Influence of iron content, surface area and charge distribution in the arsenic removal by activated carbons

• Carbons surface charge contributes in a greater extend to arsenic (V) uptake.
• Iron increases the As(V) adsorption capacity and promotes strong bonds Fe–O–As.
• Adsorption capacity correlates with pHPZC and iron content.
• As(V) adsorption is governed by OH-ligand exchange and electrostatic interactions.

Due to the high number of toxicological issues, the presence of asenic (V) in water supplies is a major problem of public concern. Adsorption by iron modified activated carbons stands as an interesting alternative for the removal of arsenic (V) from aqueous solutions. However, the question of which of the activated carbon properties have impact during arsenic (V) uptake has arisen. The influence of textural and chemical features of several activated carbons (AC), un-modified and modified with iron oxyhydroxide nanoparticles, for the removal of arsenic (V) from aqueous solution was studied. The surface area (SBET), micropore volume, surface charge and iron content of 28 ACs were determined. Results showed that the SBET of materials range from 388 to 1747  m2/g, the point of zero charge (PHPZC) from 3 to 11 and the iron content range from negligible to around 2%. A detailed data analysis demonstrated that the most important parameter of AC when removing arsenic (V) from water is the pHPZC (52.5% of contribution); however, the presence of iron is indispensable for enhancing the adsorption capacity (by 36.5%). An empirical model indicated that in order to effectively remove arsenic from water a basic AC with an iron content of about 1% is desirable. Arsenic (V) adsorption isotherms under normal conditions demonstrated that the materials studied have a great potential for water polishing. Finally it is suggested that the arsenate uptake by iron-modified AC is conducted by two simultaneous mechanisms: ligand interchange with iron oxyhydroxide particles and electrostatic attraction on basic AC.

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