Cyanide in water and soil, dzombak, ghosh, wong

CYANIDE inWATER and SOILChemistry, Risk, and Management

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A CRC title, part of the Taylor & Francis imprint, a member of theTaylor & Francis Group, the academic division of T&F Informa plc.

CYANIDE inWATER and SOIL

David A. DzombakRajat S. Ghosh

George M. Wong-Chong

Chemistry, Risk, and Management

Boca Raton London New York

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Preface

Cyanide is a chemical with a long and fascinating history of respectful and productive use bymankind. The fundamental cyanide species, the cyanide ion CN, is a highly versatile and strongbinder of metals in aqueous solution, a property that has been exploited in ingenious ways forcommercial processes that have benefited society. The best known and largest volume uses of cyanideare in the gold mining and electroplating industries. In hydrometallurgical gold mining, aqueoussolutions of CN are used to extract and concentrate gold from ores containing very small amountsof gold. In electroplating, solutions of metalCN species are used as the baths into which solidmetals are dipped and coated with the metal from solution. The deposition of the metal from solutiononto the solid metal is governed by the electrochemical gradient induced in the system, and by themetalcyanide solution chemistry. Cyanide is also produced incidentally in significant quantities in anumber of industrial processes, including coal coking and gasification, iron and steel manufacturing,aluminum manufacturing, and petroleum refining. This results in the need for control of cyanidereleases in the form of gases, solids, and liquids. The substantial use of cyanide compounds incommerce coupled with the substantial incidental production of cyanide compounds means thatsignificant amounts of cyanide are introduced into the environment on a continuous basis. Cyanidespecies are frequently occurring contaminants in water and soil.

There are also natural sources of cyanide, such as black cherry and cassava plants. Indeed, thereis a natural cycle of cyanide. However, anthropogenic inputs of cyanide to the environment are fargreater in amount than natural inputs.

Of course, cyanide is also widely known, and perhaps best known, as a potent human toxin.The most toxic form of cyanide is hydrogen cyanide, HCN, which is as toxic, and often even moreso, to wildlife, especially aquatic life. There is great fear of cyanide in society, but some chemicalforms of cyanide are nontoxic and in fact used regularly in food and cosmetic products. An exampleis the solid Prussian Blue, or ferric ferrocyanide, which is used as a blue pigment for use in inks,dyes, cosmetics, and other products.

The chemistry of cyanide is both complex and diverse, and there are many different chemicalforms of cyanide, including solid, gaseous, and aqueous species, and both inorganic and organicspecies. The particular chemical forms of cyanide that exist in a system, referred to as the speciationof the chemical, are all important in determining the environmental fate, transport, and toxicity ofthe cyanide.

In our careers in environmental engineering and science, we have encountered many differentproblems involving cyanide in water and soil. Cyanide has been a focus in engineering and researchprojects that we have performed related to industrial and municipal wastewater treatment, ground-water treatment, industrial waste management, site remediation and restoration, and water qualityassessment. These projects have been sponsored by a wide range of companies, industrial researchorganizations, and regional and federal government agencies. There is widespread interest in cyanidemanagement for environmental and human health protection. We have learned much about cyanideuse, management, emissions, and behavior in the environment in the course of these projects. Oureducation has been aided by useful knowledge and information acquired from many different sourcesand people.

We undertook the preparation of this book to bring together in one place some of the currentknowledge and information about cyanide release to, and behavior in, the environment, and means

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vi Preface

of controlling or remediating these releases. No other broad-based examination of this topic exists.While there has been much good research and engineering development performed in the gold miningindustry on cyanide management and control of environmental releases, most notably the work ofDr Terry Mudder and colleagues, this work has been focused on the industry with an orientationtoward advancement of hydrometallurgical gold mining. There is much to be learned from theextensive knowledge about cyanide that has been gained in the gold mining industry, but there is abroader range of cyanide challenges in environmental engineering and science. Our book takes onthis broader scope.

This book tries to address the full range of issues pertaining to cyanide fate, transport, treatment,and toxicity in water and soil. We examine the sources of cyanide released to the environment, bothanthropogenic and natural. We have tried to develop an appropriate balance of depth and scope ofcoverage. There have been compromises made on depth of coverage in some topical areas, but in allareas we have endeavored to provide good and current references to enable the reader to learn moreabout topics of particular interest.

We developed this book to serve as a useful reference tool for engineers and scientists, includ-ing both practitioners and researchers, in academia, industrial organizations, government, andengineering and science consulting firms. We hope we have succeeded in our goal.

Effective management and remediation approaches for cyanide in the environment require con-sideration of issues spanning many different fields. In this context, we have collaborated with a widerange of individuals possessing a wide range of expertise in our cyanide-related projects. To addressthe range of topics that we wanted to examine in this book, we engaged a number of our formerand current collaborators to help us with the book. We are most grateful to the contributing authors,listed following this preface and in the header for each chapter.

We are also grateful to Alcoa, Inc. and Niagara Mohawk Power Corporation for financial supportthat helped make this book project possible; and USFilter Corporation, the RETEC Group, Inc. andthe Carnegie Mellon University Department of Civil and Environmental Engineering for providingassistance with preparation of graphics and the manuscript. We owe special thanks to JacquelineZiemianski, Donna Silverman, and Kacey Ebbitt of the RETEC Group, Inc. for their good work withpreparation of graphics and securing permissions for use of copyrighted material, and to NicholeDwyer of Carnegie Mellon University for her careful work in helping us with revising and formattingthe text, with completing and formatting references, and with permissions. Finally, we thank ourfamilies for their understanding as we used many hours of family time to work on this book.

David A. DzombakRajat S. Ghosh

George M. Wong-Chong

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Editors

David Dzombak, Ph.D., P.E., DEE, is a professor in the Department of Civil and EnvironmentalEngineering at Carnegie Mellon. Dr Dzombaks research and professional interests include aquaticchemistry; fate and transport of chemicals in surface and subsurface waters; water and wastewatertreatment; in situ and ex situ soil treatment; hazardous waste site remediation; abandoned minedrainage remediation; and river and watershed restoration. He has over 70 peer-reviewed publicationsand is the joint holder of three patents related to water and soil treatment. He has extensive researchand consulting experience with cyanide management and treatment in soils, wastewaters, and processresiduals. He has served as a member of the U.S. Environmental Protection Agency Science AdvisoryBoard and is involved with numerous other professional service activities. Dr Dzombak receivedhis Ph.D. in Civil-Environmental Engineering from the Massachusetts Institute of Technology in1986. He also holds an M.S. in Civil-Environmental Engineering and a B.S. in Civil Engineeringfrom Carnegie Mellon University, and a B.A. in Mathematics from Saint Vincent College. He isa registered Professional Engineer in Pennsylvania, and a Diplomate of the American Academyof Environmental Engineers. Dr Dzombak was elected a Fellow of the American Society of CivilEngineers in 2002. Other awards include the Professional Research Award from the PennsylvaniaWater Environment Association (2002); Jack Edward McKee Medal from the Water EnvironmentFederation (2000); Aldo Leopold Leadership Program Fellowship from the Ecological Society ofAmerica (2000); Distinguished Service Award from the Association of Environmental Engineeringand Science Professors (1999); Walter L. Huber Civil Engineering Research Prize from the AmericanSociety of Civil Engineers (1997); Harrison Prescott Eddy Medal from the Water EnvironmentFederation (1993); and National Science Foundation Presidential Young Investigator Award (1991).

Rajat S. Ghosh, Ph.D., P.E., is a Program Manager with the EHS Science and Technology Group ofAlcoa, Inc., the worlds largest producer of aluminum. He formerly was a Senior Technical Consultantin the Pittsburgh office of The RETEC Group, Inc., a U.S. environmental engineering and consultingcompany. Dr Ghoshs research and professional interests are in geochemistry, transport and treatmentof inorganic compounds (especially cyanide and heavy metals) in the subsurface; analytical methoddevelopment for various inorganic and organic compounds; and subsurface multiphase flow andchemistry of organic compounds including coal tar, DNAPLs, and petroleum hydrocarbons. DrGhosh has extensive research and consulting experience with the electric power, natural gas, andaluminum industries in the United States in relation to cyanide management and treatment issuesin soil and groundwater. In addition, Dr Ghosh serves as a senior technical reviewer for the U.S.Department of Defense basic environmental science and technology development program for siteremediation under the auspices of the Strategic Environmental Research and Development Program(SERDP) and Environmental Security and Technology Certification Program (ESTCP). Dr Ghoshreceived his Ph.D. in Civil-Environmental Engineering from the Carnegie Mellon University in1998. He also holds an M.S. in Chemical Engineering from University of Wyoming and a B.S. inChemical Engineering from Jadavpur University, India. He is a registered Professional Engineer inPennsylvania. He has over 20 professional publications in the open literature and is a joint holderof a U.S. patent on cyanide treatment technology. Dr Ghosh serves as a member of ASTMs D-19Committee on Water. Dr Ghosh was elected as a member of the Sigma Xi Honor Society. Other

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viii Preface

awards include the Jack Edward McKee Medal from the Water Environment Federation (2000) andthe Graduate Student Award from American Chemical Society (1998).

