Since discovering electrolysis of tungsten needles, my interest has also been piqued by the discovery that electrolyte and tungsten produce hydrogen and oxygen while leaving sodium tungstate in solution (as the NaOH electrolyte is used up).
Sodium tungstate is very interesting to me because it can be used to make a "heavy solution" that is tuned by dilution to float silica (diatoms) but sink minerals (sand and silt). Perfect for separating tiny, sub 10-micron forms from minerals and other heavy detritus. This is difficult and time-consuming using the techniques that work well for larger forms.
My question (finally) is how to extract pure tungstate from the depleted electrolyte. I guessed I could just sizzle a load of tungsten until the NaOH was used up and sizzling stopped. But there's no clear "stop" and I've run out of wire I'm willing to burn. The solution is still strongly alkali and would damage or destroy diatoms. I can neutralise that with HCl, but the remaining solution would probably not be dense enough. So how can I get pure tungstate out?
Any pointers, even just clues or ideas appreciated as I'm a bit stumped at the moment (with my limited chemistry knowledge). Thanks.
Edit: just found out that HCl would convert the tungsten to WO3 (trioxide), so that's not an option anyway. Told you my knowledge was limited
Also, I may need Sodium polytungstate, but not sure about that. Is there a route from tungstate to polytungstate? And finally - I found a recipe using sodium nitrite, sodium hydroxide and tungsten - and I have those things in hand. Highly exothermic and a bit scary though, so I'll leave exploring that until all the other options (of extracting from depleted electrolyte) are proven impractical. Hopefully they won't be.