Column studies on the adsorption of As(V) by granular chitosan adsorbent prepared with backwashing iron-containing sludge

Abstract

Abstract Backwashing sludge of groundwater treatments for iron and manganese removal is an effective adsorbent to remove arsenic from water. Still, it isn t easy to apply in practice due to its powder form. A new type of granular adsorbent (GA) was prepared by using this sludge as raw material. GA was prepared by adding a homogeneous solution of iron sludge and chitosan into NH4OH solution with a separatory funnel and pipette tip. GA has a high sorption capacity of 14.95\xa0mg/g As(Ⅴ) determined by the Langmuir model. And the dynamic filtration experiment was conducted by filling the GA in the plexiglass column. The experimental results show that the adsorption capacity of the filter column increased with the increase of bed depth, while the unit adsorption capacity decreased. When the bed depth was 15\xa0cm, the total and unit adsorption capacities were 10.755\xa0mg and 0.779\xa0mg/g, respectively. In comparison, when the bed depth was 60\xa0cm, the adsorption capacity was 20.405\xa0mg, and the unit adsorption capacity was 0.370\xa0mg/g. When the bed was in the midst of 30, 45, 60\xa0cm, the breakthrough time was 13\xa0h, 100\xa0h, 200\xa0h at EBCT of 9\xa0min, 18\xa0min, and 37\xa0min, respectively. The NaOH solution with a 1% concentration was continuously injected to regenerate the exhausted GA filter column, and the desorption rate reached 25.8%. After regeneration, the adsorption capacity of GA was slightly decreased, and the GA column still had good As(Ⅴ) removal performance with Re% above 90%. The Thomas, Adams-Bohart, Yoon-Nelson models were used to fit the experimental data, and the Yoon-Nelson model was proved better to describe the breakthrough curves. GA column has a more commendable adsorption capacity compared to some other adsorbents. This study not only resourcefully utilizes waste iron sludge but also represents a step forward in investigating the possibility of extending iron sludge adsorbents from batch to fixed bed adsorption.