Digestion mechanism and crystal simulation of roasted low-grade high-sulfur bauxite

Low-grade high-sulfur bauxite was pretreated via suspension roasting and muffle furnace roasting to remove sulfur and enhance digestion properties.The results show that sulfur can be efficiently removed,and the alumina digestion properties are significantly improved after suspension roasting.Under optimal conditions(t=70 min,T=280°C,w(CaO)=8%and Nk=245 g/L),the digestion ratios are 94.45%and 92.08%for the suspension-roasted and muffle-roasted ore,respectively,and the apparent activation energies are 63.26 and 64.24 kJ/mol,respectively.Two crystal models were established by Materials Studio based on the XRD patterns.The DFT simulation shows that the existing Al—O bands after suspension roasting can improve alumina digestion.The(104)and(113)planes of Al2O3 after suspension roasting are found to combine with NaOH more easily than those of Al2O3 treated in a muffle furnace.

Suspension calcination and alkali leaching of low-grade high-sulfur bauxite:Desulfurization, mineralogical evolution and desilication

To enable the utilization of low-grade and high-sulfur bauxite, the suspension calcination was used to remove the sulfur and the activate silica minerals, and the calcinated bauxite was subjected to a desilication process in Na OH solution under atmospheric pressure. The desulfurization and desilication properties and mineralogical evolution were studied by X-ray diffraction, thermogravimetry–differential thermal analysis, scanning electron microscopy, and FactSage methods. The results demonstrate that the suspension calcination method is efficient for sulfur removal: 84.21% of S was removed after calcination at 1000°C for 2 min. During the calcination process, diaspore and pyrite were transferred to α-Al2O3, magnetite, and hematite. The phase transformation of pyrite follows the order FeS2 → Fe3O4 → Fe2O3, and the iron oxides and silica were converted into iron silicate. In the alkali-soluble desilication process, the optimum condition was an alkali solution concentration of 110 g/L, a reaction time of 20 min, and a reaction temperature of 95°C. The corresponding desilication ratio and alumina loss ratio were 44.9% and 2.4%, respectively, and the alumina-to-silica mass ratio of the concentrate was 7.9. The Al2O3·2SiO2, SiO2, and Al2O3 formed during the calcination process could react with Na OH solution, and their activity decreased in the order of Al2O3·2 SiO2, SiO2, and Al2O3.

Dissolution kinetics of aluminum and iron from coal mining waste by hydrochloric acid

The extrartion of aluminum from coal mining waste(CMW) is an important industrial process.The two major problems in applications are low aluminum dissolution efficiency and high iron content in the raw material,which affect the quantity and quality of products.To improve the aluminum recovery process,the leaching kinetics of CMW with hydrochloric acid was studied.A shrinking core model was used to investigate aluminum and iron dissolution kinetics.Based on the kinetic characteristics,a process for recovering aluminum was proposed and tested experimentally.It is found that the aluminum leaching reaction is controlled by surface reaction at low temperatures(40-80℃) and by diffusion process at higher temperatures(90-106℃).The iron dissolution process is dominated by surface reaction at 40-100℃.The results show that iron could be dissolved or separated by concentrated hydrochloric acid.Fine grinding will improve aluminum dissolution significantly.

Mechanism of electro-generating leaching of chalcopyrite-MnO_2 in presence of Acidithiobacillus thiooxidans

有黄铜矿阳极和 MnO2 阴极的一个双房间系统被用来分别地学习在电的数量和溶解在产生电镀物品的沥滤二种矿物质评价的时间和如此的数据和沥滤的 bio-electro-generating (BEGL )(EGL ) 之间的关系。结果证明溶解为 Cu2+ 评价，在 BEGL 的 Fe2+ 是比在 EGL，和 Mn2+ 的将近 3 次的那些快几乎 2 倍的；电的产量到 3 次将近增加了。黄铜矿的氧化残余被 TEM 和 XRD 代表，其模式类似于在 EGL 的未加工的矿石的。为面对 Acidithiobacillus thiooxidans CuFeS2-MnO2 沥滤的机制为阳极作为二独立子进程的连续反应被建议。第一个阶段，对两个过程普通，是黄铜矿的溶解生产 Cu2+ ， Fe2+ 和硫。第二个阶段在 BEGL 仅仅是硫的随后的氧化，它是这个过程的控制的步。然而， MnO2 的溶解持续直到站或矿石在沥滤的二种类型用尽的黄铜矿的反应。

