Thorium dioxide from electrodes

Thorium dioxide (ThO2) also known as thoria is a weakly radioactive compound used in some welding electrodes. Thorium gives off alpha radiation which can't penetrate paper and is very short ranged, so it's only dangerous if inhaled or consumed. Thorium dioxide used to be used in gas mantles but this was stopped due to concerns about the radiation. I plan to use thorium dioxide to make Thorium metal and generally explore thorium chemistry.

Thorium dioxide can be extracted from thoriated tungsten electrodes used in welding.
These are usually 2-4% thorium dioxide.

Two years ago I brought 4 thoriated tungsten electrodes. I added them to a container of 3% hydrogen peroxide and left them there until the electrodes had corroded away.  After this there were lots of yellow crystals were left. I collected the crystals and placed them in a vial.

Yesterday I decided to purify the thorium dioxide. I realized my sample was probably a mix of thorium dioxide and tungstic acid. So I added the the yellow crystals to 5ml of saturated sodium carbonate solution and heated strongly for a few seconds. The yellow tungstic acid began to react away and a white powder (presumably thorium dioxide) remained. Once this had stopped, I filtered the mixture to collect the white thorium dioxide. Then I added the thorium dioxide to another 5ml of sat sodium carbonate solution to make sure all the tungstic acid had gone. After this, I filtered off the thorium dioxide and dried it. I got 0.8g of slightly yellow thorium dioxide.

 

 left = the thoriated electrodes (image from www.ecvv.com)  /  Right = thorium dioxide

H2WO4 + Na2CO3 ==> Na2WO4 + H2O + CO2