Recovery of Metals from Sludges and Wastewaters

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Title: RECOVERY OF METALS FROM SLUDGES AND WASTEWATERSAuthor: E. Radha Krishnan, Philip W. Utrecht,Avi N. Patkar, Jeffrey S. Davis, Steve G. Pour, Mary E. FoerstPublisher: William Andrew Inc.

Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00001___97953740ff2e96355afe82a7fd282082.pdfRECOVERY OF METALS FROM SLUDGES ANDWASTEWATERS


Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00003___b1c281feb427a529b99953c8aa93bfce.pdfRECOVERY OF METALSFROM SLUDGES



E. Radha Krishnan, Philip W. Utrecht, Avi N. Patkar,Jeffrey S. Davis, Steve G. Pour, Mary E. Foerst

IT CorporationCincinnati, Ohio


Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00004___e2d0f19ea1172ea9821d6d2a0cde2270.pdfCopyright 1993 by Noyes Data CorporationLibrary of Congress Catalog Card Number: 92-25243ISBN: 0-8155-1310-0ISSN: 0090-516XPrinted in the United States

Published in the United States of America byNoyes Data CorporationMill Road, Park Ridge, New Jersey 07656

10 9 8 7 6 5 4 3 2 1

Library of Congress Cataloging-in-Publication Data

Recovery of metals from sludges and wastewaters / by E. Radha Krishnan... [et al.].

p. em. -- (pollution technology review, ISSN 0090-516X ; no.201)

Includes bibliographical references and index.ISBN 0-8155-1310-01. Sewage--Purification--Heavy metals removal. 2. Metal wastes.

1. Radha Krishnan, E. II. Series.TD758.5.H43R45 1992628.3'58--dc20 92-25243



This book presents the state-of-the-art of metals treatment and recoverytechnologies to assist in identifying waste management options for metal-bearingsludges and wastewaters. Nine metal-waste producing industries are discussed:metal coatings, smelting and refining of nonferrous metals, paint and inkproducts, petroleum refining, iron and steel manufacturing, photographic industry,leather tanning, wood preserving, and battery manufacturing. These industrieswere selected because of the high metal concentrations associated with thesludges and wastewaters generated by plants within each of these industrysegments. The techniques presented here are also applicable to metal-bearingwaste streams in all other industries.

The Resource Conservation and Recovery Act (RCRA), as amended by theHazardous and Solid Waste Amendments of 1984, prohibits the placement ofuntreated wastes in or on the land. The land disposal prohibitions are waived ifthe hazardous wastes intended for disposal are treated such that they do notexceed a maximum concentration of hazardous constituents set by EPA or if thewastes are treated using a treatment method set by EPA.

The focus of the book is on established rather than emerging technologies, inorder to provide useful information on immediately available technologies toindustry. Metals treatment and recovery technologies addressed include chemicalprecipitation, electrowinning, high temperature metals recovery, membraneseparation, leaching, adsorption, and evaporation. For each of these technologies,a discussion of the following parameters is included: design specifications ofapplicable processes, waste characteristics affecting performance,pretreatment/post-treatment requirements, available performance data, availabilityof the technology and feasibility for treating wastes, environmentalimpact/residue management, and cost-effectiveness.

The information in the book is from Recovery of Metals from Sludges andWastewaters, prepared by E. Radha Krishnan, Philip W. Utrecht, Avi N. Patkar,Jeffrey S. Davis, Steve G. Pour, and Mary E. Foerst of IT Corporation for theU.S. Environmental Protection Agency, September 1991.

The table of contents is organized in such a way as to serve as a subject indexand provides easy access to the information contained in the book.


Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00006___ba36351c8e89a3e397df4ec148a7fa74.pdfvi Foreword

Advanced composition and production methods developed by Noyes Data Corporation areemployed to bring this durably bound book to you in a minimum of time. Specialtechniques are used to close the gap between "manuscript" and "completed book." In orderto keep the price of the book to a reasonable level, it has been partially reproduced byphoto-offset directly from the original report and the cost saving passed on to the reader.Due to this method of publishing, certain portions of the book may be less legible thandesired.


This report was prepared for the U.S. Environmental Protection Agency by ITCorporation, Cincinnati, OH (formerly PEl Associates, Inc.). The EPA WorkAssignment Manager was Mr. Ronald 1. Turner. The IT Project Manager wasMr. E. Radha Krishnan, P.E. The principal authors were Messrs. Krishnan, PhilipW. Utrecht, Avi N. Patkar, Ph.D., P.E., Jeffrey S. Davis, Steve G. Pour, and Ms.Mary E. Foerst.


The material in this book was prepared as an account of work sponsored bythe U.S. Environmental Protection Agency. It has been subject to theAgency's review and it has been approved for publication. On this basis thePublisher assumes no responsibility nor liability for errors or anyconsequences arising from the use of the information contained herein.

Mention of trade names or commercial products does not constituteendorsement or recommendation for use by the Agency or the Publisher.Final determination of the suitability of any information or product for usecontemplated by any user, and the manner of that use, is the soleresponsibility of the user. The book is intended for information purposesonly. The reader is warned that caution must always be exercised withpotentially hazardous materials such as metals in sludges and wastewaters,and expert advice should be obtained before implementation of processesinvolving recovery of these metals.

Any information pertaining to law and regulations is provided forbackground only. The reader must contact the appropriate legal sources andregulatory authorities for up-to-date regulatory requirements and theirinterpretation and implementation.

The book is sold with the understanding that the Publisher is not engagedin rendering legal, engineering, or other professional service. If advice orother expert assistance is required, the service of a competent professionalshould be sought.

Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00007___fcbf4f59f90e23edb04c67f2d60a1a5c.pdfContents and Subject Index

1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1

2. WASTE CHARACTERIZATION 3Metal Coatings 3Smelting and Refining (Nonferrous Metal Manufacturing) 14Paint, Ink, and Associated Products 14Petroleum Refining 16Iron and Steel Manufacturing . . . . . . . . . . . . . . . . . . . . .. 17Photographic Industry 18Leather Tanning and Finishing . . . . . . . . . . . . . . . . . . . . . . . .. 18Wood Preserving 19Battery Manufacture 19

3. METALS RECOVERY TECHNOWGIES .. . . . . . . . . . . . . . . .. 21Chemical Precipitation 21

Process Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 21Hydroxide Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . .. 22Sulfide Precipitation 22Carbonate Precipitation 28Sodium Borohydride Precipitation 28Phosphate Precipitation 29Differential Precipitation 29Zinc Cementation 29Coagulation/Coprecipitation (Alum, Lime, and

Polyeiectrolytes) 30Waste Feed Characteristics 30Pretreatment Requirements 31


Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00008___9ecd9ead81ed011e127f405b96c8b684.pdfviii Contents and Subject Index

Posttreatment Requirements 31Perfonnance Data 31Availability 33Environmental Evaluation 36Costs 37

Electrolytic Recovery 38Electrowinning 38

Process Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 38Technical Evaluation 39

Waste Feed Considerations 39Pretreatment Requirements 41Posttreatment Requirements 41

Perfonnance Data 41Availability 43Environmental Evaluation 45Costs 45

Electrodialysis 47Process Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 47Technical Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Waste Feed Considerations 47Pretreatment Requirements 47Posttreatment Requirements 49

Availability 49Environmental Evaluation 49Costs 49

High-Temperature Metals Recovery (HTMR) 50Process Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 50Waste Feed Characteristics 52Pretreatment Requirements 53Posttreatment Requirements . . . . . . . . . . . . . . . . . . . . . . . . . .. 53Perfonnance Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 54Availability 55Environmental Evaluation 56Costs 57