Solidification and crystallization properties of CaO-SiO_2-Na_2O based mold fluxes

Crystallization properties play an important role in keeping a smooth running of continuous casting process and high surface quality of cast strands. To reduce fluorine pollution in slag, a new type of CaO-SiO2-Na2O （CSN） based mold flux was studied. The solidification and crystallization properties, including crystallization temperature, crystallization ratio and solidification mineragraphy, were measured, which were compared with the CaO-SiO2-CaF2 （GF） mold flux. The results show that the crystallization performance is equal to the high fluoride mold powder and CSN can be used for peritectic steel grades sensitive to longitudinal cracking in continuous casting.

Micro Extrusion of Ultrafine Grained Titanium Prepared by ECAP

Micro compression and micro extrusion experiments of ultrafine grained titanium cylindrical specimens in diameters of 4, 2, and 1 mm prepared by equal channel angular pressing（ECAP） were conducted on the micro plastic forming test machine. The effects of specimen size, grain size, deformation temperature and extrusion speed on the flow stress and forming properties of the ultrafine grained pure titanium were investigated. The flow stress of ultrafine grained pure titanium specimen decreases with decreasing specimen size. The yield limit of pure titanium with refined grain prepared by ECAP is significantly greater than that of coarse grained specimen. Also the research results show that the flow stress of specimen increases with decreasing deformation temperature and with the increase of the strain rate, and the ultrafine grained pure titanium possesses good micro forming properties at deformation temperature of 300 ℃.

Electrogenerative leaching for sphalerite-MnO_2 in the presence of Acidithiobacillus thiooxidans

A dual cell system was used to study the electrogenerative leaching sphalerite-MnO2 in the presence and absence of Acidithiobacillus thiooxidans (A. thiooxidans). The polarization of anode and cathode, and the relationship between the electric quantity (Q) and some factors, such as the dissolved rate of Zn2+ and Fe2+, and the time in the bio-electro-generating simultaneous leaching (BEGL) and electro-generating simultaneous leaching (EGL) were studied. A three-electrode system was applied to studying anodic and cathodic self-corrosion current, which was inappreciable compared with the galvanic current between sphalerite and MnO2. The results show that the dissolved Zn2+ in the presence of A. thiooxidans is nearly 43% higher than that in the absence of A. thiooxidans; the electrogenerative quantity in the former is about 150% more than that in the latter. The accumulated sulfur on the surface of sulfides produced in the electrogenerative leaching process can be oxidized in the presence of A. thiooxidans, and the ratio of biologic electric quantity reaches 27.9% in 72 h.

Synthesis,phase transformation and applications of CeCO_(3)OH:A review

CeCO_(3)OH has a unique crystal structure and excellent optical,electronic and catalytic properties,which has been widely investigated for many applications.Interestingly,ceria obtained from CeCO_(3)OH has a morphology that is similar to that of the precursor,and the CeO_(2)-based products obtained from CeCO_(3)OH exhibit outstanding properties,such as catalytic performances,owing to their designed morphology and oxygen vacancies(OVs).To introduce CeCO_(3)OH into a wider range of potential researchers,we first systematically review the physico-chemical properties,synthesis,reaction and morphology tuning mechanism of CeCO_(3)OH,and summarize the conversion behavior from CeCO_(3)OH to ceria.Then,we thoroughly survey the applications of CeCO_(3)OH and its conversion products.Suggestions for further investigations of CeCO_(3)OH are also made in this review.It is hoped that the exhaustive co mpilation of the valuable properties and considerable potential investigations of CeCO_(3)OH will promote further applications of CeCO_(3)OH and CeO_(2)-based functional materials.

