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74 ADSORPTION OF HEXAVALENT CHROMIUM ONTO TAILORED ZEOLITES Ivonne Santiago, Research Assistant Vincent P. Worland, Research Assistant Enrique Cazares-Rivera, Research Assistant Fernando Cadena, Professor Department of Civil Engineering New Mexico State University Las Cruces, New Mexico 88003 CHROMIUM Chromium is used in a variety of industrial applications, including electroplating and as a corrosion inhibitor in cooling towers.1 Up to a few years ago, this metal was the favored corrosion control agent in cooling towers.2 Cooling water blowdown (waste) was dumped into rivers, pits, lakes and oceans. During the 1950s chromates were also used as a highway deicing agent in the United States. Chromium (Cr) occurs in the + 2, + 3 and + 6 oxidation states in water. The divalent slate is rarely found in field conditions because it becomes rapidly oxidized to + 3 in the presence of atmospheric oxygen.3 Insoluble Cr(III) occupies much of the Chromium Eh-pH diagram.4 Chromium (III) is less toxic than Cr(VI),3 however, it can be oxidized to form the carcinogenic Cr(VI) in the presence of oxygen. The predominance diagrams for Cr(VI) extend over large ranges of Eh and pH.4 Cr(VI) is soluble and hydrolyses extensively in water, producing only neutral and anionic species as shown in Figure 1.' These properties insure rapid migration through soils, which are unable to undergo anion exchange with these hazardous materials. Hexavalent chromium can be treated by first reducing it to trivalent chromium in the presence of a reducing agent such as gaseous sulfur dioxide (S02) or a bisulfide solution (NaHS03). In addition, there are three commercially available methods that use the reducing potential of iron and/or iron salts to reduce hexavalent chromium.5 Because trivalent chromium is only soluble under acidic condi- HCrO' cro; i EXP£rWv1EfilTAL i BtP&m&fTM. range i < i RANGE o 2-3 o " -5 -6 0 2 4 Figure 1. Chemistry' of hexavalent chromium. PH 10 47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 481 If Printed in U.S.A.
Object Description
Purdue Identification Number | ETRIWC199274 |
Title | Adsorption of hexavalent chromium onto tailored zeolites |
Author |
Santiago, Ivonne Worland, Vincent P. Cazares-Rivera, Enrique Cadena, Fernando |
Date of Original | 1992 |
Conference Title | Proceedings of the 47th Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://e-archives.lib.purdue.edu/u?/engext,43678 |
Extent of Original | p. 699-710 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Date Digitized | 2009-12-10 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Resolution | 300 ppi |
Color Depth | 8 bit |
Description
Title | page 699 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | 74 ADSORPTION OF HEXAVALENT CHROMIUM ONTO TAILORED ZEOLITES Ivonne Santiago, Research Assistant Vincent P. Worland, Research Assistant Enrique Cazares-Rivera, Research Assistant Fernando Cadena, Professor Department of Civil Engineering New Mexico State University Las Cruces, New Mexico 88003 CHROMIUM Chromium is used in a variety of industrial applications, including electroplating and as a corrosion inhibitor in cooling towers.1 Up to a few years ago, this metal was the favored corrosion control agent in cooling towers.2 Cooling water blowdown (waste) was dumped into rivers, pits, lakes and oceans. During the 1950s chromates were also used as a highway deicing agent in the United States. Chromium (Cr) occurs in the + 2, + 3 and + 6 oxidation states in water. The divalent slate is rarely found in field conditions because it becomes rapidly oxidized to + 3 in the presence of atmospheric oxygen.3 Insoluble Cr(III) occupies much of the Chromium Eh-pH diagram.4 Chromium (III) is less toxic than Cr(VI),3 however, it can be oxidized to form the carcinogenic Cr(VI) in the presence of oxygen. The predominance diagrams for Cr(VI) extend over large ranges of Eh and pH.4 Cr(VI) is soluble and hydrolyses extensively in water, producing only neutral and anionic species as shown in Figure 1.' These properties insure rapid migration through soils, which are unable to undergo anion exchange with these hazardous materials. Hexavalent chromium can be treated by first reducing it to trivalent chromium in the presence of a reducing agent such as gaseous sulfur dioxide (S02) or a bisulfide solution (NaHS03). In addition, there are three commercially available methods that use the reducing potential of iron and/or iron salts to reduce hexavalent chromium.5 Because trivalent chromium is only soluble under acidic condi- HCrO' cro; i EXP£rWv1EfilTAL i BtP&m&fTM. range i < i RANGE o 2-3 o " -5 -6 0 2 4 Figure 1. Chemistry' of hexavalent chromium. PH 10 47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 481 If Printed in U.S.A. |
Resolution | 300 ppi |
Color Depth | 8 bit |
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