Membrane Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 57Microfiltration and Ultrafiltration . . . . . . . . . . . . . . . . . . . . . .. 59

Process Description 59Technical Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 59

Waste Feed Considerations 59Pretreatment Requirements . . . . . . . . . . . . . . . . . . . . . . .. 59Posttreatment Requirements 59

Perfonnance Data . . . . . . . . . . . . . . . . . . . . . . . . . . .. 59Availability 61Environmental Evaluation 62

Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00009___fb1f67987506f53c05608f41c047fa30.pdfContents and Subject Index ix

Costs 62Reserve Osmosis (RO) 62

Process Description 62Technical Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 63

Waste Feed Considerations 63Pretreatment Requirements . . . . . . . . . . . . . . . . . . . . . . .. 63Posnreatment Requirements 63

Performance Data . . .. 63Availability 65

Process Maturity 65Costs 65

Donnan Dialysis and Coupled Transport 66Applicability of Membrane Separation Systems . . . . . . . . . . . .. 69

Leaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 70Process Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 70Waste Feed Characteristics 72Pretreatment Requirements 74Posnreatment Requirements . . . . . . . . . . . . . . . . . . . . . . . . . .. 74Performance Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 74

Metals Recovery from Hydroxide Sludges 74Biohydrometallurgy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 77Ammonium Carbonate Leaching 77Aluminum-Finishing Sludges 79Zinc Sulfate Sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 80Plating Sludge Ponds Remediation 80Lead Wastes from Superfund Sites . . . . . . . . . . . . . . . . . . .. 81

Availability 81Environmental Evaluation 85Costs 85

Adsorption 86Carbon Adsorption 86

Process Description 86Technical Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 88

Waste Feed Considerations 88Pretreatment Requirements . . . . . . . . . . . . . . . . . . . . . . .. 88Posnreatment Requirements 88

Performance Data 89Chromium 89Mercury 89

Availability 91Environmental Evaluation 92Costs 92

Ion Exchange 95Process Description 95

Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00010___f4a38472f4a6326716408fab36f7b264.pdfx Contents and Subject Index

Technical Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 97Waste Feed Considerations 97Pretreatment Requirements . . . . . . . . . . . . . . . . . . . . . . .. 99Posttreatment Requirements 99

Performance Data .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 99Availability 100Environmental Evaluation 101Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 102

Enporation 102Process Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 102Technical Evaluation 105

Performance Data 108Availability 111Environmental Evaluation 112Costs 113

4. CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 123



Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00011___d04dc40bb9c4c0623478ba05c035d635.pdf1. IntroductionThe U.S. Environmental Protect1on Agency (EPA) is interested in

evaluating technologies for their capability to recover metals from sludgesand wastewaters. Section 3004 of the Re~ource Conservat10n and Recovery Act(RCRA) , as amended by the Hazardous and Solid Waste Amendments (HSWA) of1984, restricts the disposal of RCRA-regu1ated hazardous wastes in or on theland. The land disposal prohibitions are waived If the hazardous wastesintended for disposal are treated such that they do not exceed a maximllmconcentration of hazardous constituents set by EPA or if the wastes aretreated using a treatment method set by EPA. Also, HSWA authorizes waivingthe disposal of untreated hazardous wastes if facilities seeking disposal ofuntreated wastes can demonstrate to the Administrator that the hazardousconstituents of wastes intended for disposal will not migrate from thedisposal site as long as the waste remains hazardous. The EPA publishesthese land disposal restrictions in the 40 Code of Federal Regulations (CFR)Part 268.

The amendments to RCRA spec1fy dates by which land disposalrestrictions are to take effect for specific hazardous wastes. The LandDisposal Restrictions for the first third, the second third, and the lastthird of scheduled RCRA Wastes identify treatment methods and standards thatmust be met before these listed wastes can be land-disposed. The first thirdrules were finalized in August 1988, the second third rules were finalized inJune 1989, and th~ rules for the last third were proposed in late 1989 andfinalized in Hay 1990. This report presents info~ation on the state of theart of metals recovery technologies to support EPA's Office of Solid Waste inidentifying waste-management options for the recovery of metal-bearingslUdges and wastewaters that may be regulated under RCRA. Waste treatmenttechnologies (e.g., chemical precipitation) that could eventually result inrecovery of specific metals are also included in this report. The focus ofthis report is on established rather than emerging technologies in order toprovide useful information on immediately available technologies to industry.

This report covers nine major metal-waste-producing industries:I) metal coatings; Z) smelting and refining of nonferrous metals; 3) paint,ink, and associated products; 4) petroleu~ refining; 5) iron and steel manu-facturing; 6) photographic industry; 7) leather tanning; 8) wood preserving;and 9) battery manufacturing. These industries were selected because of thehigh metal concentrations associated with the sludges and wastewaters gener-ated by plants within each of these industry segments. Section 2 of thisreport characterizes the wastes generated by these industries and addressescurrent waste-management Ilractices.


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Metals recovery technologies addressed in this report include thefollowing: chemical precipitation, electrolytic recovery. high-temperaturemetals recovery (HTHR) , membrane separation, leaching. adsorption. and evapo-ration. For each of these technologies. Section 3 presents a discussion ofthe following parameters: 1) design specifications of applicable processes.2) waste characteristics affecting performance. 3) pretreatment/post-treat-ment requirements. 4) available performance data. 5) availability of thetechnology and feasibility for treating wastes addressed in Section 2. 6)environmental impact/residue management. and 7) cost-effectiveness. Ongoingresearch projects in the area of metals recovery, such as those beingconducted by the U.S. Bureau of Mines. are also highlighted.

Section 4 summarizes the conclusions of this study with respect to theapplicability of different technologies for potential treatment of varioussludges and wastewaters. A glossary of technical terms is provided at theend of this report.

Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00013___f2f28b7d716ffbb0e37a4b8c93d78554.pdf2. Waste CharacterizationMetals or metallic compounds are used during the manufacture of a

variety of products. As a result, during processing or productionoperations, Industries generate wastes centaining metals. In 1984, industrygenerated an estimated 5.8 billion gallons of metal-bearing wastes, includingsludges, wastewaters, and treatment residues.'

This section characterizes the wastes generated by major metal-waste-producing Industries and addresses current waste management practices. Thenine Industries discussed are metal coatings; smelting and refining of non-ferrous metals; paint, ink, and associated products; petroleum refining; ironand steel manufacturing; photographic industry; leather tanning; woodpreserving; and battery manufacturing. Waste streams from each of theseindustries have unique characteristics; however, the wastes also containcommon metals, such as aluminum (Al), arsenic (As), cadmium (Cd), chromium(Cr), copper (Cu), lead (Pb), nickel (Ni), silver (Ag), and zinc (Zn).

