This post’s subject is the element rhodium. Lately it has become a very valuable metal. Will be shown your properties, biggest reserves, extraction and applications.
Properties
The rhodium is a hard transition metal, has atomic number of 45. Has fusion and boiling points of 1963ºC and 3695ºC respectively, density of 12.4 g/cm^{3} and atomic mass of 102.906 g/mol.
The rhodium is silvery white and resistant to corrosion. In high temperatures, reacts with oxygen, chlorine and bromine.
Main reserves and miners
This metal is very rare and more valuable than gold and silver. The biggest miners are South Africa (80%) and Russia (12%). This graph is from 2016, but didn’t change much in 2018.
The biggest reserves are found in Bushveld Complex, in South Africa; in Noril’sk-Talnakh, in Russia; in USA and Canada.
Mining and extraction
This metal belongs to the platinum metal group (PMG), also formed by palladium, ruthenium, iridium, osmium and platinum, these element have similar properties. It is found in platinum or nickel mines. To extraction, first have to separate from other valuable metals like gold, silver, palladium and platinum by precipitation. After, treat the rest of ore with sodium bisulfate (NaHSO_{4}) and melt it, generating rhodium sulfate (Rh_{2}(SO_{4})_{3}). This sulfate is added with sodium hydroxide to precipitate the rhodium hydroxide.
Rh_{2}(SO_{4})_{3}+6NaOH\rightarrow 2Rh(OH)_{3}+3Na_{2}SO_{4}
Then is dissolved with hydrochloric acid to form the H_{3}RhCl_{6}.
2Rh(OH)_{3}+6HCl\rightarrow H_{3}RhCl_{6}+3H_{2}O
The H_{3}RhCl_{6} is treated with sodium nitrite (NaNO_{2}) and ammonium chloride (NH_{4}Cl), producing a rhodium precipitate ((NH_{4})_{3}[Rh(NO_{2})_{6}]). This precipitate is dissolved with hydrochloric acid (HCl) and heated with hydrogen gas to obtain the pure metal.
Rhodium applications
It is used in electric connectors due to low resistance and anticorrosive property.
This element is used for stabilizer in catalysts for vehicle exhaust system, to filter polluting gases like carbon monoxide, nitrogen oxide and volatile organic compounds.
When polished, has great reflectivity, by that it is used in coating of optical fibers and mirrors. Click in the button below to know how optical fibers work.
The same reflective property is applied in reflectors.
This metal is used in thermocouples to measure temperature.
Also is used is jewelry making. The figure below shows the difference between a ring without rhodium and with it.
