Study on properties of sinter mineral phases

In this study,the properties of sinter mineral phases were investigated by X-ray diffraction,optical microscopy quantitative observation,electron probe microanalysis,and the nanoindentation technique. The mechanisms that form return fines are discussed with respect to the factors of microregion composition,sintering temperature,and the reactive behavior of pisolite. The study results indicate the following：（ 1） Sinter mineral assemblage mainly comprises hematite,magnetite,calcium ferrite,and glass. In addition,the mineral assemblage of sinter products includes a great deal of calcium ferrite and melt-erosive magnetite,an abundance of secondary hematite,and a small amount of primary iron ore; whereas the mineral assemblage of return fines contains plentiful amounts of euhedral magnetite and secondary hematite,a large amount of relic pisolite with particle sizes less than1 mm,and relatively less calcium ferrite. In particular,some calcium ferrite was found to coexist with relic iron ore in a fiber-like microstructure.（ 2） Dentritic calcium ferrite has less SiO_2 and Al_2O_3,higher basicity（ w_（CaO）/w_（SiO_2））and a mole ratio of Fe_2O_3/CaO,whereas platy and blocky calcium ferrites have more SiO_2 and Al_2O_3,lower basicity and a mole ratio of Fe_2O_3/CaO.（ 3） The hardness of hematite is the highest（ around 18-22 GPa）,those of calcium ferrite and magnetite are relatively lower,and that of glass is the lowest. In terms of the formation mechanism of return fines,because of their weak ability to resist external shocks,these sorts of mineral phases and microstructures-（1） euhedral magnetite and glass formed in microregions with low basicity;（2） SFCA-Ⅰand relic iron ore formed in regions with a relatively low sintering temperature; and（3） relic pisolite and its nearby reaction regions-are inclined to form return fines.

Isothermal reduction kinetics and mineral phase of chromium-bearing vanadium–titanium sinter reduced with CO gas at 873–1273 K

Reduction of chromium-bearing vanadium–titanium sinter（CVTS） was studied under simulated conditions of a blast furnace, and thermodynamics and kinetics were theoretically analyzed. Reduction kinetics of CVTS at different temperatures was evaluated using a shrinking unreacted core model. The microstructure, mineral phase, and variation of the sinter during reduction were observed by X-ray diffraction, scanning electron microscopy, and metallographic microscopy. Results indicate that porosity of CVTS increased with temperature. Meanwhile, the reduction degree of the sinter improved with the reduction rate. Reduction of the sinter was controlled by a chemical reaction at the initial stage and inner diffusion at the final stage. Activation energies measured 29.22–99.69 k J/mol. Phase transformations in CVTS reduction are as follows： Fe_2O_3→Fe_3O_4→FeO→Fe; Fe_2TiO_5→Fe_2TiO_4→FeTiO_3; FeO·V_2O_3→V_2O_3; FeO·Cr_2O_3→Cr_2O_3.

The efficiency and accuracy of probability diagram, spatial statistic and fractal methods in the identification of shear zone gold mineralization: a case study of the Saqqez gold ore district,NW Iran

In this study,geochemical anomaly separation was carried out with methods based on the distribution model,which includes probability diagram(MPD),fractal(concentration-area technique),and U-statistic methods.The main objective is to evaluate the efficiency and accuracy of the methods in separation of anomalies on the shear zone gold mineralization.For this purpose,samples were taken from the secondary lithogeochemical environment(stream sediment samples)on the gold mineralization in Saqqez,NW of Iran.Interpretation of the histograms and diagrams showed that the MPD is capable of identifying two phases of mineralization.The fractal method could separate only one phase of change based on the fractal dimension with high concentration areas of the Au element.The spatial analysis showed two mixed subpopulations after U=0 and another subpopulation with very high U values.The MPD analysis followed spatial analysis,which shows the detail of the variations.Six mineralized zones detected from local geochemical exploration results were used for validating the methods mentioned above.The MPD method was able to identify the anomalous areas higher than 90%,whereas the two other methods identified 60%(maximum)of the anomalous areas.The raw data without any estimation for the concentration was used by the MPD method using aminimum of calculations to determine the threshold values.Therefore,the MPD method is more robust than the other methods.The spatial analysis identified the detail soft hegeological and mineralization events that were affected in the study area.MPD is recommended as the best,and the spatial U-analysis is the next reliable method to be used.The fractal method could show more detail of the events and variations in the area with asymmetrical grid net and a higher density of sampling or at the detailed exploration stage.