George M. Wong-Chong, Ph.D., P.E., DEE, retired director of process wastewater research atUSFilter Corporation (Engineering and Construction), has over 35 years of experience in techno-logy development, design, construction, operation, research and teaching of the management andtreatment of contaminated groundwater, wastewaters, and solid hazardous waste. Dr Wong-Chongsexperience spans a range of industries including iron and steel, coal tar refining, organic chemicals,petroleum refining, munitions, aluminum manufacturing, coal gasification, live stock agriculture,and municipal wastewater. His experience in the iron and steel industry, where cyanide is a majorconcern, is internationally recognized; for coke plant wastewaters he developed a patented process,NITE/DENITE, for the direct biological treatment of flushing liquor, which can contain veryhigh concentrations of ammonia, cyanide, phenols, and thiocyanate. He also holds a patent for thephysical/chemical treatment of municipal and industrial wastewaters. Dr Wong-Chong received hisPh.D. in Agricultural Engineering from Cornell University in 1974. He also holds an M.S. in Envir-onmental Engineering from the University of Western Ontario, Canada, and a B.S. in ChemicalEngineering from McGill University, Canada. He is a registered Professional Engineer in 10 states,and a Diplomate of the American Academy of Environmental Engineers. In 1999, Dr Wong-Chongreceived the Pennsylvania Water Environment Association Professional Research Award and theAmerican Institute of Chemical Engineers Pittsburgh Section Award for Outstanding ProfessionalAccomplishments in the Field of Consulting Engineering. Dr Wong-Chong has over 50 publica-tions and presentations to his credit and remains very interested in waste water treatment technologydevelopment.

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Contributors

Todd L. Anderson, P.E.Malcolm Pirnie, Inc.Emeryville, CA

Barbara D. Beck, Ph.D., DABTDABT, Gradient Corp.Cambridge, MA

Brice S. Bond, M.S.Southern Illinois UniversityCarbondale, IL

Joseph L. Borowitz, Ph.D.Purdue UniversityWest Lafayette, IN

Joseph T. Bushey, Ph.D.Syracuse UniversitySyracuse, NY

Rick D. Cardwell, Ph.D.Parametrix, Inc.Albany, OR

Jeremy M. ClarkParametrix, Inc.Albany, OR

Rula A. Deeb, Ph.D.Malcolm Pirnie, Inc.Emeryville, CA

David K. DeForestParametrix, Inc.Bellevue, WA

Peter J. Drivas, Ph.D.Gradient Corp.Cambridge, MA

Sharon M. Drop, M.S.Alcoa, Inc.Pittsburgh, PA

David A. Dzombak, Ph.D., P.E., DEECarnegie Mellon UniversityPittsburgh, PA

Stephen D. Ebbs, Ph.D.Southern Illinois UniversityCarbondale, IL

Robert W. Gensemer, Ph.D.Parametrix, Inc.Albany, OR

Rajat S. Ghosh, Ph.D., P.E.Alcoa, Inc.Pittsburgh, PA

Cortney J. Higgins, M.S.Carnegie Mellon UniversityPittsburgh, PA

Gary E. Isom, Ph.D.Purdue UniversityWest Lafayette, IN

Michael C. Kavanaugh, Ph.D., PE, DEEMalcolm Pirnie, Inc.Emeryville, CA

Roman P. Lanno, Ph.D.Ohio State UniversityColumbus, OH

Richard G. Luthy, Ph.D., P.E., DEEStanford UniversityStanford, CA

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x Contributors

Johannes C.L. Meeussen, Ph.D.Energy Research Centre of the NetherlandsPetten, The Netherlands

Charles A. Menzie, Ph.D.Menzie-Cura and AssociatesWinchester, MA

David V. Nakles, Ph.D., P.E.The RETEC GroupPittsburgh, PA

Edward F. Neuhauser, Ph.D.Niagara Mohawk Power Co.Syracuse, NY

Sujoy B. Roy, Ph.D.Tetra Tech, Inc.Lafayette, CA

Mara Seeley, Ph.D., DABTDABT, Gradient Corp.Cambridge, MA

Neil S. Shifrin, Ph.D.Gradient Corp.Cambridge, MA

John R. Smith, Ph.D., P.E.Alcoa, Inc.Pittsburgh, PA

Angela J. Stenhouse, M.S.Parametrix, Inc.Bellevue, WA

Thomas L. Theis, Ph.D., P.E., DEEUniv. of Illinois at ChicagoChicago, IL

Jeanne M. VanBriesen, Ph.D.Carnegie Mellon UniversityPittsburgh, PA

George M. Wong-Chong, Ph.D., P.E., DEEUSFilter CorporationPittsburgh, PA

Thomas C. Young, Ph.D.Clarkson UniversityPotsdam, NY

Anping Zheng, Ph.D.URS Corp.Wayne, NJ

Xiuying Zhao, Ph.D.Clarkson UniversityPotsdam, NY

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Contents

Chapter 1 Introduction 1George M. Wong-Chong, David A. Dzombak, and Rajat S. Ghosh

Chapter 2 Physical and Chemical Forms of Cyanide 15Rajat S. Ghosh, David A. Dzombak, and George M. Wong-Chong

Chapter 3 Natural Sources of Cyanide 25George M. Wong-Chong, Rajat S. Ghosh, Joseph T. Bushey, Stephen D. Ebbs,and Edward F. Neuhauser

Chapter 4 Manufacture and the Use of Cyanide 41George M. Wong-Chong, David V. Nakles, and Richard G. Luthy

Chapter 5 PhysicalChemical Properties and Reactivity of Cyanide in Water and Soil 57David A. Dzombak, Rajat S. Ghosh, and Thomas C. Young

Chapter 6 Biological Transformation of Cyanide in Water and Soil 93Stephen D. Ebbs, George M. Wong-Chong, Brice S. Bond, Joseph T. Bushey,and Edward F. Neuhauser

Chapter 7 Analysis of Cyanide in Water 123Rajat S. Ghosh, David A. Dzombak, Sharon M. Drop, and Anping Zheng

Chapter 8 Analysis of Cyanide in Solids and Semi-Solids 155David A. Dzombak, Joseph T. Bushey, Sharon M. Drop, and Rajat S. Ghosh

Chapter 9 Fate and Transport of Anthropogenic Cyanide in Surface Water 171Thomas C. Young, Xiuying Zhao, and Thomas L. Theis

Chapter 10 Fate and Transport of Anthropogenic Cyanide in Soil and Groundwater 191Rajat S. Ghosh, Johannes C.L. Meeussen, David A. Dzombak, andDavid V. Nakles

Chapter 11 Anthropogenic Cyanide in the Marine Environment 209David A. Dzombak, Sujoy B. Roy, Todd L. Anderson, Michael C. Kavanaugh,and Rula A. Deeb

Chapter 12 Cyanide Cycle in Nature 225Rajat S. Ghosh, Stephen D. Ebbs, Joseph T. Bushey, Edward F. Neuhauser,and George M. Wong-Chong

Chapter 13 Human Toxicology of Cyanide 237Joseph L. Borowitz, Gary E. Isom, and David V. Nakles

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xii Contents

Chapter 14 Aquatic Toxicity of Cyanide 251Robert W. Gensemer, David K. DeForest, Angela J. Stenhouse,Cortney J. Higgins, and Rick D. Cardwell

Chapter 15 Toxicity of Cyanide to Aquatic-Dependent Wildlife 285Jeremy M. Clark, Rick D. Cardwell, and Robert W. Gensemer

Chapter 16 Human Health Risk Assessment of Cyanide in Water and Soil 309Barbara D. Beck, Mara Seeley, Rajat S. Ghosh, Peter J. Drivas, andNeil S. Shifrin

Chapter 17 Ecological Risk Assessment of Cyanide in Water and Soil 331Roman P. Lanno and Charles A. Menzie

Chapter 18 Regulation of Cyanide in Water and Soil 351David V. Nakles, David A. Dzombak, Rajat S. Ghosh, George M. Wong-Chong,and Thomas L. Theis

Chapter 19 Cyanide Treatment Technology: Overview 387George M. Wong-Chong, Rajat S. Ghosh, and David A. Dzombak

Chapter 20 Ambient Temperature Oxidation Technologies for Treatment of Cyanide 393Rajat S. Ghosh, Thomas L. Theis, John R. Smith,and George M. Wong-Chong

Chapter 21 Separation Technologies for Treatment of Cyanide 413David A. Dzombak, Rajat S. Ghosh, George M. Wong-Chong,and John R. Smith

Chapter 22 Thermal and High Temperature Oxidation Technologies for Treatment ofCyanide 439Rajat S. Ghosh, John R. Smith, and George M. Wong-Chong

Chapter 23 Microbiological Technologies for Treatment of Cyanide 459George M. Wong-Chong and Jeanne M. VanBriesen

