Overview of Chromium(VI) in the Environment: Background and

1

1-5667-0608-4/01/$0.00+$1.50© 2004 by CRC Press LLC

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Overview of Chromium(VI) in the

Environment: Background and History

James Jacobs and Stephen M. Testa

CONTENTS

1.1 Purpose............................................................................................................21.2 Introduction to the Chromium(VI) Problem.............................................3

1.2.1 Exposure Pathways...........................................................................31.2.2 Physical and Chemical Characteristics..........................................41.2.3 Analytical Methods...........................................................................51.2.4 Remediation Overview ....................................................................61.2.5 Regulatory Levels..............................................................................61.2.6 Health..................................................................................................7

1.3 Historical Perspective ...................................................................................71.4 Origin and Properties .................................................................................141.5 Production and Use of Chromium ...........................................................14

1.5.1 Chromium Production Methods...................................................141.5.2 World Production............................................................................151.5.3 Resources ..........................................................................................151.5.4 Consumption....................................................................................151.5.5 Economics.........................................................................................161.5.6 Chromium Substitutes....................................................................161.5.7 Uses ...................................................................................................16

1.5.7.1 Paint ....................................................................................171.5.7.2 Stainless Steel ....................................................................171.5.7.3 Furnace Linings.................................................................171.5.7.4 Tanning and Dying Processes.........................................171.5.7.5 Photography ......................................................................171.5.7.6 Specialized Steels ..............................................................18

1.5.8 Chromium Processing and Alloys................................................181.5.9 Chromium Isolation........................................................................19

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Chromium(VI) Handbook

1.6 Potential Adverse Environmental Effects from Use and Disposal of Chromium ...............................................................19

Bibliography ........................................................................................... 20

1.1 Purpose

Chromium (Cr) is one of the world’s most strategic and critical materialshaving a wide range of uses in the metals and chemical industries

.

Cralloys enhance metal resistance to impact, corrosion, and oxidation. Cr isused in stainless steel and noniron alloy production for plating metals,development of pigments, leather processing, and production of catalysts,surface treatments, and in refractories. Cr occurs in various oxidationstates, of which chromium(VI) [Cr(VI)] is a suspected carcinogen and apotential soil, surface water, and groundwater contaminant. Cr(VI) mayalso occur in the natural environment, but human-caused Cr(VI) contam-ination has recently been the focus of much scientific discussion, regulatoryconcern, and legal posturing.

Owing to the many industrial uses of Cr(VI) and an active industrialbase, California and other urbanized states have sites with Cr(VI) contam-inant problems. Drinking water supply wells and water sources areaffected by Cr(VI). What is common to many Cr(VI) sites are questionsthat continue to arise regarding the safety of the drinking water supply.As with most environmental challenges, questions of science compete withemotional responses and financial interests. There is still uncertaintyregarding what daily dose of Cr(VI) is considered toxic and what ingestionlevel is acceptable.

To define the current state of technical knowledge of Cr(VI), the Ground-water Resources Association of California (www.grac.org) presented a Cr(VI)symposium in Glendale, California on January 25, 2001. At this symposium,national experts discussed the science, regulatory policies, and legal issuesassociated with this controversial pollutant. Based on disagreement on eventhe most basic of scientific points, such as safe levels of Cr(VI) to consume,it became apparent that Cr(VI) is a topic of both great importance andwidespread debate.

The Independent Environmental Technical Evaluation Group (IETEG), avolunteer research organization located in Point Richmond, California, wascreated in 1997 to objectively review scientific and engineering informationconcerning controversial environmental issues. The IETEG’s first project was

MTBE: Effects on Soil and Groundwater Resources

, a CRC Press book publishedin 2000. The project was started in early 2001 to objectively evaluate Cr(VI)issues. The IETEG group is multidisciplinary and includes geologists, engi-neers, toxicologists, lawyers, regulators, and others employed in environ-mental consulting, contracting companies, environmental equipment and

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Overview of Chromium(VI) in the Environment: Background and History

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product manufacturers, water purveyors, law firms, and academia. Theseenvironmental professionals are specialists in the assessment and cleanupof soil, groundwater, and air, including environmental compliance, legal andregulatory issues, and the design of water treatment equipment. Given thelevel of misinformation on Cr(VI), this book was prepared to help facilitatea rational approach to assuring the quality of our drinking water suppliesthat may contain Cr(VI).

1.2 Introduction to the Chromium(VI) Problem

Each contaminant has a unique set of characteristics and issues that mustbe evaluated to proceed with more detailed remediation efforts or develop-ing public policy. These factors include persistence in groundwater, taste andodor thresholds, health risk, transport and fate, current laboratory analyticalmethods, groundwater remediation, and regulatory issues. For Cr(VI), eachof these factors will be evaluated in more detail below and in this volume’schapters.

1.2.1 Exposure Pathways

For some, a significant health concern is the possible adverse effects of humaningestion of Cr(VI) in drinking contaminated groundwater or surface water.This is still being debated within the scientific community. Dermal contactthrough bathing or washing in Cr(VI)-contaminated water is another exposurepathway. Chromate (CrO

42–

) is a mineral containing the chromate ion, Cr

4

-

2

.An example of chromate is potassium chromate, K

2

CrO

4

. Chromates can enterthe bloodstream through breaks in the skin. CrO

42–

blood poisoning occurswhen CrO

42–

destroys red corpuscles. Inhalation is also an important humanexposure pathway; however, it is less likely to be associated with exposure toCr(VI)-contaminated soils and groundwater and more likely associated withindustrial processes such as welding, cutting, heating of Cr alloys, and work-related practices.

