A Study on the Removal of Chromium(VI) from Waste Solutions by Adsorption on to Sawdust in Stirred Vessels

The ability of sawdust to adsorb chromium(VI) from waste solutions has been studied in a batch reactor under forced convection conditions. Variables investigated were the rotational speed of the impeller, the initial concentration of chromium(VI) in solution and the weight and particle diameter of the sawdust. Increasing both the rotational speed of the impeller and the initial concentration of chromium(VI) in solution led to an increase in the volumetric mass transfer coefficient (k) according to the relationships k ∝ ω)^0.71 and k ∝ C^0.26, where ω is the rotational speed of the impeller (rev./min) and C₀ is the initial concentration of chromium(VI) in solution (mg/dm³). On the other hand, the volumetric mass transfer coefficient was found to decrease with increasing particle diameter of sawdust (d_p) according to the relationship k ∝ d_p^−0.87. The removal of chromium(VI) was also found to be significantly dependent on the weight of sawdust. Analysis of the equilibrium isotherm data has been undertaken using the Freundlich and Langmuir equations. The maximum adsorption capacity of sawdust for chromium(VI) was found to be 4.44 mg/g.