Mechanisms of aid-leaching reagent calcium fluoride in the extracting vanadium processes from stone coal

The mechanisms of aid-leaching reagent calcium fluoride in the extracting vanadium processes were researched by comparing the blank extraction with the extraction with calcium fluoride as aid-leaching reagent. The leaching experiments were carried out under the conditions of 95 ~C, 6 h, 1.5 ml.g-1, 15 vol % H2SO4, and 5 % calcium fluoride （mass ratio of CaF2 to stone coal）. The concentrations of hydrogen ion were adjusted from initial 1.82 and 4.79 mol.L-1 to the pH of 1.80 4- 0.05 by 200 g.L-1 lime milk, respectively. The solvent extraction experiments were carded out under the organic phase using 15 vol% D2EHPA, 5 vol% TBP, and 80 vol% sulfonated kerosene and O/A phase ratio of 1/4. The leaching rate of vanadium and six-stage countercurrent solvent extraction rate of vanadium can be remarkably improved from 66.71 to 92.97 % and 81.15 to 98.81%, respectively, when calcium fluoride was added as aid-leaching reagent. In the leaching process, fluorine can enhance the breakage of the structure of vanadium-bearing minerals. Meanwhile, fluoride ion can combine with iron ion to generate acid-insoluble iron fluoride hydrate （Fe2Fs.7H20） and consume all ferric ions and a portion of ferrous ions. In adjusting pH value process, the massive impurities are decreased to form KA1SO4 and FeA1Fs. In solvent extraction process, fluorine can prevent the formation of ferric hydroxide colloids and eliminate the formed unstable ferric hydroxide colloids and the silicon-containing colloids to promote the sufficient contact between the aqueous phase and the organic phase and the sufficient reaction.

Hydrogen permeability of slags containing calcium fluoride

To investigate the hydrogen permeability of calcium fluoride used for electroslag remelting （ESR） process, ＂Gas-slag- metal＂ osmosis process under argon atmosphere saturated with water vapor at 318 K was used to study the hydrogen permeability of slag containing calcium fluoride. The results indicate that the conventional slag, consisting of 70% CaF2 and 30% A1203, has the lowest hydrogen permeability. A parameter EH was proposed for evaluation of the hydrogen permeability of slags containing calcium fluoride. The hydrogen permeability decreases with increasing EH to a certain extent. An appropriate choice of slag for the ESR process can be obtained. These results also suggest that the hydrogen pick-up in steel after remelting might be reduced when a slag with low hydrogen permeability is used.

Viscosity estimation for slags containing calcium fluoride

Based on recently published experimental data, the Riboud model was modified for viscosity estimation of the slags containing calcium fluoride. The estimated values were in good agreement with measured data. Reasonable estimation can be achieved using the modified Riboud model for mould fluxes and ESR (eletro slag remelting) slags. Especially for ESR slags, the modified Riboud model can provide much more precise values than the original Riboud model.

Improving mold powder through crystallization using calcium fluoride and manganese oxide for continuous casting of steel

Mold powder is generally made of SiO2 and CaO with little amount of calcium fluoride(CaF_(2))and carbon.Basically,F^(-)has a crucial effect on viscosity and crystallization of the powder.However,emission of toxic materials containing F^(-)constituent such as HF and SiF4 leads to serious environmental pollution.Overall,six powder samples were made during this research to study the effects of such compounds as calcium fluoride(CaF_(2))and manganese oxide(MnO)on the crystallization of mold powder and compare with that of the original mold powder.Having considered the chemical compounds of these six samples,two were finally chosen:powder sample A and powder sample E.The former was a simulated sample of the original mold powder using CaF_(2),and the latter was a less-F^(-)sample in which MnO was used as a substitution for F^(-)in the compounds of the mold powder.In other words,the amount of F^(-)was cut in half comparing to that of the original mold powder.The thermal gravimetric analysis(TGA)was performed on the original mold powder,the simulated sample of the original mold powder and the less-F^(-)sample.The results of the TGA demonstrated the reduction of thermal loss in samples A and E comparing to the original mold powder.On the other hand,the results of differential thermal analysis(DTA)of these three samples,i.e.,original mold powder and samples A and E,demonstrated that melting and crystallization temperatures of the original mold powder were similar to those of samples A and E.Therefore,it can be concluded that samples A and E are potential laboratory-scale substitutions for the original mold powder.