Molten salt synthesis of Z-scheme CeO_(2)/C_(3)N_(4) photocatalysts with excellent properties for removal of organic pollutants:Characterization,kinetics and mechanisms

In this work,we firstly synthesized a CeO_(2)/C_(3)N_(4) photocatalyst with Z-scheme heterojunction by a facile LiC-KCI molten salt method.The synthesized catalyst has an excellent quality for removing organic pollution of dyes and antibiotics in wastewater.As an example,the CeCN-1:5 prepared with a mass ratio of Ce_(2)(CO_(3))_(3)·xH_(2)O:C_(3)H_(3)N_(6)=1:5 exhibits a methylene blue(MB)removal capacity of 100%within 90 min and tetracycline(TC)removal capacity of 94.6%.After 4 cycles,the CeCN-1:5 keeps a removal efficiency of nearly 100%in 150 min for MB and 85.7%for TC.The kinetics study reveals that the MB removal process with the CeCN-1:5 fits the modified Elovich model with strong adsorption while TC removal fits the first-order model.The large surface area(238 m^(2)/g)and negative zeta potential(-39.3 mV)of CeCN-1:5 contribute to superior adsorption capacity to MB.However,the adsorption of TC is restricted due to the positive surface/pore potential in acidic solution.CeCN-1:5has combined Z-scheme heterojunction and exhibits a low recombination rate of electrons(e^(-))/holes(h^(+))and the photo-generated active radicals of·OH/·O_(2)^(-)that promotes the photocatalytic performance.This novel CeO_(2)/C_(3)N_(4) photocatalyst with an excellent photocatalysis removal activity has an enormous potential for photocatalytic applications.

Properties of High Basicity Mold Fluxes for Peritectic Steel Slab Casting

In high speed continuous casting of peritectic steel slabs, mold fluxes with high basicity are required for less surface defect product. However, the basicity of remaining liquid slag film tends to decrease in casting process because of the crystallization of 3CaO ·2SiO2 · CaF2. Thus, a way is put forward to improve mold fluxesr properties by raising the original basicity. In order to confirm the possibility of this method, the effect of rising original basicity on the properties of mold fluxes is discussed. Properties of high fluorine based mold fluxes with different basicities and contents of CaF2 , Na2 O, and MgO were measured, respectively. Then, properties of higher basicity mold fluxes were discussed and compared with traditional ones. The results show that increasing the basicity index can improve the melting and flow property of mold fluxes. With the increasing basicity, crystallization rate of mold fluxes increases obviously and crystallization temperature tends to decrease when the basicity exceeds 1.35. The method presen- ted before is proved as a potential way to resolve the contradiction between horizontal heat transfer controlling and solidified shell lubricating for peritectic steel slab casting. But further study on improving the flow property of liquid slag is needed. This work can be used to guide mold fluxes design for high speed continuous casting of peritectic steel slabs.

Model for RuhrstahI-Heraeus （RH） decarburization process

A mathematical model was established to predict the carbon content of ultralow carbon steel in the Ruhrstahl-Heraeus （RH） process. The model was solved using the fourth-order Runge-Kutta method and assumed that the volume of steel partaking in the reaction depends on the decarburization mechanism. After analyzing the decarburization process using the proposed model, the following conclusions were drawn. First, the initial carbon and oxygen contents in the RH degasser should be stabilized in the range of （200-350） × 10^-6 and （500-700） × 10^-6, respectively. Second, in the initial stage, the pressure should be reduced as quickly as possible. Third, oxygen blowing should begin as early as possible when the forced decarburization is needed and the minimum oxygen flow rate should be 0.1923 m3/（t rain）. Finally, expanding the diameter of the snorkel tube from 480 to 600 mm clearly enhances the decarburization rate.

Facile synthesis of nanoceria by a molten hydroxide method and its photocatalytic properties

Ceria nanoparticles were facilely synthesized by a molten NaOH-KOH hydroxide flux method with the precursor of Ce(NO3)3·6H2O under different conditions in alumina crucibles or Teflon-lined stainless steel autoclave.The XRD patterns and TEM images show that both the crystal and particle sizes of synthesized nanoceria are around 10 nm.XPS results reveal that the nanoceria obtained in alumina crucible has a Ce3+fraction of 17.1%which is higher than that of ceria synthesized in the Teflon vessel,the FTIR spectra of nanoceria prepared in alumina crucible show a stronger intensity of O-H stretching mode.UV-DRS and PL spectra results show that the nanoceria synthesized in alumina crucible with a calculated band gap of 2.9 eV has a wider responding light wavelength and a lower photogene rated electron-hole recombination rate,due to a higher concentration of oxygen vacancies(Ce^3+%).The photocatalytic results show that the degradation ratio and rate of the Rhodamine B(RhB)solution with the nanoceria synthesized in alumina crucible are 98.39%and 0.02919 min-1,both of which are larger than those of the ceria obtained from Teflon vessel.This method proves to be a simple and scalable way to synthesize nanoceria with rich oxygen vacancies and high photocatalytic activity.

