Elements of Periodic table: 4) Selenium

Hi,
why Selenium? Well I was not sure what element to choose, I did not want to write about some precious metal since last two time I have covered gold and palladium. I used random generator and I got 34, which is proton number of Se.


History

Selenium is one of those elements which were find in last centuries. This usually happens because the element is not enough common for some alchemists to find it or it is always well bonded with other element (here it is sulfur) and it took some time before we were able to extract it.

Jöns Jakob Berzelius and Johan Gottlieb Gahn were chemists in Sweden and they were working close to Falun mine [1], which you can see on the next pictureThe Copper Mine in Falun, the Great Pit

Guys there wanted to know what was it what they mined so they gave sample to those two chemists. It seemed to be some kind of arsenic compound but it was smelling strange and soon they found out that it is similar to sulfur and tellurium. Tellurium was named after Earth so they named Selenium (in Greece) after Moon, this happened in 1817.

Occurrence

  • Universe: 3.0×10-6 %
  • Earth’s crust: 5.0×10-6 %
  • Ocean: 4.5×10-8 %
  • Human: 5.0×10-6 %

You see it is not very common, at least it does not seem to be. But if I compare it’s occurrence in Universe with other elements it is not so bad. Most metals have one or two magnitudes less occurrence, from what I found selenium is not produced in solar fusion which means that it is created from supernovas, which would explain it’s  relative rarity.

On the picture above you can see some Se in piece of sandstone from uranium mines.

Usually you will find it with sulfur so you need to extract it using methods as SX/EW [2].

Properties

Se is non metal element which can exist in several allotropes [3]. SeBlackRed.jpg

It is usually red powder as you can see above but if you melt it rapidly you will get this kind of grey form which is usually sold. Se makes big and complex structures.

There are five Se stable isotopes and the couple of others with half life ranging to thousands of years, than there is Se 82 which has half life of 10^20 years which is considered relatively stable.

It has extremely important property of photo-conductivity, its conductivity depends on the amount of light hitting its surface.

Selenium is toxic element.

Usage

Selenium dioxide has a great usage during manganese electrolysis because it decreases the energy needed to get manganese (it works as catalyst). China is largest consumer of this compound for such use. For ton of manganese there are two kilograms of Se used. There are 31,200,000 tonnes of manganese produced each year.

Glass gets often kind of yellow or green color because of iron or other things accidentally mixed into it so Se is used to color it into red, this is the most common usage.

Also since lead is so toxic Se is used in brass with bismuth. At low concentrations it also improves machinability of lead, which is similar usage as of vanadium which improves the strength of steel.

Because of its photo voltaic property, it is used in photo voltaic cells called CIGS (copper indium gallium selenide solar cell).

There are other trace uses like radiography.

On the pie graph you can see the production of Se. While I did not find the graph of biggest consumers of Se, on the top is clearly China, as always.

Selenium in organisms

Organisms need selenium as we found out. It is important in some cellular processes but only really small amount like tens of micro grams.

At one time people thought that it is going to be good if they get more Se through some pills. Soon it was found out that more than 200 micro grams can cause cancer and so on. More accurately in one test, doctors got their patients 17% higher chance of prostate cancer which is number two of cancers killing male humans.

There are some illnesses with the lack of selenium but they are not very common even in places where is small amount of Se in the soil like New Zealand.

The price for Se is about 60$ for pound while at some times it lowered to about 30$.

Dragallur


[1] Falun mine was extremely important mine producing 2/3 of Europe’s needs of copper. It was working for almost 1,000 years and it is now cultural heritage with museum.

[2] SX/EW (Solvent extraction and electrowinning) is method used to get some metals like nickel, cobalt, zinc and uranium.

[3] Allotrope of carbon is for example graphite and diamond, both made up of only carbon but with different shape of molecules.

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Elements of Periodic table: 2) Palladium

Hi,
this time comes the post about another element of periodic table. Last time it was Vanad and I will continue with Palladium!
Palladium is extremely important in car industry, it is also beautiful in jewelry and has surprising history.


 

What I found most interesting about Palladium (Pd for the rest of the post) is that it is related to astronomy.
In the beginning of 19th century guy named William Hyde Wollaston was PallasHST2007.jpgable to separate Pd and then he published it in a scientific journal. Some people thought that it was fake, that what he called Pd was just some kind of alloy of Nickel and Silver. Wollaston named it after dwarf planet found two months earlier called Pallas, you can see the planet on the right (Pallas is second largest dwarf planet in the belt between Mars and Jupiter).

Palladium (46 Pd).jpgPalladium is white and grey metal right above Platinum in the table of elements. There are many isotopes and lot of them naturally occur and few of them are radioactive decaying into Ruthenium, for example.

It is used on various things. In cars it is used as part of catalytic converter which is next to motor and takes CO and other toxic and poisonous molecules out. For the converter to be fully functional we had to stop using leaded petrol. (Wikipedia says that there are still companies in China that produce tetraethylead which is the source of the lead in petrol, it is making the car more efficient).
Pb (lead) was destroying these catalytic converters in very short time while now it is assumed that it should be working for over 120,000 km. On the left you can see the three way catalytic converter.

Palladium is used a lot in jewelry like “white gold”, also in dentistry because it is cheaper than gold, but some people may be allergic. Smartphones and lot of various electronic devices contain Pd.
Pd is also used as storage for hydrogen.

Now for mining. Most of Pd is mined in Russia,
South Africa is right behind then for a long time nothing and rest is produced by USA and Canada mostly.

Some sources say that Russia is running low with their storage, which would be big problem if true (it is the state secret so no one can be sure). In 2001 there was a Pd crisis when Russia had some problems with mining (the problem was linked to politics). Prices of Pd rose to over 1000$ per troy ounce (OZ=27 grams). It seemed that it would rise even more so Ford Motor Company bought a big amount and then the prices dropped rapidly, leaving Ford with loss about 1 billion $! On the picture below you can nullsee the peak of the price and then the drop to about 200$. For now the price is about 560$/OZ for the last years the price seems to drop. On the next picture you can see the graph of prices for 18th December which of course do not 1 Day Spot Palladium Prices - Palladium Price Chartchange very much. In whole Earth there is about 0,0075-0,01 ppm (mg/kg) of Palladium. PPM is parts per million which is the same as miligram per kilogram. In sea water the amount is unmeasurable, because even the most precise technology is not able to detect it. In space there is about 1 atom of Pd per 30 billions of atoms of hydrogen.

Pd is also created in nuclear reactors but this source is not used.

Usually you will find pure (100%) palladium with gold or ruthenium around. Also oxygen is not reacting with Pd, which is extremely good attribute (this is not true above 800°C, then PdO is created on the top layers). For some time Pd was used as cure for tuberculosis but there were many side effects so it was banned. Pd is not very toxic since our body is not able to absorb it, but there is some evidence that it may be carcinogenic.

Dragallur

Pallas picture
Palladium picture
Catalytic converter
Palladium demand
Pie graph of production
Kitco 2001 graph
World map of Pd production