Electrochemical mechanism of electrolysis codeposition of Mg-Sr alloy in molten salt

The electrochemical process of Mg-Sr codeposition was studied in MgCl2-SrCl2-KCl melts containing different MgCl2 concentrations at 700 ℃ by cyclic voltammetry, chronopotentiometry and chronoamperometry. The results show that the actual precipitation potential of Sr reduces by nearly 0.5 V because of the depolarization effects of Sr activity reduced by forming Mg-Sr alloy. The codeposition potential condition of Mg and Sr to form Mg-Sr alloy is as follows： When electrode potential is more negative than -1.5 V, the magnesium will precipitate; when electrode potential is more negative than -2.0 V, the magnesium and strontium will both deposit. The control step of codeposition process of Mg and Sr is not diffusion control step. The codeposition current condition of Mg and Sr to form Mg-Sr alloy by chronoptentiometry is as follows： cathode current densities are higher than 0.71, 1.57 and 2.83 A/cm^2 in MgCl2-SrCl2-KCl melts with MgCl2 concentrations of 2%, 5% and 10% （mass fraction）, respectively. Key words：

Hydrogenation reaction of metallic titanium prepared by molten salt electrolysis

The hydrogenation reaction of electrolyzed titanium, as the first step during hydrogenation-dehydrogenation for the preparation of titanium powder, was studied. The titanium hydride was prepared through the reaction between electrolyzed titanium and hydrogen at different hydrogenation temperatures and different time. The evolutions of hydrogen and oxygen contents, density, hardness and phase composition before and after hydrogenation were characterized under different hydrogenation conditions. The results show that the main phases of titanium hydride were TiHl.924, TiH1.971 and TiH2. Increasing the hydrogenation temperature could not enhance the hydrogen content but increase the oxygen content. The effect of the hydrogenation time on the hydrogen content was not obvious. The optimal parameters of the hydrogenation process were obtained： beating at 400℃ and holding for 2 h, by which the hydrogen content of 3.63% and oxygen content of 0.18% （mass fraction） can be obtained. In addition, the microstructure, orientations and tissues of electrolyzed titanium and titanium hydride were detected.

Thermodynamic analysis on the direct preparation of metallic vanadium from NaVO_3 by molten salt electrolysis

A novel and environmentally friendly route to directly prepare metallic vanadium from NaV03 by molten salt electrolysis is proposed. The feasibility about the direct electro-reduction of NaV03 to metallic vanadi- um is analyzed based on the thermodynamic calculations and experimental verifications. The theoretical decomposition voltage of NaV03 to metallic vanadium is only 0.47 V at 800 ℃ and much lower than that of the alkali and alkali earth metal chloride salts. The value is slightly higher than that of low-valence vanadium oxides such as V203, V305 and VO. However, the low-valence vanadium oxides can he further electro-reduced to metallic vanadium thermodynamically. The thermodynamic analysis is verified by the experimental results. The direct preparation of metallic vanadium from NaV03 by molten salt electrolysis is feasible.

Recovery and separation of Fe and Mn from simulated chlorinated vanadium slag by molten salt electrolysis

Tailings from the vanadium extraction process are discarded each year as waste,which contain approximately 30 wt%of Fe.In our previous work,we extracted Fe and Mn from vanadium slag,and Fe and Mn existed in the form of FeCl_(2) and MnCl_(2) after chlorination by NH_(4) Cl to achieve effective and green usage of waste containing Fe and Mn.In this work,square wave voltammetry(SWV)and cyclic voltammetry(CV)were applied to investigate the electrochemical behaviors of Fe^(2+)and Mn^(2+)in Na Cl-KCl melt at 800℃.The reduction processes of Fe^(2+)and Mn^(2+)were found to involve one step.The diffusion coefficients of FeCl_(2) and Mn Cl_(2) in molten salt of eutectic mixtures Na Cl-KCl molten salt were measured.The electrodeposition of Fe and Mn were performed using two electrodes at a constant cell voltage.The Mn/Fe mass ratio of the electrodeposited product in Na Cl-KCl-2.13 wt%FeCl_(2)-1.07 wt%Mn Cl_(2) was 0.0625 at 2.3 V.After the electrolysis of NaCl-KCl-2.13 wt%Fe Cl_(2)-1.07 wt%MnCl_(2) melted at 2.3 V,the electrolysis was again started under 3.0 V and the Mn/Fe mass ratio of the electrodeposited product was 36.4.This process provides a novel method to effectively separate Fe and Mn from simulated chlorinated vanadium slag.