Chapter 24 Cyanide Phytoremediation 479Stephen D. Ebbs, Joseph T. Bushey, Brice S. Bond, Rajat S. Ghosh, andDavid A. Dzombak

Chapter 25 Management of Cyanide in Municipal Wastewaters 501David A. Dzombak, Anping Zheng, Michael C. Kavanaugh,Todd L. Anderson, Rula A. Deeb, and George M. Wong-Chong

Chapter 26 Management of Cyanide in Industrial Process Wastewaters 517George M. Wong-Chong, David V. Nakles, and David A. Dzombak

Chapter 27 Cyanide Management in Groundwater and Soil 571Rajat S. Ghosh, David V. Nakles, David A. Dzombak, andGeorge M. Wong-Chong

Index 591

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1 IntroductionGeorge M. Wong-Chong, David A. Dzombak, andRajat S. Ghosh

CONTENTS

1.1 Cyanide in History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2 Cyanide Chemical Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Cyanide and the Origin of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.3.1 Role of Hydrogen Cyanide in the Production of Amino Acids . . . . . . . . . . . . . . . . . 21.3.2 Stanley Millers Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.4 Ubiquity of Cyanide Compounds in Nature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.4.1 Cyanide in Outer Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.4.2 Hydrogen Cyanide in Earths Atmosphere. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.5 Cyanide in Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.6 Cyanide Releases to Water and Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.7 Cyanide: Chemistry, Risk, and Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101.8 Cyanide Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111.9 Cyanide Treatment Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111.10 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Cyanide compounds are produced and used in commerce in large quantities. In the United States,for example, approximately 200 million pounds of sodium cyanide are used annually just in heapleaching extraction of gold from ore [1], with much of this use taking place in one state, Nevada,which accounts for about 70% of U.S. gold production [2]. Large amounts of sodium cyanide are alsoused in electroplating [3]. Cyanide compounds are also produced incidentally in many processes,such as in aluminum and steel production, and are associated with wastewaters, solid wastes, andair emissions from these processes. In addition, cyanide compounds are present in legacy wastesdisposed onsite at numerous manufactured gas plant sites in the United States and Europe. As aresult, cyanide is a commonly encountered contaminant in water and soil.

Because of the high degree of toxicity in certain forms of cyanide, primarily hydrogen cyanide(HCN), acceptable levels of cyanide compounds in water and soil are generally very low. For example,the U.S. drinking water maximum contaminant level for free cyanide (HCN and CN) is 0.2 mg/l,while the U.S. ambient water quality criterion for acute exposures in freshwater systems is 22 g/l.As this thousandfold difference indicates, some aquatic organisms are significantly more sensitiveto cyanide than are humans.

Addressing problems of cyanide contamination in water and soil can be very challenging.Complicating factors include the complex chemistry and speciation of cyanide; the analyticalchallenges of measuring cyanide species in water and soil; the differential toxicity, reactivity,and treatability of the various cyanide species; overlapping and sometimes inconsistent regulationspertaining to cyanide; and the widespread public fear of cyanide, regardless of its form and location.Knowledge in all these areas is needed to develop effective strategies to remedy or manage cyanide

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2 Cyanide in Water and Soil

contamination in water and soil. This book presents current scientific understanding and engineeringapproaches for managing water and soil contamination with cyanide.

1.1 CYANIDE IN HISTORY

Cyanide is a chemical well known to the public as a highly toxic agent [4]. For many, the wordcyanide evokes emotions of death. This perception is prevalent in the history of cyanide datingback to antiquity, long before any understanding of the chemistry of this family of compoundswas known. Traitorous Egyptian priests of Memphis and Thebes were poisoned using the pits ofpeaches [5]. In the 20th century, HCN gas was used in gas chambers in the World War II Holocaust,in prisons for execution of criminals with death sentences, and also as a chemical warfare agent.

In 1782, the Swedish chemist Carl Wilhelm Scheele discovered a flammable, water-soluble acidicgas, later identified as HCN, when he heated the cyanide-bearing solid Prussian Blue in an aqueoussulfuric acid solution [68]. The name given to the evolved gas was Prussian Blue Acid, also referredto as prussic acid or blue acid [7]. This same gas caused Scheeles death four years later [8]. Thewords cyanine and cyanide, derived from the Greek word kyanos for blue, soon came into useto describe the gas [7]. In 1811, Guy Lussac determined the composition of the gas as consisting ofone molecule each of carbon, hydrogen, and nitrogen [6]. He referred to the HCN gas as hydrocyanicacid, or hydrogen cyanide.

1.2 CYANIDE CHEMICAL STRUCTURE

Cyanide compounds contain the cyano-moiety, which consists of the carbon atom triply bonded tothe nitrogen atom (CN). The most basic, and most toxic, of these compounds is hydrogen cyanide(HCN), hydrocyanic acid. HCN is a gas at ambient temperature, and is freely soluble in water.In water, HCN dissociates at high pH (pKa = 9.24 at 25C) to form the cyanide anion, CN.

There are many different inorganic and organic cyanide compounds. Inorganic compoundsinclude simple salts of cyanide with various metals such as sodium cyanide, NaCN(s), potassiumcyanide, KCN(s), and more complex solids such as ferric ferrocyanide, Fe4(Fe(CN)6)3(s), also knownas Prussian Blue. The simple salts are highly soluble in water. The aqueous solubility of PrussianBlue and other similar complex cyanide solids are functions of pH and redox potential. There arealso many organocyanide compounds, such as acetonitrile (CH3CN), acrylonitrile (CH2CHCN), andcyanogenic glycosides.

1.3 CYANIDE AND THE ORIGIN OF LIFE

1.3.1 ROLE OF HYDROGEN CYANIDE IN THE PRODUCTION OFAMINO ACIDS

In the Precambrian or prebiotic period, about 4.6 billion years ago, primary components of theearths atmosphere were carbon monoxide, methane, hydrogen, nitrogen, ammonia, and water [9].The German biologist E. Pfluger hypothesized that as the earths surface slowly cooled from anincandescent mass, HCN was formed by the chemical union of carbon and nitrogen, and that thiscompound had time to transform and polymerize to form proteins which constitute living matter [10].Figure 1.1 and Figure 1.2 illustrate the polymerization of HCN, to form adenine, and the reactionof HCN and formaldehyde (another compound formed from the reaction of the constituents in theprimitive earths atmosphere) to form glycine. These two compounds allow the synthesis of manyamino compounds. Oro and Kimball [11,12] demonstrated the synthesis of adenine, a nucleic acid,and other purine intermediates from HCN under possible primitive earth conditions. These abioticallysynthesized proteins were important stepping-stones to life, as we know it today.

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Introduction 3

N+HCN

Hydrogencyanide

N

N

N

N

N

+HCN

+HCNN

N

NN

Diaminomaleonitrile (HCN)4

Adenine (HCN)5

Hydrogen Carbon Nitrogen

(HCN)2 (HCN)3

+HCN

NN

N

N

N

N

FIGURE 1.1 Polymerization of hydrogen cyanide to form adenine. (Source: Barbieri, M., The Organic Codes:An Introduction of Semantic Biology, Cambridge University Press, Cambridge, MA, 2002. With permission.)

1.3.2 STANLEY MILLERS EXPERIMENT

In 1953, Stanley Miller demonstrated that HCN and certain organic compounds, including aldehydesand amino acids, can be formed from the constituents of the prebiotic earth atmosphere, that is,methane, ammonia, hydrogen, and water [9]. The experiments, which earned Miller a Nobel Prize,were performed in a spark-discharge reaction apparatus as shown in Figure 1.3. The apparatus, whichwas claimed to be a crude model of the primitive earths atmosphere, was charged with water andair was evacuated; then, a mixture of ammonia, methane and hydrogen was added. The water in thesmall flask was boiled to initiate a circulation of gases and water vapor into the reaction flask, inwhich an electric spark was generated. The spark initiated the reaction of the ammonia, hydrogen,

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Formaldehyde AmmoniaHydrogencyanide

Ammonitrile Water Ammonia Glycine

+ +

Ammonitrile Water

+

+ +

Hydrogen Carbon NitrogenN

NN

N N

NN N N

Oxygen

FIGURE 1.2 Reaction of hydrogen cyanide and formaldehyde to form glycine. (Source: Barbieri, M., TheOrganic Codes: An Introduction of Semantic Biology, Cambridge University Press, Cambridge, MA, 2002.With permission.)

spark discharge

Electrodes

Gases

Water out

Water in

Water droplets

Liquid water in trap conainingorganic compounds

Boilingwater

To avacuumpump

Condenser

FIGURE 1.3 Apparatus for experiment by Stanley Miller that demonstrated formation of hydrogen cyanidefrom constituents of the prebiotic Earth atmosphere. (Source: Miller, S.L. and Orgel, L.E., The Origins of Lifeon Earth, Prentice-Hall, Englewood Cliffs, NJ, 1974. With permission.)

methane, and water to form HCN and aldehydes. A typical experiment entailed operating of the sparkcontinuously for about 1 week with regular analysis of samples from the system. Figure 1.4 showsthe reaction profiles for ammonia (charged material), and amino acids, HCN and aldehydes (reactionproducts). Millers data clearly demonstrated a mechanism for abiotic production of HCN in theatmosphere, one that also exists today during electrical discharges associated with thunderstorms [9].