Experimental Study of the Melting Reaction and Genetic Mechanism of Mineral Phase Transformation in Granulite Facies Metamorphism

The high-temperature and high-pressure experiment on natural block rock indicates that dehydration-melting of hydrous biotite (Bi) and partial melting of felsic minerals in garnet-biotite-plagioclase gneiss are mainly controlled by temperature, while mineral phase transformation is not only controlled by temperature-pressure conditions but also genetically associated with hydrous mineral dehydration-melting and partial melting of felsic minerals. According to the characteristics of biotite dehydration-melting and garnet transformation reaction, three stages may be distinguished: (1) when the experimental temperature is 700℃, biotite transforms to ilmenite (Ilm) + magnetite (Mt) + H2O and garnet to magnetite (Mt); (2) when the temperature is 730-760℃, biotite is dehydrated and melted and transformed into K2O-rich melt + Ilm + Mt, and garnet, into hypersthene (Hy) + cordierite (Crd); (3) when the temperature is up to or higher than 790℃, biotite is dehydrated and melted and transformed into melt + Hy + Ilm + Mt, and garnet, into the hypersthene (Hy) + spinel (Sp) + cordierite (Crd) assemblage. The melt proportion and its evolutionary characteristics are mainly controlled by dehydration-melting of hydrous minerals and partial melting of felsic minerals besides P-T conditiops: In addition to the traditional solid 4- solid (or fluid) reaction and dehydration-melting reaction, the metamorphic reaction involving melts (reaction between unmelted minerals and melts) is one of the most important reactions in granulite facies metamorphism and its attendant remelting (or regional migmatization). This experiment may provide dependable experimental data for an in-depth study of the genetic mechanism of mineral assemblage evolution and its geological dynamic significance in granulite facies metamorphism of the studied area.

Characteristics of the mineral phase constituents of lacustrine deposits from the Fildes Peninsula of King George Island,Antarctica and their environmental implication

Based on analytical data of mineral phase constituents at three sections from Tern Lake, West Lake and Kitezh Lake in the Fildes Peninsula of King George Island, Antarctica, the characteristics of mineral phase constituents, material source and their environmental implication have been discussed. Research results indicate that lacustrine deposits came primarily from widespread volcanic rocks at the peninsula. Under cold and dry condition in Antarctica, the weathering process of the parent rocks in some area is mainly physical weathering with a weak chemical one. The relation curves of abundance of kaolinite and calcite against deposition age change steeply at the boundary between lacustrine and glacial deposits, indicating that the corresponding environment changes are abrupt, which may be related to different transportation fashion of both different deposits and the protection of glacial deposits.

Prospects of utilization of waste dumped low-grade limestone for iron making: A case study

Low grade dumped limestone sample having high silica of 8.1%, 36.8% CaO, and 3% Al2O3 has been studied with the aim to reduce the silica level to below 3% for its utilization in iron making. Beneficiation study of the sample was initiated with desliming of the feed sample of -100 μm to remove the siliceous ultrafine particles and to improve the feed quality. Flotation study was carried out by column flotation technique varying the collector dosage, superficial air flow velocity and froth depth to assess their effect on silica reduction and CaO recovery. It was observed that increased collector dosage and superficial air velocity increases the recovery of CaO, and increase in the froth depth reduces the mass flow and silica content in the concentrate. The best result was found at 1.25 cm/sec superficial air velocity, 25 cm froth depth, 1.25 kgpt collector dosage and concentrate assayed 47.3% CaO, 2.8% silica with 72% CaO recovery.

Potentially harmful metals,and health risk evaluation in groundwater of Mardan,Pakistan:Application of geostatistical approach and geographic information system