For dermal exposure, chromated copper arsenate (CCA) pressure-treatedlumber is ubiquitous in residential areas. This green-colored pressure-treated lumber is used for building residential decks, picnic tables, swingsets, and other play structures. Since January 1, 2004, the United StatesEnvironmental Protection Agency (USEPA) has banned the use of CCA-treated lumber for new residential use. The exception for residential usewill be permanent wood foundations. The USEPA is not banning the useof millions of CCA-treated wood products already in backyards and parks.CCA-treated wood will still be available for industrial and agricultural uses.With low pH rain or fruit juice (orange juice and lemon juice), the chromium


4


can be leached off the wood surface. For those concerned about this possi-bility, coating that play set or picnic table with an appropriate penetratingoil every two years will minimize the potential for leaching and adversedermal contact (Morrison, 2004).

1.2.2 Physical and Chemical Characteristics

Chromium is rarely found as a free metal in nature. A clean surface of Crmetal reacts strongly with the atmospheric oxygen (Kohl, 1967). However,the reaction stops quickly owing to the formation of a strong, dense, andnonporous Cr(III) oxide (Cr

2

O

3

) surface layer, which is estimated to be oneto three formula units thick. Chromium oxide passivates the metal from anyfurther reaction with oxygen. This is why Cr does not corrode and why itretains its metallic sheen.

Cr(III) oxide is among the ten most abundant compounds in the Earth’scrust. Cr, a solid at room temperature, generally reacts with halogen gasessuch as fluorine at high temperatures of 400

∞

C and pressures of 200 to 300atm. Cr also reacts with the other halogen gases such as chlorine, bromine,and iodine to form a variety of brightly colored compounds. Cr metal dis-solves in dilute hydrochloric acid and sulfuric acid. Cr does not appear toreact with nitric acid, most likely owing to the result of passivation by surfacechromium oxides. Many of the Cr compounds are toxic.

Chromium is one of the chief ingredients in mineral and metallic colors,being responsible for the color of some gem tones. Among the gem tonescolored by Cr are emeralds, ruby, alexandrite, chrome garnet, and somesapphires.

Chromium’s physical and chemical characteristics remained largely a lab-oratory curiosity for about hundred years from 1800 to 1900. Small amountswere used to harden steel alloys and its numerous compounds were usedin many different industries. A rapid increase in Cr use occurred between1915 and 1930, when Cr became a leading industrial metal, along with iron(Fe), copper (Cu), aluminum (Al), tin (Sn), lead (Pb), and nickel (Ni). Thereason for the long delay between its discovery date and industrial use wasits high resistance to heat and chemicals. Extracting Cr from its ores byformer methods was costly and difficult. Cr’s useful properties such asbrittleness, toughness, and resistance to corrosion made it difficult to workwith. Cr’s brittleness is probably caused by oxide impurities.

With a variety of characteristics and uses, Cr(VI) has entered subsurfacesoil, surface water, and groundwater. Sampling in California and other stateshas shown that Cr(VI) can exist as CrO

42–

and dichromate (Cr

2

O

72–

) ingroundwater. The oxidation number of Cr in groundwater is governed bypH and Eh. Cr(VI) can exist naturally in groundwater that has been unaffectedby local industrial activity. At least one hypothesis indicates that naturally occur-ring fluoride forms a soluble complex with chromium(III) [Cr(III)]-bearing

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minerals, after which the dissolved Cr(III) comes in contact with manga-nese(IV) dioxide (MnO

2

)-containing aquifer material, causing oxidation toCr(VI). Cr(VI) in groundwater can be reduced to Cr(III) at low pH and underreducing conditions.

Cr(VI) is rapidly reduced to Cr(III) when Fe(II) or manganese(II) [Mn(II)]occur in reduced groundwater. There have been several examples of thisimmobilization phenomenon, both in industrial situations in the U.S. and ata Cr chemicals plant in Poland. Recent work on isotopic ratios of Cr(VI) mayprove useful in evaluating the source or distance traveled and whetherCr(VI) is natural or anthropogenic in origin.

Cr(III) is a stable oxidation state and slowly reacts to form complexes.Because of its low kinetic energy potential, Cr(III) is not a strong oxidizerand it appears that the stomach’s acidity is enough to keep the Cr in theCr(III) state. Cr(VI) is not as stable as Cr(III) because it is a strong oxidizingagent, is fast reacting, and likely forms complexes. As with many toxicsubstances, exposure to metals by inhalation poses the greatest risk. How-ever, for Cr(VI) to be inhaled a person must be exposed to Cr fumes inindustrial processes such as cutting or welding Cr metals or to Cr(VI) inairborne dust or water droplets. Some scientists suggest that Cr(VI) can causecancer even when inhaled as an aerosol by showering in Cr(VI)-contaminatedwater. Disagreements still exist over the safe limits of Cr(VI) ingested asdrinking water. There remains a debate by experts about the absorptionpotential that Cr(VI) might have in the stomach’s acid environment. Theredoes not appear to be a perceptible odor or taste that Cr in any form impartsto drinking water.

1.2.3 Analytical Methods

The investigation of a groundwater resource impacted with Cr(VI) requiresanalysis of groundwater for both Cr(VI) and total Cr. Total Cr can be detectedby atomic absorption (AA) spectroscopy and other instrumental methods.Cr(III) and Cr(VI) can be detected by ion chromatography. Cr(VI) can alsobe detected by titration with a standard mixture of Na

2

S

2

O

4

and I

2

(AmericanPublic Health Association, 1989).

Analytical methods used include the USEPA method for drinking water,EPA 218.6. The equivalent method for wastewater (used for contaminatedgroundwater as well) is SW 7196A or SW 7199. Method SW 7199 is themore sensitive method, with a low detection limit of 0.02

m

g/l [or partsper billion (ppb)] of Cr(VI). This method uses ion chromatography toestimate Cr(VI). Total Cr is analyzed using inductively coupled plasma-mass spectroscopy (ICP-MS) using methods SW 6010 or SW 6020. Whileanalyzing for Cr, it is important to account for interferences from sulfide(S

2–

), vanadium (V), Mo, and organic carbon to ensure the accuracy ofanalytical data (Winter, 2004).


