Environ. Sci. Technol. 2008, 42, 3369–3374
Preloading Hydrous Ferric Oxide into Granular Activated Carbon for Arsenic Removal M I N J A N G , † W E I F A N G C H E N , * ,‡ A N D FRED S. CANNON‡ Water Quality Research Team, Technology Research Center (TRC), Korea Mine Reclamation Corporation (MIRECO), 80-6 Coal Center, Susong-dong, Jongno-gu, Seoul, Republic of Korea, and Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802
Received October 6, 2007. Revised manuscript received February 4, 2008. Accepted February 13, 2008.
Arsenic is of concern in water treatment because of its health effects. This research focused on incorporating hydrous ferric oxide (HFO) into granular activated carbon (GAC) for the purpose of arsenic removal. Iron was incorporated into GAC via incipient wetness impregnation and cured at temperatures ranging from 60 to 90 °C. X-ray diffractions and arsenic sorption as a function of pH were conducted to investigate the effect of temperature on final iron oxide (hydroxide) and their arsenic removal capabilities. Results revealed that when curing at 60 °C, the procedure successfully created HFO in the pores of GAC, whereas at temperatures of 80 and 90 °C, the impregnated iron oxide manifested a more crystalline form. In the column tests using synthetic water, the HFO-loaded GAC prepared at 60 °C also showed higher sorption capacities than media cured at higher temperatures. These results indicated that the adsorption capacity for arsenic was closely related to the form of iron (hydr)oxide for a given iron content. For the column test using a natural groundwater, HFOloaded GAC (Fe, 11.7%) showed an arsenic sorption capacity of 26 mg As/g when the influent contained 300 µg/L As. Thus, the preloading of HFO into a stable GAC media offered the opportunity to employ fixed carbon bed reactors in water treatment plants or point-of-use filters for arsenic removal.
Introduction Throughout the world, arsenic is creating potentially serious environmental problems for humans and other living organisms. Most reported arsenic problems are found in groundwater supply systems and are caused by natural processes such as mineral weathering and dissolution of metal oxide deposits that can contain traces of arsenic, and this has resulted from a change in the geochemical environment to a reductive condition (1, 2). Arsenic contamination is also caused by human activities such as mining wastes, petroleum refining, sewage sludge, agricultural chemicals, ceramic manufacturing industries, and coal fly ash (3–5). In early 2001, the U.S. Environmental Protection Agency published a revised arsenic standard of 10 µg/L in drinking water. All * Corresponding author: phone: 814-863-0690; email: wzc102@ psu.edu. † Korea Mine Reclamation Corporation (MIRECO). ‡ The Pennsylvania State University. 10.1021/es7025399 CCC: $40.75
Published on Web 03/27/2008
2008 American Chemical Society
public water systems must have complied with this 10 µg/L standard by 2006, although waivers allow some small water systems to achieve compliance at a later date. Thus, there is great need to devise new and innovative technologies that are inexpensive to use, easy to operate, and durable through long-term use. Compared to other conventional techniques such as oxidation, coagulation/ precipitation, filtration, ion exchange, membrane/reverse osmosis, and biological treatment, adsorption has the following advantages (1): it usually does not need a large volume or additional chemicals for treatment (2); it is easier to set up as a POE/POU (point of entry/point of use) arsenic removal process. Studies have revealed that iron (III) has a high affinity toward inorganic arsenic species, and it is very selective to arsenic in the sorption process (6, 7). Recent research has focused on removing arsenic with iron (hydr)oxides as adsorbents or iron-bearing adsorbents. Hydrous ferric oxide (HFO) is one of the promising iron (hydr)oxides for removing both arsenate and arsenite from aqueous phase due to its high iso-electric points (8.1), high specific surface area, and selectivity for arsenic species (8). HFO has exhibited surface areas of about 350–600 m2/g which is much greater than those of other crystallized iron oxides such as goethite or magnetite (
