Pellet adsorbent derived from molasses and dewatered alum sludge for arsenic removal

Powder type of adsorbent has a huge surface area, but the powders are aggregated, which lowers the adsorption of arsenic(As) dramatically due to preferential flow in the adsorption bed. Pellet adsorbent to remove As was prepared to solve the problems of powder type adsorbent using dewatered alum sludge and molasses as a binder. The pellet was treated thermally under three different reaction media of air, N₂ and CO₂ to enhance the strength of pellet and to make pore structure. The air medium oxidizes the organic matter under oxygen, but the non-oxygen condition for N₂ and CO₂ carbonizes the organic matter. The adsorption characteristics, the pellet shape (i.e., the strength of the adsorbents) should be retained during the adsorption process, which is one of the major concerns for the pellet adsorbents. The shape retention was enhanced by the thermal treatment under the reaction medium of air, N₂ and CO₂. Besides the adsorption characteristics of As on the adsorbents were investigated in terms of adsorption kinetics, adsorption isotherms and surface charge of the adsorbents. The pellets thermally treated under air and CO₂ shows 2 times faster adsorption kinetics than the simply dried and N₂ medium within 10 min. The strength of pellets was enhanced by the thermal treatment under CO₂ compared to the air and N₂ medium due to the carbonization. As a result, the pellet adsorbents thermally treated under the CO₂ removed As from the aqueous phase with enhanced kinetics.