Preparation of metal zinc from hemimorphite by vacuum carbothermic reduction with CaF_2 as catalyst

Zn reduction was investigated by the vacuum carbothermic reduction of hemimorphite with or without CaF2 as catalyst.Results indicate that CaF2 can catalyze the carbothermic reduction of zinc silicate,decrease the reaction temperature and time.The lower the reaction temperature and the more the amount of CaF2,the better the catalytic effect.The optimal process condition is obtained as follows：the addition of about 10% CaF2,the reaction temperature of 1373 K,the molar ratio of C to ZnTotal of 2.5,the pressure of system lower than 20 kPa,the reaction time of about 40 min.Under the optimal process condition,the zinc reduction rate is about 93% from hemimorphite.

Synergistic effect of microwave irradiation and CaF2 on vanadium leaching

The effect and mechanism of microwave irradiation on vanadium leaching were studied via a comparison between microwave heating and conventional heating. The results show a synergistic effect of microwave irradiation and calcium fluoride （CaF2） on the vana- dium leaching efficiency. It is confirmed that the vanadium leaching process can be improved by microwave irradiation when CaF2 is present. The leaching rate of vanadium under microwave irradiation is increased by 8%-15% when 5wt% CaF2 is added; by contrast, in the absence of CaF2, the leaching rate is almost unaffected compared to that by conventional heating. Morphological analysis reveals that the particles are gradually eroded by acid under microwave irradiation, whereas some of the fine particles in samples subjected to conventional heating are tightly covered by a flocculent silicate product. Moreover, a large amount of A1 and V and a small amount of Si are dissolved from samples under microwave heating, as revealed by the elemental analysis of leachates. Fourier transform infrared spectroscopic analysis also indicates a higher mass transfer coefficient in the diffusion layer of the raw material by microwave irradiation. When CaF2 is present, the reaction energy barrier is lowered and the leaching process is controlled by the tightly covered product layer, resulting in a prominent effect of mi- crowave irradiation.

Phosphogypsum Pyrolysis by Adding Mineralization Agent:Process and Mechanism

In order to decrease energy consumption for phosphogypsum(PG)pyrolysis process,a pilot-scale vertical-retort furnace was designed initiatively,and then mineralization agent was added to pyrolysis mixture.Calcium fluoride(CaF_(2))was proven to be a suitable mineralization agent,and the optimal parameters were:pyrolysis temperature 960℃,carbon-sulfur mole ratio 0.7,reaction time 50 min,and CaF_(2)dosage 4%by weight.Under this condition,PG decomposition and sulfur dioxide(SO_(2))conversion were up to 89.6%and 67.3%,respectively.CaF_(2)could lead to the formation of fluosilicate complexes,and facilitate PG decomposition at a low temperature.During pyrolysis process,calcium sulfide(CaS)was an inevitable intermediate substance,and only a part of total sulfur in the feedstock could be converted to SO_(2).

Thermodynamic Properties of CaCl₂-CaF₂-CaO System: Phase Diagram Investigation

The CaCl2-CaF2-CaO phase diagram was investigated in the CaO low region (<40 mol.%). CaCl2-CaF2 and CaCl2-CaO binary diagrams, constituting the ternary system, were first studied by Differential Scanning Calorimetry (DSC) measurements and X-Ray Diffraction (XRD) characterization;a good agreement was obtained between the phase diagram models calculated with FactSage®software (FTsalt database) and present experimental data. As the CaF2-CaO liquidus could not be measured by DSC due to the high melting temperature, this diagram was calculated using FTsalt database combined with FToxid database of FactSage® software. The ternary phase diagram was obtained by calculations and exhibits an eutectic at the composition CaCl2-CaF2-CaO (78.2-15.7-6.1 mol.%) melting at 637°C, and five peritectic points. Measurements of relevant vertical cross-sections for three CaCl2-CaF2 compositions (50-50, 40-60 and 30-70 mol.%) up to 18 mol.% CaO are in agreement with the ternary phase diagram model. For each section, the liquidus temperature is constant up to around 11 mol.% CaO and then sharply increases. Moreover, an increase of CaF2 content in CaCl2-CaF2 melt leads to a decrease of the CaO solubility in isothermal condition.

