Sorption/desorption of aqueous mercury ions [Hg2+] onto/from sulfur-impregnated attapulgite: Process optimization, co-existing anions and regeneration studies

Present study proposed a sorption and desorption approach of aqueous mercury ion (Hg2+) on sulfur impregnated attapulgite (ATPS) adsorbent. Morphological characterization of natural and impregnated ATP confirmed the mesoporous nature of ATPS-adsorbents. The presence of various types of functional groups on the surface of ATPS was confirmed by using the zeta-potential measurement, X-ray fluorescence (XRF), and FT-IR analysis. Batch adsorption tests were carried out to detect the optimum condition of temperature for sulfur impregnation, and the results illustrated that the best adsorbent (ATPS-500) produced via the impregnation at 500 °C, with the highest equilibrium uptake of Hg2+ at initial pH 7. Different parameters like solution pHo, initial concentration of mercury (Co), temperature (T), contact time (t) and the effect of co-existing ions were optimized. Optimum pH and equilibrium contact time at the optimum dose of adsorbent (m) = 0.02 g in 50 mL and Co = 2.0 mg L − 1 were found to be pH~5 and 24 h at T = 313 K for ATPS-500.The best representation of adsorption kinetic was followed by the pseudo-first order kinetic model. The adsorption of Hg2+ions onto ATPS-500 was found to be endothermic. The heat of adsorption and changes in the entropy of Hg2+ions sorption on ATPS-500 were determined as 10.35 kJ mol−1 and 0.16 kJ mol−1 K − 1, respectively. Thermal regeneration represented that ATPS-500 was used for five desorption–sorption cycles with excellent efficiency of Hg2+ in each cycle.