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61 TREATMENT OF METAL-EDTA WASTES USING ELECTROCHEMICAL REDUCTION, CHEMICAL OXIDATION, AND METAL PRECIPITATION TECHNIQUES Jeffrey S. Allen, Assistant Project Manager Eckenfelder Inc. Nashville, Tennessee 37228 Suzanne S. Fenton, Professor James M. Fenton, Professor Donald W. Sundstrom, Professor Department of Chemical Engineering The University of Connecticut Storrs, Connecticut 06269 INTRODUCTION Ethylenediaminetetraacetic acid (EDTA) is a common chelating agent and is used in chemical cleaning solutions for scale removal from steam boilers and heat exchangers. The composition of the chemical cleaning wastestream generated in the 1985 cleaning of the Northeast Utilities Millstone Unit No. 2 steam generators was used as a model for this study. The two generators cleaned at Millstone produced approximately 567 pounds of corrosion products as iron, copper, nickel, and zinc (complexed with EDTA) in 14.000 gallons of waste solvents.1 The treatment of these wastes requires breakdown of the metal-EDTA bonds, followed by separation and removal and/or destruction of metal and EDTA species. A diagram of a proposed process for the treatment of chemical cleaning wastes is presented in Figure 1. There are three major treatment steps in this proposed process. The first step is electrochemical reduction of the copper- and iron-EDTA complexes at low pH to produce copper metal, precipitated EDTA, and a solution containing iron (II), residual copper, and EDTA (as separate or complexed species). Electrochemical reduction is followed by chemical oxidation of the residual EDTA by hydrogen peroxide addition in order to destroy the remaining EDTA. The elimination of EDTA from the waste permits the remaining free copper, iron, and other metal species (nickel and zinc) to be precipitated out of solution at high pH in the third treatment step. The treatment system effluent is then essentially free from the target pollutants of EDTA, copper, and iron. This processing scheme allows for recovery of a high percentage of pure copper and nearly pure EDTA (via electrochemical reduction) for possible reuse. Since copper and EDTA are removed in the electrochemical reactor, a smaller amount of chemicals will be required for oxidation and precipitation of the remaining wastes. In addition, destruction of the residual EDTA via hydrogen peroxide oxidation will result in smaller, less hazardous volumes of final waste for ultimate disposal. These features give the proposed system an advantage over currently available treatment alternatives, and promote the concept of "pollution prevention." Several nondestructive and destructive technologies are currently available for the treatment of EDTA-based chemical cleaning wastes.I_s The nondestructive technologies include direct solidification, precipitation, evaporation, ion exchange, membrane processes, and electrochemical reduction. Disadvantages associated with these technologies include: (1) no destruction of EDTA (solidification, evaporation, membrane processes); (2) little or no volume reduction (solidification, precipitation, ion exchange, electrochemical reduction); (3) inability to treat EDTA-contain- ing wastes (precipitation); and (4) inability to handle concentrated solutions (ion exchange). De- 51st Purdue Industrial Waste Conference Proceedings, 1996. Ann Arbor Press. Inc.. Chelsea. Michigan 48118. Printed in U.S.A. 601
Object Description
Purdue Identification Number | ETRIWC199661 |
Title | Treatment of metal-EDTA wastes using electrochemical reduction, chemical oxidation, and metal precipitation techniques |
Author |
Allen, Jeffrey S. Fenton, Suzanne S. Fenton, James M. Sundstrom, Donald W. |
Date of Original | 1996 |
Conference Title | Proceedings of the 51st Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://e-archives.lib.purdue.edu/u?/engext,46351 |
Extent of Original | p. 601-612 |
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 | 2009-10-27 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
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Color Depth | 8 bit |
Description
Title | page 601 |
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 | 61 TREATMENT OF METAL-EDTA WASTES USING ELECTROCHEMICAL REDUCTION, CHEMICAL OXIDATION, AND METAL PRECIPITATION TECHNIQUES Jeffrey S. Allen, Assistant Project Manager Eckenfelder Inc. Nashville, Tennessee 37228 Suzanne S. Fenton, Professor James M. Fenton, Professor Donald W. Sundstrom, Professor Department of Chemical Engineering The University of Connecticut Storrs, Connecticut 06269 INTRODUCTION Ethylenediaminetetraacetic acid (EDTA) is a common chelating agent and is used in chemical cleaning solutions for scale removal from steam boilers and heat exchangers. The composition of the chemical cleaning wastestream generated in the 1985 cleaning of the Northeast Utilities Millstone Unit No. 2 steam generators was used as a model for this study. The two generators cleaned at Millstone produced approximately 567 pounds of corrosion products as iron, copper, nickel, and zinc (complexed with EDTA) in 14.000 gallons of waste solvents.1 The treatment of these wastes requires breakdown of the metal-EDTA bonds, followed by separation and removal and/or destruction of metal and EDTA species. A diagram of a proposed process for the treatment of chemical cleaning wastes is presented in Figure 1. There are three major treatment steps in this proposed process. The first step is electrochemical reduction of the copper- and iron-EDTA complexes at low pH to produce copper metal, precipitated EDTA, and a solution containing iron (II), residual copper, and EDTA (as separate or complexed species). Electrochemical reduction is followed by chemical oxidation of the residual EDTA by hydrogen peroxide addition in order to destroy the remaining EDTA. The elimination of EDTA from the waste permits the remaining free copper, iron, and other metal species (nickel and zinc) to be precipitated out of solution at high pH in the third treatment step. The treatment system effluent is then essentially free from the target pollutants of EDTA, copper, and iron. This processing scheme allows for recovery of a high percentage of pure copper and nearly pure EDTA (via electrochemical reduction) for possible reuse. Since copper and EDTA are removed in the electrochemical reactor, a smaller amount of chemicals will be required for oxidation and precipitation of the remaining wastes. In addition, destruction of the residual EDTA via hydrogen peroxide oxidation will result in smaller, less hazardous volumes of final waste for ultimate disposal. These features give the proposed system an advantage over currently available treatment alternatives, and promote the concept of "pollution prevention." Several nondestructive and destructive technologies are currently available for the treatment of EDTA-based chemical cleaning wastes.I_s The nondestructive technologies include direct solidification, precipitation, evaporation, ion exchange, membrane processes, and electrochemical reduction. Disadvantages associated with these technologies include: (1) no destruction of EDTA (solidification, evaporation, membrane processes); (2) little or no volume reduction (solidification, precipitation, ion exchange, electrochemical reduction); (3) inability to treat EDTA-contain- ing wastes (precipitation); and (4) inability to handle concentrated solutions (ion exchange). De- 51st Purdue Industrial Waste Conference Proceedings, 1996. Ann Arbor Press. Inc.. Chelsea. Michigan 48118. Printed in U.S.A. 601 |
Resolution | 300 ppi |
Color Depth | 8 bit |
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