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Introduction 5

Mol

ar c

once

ntra

tion

Time (h)

Aldehydes (103)

HCN(102)

Amino acids(103)

NH3(10)8

7

6

5

4

3

2

1

25 50 75 100 125 150

FIGURE 1.4 Reactant and product concentrations in the experiment by Stanley Miller. (Source: Miller, S.L.and Orgel, L.E., The Origins of Life on the Earth, Prentice-Hall, Englewood Cliffs, NJ, 1974. With permission.)

The findings of Miller are further substantiated by the discovery of the presence of CO, HCN, OH,formaldehyde and methanol in outer space [13].

1.4 UBIQUITY OF CYANIDE COMPOUNDSIN NATURE

Cyanide compounds occur commonly in nature. HCN is present in outer space, in the earths atmo-sphere, in plants, animals, microbes, and fungi. Cyanide can be produced by certain plants, bacteria,fungi, and algae. Chapter 3, which examines natural sources of cyanide, discusses in detail the occur-rence, role, and environmental impact of cyanide in plants, animals, microbes, and fungi. The naturalcycle of cyanide in the environment is the focus of Chapter 12.

1.4.1 CYANIDE IN OUTER SPACE

Hydrogen cyanide has been detected at a number of locations in outer space. For example, it is atrace constituent in the nitrogenous atmosphere of Titan, the largest moon of Saturn [14], and in thecoma of the HaleBopp comet [15]. Polymerization products of HCN are the dominant componentsof dust grains sampled from the tail of Comet 81P/Wild2 in 2004 [16]. This presence of HCN inspace is now being used to study the birth of massive stars [17]. The detection of large amounts ofHCN toward the center of a protostar (an evolving star) means that it has already started to warm up;from this information it is possible to determine the degree of evolution and the age of the star [17].

1.4.2 HYDROGEN CYANIDE IN EARTHS ATMOSPHERE

Hydrogen cyanide is detectable in the troposphere and stratosphere of the earth. Its concentra-tion in the nonurban troposphere of the northern hemisphere has been reported as approximately160 pptv [18]. In the tropical upper troposphere, a range of HCN concentrations from 200 to 900 pptv

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has been reported [19]. From field measurements and modeling it has been established that biomassburning is a major global source of HCN emissions [19,20]. Estimates of the total release of HCNto the atmosphere from biomass burning range from 1.4 to 2.9 1012 g (as N) per year [19]. Theresidence time of HCN in the atmosphere is approximately two to four months [19]. The oceans ofthe world provide a sink for the atmospheric releases of HCN and other compounds from biomassburning [19], as discussed in Chapter 11.

1.5 CYANIDE IN INDUSTRY

Substantial quantities of cyanide compounds are used and produced in commerce (Chapter 4). Todaymost cyanide compounds are manufactured starting with HCN, which is synthesized by the platinum-catalyzed reaction of ammonia and methane [3]. HCN is a basic chemical feed stock used in themanufacture of sodium cyanide for gold mining and electroplating; adiponitrile for nylon; methylmethacrylate for clear plastic; triazines for agricultural herbicides; methionine for animal foodsupplement; and chelating agents (e.g., nitrilotriacetate) for water and wastewater treatment [3].Worldwide annual production and manufacturing capacity of HCN in 1992 were estimated to be0.95 million tons and 1.32 million tons, respectively [3]. A 2001 estimate of worldwide cyanideproduction was 2.60 million tons [7]. In 2001, 0.75 million tons of HCN were produced in the U.S.(Table 1.1). A significant fraction, estimated to range from 8 to 20%, of HCN is used to producesodium cyanide [3,21,22], much of which is used in hydrometallurgical gold mining. The productionand use of cyanide is growing, as indicated by the chronological tabulation of HCN production inthe United States in Table 1.1.

In addition to use of cyanide compounds in gold mining, electroplating, and chemical produc-tion, cyanide compounds are also used in some applications that involve direct distribution to theenvironment. Sodium ferrocyanide, Na4(Fe(CN)6) and ferric ferrocyanide, Fe4(Fe(CN)6)3(s) areused as an anticaking agent in road salt [23]. It is the presence of ferric ferrocyanide that givesa blue color to salt in which it is used. These compounds can dissolve in water after placement onroad surfaces. Sodium ferrocyanide is also used in some forest fire retardants [24].

1.6 CYANIDE RELEASES TO WATER AND SOIL

Most cyanide that occurs in water and soil is anthropogenic, derived from industrial processes, butthere are natural sources of cyanide as noted above. The combination of widespread industrial sourcesand natural sources leads to detectable concentrations of cyanide in many natural waters, though con-centrations are usually low. In a 1981 evaluation of monitoring data in the USEPA STORET database,it was determined that the mean concentration of total cyanide in surface waters of the United Statesdid not exceed 3.5g/l, but in 37 of 50 states there were sampling locations where total cyanide con-centrations in excess of this level were reported [25]. Sample results from a number of industrializedareas had total cyanide concentrations greater than 200 g/l. Total cyanide concentrations in U.S.drinking water intake supplies are usually very low (

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Introduction 7

TABLE 1.1Production of Hydrogen Cyanide inthe United States, 19832001

Production,Year 103 tons/yr

2001 7502000 7651999 7451998 7251997 7101996 6951995 6751994 6451993 6001992 5701991 5651990 5851989 5651988 5001987 4701986 4301985 3651984 3651983 330

Sources: Production estimates for 19831988:Data from Pesce, L.D., Kirk-Othmer Encyclope-dia of Chemical Technology, Vol. 7, John Wiley& Sons, New York, 1993. Production estimatesfor 19892001: Data from Myers, E., AmericanChemistry Council, Washington, DC, personalcommunication, 2002.

TABLE 1.2Concentrations of Free Cyanide and Total Cyanidein Six Surface Water Samples from Across Canada

Free cyanide (g/l) Total cyanide (g/l)

Sample Electrode Colorimetry Electrode Colorimetry

Stream 1 4 3 7 8Stream 2 6 4 10 12Stream 3 4 4 11 12Lake 1 5 6 21 19Lake 2 10 12 25 27Lake 3 17 19 48 49

Source: Reprinted from Water Res., 104, Sekerka, I. and Lechner,J.F. Potentiometric determination of low levels of simple and totalcyanides, 479, copyright (1976), with permission from Elsevier.

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TABLE 1.3Examples of Discharges from Gold Mine Heap Leaching Operations

Location Release date/period Release scenario Reference

Baia Mare, Romania January 30February 2, 2000 100,000 m3 (26 million gallons) ofcyanide-bearing tailings released due totailings dam failure

[34]

Gold Quarry Mine, Nevada, USA June 6, 1997 245,000 gallons cyanide solution leakagefrom heap leach pad; discharge to twonearby creeks

[44]

Omai, Guyana August 1924, 1995 4.2 million m3 (1.1 billion gallons) ofcyanide-bearing tailings water releaseddue to tailings dam failure

[45]

USMX Mine, Utah, USA March 1114, 1995 7 million gallons treated leach solutioncontaining 0.2 ppm cyanide, releasedfrom storage ponds to East Fork ofBeaver Dam Wash

[46]

Summitville, Colorado, USA 19861992 Sustained cyanide solution leaks fromheap leach pad, from transfer pipes, andfrom tailings pond; discharge to AlamosaRiver

[47,48]

The most dramatic releases of cyanide to water and soil have occurred in the failure of orsubstantial leakage from heap leaching pads or tailings ponds associated with gold mining operations.Table 1.3 lists some large-volume discharges that have occurred since 1992. The failure of the tailingspond dam at a gold mine near Baia Mare, Romania, in January 2000 provides an example of thelarge scale of impact that can result from such discharges. Due to heavy precipitation coupled witha rapid snowmelt, a gold mine tailings pond near Baia Mare filled to capacity and overflowed,resulting in washout of a section of the earthen containment dam for the pond. Approximately100,000 cubic meters of tailings water containing free cyanide, metalcyanide complexes, metals,and suspended solids were discharged from January 30 to February 2, 2000 [34]. Based on cyanideconcentrations in the tailings pond and the approximate spill volume, it is estimated that 50 to 100tons of cyanide were released. As shown in the map on Figure 1.5, the spill entered the SasarRiver, which subsequently joins with the Lapus River, and then the Somes River. The Somes flowsinto Hungary, and there it discharges into the Tisza River, which flows through Hungary and intoSerbia (formerly, Yugoslavia). Just north of Belgrade the Tisza discharges into the Danube, whichreturns to Romania and eventually discharges into the Black Sea. It took the plume of contaminationabout 14 days to reach the Danube, which is approximately 800 km in river distance from the spilllocation. The plume then traveled an additional 1,200 km in the Danube. Total cyanide concentrationsas high as 32.6 mg/l were measured in the Somes River at the HungarianRomanian border. Themaximum cyanide concentration observed in the Tisza River at the HungarianYugoslavian borderwas 1.5 mg/l, and in the Danube River near the YugoslavianRomanian border was 0.34 mg/l. Theseconcentrations, while demonstrating the dilution, biodegradation, and volatilization of the cyanideduring riverine transport to the Black Sea, nevertheless were 15 to 1,500 times greater than waterquality criteria to protect freshwater aquatic life to acute exposures. As a result, massive fish killswere experienced due to the cyanide plume from Baia Mare (Figure 1.6). An estimate of dead fishin the Hungarian portion of the Tisza River as a result of the spill was 1,240 tons [34]. There werealso substantial but unquantified fish kills in the Tisza River in Yugoslavia.

