Effect of Time and pH History on Arsenic Removal by Granular Iron Hydroxide Media

摘要

Granular iron hydroxide (GIH) adsorbents are widely used for arsenic removal and have been reported to operate more than 1.5 years without any regeneration. During this prolonged operational period the iron hydroxide may shift towards more stable crystalline forms that have less affinity for arsenate. The objectives of this research work were to study the effect of extended GIH media storage and shifts in pH on its arsenic removal effectiveness. Batch adsorption studies were conducted by contacting fresh, six- and nine-month old granular Bayoxide E33 media (10g/L) with 60,000 μg As (V)/L solution at pH 4 and pH 7. For 1 day batch equilibrium time, arsenate adsorption capacity was observed to decrease by 47 % (from 6.0 mg As/g media to 3.2 mg As/g media) and 83 % (from 6.0 mg As/g media to 1.0 mg As/g media) for nine-month old media in batch studies, conducted at initial pH 4 and 7, respectively. Further, pH adjustment had little impact on the arsenate adsorption capacity of the fresh media, but did show some indications of restoring capacity to the older media. For 15 days equilibrium time, the arsenate adsorption capacity was increased by 100 % (from 2.7 mg As/g media to 5.4 mg As/g media) and 27 % (from 2.6 mg As/g media to 3.3 mg As/g media) for six- and ninemonth old media, respectively. The results obtained in this research indicated that the arsenate adsorption capacity of GIH media may decrease during prolonged media use. In addition, shifts in pH have the potential to offer a means of prolonging media life by redeveloping fresh surface sites with high affinity for arsenate.