This study investigates the values of pH,total dissolved solids(TDS),elevation,oxidative reduction potential(ORP),temperature,and depth,while the concentrations of Br,and potentially harmful metals(PHMs)such as Cr,Ni,Cd,Mn,Cu,Pb,Co,Zn,and Fe in the groundwater samples.Moreover,geographic information system(GIS),XLSTAT,and IBM SPSS Statistics 20 software were used for spatial distribution modeling,principal component analysis(PCA),cluster analysis(CA),and Quantile-Quantile(Q-Q)plotting to determine groundwater pollution sources,similarity index,and normal distribution reference line for the selected parameters.The mean values of pH,TDS,elevation,ORP,temperature,depth,and Br were 7.2,322 mg/L,364 m,188 mV,29.6℃,70 m,0.20 mg/L,and PHMs like Cr,Ni,Cd,Mn,Cu,Pb,Co,Zn,and Fe were 0.38,0.26,0.08,0.27,0.36,0.22,0.04,0.43 and 0.86 mg/L,respectively.PHMs including Cr(89%),Cd(43%),Mn(23%),Pb(79%),Co(20%),and Fe(91%)exceeded the guideline values set by the world health organization(WHO).The significant R^(2)values of PCA for selected parameters were also determined(0.62,0.67,0.78,0.73,0.60,0.87,-0.50,0.69,0.70,0.74,-0.50,0.70,0.67,0.79,0.59,and-0.55,respectively).PCA revealed three geochemical processes such as geogenic,anthropogenic,and reducing conditions.The mineral phases of Cd(OH)_(2),Fe(OH)_(3),FeOOH,Mn_(3)O_(4),Fe_(2)O_(3),MnOOH,Pb(OH)_(2),Mn(OH)_(2),MnO_(2),and Zn(OH)_(2)(-3.7,3.75,9.7,-5.8,8.9,-3.6,2.2,-4.6,-7.7,-0.9,and 0.003,respectively)showed super-saturation and under-saturation conditions.Health risk assessment(HRA)values for PHMs were also calculated and the values of hazard quotient(HQ),and hazard indices(HI)for the entire study area were increased in the following order:Cd>Ni>Cu>Pb>Mn>Zn>Cr.Relatively higher HQ and HI values of Ni,Cd,Pb,and Cu were greater than one showing unsuitability of groundwater for domestic,agriculture,and drinking purposes.The long-term ingestion of groundwater could also cause severe health concerns such as kidney,brain dysfunction,liver,stomach problems,and even cancer.

The effect of extracellular polymeric substances (EPS) of iron-oxidizing bacteria (Ochrobactrum EEELCW01) on mineral transformation and arsenic (As) fate

Extracellular polymeric substances(EPS)are an importantmedium for communication and material exchange between iron-oxidizing bacteria and the external environment and could induce the iron(oxyhydr)oxides production which reduced arsenic(As)availability.The main component of EPS secreted by iron-oxidizing bacteria(Ochrobactrum EEELCW01)was composed of polysaccharides(150.76-165.33 mg/g DW)followed by considerably smaller amounts of proteins(12.98–16.12 mg/g DW).Low concentrations of As(100 or 500μmol/L)promoted the amount of EPS secretion.FTIR results showed that EPS was composed of polysaccharides,proteins,and a miniscule amount of nucleic acids.The functional groups including-COOH,-OH,-NH,-C=O,and-C-O played an important role in the adsorption of As.XPS results showed that As was bound to EPS in the form of As3+.With increasing As concentration,the proportion of As3+adsorbed on EPS increased.Ferrihydrite with a weak crystalline state was only produced in the system at 6 hr during the mineralization process of Ochrobactrum sp.At day 8,the minerals were composed of goethite,galena,and siderite.With the increasing mineralization time,the main mineral phases were transformed from weakly crystalline hydrous iron ore into higher crystallinity siderite(FeCO_(3))or goethite(α-FeOOH),and the specific surface area and active sites of minerals were reduced.It can be seen from the distribution of As elements that As is preferentially adsorbed on the edges of iron minerals.This study is potential to understand the biomineralizationmechanism of iron-oxidizing bacteria and As remediation in the environment.

Influence of Sugar Filter Mud on Formation of Portland Cement Clinker

To explore the mechanisms of filter mud （FM） in the portland cement clinker formation, and to make effective use of FM in the cement production as lime-based raw materials, the influences of FM on the apparent activation energy of calcium carbonate decomposition, liquid phase amount, crystalline phase and tricalcium silicate polymorphism were investigated by TA, SEM and XRD. The experimental results show that FM can reduce apparent activation energy of calcium carbonate decomposition, and increase liquid phase amount. Appropriate FM replacement ratios are useful to promoting the C3S formation and heightening the C3S content. New phases of ct-C2S and C2S-0.5Ca3 （PO4）2 can be found in the clinkers while the ratios are above 15%. In addition, impurities in FM can induce the C3S polymorpb to transform. Key words： filter mud; apparent activation energy; liquid phase; mineral phase; tricalcium silicate polymorphism

In-situ measurement of mineral phase transition and kinetics in roasting process of Bayan Obo mixed rare earth concentrate by sodium carbonate

