Kinetic and thermodynamic studies on biosorption of Cr(VI) on raw and chemically modified Datura stramonium fruit.

Biosorption of Cr(VI) on sulfuric and phosphoric acid-treated Datura stramonium fruit was investigated in batch mode. The various parameters that influence the biosorption process such as Cr(VI) initial concentration, biosorbent dosage, contact time, temperature, and pH value were optimized. Both linear and non-linear regression analysis of isotherm data suggest that Langmuir isotherm model mimics the behavior of Cr(VI) ion biosorption onto Datura stramonium fruit biosorbent. The maximum Cr(VI) ions adsorption capacity of 138.074 mg/g at pH 2 is achieved with phosphoric acid treated Datura stramonium (PDSF). The kinetics of adsorption process is well described by pseudo-second-order model with high R2 and low χ2 value. The estimated activation energy of < 8 kJ/mol obtained for both raw and chemically modified adsorbents suggests that the adsorption occurs mainly via physisorption. Besides, thermodynamic results reveal that biosorption of Cr(VI) on both treated and untreated Datura stramonium was endothermic, spontaneous, and randomness in nature.