Chromite is the commercial name for iron chromium oxide (FeCr2O4), a mineral containing chromium (a transition metal with multiple oxidation states) and iron oxide. In its purest form, chromite comprises chromium (Cr2O3) at 68% and iron oxide (FeO) at 32%.
Chromite occurs exclusively in ultramafic rocks such as dunite, peridotite, pyroxenite and serpentinite.
High purity deposits are rare owing to replacement by certain elements. In nature, ferrous iron tends to be partially replaced by magnesium, while chromium may be partially replaced by aluminium or ferric iron.
As a result, a range of chromite grades can occur in any deposit, with each grade suitable for a specific application.
Grades produced include metallurgical and non-metallurgical applications:
· Metallurgical grade (high chromium chromite, minimum 40% Cr2O3)
· Chemical grade (high iron chromite, 46% Cr2O3)
· Foundry grade (low silica chromite, 45% Cr2O3)
· Refractory grade (high aluminium chromite, 46% Cr2O3)
World chromite reserves are estimated to total around 7.6bn tonnes, with the majority of this located in South Africa. The country is by far the single largest holder of the worlds chromite reserves, accounting for 5.5bn tonnes (72%) much of which is held in the Bushveld Igneous Complex.
Other important sources of chromite include Zimbabwe (with 12% of the worlds reserves), Kazakhstan (4%), Finland (2%), India (1%) and smaller amounts in Turkey and elsewhere.
World production of chrome ore totalled 23.8m. tonnes in 2008 and was dominated by South Africa (41%), followed by India (16%), Kazakhstan (15%), Turkey (8%), and Oman (3.5%).
Leading non-metallurgical chromite producers include:
Assmang South Africa
Chromex UK (operating in South Africa)
Cihan Group Turkey
Dedeman Madencilik Turkey
Eti Krom Turkey
Marico Chrome South Africa
Oman Chromite Oman
Rand York Minerals South Africa
Samancor South Africa
Xstrata South Africa
Ferrochrome markets consumed 93% of the chrome ore produced in 2009, with non-metallurgical markets accounting for almost all of the balance (save for 0.1% used as chromium metal).
Chemical and foundry grade chromite consumed around 3% each of total chromite production, with about 1% used in refractories.
Chemical grade chromite: used in leather tanning, metal finishing and wood preservatives. Also used to produce light-stable and corrosion-inhibiting pigments; in addition to paints, colour glass, and ceramic glazes.
Foundry grade chromite: specialist foundry sand used to produce manganese, carbon and alloy steel castings and non-ferrous metal castings. Promotes rapid solidification of castings.
Refractory grade chromite: used to manufacture refractory bricks used in converters and furnaces for platinum, copper and lead production, and some secondary steelmaking processes.