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By W. D. Johnston, T. P. Thayer

THE minerals that collectively are known as chromite form an isomorphous series of the general formula (Mg,Fe) 0. (Cr,Al,Fe) 203. So wide is the range in chemical composition in this group that chrome ore consisting entirely of the mineral chromite may range from less than 30 pct to more than 60 pct Cr203. The most comprehensive published data on the chemical com- position of chromite are by Stevens,62 who made complete analyses of 52 samples of chromite concentrate from many localities in North, Cen- [ ] tral, and South America. These samples were mechanically purified to remove associated silicates and might be regarded as the cleanest chromite that could be obtained by any mechanical milling process. Fig 1 shows the predominant zone of isomorphism, within the triangular prism of composition defined by the mineralogical end members of the series, wherein his analyzed samples fell.

Jan 1, 1949

By John F. Papp

Chromite is used both as a metallic and nonmetallic mineral. Chromite ore is used as the source of chromium by the metals industry and is used, without chemical alteration, in the refractory and foundry industries. Chromite ore is also the source of chromium for the chemical industry. On average worldwide far more chromite ore is used by the metallurgical industry than by any other industry. Thus, although the primary purpose of this chapter is to describe the nonmetallic uses of chromite, the metallurgical uses must also be discussed in order to provide a complete description of this commodity.

Jan 1, 1994

By Harry M. Mikami, Harold A. Heiligman

The term chromite is often used to cover all chrome ores and concentrates which are the designations actually employed by most industrial users and producers. Chromite is, of course, the predominant mineral in chrome ores which are aggregates of chromite and gangue minerals, most commonly magnesian silicates. Most chrome ores now used are petrographically chromitites which is a rock, rather than an individual mineral term. The title of this chapter, following past usage, is meant in the broad sense. Chromite is the only primary commercial source of chromium. This book is intended to deal only with nonmetallic minerals and rocks. Chromite uses are both metallic (ferroalloys) and nonmetallic (refractories and chemicals), but any discussion of mineralogy, geology, and mining is common for all types. A number of the major commercial ores are interchangeable, and their uses are determined by economic considerations. Mineralogy COMPOSITION [Chromite is a term embracing a wide range of chromium-bearing spinel*-group minerals the compositions of which can be expressed as (Mg,Fe2+)0.(Cr,AI,Fe3+ )203.t This can be further generalized to R2+O.R23+03 and the molecular RO: R,03 ratio is generally close to one. The exact composition may be arbitrarily expressed as a solid solution of six end-members, MgAI2O4, MgCr2O4, MgFe2O4 FeCr2O4, FeA12O4, and Fe2+.Fe23+04 with the proportions of each stated or plotted in the six-cornered prism of Johnston and Stevens61 or this scheme may be simplified to comprise only three endmembers making up a composition triangle, Fig 1. [ ] FIG 1-Triaxial composition diagram showing molecular compositions of chromites listed in Table 1. The RO.Fe2O3 corner includes Ti02 norms listed in the table. Note that the high-alumina chromites (1, 2, 3, 9), form a cluster well apart from the high-Cr2O3 chromites. There is a tendency for high-iron chromites to be higher in Fe2O3 + TiO2 but it is not a consistent or systematic relationship. The MgO/RO ratio must also be known to characterize the chromite chemically. Simplest and most convenient method is Thayer's' in which a chromite such as (Mg.65Fe.352+)O.(Cr.40Al.50Fe.103+)203 would be written as (Mge,) Cr eAlo. The molecular pro- portions of ferrous and ferric oxides can be seen at a glance as the divalent and trivalent oxides]