Table I presents the number of metal-waste generators (as of 1983) byStandard Industrial Classification (SIC) code for several major industrycategories. Table 2 prOVides a breakdown of the metal-bearing wastes by 0,F, and K EPA Hazardous Waste codes. Table 3 presents estimates of thequantities of the wastes handled by landfill lng, storage, or treatment.Although new technologies for metal recovery have emerged, only about half ofthe industries that generate metal wastes recover the metals from wastewatersand sludges. Ion exchange for recovery of electroplating baths and chemicalprecipitation of photographic developing baths are examples of currentrecovery methods being used. Table 4 presents brief descriptions of thehazardous wastes generated from the major Industry categories Included inthis study. Table 5 presents average compositional data on six toxic metalsfor several of these waste categories; other metals such as zinc and coppermay also be found In many of the wastes, e.g. F006, K06I. Each of the majormeta1-waste-generating industries are discussed in more detail in thesubsections that follow.METAL COATINGS

The metal-coatings (plating and metal-finishing) industry segment In-cludes operations such as electroplating, anodizing, electroless plating,chemical conversion coating, etching, printed circuit board manufacturing andmilling. Metals most commonly used for these applications include chromium,cadmium, copper, nickel, silver, and zinc. All of the methods for chemicalsurface treatment involve dipping metal objects into a bath to apply the


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SIC description

Plating and surface finishingPaints and allied productsMetal coating and allied productsMotor vehicle parts and accessoriesIndustrial inorganic chemicalsMetals, nonferrous, secondaryFabricated metal productsNational securityMotors and generatorsMiscellaneous manufacturing

industriesMetal, nonferrous, rolling, drawingPrinting inkBlast furnaces, steel millsFoundries, gray ironElectric servicesIndustrial organic chemicalsPlastics materialRadio and TV communication equipmentElectronic componentsMotor vehicle bodiesMachine tool accessories

No. offacil ities







Reference 2.


PercentWaste ofvolume, total Number of

106 galsjyr metals generatorso Wastes 3685 46.9 3860

F Wastes 3920 49.9 2091

K Wastes 219 2.8 402

Reference 1.

Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00015___477b2d38afe0ea6b860ddffee339ffc5.pdfTABLE 3. WASTE VOLUMES (ALL METAL WASTES) AND DISPOSAL METHODS FOR METAL-WASTE GENERATORS bTotal land-disposed Stored Treated

Volume~andled, ~oluDle, Percent Xol Ulle , Percent ~olullle. Percent

10 gal/yr 10 gi l/yr handled 10 gal/yr handled 10 gal/yr handled

5,B30 1,460 25.0 2,463 42.2 3,114 53.4

Source: Reference 1.b Sums of volumes handled by Indlvlduil methods are greater thin reported total volumes handled because

of double-counting of those ~aste strea~s subject to more than one IIlethod of handling. This alsoaccounts for the fact that the percentage of ~aste handled by each method totals more than 100. ~




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EPA HazardousWaste No. Hazardous waste description

F006 Wastewater treatment sludges from electro-plating operations except the following:1) sulfuric acid anodizing of aluminum;2) tin plating on carbon steel; 3) zincplating (segregated basis) on carbon steel;4) aluminum or zinc-aluminum plating oncarbon steel; 5) cleaning/stripping asso-ciated with tin, zinc, and aluminum platingon carbon steel; and 6) che.ical etching andmilling of aluminum.

F007 Spent cyanide plating bath solutions fromelectroplating operations.

FOOS Plating sludges from the bottom of platingbaths from electroplating operations wherecyanides are used in the process.

F009 Spent stripping and cleaning bath solutionsfrom electroplating operations where cya-nides are used in the process.

F019 Wastewater treatment sludges from the che.i-cal conversion coating of aluminum.

F032b Wastewaters, process residuals, preservativedrippage, and discarded spent formulationsfrom wood-preserving processes at facilitiesthat currently use or have previously usedchlorophenolic formulations (except wastesfrom processes that have complied with thecleaning or replacement procedures set forthin RCRA 261.35 and do not resume or initiateuse of chlorophenolic formulations). Thislisting does not include KOOI bottom sedimentsludge from the treatment of wastewater fromwood-preserving processes that use creosoteand/or pentachlorophenol.


Li stedconstituent(s)Cadmium, hexav-alent chromium,nickel, cyanide(complexed)




Cadmium, hexav-alent chromium,cyanide(complexed)Benz(a)an-thracene,benzo(a)pyrene,dibenz(a,h)-anthracene,indeno( 1, 2,3-cd) pyrene,ch1oropheno1,arsenic,chromium,tetra-, penta-hexa-, hepta-penta-chlorodibenzo-furans.

Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00017___a71476dbf1c7e83dcab345ca0e9c98ae.pdfWaste Characterization 7

TABLE 4 (continued)EPA Hazardous

Waste No. Hazardous waste descriptionListed






Wastewaters, process residuals, protectantdrippage, and discarded spent formulationsfrom wood-surface-protection processes atfacilities that currently use or havepreviously used chlorophenolic formulations(except wastes from processes that havecomplied with the cleaning or replacementprocedures set forth in RCRA 26l.35 anddo not resume or initiate use of chlorophe-nolic formulations).Wastewaters, process residuals, preserva-tive drippage, and discarded spent formula-tions from wood-preserving processes usingcreosote formulations. This listing doesnot include KOOl bottom sediment sludge fromthe treatment of wastewater from wood-pre-serving processes that use creosote and/orpentachlorophenol.

Wastewaters, process residuals, preserva-tive drippage, and discarded spent formula-tions from wood-preserving processes usinginorganic preservatives containing arsenicor chromium. This listing does not includeKOOl bottom sediment sludge from the treat-ment of wastewater from wood-preservingprocesses that use creosote and/or penta-chlorophenol.Bottom sediment sludge from the treatmentof wastewaters from wood-preserving pro-cesses that use creosote and/or penta-chlorophenol.Wastewater treatment sludge from the pro-duction of chrome yellow and orange pigments.

Wastewater treatment sludge from the pro-duction of molybdate orange pigments.

Pentadll oro-phenol, 2,3,4,6-tetrachloro-phenol, 2,4,6-tri-chloro-phenol, tetra-penta-, hexa-,heptachloro-dibenzofurans.

Benz(a) anthra-cene, benzo(k)fluoranthene,benzo(a)pyrene,dibenz(a,h)anthracene,indeno(l,2,3-cd)pyrene,naphthalene,arsenic,chromium.


None listed

Hexavalentchromi um, 1ead

Hexavalentchromi um, 1ead

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TABLE 4 (continued)EPA Hazardous

Waste No. Hazardous waste description

K004 Wastewater treatment sludge from the pro-duction of zinc yellow pigments.

KOOS Wastewater treatment sludge from the pro-duction of chrome green plg.ents.

K006 Wastewater treatment sludge from the pro-duction of chrome oxide green pigments(anhydrous and hydrated).

K007 Wastewater treatment sludge from the pro-duct)on of Iron blue pigments.

K008 Oven residue from the production of chromeoxide green pigments.

K048 Dissolved air flotation (OAF) float from thepetroleum refining industry.

K049 Slop oil emulsion solids froll the petroleumrefining industry.

KOSO Heat exchanger bundle-cleaning sludge fromthe petroleum refining industry.

KOSI API separator sludge frOll the petroleumrefining industry.

KOS2 Tank bottoms (leaded) from the petroleumrefining industry.

K060 Ammonia still lime sludge from cokingoperations.

K061 Emission control dust/sludge from the primaryproduction of steel in electric furnaces.

K062 Spent pickle liquor generated by steel-finishing operations of facilitieswithin the iron and steel industry.


Li stedconstituent(s)Hexavalentchromium

Hexavalentchromi um, leadHexavalentchromium



Hexavalentchromium, lead

HexavalentchrOlli WI, leadHexavalentchromiulll

HexavalentthroAti um, lead



Hexavalentchromium,lead.cadmi UII

HexavalentchrOllli UII, 1ead

Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00019___f878f27943bd2ddd8baf2c84d5e27367.pdfWaste Characterization 9

TABLE 4 (continued)EPA Hazardous

Waste No. Hazardous waste descriptionK064 Acid plant blowdown slurry/sludge resulting

from the thickening of blowdown slurry fromprimary copper production.

