K2CO3 Melt Research Articles

Production of Al(HI)-K(I)-Ti(IV)-sulphate-containing leach liquor from metakaolinite-containing ash derived from South African coal fines

South African discard coal fines and K2CO3 blends were heated in a laboratory-scale rotary kiln to produce ashes for H2SO4 leaching tests. The optimized H2SO4 leaching conditions of 6.12 mol.dm3 (M) H2SO4, solid to liquid ratios 1:5 and 1:10, and 8o°C for 8 hours were used. K2CO3 was added to increase the dissolution efficiency of K. The objective was to determine if the Al present in metakaolinite (Al2O3.2SiO2), the Al, K, and Ti in the alumino-silicate glasses, and the Ti in rutile (TiO2) in the ashes could be selectively dissolved in H2SO4. XRF results show that the ashes formed at 700°C dissolved more efficiently (87% Al, 89% K and 23% Ti) compared to the ashes formed at 1050°C. This can be attributed to the presence of Al2O3.2SiO2, K2CO3 melt, K2CO3 remnants, KAl(SO4)2, and K-aluminosilicate glass in these ashes. XRD results indicate that the ashes prepared at 1050°C contained anorthite (CaAl^Og), microcline (KAlSi3O8), pseudomullite (Al2.SiO2), and silicon spinel (2Al2O3.3SiO2), which are either insoluble or only sparingly soluble in H2SO4. These minerals resulted in the lower dissolution efficiencies of Al and K. Based on the high dissolution efficiencies of Al and K for the ashes produced at 700°C, coal fines blended with K2CO3 could possibly be utilized as feedstocks for the production of aluminium(III), potassium(I), and titanium(IV) and a sulphate-containing leach liquor. Furthermore, the environmental issues and costs associated with the handling and disposal of large volumes of coal fines will also be resolved.

Investigation on the local structure and properties of molten Li2CO3-K2CO3 binary salts by machine learning potentials

In recent years, (LinK1-n)2CO3 binary melts have been investigated as the promising electrolyte matrixes of the fuel cell. Many researchers moved to the investigation of local structure and properties of the melts. In this paper, machine learning interatomic potentials were developed based on first-principle datasets in order to research the local structure and properties of molten (LinK1-n)2CO3 (n = 0.4,0.5,0.6) binary salts. The trained machine learning potentials, which enable similar accuracy relative to DFT and high efficiency, can yield precise descriptions of microstructure and macro properties of Li2CO3-K2CO3 binary melts. The information of the microstructure evolution was analyzed through partial radial distribution functions, coordination numbers and bond angle distribution functions. It is observed that lithium cation exhibits more stable coordination and destroys the C-O ion pairs. Further, comparing the inter-ionic partial radius distribution function diagrams of binary melts and those of pure Li2CO3 and K2CO3 melts, the changing regularities of interatomic strength and arrangement were obtained. Macro properties including density, self-diffusion coefficients, thermal conductivity and viscosity at target temperature range were calculated by the potentials and MD simulations. The temperature effect and concentration effect in properties were explored. This work exhibits a thorough understanding of the local structure and properties of Li2CO3-K2CO3 melts and reveals the accuracy of machine learning potentials on lithium-potassium melts for the first time.

Thermodynamic Analysis of Radioactive Graphite Oxidation in NiO-NaCl-KCl-Na2CO3-K2CO3 Melt in the Atmosphere of Argon


 
 
 Behavior of U, Pu radionuclides was investigated when heating radioactive graphite in NaCl – KCl – Na2CO3 – K2CO3 melt with NiO additives using the thermodynamic modeling method. Calculations were made by the TERRA software that is used for the determination of phase composition, thermodynamic and transport properties, taking into account chemical and phase changes in temperature range 373 – 3273 K. Calculation of equilibrium phase composition and parameters of equilibrium was carried out using reference information about properties of the individual substances (INVATERMO, HSC, etc.). This study demonstrates that at a temperature of 1273 K the condensed carbon burns down with the formation of CO and CO2. Increasing temperature to 1673 K causes the condensed compounds of uranium to evaporate. This study determined that uranium exists in the form of ionized UO−3 in temperature range from 1673 to 3273 K. Plutonium exists in the form of gaseous PuO2, PuO in temperature range 2373 – 3273 K.
 Keywords: thermodynamic modeling, radionuclides, radioactive graphite
 
 

Thermodynamic Analysis of the Oxidation of Radioactive Graphite in the CuO–NaCl–KCl–Na2CO3–K2CO3 Melt in Water Vapor

