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Ind. Eng. Chem. Res. 2008, 47, 1620-1629
Batch and Column Study: Adsorption of Arsenate Using Untreated Laterite as Adsorbent Abhijit Maiti, Sunando DasGupta, Jayant Kumar Basu, and Sirshendu De* Department of Chemical Engineering, Indian Institute of Technology, Kharagpur, Kharagpur-721302, India
Removal of arsenate (As(V)) ions by adsorption on natural laterite (NL) is investigated in the present study. Both equilibrium and kinetic study over a wide range of operating conditions are tested to evaluate the effectiveness of NL to remove As(V) from water. In the batch study, the effects of adsorbent dose, initial pH, ionic strength of solution, initial arsenate concentration, temperature, and contact time are examined. Batch study reveals that the uptake of arsenate is effective in the pH range of 5.5 to 7.5. The isotherm data is fitted well in the Langmuir isotherm model, and adsorption capacity is found to be 0.565 mg g-1. The effective intraparticle diffusion coefficient of arsenate ions in NL is observed to be in the range of 7.4 to 9.4 × 10-10 cm2 s-1. Continuous column study using a fixed bed is also carried out. The Adams-Bohart model is applied for the predicting breakthrough curve for column study. Introduction Arsenic has been classified as a carcinogen by the U. S. Environmental Protection Agency. The presence of arsenic in drinking water increases the risk of lung, skin, kidney, and bladder cancer. Over 70 to 80 million people in Bangladesh and in other regions of the Indian subcontinent are exposed to arsenic poisoning through drinking groundwater.1,2 Inorganic arsenic occurs mainly in +3 and +5 (also referred to as arsenite and arsenate, respectively) states, and their relative distribution is influenced by pH and the redox condition. In the pH range of 5 to 9 and under an oxidizing environment, arsenic mainly exists in the +5 (As(V)) state in the form of deprotonated oxyanions namely, H2AsO4- and HAsO42-. In mildly reduction conditions, (As(III)) is thermodynamically stable and exists as H3AsO3 (or HAsO2) at pH below 9.2. As(III) is more toxic in biological systems than As(V).3 It is important to mention that at low dosages (