Preparation of Mg-Li alloys by electrolysis in molten salt at low temperature

A new technology for preparation of low cost Mg-Li alloys was studied. The alloys were prepared by electrolysis in molten LiCl-KCl （weight ratio is 1：1） electrolyte with Mg rod severing as the consumed cathode. Main factors that affect current efficiency were investigated, and optimal electrolysis parameters were obtained. Mg-Li alloys with low lithium Content （about 25%） were prepared by the unique method of a higher post-thermal treatment temperature after electrolysis at low temperature. The results showed that the electrolysis can be carried out at low temperature, which resulted in reducing preparation cost due to energy saving. The new technology for the oreoaration of Mg-Li alloy by electrolysis in molten salt was laroved to be feasible.

U(VI) adsorption behavior onto polypyrrole coated 3R-MoS2 nanosheets prepared with the molten salt electrolysis method

To improve the separation capacity of uranium in aqueous solutions, 3R-MoS2 nanosheets were prepared with molten salt electro- lysis and further modified with polypyrrole (PPy) to synthesize a hybrid nanoadsorbent (PPy/3R-MoS2). The preparation conditions of PPy/3R- MoS2 were investigated and the obtained nanosheets were characterized with scanning electron microscope (SEM), high resolution transmis- sion electron microscope (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectro- scopy (XPS). The results showed that PPy/3R-MoS2 exhibited enhanced adsorption capacity toward U(VI) compared to pure 3R-MoS2 and PPy;the maximum adsorption was 200.4 mg/g. The adsorption mechanism was elucidated with XPS and FTIR: (1) negatively charged PPy/3R-MoS2 nanosheets attracted by an electrostatic interaction;(2) exposed C, N, Mo, and S atoms complexed with U(VI) through co- ordination;(3) Mo in the complex partly reduced the adsorbed U(VI) to U(IV), which further regenerated the adsorption point and continu- ously adsorbed U(VI). The design of the PPy/3R-MoS2 composite with a high adsorption capacity and chemical stability provides a new direc- tion for the removal of radionuclide.

Measurement on Physicochemical Properties ofNaCl-KCl-ScCl_3 System for Manufacture of Al-Sc Alloy by Molten Salt Electrolysis

The physicochemical properties of the system, such as density, surface tension, specific conductance and melting point were measured. The results were discussed.

Preparation of Master Alloy Cu－Sr by Molten Salt Electrolysis with Copper Consumable Cathode

The influence of electrolyte composition and temperature. cathodie current density as well as someadditives on preparation process of alloy Cu-Sr by molten salt electrolysis with consumable cathode was stu-died in laboratory. Under optimum conditions determined experimentally. the current efficiency amountedto 70% and the master alloy contained 61% Sr After vacuum distillation or the cathodic product, metallicSr of 98% purity was obtained.

Annihilating the Formation of Silicon Carbide:Molten Salt Electrolysis of Carbon-Silica Composite to Prepare the Carbon-Silicon Hybrid for Lithium-lon Battery Anode

Silicon(Si)and carbon(C)composites hold the promise for replacing the commercial graphite anode,thus increasing the energy density of lithium-ion batteries(LIBs).To mitigate the formation of SiC,this paper reports a molten salt electrolysis approach to prepare C-Si composite by the electrolysis of C-SiO2 composites.Unlike the conventional way of making a C coating on Si,C-SiO2 composites were prepared by pyrolyzing the low-cost sucrose and silica.The electrochemical deoxidation of the C-SiO2 composites not only produces nanostructured Si inside the C matrix but also introduces voids between the C and Si owing to the volume shrinkage from converting SiO2 to Si.More importantly,the use of Mg ion-containing molten salts precludes the generation of SiC,and the electrolytic Si@C composite anode delivers a capacity of about 1500 mAh g-1 after 100 cycles at a current density of 500 mA g-1.Further,the Si@C‖LiNi0.6Co0.2Mn0.2O2 full cell delivers a high energy density of 608 Wh kg-1.Overall,the molten salt approach provides a one-step electrochemical way to convert oxides@C to metals@C functional materials.

CO-DEPOSITION OF Li(Ⅰ)WITH RE(Ⅲ)AND ITS APPLICATION IN THE PRODUCTION OF Al-Li-Cu-RE ALLOY BY MOLTEN SALT ELECTROLYSIS

The possibility of co-deposition of Li(Ⅰ)and RE(Ⅲ)has been estimated by both theoretical analysis and experimental study on the influences of temperature and concen- tration of chloride on the deposition potential.Both the electrochemical and electrolytic results clearly show that Li(Ⅰ)and RE(Ⅲ)can co-deposit on the Al-Cu electrode under selected conditions.