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1.2.4 Remediation Overview

For

in situ

remediation of soil and groundwater, a variety of geochemicalfixation or anaerobic biological treatment methods have been designedwhich make use of Cr’s ability to change the valence state of the oxidized,toxic, and highly mobile nature of Cr(VI) and convert it into the more stable,nontoxic, and immobile Cr(III). Cr(III) ultimately precipitates out as Cr(III)hydroxide [Cr(OH)

3

]. In these technologies, Cr is generally not removed fromthe environment, but becomes less toxic and immobile. Many treatment meth-ods use sulfur-based reductants; anaerobic biodegradation enhancementssuch as lactic acids, molasses, or other chemical reductants; or elemental iron[Fe(0)] technologies to create a reducing environment.

A variety of technologies are used in the extraction and treatment ofsurface water or groundwater (known as pump and treat). Once on thesurface, water containing Cr(VI) can be reduced by Fe(II) compoundsfollowed by several procedures including alkaline precipitation, ionexchange with regenerant treatment, or disposal. Electrochemical reduc-tion is another method used where Cr(VI) reduction is followed by alkalineprecipitation in which Fe(II) forms electrochemically, instead of beingadded as a purchased chemical, and acidic reduction of the Cr at pH < 3.0with sulfur dioxide, sodium sulfite, sodium bisulfite, or sodium metabisulfitecompletes the conversion to Cr(III). If reduction with a sulfite compoundis used, there is a greater potential for incomplete conversion of Cr(VI) toCr(III). Consequently, these reactions must be monitored carefully to ensurecomplete conversion to Cr(III), which ultimately precipitates out of solu-tion as Cr(OH)

3

.

1.2.5 Regulatory Levels

Chromium is listed as number 16 in the Agency for Toxic Substances andDisease Registry,

Priority List of

Hazardous Substances

(ATSDR, 1999). Cr(VI)has been found in at least 120 of the 1591 current or former USEPA NationalPriority List Superfund Sites (ATSDR, 2000). Neither the federal or state gov-ernments limits Cr(VI) levels in water, but both regulate total Cr. The USEPADrinking Water Maximum Contaminant Level (MCL) for total Cr is 100

m

g/l.California limits total Cr in drinking water to 50

m

g/l. Total Cr for contaminatedsite generic soil screening levels is 390 mg/kg for ingestion, 270 mg/kg forinhalation, and 2.0 mg/kg for migration to groundwater (USEPA, 1996).

The California Office of Environmental Health Hazard Assessment(OEHHA) initially recommended a public health goal (PHG) of 2.5

m

g/l fortotal Cr and 0.02

m

g/l for Cr(VI). The OEHHA has since rescinded the PHGand the state is working to establish a Cr(VI) MCL (California Departmentof Health Services, 2002). For airborne Cr(VI), the U.S. Department of Labor,Occupational Safety and Health Administration (OSHA), regulates worker’sexposure to Cr(VI) and other toxic compounds. OSHA exposure limits forCr compounds vary with potential work activities.

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1.2.6 Health

Although the elemental Cr and Cr(VI) can have adverse human healtheffects, normal mammalian metabolism requires minute amounts of Cr asan essential trace element. In addition to insulin, Cr is responsible for low-ering blood glucose levels and is used to control certain cases of diabetes.Cr has also been used to reduce blood cholesterol levels by lowering theconcentration of the unhealthy, low-density lipoproteins (LDL) in the blood.Cr is supplied in a variety of foods such as broccoli, Brewer’s yeast, liver,cheese, whole grain breads, and cereals. Some claims have been made thatCr aids in muscle development. Chromium picolinate, a highly soluble formof Cr, is used in dietary supplements for body builders.

1.3 Historical Perspective

The history of Cr began over 200 years ago. Four Siberian Beresof gold mineshad been worked for gold, copper, silver, and lead since 1752. In 1761, JohannGottlob Lehmann obtained samples of an orange-red mineral that he termed“Siberian red lead,” while visiting the Beresof mines located on the easternslopes of the Ural Mountains. Upon his return to St. Petersburg in 1766,analysis showed that the samples contained lead “mineralized with a sele-nitic spar and Fe particles.” This mineral turned out to be

crocoisite

or

crocoite

,a lead chromate (PbCrO

4

) (Figure 1.1). Lehmann described the mineral in a

FIGURE 1.1

Crocoite.

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letter to the well known naturalist Georges-Louis Leclerc comte de Buffon(1707 to 1788). Lehmann also observed that the mineral produced an emerald-green solution when dissolved in hydrochloric acid (HCl). Lehmann diedthe following year when a retort containing arsenic burst upon heating.

In 1770, Peter Simon Pallas also visited the Beresof mines and noted:

a very remarkable red lead mineral which has never been found in anyother mine. When pulverized, it gives a handsome yellow guhr whichcould be used in miniature painting … .

In spite of its rarity and difficulty in obtaining from the Beresof mines, theuse of Siberian red lead as a paint pigment was mined both as a collector’sitem and for the painting industry as a paint pigment. A bright yellow madefrom crocoite rapidly became a fashionable color for carriages of the nobilityin both France and England.

As a boy in Normandy, Louis-Nicholas Vauquelin (1763 to 1829) wasfascinated with chemistry and mineral specimens. His father was a farmlaborer who provided for his son’s education. Progressing through schoolrapidly, at the age of 14 he became a dishwasher and assistant in anapothecary.