Jan 1, 1960

By Harry M. Mikami

Chromite is the only ore mineral of metallic chromium and chromium compounds and chemicals. Because of this fact, chromite and chrome ore are used synonymously in trade literature. In commercial market quotations, chrome ore is the term commonly used. Chromite per se, because of properties imparted by its chromium content, is used in refractories and in special purpose molding sands for metal casting. There are many other minerals containing some, generally minor, amounts of chromium, but none are commercial sources of the element (Thayer, 1956). Chromium and chromite have many diverse uses that, directly and indirectly, critically affect vast segments of our modern industrial system. Most important are probably the metallurgical applications wherein chromium is a component of heat-, abrasion-, corrosion-and oxidation-resistant and high-strength alloys of many types. Stainless steels are the largest volume category of chrome-bearing alloys. Chromium chemicals are used in leather tanning, in pigments, dyes and mordants, printing, chemical process industries, photography, pharmaceuticals, metal plating, pure chromium metal production, and for many other purposes. Chromite is a necessary constituent in basic refractories indispensable for the production of steel, copper, cement, and glass. Under present conditions, the US and North America, with the possible exception of Cuba, have no commercial ore reserves. There are chromite deposits, as will be described, but they would be used only under highly abnormal conditions if all outside sources were cut off for an extended period. All chromite used in the US is imported from the eastern hemisphere in which are contained the principal world reserves. The main suppliers in 1980 were the Republic of South Africa (43%), the USSR (21% ), the Philippines (12%), Albania (11 %), Turkey (8%), and others (5%). The strategic nature of chromite is obvious. End Uses-Grades and Specifications As noted before, the three principal uses for chromite are metallurgical, refractories, and chemical with a fourth minor use as foundry molding sand. For metallurgical applications chrome ore is first reduced in electric carbon arc furnaces to various types of ferrochromium alloys. There are high, medium, and low carbon ferrochromiums with carbon ranging from 0.01 up to 10%. Chromium itself ranges from 50 to 73 %. Ferrosilicon chromium and ferrochromium-silicon grades have chromium from 33 to 67% and silicon from 3 to about 48%. Since iron is reduced with chromium, the Cr:Fe ratio of the ore will determine the ultimate grade of the ferrochromium whereas carbon and silicon can be controlled during processing. MgO, A12O3, CaO, and excess SiO2, are removed in slag. A small amount of pure chromium metal is prepared by alumino-thermic and electrolytic processes from essentially iron-free chrome components that have been made via the chemical route. The higher grades of ferrochromium with chromium in the 66 to 73% range can only be made from ores with not only high chromium content, but low iron, i.e., high Cr:Fe ratio. These ores, conventionally termed metallurgical grade, have Cr2O3 contents of 45 to 56% with Cr: Fe ratios of 2.5 to 4.3. A standard composition is generally 48% Cr2O3 and 3:1 Cr:Fe ratio. Very high grade ores are often blended with lower grades even with the high iron chemical grade. For some ferrochromiums, additions of high alumina refractory grade are used as slag conditioners to facilitate smelting while still contributing chromium values. A lower grade ferrochromium, the high carbon charge chrome, has become the predominant grade in use today for making chromium-bearing steel alloys. This

Jan 1, 1983

By Ferid Kromer

This paper is the first in a series which will describe geology, mining methods, and production costs of some of Turkey's more important minerals. In this paper the economically significant minerals-chromite, meerschaum, and magnesite-of the Tastepe district are described. The cost data presented are believed by the author to be the first made public on Turkish chromite mining.

Jan 1, 1950

By Ferid Kromer

This paper is the first in a series which will describe geology, mining methods, and production costs of some, of Turkey's more important minerals. In this paper the economically significant minerals-chromite, meerschaum, and magnesite-of the Tagtepe district are described. The cost data presented are believed by the author to be the first made public on Turkish chromite mining.

Jan 1, 1950

Beach sands on the Morobe coast of New Guinea contain significant amounts of chromite. This chromite, together with the more abundant associated minerals such as olivine, enstatite, tremolite, antigorite and feldspar has been de- rived from rocks of the Papuan Ultramafic Belt and transported to the beaches by three rivers, the Paiawa, the Saia and the Sesimbai. Of the hundreds of samples taken, 26 have been analysed mineralogically and chemically in some detail. On this basis, five groups of samples, four on- shore and one offshore, representing character- istic mineral assemblages, have been recognized. The chromite grains themselves have been exam- ined to determine variations in amount and in the Cr/Fe ratio, since this is of economic importance. Much of the chromite fails to reach a high Cr/Fe ratio as a result of magnetite rims around chromite grains. The precious metal content of the sands is negligible.

