in water Electrolysis; electrolyzing aq. soln. of FeSiF6 with addn. of either alkali, manganese, alkaline earth sulfate, -fluoride, -chloride, or HF at 70 to 80°C, current density 2 to 3 A/dm^2, bath potential 0.25 to 0.35 V, anodes made of various iron materials;;