Evaluation of Pyrolyzed Areca Husk for the Removal of Ferrous Ions from Aqueous Solution

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 & pH 4.0±0.2 for 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 described 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. The results of the column studies suggest that the adsorption process is cost effective and can be scaled up to for continuous treatment of water. It was found that treatment efficiency improved with reduced flow rate and an increase in the height of adsorbent bed of the column. Maximum biosorption capacity of ferrous ions was observed as 0.487mg/g at bed depth of 3 cm; flow rate of 2 mL/min and initial concentration of 2 mg/L. PCA was also employed to predict the performance of the fixed bed column. It also indicated the same as the dynamic models. In conclusion, pyrolyzed areca husk can be technically & economically feasible alternative adsorbent material.