A green approach for the removal of Sr(II) from aqueous media: Kinetics, isotherms and thermodynamic studies

Adsorption efficiency of native, NaOH-treated and immobilized peanut husk and sugarcane bagasse for Sr(II) removal was studied in batch mode. In view of promising adsorption efficiency of peanut husk versus sugarcane bagasse, the biosorption behaviour of the Sr(II) ions onto peanut husk (native and modified) was studied as a function of pH, biosorbent dose, contact time, initial metal ion concentration and temperature for the maximum removal of Sr(II) ions. Linear and non-linear pseudo-first and second-order kinetic models were applied and value of R² and six non-linear regression error functions, namely hybrid fractional error function (HYBRID), Marquardt's percent standard deviation (MPSD), average relative error (ARE), the sum of the errors squared (ERRSQ/SSE), the sum of the absolute errors (EABS) and Chi-square test (χ²) were used to predict the most optimum kinetic model. Sorbent-sorbate reaction nature was estimated by fitting equilibrium data by non-linear and transformed linear forms of the Langmuir, Freundlich and Redlich-Peterson isotherms and most optimum isothermal model was optimized by comparing linear and non-linear R² value and non-linear regression error functions. HCl proved most successful eluating agents for sorbed Sr(II) ions. Biosorption characteristics and effectiveness of the process was also confirmed by Fourier transform infra-red spectroscopy (FTIR), scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDX). In view of promising efficiency of peanut husk as an adsorbent, it could possibly be used for the removal of Sr(II) ions from aqueous medium and is also extendable to other radionuclide.