Chromi­um ores. Prop­er­ties, gen­e­sis and use

Chromi­um ores (chromites) were first dis­cov­ered in France (Car­rade de Cav­alaire deposit) at the end of the 18th cen­tu­ry. Ini­tial­ly, they were used as a refrac­to­ry mate­r­i­al and to pro­duce paints. Lat­er, chromi­um was wide­ly used as an alloy­ing mate­r­i­al for steel pro­duc­tion.

Metal­lic chromi­um was first dis­cov­ered in the min­er­al crocite by French researcher L.N. Vau­clin. There are 25 known chromi­um min­er­als. The most com­mon and valu­able from an indus­tri­al point of view are mag­nochromite (Mg, Fe)Cr₂O₄, chro­mopi­cotite (Mg, Fe)(Cr, Al)₂O₄ and alu­minochromite (Fe, Mg)(Cr, Al)₂O₄, which are almost indis­tin­guish­able in appear­ance and are there­fore called ‘chromites’.

In addi­tion to chromites, chromi­um is also found in fuch­site, chromi­um chlo­rite, chrome­su­vian, chrom­diop­side, uvarovite, etc. Under exoge­nous con­di­tions, chromi­um com­pounds are sta­ble, which deter­mines their abil­i­ty to form plac­ers.

Chromi­um ores are is includ­ed in the list of min­er­als of nation­al impor­tance approved by the Res­o­lu­tion of the Cab­i­net of Min­is­ters of Ukraine dat­ed Decem­ber 12, 1994, No. 827, as fer­rous ores.

Properties of chromium

Chromi­um is a shiny, grey­ish-white duc­tile met­al with a spe­cif­ic grav­i­ty of 7.19 g/cm³, char­ac­terised by a high melt­ing point (1890°C) and cor­ro­sion resis­tance due to its oxide film on the sur­face.

At high tem­per­a­tures (above 1800°C), chromi­um can react with halo­gens, sul­phur, nitro­gen and oth­er ele­ments, and at nor­mal tem­per­a­tures it reacts eas­i­ly with dilute acids. In its pure form, chromi­um is duc­tile, but impu­ri­ties make it brit­tle. The addi­tion of fer­rochromi­um increas­es the strength, hard­ness and cor­ro­sion resis­tance of steels, which is essen­tial for the pro­duc­tion of stain­less, heat-resis­tant and acid-resis­tant steels. Chromite refrac­to­ries are high­ly resis­tant to tem­per­a­ture and slag, mak­ing them indis­pens­able for lin­ing indus­tri­al fur­naces.

Chromi­um ore deposits include:

• mag­mat­ic (ear­ly and late mag­mat­ic);
• allu­vial (elu­vial-delu­vial and coastal-sea).

Mag­mat­ic chromi­um deposits were formed in dif­fer­ent geo­log­i­cal epochs, from the Pre­cam­bri­an to the Ceno­zoic. They are close­ly asso­ci­at­ed with mas­sifs of ultra­ba­sic rocks (dunites and peri­dotites) that pen­e­trat­ed along deep faults.

Mas­sifs of chromite-bear­ing rocks often form belts of con­sid­er­able length:

• Her­cyn­ian intru­sions of peri­dotites and dunites in the Urals;
• The Mediter­ranean belt of Cre­ta­ceous and Pale­o­gene hyper­b­a­site intru­sions (from the Balka­ns through Turkey and the Cau­ca­sus to India);
• Pre­cam­bri­an mas­sifs of the Bushveld Com­plex and the Great Dyke in South Africa and Zim­bab­we.

The forms of ore bod­ies and struc­tur­al and tex­tur­al fea­tures of ores depend on the geo­log­i­cal con­di­tions of their for­ma­tion (plat­form or fold­ed mode), name­ly, crys­talli­sa­tion of host rocks among hor­i­zon­tal­ly lying stra­ta of acti­vat­ed plat­forms or in the process of devel­op­ment of fold­ed areas under tec­ton­ic com­pres­sion.

