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.