K06S Surface impoundment solids contained In anddredged from surface impoundments at primarylead smelting facilities.

K066 Sludge from treatment of process wastewaterand/or acid plant blowdown from primary zincproduction.

K069 Emission control dust/sludge from secondarylead smelting.

K086 Solvent washes and sludges, caustic washes,and sludges from cleaning tubs and equipmentused in the formulation of ink from pigments,driers, soaps, and stabilizers containingchromium and lead.

K090 Emission control dust or sludge from ferrochromium silicon production.

L1 stedconstituent(s)Lead, cadmium

Lead, cadmi um

Lead, cadmi um








Waste leaching solution from acid leachingof emission control dust/sludge fromsecondary lead smelting.

Hexavalentchromium, lead,cadmiumArsenic



Sil ver

Reference 3.b Proposed for listing as hazardous wastes.

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ous WasteNo. CN As Cd Cr Pb Hg Hi

F006 5.Sb 6.24 1,320 39,730 408 0.32 14,760131e 25.4d0.1

F007 14,547

FooS 64

Fo09 350,000 21.6 525.9 25.39 2,954

F019 597

3.0 0.5 100 24 10 6 0 30 24 100 24 100 24 n01.0 70 12 10 6 0 20 24 80 24 85 24 ~

"Reference 46. ~n::r::s00-



Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00084___894950e32289185245970cda776b3ef6.pdf74 Recovery of Metals from Sludges and Wastewaters

Pretreatment Regyirements

Pretreatment is generally not necessary before the leaching of asludge. Dewatering of the sludge to 1 percent solids. however. may provide ahigher acidification efficiency while still extracting most of the metalscontent.

Posttreatment Reguirements

The leaching procedure used for metals removal from sludge isintimately related to the procedures chosen for recovery of the metals fromthe resulting solutions. Leaching is not a stand-alone method for metalsrecovery unless the leaching extract (liquid stream concentrated with theleached metals) Is directly reused in a process; i.e., leaching may meet thegoal of rendering the sludge nonhazardous. but It usually will not meet thegoal of recovering the metals in a directly reusable form. Complete "ecoveryof metals will usually involve a process train of which leaching is only thefirst step. Often. the leached solutions can be electrolyzed to recover puremetals. Chemical precipitation can also be used to attain highconcentrations of the metallic constituents of interest, which can be furthertreated in metals recovery processes.

A leaching process will produce a secondary sludge that must be dis-posed. Because rinse baths from electroplating operations usually containsulfates. the addition of lime in the wastewater treatment plant will createa calcium sulfate precipitate. This sludge is insoluble in an acid leach andwill therefore be the secondary sludge resulting from an acid leaching proce-dure.

Performance Data

Several leaching technologies have been proposed for the recovery ofmetals from various kinds of sludges. Leaching has been implemented on anindustrial scale. and several laboratory-scale tests have been conducted.Some of the leaching processes are discussed in the following subsections.Brief descriptions of the posttreatment requirements are also included. Theposttreatment requirements are generally metals-recovery techniques that arediscussed in other sections of this report.

Metals Recovery From Hydroxide Sludges--

In an EPA-sponsored project conducted by the Montana College ofMineral Science and Technology, the use of well-established metallurgicaltechniques to recover metals from metal-finishing hydroxide sludges wasinvestigated. 4 The process train consisted of sulfuric acid leaching; ironremoval by jarosite [KFe3 (OH)6(S04)z] precipitation (for iron concentrationsfrom 5 to 20 percent) or solvent extraction (for iron concentrations below 5percent); copper removal by solvent extraction and copper recovery byelectrowinning or copper sulfate crystallization; zinc recovery by solventextraction; chromium oxidation and recovery by lead chromate precipitation;nickel removal by sulfide precipitation or nickel sulfate crystallization;

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and final solution purification of low concentration residual ions by ionexchange. Pilot-scale tests were conducted to investigate solvent reagentdegradation, to develop mass balances, and to determine what operationalproblems may occur in full-scale operations.

The equipment required for the process consisted of leach vessels,settlers, a filter press, solvent extraction mixer-settlers, chlorine orelectrochemical oXidizer, pH monitors and controllers, precipitating vessels,crystallizers, and an ion exchange column. No problems were encountered withmechanical control of the system. Chemicals were necessary to maintain thepH.

The sulfuric acid leaching solution was effective in dissolVing metalsfrom a sludge containing 23 weight percent solids under relatively mildconditions; i.e., a residence time of 30 minutes, a temperature of 40 to50C, a sludge-to-added-liquid ratio of 0.8, sufficient acid content tomaintain a pH of 0.5 to 1.5, and enough agitation to suspend particulates inthe liquid phase. Approximate removal rates obtained were 56 to 95 percentfor iron, 94 to 95 percent for copper, 91 to 96 percent for zinc, 85 to 98percent for nickel, 97 percent for chromium, 93 to 100 percent for calcium,and 90 to 97 percent for aluminum.

A 270 L leach vessel was capable of processing more than a ton of'sludge per 8-hour day. Because the filterability of the leach residue wasdifficult, the jarosite precipitation operation was conducted in the samevessel as the leach process. The resulting precipitate was easy to filter.Filterability of this leach residue can also be improved by using filteraids. In this process scheme, the precipitation rather than the leaching stepwas the rate-limiting factor.

For every 100 pounds of metal-finishing hydroxide sludge (23 percentsolids content) that was treated, 15 pounds of leach residue was generated.This residue was EP Toxic for cadmium and chromium; however, the leachingprocess was effective in achieving a reduction in the total quantity ofhazardous metal-bearing sludges. In this study, 45 pounds of jarosite wereproduced per 100 pounds of hydroxide sludge. The precipitate from the jaro-site precipitation process contained 10 percent of the copper, 6 percent ofthe zinc, 18 percent of the chromium, and 6 percent of the nickel.Subsequent leaching of the jarosite-based precipitate may be desirable torecover additional metals. Higher iron concentrations created larger amountsof slUdge and resulted in greater losses of chromium.

This process was also used to investigate the removal of metall from ahydroxide sludge generated at an electrochemical machining facility. Theprimary ~tals in the slUdge were iron, chro.ium, and nickel; however,significant amounts of niobium, titanium, and cobalt were also present.Sulfuric acid leaching at 18C and a pH of 0.7 dissolved 97 percent of thesludge (with a solids concentration of 33 percent), 93.5 percent of the iron,95.4 percent of the chromium, 95.1 percent of the nickel, 100 percent of thecobalt, 73 percent of the titanium, and none of the cobalt. Some of thenickel present with niobium as metallic particles did not readily dissolve.

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The leach residue contained 19.3 percent nickel, 43.1 percent niobium, and7.2 percent titanium; this metal content is high enough to be a marketableproduct. The leach residue contained all of the niobium and 27 percent ofthe titanium in the original sludge. By selective phosphate precipitation atvarious pH values, 87 percent of the chromium and 94.6 percent of the nickelwere recovered as separate (and therefore reusable or marketable) sludges.The combined leach residue and ferric phosphate sludge was not EP Toxic forchromium, but the EP extract contained nickel at concentrations more than 100times the drinking water standard. The sludges were combined because theavailable filter apparatus was not appropriate for separating the leachresidue from the sulfuric acid solution.