Smaller in scale but more widespread are the many continuing releases of cyanide from solidwastes disposed on land in the past and from ongoing wastewater discharges. Cyanide-bearing oxide

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Introduction 9

SLOVAKIA

HUNGARY

Budapest

Miskoic

Szeged

UKRAINE

Baia Mare

Bucharest

Sasar

ROMANIA

MOLDOVA

Blacksea

BUICARIA

YUGOSLAVIA

Belgrade

1 2

4

5

67 8

9

3

Timisoara

Tiza

FIGURE 1.5 Map showing the river transport route for the cyanide plume from the spill at BaiaMare, Romania, JanuaryFebruary 2000. (Source: Data from: UNEP, http://www.rec.org/REC/Publications/CyanideSpill/ENGCyanide.pdf, 2000.)

FIGURE 1.6 Worker removing dead fish killed by a cyanide spill in Hungarys Tisza River, at Kiskore onFebruary 9, 2000. Photo by Laszlo Balogh. Reuters 2000. Used with permission.

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box wastes at thousands of former manufactured gas plant (MGP) sites throughout the United Statesand Europe are an example of a widely distributed industrial legacy waste. These wastes, whichcontain the iron cyanide solid Prussian Blue, were disposed in onsite landfills at many MGP sites.Dissolved cyanide is generated by contact of these solids with groundwater, resulting in under-ground plumes of contamination that can move significant distances, depending on subsurfaceconditions [31,35,36]. At a former MGP site in Wisconsin, it was demonstrated that dissolvedcyanide moved with the groundwater through the sand and gravel aquifer beneath the site, toward amunicipal drinking water supply well located 500 m from the site [31]. In another area of Wisconsin,oxide box wastes from an MGP operation were placed as landfill material in three-foot thicklayers along an electric transmission line corridor, amounting in just one section of the corridor to26,000 tons of fill material [37]. Remediation efforts involving removal of the material commencedin the 1990s. Related legal actions eventually resulted in settlements totaling $21.8 million againstthe responsible company [38,39]. Thus, even localized cyanide contamination problems can havesignificant technical, regulatory, and legal implications.

1.7 CYANIDE: CHEMISTRY, RISK, AND MANAGEMENT

The management and regulation of cyanide in water and soil can be very challenging because of thecomplexity of the chemistry and toxicology of cyanide, the risk it poses in different environmentalcontexts, and stringent regulatory requirements to be satisfied [32,40,41]. Many different chemicalforms of cyanide occur in water and soil, including dissolved free cyanide (HCN, CN), metal-cyanide complexes (e.g., Ni(CN)24 , Fe(CN)46 ), and organocyanide (e.g., acetonitrile, CH3CN)species, as well as metal-cyanide solids (e.g., ferric ferrocyanide, Fe4(Fe(CN)6)3(s)). In addition,HCN in water can volatilize, forming HCN(g). The different chemical forms of cyanide and theirreactivity and properties are discussed in Chapters 2, 5, and 6. Each of these species is formed andaffected by different chemical reactions, and each has different physical, chemical, and toxicologicalproperties. For example, the toxicological significance of each individual metalcyanide complexis determined by its ability to release free cyanide (CN or HCN), the target species of concern,under pertinent exposure conditions. The chemical dissociative properties of each complex thuscontrol the release of free cyanide and hence toxicity. Thus, the differences in properties mean thatthe various cyanide species vary in their toxicity to animals and plants, in their fate and transportin the environment (Chapters 911), and in their treatability by physical, chemical, and biologicaltreatment technologies (Chapters 1924).

Until recently, regulation and management of cyanide in water and soil have been focused on total(inorganic) cyanide content (Chapter 18). This focus has been driven in large part by the availabilityof a long-standing, simple, robust technique for measuring total inorganic cyanide content: strongacid digestion to transform all inorganic cyanide compounds to HCN followed by distillation tovolatilize and capture the HCN(g). While such total cyanide measurements are useful and indeedcontinue to be the predominant means of monitoring cyanide, they provide no direct informationabout cyanide speciation. The focus on total cyanide content has made regulations of cyanide inwater and soil confusing and inconsistent, and has led to management and treatment approaches ofvarying effectiveness.

Knowledge of cyanide speciation is critical to technically and economically effective managementof cyanide in water and soil. This is now fairly well recognized in the engineering, science, andregulatory professional communities, but measurements, regulations, treatment technologies, andsite management plans with a species-specific focus are still evolving for cyanide. We are in themidst of transitioning to species-specific approaches with respect to cyanide, similar to the transitionthat occurred through the 1980s for management of metal contaminants in water and soil. This bookis intended to help with and to accelerate that transition.

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Introduction 11

1.8 CYANIDE REGULATIONS

Cyanide aqueous discharge regulations in the United States are based on effluent discharge limitationsfor categorical industries (e.g., iron and steel, organic chemicals manufacturing, and electroplating)and receiving water quality criteria. Effluent limits for categorical industries are largely based on theperformance of Best Available Technology Economically Achievable (BAT) and are contained inthe U.S. Code of Federal Regulations (40CFR, Parts 425471). Thirteen major industry categoriesare identified in the federal regulations, including 43 subcategories with cyanide discharge limits(see Chapter 18). It is interesting to note that the gold mining industry, a major cyanide user anddischarger, is not included in these industry categories.

Receiving water quality criteria, which are based on aquatic toxicity studies and aimed at pro-tection of aquatic life, are significantly more stringent than BAT discharge limits. For discharges towater bodies in which the designated use mandates protection of aquatic life, cyanide effluent limitsare usually developed with the objective of not exceeding water quality criteria. Discharge limitsbased on consideration of water quality criteria tend to be very stringent, and can be at or below detec-tion limits achieved in routine commercial analyses. For example, effluent limits for shallow-watermarine discharges in the United States are often set at the marine water quality criterion of 1 g/lfree cyanide. The detection limit for free cyanide with standard analytical methods often exceedsthis amount by factors of 2 to 5 or more. Chapters 7 and 8 discuss the analytical issues associatedwith measuring cyanide in water, wastewater, soil and sludges, and the very troublesome issues ofdetection, practical quantitation limits, and measurement precision. In addition, water quality cri-teria reflect toxicity to very sensitive aquatic species that may not be present in a particular receivingwater.

Soil cleanup standards for cyanide have been established by some states in the United Statesand by some countries in Europe (see Chapter 18). Many other government organizations haveestablished soil screening or action levels to define when additional remedial investigation or actionis needed. Soil cleanup standards or screening levels for cyanide vary widely. For example, soilcleanup standards for free cyanide in residential surface soils, where direct human contact can occur,have been set at 30, 160, 1,600, and 4,400 mg/kg by Florida, Maryland, New Jersey, and Pennsylvania,respectively. Free cyanide cleanup standards for nonresidential surface soils established by the samefour states are 39,000, 4,100, 56,000, and 23,000 mg/kg. By contrast, the Netherlands has set theintervention value for free cyanide in soil at the low value of 20 mg/kg based on human health riskconsiderations, and has established separate values for complexed cyanide at 50 mg/kg for soils withpH 5 and at 650 mg/kg for soils with pH< 5 [42]. The Dutch soil target values for protection ofecosystems are even lower: 1.0 mg/kg for free cyanide and 5.0 mg/kg for complexed cyanide [42].

Acceptable concentrations of free and complexed cyanide in water and soil are determined byrisk assessment. Chapters 13 to 17 examine the toxicity and risk issues that drive the establishment ofcyanide aqueous discharge limits and treatment/management objectives for soil and other cyanide-contaminated media.

1.9 CYANIDE TREATMENT TECHNOLOGY

An array of technologies is available for the treatment of cyanide in surface water and ground-water, wastewaters, and contaminated soils and sludges. These technologies, discussed in detail inChapters 1924, span the gamut of biological, chemical, electrolytic, physical, and thermal treatmentprocessing. Example applications of the technologies employed most commonly in municipal andindustrial settings are presented in Chapters 2527. An important message from these examinationsof cyanide contamination management is that commercial applications of the technologies in aneconomical mode of operation may not yield treated water, soil, or sludge with cyanide concentra-tions that meet specified regulatory limits. Careful evaluation of technology performance, includingtreatability testing, is needed prior to application of technologies for cyanide management.

