Sorption of Hg(II) from aqueous solutions onto Carica papaya:: Application of isotherms

The biosorption potential of Carica papaya for mercury from aqueous solutions was investigated. The biomass exhibited the highest mercury sorption capacity at optimum conditions of pH 6.5 and biomass dosage of 1.0 g/L. To predict the biosorption isotherms and to determine the characteristic parameters for process design, seven single and two parameter isotherm models-Henry's law, Freundlich, Langmuir, Dubinin-Radushkevich, Temkin, Halsey, and Gin-six three-parameter equations-the Redlich -Peterson, Sips, Khan, Radke-Prausnitz, Toth, and Koble-Corrigan-and four- and five-parameter isotherm equations of Fritz and Schluender isotherm models were applied to experimental data. Three error analysis methods were used to evaluate the experimental data, viz., correlation coefficient, standard error (SE), and sum of squares error (SSE) of the estimate, to find the best fitting isotherm. The best fitting isotherms were found to be Langmuir, Khan, and Fritz - Schluender among the two-, three-, and five-parameter models, respectively. The amide groups of the biomass are involved in chemical interaction with the mercury ion forming a cagelike structure depicted by scanning electron microscopic (SEM) and Fourier transform infrared spectroscopic (FTIR) results.