AMAX Extractive Research and Deve19pment, Inc., under contract to theU.S. Army Toxic and Hazardous Materials Agency (USATHAHA), conducted a studyaimed at identifying alternatives for recove~ing metals from Army depotelectroplating wastewater treatment sludges. 5 The researchers consideredthree processes: 1) an ammonia leach followed by an acid or causticleach, 2) a caustic leach, and 3) an acid leach. Sulfuric acid was chosenfor laboratory-scale testing because of the advantages listed earlier.

For laboratory testing, a synthetic sludge similar to sludges expectedfrom Army depot electroplating operations was prepared. This slUdge con-tained 10 percent chromium hydroxide; 7 percent each of copper hydroXide,iron (II) hydroXide, nickel hydroxide and zinc hydroxide; 1 percent cadmiumhydroxide; and 61 percent calciWl sulfate. The sludge was prepared at threeconditions: 1) no aging, 2) 7-day aging at 65OC, and 3) 6-week aging at roomtemperature. The third condition is the most representative of actual waste-water treatment sludges. The sludges were leached with sulfuric acid for 90minutes at a pH of 1.5. Hore than 99 percent of each of the metals wasremoved except cadmium, which had a metal-removal efficiency near 98 percent.Most of the metals were leached within 30 minutes. The age of the sludge hadlittle effect on the efficiency of metals removal.

The sludge remaining after the leaching procedure was found to be EPToxic for cadmium and chromium. The EP extract from the sludge that was agedfor 7 days at 65C had the highest metals concentrations--nearly an order ofmagnitude higher than those in the sludge that was not aged. The slUdgethat was aged for 6 weeks also had higher concentrations of metals in theextract than the sludge that was not aged. Photomicrographs of the agedsludge showed a different crystalline structure than the nonaged sludge,which could perhaps trap some heavy metals by chemisorption, mechanicalocclusion, or lattice substitution. As a result, the sulfuric acid was lesseffective in the removal of all the heavy metals under the test conditions,although the metals were leached under the conditions (24-hour leach by anaqueous solution maintained at a pH of 5 with acetic acid) of the EP Toxicitytest. One sample of the sludge that was aged for 6 weeks was leached in ablender, which apparently broke down the crystalline structure and resultedin an EP extract with lower metal concentrations than all other results.After the filter cake was leached, it was made nonhazardous by mixing 10percent by weight of lime with the solids.


Metals Recovery Technologies 77

Selective sulfide precipitation was used to remove the metals from theleaching solution. Copper and cadmium were precipitated from the solutionwith the least amount of sulfide addition, and zinc was nearly quantitativelyremoved by the additional sulfide. Hickel and iron were only partially re-moved, whereas more than 90 percent of the chromium stayed in solution.After the pH was raised, chromium and iron precipitated and the nickelremained in solution. The precipitate was then leached with three organicsolvents, which concentrated the chromium in the aqueous phase and the ironin the organic phase.

Biohydrometallurgy--Biohydrometallurgy or bacterial leaching is emerging as a metals

recovery technology. A mixed bacterial culture containing Thiobacillusferrooxidans and Thiobacjllus thioxidans has been used to extract Zn, Cu, Pb,and Cd from waste sludges. Q These bacteria use elemental sulfur to grow.The metals in the waste are solubilized by the sulfuric acid produced by thebacteria, as shown in the following equation:

bacteria25 + 302 + 2H20 - 2H2S04

This process has shown removal rates as high as 80 to 90 percent forCd. Leptosperrillum ferroxidans and a thermophilic Sulfolobus species havealso shown promise as bacterial leaching cultures."

Ammonium Carbonate Leaching--In a 1977 study conducted by EPA, the use of ammonium carbonate was

investigated to remove copper and nickel from hldroxide sludge producedduring treatment of electroplating wastewater. 4 The slUdge also containedchromium. Upon the addition of ammonium carbonate, copper and nickel formedwater-soluble amine complexes. These complexes could then be separated fromthe chromium, which does not fOnl complexes with ammonia. The leach residuewas then treated by roasting it with sodium carbonate and leaching the fusedmass with water to return soluble chromates and dichromates into solution,from which they could be recovered as anhydrous chromic acid. The processwas successful in reducing copper, nickel, and chromium from levels of 10 to20 percent in the sludges to a level of I percent in the leach residue. Theexperiments removed more than 90 percent of the copper, 60 percent of thenickel, and less than 10 percent of the chromium in the leaching stages. Therecovery of nickel was less than desired; additional optimization couldproduce better results.

Because ammonium carbonate leaching is ~re metal-specific than acidleaching, chromium can be separated from copper and nickel in the leachingstep itself rather than in the posttreatment phase. Removal of chromium isnecessary because it interferes with the electrodeposition of copper andnickel.

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Leaching studies were also conducted to evaluate the influence of cer-tain variables on the ability of the process to dissolve copper and nickeland yet leave chromium in the sludge. A summary of the conclusions of thesestudies is provided here.

Sludge pretreatment. Four forms of the sludge were examined:1) the raw sludge containing 20 percent solids; 2) sludge dried at110C and then pulverized and blended; 3) dried sludge that had beenball-milled with water to create a slurry suspension; and 4) driedsludge washed with water to remove 10 percent of its weight aswater-soluble material, followed by filtering, redrying, andgrinding. The data showed that conditioning the sludge was notadvantageous for copper and nickel recovery. Creating a slurrysuspension seemed to enhance chromium solubility, which was un-desirable.

Choice of leachant. Three leaching agents were studied: ammoniumcarbonate, ammonium hydroxide, and ammonium sulfate. Ammoniumcarbonate at a concentration of 10 weight percent of ammonia pro-vided the best removal rates for copper and nickel.

Temperature. 50C provided the most rapid extractions.

Number of leaching stages. A two-stage leach was required becausethe dissolution of nickel is inhibited by high concentrations ofcopper in solution. The reason for this is that the leaching ofcopper proceeds best at a pH of about 10, whereas the leaching ofnickel proceeds best at a pH of 8 or 9. Most of the copper isremoved in the first stage, and most of the nickel is removed in thesecond stage.

Leaching time. Extending the leaching time beyond 3 hours improvedthe efficiency of extraction only margina1ly--not enough to justifythe additional costs. Extended leaching times at elevated tempera-tures volatilized some of the ammonia values and resulted in lowleaching efficiencies.

Aeration. Bubbling air and carbon dioxide through the leachingsolution was ineffective in improving copper and nickel dissolution.

Metal form. Metals in wastewater treatment sludges are present inboth hydroxide and oxide forms. Experiments were conducted tocompare the amount of dissolution of oxide versus hydroxide sludges.Approximately 50 percent of the copper was recovered from the oxide,whereas all of the copper was recovered from the hydroxide. Theoxides of chromium and nickel were not leached to any significantdegree. All of the nickel was recovered from its hydrOXide, whereasthe hydroxide of chromium was not affected.

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Aluminum-finishing Sludges--Sulfuric acid leaching of aluminum sludges from water treatment plants

has often been used for the rr,covery of aluminum as aluminum sulfate forreuse in the treatment plant. 0 The process has been practiced since asearly a~ 1903 and has been widely applied in Japan, Great Britain, andPoland. 1 Alum sludge is gravity-thickened, and the underflow sludge fromthe thickener is mixed with sulfuric acid in a rapid-mix tank. Acidifiedsludge is transferred to a separator, where supernatant liquid (i.e., theleachate) is recovered for reuse as a coagulant in the water treatmentprocess. Sludge from the underflow of the separator is neutralized withlime, dewatered, and disposed.

