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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 degrees 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 degrees C, the procedure successfully created HFO in the pores of GAC, whereas at temperatures of 80 and 90 degrees C, the impregnated iron oxide manifested a more crystalline form. In the column tests using synthetic water, the HFO-loaded GAC prepared at 60 degrees 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, HFO-loaded GAC (Fe, 11.7%) showed an arsenic sorption capacity of 26 mg As/g when the influent contained 300 microg/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.

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Hydrous oxides of iron (HFO) and aluminum (HAO) were studied for their ability to reduce Cu (initially 4.3 mg/L) to microgram per liter levels typical of increasingly stringent wastewater discharge limits. Residual soluble Cu was compared following adsorption (ADS), where Cu was contacted with preformed oxide flocs, and coprecipitation (CPT), where Cu was added prior to HFO or HAO precipitation. For the HAO-ADS system, soluble Cu levels were markedly undersaturated with respect to homogeneous precipitation (PPT) of Cu(OH)2(s) over the pH 6−9 range. In contrast, soluble Cu was lowered by HFO-ADS for pH <7.5 but comparable to PPT at higher pH. Isotherms suggest a Cu surface precipitate formed on HAO with solubility product lower than its HFO analogue. Compared to ADS, soluble Cu after CPT was similar for HAO but was dramatically lower for HFO. More Cu was incorporated internal to the HFO flocs during CPT, suggesting some Cu substitution into the HFO lattice. Removal of Cu was significantly influenced by oxide type and contact methodology.

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