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1.10 SUMMARY AND CONCLUSIONS

Cyanide compounds are produced and used in commerce in large quantities. Many different chemical forms of cyanide can exist in water and soil, each of which has

different physical, chemical, and toxicological properties. Because of the high degree of toxicity of certain forms of cyanide, primarily hydrogen

cyanide (HCN), acceptable levels of cyanide compounds in water and soil can be verylow, for example, 1 g/l for free cyanide in marine waters of the United States.

Many aquatic organisms are significantly more sensitive to cyanide than are humans. Cyanide species can be formed in nature by both abiotic and biotic processes. Cyanide

can be produced by certain plants, bacteria, fungi, and algae. Background concentrations of cyanide in water and soil are very low. Most cyanide found

in water and soil is the result of anthropogenic contamination from industrial sources. The major sources of cyanide in water and soil are discharges and wastes from metal

mining processes, metal manufacturing and finishing processes, chemical production,coal conversion processes, and petroleum refining.

The management and regulation of cyanide in water and soil can be very challengingbecause of the complexity of the chemistry and toxicology of cyanide and, accordingly,the risk it poses in different environmental contexts. A further complication is that thereis widespread public fear of cyanide, regardless of its form and location.

The focus on total cyanide content has made regulations of cyanide in water and soilconfusing and inconsistent, and has led to management and treatment approaches ofvarying effectiveness.

We are in the midst of transitioning to species-specific approaches with respect to cyanide,similar to the transition that occurred for management of metal contaminants in waterand soil.

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35. Meeussen, J.L., Keizer, M.G., van Riemsdijk, W.H. and de Haan, F.A.M., Dissolution behavior of ironcyanide (Prussian Blue) in contaminated soils, Environ. Sci. Technol., 26, 1832, 1992.

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38. Hawkins, L., Wisconsin Energy settles cyanide suit, Milwaukee Journal Sentinel, September 4, 2002.39. Johnson, A. and Held, T., Deal reached over tainted wood chips, Milwaukee Journal Sentinel, May 28,

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2 Physical and Chemical Forms ofCyanide

Rajat S. Ghosh, David A. Dzombak, andGeorge M. Wong-Chong

CONTENTS

2.1 Gaseous Forms of Cyanide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.2 Aqueous Forms of Cyanide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.2.1 Free Cyanide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.2.2 MetalCyanide Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.2.2.1 Weak MetalCyanide Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192.2.2.2 Strong MetalCyanide Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.2.3 Cyanate and Thiocyanate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192.2.4 Organocyanide Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2.3 Solid Forms of Cyanide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202.3.1 Simple MetalCyanide Solids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.3.2 MetalMetal Cyanide Solids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.3.2.1 Alkali/Alkaline Earth MetalMetal Solids . . . . . . . . . . . . . . . . . . . . . . . . . . 212.3.2.2 Other MetalMetal Cyanide Complex Salts . . . . . . . . . . . . . . . . . . . . . . . . . 22

2.4 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Cyanide occurs in many different forms in water and soil systems. The specific form of cyanidedetermines the environmental fate and transport of cyanide, as well as its toxicity. Understanding thespecific form(s) of cyanide present in a particular water, soil, or sediment is critical for assessmentof how to manage or treat the cyanide present. This cannot be overemphasized! While cyanideis often discussed as a single entity in the popular press and even in professional publications,this is a misleading portrayal. The various forms of cyanide are quite different in their reactivityand their toxicity. Proper professional evaluation, assessment, and design activities pertaining tocyanide contamination management requires knowledge about and careful consideration of cyanidespeciation.

This chapter provides an introductory overview of the various forms of cyanide that can exist inwater and soil systems. All of the remaining chapters of this book assume a basic knowledge of thespeciation of cyanide as presented here. A detailed examination of the properties and reactivity of themost commonly occurring aqueous, gaseous, and solid forms of cyanide is provided in Chapter 5.

In water and soil systems, cyanide occurs in various physical forms, including many differentkinds of species dissolved in water, many different solid species, and several gaseous species. Thecyanide species that occur in the aqueous, solid, and gas phases are indicated in Figure 2.1.

Chemically, cyanide can be classified into inorganic and organic forms, as indicated in Figure 2.1.Inorganic forms, which occur in all three physical states, include free cyanide, weak metalcyanidecomplexes, strong metalcyanide complexes, thiocyanate and metalthiocyanate complexes, cyanate

15

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WATER

GAS SOLID

Freecyanide

Metalcyanidecomplexes

Cyanate, thiocyanate

Organocyanides

FreecyanideHCN(g)

CyanogenhalidesCNCl(g),CNBr(g)

Simple metalcyanide solidsNaCN(s), KCN(s),CuCN(s)

Alkali or alkaline earthmetal-metalcyanide solidsK3Fe(CN)6(s), K4Fe(CN)6(s),KAg(CN)2(s),

Othermetal-metalcyanide solidsFe4[Fe(CN)6 ]3(s),Fe3[Fe(CN)6]2(s),

HCN, CN Weak complexes:Ag(CN)2, CdCN, Strong complexes:Fe(CN)4 Fe(CN)3

CNO, SCN Nitriles, cyanohydrins,

6, 6,

FIGURE 2.1 Forms and species of cyanide in water and soil.

and metalcyanate complexes, and cyanogen halides. Aqueous free cyanide is the sum of hydrogencyanide, HCN, and its deprotonated form, the cyanide anion, CN. HCN is volatile under environ-mental conditions and occurs as both aqueous and gaseous species. Many metals can bond with thecyanide anion to form dissolved metalcyanide complexes, as well as metalcyanide solids. Cyanate,CNO, requires the presence of strong oxidizing agents for its formation and thus is rarely foundin the environment. Thiocyanate, SCN, can be formed in the environment and is also present in avariety of industrial wastewater discharges. The cyanogen halides of interest, CNCl and CNBr, formupon chlorination or bromination of water containing free cyanide. These species are volatile underenvironmental conditions, and thus occur as both aqueous and gaseous species. Organic cyanidescontain carboncarbon covalent bonding between hydrocarbon and cyanide moieties, and are usuallypresent as dissolved species.

Natural as well as anthropogenic sources discharge a wide range of cyanide species to the envir-onment. Over 2650 species of plants (130 families) produce cyanogenic glycosides as part of naturaldefense mechanisms (Chapter 3). Upon stress or injury, cyanogenic glycosides are hydrolyzed by acoexisting plant enzyme and release HCN. In addition, almost all fruit-bearing plants release HCNduring ethylene synthesis, which aids in the fruit ripening process (Chapter 3).

Cyanide (as free, organic and metal-complexed cyanide compounds) is used as a raw mater-ial during the production of chemicals (nylon and plastics), pesticides, rodenticides, gold, wine,anticaking agents for road salt, fire retardants, cosmetics, pharmaceuticals, painting inks, and othermaterials (Chapter 4). Cyanide is also used directly in a variety of processes, including electroplatingand hydrometallurgical gold extraction (Chapter 4). One of the earliest uses of cyanide dates back to1704, when the solid phase ironcyanide compound ferric ferrocyanide (FFC), Fe4[Fe(CN)6]3(s),also referred to as Prussian Blue, was first used as a pigment for artist colors [1,2]. In addition, freecyanide, weak and strong metalcyanide complexes, and thiocyanates also occur as by-products ofmany current and former industrial processes (Chapter 4). Current industries that produce cyanideas a by-product include chemical manufacturing, iron and steel making, petroleum refining, andaluminum smelting. An example of a past industry that generated cyanide-bearing wastewaters andsolid wastes in substantial quantities is gas manufacture by coal gasification. There are thousands offormer manufactured gas plant (MGP) sites throughout the eastern and midwestern United States and

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Physical and Chemical Forms of Cyanide 17

Europe with soil containing FFC, which was generated as a process by-product and often managedonsite as fill [3]. Cyanide contamination exists at many other former industrial sites. It is one of themost common contaminants identified at Superfund sites in the United States [4].

The aim of this chapter is to provide an overview of the common physical and chemical forms ofcyanide that occur in water and soil systems. In the following sections, the cyanide species of primaryinterest in gaseous form, dissolved in water, and in solid form are listed and briefly described.

2.1 GASEOUS FORMS OF CYANIDE

Three gaseous forms of cyanide are of interest in water and soil systems: hydrogen cyanide (HCN),cyanogen chloride (CNCl), and cyanogen bromide (CNBr). Cyanogen chloride and cyanogen brom-ide are disinfection by-products formed in water and wastewater treatment [5,6]. HCN is present inwastewater discharges and leachates from certain industrial waste sites, and can be formed in natureas well.

Hydrogen cyanide gas is colorless with an odor of bitter almonds. It is highly toxic to humans(see Chapter 13). HCN(g) is very soluble in water, forming a weak acid, HCN(aq), upon dissolution.HCN has a high vapor pressure (630 mm Hg at 20C; Ref [7]) and is readily volatilized from waterat pH values less than 9, where HCN remains fully protonated.

