Kinetics of Cadmium Adsorption by Bentonite and Nanobentonite in the Presence of Humic Acid

Heavy metals pollution is one of the major environmental concerns in the world, as these metals are a threat to humans, animals, and plants due to their toxicity. Clay minerals which are a major component of the soil, play an important role in the absorption of various contaminants in soil and water. Bentonite (B) and its modified forms have a much higher capacity to adsorb toxic metals than other clays. This experiment was accomplished in a completely randomized design in a factorial arrangement with three replications. The experimental treatments consisted: time (5, 10, 20, 30, 60, 120, 240 min), B and nanobentonite (NB) adsorbents (2 g l-1) and humic acid concentrations (0, 100 and 500 mg l-1). The results showed that humic acid increased Cd adsorption by B and NB in different times. The highest amount of Cd adsorption by B adsorbent was 4370 mg kg-1 recorded in 500 m l-1 humic acid treatment and the lowest amount of adsorption was observed in the absence of humic acid 1134 mg.kg-1 by bentonite adsorbent. Semi second-order kinetic model was significantly fitted to Cd adsorption by B and NB in all of the humic acid concentrations (R2 for all three levels of humic acid in bentonite adsorbent and treatment of 100 mg.l-1 humic acid in nano bentonite adsorbent was 0.99,  for treatment of zero and 500 mg l-1 humic acid was 0.97 and 1.00, respectively). The results of current study showed that humic acid could markedly promote the Cd adsorption by adsorbents, which had a greater effect on the adsorption of B than NB.