Heavy metals biosorption by Thapsia transtagana stems powder: Kinetics, equilibrium and thermodynamics

Abstract

The present study investigates the biosorption potential of natural and low-cost biosorbent Thapsia transtagana stems (TTS) form for the removal of cadmium (II) and cobalt (II) ions from aqueous solution. The surface of TTS has been thoroughly characterized by FTIR spectroscopy, scanning electron microscopy–energy-dispersive X-ray spectroscopy, Boehm titration, and point of zero charge. Batch biosorption experiments were carried out to evaluate the effect of process parameters, viz solution pH, biosorbent dosage, contact time, initial metal ion concentration and temperature on the biosorption of Cd(II) and Co(II) ions using the biosorbent. Experimental results show that, the biosorption process is very rapid and the biosorption yield increases with an increase in biosorbent dosage. Maximum biosorption was occurred at pH between 6 and 7. Kinetic data were properly fitted with the pseudo-first-order model instead of pseudo-second-order model. Biosorption isotherms were best correlated with Langmuir model than with Freundlich model. The biosorption of the metals ions was exothermic in nature (ΔH° = –20.10 kJ/mol for Cd(II) and –20.87 kJ/mol for Co(II)). When the temperature was increased from 25°C to 55 °C, the reaction was accompanied by a decrease in entropy (ΔS° = –73.42J/K.mol for Cd(II) and –84.38 J/K.mol for Co(II)).