Graphite is widely used in the atomic industry and nuclear power engineering. In the next 10–15 years, the resource of most blocks in the uranium–graphite reactors in Russia will be exhausted with allowance for the elongation of the service life, as follows from the results of repair-and-renewal operations. High-activity graphite can be processed by flameless oxidation in molten salts. The purpose of this work is to study the behavior of radionuclides during the flameless oxidation of radioactive graphite in the CuO–NaCl–KCl–Na2CO3–K2CO3 melt in water vapor using a thermodynamic simulation and the Terra software package. A thermodynamic simulation is an effective and unique method used to investigate diverse high-temperature processes of thermal decomposition, reduction, and synthesis. The calculation is performed using a reference datable of the properties of individual substances. Graphite burns up at 573 K. The condensed compounds of cesium, chlorine, and uranium evaporate at 1673 K. An increase in the temperature to 1973 K leads to the vapor pressure of the condensed compounds of beryllium, calcium, and strontium. The condensed oxide of europium(III) and the condensed oxide of plutonium(IV) transform into a vapor state at 2173 K. The condensed oxide of nickel transforms into a vapor state at 2473 K. A further increase in the temperature to 2773 K leads to the transformation of the condensed oxide of americium(III) into a vapor state. Only a vapor–gas phase is present in the isolated system in the temperature range from 2773 to 3273 K.

Thermodynamic Analysis of the Oxidation of Radioactive Graphite in a Multicomponent Melt in an Inert Atmosphere

Graphite occupies a specific place among the entire mass of accumulated radioactive wastes. The problem of reclamation of spent graphite has not yet been solved in the world. The behavior of radioactive graphite in the multicomponent CuO–NaCl–KCl–Na2CO3–K2CO3 melt in an argon atmosphere in the temperature range 373–3273 K is studied by thermodynamic simulation with the Terra software package, which is intended for calculating the phase compositions and the thermodynamic and transport properties of arbitrary systems. The calculation was performed using a database on the properties of individual substances. At 1273 K, graphite burns to form carbon monoxide and carbon dioxide. The condensed compounds of cesium, chlorine, and uranium evaporate at 1573 K. An increase in the system temperature to 1873 K leads to the vapor pressure of condensed nickel. Condensed strontium oxide transforms into a vaporized state at 2273 K. The condensed compounds of plutonium, calcium, and europium transforms into a vaporized state at 2373 K. Condensed beryllium oxide evaporates at 2473 K. A further increase in the temperature to 2673 K leads to the evaporation of condensed americium(III) oxide. Only a vapor–gas phase is present in the isolated system in the temperature range 2673–3273 K.

Surface graphitization of diamond in K2CO3 melt at high pressure

Surface graphitization of diamond is a chemical catalytic process, in contrast to bulk graphitization, a physical process of diamond/graphite polymorphic transition. Both processes occur at P–T parameters of graphite thermodynamic stability. The boundary tem� perature between these two processes in a vacuum, i.e., at low values of oxygen partial pressure, is 1600– 1700°C [1, 2]. Because of this, surface graphitization

Electrochemical deposition of carbon films on titanium in molten LiCl–KCl–K2CO3

Electrodeposition of carbon films on the oxide-scale-coated titanium has been performed in a LiCl–KCl–K2CO3 melt, which are characterized by scanning electron microscopy, Raman spectroscopy and X-ray diffraction analysis. The electrochemical process of carbon deposition is investigated by cyclic voltammetry on the graphite, titanium and oxide-scale-coated titanium electrodes. The particle-size-gradient carbon films over the oxide-scale-coated titanium can be achieved by electrodeposition under the controlled potentials for avoiding codeposition of lithium carbide. The deposited carbon films are comprised of micron-sized ‘quasi-spherical’ carbon particles with graphitized and amorphous phases. The cyclic voltammetry behavior on the graphite, titanium and oxide-scale-coated titanium electrodes shows that CO32− ions are reduced most favorably on the graphite for the three electrodes. Lithium ions can discharge under the less negative potential on the electrode containing carbon compared with titanium electrode because of the formation of lithium carbide from the reaction between lithium and carbon.

Lead Recovery from PbO, PbCl2 , PbS, PbSO4 , and Their Mixtures in Carbonate Melts

The reduction (with and without carbon) of PbO, PbCl2 , PbS, PbSO4 , and their mixtures in Na2CO3 and K2CO3 melts was studied by thermodynamic modeling and experimentally.