Jan 1, 1973

By S A. Prevec

"An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation. Traditional models employed to genetically link associated chromite and platinum-group elements have favoured crustal contamination as the primary process for inducing sulfide and oxide saturation. The association of chromite ores with crustal contamination is well established in the literature. However, in the 1970s (cf Irvine, 1973, 1975), Irvine demonstrated that crustal contamination was in fact problematic as a tool for inducing chromite precipitation in mafic to ultramafic magmas. His results are re-examined here, along with some attempts to reconcile them with the effects of adding Fe to the models. It is concluded that crustal contamination is indeed problematic based on phase relationships alone. However, the role of fluids as a compensating agent is evaluated, which may explain why crustal contamination may indeed facilitate oxide and sulfide precipitation.CITATION:Prevec, S A, 2015. Chromite and platinum-group elements coprecipitation by crustal contamination or magma mixing revisited – genetic and exploration implications, in Proceedings PACRIM 2015 Congress, pp 311–316 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Mar 18, 2015

By C. H. Stockwell

THE Eastern Townships of Quebec have been the chief Canadian source of chromite. Production, however, has never been large and, except for a period of steady but small output between 1894 and 1909, mining has been active only in war time. The known deposits are too small or too low grade to compete with overseas sources in normal times. During the last war, shipping difficulties and a greatly increased demand in the United States resulted in high prices and a ready market for low-.grade material. The Quebec chromite industry flourished and played an important part in relieving the wartime shortage. Shipments in 1918 .amounted to 15,600 tons of crude ore and 6,400 tons of concentrates. At the outbreak of the present war it was natural to turn again to the Quebec field as a possible source of this strategic mineral. Some of the old properties have since been opened by private and government money and some new deposits have been found. Total mill capacity is 750 tons per day, as compared with 200 to 300 tons in 1918. During 1940, 1941, and 1942, about 85 chromite deposits were examined by the Geological Survey in a belt 100 miles long and up to 7 miles wide. A part of this belt, about 35 miles long, in which the geological features ?were not well known, was mapped on a scale of 1/2; mile to an inch.? Small ..areas around some of the deposits were mapped in detail, on scales of 20 to 200 feet to an inch. Some geophysical work was done but did not result in the discovery of ore. Prospecting by stripping and trenching was then undertaken and chromite ore was uncovered at several localities. The above work was done by the writer and by J. W. Ambrose, who has kindly contributed his results for incorporation in this paper. Y. O. Fortier actd as assistant in the geological work and, in 1942, was in charge of a sub-party engaged in geological mapping. The author is indebted to H. C. Cooke and J. W. Ambrose for reading the original manuscript and for offering many helpful suggestions for its improvement.

Jan 1, 1944

By V. Distler, E. F. Stumpfl

Paper presented at the IAGOD international symposium on mineralisation related to mafic and ultramafic rocks held in Orleans, France, 1-3 September 1993. The massif contains large chromite bodies of "Alpine-type", ophiolitic affinity. Orebodies reach thicknesses of 150 m and sizes of more than 150 000 000 t chromite ore with average grades of 55-60 wt% Cr2O3. Chromites in the Main ore field are low-Al, high-Cr spinels which exhibit some variation in their Mg-Fe distribution. This differs markedly from high-Al spinels in peridotite host rocks and in narrow chromite pods which occur in the western and northern parts of the massif. Chromites carry silicate inclusions, often hydrous silicates such as amphibole. Chromites in massive chromitites contain micron size inclusions of platinum group minerals (PGM). Composite grains containing two PGM and, occasionally, a hydrous silicate are common. Os-Ir alloys rimmed by PGM sulpharsenides occur in narrow serpentine veinlets that cut chromite and are evidence for the reconcentration of PGE concomitant with introduction of As, probably during serpentinisation. Whole-rock PGE contents are highest in massive chromitites of Diamond Pearl mine (totals of 500 ppb). Chondrite-normalised PGE patterns of chromitites show negative slopes which are typical for ophiolitic, podiform chromitites in mantle sequences. The PGE patterns of host rocks are flat and rather depleted compared with those of chondrites and chromitites. Petrological data from unaltered host peridotites suggest a high temperature overprint leading to sub-solidus re-equilibration of olivine and spinel and to the growth of pargasitic and edenitic amphiboles

Jun 16, 1905

By Lawson F

Chrome chemicals are commercially produced by the alkali roasting of the chrome-bearing ore chromite with sodium carbonate. In order to ascertain the influence on the extent of reaction of the replacement of Mg(II) for Fe(II) in the chromite spinel structure and the presence of acidic oxides in the gangue material, a series of roasting experiments was conducted using chromite materials from a number of different locations. The roast feeds and products were chemically analysed and the major compounds identified using X-ray diffraction and scanning electron microscope techniques.Mg(II) replacement for Fe(II) in the chromite structure does not appear to restrict the amount of "available" chromium for reaction.Under the test conditions, namely an atmosphere of pure oxygen, finely ground chrome-bearing material, a roast temperature of 950°C and the stoichiometric amount of sodium carbonate to react with the chromite, the yield of water-soluble sodium chromate was able to be expressed as %yield = 104.5 -1.58 × %AI2O3 - 2.23 × %SiO2 for chromite samples containing alumina in the range 7.8 to 27.8 per cent and silica in the range 2.9 to 7.4 per cent.

