Novel alkylammonium-enhanced bentonite for effective Cr removal from wastewater

The contamination of water resources by tannery wastewater containing Cr(III) presents significant public health risks due to its carcinogenic nature. Addressing this critical issue, the purpose of this research is to develop and evaluate novel alkylammonium-modified bentonite adsorbents for the efficient removal of Cr(III) from tannery wastewater. Batch experiments were conducted to investigate the effects of Cr concentration (0.02-0.2 mg/L), adsorbent dose (0.25-2.5 g/L), pH (2.0-8.0), and temperature (293-313 K) on adsorption performance. The alkylammonium modifications enhanced the surface area and ion-exchange capacity of bentonite by 40% and 50%, respectively. Optimal conditions for Cr adsorption were identified as 313 K, 1 g/L adsorbent dosage, pH 2.0, 30 min of reaction time, and 150 rpm of agitation speed. The Langmuir isotherm model (R² = 0.998 for trimethylammonium bentonite [TMB], 0.994 for triethylammonium bentonite [TEB]) confirmed monolayer adsorption, while negative Gibbs free energy values demonstrated the spontaneous nature of the process. Enthalpy changes (ΔH°) of 21.1 kJ/mol (natural Navbahor bentonite [NNB]), 26.7 kJ/mol (TMB), and 28.4 kJ/mol (TEB) indicated endothermic reactions. This work highlights the novelty of alkylammonium-modified bentonite as a cost-effective and scalable solution for reducing Cr(III) in wastewater, providing a promising pathway for sustainable water resource management. PRACTITIONER POINTS: Optimum conditions: 313 K, 1 g/L of dose, pH 2.0, 30 min of reaction, and 150 rpm of speed. Alkylammonium-modified bentonites remove 95% of Cr ions at pH 2.0 and 80% at pH 7.0. The adsorption capacity of modified bentonites is 19, 21, and 22 mg/g for NNB, TMB, and TEB. The modified bentonites retained 55% of their adsorption capacity after five regeneration cycles.