The article investigates the behaviour of rare earth metals in carbonate-alkaline systems. The results of experimental studies on rare earth element extraction from phosphogypsum, a large-tonnage industrial waste forming in production of phosphoric acid are presented. Using the liquid phase leaching method, it was possible to extract more than 53 % of rare earth elements from old phosphogypsum and more than 69 % from fresh phosphogypsum due to solid phase treatment with a 4 mol/l potassium carbonate solution at temperature 90 °C. The behaviour of model cerium (III) phosphate in a carbonate-alkaline medium is characterized: a solubility isotherm is obtained as well as the dependences of the degree of cerium extraction into solution on temperature, carbonate ion concentration, interphase ratio, stirring intensity, and pH. The ability of soluble rare earth element complexes to precipitate over time was established, which was confirmed using cerium and neodymium as an example. Within 240 h after the end of the experiment, approximately 25 % of cerium and 17 % of neodymium were precipitated from the liquid phase. A similar property was recorded in representatives of the light group and was not noted in elements of the heavy group. The ability to self-precipitate in future can serve as a basis for developing an alternative approach to separating rare earth metals into groups after extraction in a carbonate ion medium. Also, based on the analysis of experimental data, the mechanism of cerium (III) phosphate dissolution in a carbonate-alkaline medium was characterized. An assumption was made that rare earth metal phosphates dissolve sequentially passing into an insoluble carbonate and then into a soluble carbonate complex.
The low-quality petcoke does not find qualified application and is stockpiled at refineries or used as solid fuel. One of the promising ways to use low-quality petroleum coke is its physical or chemical activation in order to obtain a highly porous carbon material that can be used as a catalyst carrier, adsorbent, base for electrodes, etc. The possibility of using petroleum coke to produce sorbent for organic compounds was studied. The activated petroleum cake was obtained by chemical activation with KOH, a specific surface area is 1218 m2/g. Sorption of ethyl alcohol was studied at temperatures 285, 293 and 300 K. It is a physical process proceeding mainly in pores of activated petroleum coke, also sorption can be described as a reversible exothermic process. The effective Gibbs energy at a temperature of 293 K is –12.74 kJ/mol, the heat of sorption is –26.07 kJ/mol. The obtained data confirm that porous carbon material obtained from petroleum coke can be used as sorbent for ethanol at room temperature. For example, for adsorption of bioethanol from the effluent of the fermentation process or for purification of wastewater from organic compounds.
The study is devoted to the development of a method for the technogenic raw materials utilization. Special attention is paid to the prospect of involving products based on them in the production of new building materials. The results of Russian and foreign studies on the reuse of wastes, such as phosphogypsum, metallurgical slag, waste from municipal and industrial wastewater treatment, etc., in the building materials industry are considered. It has been established that the use of incinerated sewage sludge ash in construction is a promising direction in terms of environmental and economic efficiency. The research confirmed the compliance of the lightweight ash-based concrete components to the regulatory documentation requirements for a number of indicators. As a result of the research, the composition of the raw mixture for the lightweight concrete production with incinerated sewage sludge ash as a replacement for a part of the cement has been developed. In terms of parameters, the developed concrete corresponds to standard lightweight concrete, marked in accordance with the regulatory documents of the Russian Federation as D1300 (density not less than 1.3 g/cm3), Btb2 (flexural strength not less than 2 MPa), M200/B15 (compressive strength not less than 15 MPa). Lightweight ash-based concrete is suitable for use in construction, repair of roads and improvement of urban areas.