Jan 1, 1984

By Baker G

Chromite was recorded among the rare minerals in the natural beach sand concentrates on the coast of Northern New South Wales by Whitworth(l) in 1931, and the commercial production of zircon and rutile from these beach sands has yielded concentrates of ilmenite with small amounts of chromium. The chromite is a detrimental impurity in the utilisation of the ilmenite, and the difficulties that attend the separation of the small amount of chromite from the ilmunite have raised suggestions from time to time that chromite occurs with ilmenite in composite grains. The absence of such composite grains and the nature of the chromite grains has been indicated by the following mineragraphic examination of magnetic concentrates containing chromite which were prepared by the C.S.I.R. Ore Dressing Laboratory, Melbourne University, from ilmenite concentrates from beach sands at Norrie's Head, County Rous, New South Wales and Stradbroke Island, Queensland.The magnetic concentrates from each locality are divided into five fractions, and the No. 1 concentrate is the most highly magnetic and the tailing the least magnetic. Chromium assays as determined by the Ore Dressing Laboratory are as follows:-

Jan 1, 1948

By N. Kacira

"Canada's largest known chromite deposit occurs in a layered intrusion in the Bird River area of Manitoba. However, numerically most of the chromite occurrences are in the Appalachians. Few, apparently minor, occurrences are also known in the Cordillera.In the Appalachians, chromite occurs as lenses and pods in dunite; they are of ""podiform"" type. The individual concentrations vary in size from a few pounds to tens of thousands of tons. Locally, chromite concentrations form discontinuous zones extending several hundred feet along strike and presumably down dip, therefore resembling boudinaged layers. Chromite layering and lineation are commonly concordant to those of the host rocks.The Appalachian chromite occurrences are thought to have been formed by fractional crystallization and perhaps also by liquid immiscibility. Their present shape and distribution are largely the result of deformation mostly prior to complete solidification of their host rocks. Therefore, the attitude of layering, foliation, lineation and other features related to deformation provide valuable guides in predicting the probable distribution of chromite, and hence are helpful in exploration.Chromites fulfilling the requirements for metallurgical, refractory and chemical grades occur in the Appalachians. Although the Appalachian deposits are similar in size and grade to some of the chromite deposits being mined elsewhere, they are unlikely to be economic, at present, in the higher wage Canadian environment. However, in case of shortages in chromite ore supply which may result, among other reasons, from increasing tendency to further processing in the producing countries, the Appalachian occurrences may become sources of ore. Such eventual shortages combined with relative abundance of electricity in Canada and recent innovations in oxide ore reduction technology may hasten the time when ferrochrome manufacture based on local chromite sources becomes economically viable."

Jan 1, 1982

By M I. Pownceby, W J. Bruckard

A South African chromite sample was subjected to characterisation and physical beneficiation testwork in order to assess its suitability to produce an upgraded chromite product with a silica level of <1 per cent SiO2 and a chromite level of >46 per cent Cr2O3. Chemical analysis by XRF indicated that the bulk material had a Cr2O3 content of 40.5 per cent w/w and a SiO2 content of 7.5 per cent w/w. Combined XRF analysis with sizing data showed that the majority (~70 per cent) of the siliceous material was present in the +600 ¦m fraction while ~70 per cent of the Cr2O3 was in the -600 ¦m fraction. Qualitative mineral phase analysis by XRD indicated that the sample mineralogy was dominated by ferrian-magnesiochromite spinel ([Fe,Mg]Cr2O4) and aluminium-chromite spinel (Fe[Al,Cr]2O4), with enstatite (Mg2Si2O6), haematite (Fe2O3) and anorthite (CaAl2Si2O8) as minor phases. SEM and EMP characterisation showed that the silica was mainly present in discrete enstatite grains but lesser amounts were also present as the high silica phases plagioclase and enstatite on the edge of grains. Wet gravity separation performed on sized fractions (-600+106 ¦m size range) from the -2.0 mm (primary) ore as well as the ore that had been crushed to pass 0.6 mm (secondary) showed that stage crushing of the -2 mm +600 ¦m fraction followed by wet gravity separation upgraded the Cr2O3 grade at 70 per cent Cr2O3 recovery from ~44 per cent Cr2O3 in the primary material to 46 per cent Cr2O3 (the target grade specification) in the secondary sample. It also showed that the stage crushing of this +600 ¦m fraction at a cut-off level of one per cent SiO2 increased the cumulative Cr2O3 recovery from ~50 per cent in the primary material to ~63 per cent in the secondary sample in the same size range of -600+106 ¦m. The extent to which additional crushing could lead to improved chromite recoveries at the required chromite and silica grade target specifications was not determined. This experience demonstrates that prior to processing test work being conducted, a thorough understanding of the chemistry and mineralogy of the test sample promotes efficient and targeted processing research.

