Evaluation of VSK separation in the classification of two mineralogically different iron ore fines

With gradually diminishing Fe grade in tandem with the ever-increasing demand for high-grade iron ores,iron ore industries are now focusing on the beneficiation of low-grade iron ore fines,mainly considered waste.Besides,the scarcity of water at many of the mines’sites and the new water conservation policies of the governments have necessitated research on suitable dry beneficiation routes.In this context,an effort has been made to evaluate the efficacy of a dry classification unit,such as the VSK separator,in upgrading the iron values of two low-grade Indian iron ore fines,named Sample 1 and Sample 2.The mineralogical studies,involving scanning electron microscopy and X-ray diffraction,suggest that Sample 1 is a low-grade blue dust sample(51.2wt%Fe)containing hematite and quartz as the major minerals,while Sample 2(53.3wt%Fe)shows the presence of goethite in addition to hematite and quartz.The experiments,carried out using Box-Benkhen statistical design,indicate that blower speed,followed by feed rate,is the most influencing operating parameter in obtaining a good product in the VSK separator.At optimum levels of the operating factors,a fines product with~55wt%Fe at a yield of~40%can be obtained from Sample 1,while Sample 2 can be upgraded to~56wt%Fe at a yield of~85%.The results suggest that the VSK separator can be employed as an efficient intermediate unit operation in a processing circuit to upgrade the iron contents of iron ore fines.

Carburization of ferrochromium metals in chromium ore fines containing coal during voluminal reduction by microwave heating

Chromium ore fines containing coal (COFCC) can be rapidly heated by microwave to conduct the voluminal reduction, which lays a foundation of getting sponge ferrochromium powders with a lower content of C. Under the conditions of COFCC with n(O)-n(C) (molar ratio) as 1.00-0.84 and n(SiO2)-n(CaO) as 1.00-0.39, the samples were heated by 10 kW microwave power to reach the given temperatures and held for different times respectively. The results show that the low-C-Cr ferrochromium metal phase in the reduced materials forms before the high-C-Cr ferrochromium metal phase does. With increasing temperature the C content of ferrochromium metals is in a positive correlation with the content of Cr. The C content of ferrochromium metal in reduced materials is 0-10.07% with an average value of 4.68%. With the increase of holding time the Cr content in ferrochromium metals is in a negative correlation with the content of C, while the content of Fe changes in the contrary way. In the microwave field the kinetic conditions of carburization are closely related with the temperature of microwave heating, holding time and carbon fitting ratio.

Strengthening pelletization of manganese ore fines containing high combined water by high pressure roll grinding and optimized temperature elevation system

Pelletization is one of useful processes for the agglomeration of iron ore or concentrates. However, manganese ore fines are mainly agglomerated by sintering due to its high combined water which adversely affects the roasting performance of pellets. In this work, high pressure roll grinding(HPRG) process and optimization of temperature elevation system were investigated to improve the strength of fired manganese ore pellets. It is shown that the manganese ore possesses good ballability after being pretreated by HPRG twice, and good green balls were produced under the conditions of blending 2.0% bentonite in the feed, balling for 7 min at 16.00% moisture. High quality roasted pellets with the compressive strength of 2711 N per pellet were manufactured through preheating at 1050 °C for 10 min and firing at 1335 °C for 15 min by controlling the cracks formation. The fired manganese pellets keep the strength by the solid interconnection of recrystallized pyrolusite grains and the binding of manganite liquid phase which filled the pores and clearance among minerals. The product pellets contain high Mn grade and low impurities, and can be used to smelt ferromanganese, which provides a possible way to use imported manganese ore fines containing high combined water to produce high value ferromanganese.

The process analysis of fine iron ore reduced in fluidized bed

The processes of fine iron ore reduced in fluidized bed have been reviewed in this paper,the superiorities and limitations of the processes of direct reduction,pre-reduction in fluidized bed have also been comprehensively analysed,which matches with bath smelting furnace or coke bed type furnace.The analysis has also been made on several controversial topics,and the gas use ratio has been point out to be the key of the competition of the reduction process in fluidized bed.The suitability with final reduction furnace is also important to the energy saving in the whole smelting reduction process.