Corrosion protection of steel in molten Li2CO3–K2CO3 and Na2CO3–K2CO3 mixtures in a hydrogen-containing atmosphere

The electrochemical behaviour of TiN-, TiN–AlN-, Cr- and CrN-coated 316L stainless steel in molten Li2CO3–K2CO3 and Na2CO3–K2CO3 melts in a reducing gaseous atmosphere (10% H2–90% N2) was studied using voltammetry and scanning electron microscopy combined with energy-dispersed X-ray analysis in the temperature range of 600–730 ∘C. To facilitate the identification of the electrochemical reactions the voltammetric behaviour of stainless steel, titanium, nickel and gold was also investigated. Voltammetric characteristics obtained at AlN–TiN coated electrodes showed no anodic reactions at potentials more negative than that of CO2−3 oxidation. Cr- and CrN-coated electrodes demonstrated a suppressed anodic dissolution after the first steady state voltammetric cycle. The voltammograms obtained for the other electrodes studied displayed the corresponding anodic metal-dissolution waves. TiN, AlN, Cr and CrN coatings seem to be the most promising as corrosion-resistant materials for the anodic compartments of molten carbonate fuel cells.

Electrodeposition of cohesive carbon films on aluminum in a LiCl-KCl-K2CO3 melt

Electrodeposition of carbon on an aluminum electrode was studied in a LiCl–KCl–K2CO3 melt. A cyclic voltammogram for an aluminum electrode indicates that the cathodic current is due to the reduction of CO3 2− ions. Carbon films on aluminum substrates were obtained by potentiostatic electrolysis, and the cohesiveness of the films depended on the potential. SEM observations showed that the morphology of the deposited carbon film depends on the electrolytic conditions. Raman spectroscopy, XPS and XAES measurement showed that the film consisted of carbon in the sp2 state.

Corrosion and strength degradation of sintered ?-SiC in K2CO3 melts

Corrosion and strength degradation of sintered ?-SiC in K2CO3 melts

Ｓｉ３Ｎ４セラミックスのアルカリ溶融塩腐食による強度劣化

Si3N4-based ceramics such as hot isostatically pressed Si3N4, hot pressed Si3N4, and hot pressed sialons containing 0, 30, 60 and 100% of α phase were corroded by K2SO4 and K2CO3 melts at 1150-1300°C and 925-1150°C, respectively. The surface reaction-controlled shrinking core model adequately described the relationship between the weight loss of the specimen and the time for the corrosion reactions in both K2SO4 and K2CO3 melts. The corrosion rate in K2CO3 melts decreased with increasing the content of Al and Y ions in the specimens. The fracture strength of the specimens corroded by K2SO4 and K2CO3 melts degraded to 2/3-2/5 of the original values before lossing 2% of its weight, and then became almost constant up to 30% of weight loss.

Corrosion and strength degradation of Si3N4 and sialons in K2CO3 and K2SO4 melts

Si3N4-based ceramics, such as hot isostatically pressed Si3N4, hot-pressed Si3N4, hot-pressed sialons containing 0, 30, 60 and 100% a phase, were corroded by K2SO4 and K2CO3 melts at 1150 to 1300 and 925 to 1150° C, respectively. The surface chemical reaction-controlled shrinking core model adequately described the relationship between the weight loss of the specimen and time for the corrosion reactions in both K2SO4 and K2CO3 melts, and the apparent activation energies were 380 to 608 and 157 to 344 kJ mol−1, respectively. The corrosion rate in K2CO3 melt decreased with increasing content of aluminium and yttrium ions in the specimens, but no systematic relation was observed for the reaction in K2SO4 melts. The fracture strength of the specimens corroded by K2SO4 and K2CO3 melts degraded to 2/3 to 2/5 of the original values up to a 2% weight loss, and then was almost constant up to 30% weight loss.

Zur Kenntnis der Kaliumthiochromite

KCrS2, KCr5S8 and the new compound KCr3S5 were prepared by the reaction of H2S with chromium in K2CO3 melts. KCr3S5 (space group C2/m,a=19.16 A,b=3.49 A,c=12.02 A, β=123.0°) is isotypic with TlCr3S5 having a psilomelane like channel structure. The thermal degradation: $$KCrS_2 \xrightarrow{{ - K_2 S}}KCr_3 S_5 \xrightarrow{{ - K_2 S}}KCr_5 S_8$$ was studied and the topochemical relations between the products are discussed.