High-chromium vanadium-titanium magnetite all-pellet integrated burden optimization and softening-melting behavior based on flux pellets

High-chromium vanadium-titanium magnetite(HVTM)is a crucial polymetallic-associated resource to be developed.The allpellet operation is a blast furnace trend that aims to reduce carbon dioxide emissions in the future.By referencing the production data of vanadium-titanium magnetite blast furnaces,this study explored the softening-melting behavior of high-chromium vanadium-titanium magnetite and obtained the optimal integrated burden based on flux pellets.The results show that the burden with a composition of 70wt%flux pellets and 30wt%acid pellets exhibits the best softening-melting properties.In comparison to that of the single burden,the softening-melting characteristic temperature of this burden composition was higher.The melting interval first increased from 307 to 362℃and then decreased to 282℃.The maximum pressure drop(ΔPmax)decreased from 26.76 to 19.01 kPa.The permeability index(S)dropped from 4643.5 to 2446.8 kPa·℃.The softening-melting properties of the integrated burden were apparently improved.The acid pellets played a role in withstanding load during the softening process.The flux pellets in the integrated burden exhibited a higher slag melting point,which increased the melting temperature during the melting process.The slag homogeneity and the TiC produced by over-reduction led to the gas permeability deterioration of the single burden.The segregation of the flux and acid pellets in the HVTM proportion and basicity mainly led to the better softening-melting properties of the integrated burden.

Production and Characterization of Green Biosorbent Based on Modified Corn Cob Decorated Magnetite Nanoparticles

In most developing countries, particularly in the countries of sub-Saharan Africa, corn cobs are considered as waste polluting the environment during the harvest period of this cereal. In order to valorize this agricultural waste, high-performance, inexpensive and low-energy consumption magnetic bioadsorbents were prepared from corn cobs. The chemically activated raw corn cob was magnetized by coating the surface with magnetite nanoparticles. The prepared biosorbents were characterized by FT-IR, XRD, FE-SEM associated with EDX, HR-TEM, TG analysis, BET surface area analysis and XPS. The maximum specific surface area of 35.22 m2/g was reached. An attempt to use of these magnetic biosorbents for the removal of heavy metal like Cr(VI) from aqueous solution was envisaged.

Effect of basicity on sintering behavior of low-titanium vanadium-titanium magnetite

Basicity has an important effect on the sinter quality, especially for low-titanium vanadium-titanium sinter. The effect of basieity on sintering behavior of low-titanium vanadium-titanium mixture, and the transference and distribution of element in sintering process were researched by sinter pot test, mineralogical analysis, scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS） analysis. The results show that CaO preferentially reacts with TiO2, generating pervoskite, so that the total liquid phase content of the sinter is low. There is an increase in the perovskite concentration of the sinter with the basicity ranging from 1.9：1 to 2.7：1. With increasing the basicity, the calcium ferrite content increases slightly and then rises rapidly, while the silicate content decreases and the metallurgical property of the sinter is improved. As for the distribution of these elements in the sinter, Ti occurs mainly in perovskite, V occurs mainly in silicate, and Fe occurs mainly in magnetite and hematite. The most abundant occurrence of Ca and Si occurs in silicate and perovskite. With increasing the basicity, the contents of A1 and Mg increase in calcium ferrite, while they decrease in other minerals.

Solid-state reduction kinetics and mechanism of pre-oxidized vanadium-titanium magnetite concentrate

The solid-state reduction kinetics of pre-oxidized vanadium-titanium magnetite concentrate was studied. The phase and microstructure of the reduction product were characterized by XRD, SEM and EDS methods, based on which the mechanism of the solid-state reduction was investigated. The results showed that using coal as reductant at 950-1100 °C, the solid-state reduction of the pre-oxidized vanadium-titanium magnetite concentrate was controlled by interface chemical reaction and the apparent activation energy was 67.719 k J/mol. The mineral phase transformation during the reduction process can be described as follows： pre-oxidized vanadium-titanium magnetite concentrate → ulvospinel → ilmenite → Fe Ti2O5 →（FenTi1-n）Ti2O5. M3O5-type（M can be Fe, Ti, Mg, Mn, etc） solid solutions would be formed during the reduction process of the pre-oxidized vanadium-titanium magnetite concentrate at 1050 °C for 60 min. The poor reducibility of iron in M3O5 solid solutions is the main reason to limit the reduction property of pre-oxidized vanadium-titanium magnetite concentrate.