Under plat­form con­di­tions of for­ma­tion, chromite interbed­ded mas­sifs are char­ac­terised by pseu­dos­trat­i­fi­ca­tion, expressed by alter­nat­ing lay­ers of basic and ultra­ba­sic rocks, hor­i­zon­tal or gen­tle occur­rence. Depend­ing on the posi­tion of the chromite mas­sifs, ore bod­ies occur as lay­ers of sus­tained thick­ness and con­sid­er­able length.

Under fold­ed con­di­tions, chromite mas­sifs were formed as a result of the sep­a­ra­tion of ultra­maf­ic peri­dotite mag­ma from the basalt sub­strate in sub­crustal con­di­tions. The min­er­al­i­sa­tion process con­tin­ued at all stages of mag­mat­ic cen­tre devel­op­ment and at dif­fer­ent lev­els, often in the tran­si­tion zones from gab­bro-norite to peri­dotite and dunite. Ores are localised due to grav­i­ta­tion­al dif­fer­en­ti­a­tion and melt move­ment under the influ­ence of tec­ton­ic forces. This leads to the for­ma­tion of var­i­ous mor­pho­log­i­cal types of ore bod­ies: slots, lens­es, vein-like bod­ies and brec­cias, with clear con­tacts and band­ed tex­tures.

The ear­ly mag­mat­ic deposits are formed in calm tec­ton­ic con­di­tions (plat­form mode) and are char­ac­terised by interbed­ded lopo­lites or slab-like bod­ies (Bushveld Com­plex, Velikaya Dyka). The ores occur as aged lay­ered deposits in the base of strat­i­fied intru­sive mas­sifs. The ore-bear­ing mas­sifs are dis­tin­guished by strat­i­fi­ca­tion with a grad­ual tran­si­tion (from bot­tom to top) from peri­dotites to gab­broids and gran­i­toids.

The for­ma­tion of late-mag­mat­ic deposits is accom­pa­nied by tec­ton­ic defor­ma­tions, as a result of which the chromite-bear­ing mas­sifs are deformed. The deposits are con­fined to the hyper­b­a­site for­ma­tion. The ores occur in ser­pen­tinised dunites that make up large mas­sifs. The ore bod­ies are shaped like veins and lens­es with sharp bound­aries and capri­cious out­lines, some­times inter­sect­ed by gab­bro and dunite dykes.

Elu­vial-delu­vial plac­ers are formed as a result of weath­er­ing of the host igneous rocks and move­ment of chromite par­ti­cles down slopes. Elu­vial for­ma­tions (lat­erite type) are rep­re­sent­ed by crys­tals and frag­ments of chromite among the loose limonite mass. Such deposits are known in Cuba, the Philip­pines, and New Cale­do­nia. The largest delu­vial chromite deposit is locat­ed in the Great Dyke of Zim­bab­we in the sed­i­ments of trans­verse val­leys and along rivers, where chromite reserves amount to 60 mil­lion tonnes.

Coastal and marine plac­ers are formed in coastal areas due to the depo­si­tion of chromite in the form of black sands. They are known on the Pacif­ic coast of the USA, in Alba­nia and Turkey.

Deposits in Ukraine

Chromi­um ores were first dis­cov­ered in Ukraine in 1932 on the left bank of the South­ern Bug Riv­er near the vil­lage of Zaval­lia in Kirovo­grad Oblast. These ores were of low grade and not suit­able for use in metallurgy.Chromium ore deposits in Ukraine are known in the Mid­dle Pobuzhzhya region near the vil­lages of Kap­i­taniv­ka, Lipovenky and Lip­nyagy in Kirovo­grad Oblast. All these deposits are part of the Kap­i­tanivske ore field of the Dnis­ter-Bug met­al­lo­genic sub­province.

