Kinetic and thermodynamics of chromium ions adsorption onto low-cost dolomite adsorbent

The chromium bearing wastewater in this study was used to simulate the low concentration discharge from a major aerospace manufacturing facility in the UK. Removal of chromium ions from aqueous solutions using raw dolomite was achieved using batch adsorption experiments. The effect of; initial Cr(VI) concentration, amount of adsorbent, solution temperature, dolomite particle size and shaking speed was studied. Maximum chromium removal was found at pH 2.0. A kinetic study yielded an optimum equilibrium time of 96h with an adsorbent dose of 1g/L. Sorption studies were conducted over a concentration range of 5-50mg/L. Cr(VI) removal decreased with an increase in temperature (q _max: 20°C=10.01mg/g; 30°C=8.385mg/g; 40°C=6.654mg/g; and 60°C=5.669mg/g). Results suggest that the equilibrium adsorption was described by the Freundlich model. The kinetic processes of Cr(VI) adsorption onto dolomite were described in order to provide a more clear interpretation of the adsorption rate and uptake mechanism. The overall kinetic data was acceptably explained by a pseudo first-order rate model. Evaluated ΔG ^o and ΔH ^o specify the spontaneous and exothermic nature of the reaction. The adsorption takes place with a decrease in entropy (ΔS ^o is negative).