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Chromium is discharged from various industries such as chromium plating, leather tanning and textile, and exists as hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) in wastewater. Especially, Cr(VI) has high toxicity and oncogenicity to human being. The permissible concentration limit in drinking water is regulated by each health organization; 0.05 mg/L is the limit of WHO, EU and Japan, 0.1 mg/L is the limit of US EPA. Ion exchange, chemical reduction and precipitation processes are used for the removal of Cr(VI). However, ion exchange process requires the high cost resin, and chemical reduction and precipitation process produces a great deal of sludge. On the other hand, adsorption process using activated carbon (AC), bauxite, dolomite and/or fly ash is one of the simplest techniques for the removal of Cr(VI) and is extensively studied1-15). AC has a high surface area of over 1000 m2/g due to the porous structure and shows a strong affinity to aromatic compounds due to the π-π interaction between AC and adsorbate. AC is prepared by various materials, e.g. secondary products6, 13), and therefore, low in cost. There have been many researches on the adsorption of high toxic heavy metals2, 12). AC with little amount of surface functional groups prepared by high temperature treatment adsorbs heavy metals in the form of π-cation interaction. It is also known that oxidized AC possessing the acidic functional groups shows the high performance on heavy metals adsorption because of the ion exchange between the acidic functional groups and heavy metals12). The effects of various parameters such as initial concentration of adsorbate, contact time, pH and temperature of solution on Cr(VI) adsorption by AC have been investigated6, 7, 9-13, 15). Also, recent studies showed that Cr(VI) was reduced to Cr(III) on AC surface8, 11, 13). Módenes et al. confirmed the reduction of Cr(VI) on AC using Cr-kß spectroscopy11). On the other hand, the reduction of Cr(VI) was not observed in the process of Cr(VI) removal using cationic-exchange resin11). Although several researches proposed the mechanisms of Cr(VI) reduction3, 9, 13), the details of reaction and the effects of various parameters for Cr(III) production have not been clarified. In this study, the effects of different pH and temperature of solution on Cr(VI) removal using different adsorbent were examined to investigate the role of adsorbent surface and aqueous condition on the Cr(VI) reduction.

Reduction of Cr(VI) Varying with the Surface Properties of Activated Carbon