Simultaneous sorption of As, B, Cr, Mo and Se from coal fly ash leachates by Al³⁺-pillared bentonite clay: implication for the construction of activated geo-synthetic clay liner

The present study reports the optimum conditions for intercalating the Al³⁺ species to bentonite clay matrices and evaluate the potential of using Al³⁺-modified bentonite clay (Alum-Bent) for removal of oxyanionic species of As, B, Cr, Mo and Se from coal fly ash (FA) leachates. Removal of oxyanionic species was done in batch experimental procedures. Parameters optimized were: contact time, adsorbent dosage, concentration and pH. The adsorption affinity of Al³⁺-bentonite clay for oxyanionic species varied as follows: B ≈ Se > Mo > Cr ≈ As respectively. The adsorption data fitted better to Langmuir adsorption isotherm than Freundlich adsorption isotherm hence confirming mono-site adsorption. The adsorption kinetics fitted well pseudo-second-order kinetic model hence confirming chemisorption. The fact that most of the oxyanion were adsorbed at pH ≥ pHpzc indicated that both electrostatic and chemical interactions occurred with the clay surface and interlayers. The Al³⁺-modified bentonite clay successfully removed oxyanion species from generated coal FA leachates. This study shows that Al³⁺-modified bentonite clay is an effective adsorbent for oxyanion species in coal FA leachates and could be applied as a reactive barrier in coal FA retention ponds.