He eventually went to Paris

with a letter of introduction andworked for several apothecary shops. One pharmacy was owned by hiscousin, Antoine-François comte de Fourcroy (1755 to 1809). Upon hearingof

Vauquelin’s interest in chemistry, Fourcroy hired his younger cousinas his assistant. Vauquelin continued to learn physics, chemistry, andphilosophy while assisting Fourcroy with chemistry and teaching Four-croy’s students. With the onset of the French Revolution, Vauquelin leftParis in 1793, served as a pharmacist in a military hospital, and then returnedto teach chemistry at the Central School of Public Works which laterbecame the École Polytechnique. In 1797, Vauquelin, a professor of chem-istry and assaying at the School of Mines in Paris, received samples ofthe crocoite ore.

Vauquelin noted the beauty and scarcity of this Cr ore (Figure 1.2). Henoted its value equal to that of gold, and in an attempt to address severalcontradictory chemical analyses, he set out to determine the correct chem-ical composition of crocoite. Vauquelin boiled one part of pulverized cro-coite with two parts of standard potash (K

2

CO

3

), which resulted in ayellow-colored solution. The solution formed a red precipitate with a mer-cury salt and a yellow precipitate with lead. Adding HCl turned the solu-tion green. In 1798, he was able to precipitate lead with HCl, dried thegreen solid, and then heated it for 0.5 h in a charcoal crucible with charcoaldust. The charcoal was used as a reducing agent. Upon cooling, he observeda mass of metallic needles with a mass of about half of that of the original.He thus discovered through subsequent analysis via heating Cr

2

O

3

withcharcoal that crocoite was combined with an oxide of an unknown metal.Noting the many colors produced by the compounds, Fourcroy and AbbéRené-Just Haüy (1743 to 1822) suggested the name chromium from the

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Greek word

crwma

(chroma) meaning color, reflecting the brilliant hues ofreds, yellows, and greens of its compounds. With further research, Vau-quelin analyzed an emerald from Peru and discovered that the lustrousgreen color was related to trace amounts of Cr. Vauquelin went on todetermine that the red color of rubies was also related to trace amounts ofCr. Vauquelin later became an inspector of mines and professor of assayingat the School of Mines (Figure 1.3).

In 1798, the German chemists Louwitz and Klaproth (the latter along withVauquelin and Fourcroy were the top chemists of their times) shortly there-after independently identified Cr in rocks located further north of the Beresofmines as a major component of the heavy black mineral later named chromite(FeCr

2

O

4

). In 1799, another German chemist Tassaert identified the samemineral from a small deposit in the Var region of southeastern France. Thismineral was to be identified as Cr-Fe spinel and now known as chromite.

FIGURE 1.2

Chromium ore.


10


Chromium is found in various minerals. However, FeCr

2

O

4

is the solesource of Cr used commercially. From 1797 until 1827, FeCr

2

O

4

was primarilyproduced for chemical use and was derived from the Ural Mountains ofRussia, the principal source for world supply at this time. About 1808, thesupply of Cr from the Ural Mountains greatly supported a growing paintindustry and resulted in a Cr chemical factory being set up in Manchester,England. Russia did not dominate the market for long, however.

With the discovery of FeCr

2

O

4

in Maryland in 1827, followed by sub-sequent discoveries in Pennsylvania and Virginia, the U.S. became theprincipal supplier for what would be considered a limited world demand(Morning et al., 1980). In 1808 or 1810, an English gardener namedHenfrey discovered what he thought was Cr ore in some black rocks onor near the summer estate of Jesse Tyson in the Bare Hills situatednorthwest of Baltimore, Maryland (Abbott, 1965). These rocks, called theTwin Sisters Dunite, were shown to Isaac Tyson who confirmed theiridentification, and subsequent analysis showed them to be rich in Cr(III)ore (Figure 1.4).

With financial assistance from his father, Isaac Tyson went into the businessof shipping Cr to England for the manufacturing of paint. Recognizing theassociation of FeCr

2

O

4

with serpentine deposits, Tyson discovered andacquired control of other Cr deposits. In 1827, Tyson tried to make Cr com-pounds but failed to establish a commercial process.

FIGURE 1.3

Vauquelin isolated chromium in 1978 by charcoal reduction of the oxide.



11

Isaac Tyson, Jr. (1792 to 1861) was considered one of the best “practicalchemists,” and his main success was in establishing the Cr chemicals indus-try in America (Gould, 1985). Along with Howard Sims, a member of thePhiladelphia Academy of Natural Sciences, Tyson established a plant inBaltimore, Maryland, which was incorporated in 1823 and by 1833 becameknown as the Baltimore Chemical Company. In 1827, Tyson was granted apatent for making copperas (iron sulfate). Besides exporting FeCr

2

O

4

, Tysonalso attempted to manufacture chrome yellow and other chrome colors.Encountering technical difficulties and a highly competitive market, Tysonturned to the increasing demand for the manufacturing of Cr

2

O

72–

.Between 1828 and 1850, the Baltimore Chemical Company supplied most

of the Cr ore consumed by the world, with the remainder being supplied fromserpentine deposits and platinum washings in the Urals. Tyson eventuallysucceeded in developing a commercially viable process for the manufacturingof Cr compounds in 1845. He applied to Yale for a technical expert, and WilliamPhipps Blake (1829 to 1910) was sent.

This was a historic step since Blake was a young chemistry student at thenewly established Sheffield Scientific School. Blake would be consideredthe first professional chemist to be employed in technology and industry in

FIGURE 1.4

Twin sisters dunite Cr(III) ore.

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the U.S. (Abbott, 1965). Blake eventually graduated from Sheffield ScientificSchool where he served as assistant professor at New York College. In 1853,Blake accepted the position of geologist and mineralogist for the Williamsonparty of the Pacific Railroad Survey. On that survey, Blake was to ascertaina practical railroad route from the Mississippi River to the Pacific Ocean,notably in southern California (Testa et al., 2002). Blake went on to a presti-gious career as a mineralogist, geologist, and mining engineer and eventuallyserved as the third territorial geologist of Arizona (Dill, 1991) (Figure 1.5).Blake also developed an early version of a decimal book classification system,which was later copied in large part by the American librarian Melville LouisKossuth Dewey (1851 to 1931).

