Enhanced aqueous phase arsenic removal by a biochar based iron nanocomposite

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 (r(2) > 0.96 for As(III) and r(2) > 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 mu g 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. (C) 2020 Elsevier B.V. All rights reserved.