Kinetic and thermodynamic studies on biosorption of Cr(VI) on raw and chemically modified Datura stramonium fruit Shravan Kumar & Tasrin Shahnaz & N. Selvaraju & Prasanna Venkatesh Rajaraman Received: 29 March 2019 /Accepted: 24 February 2020 # Springer Nature Switzerland AG 2020 Abstract Biosorption of Cr(VI) on sulfuric and phos- phoric acid–treated Datura stramonium fruit was inves- tigated in batch mode. The various parameters that influence the biosorption process such as Cr(VI) initial concentration, biosorbent dosage, contact time, temper- ature, 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 ca- pacity 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 R 2 and low χ 2 value. The estimated activation energy of < 8 kJ/mol obtained for both raw and chemically modified adsor- bents 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. Keywords Biosorption . Chromium (VI) . Physico- chemical . Thermodynamics . Kinetics . Datura stramonium Introduction Environmental pollution is the result of rapid urban- ization, globalization, industrialization, and unprec- edented increment of the population. Water pollution is one of the vital issues that the humanities face today. The emerging economics of the societies in terms of industry, agriculture, and several facilities depend on indispensable resources of water. Pollu- tion is the adverse changes in the environment by the introduction of contaminants as well as of for- eign entities. Various industries discharge their ef- fluent without proper treatment into the river stream, in the ocean, and in open land. Discharging of effluents containing heavy metal (metals having spe- cific weight more than 5 g/cm 3 ) from industries is of Environ Monit Assess (2020) 192:248 https://doi.org/10.1007/s10661-020-8181-x Highlights • Datura stramonium fruit was used as novel biosorbent for the biosorption of Cr(VI). • The maximum Cr(VI) uptake on RDSF, SDSF, and PDSF biosorbents obtained was found to be 85.916, 119.632, and 138.074 mg/g respectively at optimum pH 2.0. • The observed free energy (ΔG° (kJ/mol)) values were - 0.249, - 0.026, and - 0.107 for RDSF, PDSF, and SDSF biosorbents re- spectively. • The Langmuir isotherm and pseudo-second-order kinetics models mimic the biosorption behavior of Cr(VI). • The activation energy onto RDSF, SDSF, and PDSF adsorbent was estimated to be 0.192, 7.632, and 7.794 kJ/mol respectively S. Kumar : P. V. Rajaraman (*) Department of Chemical engineering, Indian Institute of Technology Guwahati, Guwahati, Assam, India e-mail: rprasanna@iitg.ac.in T. Shahnaz : N. Selvaraju (*) Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati, Assam, India e-mail: selva@iitg.ac.in