Equilibrium, kinetic and thermodynamic studies for adsorption of As(III) on coconut (Cocos nucifera L.) fiber

• A new biosorbent using coconut fiber is developed for As(III) removal from water.
• 96.20% As(III) removal is obtained at optimised conditions.
• The As(III) adsorption follows Freundlich isotherm.
• The first order kinetic model fits well with constant (k1) 0.0069 min−1.
• Thermodynamic study reveals endothermic nature of As(III) adsorption.

Contamination of drinking water due to arsenic poses severe health problems. Investigation of Arsenite [As(III)] removal from water by adsorption on coconut fiber (Cocos nucifera L.) adsorbent was conducted in the present study. Surface area of the adsorbent was determined by the Brunauer–Emmett–Teller (BET) method and scanning electron microscopy (SEM) was used to analyze surface morphology of coconut fiber adsorbent before and after adsorption process. Equilibrium study revealed that the uptake increased almost linearly with increase in initial As(III) concentration. The data was analyzed for Freundlich and Langmuir isotherm models at varying initial adsorbate concentration (0.5 mg/L to 2.0 mg/L) and found that the adsorption of As(III) on coconut fiber adsorbent followed Freundlich isotherm. Freundlich isotherm constants ‘k’ and ‘n’ were found to be 0.118 mg/g and 3.571, respectively at adsorbent respectively at adsorbent dose of 10 g/L and ambient temperature 25 °C. Kinetics study showed that the equilibrium approached at contact time of 8 h. The data fitted well with the pseudo first order kinetic model. Estimated kinetic rate constant (k1) was 0.0069 min−1. Thermodynamic study indicated spontaneous and endothermic nature of As(III) adsorption.