Utilisation of Cymbopogon citratus (lemon grass) as biosorbent for the sequestration of nickel ions from aqueous solution: Equilibrium, kinetic, thermodynamics and mechanism studies

•Cymbopogon citratus (C. citratus) biomass was used as biosorbent for Ni2+ removal.•Equilibrium data were best represented by the Temkin isotherm.•Kinetic data were fitted well by the pseudo-second order model.•The Boyd model revealed that boundary layer diffusion was the controlling step.•Ni2+ biosorption by C. citratus was found to be endothermic in nature.

This study explored the potential of Cymbopogon citratus (C. citratus) as a new biosorbent for the removal of nickel (Ni2+) from aqueous media. The effects of biosorbent concentration, initial pH, initial concentration, contact time and temperature on Ni2+ biosorption were investigated. It was found that pH has a significant impact on the metal ion removal. Increasing biosorbent concentration up to 1 g/L, temperature up to 45 °C, initial concentration up to 150 mg/L and contact time up to 1 h resulted in the increase in Ni2+ biosorption. FTIR analysis demonstrated that hydroxyl, carbonyl, and alkyl halides groups present on C. citratus surface were involved in Ni2+ biosorption. The equilibrium data were fitted well by the Temkin model exhibiting lowest Chi-square, Marquardt's percent standard deviation and residual root mean square errors. The kinetic data were better represented by the pseudo-second-order than the pseudo-first-order kinetic model. Further data analysis by the intra-particle kinetic and Boyd models suggested that the biosorption rate was affected by Ni2+ transport across the boundary layer and intra-particle diffusion. Thermodynamic studies showed that the process was endothermic and non-spontaneous within the temperature range studied (25–45 °C). The results of this investigation suggest that C. citratus is an effective alternative biosorbent for Ni2+ removal.