Conversion of ferric oxide to magnetite by hydrothermal reduction in Bayer digestion process

Digesting aluminum-bearing minerals and converting ferric oxide to magnetite simultaneously in Bayer digestion process is crucially important to deal with high-iron diasporic bauxite economically for alumina production.The reaction behaviors of hydrothermal reduction of ferric oxide in alkali solution were studied by both thermodynamic calculation and experimental investigation.The thermodynamic calculation indicates that Fe3O4 can be formed by the conversion of Fe2O3 at proper redox potentials in alkaline solution.The experimental results show that the formation ratio of Fe3O4 either through the reaction of Fe and Fe2O3 or through the reaction of Fe and H2O in alkaline aqueous solution increases remarkably with raising the temperature and alkali concentration,suggesting that Fe（OH）3- and Fe（OH）4- form by dissolving Fe and Fe2O3,respectively,in alkaline aqueous solution and further react to form Fe3O4.Moreover,aluminate ions have little influence on the hydrothermal reduction of Fe2O3 in alkaline aqueous solution,and converting iron minerals to magnetite can be realized in the Bayer digestion process of diasporic bauxite.

Effect of MgO content in sinter on the softening–melting behavior of mixed burden made from chromium-bearing vanadium–titanium magnetite

The effect of sinter with different MgO contents on the softening-melting behavior of mixed burden made from chro- mium-bearing vanadium-titanium magnetite was investigated. The results show that with increasing MgO content in the sinter, the softening interval and melting interval increased and the location of the cohesive zone shifted downward slightly and became moderately thicker. The softening-melting characteristic value was less pronounced when the MgO content in the sinter was 2.98wt%-3.40wt%. Increasing MgO content in the sinter reduced the content and recovery of V and Cr in the dripped iron. In addition, greater MgO contents in the sinter resulted in the generation of greater amounts of high-melting-point components, which adversely affected the permeability of the mixed burden. When the softening-melting behavior of the mixed burden and the recovery of valuable elements were taken into account, proper MgO con- tents in the sinter and slag ranged from 2.98wt% to 3.40wt% and from 11.46wt% to 12.72wt%, respectively, for the smelting of burden made from chromium-bearing vanadium-titanium magnetite in a blast furnace.

Trace Element Geochemistry of Magnetite from the Fe(-Cu) Deposits in the Hami Region, Eastern Tianshan Orogenic Belt, NW China

Laser ablation–inductively coupled plasma–mass spectrometry（LA–ICP–MS） was used to determine the trace element concentrations of magnetite from the Heifengshan, Shuangfengshan, and Shaquanzi Fe（–Cu） deposits in the Eastern Tianshan Orogenic Belt. The magnetite from these deposits typically contains detectable Mg, Al, Ti, V, Cr, Mn, Co, Ni, Zn and Ga. The trace element contents in magnetite generally vary less than one order of magnitude. The subtle variations of trace element concentrations within a magnetite grain and between the magnetite grains in the same sample probably indicate local inhomogeneity of ore–forming fluids. The variations of Co in magnetite between samples are probably due to the mineral proportion of magnetite and pyrite. Factor analysis has discriminated three types of magnetite： Ni–Mn–V–Ti（Factor 1）, Mg–Al–Zn（Factor 2）, and Ga– Co（Factor 3） magnetite. Magnetite from the Heifengshan and Shuangfengshan Fe deposits has similar normalized trace element spider patterns and cannot be discriminated according to these factors. However, magnetite from the Shaquanzi Fe–Cu deposit has affinity to Factor 2 with lower Mg and Al but higher Zn concentrations, indicating that the ore–forming fluids responsible for the Fe–Cu deposit are different from those for Fe deposits. Chemical composition of magnetite indicates that magnetite from these Fe（–Cu） deposits was formed by hydrothermal processes rather than magmatic differentiation. The formation of these Fe（–Cu） deposits may be related to felsic magmatism.