The Kap­i­tanivske ore field is com­posed of a com­plex of Pre­cam­bri­an sed­i­men­ta­ry, metased­i­men­ta­ry and igneous rocks over­lain by Mesocene rocks. The fold­ed Pre­cam­bri­an base­ment is com­pli­cat­ed by faults. The study revealed 62 ultra­maf­ic mas­sifs rep­re­sent­ed by two for­ma­tions: dunite-harzbur­gite (hyper­b­a­site) and dunite-peri­dotite-gab­broite. The mas­sifs of ultra­maf­ic rocks are con­cen­trat­ed with­in the Khashche­va­to-Zaval­livs­ka and Per­vo­maysko-Golo­vanivs­ka struc­tures. All known ore occur­rences and deposits with­in Ukraine are ultra­maf­ic of the hyper­b­a­site for­ma­tion.

The chromite ultra­b­a­site mas­sifs of the Kap­i­tanivske ore field are rep­re­sent­ed by steeply dip­ping dike- and tube-shaped cross-sec­tion­al bod­ies. These mas­sifs are con­trolled by deep faults. The mas­sifs have a dif­fer­en­ti­at­ed strat­i­fied struc­ture and are enriched with sul­phides. The ore-bear­ing for­ma­tion is rep­re­sent­ed by ser­pen­tinised dunites, peri­dotites, harzbur­gites and lher­zo­lites, as well as vein pyrox­en­ites, hyper­s­then­ites and bronzites. The chromi­um oxide con­tent in the rocks ranges from 0.4% to 7.2%.

The Kap­i­tanivske deposit con­sists of 9 ore bod­ies of rel­a­tive­ly low thick­ness (0.5–12 m), which have been drilled over a strike length of 50–160 m and a dip of 75–300 m. The aver­age chromi­um oxide con­tent is 29%. The ores are poor, dis­sem­i­nat­ed, dense­ly dis­sem­i­nat­ed and mas­sive con­tin­u­ous. Lin­ear weath­er­ing crusts com­posed of chrome-nick­el ores devel­op in the upper parts of the ore bod­ies. The West Lypovenkivske deposit con­sists of 2 ore bod­ies, which are traced for 40–80 m along strike and 50–75 m down dip. The ores are con­tin­u­ous, dense­ly dis­sem­i­nat­ed and rarely dis­sem­i­nat­ed.

Prospects for chrome ore explo­ration in Ukraine are lim­it­ed, but it is pos­si­ble to fur­ther explore the already known deposits, as well as to con­duct detailed explo­ration of pre­vi­ous­ly dis­cov­ered chromite occur­rences (Per­shotravn­eve, Lypovenkivske and Lyp­nya­givske groups).

Chromium ore deposits in the world

South Africa is one of the largest sup­pli­ers of chrome ore in the world and has the largest known reserves of chrome ore. The Bushveld Com­plex is the main source of chrome ore, with lentic­u­lar deposits in the east­ern and west­ern parts of the com­plex. Chromite deposits in South Africa are gen­er­al­ly asso­ci­at­ed with basic and ultra­ba­sic rocks.

Kaza­khstan is anoth­er major chrome pro­duc­er and has sig­nif­i­cant chrome ore reserves. The chromite deposits in Kaza­khstan are locat­ed in the Urals-Alta­ic region, in par­tic­u­lar in the Aktobe, Kara­gan­da and Ust-Kamen­ka regions. The chromite deposits in Kaza­khstan are main­ly of lentic­u­lar and strat­i­form type asso­ci­at­ed with ultra­maf­ic rocks.

India is also a major pro­duc­er of chromite, with sig­nif­i­cant deposits found in the states of Odisha, Kar­nata­ka and Manipur. The chromite deposits in India are main­ly of lentic­u­lar and strat­i­form types, occur­ring in ophi­o­lite com­plex­es and lay­ered mag­mat­ic com­plex­es.

