Optimization of arsenic(III) and mercury(II) removal from non-competitive and competitive sorption systems onto activated carbon

Abstract

Heavy metals exist in the ecosystem both naturally and due to anthropogenic activities and as recalcitrant pollutants; they are non-biodegradable and cause acute and chronic diseases to human beings and many lifeforms. As a result, the removal of heavy metals from aqueous systems using sorbent materials produced from agricultural wastes is one of the new innovative treatment techniques. In this study, the biosorption and desorption characteristics of heavy metal ions from non-competitive and competitive aqueous solutions onto hybrid granular activated carbon produced from maize residues were investigated. The efficient sequestration of As(III) and Hg(II) ions from both monocomponent and bicomponent synthetic wastewater was found to show dependence on the physicochemical properties of the biosorbent and the studied independent biosorption process factors. The regenerated biosorbent could be reused up to the eighth cycle for the sequestration of As(III) and Hg(II) ions from the synthetic wastewater without significantly losing its adsorptive properties. The applicability of the biosorbent synthesized from the maize residues for the simultaneous decontamination of heavy metals found in real industrial wastewater as a function of several biosorption factors showed that the biosorbent could competitively decontaminate over 96% of As, Hg, Pb, Cd, and Cr in 100 mL textile wastewater in batch mode. The regeneration of the spent biosorbent using 0.10 M HCl showed that the biosorbent is capable of being recycled and reused severally for the sequestration of As, Hg, Pb, Cd, and Cr from the textile wastewater and even up to the ten cycles for a duration of 4 h. The optimization of the competitive removal of As and Hg ions in the co-existence of other heavy metals in the textile wastewater by the CCD-RSM resulted in maximum removal efficiencies of 97.72 and 99.99%, respectively. The characterization of the hybrid granular activated carbon using SEM, TEM, XRD, BET, and FTIR showed that the biosorbent surface characteristics could facilitate the removal of heavy metals from the non competitive and competitive biosorption media. The main biosorption mechanism of the heavy metal ions on the biosorbent was mainly chemisorption involving surface complexation. Therefore, this novel biosorbent is found to be promising and could effectively be employed for heavy metals remediation in aquatic environments. The outcomes of this study are expected to make a significant contribution to the design of low-cost and efficient industrial wastewater treatment systems such as a dynamic batch rector for heavy metal removal using locally available bio-adsorbents.