Evaluation of pyrolyzed areca husk as a potential adsorbent for the removal of Fe2+ ions from aqueous solutions

Abstract

The hurdle of valorisation of Arecanut husk on one side and the pollution of aquatic bodies by heavy metals like Iron on the other end are contemplated together in this study. The areca husk is pyrolyzed at 450°C for two hours to obtain Biochar. Batch adsorption studies were employed to investigate the effect of adsorbent dosage (2-10 g/l), initial concentration of adsorbate (1-5 mg/l) and contact time (30 -360 min) at temperature of 28±2 °C & pH4.0±0.2 on the removal of Iron from pyrolyzed areca husk. The adsorption capacity was found to increase with increase in initial Iron concentartion and contact time, but decreases with the adsorbent dosage. Langmuir, Freundlich, Temkin and Dubinin-Radushkevich Isotherms was used to analyse the equilibrium data. Langmuir and Dubinin-Radushkevich model best describe the uptake of Iron ions implying a monolayer adsorption with physisorption. Pseudo second order, exhibited the best fit for the effectiveness of Iron adsorbtion indicating the maximum limit of chemisorption. Thermodynamic studies indicated that the adsorption was spontaneous and exothermic in nature. The mechanisms responsible for adsorption of Iron on pyrolysed areca husk was conducted by SEM-EDAX, XRD and FTIR indicating oxidation and precipitaion of Iron into complex compounds of jarosite and ferrous hydroxy sulphates. In conclusion, pyrolyzed areca husk can be technically & economically feasible alternative adsorbent material.