ferrochrome

Posts Tagged ‘ferrochrome’

Purchase includes free access to book updates online and a free trial membership in the publisher’s book club where you can select from more than a million books without charge. Chapters: ferrochrome, ferrosilicon, ferrocerium, ferrouranium, ferroalloy, ferrotitanium, ferroniobium, ferromolybdenum, ferromanganese, silicomanganese. Excerpt: Ferrochrome (FeCr) is an alloy of chromium and iron containing between 50% and 70% chromium. The ferrochrome is produced by electric arc melting of chromite, an iron magnesium chromium oxide and the most important chromium ore. Most of the world’s ferrochrome is produced in South Africa, Kazakhstan and India, which have large domestic chromite resources. Increasing amounts are coming from Russia and China. The production of steel is the largest consumer of ferrochrome, especially the production of stainless steel with chromium content of 10 to 20% is the main application of ferrochrome. Over 80% of the world’s ferrochrome is utilised in the production of stainless steel. In 2006 28 Mt of stainless steel were produced. Stainless steel depends on chromium for its appearance and its resistance to corrosion. The average chrome content in stainless steel is approximately 18%. It is also used when it is desired to add chromium to carbon steel. FeCr from Southern Africa, known as ‘charge chrome’ and produced from a Cr containing ore with a low Cr content, is most commonly used in stainless steel production. Alternatively, high carbon FeCr produced from high grade ore found in Kazakhstan (among other places) is more commonly used in specialist applications such as engineering steels where a high Cr to Fe ratio and minimum levels of other elements such as sulfur, phosphorus and titanium are important and production of finished metals takes place in small electric arc furnaces compared to large scale blast furnaces. Ferrochrome production is essentially a carbothermic reduction operation taking plac

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.