Some basic properties of granules from ore blends consisting of ultrafine magnetite and hematite ores

Some basic properties of granules,including the granule size distribution,packed-bed permeability,and chemical composition of the adhering layer,were investigated in this study for four iron ore blends consisting of 5wt%,25wt%,and 45wt%ultrafine magnetite and 25wt%ultrafine hematite concentrates.The effects of varying the sinter basicity(CaO/SiO2 mass ratio=1.4 to 2.2)and adding ultrafine concentrates on the variation of the adhering-layer composition and granule microstructure were studied.Moreover,the effect of adhering-layer compositional changes on sintering reactions was discussed in combination with pot sintering results of ore blends.Increasing sinter basicity led to an increase in the basicities of both the adhering layer and the fine part of the sinter mix,which were higher than the overall sinter basicity.When the sinter chemistry was fixed and fine Si-bearing materials(e.g.,quartz sand)were used,increasing the amount of ultrafine ores in the ore blends tended to reduce the adhering-layer basicity and increase the SiO2 content in both the adhering layer and the fine part of the sinter mix,which will induce the formation of low-strength bonding phases and the deterioration of sinter strength.The adhering-layer composition in granules can be estimated in advance from the compositions of the-1 mm fractions of the raw materials.

Exsolutions of Diopside and Magnetite in Olivine from Mantle Dunite,Luobusa Ophiolite,Tibet,China

The exsolutious of diopside and magnetite occur as intergrowth and orient within olivine from the mantle dunite, Luobusa ophiolite, Tibet. The dunite is very fresh with a mineral assemblage of olivine （〉95%） ＋ chromite （1%-4%） ＋ diopside （〈1%）. Two types of olivine are found in thin sections： one （Fo = 94） is coarse-grained, elongated with development of kink bands, wavy extinction and irregular margins; and the other （Fo = 96） is fine-grained and poly-angied. Some of the olivine grains contain minor Ca, Cr and Ni. Besides the exsolutions in olivine, three micron-size inclusions are also discovered. Analyzed through energy dispersive system （EDS） with unitary analytical method, the average compositions of the inclusions are： Na20, 3.12%-3.84%; MgO, 19.51%-23.79%; Al2O3, 9.33%-11.31%; SiO2, 44.89%-46.29%; CaO, 11.46%-12.90%; Cr2O3, 0.74%-2.29%; FeO, 4.26%- 5.27%, which is quite similar to those of amphibole. Diopside is anhedral f＇dling between olivines, or as micro-inclusions oriented in olivines. Chromite appears euhedral distributed between olivines, sometimes with apparent compositional zone. From core to rim of the chromite, Fe content increases and Cr decreases; and A! and Mg drop greatly on the rim. There is always incomplete magnetite zone around the chromite. Compared with the nodular chromite in the same section, the euhedral chromite has higher Fe3O4 and lower MgCr2O4 and MgAI2O4 end member contents, which means it formed under higher oxygen fugacity environment. With a geothermometer estimation, the equilibrium crystalline temperature is 820℃-960℃ for olivine and nodular chromite, 630℃-770℃ for olivine and euhedral chromite, and 350℃-550℃ for olivine and exsoluted magnetite, showing that the exsolutions occurred late at low temperature. Thus we propose that previously depleted mantle harzburgite reacted with the melt containing Na, Al and Ca, and produced an olivine solid solution added with Na^＋, Al^3＋, Ca^2＋, Fe^3＋, Cr^3＋. With temperature decreasing, the olivine solid solution decomposed; and Fe^3＋, Cr^3＋ diffused into magnetite and Ca^2＋ and Na^＋ into clinopyroxene, both of which formed intergrowth textures. A few Fe^3＋ and Cr^3＋ entered interstitial chromite. Through later tectonism, the peridotite recrystallized and formed deformational coarse grained olivine, fine grained and poly-angled olivine, and euhedral grained chromite. Due to the fast cooling rate of the rock or rapid tectonic emplacement, the exsolution textures in olivine and compositional zones of chromite are preserved.

