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 ²⁺ ) as a model contaminant. The maximum adsorption capacity of BB was obtained as 55 mg g ^-1 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 ²⁺ percentage removal, while adsorption capacity decreased. Ionic strength, salt concentration, valency and ionic radius played a critical role in suppressing the adsorption of Pb ²⁺ . 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 ²⁺ 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 ²⁺ on BB. Based on the thermodynamic analysis, it was noted that Pb ²⁺ adsorption on BB is exothermic, spontaneous and adsorption reaction is less favorable at a higher temperature.
Competing Interests: Declaration of Competing Interest The authors declare that there are no competing financial interests.
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