Enhanced removal of arsenite from water by a mesoporous hybrid material - Thiol-functionalized silica coated activated alumina

A novel mesoporous hybrid adsorbent prepared by coating an activated alumina (AA) with a mercaptopropyl-functionalized silica was tested for removal of arsenite [As(III)]. Batch experimental results indicated that the thiol-functionalized AA (AA-SH) had an improved adsorption capacity and an enhanced adsorption rate for As(III) compared with AA. In the pH range from 4 to 11, AA-SH exhibited much higher removal efficiency than AA, and the maximum percent removal appeared at pH 7.0 and 8.5 for AA-SH and AA, respectively. The advantages of the hybrid material were further demonstrated by column filtrations using As(III)-spiked aged tap water and groundwater. Approximately 3200 and 350 bed volumes of spiked tap water containing 300 μg/L of As(III) were filtered by AA-SH and AA at pH 7, respectively, before the effluent arsenic concentration increased to the USEPA MCL of 10 μg/L. In a field column test with actual raw groundwater containing ∼70 μg/L of total arsenic (∼80% as As(III)) and having a pH value of ∼7.3, the breakthrough bed volumes were found to be ∼3100 and ∼800 for the AA-SH and AA, respectively. Batch and column studies also indicated that the AA-SH performed better than or similar to some common adsorbents such as granular ferric oxide (GFO) and granular TiO₂.