When Tyson died in 1861, the Baltimore Chrome Works was left to twoof his sons; in 1902 it was acquired by the Kalion Chemical Company ofPhiladelphia and in 1906 acquired by the Henry Bower Chemical andManufacturing Company, which merged with Mutual Chemical Company.Later, Allied Chemical and Dye Company acquired Mutual Chemical Com-pany in 1954.

Tyson’s monopoly on the world’s FeCr

2

O

4

ore industry continued until1850, when exports began to decline. Reflecting newly discovered FeCr

2

O

4

FIGURE 1.5

Blake provided technical expertise regarding chromium. Blake became renowned as a miner-alogist, geologist, and mining engineer.

Au: The year in text does not match with the one in the list. Please check.



13

deposits near Bursa in Turkey in 1848, and with the depletion of thedeposits in Maryland around 1860, relatively large Turkish deposits were devel-oped in 1860. Since the 1860s, production of FeCr

2

O

4

ore has been primarilyin the Eastern Hemisphere from over 20 countries, with only a few withlarge reserves. FeCr

2

O

4

ore was discovered in California in 1873, and from1886 until 1893 California was the only state to produce this commodity;however, 2000 to 4000 metric tons of ore from Turkey was annuallyimported to the U.S., most of it being manufactured in Baltimore, Maryland(Glenn, 1893).

Mining of FeCr

2

O

4

ore commenced in India and Southern Africa around1906. Although paint pigments remained the main application, other applica-tions were being found. Kochin introduced the use of potassium dichromate(K

2

Cr

2

O

7

) as a mordant in the dyeing industry in 1820. Commercial use of Crsalts was introduced in leather tanning in 1884. First used as a refractory inFrance in 1879, its actual use started in Britain in 1886.

The first patent for the use of Cr in steel was issued in 1865. However,large-scale use of Cr had to wait until development of the aluminothermicmethod in the early 1900s and when the electric arc furnace could smeltFeCr

2

O

4

into the master alloy, ferrochromium. Although Cr provided bril-liance and shine, its true importance came with the development of stain-less steel, because it is Cr that makes the steel shiny and stainless. Stainlesssteels were developed from the initial work of Brearly and Sheffield in1913. Stainless steels containing 12% or more Cr, together with Fe and Ni,titanium (Ti), or Mn (commonly with 18% Cr, 8% Ni, 74% Fe) are exten-sively used in fabricating vessels for corrosive fluids and in a wide rangeof industrial and domestic appliances. New or less costly corrosion-resis-tant steels, such as type 304 or 3 CR 12, are finding increasing applicationin mining and construction.

In the 1920s, the process of electroplating was developed. Electroplatingutilizes an electric current to bond Cr atoms with atoms of the originalsurface, creating a bond between the metals so strong that it will remainintact even when subjected to extreme force. Electroplating soon thereafterbecame a standard requirement for engine and machinery parts subjectedto high loads, corrosion, and wear from friction. During the 1940s, platingproduction was important during the war effort with the production of hardchrome, a process that puts new life into many types of engine components.The first engine cylinders were restored using electroplated hard Cr duringthis period.

During the 1960s and 1970s, new federal engine emission standards gen-erated improvements to reduce the amount of lube oil consumed by dieselfuels. New finishing techniques were thus developed and applied to enginesfor the rail, gas transmission, marine, and stationary power industries. Pri-mary developments during the 1980s pertained to more specialized finishesto reduce oil consumption, resistance to abrasion, ring seating, and controlledpercent of load bearing surface and porosity.


14


1.4 Origin and Properties

Chromium metal is shiny and silvery in color, as well as hard and brittle. Ithas a high melting point (1857.0

∞

C) and boiling point (2672.0

∞

C). Oxidationstates from –2 to +6 are known, however, the most stable oxidation state is +3.The natural isotopes for Cr are

50

Cr (4.3%),

52

Cr (83.8%),

53

Cr (9.6%), and

54

Cr (2.4%).The abundance of Cr in the universe and on Earth varies considerably. Cr

is found in the universe at 15 parts per million (ppm) by mass, in the sun at20 ppm, and in carbonaceous meteorites at 3.1 parts per thousand by mass.Crustal rocks on the earth contain an average of 140 ppm of Cr, seawatercontains 0.6 ppb, stream water has 1 ppb, and humans have 30 ppb Cr by mass.

Chromite, also called iron(II)-Cr(III) oxide (FeCr

2

O

4

), is the principal oreof Cr. FeCr

2

O

4

is a weakly magnetic, Fe-black, brownish black to silverywhite metal. FeCr

2

O

4

is of igneous origin and forms in peridotite of plutonicrocks. FeCr

2

O

4

occurs exclusively in mafic and ultramafic rocks as a crystalaccumulated in the early stages of magmatic crystallization. FeCr

2

O

4

has alsobeen identified in serpentinites, which may be developed through hydro-thermal alteration of a peridotite. Uvarovite, the Cr garnet, is commonlyassociated in the field with FeCr

2

O4. The Moh’s hardness of FeCr2O4 is 5.5and the specific gravity is 4.3 to 5.0 and because of these physical character-istics of FeCr2O4, the metal is occasionally concentrated in placer deposits.

1.5 Production and Use of Chromium

The primary uses of Cr relate to the production of nonferrous alloys, orna-mental plating of metal, and creation of green-colored glass. Prior to thedevelopment of hard rigid plastics, automobile fenders and hubcaps werefrequently chrome-plated from the 1920s through the 1980s. The aircraftindustry used Cr for anodizing aluminum. Cr has been used as a catalystfor particular chemical reactions. Oxidizing agents such as K2Cr2O7, andother Cr2O7

2– compounds, are used in quantitative analysis.