Turkey is known to have sig­nif­i­cant chromite deposits, par­tic­u­lar­ly in the provinces of Elazığ and Malatya. The chromite deposits in Turkey are main­ly lentic­u­lar and strat­i­form, asso­ci­at­ed with ophi­o­lite com­plex­es and lay­ered mag­mat­ic com­plex­es.

Chromite deposits are also found in oth­er coun­tries such as Alba­nia, Fin­land, Iran, Mada­gas­car, Philip­pines, Zim­bab­we, Brazil and Cuba, among oth­ers. These deposits can be of var­i­ous types, includ­ing lentic­u­lar, strat­i­form, beach plac­ers and lat­erite for­ma­tions, depend­ing on the geo­log­i­cal set­ting.

Areas of use

Chromi­um ores play an impor­tant role in var­i­ous indus­tries due to their prop­er­ties. Its resis­tance to cor­ro­sion, high melt­ing point and ver­sa­til­i­ty make it an impor­tant ele­ment in the pro­duc­tion of many mate­ri­als and prod­ucts that are wide­ly used in mod­ern indus­try.

Chromi­um ores are used for:

• Stain­less steel pro­duc­tion — chromi­um is the main alloy­ing com­po­nent in the pro­duc­tion of stain­less steel. Chromi­um gives steel its cor­ro­sion resis­tance, high ten­sile strength and dura­bil­i­ty.
• Alloys — chromi­um is used in the pro­duc­tion of var­i­ous alloy steels, includ­ing high-strength and heat-resis­tant steels. These alloys are used in the man­u­fac­ture of air­craft, gas tur­bines, auto­mo­tive parts and indus­tri­al equip­ment, where strength and resis­tance to high tem­per­a­tures are crit­i­cal.
• Elec­tro­plat­ing — Chromi­um is wide­ly used in elec­tro­plat­ing, a process used to apply a thin lay­er of chromi­um to the sur­face of oth­er mate­ri­als to improve appear­ance, dura­bil­i­ty and cor­ro­sion resis­tance. Elec­tro­plat­ed chrome is used to pro­duce auto­mo­tive parts, house­hold appli­ances and oth­er items.
• Refrac­to­ry mate­ri­als — chromi­um com­pounds are used in the pro­duc­tion of refrac­to­ry mate­ri­als used in high-tem­per­a­ture appli­ca­tions such as open-hearth and induc­tion fur­naces.
• Pig­ments and colourants — chromi­um com­pounds are used as pig­ments and colourants in the pro­duc­tion of paints, coat­ings and inks. Chromi­um-based pig­ments, such as chromi­um yel­low and chromi­um green, are known for their bright colours, excel­lent light­fast­ness and heat resis­tance.
• Chem­i­cals — chromi­um is used in the pro­duc­tion of var­i­ous chem­i­cals, includ­ing chromic acid, which is used in the pro­duc­tion of met­al fin­ish­es and met­al coat­ings, and in the pro­duc­tion of oth­er chromi­um com­pounds used in leather tan­ning, wood preser­v­a­tives and tex­tile dyes.
• Oth­er appli­ca­tions — Chromi­um has oth­er indus­tri­al uses, for exam­ple, in the aero­space indus­try for the man­u­fac­ture of air­craft com­po­nents, in the elec­tri­cal indus­try for the pro­duc­tion of con­duc­tive coat­ings and in the auto­mo­tive indus­try for the pro­duc­tion of exhaust gas cat­a­lysts.

Chromi­um is an impor­tant met­al due to its high melt­ing point, cor­ro­sion resis­tance and duc­til­i­ty. It is used in the pro­duc­tion of stain­less steel, alloyed alloys, elec­tro­plat­ing, refrac­to­ry mate­ri­als, pig­ments and dyes, and in the chem­i­cal indus­try.

Chromi­um con­tin­ues to play a key role in var­i­ous indus­tri­al sec­tors, under­lin­ing its strate­gic impor­tance for the mod­ern econ­o­my. Ukraine’s chrome ores have poten­tial, but their devel­op­ment requires fur­ther research and effec­tive resource man­age­ment.