Extraction of Mo from solutions in HNO3 and other mineral acids with solutions of dibutyl hydrogen phosphate in a diluent

Abstract

Extraction of Mo from HNO3 solutions with solutions of HDBP in xylene and CCl4 in a wide range of Mo concentrations was studied. The Mo distribution ratios are considerably higher with CCl4 diluent compared to xylene, but the extractant capacity in both cases is the same and corresponds to the ratio HDBP: Mo = 2. The active species in the Mo extraction is the HDBP dimer. In the first step, an acidic molybdenyl salt with HDBP of the composition MoO2(DBP)2(HDBP)2, exhibiting certain secondary extraction properties toward rare-earth elements, is formed in all the cases. The dependence of the Mo extraction on the aqueous solution acidity passes through a minimum at 3–4 M HNO3. The subsequent increase in the Mo distribution ratios is associated with the simultaneous extraction of HNO3 (or nitrate ion) whose concentration in the extract is considerably lower than the Mo concentration. With an increase in the loading of the extract with molybdenum, the acidic molybdenum salt of HDBP undergoes restructurization, probably associated with additional coordination of H2MoO4 to it. The dependence of the Mo distribution ratio on the acid concentration in the extraction from sulfuric acid solutions passes through a minimum at 3–4 M H2SO4, which correlates with the first step of the acid dissociation, and in the extraction from HClO4 the dependence passes through a minimum and a maximum. In the extraction from hydrochloric acid solutions, the Mo extractability decreases with an increase in the acid concentration, owing to complexation in the aqueous phase. The nature of processes occurring at various loadings of the extract with molybdenum are discussed.