1.5.1 Chromium Production Methods

Chromite is the most commercially useful of the Cr ores. Cr is produced intwo forms: ferrochrome and Cr metal produced by the reduction of Cr2O3.

Ferrochrome is produced by the reduction of FeCr2O4 with coke in anelectric arc furnace. Using ferrosilicon instead of coke as the reductant canproduce a low-carbon ferrochrome. This is a popular Fe-Cr alloy useddirectly as an additive to produce stainless and hard Cr-steels.


Overview of Chromium(VI) in the Environment: Background and History 15

The reduction of chrome ochre (Cr2O3) produces Cr metal. This is obtainedby oxidation of FeCr2O4 (by air) in molten alkali to yield sodium chromate(Na2CrO4), which is leached out with water, precipitated, and then reducedto the Cr(III) oxide using carbon. The oxide can be reduced by aluminum inthe aluminothermic process:

Cr2O3 + 2A1Æ 2Cr + A12O3

The chrome oxide can also be reduced using silicon:

2Cr2O3 + 3SiÆ 4Cr + 3SiO2

Chrome ochre (Cr2O3) can be dissolved in sulfuric acid (H2SO4) to yield thecommon electrolyte solution used in the production of decorative and protec-tive Cr plating. Sodium chromate (Na2CrO4) produced in the isolation of Cris itself the basis for the manufacture of all industrially produced Cr chemicals.

1.5.2 World Production

Chromite world mine production was estimated at a gross mass of 13million metric tons in 2002 (Papp, 2003). Cr ore is mined in over 20 coun-tries, but 81% of the production is concentrated in four countries: SouthAfrica accounts for 49% of the world total and 32% of the world total isaccounted for by Kazakhstan, India, and to a lesser extent, Turkey. FeCr2O4

ore is found in Brazil and Cuba, the only countries in FeCr2O4 productionin the Western Hemisphere. The largest U.S. Cr resource is in the StillwaterComplex in Montana. The U.S. base is estimated to be about 7 millionmetric tons (Papp, 2003).

1.5.3 Resources

Approximately 95% of the worldwide Cr resources are concentrated insouthern South Africa. According to the U.S. Geological Survey (USGS),worldwide resources exceed 12 billion metric tons of shipping-grade FeCr2O4,enough to meet demand for centuries (Papp, 2003). Remaining resources arelocated in the Independent States (former USSR), the Philippines, andselected other countries.

1.5.4 Consumption

In 1998, ferrochrome accounted for approximately 85% of FeCr2O4 consump-tion. Remaining FeCr2O4 consumption includes Cr chemicals at 8%, foundryapplications for 5%, and refractories for 2%. About 12% of the world Crproduction is consumed by the U.S., in the form of FeCr2O4 ore, Cr ferroalloys,Cr metal, and Cr chemicals (Papp, 2003).


16 Chromium(VI) Handbook

1.5.5 Economics

Prices for the ferrochrome industry are highly cyclic and have beenunstable in recent years. During the most recent price reductions forchrome at $0.35 to $0.50 per pound for high-carbon, charge grade ferro-chromium, integrated producers consolidated and expansions wereaccomplished through process improvements. The largest market for Crmetal is in superalloys for aircraft and industrial gas turbines. At thistime, production capacity for Cr metal exceeds demand and when pricesexceed the benchmark of US $5000 per metric ton, low-cost producersfrom the Independent States in central Asia and China increase produc-tion to meet Western market demands (Roskill Co., 2002). According tothe USGS, Cr contained in recycled stainless steel scrap accounted for37% of the apparent consumption in 2002 (Papp, 2003).

1.5.6 Chromium Substitutes

According to the USGS, FeCr2O4 ore has no substitute in the production offerrochromium, Cr chemicals, or FeCr2O4 refractories. Cr has no substitutesin stainless steels, which is the largest use for FeCr2O4, or in superalloys.

1.5.7 Uses

Chromium is a strategic metal of the twentieth century but it is also used indozens of industrial processes (Table 1.1) creating thousands of consumerproducts. Cr is used in the manufacturing of stainless steel, numerous alloys,

TABLE 1.1

Chromium Use

Antifouling pigments High-temperature batteriesAntiknock compounds Magnetic tapeAlloy manufacturing Metal finishingCatalysts Metal primersCeramics MordantsCorrosion inhibitors Phosphate coatingsDrilling muds PhotosensitizationElectroplating (decorative finishes, hard-wearing surfaces)

Pyrotechnics

Electronics RefractoriesEmulsion hardeners TanningFlexible printing Textile preservativesFungicides Textile printing and dyeingGas absorbers Wash primersHarden steel (armor plating, armor piercing projectiles)

Wood preservatives

Source: Modified after Stern, R. M., 1982, Biological and Environmental Aspects ofChromium, Langard, S., Ed., Elsevier, New York.

Au: Please check dele-tion of the bracket.



chrome plating, pigments, catalysts, dye, tanning, wood impregnation,refractory bricks, magnetic tapes, and more. Until the early 1900s, FeCr2O4

was used mainly in the manufacturing of chemicals. In the early 1900s,FeCr2O4 became widely used in the manufacturing of metallurgical andrefractory products, notably in stainless steels and basic refractory bricks(Morning et al., 1980). Refractory bricks and shapes formed of Cr are usefulowing to the high melting temperature of Cr, moderate thermal expansion,and the general stability of the Cr crystalline structure. Chrome steels haveno substitute when combined high-temperature rigidity and resistance totarnish and abrasion are required as in the case of roller bearings or in theaerospace and machine tool industries.

