Biosorption of Hg(II) ions, Congo red and their binary mixture using raw and chemically activated mango leaves

Abstract

This study reports the investigation performed by comparing the ability of raw and treated mango leaves powder (with potassium persulphate, K2S2O8) to adsorb Hg2+, Congo red dye and their binary mixture from their aqueous solutions through batch experiments. Both adsorbents were characterized by Fourier-transform infrared spectroscopy to reveal the active sites of both adsorbent. The experimental parameters such as pH, contact time, adsorbent dosage, initial concentration and temperature were investigated. The maximum removal of Hg2+, Congo red and binary mixture obtained were 42.86%, 54.72% and 62.5% using raw mango leaves powder and 64.29%, 81.25% and 63.82% using treated mango leaves respectively at pH 7. The experimental data better fit the Langmuir isotherm model for binary mixture adsorption on both adsorbent, the Freundlich isotherm model for Congo red dye adsorption on raw adsorbent and Hg2+ adsorption on both adsorbents, the Brunauer–Emmett–Teller isotherm model for Congo red adsorption onto the treated adsorbent. Kinetic data were best fit to a pseudo-second-order rate equation except the adsorption of Congo red onto untreated adsorbent that supported pseudo-first-order rate equation. Thermodynamic parameters shows that adsorption of binary mixture onto treated adsorbent and Hg2+ adsorption on both adsorbents were spontaneous and endothermic in nature while adsorption of binary mixture onto untreated adsorbent and Congo red adsorption on both adsorbents were non-spontaneous and endothermic in nature between temperatures of 30 and 60 °C. This study revealed a great potential of raw and treated mango leaves in the effective removal of Hg2+, Congo red and their binary mixture from waste water.