The cyanogen halides CNCl and CNBr are also colorless gases with high vapor pressures(1230 mm Hg and 121 mm Hg at 25C for CNCl and CNBr, respectively [8,9]). Like hydrogencyanide gas, CNCl and CNBr are highly toxic to humans if inhaled or absorbed. These are solublein water, but degrade by hydrolysis, very rapidly at high pH [5]. Degradation is rapid at any pH ifthere is free chlorine or sulfite present [5]. At pH 10, degradation of CNCl and CNBr by hydrolysisoccurs with half-lives in the range of 20 to 40 min [5]. The hydrolysis degradation product is cyanateion (CNO), which can subsequently hydrolyze to CO2 and NH3 at alkaline pH conditions (seeChapter 5).

2.2 AQUEOUS FORMS OF CYANIDE

Common aqueous forms of cyanide, listed in Table 2.1, can be broadly divided into four major classes:free cyanide, metalcyanide complexes, cyanate and thiocyanate species, and organocyanide com-pounds. Free cyanide comprises molecular HCN and cyanide anion. Metalcyanide complexes rangefrom weak metalcyanide complexes (e.g., complexes of copper, zinc, and nickel with CN) to strongmetalcyanide complexes (e.g., complexes of cobalt and iron with CN). Cyanate and thiocyanateform by oxidation of free cyanide, in the presence of sulfide compounds in the case of thiocyanate.Both of these species are anionic for the environmental pH range, and form complexes with metals.Finally, there are organocyanide complexes, where the cyanide anion is covalently bonded to ahydrocarbon group.

2.2.1 FREE CYANIDE

Free cyanide represents the most toxic cyanide forms (see Chapters 13 and 14). It refers to eithersoluble hydrogen cyanide, HCN(aq), or soluble cyanide anion (CN). HCN(aq) is a weak acidwith a pKa of 9.24 at 25 (Chapter 5). It can dissociate into cyanide ion according to the followingdissociation reaction:

HCN(aq) = H+ + CN, pKa = 9.24 at 25C (2.1)

where the = sign denotes a two-way, equilibrium reaction. Thus, at pH values less than 9.24, HCNis the dominant free cyanide species, while at greater pH values cyanide ion dominates free cyanide.

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TABLE 2.1Common Aqueous Cyanide Species

Classication Cyanide species

Free cyanide HCN, CNWeak metalcyanide AgCN(OH), Ag(CN)2 , Ag(CN)23 , Ag(OCN)2

complexes CdCN, Cd(CN)02, Cd(CN)3 , Cd(CN)24Cu(CN)2 , Cu(CN)23 , Cu(CN)34Ni(CN)02, Ni(CN)3 , Ni(CN)24 , NiH(CN)4 , NiH2(CN)04, NiH3(CN)+4Zn(CN)02, Zn(CN)3 , Zn(CN)24HgCN+, Hg(CN)02, Hg(CN)3 , Hg(CN)24 , Hg(CN)2Cl, Hg(CN)3Cl2, Hg(CN)3Br2

Strong metalcyanide BaFe(CN)26 , BaFe(CN)6complexes CaFe(CN)26 , CaFe(CN)6 , Ca2Fe(CN)06, CaHFe(CN)26

Fe(CN)46 , HFe(CN)36 , H2Fe(CN)26 , Fe2(CN)06K2H2Fe(CN)06, K3HFe(CN)06, KHFe(CN)26K2Fe(CN)26 , KFe(CN)36LiFe(CN)36 , Li2Fe(CN)26 , LiHFe(CN)26Fe(CN)36MgFe(CN)6 , MgFe(CN)26NH4Fe(CN)36 , (NH4)2Fe(CN)26 , NH5Fe(CN)26NaFe(CN)36 , Na2Fe(CN)26 , NaHFe(CN)26SrFe(CN)6TlFe(CN)36Au(CN)2Co(CN)36Pt(CN)24

Cyanate HOCN, OCN

Metalcyanate complexes Ag(OCN)2 , and othersThiocyanate HSCN, SCN

Metalthiocyanate MgSCN+

complexes MnSCN+

FeSCN+

FeSCN2+, Fe(SCN)+2 , Fe(SCN)03, Fe(SCN)4 , FeOHSCN+CoSCN+, Co(SCN)02CuSCN+, Cu(SCN)02NiSCN+, Ni(SCN)02CrSCN2+, Cr(SCN)+2CdSCN+, Cd(SCN)02, Cd(SCN)3 , Cd(SCN)24ZnSCN+, Zn(SCN)02, Zn(SCN)3 , Zn(SCN)24 , and others

Organocyanides Nitriles (e.g., acetonitrile)CyanohydrinsCyanocobalamin and others

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2.2.2 METALCYANIDE COMPLEXES

The cyanide anion is a versatile ligand that reacts with many metal cations to form metalcyanidecomplexes. These species, which are typically anionic, have a general formula of M(CN)nx , where Mis a metal cation, x is the number of cyanide groups, and n is the ionic charge of the metalcyanidecomplex.

The stability of metalcyanide complexes is variable and requires moderate to highly acidic pHconditions in order to dissociate. Metalcyanide complex dissociation yields free cyanide:

M(CN)nx = M+ + xCN (2.2)

Metalcyanide complexes are classified into two broad categories, namely, weak metalcyanidecomplexes and strong metalcyanide complexes, based on the strength of the bonding betweenthe metal and the cyanide ion. Complexes with greater strength of the metalcyanide bond are morestable in aqueous solution, that is, they dissociate only to a limited extent, and the dissolution processmay be very slow.

2.2.2.1 Weak MetalCyanide Complexes

Weak metalcyanide complexes are those in which the cyanide ions are weakly bonded to the metalcation, such that they can dissociate under mildly acidic conditions (pH = 4 to 6) to produce freecyanide. Because of their dissociative nature, they are often regulated along with free cyanide inwater. Common examples of weak metalcyanide complexes include copper cyanide (Cu(CN)23 ),zinc cyanide (Zn(CN)24 ), nickel cyanide (Ni(CN)24 ), cadmium cyanide (Cd(CN)24 ), mercurycyanide (Hg(CN)2), and silver cyanide (Ag(CN)2 ).

2.2.2.2 Strong MetalCyanide Complexes

Strong metalcyanide complexes include cyanide complexes with transition heavy metals such as,iron, cobalt, platinum, and gold that require strong acidic conditions (pH < 2) in order to dissociateand form free cyanide. Strong metalcyanide complexes are much more stable in aqueous solutionthan the weak ones and are relatively less toxic. Common examples of strong metalcyanide com-plexes include ferrocyanide (Fe(CN)46 ), ferricyanide (Fe(CN)36 ), gold cyanide (Au(CN)2 ), cobaltcyanide (Co(CN)36 ), and platinum cyanide (Pt(CN)24 ).

2.2.3 CYANATE AND THIOCYANATE

Free cyanide can be oxidized to form cyanate, CNO, or, depending on the pH, its protonatedform HOCN (pKa = 3.45 at 25C). Cyanate is substantially less toxic than free cyanide. It is rarelyencountered in aqueous systems, as a strong oxidizing agent and a catalyst are required for conversionof free cyanide to CNO or HOCN [10]. When cyanate does form it can react with metals to formmetalcyanate complexes, though these reactions have not been studied extensively (Chapter 5).

Free cyanide can react with various forms of sulfur to form thiocyanate, SCN, which is relativelynontoxic. The two forms of sulfur in the environment most reactive with free CN are polysulfides,SxS2, and thiosulfate, S2O23 (Chapter 5). Thiocyanate can protonate to form HCNS0, but thisrarely occurs in natural systems as the pKa for this reaction is 1.1. Thiocyanate can form complexeswith many metals (Chapter 5).

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(sugar O)n C CN

H,R

R

FIGURE 2.2 General structure of cyanogenic glycosides (R represents CH3 group).

O

OCHCN

O

CH2OHCH2OH

O

HO OH

OH

HOO

HO HO OCH2HO O

HO OH OCHCN

Amygdalin (Cherry, Apricot) Dhurrin (Cassava)

O C CH3

CN

CH3

FIGURE 2.3 Common plant cyanogenic glycosides.

2.2.4 ORGANOCYANIDE COMPLEXES

Organic cyanide compounds contain a cyanide functional group that is attached to a carbon atom ofthe organic molecule via covalent bonding. Common examples include nitriles, such as acetonitrile(CH3CN) or cyanobenzene (C6H5CN), which are used as industrial solvents and as raw materials formaking nylon products and pesticides. Nitriles can also exist in the natural environment in shale oils[11], in plants [12], or as a plant-growth hormone [13]. Several classes of nitriles can be producednaturally or synthesized chemically, the most common of which are the cyanogenic glycosides andcyanohydrins. Cyanohydrins, also known as -hydroxynitriles, are organic cyanides with the generalstructure R1R2C(OH)(CN), where the hydroxide group and the cyanide group are attached to thesame carbon atom.

