A. A. Baikov Institute of Metallurgy and Materials Science, Moscow, Russia:

A. A. Palant, Leading Researcher
V. A. Bryukvin, Head of Laboratory
S. V. Palant, Research Engineer

Existing specifications provide the content of molybdenum in a finished ammonium paratungstate no more than 0.01%. However, during the accepted leaching of tungsten raw materials (even low-grade molybdenum), received solutions contain 60–150 g/l of WO₃ and till 1.0 g/l of Mo that defines necessity of their preliminary molybdenum removal. Extended process of sulphide purification of molybdenum of tungsten solutions less appropriate in this case because of the increased losses of W, filtration problems, etc. In this regard selectively extracting purification of tungstate sodium solutions (Na₂WO₄) of molybdenum impurities was studied, using Di-(2-ethylhexyl)phosphoric acid (DEHPA) and polyalkylphosphonitryl acid dissolved in kerosene as an extractants. Application of these reagents was defined by that (рН ~ 2) Mo (VI) is present generally in cation, W (VI) — in anion forms. Considering that in the acid environment W (VI) and Mo (VI) ions form the joint heteropolycomplexes decreasing a selective molybdenum extraction, process carried out at the increased temperatures promoting disintegration of these complexes and shifting balance to the left. It was shown the possibility of removal general molybdenum quantity (after standard precipitating arsenic treatment) from tungsten solutions with receiving ammonium paratungstate, containing <0.01% Mo on the basis of conducted experiments. The optimum extraction condition was determined: ~100 ^оC, рН = 1.5–2.0; ratio aqueous solution : organic phase = 1; 2 or 3 extraction stages. The removal of molybdenum to organic phase is more than ≥90%.

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