Impact of Buffering Agent on Lead Adsorption of Bentonite: An Appraisal

Abstract

The knowledge of adsorption characteristics of bentonite (B) is mandatory for heavy metals removal from the wastewater and contaminant retention in landfill liner. Adsorption characterization of geomaterials requires the use of a buffer for pH adjustment. Previous studies have not investigated the impact of using a buffer on the adsorption characteristics of swelling soils such as B. This study quantified the influence of sodium acetate (Na-Ac) buffer on the adsorption capacity of B and percentage removal of lead (Pb2+) using a batch adsorption study (BAS). The solution was adjusted using either nitric acid or Na-Ac buffer to maintain pH=5. The sediment volume of bentonite suspension in water at pH 5 adjusted with Na-Ac buffer was less than that using nitric acid. The lesser sediment volume was due mainly to the agglomeration of bentonite particles in the presence of Na-Ac buffer. The experimental findings corroborate that the use of Na-Ac buffer results in a notable reduction of adsorption capacity and percentage removal of Pb2+ by B. The highest percentage removal of Pb2+ ions was observed at a liquid-to-solid ratio (L/S) of 20 when pH was adjusted with nitric acid. The lowest percentage removal was noted at L/S=100 when pH was maintained using Na-Ac buffer. The influence of Na-Ac buffer also was evaluated by conducting a BAS for Pb2+ removal under a competitive environment of Na+ using sodium chloride (NaCl) and Na-Ac buffer. The interaction of Pb2+ with B in two different environments was confirmed by mineralogical, morphological, and spectral analysis postadsorption. According to this study, nitric acid can be a better alternative to Na-Ac buffer for the adsorption study of B in a controlled pH environment. If a buffer is used for the adjustment of pH in a BAS, its effect on the adsorption capacity and percentage removal should be taken into account when characterizing B for its practical application in water decontamination, waste containment system, and chemical reactive barrier projects.