Removal of mercury(II) from aqueous solutions and chlor-alkali industry effluent by steam activated and sulphurised activated carbons prepared from bagasse pith: kinetics and equilibrium studies

Abstract

The adsorption of mercury from aqueous solutions and chlor-alkali industry effluent on steam activated and sulphurised steam activated carbons prepared from bagasse pith have been studied comparatively. The uptake of mercury(II) (Hg(II)) was maximum by steam activated carbon in presence of SO 2 and H 2S (SA–SO 2–H 2S–C) followed by steam activated carbon in presence of SO 2 (SA–SO 2–C), steam activated carbon in presence of H 2S (SA–H 2S–C) and steam activated carbon (SA–C) at the same concentration, pH and temperature of the solution. Adsorption experiments demonstrate that the adsorption process corresponds to the pseudo-second-order kinetic model and equilibrium results correspond to the Langmuir adsorption isotherm. Kinetic parameters as a function of initial concentration, for all adsorbents were calculated. Batch studies indicated that the optimum pH range for the adsorption of Hg(II) on sulphurised carbons was between 4 and 9 and for sulphur free carbon was between 6 and 9 at 30 °C. The adsorptive behaviour of the activated carbons is explained on the basis of their chemical nature and porous texture. Decrease in ionic strength and increase in temperature of the solution has been found to improve the uptake of Hg(II). Synthetic and chlor-alkali industrial wastewaters were also treated by sulphurised activated carbons to demonstrate their efficiencies in removing Hg(II) from wastewaters. Some feasibility experiments have been carried out with a view to recover the adsorbed Hg(II) and regenerate the spent activated carbons using 0.2 M HCl solution. The data obtained point towards viable adsorbents, which are both effective as well as economically attractive for Hg(II) removal from wastewaters.