A. I. Nikolaev

Extraction of tantalum, niobium, and antimony fluorides

This report deals with the effects of the HF and H2SO4 concentrations and the organic-to-aqueous phase ratio Vorg: Vaq on the distribution of Ta, Nb, and Sb in their extraction with tributyl phosphate and n-octanol from model solutions that are similar in composition to those obtained in columbite-tantalite processing. The recovery of these elements decreases in the order Ta ≫ Sb ≥ Nb. Process conditions for efficient separation of Ta from Nb and Sb have been found.

Application of titanium-containing sorbents for treating liquid radioactive waste with the subsequent conservation of radionuclides in Synroc-type titanate ceramics

New nanocrystalline titanium-containing sorbents, namely, layered hydrazinium titanate LHT-9, (N2H5)0.5Ti1.87O4 and synthetic ivanyukite-Na Na2K[Ti4(OH)O3(SiO4)3] · 7H2O, possess high sorption capacity towards cations of different valences and, due to their high chemical stability in acidic and alkaline media, provide the purification of liquid radioactive waste of any composition. The calcination of the product of the radionuclide sorption on LHT-9 and ivanyukite at 1000–1200°C yields mineral-like Synroc-type titanate ceramics applicable for long-term immobilization of sorbed radionuclides with a significant (by 17–250 times) decrease in the amount of radioactive waste.

Utilization of waste containing rare-earth elements

The sulfuric acid method of dissolving metallic waste containing rare-earth elements and iron with the obtainment of a sulfate rare-earth concentrate and an iron-containing solution is described. The distribution of the components into solid and liquid reaction products has been studied. The conditions of the conversion of rare-earth sulfate elements into hydroxide and fluoride compounds have been found. The principal possibility of utilizing iron-containing sulfuric acid filtrates with the obtainment of iron oxide pigments of a wide range of colors, catalysts, and coating components of welding electrodes is shown.

Interaction of loparite concentrate with ammonium hydrodifluoride

Results obtained in a study of the interaction between the loparite concentrate and ammonium hydrodifluoride are reported. It was found that the reactions of the main components of the concentrate with NH4HF2 yield complex ammonium fluorometallates. It was shown that water leaching of the fluorinated product makes it possible to transfer niobium and tantalum into solution together with fluoroammonium salts of titanium and silicon and to concentrate rare-earth elements in the insoluble residue in the form of complex salts of general formula NaLnF4.

Synthesis of the new nano-porous titanosilicates using ammonium oxysulphotitanite

In the last years the interest in new synthetic and natural titanosilicates has increased. Due to the tunable pore diameter and other distinct characteristics, these materials can be utilized for commercially important separations of gas mixtures of similar size molecules, catalysts and removal of radioactive elements from nuclear waste. However, from the point of view of industrial synthesis, scale-up complicated technology and high cost of the agents are limiting factors, hence it is of interest to research new materials to replace expensive pure titanium precursors and stimulate studies to develop an efficient technology. The results of synthesis of the new nanoporous titanosilicates using cost efficient ammonium oxysulphotitanate are presented. By carefully selecting the titanium sources and synthesis parameters, it is possible to obtain titanosilicate Na2K(Ti4(OH)(SiO4)3 analogue of the mineral pharmacosiderite.

Preparation of concentrated alkali solutions of niobium

Concentrated alkali solutions of niobium containing up to 238 g/L of Nb2O5 have been obtained by sintering of Nb2O5 with K2CO3 · 1.5 H2O. These solutions are recommended for use in the production of welding and other functional materials.

Solid-Phase Synthesis in the Technology of Functional Materials Based on Titanium(IV)

A study was made of structural, morphological, and chemical transformations in solid-phase systems based on sulfate, oxide, and hydroxide compounds of titanium(IV) under the intense mechanical activation of solid particles. This enabled one to substantiate the phase formation mechanism initiated by the intense homogenization of the reaction mixture, which is accompanied by a decrease in the particle size, deformation of the particle structure, and the formation of a new active surface. The obtained results formed the physicochemical basis for developing an innovative nonwaste technology for producing a new grade of titanium dioxide in the rutile modification from titanium sulfate salt under a program performed by the Roscosmos State Corporation for Space Activities.

Processing of perovskite concentrate by ammonium hydrodifluoride

The results of studies of the hydrodifluoride leaching of the perovskite concentrate have been presented. It has been shown that processing the perovskite concentrate using fluoride technology enables one to transform niobium and tantalum into a solution, along with fluoroammonium salts of titanium, iron, and silicon, and to isolate rare-earth elements in the form of complex fluoroammonium salts mixed with CaF2 within a few stages.

REE formation in hydrodifluoride processing of the perovskite concentrate

The results of studies of the distribution and forms of existence of rare earth elements in hydrodifluoride leaching of the perovskite concentrate have been presented. It has been established that, in the course of concentrate fluorination, rare earth elements form complex fluoroammonium salts. It has been shown that processing the perovskite concentrate using the fluoride technology enables one to extract 82 of rare earth elements and to obtain a concentrate of rare earth elements that contain oxides with admixtures of fluorides in a few stages.

Extraction of antimony and niobium with tributyl phosphate from fluoride-ammonium solutions

The purification of niobium from antimony impurity via extraction with tributyl phosphate from solutions of the HF + NH4F mixture has been studied. It has been established that at an HF + NH4F content equal to 7–16 mol/L and an NH4F concentration of 30% in the mixture, Sb extraction hardly changes (70–80% for one stage), and Nb coextraction abruptly decreases to values of less than 0.5%.