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Adsorption technologies are one of the preferred methods for removing arsenic insmall-scale drinking water systems. Because of its low cost and high surface area,activated alumina has been the preferred adsorbent. However, adsorption processesemploying activated alumina are sensitive to pH, with the optimum pH for arsenateremoval ranging from 5.5 to 6.0. Because the pH of most groundwaters lies abovethis range, water treatment plants must often adjust pH prior to the adsorption process.This effect is most likely due to a decrease in adsorption of As (V) or other protolyzableanions as the pH increases and the surface charge of the adsorbent becomes lesspositive. Even though the isoelectric point (pHiep) of pure gamma alumina (the crystalform of many activated alumina) is 8.0, its pHiep shifts to 6.0 when the ratio of massof adsorbate to surface area of adsorbent is 164 ug/m2, resulting in an unfavorable pHrange for arsenate removal in most water treatment scenarios. Although this effectwill occur with most adsorption media, materials having higher pHiep than activatedalumina have higher arsenate adsorption capacities at pH values typical of drinkingwater (pH = 6.0 ~ 8.0). Magnesium aluminate spinel (pHiep = 10.2) was prepared bya sol-gel process and investigated as an arsenate adsorbent to overcome this pH effect.This spinel provides greater arsenate adsorption (g of arsenate adsorbed per m2 ofactive surface) over the pH range of typical drinking water than does *-alumina (pHiep= 8.0) prepared by a similar process. Includes 34 references, table, figures.

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Edition: Vol. - No. Published: 06/15/2003 Number of Pages: 12File Size: 1 file , 470 KB