Overview of CO_(2) capture and electrolysis technology in molten salts: operational parameters and their effects

Carbon capture and storage(CCS)technology is believed to be a promising solution for global CO_(2) emission control and climate change.However,the application of CCS projects is facing a dilemma due to their negative cash flow.To address the challenge,it is critical to adopt an innovative technology that can capture and convert CO_(2) simultaneously with satisfying efficiencies and can make a profit for the end users.Recently,molten salt CO_(2) electrolysis that splits CO_(2) into carbon and oxygen has been extensively studied.This study reviews the process mechanisms,the salt selection,and the effects of operating conditions,including temperature and voltage.In most reported articles,the CO_(2) to carbon conversion efficiency reached at least 80%,and the current efficiency is over 90%,proving the promising potential of the molten salt CO_(2) electrolysis method.Still,some aspects,such as the impurities'influences and electrode corrosion,have not been thoroughly investigated.Therefore,some suggestions are recommended for future work.

Electrical conductivity of NaF-AlF_3-CaF_2-Al_2O_3-ZrO_2 molten salts

The electrical conductivity of NaF-AlF3-CaF2-Al2O3-ZrO2 system was studied by a tube-type cell with fixed cell constant. The results show that the electrical conductivity of NaF-AlF3-3%Al2O3-3%CaF2-ZrO2 molten salt system decreases with increase of ZrO2 content in an interval of 0-5%. The increase of 1%ZrO2 results in a corresponding electrical conductivity decrease of 0.02 S/cm, and the equivalent conductivity increases with the increase of molar ratio of NaF to AlF3. When the temperature increases by 1 °C, the electrical conductivity increases by 0.004 S/cm. At last, the regression equations of electrical conductivity relative to temperature and ZrO2 are obtained by quadratic regression analysis.

Valence states, impurities and electrocrystallization behaviors during molten salt electrorefining for preparation of high-purity titanium powder from sponge titanium

High-purity titanium powder was prepared by molten salt electrorefining from sponge titanium in NaCl-KCl-TiClx salts. The titanium valence, purity and electrocrystallization during electrolysis process were studied. The XPS analysis showed that the titanium valences are mainly ＋4, ＋3 and ＋2 at the earlier, medium and later stages of electrolysis, respectively. During the electrolysis process, the contents of impurities Si, Cr, Mn, Al vary little, and the contents of impurities Fe, Cu, Ni decrease markedly, while the contents of impurities O, N, H increase obviously. The residual impurities are usually distributed in small tunnel of dendritic crystals. Enhancing the electrolysis temperature and prolonging the electrolysis time can increase the titanium particle size. The TEM analysis showed that the electrodeposited titanium is not a single crystal, but contains many nanostructured grains and subgrains, with grain size of 100-500 nm. The electrolysis mechanisms were also discussed.

Electrolytic production of Cu-Ni alloys in CaCl_2-Cu_2S-NiS molten salt

An alternative metal/alloy production method,known as direct electrochemical reduction(DER),was introduced for the fabrication of CuNi alloys from mixed sulfides(Cu2S,NiS)under both galvanostatic and potentiostatic conditions.The influences of the process parameters(e.g.,cell voltage and current)on the compositions of the reduced compounds were investigated to yield industrially desirable alloys,namely,CuNi10,CuNi20,and CuNi30.The electrochemical behaviors of Cu2S and NiS in CaCl2 melt were examined at a temperature of 1200°C via cyclic voltammetry(CV).Based on the CV results,the cathodic reduction of Cu2S occurred in one step and cathodic reductions of NiS occurred in two steps,i.e.,Cu2S?Cu for copper reduction and NiS?Ni3S2?Ni for nickel reduction.Galvanostatic studies revealed that it was possible to fabricate high-purity CuNi10 alloys containing a maximum sulfur content of 320×10-6 via electrolysis at 10 A for 15 min.Scanning electron microscopy along with energy-dispersive X-ray spectrometry and optical emission spectroscopy(OES)examinations showed that it was possible to fabricate CuNi alloys of preferred compositions and with low levels of impurities,i.e.,less than 60×10-6 sulfur,via DER at 2.5 V for 15 min.

Towards a sustainable technology for production of extra-pure Ti metal:Electrolysis of sulfurized Ti(C,N)in molten CaCl_(2)

A new concept for producing highly pure Ti metal powder from ilmenite(FeTiO)_(3))is proposed in this article.Titanium nitride(TiN)or titanium oxycarbonitride(TiO_(x)C_(y)N_(z))could be synthesized in the first step via the simultaneous carbothermal reduction and nitridation(CTRN)of FeTiO3 to remove oxygen roughly.To separate oxygen completely,high-quality TiS2 samples were then synthesized from TiN and TiC using S2 gas,and the clean sulfides were finally reduced toα-Ti powders with spherical morphology using electrolysis in molten CaCl_(2).Xray diffraction(XRD),scanning electron microscopy(SEM)in conjunction with energy-dispersive X-ray spectroscopy(EDS),and elemental LECO analysis were used to study the phases and microstructures of the sulfides and the electrochemically reduced powders.The Ti powder showed no carbon contamination and consisted of high-purity foil-like Ti sheets with very low oxygen,carbon,and nitrogen contents of less than 0.15 wt%O,0.02 wt%C,and 0.003 wt%N,respectively.The quality of the Ti powder was much higher than that of the powder obtained using the conventional OS process(proposed by K.Ono and R.O.Suzuki)starting directly from the oxides.

