Lion850
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Report on making erbium tungstate
I wanted to try and make something with my newly acquired tungstic acid and decided on erbium tungstate after reading on supplier’s specs that it is
a pink solid and insoluble.
To do the double displacement I needed erbium chloride and sodium tungstate:
2ErCl3 + 3Na2WO4 = 1Er2(WO4)3 + 6NaCl
Erbium chloride prep: 10g 35% hydrochloric acid was added to a small beaker followed by 5.6g of erbium oxide Er2O3. It was stirred and heated
slightly. Some oxide remained in suspension so another 2ml HCl was added. Finally a pale pink solution was obtained with all oxide dissolved. The
solution was so clear that I did not see the need to filter it.
Sodium tungstate prep: 3.5g sodium hydroxide was placed in a small beaker and 5ml of water added. After the NaOH dissolved, 6g of tungstic acid was
added (a yellow powder). There was an unexpectedly vigorous reaction and I had to quickly add another 10ml or so water to calm things down. The yellow
color quickly disappeared to a clear solution. Another 5g of tungstic acid was then added, this time it took much longer for the yellow color to fade
and eventually I had a nearly clear solution with a hint of very pale green.
This should have resulted in approx. 13g of Na2WO4 and approx. 8g of ErCl3, both in solution, and the expected erbium tungstate was to be around 15g.
The ErCl3 solution was left on the stirring hot plate and was still warm. The sodium tungstate solution was slowly added under stirring. A voluminous
pink mass of erbium tungstate precipitated out, it gummed up the stir bar as it sucked up the available water. 40ml of water was added resulting in a
thick pale pink solution that was stirred for some 15 minutes.
The solution was vacuum filtered. Filtering took a while as the product was very fine. The filtrate was nearly clear, with a remainder of pink powder.
The remainder was washed twice with water. The moist paste was transferred in a crucible and left to air dry overnight.
The next day the weight was 34g. 10g was placed on a steam bath – I tried only 10g first because I did not know the decomposition temperature. The
10g dried out nicely and after an hour the weight was 5.2g. Another 30 minutes did not see to reduce the weight any further. The rest of the product
was then dried on the steam bath for 2 hours. The loss of water due to drying also made the color a bit stronger pink.
Total final recovered product was 16.5g, which was close to the expected minimum of 15.
The only test I did on the product was to add a few mg to concentrated hydrochloric acid: the acid seems to decompose it with yellow color appearing.
I also made manganese tungstate, which will be dried tomorrow. It was also made by double displacement, but I had MnCl2.4H2O in my inventory so did
not need to make it first. The manganese tungstate is even more voluminous when it precipitates out than the erbium tungstate but somewhat
surprisingly it filtered much easier. The color is “seashell” (when I compare it to an online color chart) or close to light tan. It also gives
yellow color when treated with concentrated HCl.
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Bedlasky
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You have very interesting ideas.
Btw cobalt tungstate is also pink, maybe a little bit intense.
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Lion850
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Update to my original post above: The manganese tungstate turned out very light tan color when wet ("seashell") and as it is dried on a steam bath it
turns white. It held on to the water stronger than the erbium tungstate and was on the steam bath some 5 hours before the weight loss slowed down to
nearly nothing. Final recovery was 16.4g; aim was 15 so quite close.
Not a particularly attractive looking compound and I have no idea what it can be used for, but another for the inventory 
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