Extraction of molybdenum from nitric acid solutions with solutions of dibutyl hydrogen phosphate zirconium salt

The extraction of Mo with a solution of dibutyl hydrogen phosphate (HDBP) zirconium salt (ZS) in xylene and in TBP-xylene and TBP-decane mixtures was studied in comparison with the Mo extraction in similar systems without Zr. The Mo extraction is enhanced to the largest extent (by a factor of 7 with 1.5 M HNO3) at the HDBP: Zr ratio of 12, but the majority of experiments were performed at the ratio HDBP: Zr = 9, characteristic of the extraction of TPE and REE. The plots of DMo vs. HNO3 concentration in all the cases pass through a minimum at ∼3 M HNO3, and the minimum is the deeper, the higher the TBP concentration. At the same time, in the system with HDBP ZS at the TBP concentration in the solvent exceeding 50%, further decrease in DMo is not observed. The dependence of the Mo distribution ratio DMo on the HDBP concentration at a fixed ratio HDBP: Zr = 9, the composition of the saturated systems, and the spectra of the saturated and unsaturated (with respect to Mo) systems suggest formation of mixed HDBP-Zr-Mo complexes. Assumptions concerning their composition and structure were made. According to the IR data, in these complexes in the absence of TBP the nitrate ion is not coordinated to the Mo atom. Bridged structures Mo-O-Mo are not formed either. Addition of TBP leads to a decrease in DMo in the extraction with HDBP ZS, but, at the same time, the slope of the dependence of DMo on the HDBP concentration increases, and the limiting capacity of the solvent for Mo also somewhat increases. These effects are primarily attributed to an increase in the HNO3 concentration in the organic phase in the presence of TBP.