ARSENIC REMOVAL USING IRON-MODIFIED ZEOLITES
Lab-based batch experiments were performed on each material to estimate the adsorption capacity. All batch tests were performed using synthetic water based on the chemistry of Socorro Springs water from Socorro, NM. The arsenic adsorption capacity varied greatly between the different types of IMZ and was heavily dependent on the procedures used for iron application. A single IMZ batch material and the SMZ/ZVI was further tested by looking at the effects of pH on adsorption and by performing column breakthrough experiments with media regeneration at the end of each breakthrough cycle.
The chosen IMZ material contained 28,400 mg of iron per kg. Compared with the raw zeolite that had a surface are of 13.8 m²/g, the surface area of the IMZ increased about 150% to 21.4 m²/g. Using the Langmuir isotherm, the IMZ had a maximum arsenic adsorption capacity of 654 mg/ kg and a Langmuir coefficient of 4.65 L/mg.
The IMZ material was found to have maximum arsenic adsorption between pH 2.0 and 7.0. Using Socorro Springs water (containing 41-45 μg/L arsenate, pH = 8.1, and TDS = 356 μS/cm) as the influent, the column effluent arsenic concentration remained below 10 μg/L for 800 pore volumes. The IMZ-8 column was successfully regenerated 3 times with no loss of adsorption capacity using 1 L of 0.25 M NaOH and 6 L of reverse osmosis water. The IMZ material may be a viable alternative for municipal water treatment due to the low cost of zeolite, the high arsenic adsorption capacity, and the easily regenerated media. The estimated cost of treating the local water with IMZ-8 was about $0.50 per 1,000 L.