Adsorption behavior of lead and chromium onto MgO impregnated biochar derived from banana peels and rice husk in binary environment

Abstract In current research, raw- and MgO-impregnated biochar derived via (co)pyrolysis of rice husk (RH) and banana peel (BP) in mass ratios (0:1, 1:0 and 1:1) were synthesized and examined for their physiochemical properties and adsorption performance for Cr(VI) and Pb(II) ions removal from synthetic solutions. Owing to excellent removal capability (Cr(VI): 94% at pH 2; Pb(II): 100% at pH 4) of 2 g/L MgO-impregnated biochar with mass ratio 1:1 (MgO@CBC) for 20 mg/L metals ions loading in single solute system with 120 min contact time, removal performance of MgO@CBC was examined under binary environment. Interestingly, binary solute system showed significant MgO@CBC adsorption performance for Pb(II) removal (99%) with slight decrease in Cr(VI) removal (88.5%) at pH 2 under similar boundary conditions. Moreover, increasing metal ions concentration showed improved MgO@CBC adsorption potential for Cr(VI) at pH 4 and Pb(II) at pH 2, due to porous matrix Mg 2+ -mediated compounds and unique surface characteristics. Furthermore, the underlying removal mechanism using MgO@CBC was identified as (Cr(VI): reduction/complexation coupled with electrostatic attraction) and (Pb(II): ligand exchange followed by surface complexation) and in binary system as (Cr(VI) and Pb(II): ligand exchange, electrostatic attraction, bimetallic bonding (Pb–O–Cr) and surface complexation). In addition, MgO@CBC displayed promising recyclability potential for metal ions removal up to five cycles. In general, these experimental and mechanistic insights may provide feasible and ecofriendly solutions to tanneries, when dealing with toxic metal ions from their effluents.