Treatment of apatite raw materials is associated with the formation of large-tonnage waste – phosphogypsum. The content of rare earth metals in such waste reaches 1 %, which makes it possible to consider it a technogenic source for obtaining rare earth metals and their compounds. Up to the present moment, there are neither processing plants, nor an efficient process flow to handle phosphogypsum dumps. It is rational to use a way that involves extraction of valuable components and overall reduction of phosphogypsum dumps. Such process flow is available with carbonate conversion of phosphogypsum to alkali metal or ammonium sulfate and calcium carbonate upon the condition of associated extraction of rare earth metal (REM) compounds. Associated extraction of REM compounds becomes possible since they form strong and stable complexes with hard bases according to Pearson, which among other things include carbonate, phosphate and sulfate anions. Formation of lanthanide complexes with inorganic oxygen-containing anions is facilitated by the formation of high-energy Ln-O bonds. The study focuses on the dissolution of lanthanide phosphates in carbonate media. It was established that formation of REM carbonate complexes from their phosphates is a spontaneous endothermic process and that formation of lanthanide carbonates and hydroxides serves as thermodynamic limitation of dissolution. A shift in equilibrium towards the formation of carbonate complexes is achieved by increasing the temperature to 90-100 °C and providing an excess of carbonate. The limiting stage of REM phosphate dissolution in carbonate media is external diffusion. This is indicated by increasing rate of the process with an intensification of stirring, first order of the reaction and the value of activation energy for phosphate dissolution from 27 to 60 kJ/mol. A combination of physical and chemical parameters of the process allowed to develop an engineering solution for associated REM extraction during carbonate conversion of phosphogypsum, which included a 4-5 h conversion of phosphogypsum at temperature of 90-110 °C by an alkali metal or ammonium carbonate solution with a concentration of 2-3 mol/l. As a result, a solution with alkali metal (ammonium) sulfate is obtained, which contains REMs in the form of carbonate complexes and calcium carbonate. The rate of REM extraction into the solution reaches no less than 93 %. Rare earth metals are separated from the mother liquor by precipitation or sorption on anion exchange resins, while the excess of alkali metal or ammonium carbonate is returned to the start of the process.
Population balance model is crucial for improving the method of aluminum hydroxide massive crystallization and enhancing the quality of control over industrial precipitation trains. This paper presents the updated population balance model, which can be used for simulation of industrial-scale precipitation. Processes of birth-and-spread and particle breakage are considered integral parts of the precipitation process along with secondary nucleation, growth and agglomeration of particles. The conceptual difference of the proposed system of equations is its ability to reproduce the oscillatory process that occurs in precipitation circuits as a result of cyclic changes in the quality of the seed surface. It is demonstrated that self-oscillations can occur in the system without any external influence. The updated model is adjusted and verified using historical industrial data. The simulation of seed-recycle precipitation circuit showed an exact correspondence between the calculated dynamic pattern of changes in particle size distribution of aluminum hydroxide and the actual data.
Equilibrium and non-equilibrium states of systems Na 2 O–Al 2 O 3 –H 2 O and K 2 O–Al 2 O 3 –H 2 O are crucial for establishing key technological parameters in alumina production and their optimization. Due to a noticeable discrepancy between experimental results and thermodynamic calculations based on materials of individual researchers the necessity of systematization and statistical processing of equilibrium data in these systems to create a reliable base of their physicochemical state, analysis and mathematical modeling of phase equilibria is substantiated. The tendency to a decrease of the hydration degree of solid sodium aluminates with increasing temperature and the transition of systems from the steady state of gibbsite to equilibrium with boehmite is revealed. The paper contains approximating functions that provide high-precision description of equilibrium isotherms in technologically significant area of Na 2 O–Al 2 O 3 –H 2 O and K 2 O–Al 2 O 3 –H 2 O concentrations. Approximating function can be simplified by dividing the isotherm into two sections with the intervals of alkaline content 0-0.25 and 0.25-0.4 mole/100 g of solution. The differences in solubility isotherms for Na 2 O–Al 2 O 3 –H 2 O and K 2 O–Al 2 O 3 –H 2 O systems provide are associated with changes in the ionic composition solutions that depends on concentration and temperature, as well as differences connecting with alkali cation hydration, which is crucially important for thermodynamic modeling of equilibria under consideration.
