Arsenic coagulation/flocculation with iron (iii) hydroxide: Adsorption mechanisms and stability constants of surface complexes

The adsorption of arsenic (V) on iron (III) hydroxide had investigated in function of sorbent amount, pH, and contact time. The surface complexation method is used to establish the interaction mechanisms. H3O+/OH-stoichiometry is evaluated and varied between -2 and 2, in pH range of 3 to 12. This suggests that As (V) adsorbs in this conditions, via six predominant adsorption reactions. Stability constants of predominant species which are protonated and unprotonated, are obtained. The contribution of electrostatic effect to arsenic (V) uptake by Fe-hydroxide is evaluated. Obtained results show that adsorption is of electrostatic nature for pH ≤ 6, and of chemical character at pH ≥ 7. While the kinetics adsorption data suggest a complex changing of predominant adsorption reaction with time, involving the intrinsic (n= 0), and 1 or 2 H+ or OH- exchange reactions.

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