Selective leaching of vanadium from V-Ti magnetite concentrates by pellet calcification roasting-H_(2)SO_(4) leaching process

A novel method of pellet calcification roasting-H_(2)SO_(4) leaching was proposed to efficiently separate and extract vanadium(V)from vanadium-titanium(V-Ti)magnetite concentrates.The leaching rate of V is as high as 88.98%,while the leaching rate of impurity iron is only 1.79%.Moreover,the leached pellets can be used as raw materials for blast furnace ironmaking after secondary roasting.X-ray photoelectron spectroscopy(XPS)and scanning electron microscopy with energy dispersive X-ray spectrometry(SEMEDS)analyses showed that V^(3+)was oxidized to V^(5+)after roasting at 1200℃,and V^(5+)was then leached by H_(2)SO_(4).X-ray diffraction(XRD)analyses and single factor experiment revealed a minimal amount of dissolved Fe_(2)O_(3) during H_(2)SO_(4) leaching.Therefore,a high separation degree of V and iron(Fe)from V-Ti magnetite concentrate was achieved through H_(2)SO_(4) leaching.Compared with the traditional roastingleaching process,this process can achieve a high selectivity of V and Fe,and has excellent prospects for industrial production.

Mineralogy and carbothermal reduction behaviour of vanadium-bearing titaniferous magnetite ore in Eastern India

Vanadium-beaxing titaniferous magnetite bands hosted by Precambrian gabbro-norite-anorthositic rocks or their metamorphic equivalents were discovered in some parts of Eastern Indian Shield, containing 48%-49% Fe （total）, 10%-25% TiO2, and 0.3%-2.20% V2O5 by mass. Mineralogical and petrological study, composition, and characterization of the vanadium-bearing titaniferous magnetite ore were carried out by scanning electron microscopy-energy dispersive X-ray （SEM-EDX）, wave length X-ray florescence （WDXRF）, inductively coupled plasma-atomic emission spectroscopy （ICP-AES）, X-ray diffraction （XRD）, etc. Chemical beneficiation for valuable metals, such as Fe, Ti, andV, was performed by reduction roasting. The direct and indirect reduction were investigated by mixing the lump ore with solid activated charcoal in a closed reactor and purging the reducing gas mixture in standard reducibility index apparatus at different temperatures and time intervals. The reduction roasting parameters were optimized. Finally, the reduced samples were crushed and upgraded by magnetic separation. The results show that, the maximum mass fractions of magnetic and nonmagnetic parts achieved axe 69.36% and 30.64%, respectively, which contain 10.6% TiO2 and 0.84% V205 in the magnetic part and 36.5% TiO2 and 0.22% V205 in the nonmagnetic part.

Metalizing reduction and magnetic separation of vanadium titano-magnetite based on hot briquetting

To achieve high efficiency utilization of Panzhihua vanadium titano-magnetite, a new process of metalizing reduction and magnetic separation based on hot briquetting is proposed, and factors that affect the cold strength of the hot-briquetting products and the efficiency of reduction and magnetic separation are successively investigated through laboratory experiments. The relevant mechanisms are elucidated on the basis of microstructural observations. Experimental results show that the optimal process parameters for hot briquetting include a hot briquetting temperature of 475°C, a carbon ratio of 1.2, ore and coal particle sizes of less than 74 μm. Additionally, with respect to metalizing reduction and magnetic separation, the rational parameters include a magnetic field intensity of 50 mT, a reduction temperature of 1350°C, a reduction time of 60 min, and a carbon ratio of 1.2. Under these above conditions, the crushing strength of the hot-briquetting agglomerates is 1480 N, and the recovery ratios of iron, vanadium, and titanium are as high as 91.19%, 61.82%, and 85.31%, respectively. The new process of metalizing reduction and magnetic separation based on hot briquetting demonstrates the evident technological advantages of high efficiency separation of iron from other valuable elements in the vanadium titano-magnetite.

Oxidation behavior of artificial magnetite pellets

The oxidation behavior of artificial magnetite pellets was investigated through measurements of the oxidation degree and mineralogical analysis. The results show that artificial magnetite pellets are much easier to oxidize than natural magnetite. The oxidation is controlled through two different reaction mechanisms. The oxidation of artificial magnetite is dominated by internal diffusion, with an activation energy of 8.40 kJ/mol, at temperatures less than 800°C, whereas it is controlled by chemical reaction, with a reaction activation energy of 67.79 kJ/mol, at temperatures greater than 800°C. In addition, factors such as the oxygen volume fraction and the pellet diameter strongly influence the oxidation of artificial magnetite: a larger oxygen volume fraction and a smaller pellet diameter result in a much faster oxidation process.