Because the primary constituent of most slUdges from the aluminum-finishing industries is aluminum hydroxide, the sulfuric acid leachingprocess may be applicable to aluminum-finishing sludges. A 1987 researchstudy sponsored by EPA and conducted by the Georgia Institute of Technologyfocused on producing commercial-strength solut~ons of aluminum sulfate(liqUid alum) from aluminum-finishing sludges. 2 Three sludges wereinvestigated: 1) a gelatinous aluminum hydrOXide suspension produced by con-ventional lime neutralization of dilute aluminum anodizing rinse waters in awastewater treatment plant; 2) a crystalline aluminum hydroxide slUdge pro-duced from neutraliZing spent caustic etch with spent finishing acid (refer-red to as segregated neutralization); and 3) a high-solids sludge produced byrecovering aluminum trihydrate crystals from caustic etch solutions.

Commercial-strength solutions of liquid alum require concentrations of8 weight percent aluminum oxide. Obtaining this strength requires a minimumsludge solids content of at least 20 percent. Sludges obtained from anactual aluminum-finishing plant were therefore dewatered before leaching.After dewatering, the sludges were leached separately with stoichiometricquantities of sulfuric acid (based on the sludge aluminum content) at leach-ing times of 30 to 60 minutes, an initial temperature greater than 95C, anda maintained temperature of 50 to 90C for the remainder of the experiments.

Conventional neutralization sludge filter cakes with solids contentsafter dewatering of 17.4 to 18.1 percent were extracted to produce liquidalum with concentrations of 7.4 to 8.8 percent aluminum oxide. A total of 93to 97 percent of the aluminum was leached, and 95 to 99 percent of the ini-tial suspended solids were destroyed.

Segregated neutralization slUdge filter cakes with solids contents of36.8 percent were extracted to produce liquid alum with concentrations of 8.1to 9.0 percent aluminum oxide by the addition of water equal to 80 to 100percent of the mass of wet sludge extracted. The etch recovery sludge with asolids content of 91.6 percent produced a liquid alum with a concentration of8.3 to 9.2 percent aluminum oxide by the addition of water equal to 200 to370 percent of the wet sludge extracted. A total of 70 to 85 percent of thealuminum was extracted, and 54 to 85 percent of the suspended solids weredestroyed. The purity of the final liquid alum was comparable to othercommercial products except that the concentration~ of nickel and tin were

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high. These metals may have been the result of drag-out from the anodizingprocess and the use of nickel in seal tanks; segregation of these wastewaterswould prevent these metals from contaminating the aluminum sludges.

Zinc Sulfate Sludge--

Leaching has als~ been applied to the recovery of zinc sulfate fromviscose manufacturing. 3 More than 100,000 tons of zinc sulfate is used inthe manufacture of viscose rayon in the United States. Because zinc sulfateis not consumed in the production reactions, this quantity represents a lossof nonrenewable resources. Currently, the zinc is usually precipitated withlime at a pH of 10 and is not recovered. In a two-stage system developed byAmerican Enka Co., the pH is raised to 6.~ in the first stage, which resultsin precipitation of most of the iron, calcium sulfate, and otherconstituents, but not zinc hydroxide. The pH is then raised to 9.5 to 10 ina separate vessel, the zinc solution is contacted with a slurry of preViouslyprecipitated zinc hydroxide crystals, and additional zinc hydroxide precipi-tates onto the surface of the crystals. The dense sludge is first allowed tosettle and is then leached with sulfuric acid. The resulting zinc sulfatesolution can be directly reused in the rayon manufacturing process.

FMC Corporation recovers zinc from zinc hydroxide sludge generatedduring the manufacture of rayon fiber. Sludge containing 2 to 6 percentsolids is heated to approximately 150C to make the sludge more amenable tofiltration. The cake solids after filtration contain approximately 34percent zinc. The cake is leached with sulfuric acid, and a 25 to 30 percentzinc sulfate solution is produced. To remove iron contamination, ferrousiron is converted to ferric iron with hydrogen peroxide and precipitated outat a pH of 4.5. After the iron \s filtered out, the zinc sulfate solution isrecycled to the rayon plant.

Another manufacturer of vulcanized fiber treats100 to 300 mgjL zinc by raising the pH to 8.5 to 9.5.then leached with hydrochloric acid, which results intion. After it is concentrated in an evaporator, thereused in the manufacturing process.

a wastewater containingThe precipitate is

a zinc chloride solu-zinc solution can be

Plating Sludge Ponds Remediation--

In late 1988-early 1989. Davy HcKee conducted a feasibility and treat-ability study for the remediation of a large electroplating sludge pond.These studies focused on utilizing metals recovery techniques to produce acopper-nickel carbonate for sale. and a caa.,~-zinc sulfide for furtherprocessing. A multi-step dissolution-precIpItation process using a sulfuricacid leach followed by lime soda softening was selected for recovery of ~ixedcopper and nickel values as their carbonates; a sulfidt precipitation stepwas evaluated for recovery of cadmium and ZInc values.

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Lead Wastes from Superfund Sites--The Bureau of Hines is developing a technique for recovery of lead from

battery casings and contaminated soils from several Superfund sites. Crushedebonite casing material containing 3,000 to 4,000 ppm lead Is the majorsource of lead contamination at these sites. The leaching technique consistsof prewashing in an ammonium carbonate solution followed by leaching withfluosilicic and/or nitric acid. Thr lead can then be recovered from theleached solution by electrowinning. '

Aya; labilityAmerican Enka Co. recycles zinc sulfate sludge, and FMC recovers zinc

from hydroxide sludges as zinc sulfate. The leaching of aluminum sludgesfrom water treatment plants for the recovery of aluminum as aluminu~ sulfatehas been widely practiced. The ammonium carbonate leaching process, whichwas developed by a Swedish company, HX-Processor, has been used for metalsrecovery at several companies, some of which have gone out of business as aresult of the falling prices of some metals.

Most of the leaching procedures discussed in previous sections have notbeen implemented at full scale. The technology, however, consists of rela-tively simple equipment for the leaching step itself. The basic unit opera-tions have been practiced widely in metallurgical industries, and adaptationsto metals recovery from sludges would be easy if the value of the recoveredmetals is determined to be sufficient to justify the expense of the opera-tion.

At the Recontek waste recycling facility, zinc-bearing solutions areleached with alkaline solutions, whereas non-zinc sludges are treated withacidic solutions. Zinc-bearing sludges are digested at approximately SOoCwith sodium hydroxide for a sufficient period of time, cooled and filtered.The filtrate is processed in a zinc cementation tank to precipitate metalsmore electro-negative than zinc (e.g., lead, cadmiu~) and then pumped to azinc electrowinning system. The non-zinc sludge waste fro. the digester(primarily copper and nickel) is digested with sulfuric acid, filtered toproduce a residue containing precious metals (e.g., gold, silver), and thefiltrate sent to the copper electrowinning system for production of coppercathodes. The solution leaving the copper electrowinning system Is sent to acrystallizer for nickel sulfate recovery.22

Table 39 presents the potential appl icability of leaching for the var-ious RCRA waste codes discussed In Section 2. Performance data do not existfor all of the waste codes, and bench- and pilot-scale studies need to beconducted to determine the viability of leaching as a metals recovery processfor these wastes. Table 40 presents the solubility of various metal co.-pounds in different solvents. The compounds listed are those that resultfrom precipitation processes as well as those that may be present in RCRAwaste sludges. Table 39 can be used to select a solvent for leachingparticular metals from a specific slUdge.

