I found a way
1- electrolysis the electrodes in 7.5 mol NaOH solution.
2- filter the participate powder.
3- Wash it with distilled water
4- add H2O2 37% and leave it for a day
5- wash with 25% ammonia solution
6- filter the powder.
Done.
According to this method, in 1 liter of 7.5 M (30%) aqueous solution of sodium hydroxide was dissolved electrodes with a total mass of 300 g. For oxidation and neutralization it took 150 ml and 25 ml of aqueous solutions of hydrogen peroxide (37%) and ammonia (25%), respectively. Thorium oxide obtained 5.7 g, which is 1.9%. This is 95% of expected.
Found it in some Russian site with pictures
Translate with Google if you are interested
Vydelenie_oksida_toriya_iz_torirovannyh_volframovyh_elektrodov-1.pdf