Sintering behaviors and consolidation mechanism of high-chromium vanadium and titanium magnetite fines

To achieve high efficiency utilization of high-chromium vanadium-titanium magnetite （V-Ti-Cr） fines, an investigation of V Ti42r fines was conducted using a sinter pot. The chemical composition, particle parameters, and granulation of V-Ti-Cr mixtures were analyzed, and the effects of sintering parameters on the sintering behaviors were investigated. The results indicated that the optimum quicklime dosage, mixture moisture, wetting time, and granulation time for V-Ti-Cr fines are 5wt%, 7.5wt%, 10 min, and 5-8 min, respectively. Meanwhile, the vertical sintering speed, yield, tumbler strength, and productivity gains were shown to be 21.28 mm/min, 60.50wt% , 58.26wt%, and 1.36 t·m^-2·h^-1, respectively. Furthermore, the consolidation mechanism of V-Ti-Cr fines was clarified, revealing that the consolidation of a V-Ti-Cr sinter requires an approximately 14vo1% calcium ferrite liquid-state, an approximately 15vo1% silicate liq- uid-state, a solid-state reaction, and the recrystallization of magnetite. Compared to an ordinary sinter, calcium ferrite content in a V-Ti-Cr sinter is lower, while the perovskite content is higher, possibly resulting in unsatisfactory sinter outcomes.

Shear behavior of ultrafine magnetite tailings subjected to freeze-thaw cycles

To study the shear behavior of the ultrafine magnetite tailings subjected to freeze-thaw cycles,unconsolidated-undrained shear tests were conducted on ultrafine-grained tailings that were subjected to 1-11 cycles of freeze-thaw and defined as a type of clayey silt under confining pressures of 100,200,and 300 kPa.Taking the number of freeze-thaw cycles,cooling temperature,initial dry density,and moisture content as the four main influencing factors of shear behavior of the tailings samples,the shear stress-strain curve,compression modulus,failure strength,cohesion,and internal friction angle were measured.The results show that the freeze-thaw cycle has an obvious weakening effect on the shear behavior of the tailings material,and the shear mechanical parameters are affected by a combination of confining pressure,freeze-thaw cycle condition,and initial physical-mechanical properties of the tailings samples.Through the microstructural analysis of the tailings samples subjected to freeze-thaw cycles,it shows that the freeze-thaw cycle mainly affects the porosity,bound water,and arrangement of the tailings particles.Subsequently,the macroscopic changes in shear strength indexes emerge,and then the stability of the tailings dam will decrease.

Optimized use of MgO flux in the agglomeration of high-chromium vanadium–titanium magnetite

The optimized use of MgO flux in the agglomeration of high-chromium vanadium-titanium magnetite was investigated system- atically through sinter and pellet experiments. MgO was added in the form of magnesite. When the content of MgO in the sinter was in- creased from 1.95wt% to 2.63wt%, the low-temperature reduction degradation index increased from 80.57% to 82.71%. When the content of MgO in the pellet was increased from 1.14wt% to 2.40wt%, the reduction swelling index decreased from 15.2% to 8.6%; however, the com- pressive strength of the oxidized pellet decreased dramatically and it was 1985 N with an MgO content of 1.14wt%. This compressive strength does not satisfy the requirements for blast-furnace production. When all of the aforementioned results were taken into account, the sinter with a high MgO content （2.63wt%） matching the pellet with a low MgO content （less than 1.14wt%） was the rational burden structure for smelting high-chromium vanadium-titanium magnetite in blast furnaces.

Effect of diboron trioxide on the crushing strength and smelting mechanism of high-chromium vanadium–titanium magnetite pellets

The effect of diboron trioxide(B_2O_3) on the crushing strength and smelting mechanism of high-chromium vanadium–titanium magnetite pellets was investigated in this work. The main characterization methods were X-ray fluorescence, inductively coupled plasma–atomic emission spectroscopy, mercury injection porosimetry, X-ray diffraction, metallographic microscopy, and scanning electron microscopy–energy-dispersive X-ray spectroscopy. The results showed that the crushing strength increased greatly with increasing B_2O_3 content and that the increase in crushing strength was strongly correlated with a decrease in porosity, the formation of liquid phases, and the growth and recrystallization consolidation of hematite crystalline grains. The smelting properties were measured under simulated blast furnace conditions; the results showed that the smelting properties within a certain B_2O_3 content range were improved and optimized except in the softening stage. The valuable element B was easily transformed to the slag, and this phenomenon became increasingly evident with increasing B_2O_3 content. The formation of Ti(C,N) was mostly avoided, and the slag and melted iron were separated well during smelting with the addition of B_2O_3. The size increase of the melted iron was consistent with the gradual optimization of the dripping characteristics with increasing B_2O_3 content.

