Metal purification and fabrication
Rhenium metallurgy and recycling

Purification is carried out on ammonium perrhenate, NH₄ReO₄, obtained by ammonia neutralization of a solution containing perrhenic acid. Since the solubility of perrhenate varies widely with temperature (29 g/L at 0 ˚C, 173 g/L at 50 ˚C and 250 g/L at 100 ˚C), fractional crystallizations are carried out in four or five stages, with the aid of which a 99.5% pure salt is obtained.

The metal is obtained by hydrogen reduction of ammonium perrhenate:

We operate either at 1,100 ˚C under a hydrogen atmosphere, or at 200-300 ˚C under a H₂ pressure of 20 to 100 at (1 at = 9.8 · 10⁴ Pa).

Another approach, which remains technically feasible for the moment, is to obtain...