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RCRAWaste Code




Reference 3


Principal Toxic Metals

ArsenicBariumCadmiumChromiumLeadMercurySeleniumSil ver

Cadmium, Hexavalent Chromium, NickelCadmium, Hexavalent Chromium, NickelHexavalent Chromium

Hexavalent Chromium, LeadHexavalent Chromium, LeadHexavalent ChromiumHexavalent Chromium, LeadHexavalent ChromiumHexavalent ChromiumHexavalent ChromiumHexavalent Chromium, LeadHexavalent ChromiumHexavalent Chromium, LeadLeadArsenicHexavalent Chromium, Lead, CadmiumLead, CadmiumLead, CadmiumLead, CadmiumHexavalent Chromium, Lead, CadmiumHexavalent Chromium, LeadChromium



Barl um




Hydroxide Oxide Sulfate Sulfide Carbonate Phosphate

Acids, alkali Slightly Acids Acids Acids, alkalicsoluble Inacids, alkalljbAclgs, alkali, Alkali, alkalineHCl sulfur, NaHC03

Water, esp. Water, acid; Slightly Waterd Acids, NH 4Cl Acids, NH4Cld

hot Insoluble In solubleNH 3 In HC1,H.S04Act.,~, ~H~ Acids. NH. 511ts; Water; Acids Acids, NH. Acids. NH4 salts,511U; In- Insoluble in Insoluble salts Insoluble dsoluble In ,h,lt in NH3 In NH3 NH311 .. 11

Act.,s eroS: "ater'e WIter f Aci dS. HN03 Acids. alkaliHZ 04' HN03Acids, NH 40H HC1, NH 4Cl, NH 40H Watelj. HNO ; hot HCl Acids. NH 40H Acids, NH OH,acids acids hot, H.S04;NH4OH H3P04; I~solubleIn NH3Acids, alkali, HC1'd HN03' alkali, NH1 salts; Acids Acid, alkali, HN03, alkali

dHN03 acid sl ghtly Insoluble Insoluble In acids


Recovery_of_Metals_from_Sludges_and_Wastewaters/0815513100/files/00094___1504c1ac0fe45a6c8e8a11f9be5dac67.pdfNH)Acids, alkali,

NH40H, NH 4 sa lts


Acids, alkali,NH 4 salts




Water HNO)

Sulfate Sulfide

Acids, NH 40H Acids, cone.

HNO), H2S04

and Insoluble forms.

aci ds.acids and alkali; aluminum metaphosphate [AI (PO)))] is not.

Table 40 (cont Inued)Hydroxide Oxide

Mercury HNO), acids

Nickel Aci ds, NH.OH Acids, NH.OH

Selenium Water, cone.,H2S0.

5 i lver Acids, NH 40HNH 40H, ac Ids,

I inc Acids, alkali Acids, alkali ,NH 4Cl

aReference 55.bAlu~inum oxide trihydrates are soluble tn hot~Alumlnu~ orthophosphate (AIP04) Is soluble tnDepends on for. of compound.eCr20) Is insoluble; CrO) 15 soluble.fSome chromic acid salts exist In both soluble9SeSO) 15 soluble In H2S04,

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Environmental Evaluation

Two products result from the leaching step: the liquid streamcontaining dissolved metals and a secondary sludge. The liquid stream may bereused in the process or further treated to recover valuable metals.Depending on the degree of metals recovery, the resulting wastewater may befurther treated to adjust the pH and to remove residual metals.

Constituents that are not soluble in a strong leaching medium (such assulfuric acid) may not be soluble under the conditions of the ToxicityCharacteristic Leaching Procedure (TCLP) test standards. In any case, thevolume of sludge to be disposed of will be reduced.

For a previous EPA study of metals recovery from metal hydroxidesludges, an order-of-magnitude cost estimate was performed on the leaching/precipitation step and on the overall process train. 7 A return-on-invest-ment (ROI) calculation for the leaching process alone Is not useful becausethe metals are not immediately reusable and the only economic benefit wouldbe the reduction in sludge. The overall ROI for the entire process train was41 t 12 percent.

A first-order cost estimate was previously prepared for a theoreticalcomposite of the sludges studied during the second phase of the previous EPAproject, which had a solids concentration of 32.7 percent and metal concen-trations of 5.0 percent copper, 5.1 percent iron, 4.3 percent chromium, 1.Bpercent Zinc, 10.4 percent nickel, 0.4 percent aluninum, 0.9 percent calcium,15.0 percent silicon, and 3.0 percent phosphorus. The overall design of theprocess train consisted of sulfuric acid leaching, solvent extraction ofcopper, phosphate precipitation of Iron and chromium, zinc sulfate crystal-lization, and solvent extraction of nickel. The total yearly cost for theleaching step alone ranged from S148,900 for a 10 tons/day plant, to S391,200for a 50 tons/day plant. The ROI for the overall process depends on plantsize; the ROIs are 27 t 8 percent for a 10 tons/day plant, 75 t 23 percentfor a 30 tons/day plant, and 106 t 32 percent for a 50 tons/day plant.

Davy McKee estimates the installed capital cost of a plant to treatapproximately 160 tons per day of electroplating sludge for recovery ofcopper-nickel carbonate and a cadmium-zinc sulfide to be approximately S3.5million. Annual operating costs are estimated at Sl.3 million per year forthe two years of operation needed. The estimated operating costs includereagents (H2S0~, Na)C~, Ca(OH)2' and NaHS). utilities (electricity, water,steam and gaSOline), maintenance costs, and operating labor (4 operators for3 shifts). Revenues are based on the sale of the mixed copper nickelcar.bonate and do not take credit for the potential sale of the cadmium-zincsulfide. The estimate indicates that the overall cost of the project ~an berecovered by revenue sales from the remediation of the plating sludge.

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CarbQn AdsQrptiQnPrQcess DescriptiQn--

Activated carbQn has been widely used fQr the removal Qf Qrganicspresent in lQW levels (usually less than 1,000 mg/l) in cQntaminated liquids;relatively little attentiQn, however, has been given tQ the remQval QfinQrganics (e.g., metals) by carbQn adsQrptiQn. Studies cQnducted Qn theremoval Qf metals indicate the applicability Qf activated carbQn fQrtreatment of wastewaters; hQwever, this prQcess is not directly applicable tothe recovery of metallic cQmpQunds frQm ~ontaminated waste streams.

Activated carbQn is available in either powder (PAC) Qr granular form.Granular activated carbon (GAC) Is more convenient for use in conventiQnalunit prQcesses and regeneratiQn equipment, whereas the pQwdered fQrm Qffershigher surface area and maximum rate for sorption Qf cQntamiyants. Bothtypes have large surface areas In the Qrder Qf 600 tQ 2600 m/g, which resultfrQm a network Qf pQres 20 to 100 angstroms in diameter.

Activated carbQn has a fixed adsQrptlQn capacity fQr each type ofmetallic cQmpound. Once this capacity is saturated, cQntaminants will nolQnger be adsQrbed and the activated carbon must be regenerated or replaced.The carbon can be reactivated by using a strong acid or base to remove metalparticles and bring them back intQ the sQlution.

The adsorption characteristics Qf activated carbon for metals removalare more complex than thQse for organic compounds because the charged natureQf the metals affects their rate of removal from the solution. In general,the specific surface area, pore structure, and surface chemistry of theactivated carbon significantly affect its adsorption characteristics forremoval of contaminants.