Jan 1, 2008

By A. Acar, E. T. Tuzcu, Y. O. Vural

"In order to sustain the operations in chromite processing plants, due to concentrate selling cost, plants are in need of optimization in terms of capacity and recovery increase. In this study, DAMA Engineering carried out a methodological study for the purpose after a detailed sampling campaign in a plant which is situated in one the main chromite zones in Turkey; 1 The current status of the plant was investigated quantitatively with the bottlenecks, Plant overall efficiency in terms of recovery, Efficiencies of the particular equipment (mill, screen, gravity circuit), 2 A new circuit was proposed with the available equipment, 3 The new circuit that is product of modeling and experimental effort, was evaluated quantitatively as if it is a running plant, After 4-5 months continuous effort, the capacity of the plant was almost doubled (37 tph to 70 tph) and the plant overall recovery was increased from 48% to 63% by grinding adjustments and additional shaking tables theoretically. It was shown that the plant may move into profit with the minimum amount investment using readily available system. INTRODUCTION TO THE CURRENT PLANT The objective of the study is to increase the capacity and recovery of the chromite plant owned by Kurmel Group, Akmetal Inc. The complete study is given elsewhere (DAMA, 2016). The plant is situated in one of the main chromite zones in Turkey; Aladag. The current capacity of the plant is around 35 tph and the overall recovery declared by plant engineer is around 47 %. The chromite plant mainly has 3 units; crushing, grinding and gravitational circuits. The crushing circuit has 3 stages; a jaw crusher, a secondary cone crusher and a tertiary cone crusher operating in closed circuit with a vibrating screen with the aperture size of 15mm. In grinding circuit, a rod mill (2.44 6m x 3.6) and a ball mill (2.13 x 2.3m) are used for primary and secondary grinding, respectively. Derrick screens are used for the size separation. Additionally, for the size classification of the system, hydrosizers are used and each size fraction is sent to the shaking table sets. The middling product of the tables is subjected to re-grinding with a ball mill with the dimensions of 2.1 x 2.9 m. The capacity and the recovery are affected by several bottle necks; hydrosizers’ pure classification, primary/secondary mill power vs capacity problems, re-grinding product’s high slime content and so on. These combined factors made the plant to run in low recovery and capacity. Hence, DAMA was asked to make a study to investigate current status of the plant and propose a new solution to increase capacity and recovery of the plant. The conceptual flowsheet of the circuit is given in Figure 1 below."

Jan 1, 2017

By Charles J. Johnson

The United States is totally dependent on imports for all primary chromite and most ferrochrome supplies. Although the United States imports chromite and ferrochrome from a number of countries, the long-term future of chromite supplies appears to lie in southern Africa (Republic of South Africa and Zimbabwe) where 88 percent of known world reserves exist. Floreover, low mining costs and the availability of low-cost electricity for ferrochrome production gives South Africa a comparative advantage over most other chromite and ferrochrome-producing nations. A well-known problem faced by the United States is that when viewed from a longer-term perspective, the major sources of supply of metallurgical grade chromite and ferrochrome may be subject to disruption. The three countries that have caused the greatest concern have been the Republic of South Africa, the Soviet Union, and Zimbabwe. South Africa presents a particularly difficult problem because it may be subject to internal political unrest and/or U. N, economic sanctions. South Africa has increased its share of world chromium production from about 30 percent in 1968 to 62 percent in 1978.1

Jan 1, 1982

By N. McEwan

Keywords: refractories, chromite, Marico This paper examines the role of refractory-grade chromite in refractories. The chromite deposit at Verref?s Marico Chrome mine is described. The refractory properties of chromite and their role in basic refractories are described. The properties and metallurgical applications of chrome-containing refractories are described and finally environmental issues associated with chrome-containing refractories are discussed.

