Determination of surface properties of iron hydroxide-coated alumina adsorbent prepared for removal of arsenic 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 0.31±0.003%m/m (56.1 mmol/g); its mechanical and chemical stability proved to be appropriate in solutions. The total capacity of the adsorbent was 0.12 mmol/g, and the pH of zero point of charge, pHzpc=6.9±0.3. Depending on the pH of solutions, the adsorbent can be used for binding of both anions and cations, if pHeq < pHzpc anions are sorbed on the surface of adsorbent (S) through {SOH2+} and {SOH} groups. A graphical method was used for the determination of pHiep (isoelectric points) of the adsorbent and values of pHiep=6.1±0.3 for As(III) and pHiep=8.0±0.3 for As(V) ions were found. The amount of surface charged groups (Q) was about zero within the a 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=0.19mol/kg was obtained. The adsorption of arsenate and arsenite ions from solutions of 0.1-0.4 mmol/L was represented by Langmuir-type isotherms. A great advantage of the adsorbent is that it can be used in adsorption columns, and low waste technology for removal of arsenic from drinking water can be developed.