Effect of cross-section shape of rotating chute on particle movement and distribution at the throat of a bell-less top blast furnace

Rotating chutes are widely used to control the burden distribution and enhance the gas distribution in a blast furnace.The chute cross-section shape has a significant effect on the particle movement and distribution.Therefore,this study developed a three-dimensional model of a blast furnace top with rotating chute using the discrete element method.The effect of different chute shapes on the particle movement and radial burden distribution was then investigated.The results showed that the burden stream height at the chute discharge agrees well with the burden stream thickness at the burden surface.A semicircular chute had the largest main striking point,where the chute discharge joins the burden surface,and trapezoidal and rectangular chutes had successively smaller MSPs.The semicircular chute helped to obtain a uniform radial size distribution.The trapezoidal chute helped form an aggregated burden stream at low rotating speeds,while the rectangular shape chute achieved this at higher rotating speeds and different chute angles.

Solidification Properties of CaO-SiO_2-TiO_2 Based Mold Fluxes

In continuous casting of peritectic steel grades sensitive to longitudinal cracking, the solidification properties of mold fluxes play an important role in keeping smooth running of continuous casting process and achieving high surface quality of casting strands. To reduce fluorine pollution in molten slag, types of CaO-SiO2-TiO2 （CTS） based mold fluxes were investigated. The solidification and crystallization properties, including viscosity η at 1 573 K, break temperature Tbr, crystallization ratio Rc and solidification mineragraphy were measured, which were compared with those of CaO-SiO2-CaF2 based mold fluxes. The experiments show that there are unstable viscosity-high tem- perature properties and high Tbr in part of CTS slag system, which are bad for lubrication between liquid flux film and strand. And when temperature is below Tbr, the viscosities change slowly during cooling in some part of this slag system, which imply that liquid mold fluxes solidify slowly and it is easy to cause surface longitudinal cracks on strand. Major mineragraphy of the CaO-SiO2-TiO2 based mold fluxes are CaO · TiO2 or CaO · TiO2 and CaO · SiO2 · TiO2. TiN and Ti（C,N） can be formed in mold fluxes bearing high TiO2 during the continuous casting.

Optimization of iron and aluminum recovery in bauxite

Recovering iron and aluminum efficiently is the key route to utilize low-grade high-iron bauxite.Aiming to optimize the iron separating process and elevate both Fe and Al recovery ratio,three different Fe-Al recovery processes with different magnetic roasting(R),Bayer leaching process(L)and magnetic separation(S)orders were investigated.The studied processes include bauxite leaching→red mud roasting→magnetic separation(L-R-S),bauxite roasting→magnetic separation→leaching(R-S-L)and bauxite roasting→leaching→magnetic separation(R-L-S).The iron recovery ratio,Fe2O3 content in iron concentration and the bauxite dissolution ratio of each process were investigated.Moreover,the optimizations of the leaching,roasting and magnetic separation conditions were studied.Results indicate that the R-S-L process should be an advisable order to recover both alumina and iron.In the three processes,the R-S-L route had the highest alumina dissolution ratio and iron recovery ratio,which was 86.20%and 69.58%,respectively,while the Fe2O3 content of the iron concentrate was 40.66%.

Chromium Recycling from Argon-oxygen Decarburization Dust in Hot Metal Pre-dephosphorization Process

The chromium recycling from the stainless steel dust of an argon-oxygen decarburization （AOD） furnace during a hot metal pretreatment process was investigated. Experiments at different temperatures or with different amounts of AOD dusts were carried out in a laboratory furnace equipped with MoSi2 heating elements and subsequently industrial experiments were conducted in a stainless steelmaking factory, in order to study the thermodynamic mechanism of C and Si reacted with Cr2O3 to get Cr from AOD dust. The results showed that the reaction between C and Cr2 O1 occurred below 1572.18 K. Although its reducing ability was weaker than that of Si, C enabled the Cr in Cr2O3 in the AOD dust to be recycled using the Si in the slag. By combining the AOD dust added in an earlier stage, the hot metal pretreatment slag added in a later stage could not only recycle Cr from AOD dust but also remove Si, S, and P. Higher hot metal temperatures resulted in higher Cr content and lower remained P concentration in the molten iron.