Surface properties of an advanced adsorbent developed for arsenic removal from drinking water

A novel type adsorbent was prepared by in-situ precipitation of Fe(OH)(3) on the surface of activated Al2O3 as a support material. The iron content of the adsorbent was found as 0.313 +/- 0.003 m/m% Fe (56.1 mmol/g), its mechanical and chemical stability proved to be appropriate in solutions. The total capacity of the adsorbent was found as 0.115 mmol/g, the pH of zero point of charge, pH,p, = 6.9 +/- 0.4. Depending on the pH of the solutions the adsorbent can both be used for binding of anions and cations. If pH(eq) < pH(zpc) anions are sorbed on the surface of adsorbent through {S-OH2+} and {S-OH} groups. The graphical method was used for the determination of pH(icp) of the surface of the Al2O3/Fe(OH)(3) adsorbent formed due to the adsorption of arsenic ions. Values of pH(iep) = 6.3 +/- 0.3 for As(III)- and pH(iep) = 8.0 +/- 0.2 for As(V)-ions were found. The amount of surface-charged groups (Q) was about zero within the pH range of 6.5-8.6, due to the practically neutral surface formed on the adsorption of As(V)-ions. At acidic pH (pH = 4.7), Q = 0.192 mol/kg was obtained. The adsorption of arsenic ions from dilute solutions (0.1-1.8 mmol/l) was represented by Langmuir-type isotherms. With increasing equilibrium concentration, the monolayer was restructured and new layers were formed.