Enhanced adsorption of arsenic onto alum sludge modified by calcination

Alum sludge from water treatment facilities is composed mainly of aluminum hydroxide or aluminum oxide, which can adsorb As(V). However, microorganisms and organic/inorganic matter agglomerated together with raw alum sludge inhibit the adsorption of As(V) onto the material. Calcination was used to remove organic matter and activate the material, and the physical properties and adsorption characteristics were evaluated by using field-emission scanning electron microscopy, elemental analysis, X-ray diffraction, Fourier transform infrared, zeta potential, and Brunauer-Emmett-Teller surface analysis. At a higher calcination temperature, a larger proportion of organic matter was removed and the adsorption capacity for As(V) was 5.4–8.7 times greater than that of the raw adsorbent. However, calcination at 500 °C changed the structure of aluminum oxide into a crystallized form, reduced the surface area, and the adsorption capacity for As(V) decreased. In comparison, calcination at 300 °C removed organic matter efficiently without changing the structure of the adsorbent, and showed greater adsorption capacity for As(V). The results suggested that calcination is a suitable process for producing alum sludge-based adsorbent for As(V) removal.