Photometric determination of phosphorus in ferrovanadium

Abstract

In order to determine phosphorus in ferrovanadium without separation of vanadium, a method which involves the extraction of phosphovanadomolybdic acid with methyl isobutyl ketone was presented. It was noticed that, in this method, arsenic which is usually only a minute component in ferrovanadium had an effect to give higher values, especially when the content of vanadium was so great in the sample solution. This effect was eliminated with the recommended procedure by adding a masking reagent for arsenic before the extraction or by removing arsenic itself.
(1) A sample containing 50±10 mg of vanadium was dissolved with 2ml of HNO₃ and 7ml of HClO₄ and fumed for a few minutes. The precipitate of vanadic acid was dissolved with about 30ml of water by gentle boiling. Five milliliters of 10% ammonium molybdate was added after cooling and the whole was diluted to about 50ml with water. After standing for 10 minutes, of sodium thiosulfate (4%, 67ml), organic acid or its salt such as citric acid (50%, 5ml) ammonium tartrate (25%, 10ml) or ammonium oxalate (4%, 10ml) as the masking reagent was added. Then it was extracted with 10ml of methyl isobutyl ketone. An immediate extraction after the addition was necessary when organic acid or its salt was used. The organic layer was then dry-filtered and the absorbance of the filtrate was measured at 420 mμ.
(2) A sample was dissolved with 12 ml of HNO₃ and 1ml of (1 : 1) H₂SO₄ and fumed for a few minutes. Ten milli liters of HCl and 2 ml of HBr were added and the mixture was evaporated nearly to dryness. Six milli liters of HClO₄ and about 30ml of water were added and the salt was dissolved by gentle holing with drops of H₂O₂ (30%) in order to oxidize vanadium. Then the procedure was carried through as above (1) without an addition of the masking reagent.
The methods were very rapid and the accuracy was within 3%.