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Granular activated carbon-based, iron-containing adsorbents (As-GAC) were developed for effective removal of arsenic from drinking water. Granular activated carbon (GAC) was used primarily as a supporting medium for ferric iron that was impregnated by ferrous chloride (FeCl2) treatment, followed by chemical oxidation. Sodium hypochlorite (NaClO) was the most effective oxidant, and carbons produced from steam activation of lignite were most suitable for iron impregnation and arsenic removal. Two As-GAC materials prepared by FeCl2 treatment (0.025 -0.40 M) of Dacro 20 x 50 and Dacro 20 x 40LI resulted in a maximum impregnated iron of 7.89% for Dacro 20 x 50 and 7.65% for Dacro 20 x 40Ll. Nitrogen adsorption-desorption analyses showed the BET specific surface area, total pore volume, porosity, and average mesoporous diameter all decreased with iron impregnation, indicating that some micropores were blocked. SEM studies with associated EDS indicated that the distribution of iron in the adsorbents was mainly on the edge of As-GAC in the low iron content (approximately 1% Fe) sample but extended to the center at the higher iron content (approximately 6% Fe). When the iron content was > approximately 7%, an iron ring formed at the edge of the GAC particles. No difference in X-ray diffraction patterns was observed between untreated GAC and the one with 4.12% iron, suggesting that the impregnated iron was predominantly in amorphous form. As-GAC could remove arsenic most efficiently when the iron content was approximately 6%; further increases of iron decreased arsenic adsorption. The removal of arsenate occurred in a wide range of pH as examined from 4.4 to 11, but efficiency was decreased when pH was higher than 9.0. The presence of phosphate and silicate could significantly decrease arsenate removal at pH > 8.5, while the effects of sulfate, chloride, and fluoride were minimal. Column studies showed that both As(V) and As(III) could be removed to below 10 microg/L within 6000 empty bed volume when the groundwater containing approximately 50 microg/L of arsenic was treated.

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CrVI reduction by low molecular weight organic compounds with various functional groups was examined in the presence and absence of oxide surfaces. Surface-catalyzed CrVI reduction has been demonstrated with α-hydroxyl carboxylic acids (glycolic acid, lactic acid, mandelic acid, and tartaric acid) and their esters (methyl glycolate, methyl lactate, and methyl mandelate), with α-carbonyl carboxylic acids (glyoxylic acid and pyruvic acid), with oxalic acid, and with substituted phenols (salicylic acid, 4-methoxyphenol, and resorcinol). Both goethite (α-FeOOH) and aluminum oxide (γ-Al2O3) exert an appreciable catalytic effect, although somewhat less than that observed with titanium dioxide. This study indicates that surface-catalyzed CrVI reduction may occur in soils, sediments, aquifers, and other aquatic environments rich in mineral surfaces.

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Acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) are operationally defined niethocls for tlie analysis of sulfide and associated metals in aquatic sediments. The SEMto-AVS ratio has been useful in explaining tlie results of bioassay tests of' metal toxicants. This paper describes apparatus that can be used in the evolution of sulfide from sediments and a method for the analysis of tlie evolved sulfide and the liberated metal. The niethocl was studied with respect to gas flow rate, digestion time, aiid acid concentration. Liberated and trapped sulfide was determined by a colorimetric method of analysis. Using the apparatus and conditions described in this paper, the colorimetric method of analysis is capable of' detecting AVS at concentrations normally encotintered with a recovery of sulfide of at least 90%. High precision is possible if this apparatus is used. Tlie limit of detection of tlie method is approximately 0.01 pniol/g dry sediment. We added 6 M HCI to procluce a final concentration of approxiinately I M for tlie release of the AVS and SEM from unheated samples. We found that sulfide was riot released from pyrite (FeS2) or copper sulfide (CuS) under these conditions. The liberation of copper from the two studied sediments indicates that copper was probably associated with another phase in these secliments. AVS is stable for several weeks in refrigerated or frozen samples.