Arsenic mitigation by chitosan-based porous magnesiaimpregnated alumina: performance evaluation in continuous packed bed column

Dissolved arsenic in contaminated groundwater is a major concern on a global scale due to its extreme toxicity. This paper reports a magnesium oxide-impregnated mesoporous alumina synthesized using biopolymer chitosan template. The adsorbent was first characterized by BET, SEM and EDAX analysis. The packed column performed effectively over wide range of pH and exhibited a maximum adsorption capacity of 17.2 mg/g for an input arsenic concentration of 20 mg/L. The experimental data fitted well with pseudo-second-order kinetics. Thermodynamic study on the adsorption phenomena revealed that arsenic adsorption on the porous adsorbent was spontaneous, and the process was exothermic. The arsenic sorption capacity at breakthrough point was greatly dependent on bed depth. A bed depth service time approach was adopted to describe the continuous flow system. The column after exhaustion was regenerated by eluting the bound arsenate [As(V)] with ~15 bed volume sodium hydroxide solution. The adsorbent could retain its capacity up to five cycles of such regeneration. The influence of different operating conditions such as bed depth, flow rate and initial arsenic concentration was investigated statistically by the two-level full-factorial experimental designs to evaluate optimum operating conditions.