[en] Dibutyl phosphoric acid zirconium salt (ZS HDBP) dissolved in 30% tributyl phosphate (TBP) is considered as an effective solvent for extraction of rare-earth (RE) and transplutonium elements (TPE) from nitric acid solutions. As nitric acid is one of the basic components of the system, investigation on its interaction with the solvent seems also to be useful. The spectra of Zr compounds with HDBP in organic phase showed presence of valence bonds not only between Zr and dibutyl phosphate ions, but also between Zr and nitrate ions at molar ratios R of 1:4 and 1:6 in the solvent (R = Zr:HDBP), while at R = 1:9 no bonds of the nitrate group coordinated to Zr atom were found in the spectra. Evidently, nitrate and dibutyl phosphate ions compete to occupy places in coordination sphere of Zr ion, and full replacement of nitrate by dibutyl phosphate occurs at a significant excess of HDBP. Afterwards nitrate ions were found in the organic phase only as components of extracted RE complexes. HNO₃ associated beyond the first coordination sphere of the extracted complexes is also of interest. The data show that in the absence of TBP in the system, HDBP extracts nitric acid very weakly at low and moderate acidity, while considerable extraction is observed only at aqueous phase acidity above 4 - 5 mole/L HNO₃. Zr influence on nitric acid extraction in the presence of TBP is of similar character. At low acidity, ZS-HDBP contribution to extraction of nitric acid is considerable, while HDBP alone depresses HNO₃ extraction, evidently, due to hydrogen bond formation to form HDBP-TBP. At higher acidity, to where HDBP begins to extract nitric acid, extraction of the latter by ZS-HDBP is less significant as comparable to that by TBP alone. (authors)