Cyanogenic glycosides are produced by the plants under natural environmental conditions to aidin their defense mechanism (Chapter 3). These species comprise a cyanide anion that is covalentlybonded to a carbon atom, which in turn is bound by a glycosidic linkage to one or more sugarsdepicted in Figure 2.2. Some common cyanogenic glycosides produced by plants are shown inFigure 2.3. Certain groups of nitriles such as, cyanogenic glycosides, exhibit high stability in wateras far as dissociation to free cyanide is concerned.

Other organocyanide compounds of interest include cyanocobalamin, also known as Vitamin B12.It consists of single cyanide group bonded to a central trivalent cobalt cation. Vitamin B12 is syn-thesized by microorganisms, not by plants, and is found in animal tissues as a result of intestinalsynthesis [14]. It is essential for human life, serving numerous functions and being an especiallyimportant vitamin for maintaining healthy nerve cells and aiding the production of genetic buildingblocks DNA and RNA [15]. There are cyanide and noncyanide forms of Vitamin B12. The noncyan-ide forms include methylcobalamin, adenosylcobalamin, chlorocobalamin, and hydroxycobalamin.These compounds, also produced by microorganisms, are less stable than cyanocobalamin but alsoessential to human life.

2.3 SOLID FORMS OF CYANIDE

In systems with metals and cyanide present in sufficient quantities, metals can react with cyan-ide to form a wide range of solids. The solid forms of cyanide may be divided into two general

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TABLE 2.2Common Solid Phase Cyanide Species

Classication Cyanide species

Simple metalcyanide solids KCN(s)NaCN(s)AgCN(s)CuCN(s)Hg(CN)2(s)

Alkali or alkaline earth metalmetal K4Fe(CN)6(s)cyanide solids K3Fe(CN)6(s)

K4Ni4(Fe(CN)6)3(s)K2CdFe(CN)6(s)K2Cu2Fe(CN)6(s)KZn1.5Fe(CN)6(s)

Other metalmetal cyanide solids Fe4[Fe(CN)6]3(s)Fe3[Fe(CN)6]2(s)Fe[Fe(CN)6](s)Fe2[Fe(CN)6](s)Ag4Fe(CN)6(s)Cd2Fe(CN)6(s)Cu2Fe(CN)6(s)Zn2Fe(CN)6(s)

categories: simple metalcyanide solids, which are relatively soluble, and metalmetal cyanide com-plex solids with varying degree of solubility. Some common metalcyanide and metalmetal cyanidesolids are listed in Table 2.2.

2.3.1 SIMPLE METALCYANIDE SOLIDS

This class of cyanide solids consist of structurally simple, metal cyanides of the form M(CN)x ,where M is an alkali, alkaline earth metal or a heavy metal. Common examples include sodiumcyanide (NaCN(s)), potassium cyanide (KCN(s)), calcium cyanide, (Ca(CN)2(s)), zinc cyanide(Zn(CN)2(s)), and others (see Table 2.2). Most of these solids are highly soluble in water and readilydissociate, releasing the cyanide ion, and therefore are potentially toxic.

2.3.2 METALMETAL CYANIDE SOLIDS

This class of cyanide solids consists of one or more alkali, alkaline earth, or transition metalcations combined with an anionic metalcyanide complex. Based on whether the metal cation isalkali/alkaline earth or transition metal, this class of compounds is again subdivided into two cat-egories: alkali/alkaline earth metalmetal cyanide solids and other metalmetal cyanide solids. In thelatter, the metals involved are B-type or transition metals [16].

2.3.2.1 Alkali/Alkaline Earth MetalMetal Solids

This class of structurally complex solids comprises one or more alkali or alkaline earth metalcations ionically bonded to an anionic metalcyanide complex with the general formula ofAx[M(CN)y] nH2O, where A is an alkali or alkaline earth metal cation (or ammonium ion), Mis a transition metal atom, x is the number of alkali metal atoms, y is the number of cyanide groups,

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and n is the number of water molecules incorporated in the solid structure. A common exampleof this class of compound is potassium ferrocyanide (K4Fe(CN)6(s)). Alkali/alkaline earth metalmetal cyanide complex salts can readily dissociate in aqueous solutions, releasing the alkali metalcation and the anionic metal cyanide complex according to the following equation:

Ax[M(CN)y] nH2O = xA+ + [M(CN)y]m (2.3)

where m is the ionic charge of the metalcyanide complex released to solution.

2.3.2.2 Other MetalMetal Cyanide Complex Salts

This class of structurally complex compound comprises one or more transition metal cationsionically bonded to an anionic transition metal cyanide complex with the general formula ofMx[M(CN)y]z nH2O where M is a B-type or transition metal cation, x number of transition metalcations, y is the number of cyanide groups, z is the number of metalcyanide complexes, and nis the number of water molecules in the structure. Due to the versatility of the cyanide anion as aligand, there are many different kinds of metalmetal cyanide compounds that exhibit a wide rangeof structural properties [17].

Metalmetal cyanide solids involving all B-type and transition metals are very stable and relat-ively insoluble under acidic and neutral conditions (Chapter 5). However, under alkaline conditions,these compounds are relatively soluble, releasing metal cations and anionic metalcyanide complexesto solution according to the following general reaction:

Mx[M(CN)y]z nH2O = xM+ + z[M(CN)y]m (2.4)

where m is the ionic charge of the metalcyanide complex released to aqueous solution.A well-known example of a transition metalmetal cyanide is ferric ferrocyanide

Fe4(Fe(CN)6)3(s), or Prussian Blue, which has various commercial and medicinal uses (Chapter 4).

2.4 SUMMARY AND CONCLUSIONS

Cyanide is present in gas, liquid, and solid forms in water and soil systems. Many different species of cyanide occur in water and soil systems. The specific form

of cyanide determines the environmental fate and transport of cyanide, as well as itstoxicity. Understanding the specific form(s) of cyanide present in a particular water, soil,or sediment is critical for assessment of how to manage or treat the cyanide present.

Cyanide mostly occurs in inorganic forms. The dissolved forms of primary interest arefree cyanide (HCN and CN) and metalcyanide complexes. Solid forms of cyanideinclude simple metalcyanide solids (e.g., NaCN(s), KCN(s)), which are relatively sol-uble, and more complex, less soluble metalmetal cyanide solids (e.g., Fe4(Fe(CN)6)3(s),or Prussian Blue). The gaseous form of cyanide of primary interest is HCN(g).

Free cyanide, either in dissolved (HCN and CN) or gaseous form (HCN(g)), are thespecies of primary interest with respect to human health and aquatic toxicity.

Dissolved inorganic metalcyanide complexes can be categorized as weak metalcyanidecomplexes and strong metalcyanide complexes, based on the strength of the bondingbetween the metal and the cyanide ion.

Cyanate (CNO) is formed from oxidation of free cyanide. It can react with metals andform metalcyanate complexes.

Thiocyanate (SCN) is formed from reaction of free cyanide with various forms of sulfur.It can react with metals to form metal-thiocyanate complexes.

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Organic compounds containing cyanide are produced by both natural and anthropogenicactivities. They consist of molecules with carboncarbon covalent bonding with theCN group. Common organocyanide compounds include the nitriles, such as acetonitrile(CH3CN).

REFERENCES

1. ACC, The Chemistry of the Ferrocyanides, American Cyanamid Co., New York, NY, 1953.2. Feller, R.L., Ed., Artists Pigments: A Handbook of Their History and Characteristics, National Gallery

of Art, Washington, DC, 1986.3. Hayes, T.D., Linz, D.G., Nakles, D.V., and Leuschner, A.P., Eds., Management of Manufactured Gas

Plant Sites, Vol. 1 & 2, Amherst Scientific Publishers, Amherst, MA, 1996.4. USEPA, Common chemicals found at Superfund sites, U.S. Environmental Protection Agency, Office

of Solid Waste and Emergency Response, http://www.epa.gov/superfund/resources/chemicals.htm,accessed: March 22, 2005.

5. Xie, Y. and Hwang, C.J., Cyanogen chloride and cyangen bromide analysis in drinking water, inEncyclopedia of Analytical Chemistry, Meyers, R.A., Ed., John Wiley & Sons, Chichester, UK, 2000,p. 2333.

6. Zheng, A., Dzombak, D.A., and Luthy, R.G., Formation of free cyanide and cyanogen chloride fromchlorination of POTW secondary effluent: laboratory study with model compounds, Water Environ.Res., 76, 113, 2004.

7. ATSDR, Toxicological profile for cyanide (update), U.S. Department of Health and Human Services,Public Health Service, Agency for Toxic Substances and Disease Registry, Atlanta, GA, 1997.

8. CDC, NIOSH emergency response card: Cyanogen chloride, Centers for Disease Control and Prevention,http://www.bt.cdc.gov/agent/cyanide/erc506-77-4.asp, accessed: April 3, 2005.

9. IPCS/INCHEM, Cyanogen bromide, International Programme on Chemical Safety and the Commissionof the European Communities, http://www.inchem.org/documents/icsc/icsc/eics0136.htm, accessed:April 3, 2005.

10. Smith, A. and Mudd

Cyanide in water and soil, dzombak, ghosh, wong

Education

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