Enhanced aqueous phase arsenic removal by a biochar based iron nanocomposite

Abstract

Zerovalent iron nanoparticles (nZVI) were initially prepared via reduction of ferric chloride (FeCl3) using sodium borohydride (NaBH4) and then precipitated onto a biochar prepared from the pods of Cassia fistula via pyrolysis. The biochar based iron nanocomposite (nZVI-BC) so fabricated was then fully characterized and a series of adsorptive experiments performed in aqueous solution to optimize the removal efficiency of two inorganic As species (As(III) and As(V)) over a range of operating parameters including adsorbent dose, contact time, initial As concentration, pH, stirring rate and temperature. Batch adsorption isotherms best fit the Langmuir adsorption model (r2 > 0.96 for As(III) and r2 > 0.98 for As(V)), yielding maximum adsorption capacities of 1.04 and 1.40 mg g−1 for As(III) and As(V), respectively with residual As concentrations well below the WHO prescribed limit of 10 μg L−1 for drinking water. Optimum removal efficiencies of 99.1% for As(III) and 96.1% for As(V) were achieved at initial As concentration of 1.00 and 1.25 mg L−1, respectively. The mechanism of As removal involved a combination of surface specific electrostatic, H-bonding and redox reactions, where redox reactions eliminated formation of highly toxic As(III) in favor of As(0) and As (V). Using the optimized conditions nZVI-BC was employed to remove 91.5–93.2% of As from a real As laden groundwater collected from the Sahibganj district in Jharkhand, India. Overall, the nanocomposite showed great promise as a cost-effective material for quickly adsorbing As from aqueous solution and could thus potentially be used for remediating As contaminated ground water in any part of the world.