Aqueous conc soln of tantalum oxalate

摘要

The soln. contng. at least 150 g/l of Ta, is prepd. by ammoniating a soln. contng. TaF7-- in a concn of at least g/l, expressed as Ta2O5, to a pH of 7.8-8.2 to ppt Ta(OH)5, washing the pppt till free of F- ions, then filtering the washed ppt. to remove as much entrained water as possible from it. The filler cake is then allowed to stand for 7 days, and during this time 2 p.b.w. oxalic acid dihydrate per part Ta2O5 are added, at a temp. between ambient and 70 degrees C to form an aqs. mass contng. dissolved Ta oxalate. This soln is cooled to less than ambient temp. to ppt. unreacted oxalic acid which is filtered off, leaving the reqd. soln. as the filtrate.