbents with oxalic acid enhanced their adsorption capacity.