Adsorption characteristics of Barmer bentonite for hazardous waste containment application.

Low hydraulic conductivity and high chemical immobilization are the two characteristics that make bentonite a mandatory construction material for hazardous waste containment applications. We performed a comprehensive batch sorption study on Barmer bentonite (BB), an exclusive construction clay mined in India, using lead (Pb) as a model contaminant. The maximum adsorption capacity of BB was obtained as 55 mg g at pH 5 and 27 ± 2℃. Adsorption was extremely rapid, with equilibrium attained <5 min for the BB. Increased adsorbent dosage resulted in higher Pb percentage removal, while adsorption capacity decreased. Ionic strength, salt concentration, valency and ionic radius played a critical role in suppressing the adsorption of Pb. Clay fabric change was observed to be dispersed at low ionic strength and gradually attained aggregated face-to-face structures at high ionic strength. The simultaneous presence of other metals/salts strongly influenced Pb removal by BB, while divalent salt exhibited high suppression of adsorptive reaction at low concentrations. Sorption isotherm and kinetic modeling results indicated the possibility of chemisorption of Pb on BB. Based on the thermodynamic analysis, it was noted that Pb adsorption on BB is exothermic, spontaneous and adsorption reaction is less favorable at a higher temperature.