1.5.7.1 Paint

Chromium compounds are used in paint pigments. Chromates of barium(Ba), lead (Pb), and zinc (Zn) give us the pigments of lemon chrome, chromeyellow, chrome red, chrome orange, zinc yellow, and zinc green. Chromegreen is used in the making of green glass. Cr chemicals enhance the colorsof fabrics and are used to achieve the brightly colored Cr-based paints forautomobiles and buildings.

1.5.7.2 Stainless Steel

As an alloy, Cr has been referred to as the “guardian metal.” With as little as10% Cr, an alloy made with steel or Fe protects these materials from corrosion,yielding the stainless steel and rustless Fe which are common household items,such as stainless steel knives, ball bearings, watch cases, and chrome front andrear vehicle bumpers. The ball bearings of chrome steel have been subject tomore than 1,000,000 lb/in.2 or 6.895 ¥ 109 Pa (N/m2).

1.5.7.3 Furnace Linings

Chrome plating has replaced Ni-plating owing to Cr’s superior hardnessand resistance to chemical action. Heat-resistant Cr oxides are used for high-temperature applications, such as the bricks used in lining furnaces.

1.5.7.4 Tanning and Dying Processes

Chrome alum and chromic acid are used in the tanning and dyeing processes.

1.5.7.5 Photography

When K2Cr2O7 is mixed with water and the solution is dried and exposedto light, it becomes solid again. This property is applied to the manufactureof waterproof glues and in photography and photoengravings. Photochem-icals containing Cr2O7

2– compounds are toxic.



1.5.7.6 Specialized Steels

Characterized as bright, hard, and tarnish resistant, these attributes haveenhanced various ferroalloys. Most importantly, Cr-based steels supportmodern industry. The shift from paints and electroplating industries tochrome-hardened and corrosion-resistant steels occurred concurrent withevolving metallurgical technology with the introduction of more energy- andcost-effective processes that could utilize low-grade ores.

1.5.8 Chromium Processing and Alloys

About 13 million metric tons of Cr was produced annually in 2002 (Papp,2003). Historically, about 60 to 70% of Cr ores are used in alloys (Stern, 1982).These alloys include stainless steel, which contains Fe, Cr, and Ni in varyingproportions to fulfill final product requirements. Alloy steels contain about10 to 26% Cr. Cr alloys have a high electrical resistivity and are used forheating elements. Cr has also been used for its catalytic properties. Cr isbrittle at low temperatures. Substances such as Ni, Mn, and small amountsof Mo, tungsten (W), or palladium (Pd) are added to Cr to enhance variousphysical properties of the alloys. Cr can be highly polished and is resistantto attack by continued oxidation, leading to its use in alloys that are resistantto corrosion. Cr also increases hardness and resistance to mechanical wear(McGrath and Smith, 1990). Refractory brick manufacturing utilizes about15% of the Cr ore used for lining furnaces and kilns. About 15% is used inthe chemical industries. Cr(III), referred to as chrome alum, is used fortanning leather, pigments, and wood preservatives [sodium dichromate(Na2Cr2O7)]. About 4% is used as chromic acid and used for electroplatingor as an oxidant.

Chromium is used as a corrosion-resistant decorative plating agent. It isalso used as a pigment to give glass an emerald color. Both the green inemeralds and the red in rubies are credited to trace amounts of Cr oxides inthe crystal lattice structure. PbCrO4 as chrome yellow is used as a pigmentin yellow paint. K2Cr2O7, a form of Cr, has been used in the leather produc-tion business as a tanning agent. Chromates are compounds used in thetextile industry as a mordant. Products that contain Cr(VI) include paints,pigments, inks, fungicides, and wood preservatives. Since FeCr2O4 has a highmelting point, moderate thermal expansion, and a relatively stable crystal-line structure, it has been used in the refractory industry for forming bricksand shapes. Cr in superalloys is used to improve heat flow and increasesresistance to wear and corrosion. Cr hard-facing alloys increase hardnesswhile resisting wear. In a specialized medical use, since Cr is a hard transitionmetal, it is amalgamated with Ti to make replacement hips in the U.S. andGreat Britain.

Cr(VI) has been used in paint pigments, chrome plating, and other manu-facturing processes such as leather tanning. Cr(VI) is also used by the aircraftand other industries for anodizing aluminum. The refractory industry uses



FeCr2O4 for forming bricks and shapes. Because FeCr2O4 has a high meltingpoint, moderate thermal expansion, and stable crystalline structure, it is usedin the refractory industries.

1.5.9 Chromium Isolation

Starting with commercially available FeCr2O4, if this ore is oxidized by air inmolten alkali, sodium chromate (Na2CrO4) is created wherein the Cr has beenoxidized and is in the hexavalent state, Cr(VI). Reducing the Cr(VI) in sodiumchromate produces Cr(III) oxide or Cr2O3 wherein the Cr is in the Cr(III) form.The main Cr(III) species include Cr3+ and Cr2O3. Cr(III) exists in a moderatelyoxidizing or reducing environment. Cr(VI) species include CrO4

2– and Cr2O72–.

Cr(VI) exists in an alkaline, strongly oxidizing environment. The reduction ofCr(III) oxide takes place by the extraction of water, precipitation, and thereduction of the Cr with carbon. The oxide is continued to be reduced withsilicon or aluminum to form Cr metal for the industrial processes.

There are other ways of isolating and producing Cr metal; an example iselectroplating, which requires the dissolution of Cr(III) oxide (Cr2O3) insulfur acid to produce an electrolyte that is used for Cr electroplating. Con-sequently, plating shops are typical sources of Cr(VI) leaks, spills, and acidcontamination in the soil and shallow groundwater.

Chromium has been in the industrial environment in large supplies forwell over a century. Based on the numerous and varied uses and industrialsettings, Cr’s potential for contaminating soil and groundwater resourcesand for worker exposure is large.

