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Chromium is a chemical element; it has symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. [10] Chromium is valued for its high corrosion resistance and hardness.
Chromium(III) oxide (or chromia) is an inorganic compound with the formula Cr 2 O 3. It is one of the principal oxides of chromium and is used as a pigment. In nature
[5] [6] Various amalgams of silver and mercury or other metals and mercury do occur rarely as minerals in nature. An example is the mineral eugenite (Ag 11 Hg 2 ) and related forms. [ 7 ] Silver nuggets, wires, and grains are relatively common, but there are also a large number of silver compound minerals owing to silver being more reactive ...
Hexavalent chromium occurs only rarely in nature, an exception being crocoite (PbCrO 4). [3] It is however produced on a large scale industrially. Virtually all chromium ore is processed via the formation of hexavalent chromium, specifically the salt sodium dichromate. [2]
Chromium compounds are compounds containing the element chromium (Cr). Chromium is a member of group 6 of the transition metals. The +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium are rare, but do nevertheless occasionally exist. [3] [4]
Hexavalent chromium has negative impacts towards soil ecology because it decreases soil micro-organism presence, function, and diversity. [23] Chromium concentrations in soil diversify depending on the different compositions of the sediments and rocks that the soil is made from. The chromium present in soil is a mixture of both Cr(VI) and Cr ...
The primary chromium ore is the mixed metal oxide chromite, FeCr 2 O 4, found as brittle metallic black crystals or granules. Chromite ore is heated with a mixture of calcium carbonate and sodium carbonate in the presence of air. The chromium is oxidized to the hexavalent form, while the iron forms iron(III) oxide, Fe 2 O 3:
Soluble hexavalent chromium is the most common type of chromium in oceans, where over 70% of dissolved chromium in the ocean is found in oxyanions such as chromate (CrO 2− 4). Soluble trivalent chromium is also found in the oceans where complexation with organic ligands occurs. Chromium is estimated to have a residence time of