Removal of arsenate from aqueous solutions by biochar supported by Iron

Arsenic contamination is one of the serious environmental challenges in developing countries. Contaminated water is the main source of human and animal exposure to inorganic arsenic. There are various physicochemical and biological methods used for arsenic removal from aquatic environments. Compared to all the advantages and disadvantages of arsenic removal methods, adsorption processes considered as an effective method due to its low cost and ease of application. Iron - rich materials have a high capacity to sorption of arsenic in aqueous solutions. The objective of this study is an assessment of arsenate removal from water using biochar modification by iron salt, which can be used for the recovery of arsenate contaminated water resources for drinking water supply and reuse of industrial effluents.

In order to preparation of iron modified biochar 0.1 (0.1FeBC) and 0.4 (0.4FeBC) ratios of FeCl3.6H2O were added to apple pruning residues powder and pyrolized in the furnace for an hour at 300 °C under limited oxygen condition as well as a control sample without iron. SEM images were used for characterization of the morphology of the adsorbents. The isotherm experiment was carried out at initial concentrations of 0, 1, 2, 4, 6, 8, and 10 mg arsenate/L and remaining arsenate in solution was determined using hydride generation atomic absorption spectroscopy (HG-AAS). Experimental data were fitted to Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models, and parameters such as apparent energy of adsorption (E), adsorption efficiency, Gibb’s free energy (ΔG) and separation factor were calculated.

Iron modified the surface properties of biochar and increased the amount of the granular compounds on the adsorbents surface. The results showed that by increasing of the adsorbent iron content, the removal of arsenate from solution increased and the highest removal efficiency (86%) was obtained for the 0.4FeBC adsorbent at 1 mg Arsenate/L. The ability of the Freundlich model to simulate the process of arsenate adsorption by iron-modified adsorbents was higher than the Langmuir, Dubinin–Radushkevich and Temkin models. By increasing the iron content in the adsorbents Freundlich (KF and n), Temkin (KT and A), Langmuir (KL and qmax) coefficients increased, while the Dubinin–Radushkevich (KDR) coefficient and separation factor (RL) decreased. The highest value for the maximum absorption capacity (qmax) was obtained for 0.4FeBC in the amount of 7.66 mg of arsenate per gram of adsorbent. According to the values of apparent energy of adsorption (E), adsorption process for unmodified biochar is physical (less than 8 kJ / mol) and for the modified biochar is chemisorption. Based on Gibbs free energy (ΔG) values, the adsorption process of arsenate by adsorbents is spontaneous.

According to the results of this study, modification of biochar by iron salt can be considered as an inexpensive absorbent due to local accessibility and easy application for removal of arsenate from water.