Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
by Paul Hawkins
Rhodium, atomic number 45, is one of the varieties of platinum that exists on
our planet is a rare and very useful transition metal. It was discovered by
William Hyde Wollaston shortly after his discovery of one of the other
platinumís, Palladium. Rhodium is also very hard; its hardness on the Mohs
Hardness Scale is 6.0.Which makes it harder than most metals. It is
silvery in color and has a high reflectance which makes it very shiny and mirror
like. Not to mention, it is extremely resistant to erosion and tarnish, it
cannot be attacked by most acids and is insoluble in nitric acid. Rhodium
is also one of the most expensive metals out there, far exceeding gold many
times over. As of 2010 for one ounce of rhodium it would cost about
The mining of rhodium is difficult as there are few places where
it, like its platinum brethren, exist. It is mainly mined out of South
America where about 80%+ of it is mined. Russia comes in second when
mining the element and thirdly the United States. Rhodium extraction is very
complex as it takes a lot to actually make pure Rhodium.
OBTAINING RHODIUM PROCESS:
The other metals that it normally mixes with must be removed, such as gold,
platinum, and silver.
2nd: The left over residue is melted with sodium bisulphate (NaHSO4). It then extracts a water solution containing rhodium sulfate Rh2(SO4)3.
3rd: The Rhodium is precipitated out as the hydroxide by adding Sodium Hydroxide (NaOH) and redissolved in Hydrochloric Acid (HCL) to get H3RhCl6.
4th: It is then treated with NaNO2 and NH4Cl to form a precipitate of Rhodium (NH4)3[Rh(NO2)6].
5th: It is then dissolved in more hydrochloric acid (HCl) to gain (NH4)3RhCl6.
6th: Finally, it is left to evaporate and then burned with hydrogen gas to produce pure Rhodium.
With as many processes as it has to go through to be obtained, no wonder
Rhodium is so high in price.
However, it is very much worth all the work and effort for rhodium has many uses. It has uses for things like cars and airplanes. In cars rhodiumís ability to become a catalyst is highly desirable. It is used in catalytic converters to change the harmful emissions from the engine into a less dangerous pollutant. In airplanes Rhodiumís high resistance to erosion is highly desirable. A plane in order to fly needs working engines. Inside the engines are spark plugs that cause the explosions that propel the plane forward. If the spark plugs go, then there is a major problem. Rhodium has a low resistance to electricity so it is ideal for usage in spark plugs. A nice coating on the spark plug will ensure that it lasts for when it is truly needed, in the air. This is the industry that mainly buys rhodium from companies who produce this valuable material. Here are a few pictures of items that use rhodium. Such as the spark plugs for an airplane, dental and surgical equipment, a fancy pen, and a catalyst used to filter out emissions.
RHODIUM HAS MORE USEFULNESS
Rhodium also has more uses. At nuclear power plants there are special detectors that contain a very pure rhodium inside of it and are insulated by minerals. These detectors take in-core measurements of neutron flux levels. Many detectors are places in a single reactor. In the Palo Verde nuclear reactors there are 61 detectors on each of 5 vertical levels. This gives a 3D look at the cores reactivity, allowing the power plant to more efficiently use the nuclear fuel. Rhodiumís resistance to erosion and high melting point make it a perfect metal for helping the detectors last longer, though they do eventually burn up and have to be replaced as it is normal maintenance. Here is a picture of what the detectors look like.
One of Rhodiumís finest uses though is for jewelry. It can be electroplated onto white gold, platinum, and silver to give it that awesome shine and ultimate protection. This process is called Rhodium Flashing. The rhodium protects the jewelry from being scratched as it is very hard and protects the jewelry from tarnishing because of its ability to be resistant against erosion. Rhodium Flashing is quite the cool process.
Here is a link to see what it looks like on YouTube. - http://www.youtube.com/watch?v=SuqB6H18svI
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THE PROCESS OF RHODIUM FLASHING:
1st: The jewelry piece is buffed out to get rid of as many scratches as possible.
2nd: The jewelry is thoroughly cleaned and all polishing compounds are removed from the first step.
3rd: The jewelry is steamed to double check to make sure all the compound material is off.
4th: The jewelry is electro cleaned in a solution. The ring is now 100% clean.
5th: The actual rhodium plating. The jewelry is dipped into the rhodium solution where it clings to the metal of the jewelry.
6th: The jewelry is again dipped into water to remove any excess solution and finally it is steamed again. Your jewelry is now protected and beautiful.
In conclusion, rhodium is a very unique and wonderful form of platinum. Itís worth a whole heck of a lot of money and itís important in many uses for many industries. Without it human beings would have to figure out another way to keep things from eroding and melting. Not to mention lots of jewelry would have tarnished. My hopes for this article is that people will now know more about this important, not well known element and utilize it as much as they can. Save your jewelry, use rRhodium today.
Rhodium 1 Ounce Plate