Determination of surface properties of iron hydroxide-coated alumina adsorbent prepared for removal of arsenic from drinking water

Abstract

A novel type adsorbent was prepared by in situ precipitation of Fe(OH) 3 on the surface of activated Al 2O 3 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, pH zpc = 6.9 ± 0.3 . Depending on the pH of solutions, the adsorbent can be used for binding of both anions and cations, if pH eq < pH zpc anions are sorbed on the surface of adsorbent (S) through {S OH 2 + } and {S OH} groups. A graphical method was used for the determination of pH iep (isoelectric points) of the adsorbent and values of pH iep = 6.1 ± 0.3 for As(III) and pH iep = 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 = 0.19 mol / 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.