application of modified bentonite for efficient water purification: a case of cr(vi) adsorption

This study explores the use of acid-activated bentonite as an efficient adsorbent for removing hexavalent chromium (cr(vi)) from water. acid activation enhances the surface area and adsorption capacity of bentonite, improving its water treatment efficiency. various techniques, including bet, ft-ir, xrd, xrf, and sem, were used to analyze structural and compositional changes after activation. adsorption experiments showed that under optimal conditions - room temperature, 0.1 ppm cr(vi), and 1 g of acid-activated bentonite - 100 % removal was achieved. the adsorption followed the langmuir isotherm with a maximum capacity of 0.122 mg.g-1. kinetic studies confirmed a pseudo-second-order reaction model (r² = 0.99), indicating a chemisorption mechanism. thermodynamic analysis showed the process is spontaneous and exothermic, requiring no external energy input. groundwater tests from the forumad region (semnan province) compared raw and acid-modified bentonite, revealing a 92 % cr(vi) removal efficiency with the modified form, reducing contamination to safe levels. these results highlight acid-activated bentonite as a cost-effective, eco-friendly adsorbent for water purification, demonstrating its real-world potential for ensuring safer drinking water.