Jan 1, 2011

By David Swan

No mystery shrouds the discovery of chromium. The indefatigable French chemist Vauquelin, in reporting his discovery of this chemical element to 1'Institut National in 1798, concluded his discourse with the statement: "I place before the eyes of the Institute a small quantity of chromium and several of its most re- markable combinations." Working with the so-called "red lead of Siberia, Vauquelin not only prepared numerous chemical compounds of the new metal, but he reduced the oxide to the metallic state. These chemical compounds possessed a variety of remarkably distinctive colors; so, acceding to suggestion, Vauquelin named the new element chrome (chromium), a derivative of the Greek word chroma, meaning color. Siberian "red lead" (crocoite) was not plentiful; however, it was not long before Vauquelin's prediction was realized that the chemical compounds of chromium would become useful in the arts when sources of chromium became more readily available. Although chrome-iron ore (chromite) became obtainable in France, the United States and elsewhere during the early part of the nineteenth century, it is interesting to note that from 1828 to about 1860, Maryland, Pennsylvania, and others of the eastern United States furnished almost the entire chrome-ore requirements of the world. Several countries each in turn have since dominated for certain periods the supply of chromite. In recent years, the largest tonnages have come

Jan 1, 1953

By N. S. Dalal, X. Shi

"Electron spin resonance measurements provide evidence for the formation of long-lived Cr(V) intermediates in the reduction of Cr(Vl) by glutathione redtuctase in the presence of NADPH and for the hydroxyl radical formation during the glutathione reductase catalyzed reduction of Cr(Vl). Hydrogen peroxide suppresses Cr(V) and enhances the formation of hydroxyl radicals. Thus Cr(V) intermediates catalyze generation of hydroxyl radicals from hydrogen peroxide through a Fenton-like reaction. Thus the mechanism of Cr(VI) toxicity might involve the interaction between macromolecules and the hydroxyl radicals.C(Vl) compounds have been found to exert serious toxic and carcinogenic effects on humans and animals (1-3). In contrast, most Cr(III) compounds are relatively nontoxic, noncarcinogenic, and nonmutagenic (1,4). Cr(VI) and Cr(III) oxidation states are different in their metabolic pathways: Cr(VI) , ions are rapidly transported across cellular membrane (1,4,5), while Cr[III) moieties do not easily penetrate cells and are not oxidized by cellular constituents (!). Since it is known that the reduction of Cr(VI) ion is required for its reaction with DNA (1), the molecular mechanisms for the intracellular Cr(Vl) reduction has been the focus of current studies but the details are still not understood.Earlier studies on the mechanism of Cr(Vl) reduction include those on the reduction of Cr(VIJ by glutathione (GSH) .0,6-8), ascorbic acid (9), glucose (10), lactose (IO), galacturonic acid (11), microsome (12), and mitochondrial electron transport chain complexes (13). These studies have shown that the Cr(VI) reduction involves the formation of Cr(V)-containing species which are often considered to be the toxic form of chromium. Thus far, however, no information is· available on the subsequent fate of those biologically formed Cr(V) species, in particular employing well defined biochemical systems. In this context, we report here our investigations of the reduction of Cr(VI) by glutathione reductase (GSSG-R). This enzyme was selected because it is ubiquitously present in cellular systems and it has been postulated to be involved in the Cr(VI) reduction (14-17) but the underlying mechanism has not been clarified. We find that the reduction proces·s involves not only Cr(V) but also ·OH radicals. We further investigate the reactivity of Cr(V) and find that it catalyzes generation of OH radical from H2O 2 through a Fenton-like reaction. The role of ·OH in Cr(VI) carcinogenicity is suggested from this study."

Jan 1, 1989

By Becket, Frederick M.

CHROMIUM is but one hundred and thirty years of age-a mere youngster as related to many metals that' have speeded world progress. It was Vauquelin of France who proved conclusively that the so called red lead of. Siberia contained a new element. The variety and characteristic colors of the compounds suggested the name chromium. He also succeeded in reducing oxide of chromium to the metallic form and described the product as very brittle, infusible, needle- like crystals on which acids had very feeble action. His metal was not pure chromium, of course; it must have contained appreciable carbon in the combined form as a result of reducing the oxide by carbon at high temperatures. Vauquelin's description in 1798 of this work is a gem-indeed, literally, he went so far as to discover the presence of chromium oxide in the emerald. The metallic product did not seem to interest Vauquelin greatly, but a new chemical industry began shortly after his discoveries.

Jan 1, 1928