At the present time, the unique physical and chemical properties of rare earth metals (REM) mean they can find wide application in the metallurgy, mechanical engineering, avionics, petrochemical, laser and glass industries. In metallurgy, rare earth metals using for production of special grades of steel and cast iron. Adding REM can improve their mechanical properties: hardness, toughness, resistance to corrosion. REM are also used for the deoxidation of metals and alloys. The REM production technology from loparite concentrate that already exists in Russia is not enough for the metal-lurgical, oil, glass, ceramic, nuclear and military industries (just 2 % of the world’s REM are produced in Russia). REM for these industrial proposes is purchased in China, which is recog-nized as having a monopoly on the production of rare metals (96% of REM produced world-wide). If we want to supply these needs in future, we will have to produce 10 tons per year of REM, which requires processing all available resources: mono- and polymineral raw materials. One of the most acceptable source of rare earth metals and some rare metals (zirconium, niobium, hafnium) is eudialyte. The world’s biggest deposits of eudialyte are found on the Kola Peninsula in northwest Russia, near the Lovozero mining and processing plant. Eudialyte concentrate is easily decomposed by acids, which explains its layered structure and weak chemical bonds between its constituent groups. The easy leaching process is the main reason that it is processed. In our work the technological possibility of extraction and separation of lanthanides has been shown, using solutions of naphthenic and oleic acid in an inert diluent with a stoichiometric reagent consumption, without the preoxidation step of the cerium to the tetravalent state. The technological parameters and stages of the process have been established.
Experimental data on solvent extraction of lanthanum (III) and samarium (III) by solutions of naphthenic acid from nitrate medium was obtained. Dependences of distribution coefficient of pH, concentration of organic and aqueous phase was obtained. thermodynamic characteristics of extraction equilibrium was calculated.
Technology of solvent extraction and separation of cerium lanthanides by solutions of naphthenic acid in o-dimethylbenzene was obtained. The sequence of extraction Eu > Sm > Ce > La from nitrate media was calculated.
Experimental data on solvent extraction of lanthanum (III) and samarium (III) by solutions of naphthenic acid from nitrate medium was obtained. Dependences of distribution coefficient of pH, concentration of organic and aqueous phase was obtained. thermodynamic characteristics of extraction equilibrium was calculated.
The data on the extraction of aluminum and manganese by solution of oleic acid in o-xylene. The possibility of extraction separation of aluminum, manganese and cerium group lanthanides by solvent extraction from nitrate media.
Extraction of iron (III) from nitrate solutions by acid in 1,2-dymethilbenzine was investigated. Dependences of pH and distribution coefficient was obtained. Optimal iron (III) and REM separation conditions was acquired.
Experimental data on solvent extraction of cerium (III), yttrium (III), lanthanum (III) by solutions of oleinic acid in o-dimethylbenzene was obtained. The possibility of extraction sepa- ration of cerium(III), yttrium(III), lanthanum (III) from nitrate media was shown.
Experimental data on the solvate extraction of cerium(III) and yttrium(III) by solutions of oleic and naphthenic acids in o-dimethylbenzene were obtained. After mathematical analysis of the dependences of the distribution coefficient on pH and the composition of the organic and aqueous phases, the structure and composition of the solvate complexes were determined, as well as the values of Gibbs free energies and equilibrium constants of the reaction.
Data on the extraction of cerium(III) and yttrium(III) by naphthenic acid solution in o-xylene from chloride media were obtained. The experiment showed W-shaped dependence of the distribution coefficient of cerium(III) and yttrium(III) on the Cl content in the equilibrium aqueous phase. The minima of the dependence are explained by the formation of non-extractable complexes MeCl 2 +and MeOH 2 +, the maxima - by the increase in the degree of dissociation of naphthenic acid and the increase in the ionic strength of the solution.
The technology of obtaining zirconium oxide, zirconium halide compounds (chlorides, fluorides) from eudialyte concentrate with subsequent production of zirconium powders, titanium-zirconium and aluminum-zirconium ligatures by metal-thermal method has been investigated. It is shown that different zirconium materials can be obtained by applying different reducing agents: sodium, magnesium or aluminum-magnesium alloys.
