Biosorption of Cr(VI) Ions onto Walnut Flowers: Application of Isotherm Models

Biosorption of Cr(VI) ions onto Walnut Flowers (WF) is studied in a batch system in relation to the physical parameters. The efficiency approaches 100% with 5 g WF/L at pH~1.5  for a Cr(VI) concentration of 100 mg/L in less than 1 h. The experimental data are analyzed using two-parameter models (Langmuir, Freundlich, and Temkin), and three-parameter models (Redlich–Peterson, Sips, and Toth). In order to determine the best isotherm, two error analysis methods are used to evaluate the correlation coefficient and chi-square test. The error analysis demonstrates that the three-parameter models better describe the Cr(VI) biosorption data. The Sips equation provides the best fitting. The possible interaction between the Cr(VI) and the biosorbent surface was evaluated by FT-IR analyses. Overall, the proposed biosorbent material was successfully used for the removal of a Cr(VI) from contaminated solutions.