1.6 Potential Adverse Environmental Effects from Use and Disposal of Chromium

Because of its toxic nature, Cr creates numerous environmental problems inwaste products, mine wastes, and postmanufacturing slag piles. Cr wasteproducts are inevitably formed during the numerous industrial processesusing Cr. The electroplating and manufacturing industries use high volumesof Cr in their processes. Waste products from these processes normallycontain Cr(VI) compounds, such as chromic acid and other oxidizing Cr(VI)cleaners. Cr(VI) comprises most of the wastes; a smaller amount of reducedCr(III), and Cr as a solid metal are also produced. Management of wasteproducts from industrial processes is always problematic and is associatedwith poor housekeeping. Therefore, Cr(VI) is commonly spilled or leakedinto the environment as a contaminant, frequently with other associatedwastes, ultimately moving into the soil and groundwater.

The characteristics of Cr(VI) in the subsurface make assessment andremediation of Cr(VI)-impacted sites challenging. Cr(VI)-impacted sites are

Au: Replace-ment hips for the medical industry perhaps? Pls. verify.



difficult to delineate vertically and laterally, and may be complicated bynaturally occurring Cr(VI) that has not been characterized. Competentenvironmental professionals should be employed to assess and remediateCr(VI)-impacted soil and groundwater resources. The environmental con-sulting industry in conjunction with the regulatory agencies, including theUSEPA, must continue to establish reliable, accurate analytical methodsfor Cr(VI). The environmental industry must develop and optimize effec-tive ex situ treatment systems for Cr(VI) in groundwater, especially in areaswhere trace levels exist. Environmental regulatory agencies must evaluatehealth risks posed by low Cr(VI) concentrations and establish backgroundlevels for groundwater (accompanied by health effect studies) beforeimplementing new regulations.

Bibliography

Abbott, C.M., 1965, Isaac Tyson Jr. Pioneer Mining Engineer and Metallurgist, Mary-land Historical Magazine, March, pp. 15–25.

Agency for Toxic Substances and Disease Registry (ATSDR), 1999a, Priority List ofHazardous Substances, Division of Toxicology, U.S. Department of Health andHuman Services.

Agency for Toxic Substances and Disease Registry (ATSDR), 1999b, ToxFAQs, Divisionof Toxicology, U.S. Department of Health and Human Services.

Agency for Toxic Substances and Disease Registry (ATSDR), 2000, Toxicological Profilefor Chromium, Division of Toxicology, U.S. Department of Health and HumanServices.

American Public Health Association, 1989, Standard Methods for the Examination ofWater and Wastewater, 17th ed., Washington, DC.

California Department of Health Services, 2002, http://www.dhs.ca.gov/ps/ddwem/chemicals/Chromium6/Cr+6index.htm_

Dill, Jr., D.B., 1991, William Phipps Blake-Yankee Gentleman and Pioneer Geologistof the Far West, J. Ariz. Hist., Winter, 385–412.

Glenn, W., 1893, Chrome: In Maryland, its Resources, Industries and Institutions, pre-pared for the Board of World’s Fair, Chicago, IL, Mannigers, Baltimore, MD,pp. 120–122.

Gould, R.F., 1985, Eminent Chemists of Maryland, Maryland Historical Magazine, Vol.80, No. 1, Spring, pp. 19–21.

Hartung, W.H., 1939, Early Chemistry in Maryland, Baltimore, Vol. 32, No. 6, pp. 42–44.Jacobs, J., Foreman, T., Mavis, J., and Gopalan, R., Groundwater, Hexavalent Chromium

White Paper, Groundwater Resources Association of California (in press).Kohl, W.H., 1967, Handbook of Materials and Techniques for Vacuum Devices, Reinhold

Publishing, New York, p. 161.McGrath and Smith, 1990.Morning, J.L., Matthews, N.A., and Peterson, E.C., 1980, Chromium: In Mineral Facts

and Problems, 1980 ed., U.S. Bureau of Mines, Bulletin 671, pp. 167–182.Morrison, D.S., 2004, Pressure Treated Wood: The Next Generation, Fine Homebuilding,

The Tauton Press, Newtown, CT, No. 160, pp. 82–85.

Au: Please provide volume no.

Au: Please provide full title.

Au: Please provide volume no.

Au: Should “Maryland Historical Magazine” be added in the ref-erence? Please check.

Au: Please provide published information if available.

Au: Please provide complete informa-tion for this reference.



Papp, J.F., 2003, U.S. Geological Survey (USGS) Minerals Commodity Summaries,http://minerals.er.U.S.G.S.gov/minerals/pubs/commodity/chromium/Roskill Company, 2002, Chromium World Market Overview, Company Brochure,www.roskill.co.uk/chrome.html.

Stern, R.M., 1982, Biological and Environmental Aspects of Chromium, Langard, S., Ed.,Elsevier, New York.

Stowe, C.W., 1987, Evolution of Chromium Ore Fields, Van Nostrand Reinhold, NewYork, 340 p.

Testa, S.M., Whitney, J.D., and Blake, W.P., 2001, Conflicts in Relation to CaliforniaGeology and the Fate of the First California Geological Survey, Earth Sci. Hist.,21, 1, 46–76.

U.S. Environmental Protection Agency (USEPA), 1996, Soil Screening Guidance, Tech-nical Background Document, OSWER, EPA/540/R-95/128.

Winter, M., 2004, Web Elements: History of Chromium, http://www.webelements.com/webelements/scholar/elements/chromium/history.html.

See http://www.amm.com/ref/chrom.HTM.See http://www.acornusers.org/education/HNC-Web/Theory.html.See http://www.ccaresearch.ort/tag12/present/CR.



Documents

Overview of Chromium(VI) in the Environment: Background and