Effect of Boron Mud and CaF_2 on Surface Tension and Density of CaO-SiO_2-B_2O_3 Ternary Slag Systems

The effect of boron mud and CaF2,which were used as fluxing agents,on surface tension and density of CaO-SiO2-B2O3 ternary slag systems was investigated.The surface tension and density were measured by using the ring detachment method and Archimedean method,respectively.The results indicated that surface tension and density of the slag systems decreased with increasing temperature in the range of 1380-1480℃.When 5%-10% CaF2 was employed as fluxing agent,the surface tension and density of slag were decreased with increasing CaF2 content,and the surface tension changed from 0.3to 0.6N/m,while the density changed from 3.4to 4.1g/cm3.However,when using 5%-10%boron mud as fluxing agent,the surface tension was enhanced,whereas the density decreased with the increase of boron mud content,and the variation range was 0.4-0.6N/m for surface tension and 3.2-3.9g/cm3 for the density.As a conclusion,using boron mud as fluxing agent to substitute for CaF2 did not cause significant changes in slag surface tension and density.

Effects of B_2O_3 and CaF_2 on Melting Temperatures of CaO-SiO_2-Fe_2O_3 System Fluxes

Fluorite is widely employed as fluxing agent in metallurgy flux , which inevitably leads to serious fluorine pollution.B2O3 is employed as fluxing agent of CaO-SiO2-Fe2O3steelmaking fluxes to substitute for CaF2.The effects of B2O3 and CaF2 on the melting properties of this system were investigated.The melting temperatures of fluxes including softening temperature （Ts）, hemispherical temperature （Th）, and flow temperature （Tf） were measured using the hemisphere method.The results indicate that the fluxing effect of B2O3is more significant than that of CaF2 .When the addition amount of B2O3 （mass percent） exceeds 6% , the melting temperatures of fluxes including Ts , Th and Tf are decreased lower than 1 300℃.The basicity of fluxes has a significant effect on the melting temperature , and the melting temperatures of the fluxes increase with the increase of fluxes basicity.However , when B2O3 is used as fluxing agent , the melting temperature changes little with the basicity increasing from 2.5 to 5.0. These characteristics are suitable for steelmaking process.Moreover , Fe2O3 has an important fluxing effect on this CaO-based steelmaking fluxes.This indicates that the fluxes system is suitable for steelmaking process.

Hydrogen Pick-Up During Electroslag Remelting Process

The pick-up of hydrogen during electroslag remelting process for several slags consisting of CaF2-Al2O3-CaO-SiO2-MgO had been investigated.The laboratory-scale remelting experiments had been carried out in open air and water-free argon atmosphere,and then the influencing factors were analyzed.It had been found that the hydrogen content in steel varied with different slag compositions.The compositions and state of slag had significant effect on the hydrogen level in steel.Partial return slag and premelted slag could avoid the hydrogen pick-up especially in the early stages of the process.However,premelted slag was the optimum state to control the hydrogen pick-up in steel.Experimental results indicated that water-free argon atmosphere was very favorable to the control of hydrogen in steel in the normal remelting period.

Investigation of effect of electrode polarity on electrochemistry and magnetohydrodynamics using tertiary current distribution in electroslag remelting process

Transport phenomena including the electromagnetic,concentration of ions,flow,and thermal fields in the electroslag remelting(ESR)process made of slag,electrode,air,mold,and melt pool are computed considering tertiary current distribution.Nernst-Planck equations are solved in the bulk of slag,and faradaic reactions are regarded at the metal-slag interface.Aiming at exploring electrochemical effects on the behavior of the ESR process,the calculated field structures are compared with those obtained using the classical ohmic approach,namely,primary current distribution whereby variations in concentrations of ions and faradaic reactions are ignored.Also,the influence of the earth magnetic field on magnetohydrodynamics in the melt pool and slag is considered.The impact of the polarity of electrode,whether positive,also known as direct current reverse polarity(DCRP),or negative,as known as direct current straight polarity(DCSP),on the transport of oxygen to the ingot of ESR is investigated.The obtained modeling results enabled us to explain the experimental observation of higher oxygen content in DCSP than that of DCRP operated ESR process.

Thermal bleaching of optical absorption and photoluminescence spectra of γ-irradiated CaF_2:Dy:Pb:Na single crystals

The variation of the optical absorption (OA) and photoluminescence (PL) spectra with temperature was studied on γ-irradiated CaF2:Dy:Pb:Na single crystals. The OA spectrum showed bands around 2.05, 3.20, 3.82 and 6.20 eV which could be attributed to different sodium associated (SA) colour centres (CCs) such as MNa and RA+ . Heating the crystal indicated the annihilation and formation of different SACCs. The excitation spectrum for the characteristic Dy3+ emission at 2.14 eV immediately after irradiation was...