Electrolysis of Magnesia from Bischofite in Qinghai Salt Lakes

A new technique of magnesia electrolysis from bischofite in Qinghai salt lakes was investigated experimentally. Magnesia was prepared by ammonia processing. On an electrolysis cell of about 100 A capacity at 700degreesC, magnesium metal was obtained with a current efficiency of 90.23% and a specific energy consumption of 11.5 kW(.)h. The new technique has the advantages of energy saving, high current efficiency and environmental amity.

Enhanced preparation of dendritic metallic vanadium in recyclable NaCl-KCl-VCl_(2) molten salt by V_(2)CO electrolysis

A promising method for the preparation of pure metallic vanadium via V_(2)CO anode electrolysis was proposed and confirmed.The simple and controllable synthesis of a molten chloride salt containing VCl_(2) by an insitu reaction between VCl_(3) and metallic vanadium was verified through thermodynamic analysis and experiments.NaCl-KCl-VCl_(2) molten salt exhibited excellent recycling performance and could be repetitively used to prepare metallic vanadium by V_(2)CO electrolysis.The V^(2+) ions remained in the molten salt after electrolysis.The electrolysis conditions,such as the cathode diameter,current density,V^(2+) ion concentration,and temperature,were optimised to maximise the current efficiency.Electrolysis was also simulated to reveal the regulatory mechanism.The highest current efficiency was 85%.The purity of metallic vanadium was up to 99.8%.In this study,an easy and efficient preparation of pure metallic vanadium was achieved.

Optimal V_(2)O_(3) extraction by sustainable vanadate electrolysis in molten salts

Recently,an environmentally friendly electrolysis process of soluble vanadates is proposed and successfully confirmed for V_(2)O_(3) extraction.In this paper,the solubilities of various vanadates(i.e.NaVO_(3),Na_(4)V_(2)O_(7) and Na_(3)VO_(4))in NaCl molten salt are measured.The dependences of V_(2)O_(3) extraction on vanadate form,anode material and molten salt system are studied.A long-term electrolysis is carried out.The result indicates that the solubilities of all vanadates are high and meet electrolytic requirements.Compared to Na_(4)V_(2)O_(7) and Na_(3)VO_(4),NaVO_(3) exhibits larger current efficiency and lower electricity consumption.By using SnO_(2) anode instead of graphite anode,the current efficiency of NaVO_(3) electrolysis can be increased to 58.1%and carbon pollution is avoided at 700℃.The extraction rate of V_(2)O_(3) reaches 81.3%after long-term electrolysis of 51 h.This work optimizes the electrochemical preparation process of V_(2)O_(3) from various vanadates and contributes to the improvement of current efficiency and extraction rate.

Direct electrochemical N-doping to carbon paper in molten LiCl-KCl-Li3N

Graphite materials are widely used as electrode materials for electrochemical energy storage.N-doping is an effective method for enhancing the electrochemical properties of graphite.A novel one-step N-doping method for complete and compact carbon paper was proposed for molten salt electrolysis in the Li Cl-KCl-Li3 N system.The results show that the degree of graphitization of carbon paper can be improved by the electrolysis of molten salts,especially at 2.0 V.Nitrogen gas was produced at the anode and nitrogen atoms can substitute carbon atoms of carbon paper at different sites to create nitrogen doping during the electrolysis process.The doping content of N in carbon paper is up to 13.0 wt%.There were three groups of nitrogen atoms,i.e.quaternary N(N-Q),pyrrolic N(N-5),and pyridinic N(N-6)in N-doping carbon paper.N-doping carbon paper as an Al-ion battery cathode shows strong charge-recharge properties.

Preparation of Al-Si-Ti Master Alloys by Electrolysis of Silica and Titania in Cryolite-Alumina Melts

Aluminum silicon titanium master alloys were prepared in the laboratory by electrolysis of silica and titania dissolved in cryolite alumina melts. Alloys containing up to 12 mass% Si and 2.6 mass% Ti were formed after about 90 min of electrolysis at 950℃. The current efficiency for the preparation of the Al Si Ti alloys varied with time, temperature and cathodic current density. It is concluded that this electrolytic method may be an interesting alternative to the direct metal mixing process for formation of Al Si Ti master alloys.