Platinum-group Element Geochemistry of Magnetite from Porphyry-Cu-Mo Deposits and their Host Rocks(Siberia,Russia)

The concentrations of platinum-group elements （PGE） have been analyzed in primary magmatic magnetite samples from the Zhireken, Shakhtama and Aksug porphyry Cu-Mo deposits （Siberia, Russia） by laser ablation-inductively coupled plasma mass spectrometry to determine the range of PGE contents in magnetites and to check whether magnetite from two main rock suites （barren plutonic suite and mineralized porphyry suite） has distinct PGE composition. The results presented here indicate that magnetites are enriched in PGE relative to whole-rocks. Comparison of ore-related porphyry and barren plutonic suites shows that magnetite exhibit relatively similar PGE distribution patterns in both suites. Variations in Rh and Ru contents were controlled by the oxygen fugacity during magma crystallization.

Using trace elements of magnetite to constrain the origin of the Pingchuan hydrothermal low-Ti magnetite deposit in the Panxi area, SW China

The Pingchuan iron deposit, located in the Yanyuan region of Sichuan Province, SW China, has an ore reserve of 40 Mt with ~60 wt% Fe. Its genesis is still poorly understood. The Pingchuan iron deposit has a paragenetic sequence of an early Fe-oxide–Pyrite stage(Ⅰ) and a late Fe-oxide–pyrrhotite stage(Ⅱ). Stage Ⅰ magnetite grains are generally fragmented, euhedral–subhedral, largesized crystals accompanying with slightly postdated pyrite.Stage Ⅱ magnetite grains are mostly unfragmented, anhedral, relatively small-sized grains that co-exist with pyrrhotite. Combined with micro-textural features and previously-obtained geochronological data, we consider that these two stages of iron mineralization in the Pingchuan deposit correspond to the Permian ELIP magmatism and Cenozoic fault activity event. Both the Stage Ⅰ and Ⅱ magnetites are characterized with overall lower contents of trace elements(including Cr, Ti, V, and Ni) than the ELIP magmatic magnetite, which suggests a hydrothermal origin for them. ‘‘Skarn-like'' enrichment in Sn, Mn, and Zn in the Stage Ⅰ magnetite grains indicate significant material contributions from carbonate wall-rocks due to water–rock interaction in ore-forming processes. Stage Ⅱ magnetite grains contain higher Mn concentrations than Stage Ⅰ magnetite grains, which possibly implies more contribution from carbonate rocks. In multiple-element diagrams, the Stage Ⅰ magnetite shows systematic similarities to Kiruna-type magnetite rather than those from other types of deposits. Combined with geological features and previous studies on oxygen isotopes, we conclude that hydrothermal fluids have played a key role in the generation of the Pingchuan low-Ti iron deposit.

Oxidation and roasting characteristics of artificial magnetite pellets

Compared with natural magnetite concentrate, artificial magnetite with more lattice defects and higher activity tends to be oxidized. And the artificial magnetite pellet at the temperature of 400℃ has the oxidation degree approaching to natural magnetite concentrate pellet fired at 1000℃. Besides, two kinds of pellets displayed quite different roasting characteristics. When preheated at the same temperature for the same period of time, natural magnetite concentrate pellet and artificial magnetite concentrate pellet need to be roasted at the temperature of 1100℃ and 1250℃, respectively, for 25 min to reach the compressive strength of 3000 N per pellet. When roasted at the same temperature of 1200℃, natural magnetite pellet and artificial magnetite pellet need to be roasted for 15 min and 30 min, respectively, to reach the compressive strength over 3000 N per pellet. It can be seen from the test that artificial magnetite pellet has a faster oxidation, resulting in the high porosity in the produced pellet, and it requires a roasting process at higher temperature for a longer time to reach the desired compressive strength for industrial production.