The purpose of this research is to develop a new method of extraction and separation of rare earth metals, which will be effective in hydrometallurgical processes, i.e. in the processing of eudialyte concentrate. The task of the research is the experimental determination of distribution and separation coefficients in solvent extraction of rare earth metals from aqueous solutions with organic extractants, as well as the calculation of the extraction mechanism and thermodynamic constants on the basis of experimental data.
Extraction of cerium (3+) with tributyl phosphate was studied. The extraction constants were calculated from the dependences of the distribution coefficient on the concentration of salvent and extractant. According to their values, cerium salts are arranged in the series chloride < sulfate < nitrate corresponding to the Pearson reduction of the "hardness" of anions.
In order to calculate parameters of purification of soils from 90 Sr the exchange isotherm of Sr 2+ Ha cations of iron (III) between Cambrian clay and aqueous solution with pH = 3 was studied. Isotherms of joint cation adsorption in joint presence are described by the Langmuir equation. Using the values of the Langmuir constants, the Gibbs constant and energy of ion exchange equal to 15 and -6.7 kJ/mol, respectively, were calculated. These values coincide with those calculated from the individual adsorption isotherms of Sr 2+ and Fe (III) cations on clay. According to the obtained constants it is possible to deactivate soils from 90 Sr contamination by means of ion-exchange washing with solutions of iron (III) salts, which is confirmed by field studies in the 5th quarter of Vasilievsky Island. The performed technical-economic assessment of the decontamination of the 5th quarter shows that the washing cleaning will give an economic effect of about 150 million rubles compared to soil removal and burial.
It is experimentally proved that adsorption of Fe(3+) and Sr(2+) cations on Cambrian clay is described by the Langmuir isotherm. The adsorption limit is 0.026 and 0.034 mol/kg, respectively, and the capacity of the clay is 73±5 mEq/kg. The landing sites of cations are 38.0 and 28.6 Å 2 , respectively, and the radii of hydrated cations are 348 and 302 pm. The latter value agrees with the Stokes radius of 309 pm. The Langmuir constants are 731 and 294, respectively, and the distribution coefficients between the solid and liquid phases at rn = 3.0+3.5 are 27±4 and 10±1.8. The ion exchange constant for the reaction ½ Sr 2+ (s) + 1/3 Fe 3+ (aq) ↔ ½ Sr 2+ (aq) + 1/3 Fe 3+ (s) is 0.95. Based on the data obtained, it is feasible to clean the pounds from strontium-90 contamination by washing with a Fe(3+) salt solution. Field tests in the 5th quarter of Vasilievsky Island of St. Petersburg confirmed the conclusion. The initial specific radioactivity of the pound reached up to 1.07 10 -4 Ci/kg. At heap leaching the purification degree of 60% was obtained, in conditions of convective leaching 90%. A formula for calculating the conditions for obtaining a given degree of purification is proposed.
The content of rare-earth metals (REM) in Kola apatite is about 1%. In the production of concentrates over 8 million tons per year, more than 80 thousand tons of REM are dumped into waste dumps annually, polluting the environment. The main bulk of apatite is processed according to the sulfuric acid scheme to produce extractive phosphoric acids. To extract rare-earth metals from phosphoric acid streams with a capacity of 45 t/h, it is necessary to develop a process lasting several minutes, which does not affect the basic technology and does not require expensive costs of reagents. Crystallization of lanthanide combinations on inoculum directly from production solutions of extractive phosphoric acids meets the requirements. Another pressing problem is the purification of soils contaminated with heavy metals and radionuclides. In laboratory and natural conditions, the purification of soils from 90Sr contamination of the 5th quarter of Vasilievsky Island and Novozybkovsky district of the Bryansk region from 137Cs contamination has been studied. Among different methods of soil decontamination, the most cost-effective and suitable for large soil masses and large territories is soil washing with diluted solutions of mixtures of ammonium and iron (3+) salts. This method can also be used to clean soils from heavy metal contamination in mining regions.