Other parameters that influence the metals removal efficiency of acti-vated carbon are pH, temperature, presence of chelating agents, ionicstrength, carbon dose, and ~tal CQncentration. The pH of the solutionaffects cQntaminant removal by influencing the surface charge of the acti-vated carbon and affecting the distribution of the metal ions in the solu-tion. As the pH decreases, the solubility of metal ions generally increases.Complexing the metal ions in the solution by using chelating agents consider-ably increases the adsorption of metallic compounds onto the activatedcarbon. Chelating agents such as ethylenediaminetetraacetic acid (EDTAl andnitrilotriacetic acid (NTA) significantly increase the removal of mercury andcadmium by carbon material. 5

The process of metals removal by activated carbon often involves theuse of multiple columns or tanks filled with carbon and operated in series orparallel configurations. Figure 13 is a schematic Qf column arrangementsused to treat contaminated solutions. The carbon bed depth should be highenough to remove all the metals frQm the sQlution tQ the required CQncentra-

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out In

~,.~.~,. -1 percent) in contaminated soil; however, removals falloff dramatically as contaminant concentrations decrease. The performance ofchelating agents depends greatly ~n the specific waste matrix and must beevaluated on an individual basis. 7

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Treatment Ion Infl uent Effl uentoperation exchange concentration, concentration.

Metal type medium mg/L mg/L

Arsenicb Laboratory Anion 2.3 0.52Barium Commercial Cation 11. 7 0.17Chromium (VI)" Commerci a1 Anion 44.8 0.025Copper Commercial Cation 45.0 NOdLead Pilot-plant Cation 126.7-144.8 0.020-0.053Mercury Commercial Cation 5-25 0.001Urani urn Laboratory Anion 84.8 0.03Zinc Pilot-plant Cation 6.0 0.4

References 66 and 67.b Arsenic present as arsenite (AsO'z) or arsenate (As04])." Chromium (VI) present as chromate (Cr04'z) or dichromate (CrZ07z).d Not detected. Uranium present as uranyl carbonates (UOZ(C03}z'z and U02(C~h41.

Chelating ion exchange resins have shown promise in the printed circuitboard industry for recovery of copper. When operated at a pH of 4 to 5.these resins have been sufficiently selective in removing this metal fromcomplexin~ agents. allowing the complexing agents to pass through to theeffluent. The resin is then regenerated with sulfuric acid. producing amixture of sulfuric acid and copper sulfate. The copper is recovered byelectrowinning onto flat stainless steel plates. The effluent from theelectrowinning cell should contain 1 to 2 grams of copper per liter andtherefore needs to be returned for treatment. Activated carbon adsorption isused to remove organics that could foul the ion exchange resin.


Ion exchange is a common commercial method for removal/reuse of metalsfrom wastewaters generated in the metal-finishing. electroplating. fertilizermanufacture. printed circuit board. and pigment .anufacturing industries.The ion exchange process is also being used to recover chromates from coolingwater blowdown. 69 General Dynamics is currently using an ion exchange systemcoupled with electrowinning equipment to recover copper from rinse water andprocess bath solutions generated from the ~anufacture of printed circuitboards. ro Full-scale commercial ion-exchange electrolytic recovery systems(Memtek Corp.J have been used to remove tIn and lead from contaminatedwastewaters. 6 Pilot-scale studies have ~een conducted on bleach-fix process

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baths for the recovery of silver in the photographic industry. Currently,to 2 percent of the photographic industry is using ion exchangr to recoversilver. Because of EPA regulations, the majority of the photoyraphicindustry is expected to be using this technology within the next 5 years.Ion exchange has been used by the electroplating industry for wastewaterssince 1910, and with the advent of new synthetic selective ion resins, ionexchange systems are improving. The resins, however, are highly specializedorganic chemicals and are often expensive.

Table 46 shows the potential applicability of the ion exchange processfor metal-bearing RCRA wastes. Although the ion exchange process is usedprimarily for wastewaters, sludge leachates can also be treated; however, nocommercial use of ion exchange on sludge leachates for metals removal/reusehas been reported. .






Sludge leachates


Environmental Evaluation--





Ion exchange can provide 90+ percent removal of metal ions from waste-waters and, as a final polishing system, yields satisfactory effluent dis-charges under current regulations.'o Brine solutions created by regenerationare highly concentrated with metals; therefore, they must be treated byelectrowinning to recover soluble metal concentrations or returned to theprocess bath for reuse. Spent resins may need to be further treated prior toland disposal in order to comply with land disposal requirements set in 40CFR Part 268.

Personal communication with T. J. Dagon, Environmental Technical Services,Eastman Kodak, Rochester, NY, February 1982.

** Personal commun;cation with R. Slater, Rochester Institute of Technology,July 28, 1989.

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The costs of ion exchange treatment per unit volume of wastewater de-creases with a decrease in the concentration of the metal ion; therefore, ionexchange provides an economically attractive means for treating wastewaterswith metal concentrations of less than 200 mg/L.~ When a reduction in dis-solved solids is of primary interest, ion exchange is considered economicallypractical if the solids concentration is less than 1000 rng/L. For solidsconcentrations greater than 1000 mg/L, processes such as reverse osmosis andelectrodialysis are more economical.~

The capital cost of a copper recovery system using chelating ionexchange/ electrowinning (50 gpm) is estimated to be approximately Sl.3million with operating costs of approximately SI50,OOO/yr.~

Figure 16 shows typical costs of various ion exchange units and differ-ent types of resins. Capital costs include the purchase of columns, resinvalving, piping, and storage of regenerating material. Depending on thewaste stream operation, reported 1974 costs ranged from a low of about SO.13per 1000 gallons to a high of about Sl.75 per 1000 gallons. M


Process Description

Evaporation is a simplified recovery system for the separation of sub-stances based on volatility differences. Although the technology is estab-lished, recent advancements have made mechanical evaporation a more viablecost-efficient method for metals recovery. The four basic types of evapora-tors used in the electroplating industry today are rising-film, flash, sub-merged-tube, and atmospheric.

Rising-film evaporator systems consist of 1) a reboiler, which isusually a shell-and-tube heat exchanger; 2) a separator; and 3) a condenser(as shown in Figure 17). A rising-film evaporator system may be a singleunit or made up of two or more units. The heating surface of the reboiler iscovered by a wastewater film to which a heat source is applied (usually low-pressure steam). The wastewater can be circulated naturally, can be forcedthrough the tubes, or can form a rising film on the outside of the tubes.Wastewater enters the separator as a vapor/droplet mixture. The separatoracts as a collection area for the concentrated solution if the solution is tobe recycled, and it separates the water vapor from the more concentratedsolution. The condenser receives the vapor from the separator and condensesit into distillate for further use or disposal. A recirculation loopcontinuously circulates the concentrated solution through the reboiler andseparator until the desired concentration level is achieved. Evaporation canbe accomplished at gressures ranging from 1.3 to 7.5 psia to lower theboiling point to 40 to 80C for materials susceptible to decomposition athigh temperatures. Flash evaporators are similar to rising-film evaporatorsexcept that the solution is continuously recirculated through the evaporator(as shown in Figure 18), which reduces the energy required for vaporization.

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ooo 100


(1) Mixed-Bed(2) Strong-Base(3) Weak-Base

0.01 0.1

High TDS(1000-4000 mgIL)

LowTDS(1 Q-600 mgIL)








o+--,......"""T-........-.---,.--y-------.-........-.-----.---! IJla 1000 2000 3000

gpm4000 5000 6000

a Updated to 1988 values

Figure 24. Total capital costs compared with capacity.

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ENERGY REQUIREMENTS30...,....------------------....,