Treatment of Aqueous Arsenite Using Modified Biomass-Based Sorbent

The occurrence of high concentrations of arsenic (As) in water has been recognized as a global health and environmental problem. Sorption is regarded as a promising As treatment method due to its simplicity and potential for high efficiency. Canada has a strong agricultural industry that produces waste products that can be converted to value-added products. Considering the availability of agricultural residue in Canada, the cost of the sorption process can be decreased by using agricultural residue-based sorbents (biosorbents) as an eco-friendly alternative for commercial sorbents. In this study, sorption of arsenite, As(III), from aqueous solutions onto Fe oxide-modified canola straw (MCS) was investigated. The results showed that the negligible As(III) sorption capacity of raw canola straw increased significantly to 791 µg/g after modification in the removal of As(III) from a 1000 µg/L solution. Studying the effect of solution pH showed that As(III) sorption capacity of MCS increased by increasing the solution pH from 3 to 10. A kinetic study showed that about 66% of the ultimate sorption capacity was reached within four hours. The sorption kinetic data was best represented by pseudo-second-order and Elovich models suggesting that chemisorption may be the rate-determining step of the sorption process. The isothermal data of As(III) sorption followed Freundlich and Redlich–Peterson models indicating a hybrid adsorption mechanism with a higher probability of a multilayer heterogeneous adsorption. Studying the effect of co-existing anions in the solution upon the As(III) removal efficiency of MCS indicated a significant antagonistic impact of selenate (SeO42−), selenite (SeO32−), and phosphate (PO43−). However, the effect of nitrate (NO3−) and chloride (Cl−) on As(III) removal efficiency was insignificant, indicating that inner-sphere complexation was the leading mechanism in As(III) sorption.