In this study,the Bayan Obo rare earth concentrates mixed with Na_(2)CO_(3)were used for roasting research.The phase change process of each firing stage was analyzed.The kinetic mechanism model of the continuous heating process was calculated.This study aims to recover valuable elements and optimize the production process to provide a certain theoretical basis.Using X-ray diffraction(XRD),Fourier infrared spectroscopy,scanning electron microscopy with energy dispersive spectrometry,the reaction process and the existence of mineral phases were analyzed.The variable temperature XRD and thermogravimetric method were used to calculate the roasting kinetics.The phase transition results show that carbonate-like substances first decompose into fine mineral particles,and CaO,MgO,and SiO_(2)react to form silicates,causing hardening.Further,REPO_(4)and NaF can directly generate CeF_(3) and CeF_(4)at high temperatures,and a part of CeF_(4)and NaF forms a solid solution substance Na_(3)CeF_(7).Rare earth oxides calcined at a high temperature of 750℃were separated to produce Ce_(0.6)Nd_(0.4)O_(1.8),Ce_(4)O_(7),and LaPrO_(3+x).Then,BaSO_(4),Na_(2)CO_(3),and Fe_(2)O_(3)react to form barium ferrite BaFe_(12)O_(19);the kinetic calculation results show that during the continuous heating process,the apparent activation energy E reaches the minimum in the entire reaction stage in the temperature range of 440-524℃,and the reaction order n reaches the maximum,which indicates that the decomposition product REFO significantly impacts the reaction system and reduces the activation energy.The mechanism function is F(α)=[-In(1-α)]^(1/3).The reaction order n reaches the minimum in the temperature range of 680-757℃,and the apparent activation energy E is large.The difficulty of the reaction increases during the final stage.The reaction mechanism function is F(α)=[1-(1-α)^(1/3)]^(2).Observing the entire reaction stage,the step of controlling the reaction rate changes from random nucleation to three-dimensional diffusion(spherical symmetry).

Phase transition of bastnaesite concentrate in calcification process

The phase transformation in calcification process was investigated by X-ray diffraction （XRD） and differential scanning calorimeter （DSC）, and the effect of calcification on the leaching rate of rare earth was analyzed. The results show that bastnaesite transforms into rare earth hydrate at the cal- cification temperature range of 225-300 ℃. However, this transition is verified to be an efficient reaction for the acti- vating bastnaesite when the temperature is higher than 200 ℃. The leaching rate of rare earth increases to 89.17 % for activating bastnaesite from 36.27 % for the bastnaesite, and it is the highest with calcification temperature of 250 ℃, which is consistent with the result of DSC analysis. The transition of rare earth oxyfluoride into RE（OH）3 is acceler- ated by the addition of NaOH according to the experiments of different calcification systems.

Properties of ten-year-aged argon oxygen decarburization stainless steel slag

The characteristics of argon oxygen decarburization slag(AODS)for smelting stainless steel that has been aged for 10 years were analyzed.Three types of AODSs distributed at three positions in a slag heap were sampled for comparison experiments.Chemical analysis,mineral phase identification,thermogravimetric analysis,and micromorphology analysis were used to study the element migration trends and carbonation behavior of AODS after long-term aging.Sequential leaching tests were performed to study the chromium leachability of the aged AODS.The results show that during the long-term aging process,the AODS heap had undergone oxidation and carbonation,accompanied by element migration and mineralogical evolution.The surface slag had the highest degree of carbonation but the weakest chromium leachability.The chemical composition of the middle slag was the closest to that of the original slag.In the bottom steel slag,in addition to magnesium,certain depositions of other elements were present.The matrix phases in the aged slag were dicalcium silicate and merwinite,and the chromium was mainly wrapped in these matrix phases in the form of oxides,spinels,or alloys.Under the combined effects of carbonation and oxidation,the leaching characteristics of the chromium in the aged slag varied greatly depending on the location.The bottom slag had the strongest chromium leachability,and the hexavalent chromium had long-term continuous leachability.

Research progress on multiscale structural characteristics and characterization methods of iron ore sinter

At present,blast furnace ironmaking is still the main process for producing molten iron,and sinters are the main raw material for blast furnace ironmaking.A sinter with good metallurgical performance can not only ensure smooth operation of the blast furnace but also reduce the blast furnace fuel ratio and increase the molten iron production.Structure is the most important factor affecting the metallurgical properties of the sinter.Thus,the research progress of sinter pore and mineral phase structures was reviewed and the mechanism by which they influence sinter properties was expounded.Multiscale characterization methods for the sinter and their advantages and disadvantages were introduced,and the future research direction of sinter was discussed.