ferrochrome

Posts Tagged ‘chrom-mining’

Chrome is recognized as a mineral by the International Mineralogical Association (IMA) (System-Nr. after Strunz: 1.AE.05 I/A.06-10 or former), but occurs in nature only rarely in pure form on. So far, only 10 sites are known. For the most part is chrome, therefore, only in combined form especially as the mineral chromite (chrome iron ore) mined FeCr2O4 with a chromium content of about 46% in surface or at shallow depths. Some other minerals, while containing more chromium such as Ferchromid (~ 87%) or Grimaldiit (~ 61%), but are concerning chromite remains very much rarer. In total there are currently (as of 2010) about 100 known minerals containing chromium.

In 2003 South Africa mined 50% of world production for chrome ore. Other significant producing countries are Kazakhstan (15.2%), India (12.1%), Zimbabwe (3.7%) and Finland (3%). In 2006 South Africa according to ICDA was mining 36%, India 19%, Kazakhstan 17%, and Brazil, Zimbabwe, Turkey and Finland, together 13%.

In 2000 about 15 million tons of marketable chrome ore were mined. From this 4 million tons of ferrochrome with a market value of $ 2,500,000,000 were gained. Metallic chromium is very rare in deposits. In the Udachnaya pipe mine in Russia a kimberlite “pipe” containing diamonds are exploited. In the reducing matrix diamonds and metallic chromium were formed.

The mined chrome ore is freed from the rock dove. In the second step, an oxidative decomposition takes place at about 1200 ° C to chromate:

\ Mathrm (4 \ FeCr_2O_4 + 8 \ Na_2CO_3 + 7 \ O_2 \ longrightarrow) \ mathrm (8 \ Na_2CrO_4 + 2 \ Fe_2O_3 + 8 \ CO_2 \)

The sodium chromate is extracted with hot water and sulfuric acid converts it into dichromate:

\ Mathrm (2 \ Na_2CrO_4 H_2SO_4 + \ longrightarrow) \ mathrm (Na_2Cr_2O_7 Na_2SO_4 + + H 2 O \)

The sodium dichromate dihydrates and crystallizes on cooling from the solution. A subsequent reduction with carbon obtains chromium (III) oxide:

\ Mathrm (Na_2Cr_2O_7 \ cdot 2 \ H_2O + 2 \ C \ longrightarrow) \ mathrm (Cr_2O_3 Na_2CO_3 + + 2 \ H_2O + CO \)

Here is the aluminothermic reduction of chromium (III) oxide to chromium:

\ Mathrm (Cr_2O_3 + 2 \ al \ longrightarrow Al_2O_3 + 2 \ Cr \)

Chrome can not be won by reduction with coal from the oxide ores, since in this case chromium carbide formed. Purer chromium is represented by electrolytic deposition of the Cr3 + ion from sulfuric acid solution. Such solutions are prepared by dissolving chromium (III) oxide and ferro-chrome produced in sulfuric acid. Ferrochrome as a source requires however prior separation of iron.

Extremely pure chromium is produced by further purification steps after the van Arkel-de-Boer method.

Ferrochrome is produced by reduction of chromite in furnace at 2800 ° C.