Kinetics of Voluminal Reduction of Chromium Ore Fines Containing Coal by Microwave Heating

The kinetics of voluminal reduction of chromium ore fines containing coal （COFCC） by microwave heating was studied. When the molar ratio of carbon to oxygen was 0.84 and that of CaO to SiO2 was 0.39 in COFCC, the temperature rising rate of COFCC by microwave heating was 62.5 ℃/min, 68.75 ℃/min, 70. 59 ℃/min, and 72.22 ℃/min at 1 000 ℃, 1 100 ℃, 1 200 ℃, and 1 300 ℃, respectively. The results show that the voluminal re duction of COFCC by microwave heating at solid-solid phase is first order reaction, with the apparent activation energy of 51. 480 kJ/mol. The limiting step of reaction rate for the overall reaction is the mass transfer of CO in the reduced product layer between dielectric particles of chromium ore and coal.

Temperature Rise Characteristics of Carbon-Containing Chromite Ore Fines in Microwave Field

To avoid the nonuniform phenomena of heat and mass transfer of metallurgical powdery materials caused by conventional heating method,the temperature rise characteristics of carbon-containing chromite ore fines in the microwave field were investigated using microwave heating in a microwave metallurgical furnace.The experimental results show that the carbon-containing chromite ore fines have better temperature rise characteristics in the microwave field at a frequency of 2.45 GHz.After heated in the microwave field of 10 kW,the temperature of 1 kg carbon-containing chromite ore fines rose up to 1 100 ℃ in 7 min,at a temperature rise rate of 157.1（℃·min-1·kg-1）,whereas the temperature of 1 kg carbon-containing magnetite ore fines rose only up to 1 000 ℃ in 10 min,at a temperature rise rate of 100（℃·min-1·kg-1）.With increasing carbon-fitting ratios and by adding calcic lime,their heating effects changed regularly.

Intensifying Gaseous Reduction of High Phosphorus Iron Ore Fines by Microwave Pretreatment

Gaseous reduction kinetics of the high phosphorus iron ore fines from Hubei in China and effect of microwave pretreatment on the gaseous reduction behavior were studied. Gaseous reduction kinetics were investigated by TG （Thermogravimetric） methods using LINSEIS STA PT 1600 thermal analysis equipment. Microwave pretreatments to the ore fines with four power levels were performed using a high temperature microwave reactor. Its effect was examined by TG methods and its mechanism was analyzed by SEM （scanning electron microscope） and EDS （energy dispersive spectrometer）. Gaseous reduction tests were carried out using a tubular furnace. Results of kinetic study indicate that controlling step of the gaseous reduction of the ore fines is a mixing control of gas internal diffusion and interface chemical reaction when reduction fraction is less than 0.8 and is solid state diffusion when reduction fraction is more than 0.8. Microwave pretreatment of the ore fines could change the pore structure of the oolitic unit to generate cracks, fissures and loose zones, which promotes reduction in the early stage and delays the occurrence of sintering. Gaseous reduction tests show in the condition that the ore fines are pretreated with a microwave power of 450 W for 4 min and reduced under temperature of 1 273 K, the gaseous reduction of the ore fines could be apparently intensified. Using CO or H2 as a reductant and ore fines being reduced for 1.5 to 2 h , increase of metallization rate of the ore fines is 10% to 13%.

Microstructure of Solid Phase Reduction on Manganese Oxide Ore Fines Containing Coal by Microwave Heating

Microstructure of solid phase reduction on manganese oxide ore fines containing coal （MOOFCC） is one of important kinetics conditions of influencing microwave heating. On condition thai an atomic molar ratio of ro ： rc in MOOFCC is 1 ： 1.06 as well as a molecular molar ratio of rSiO2： rCaO is 1 ： 1.28, 1 kg of MOOFCC is heated by microwave to reach 1 000-1 300℃ and hold different time respectively. Experiments show that the metal phase takes the iron-based metal compounds containing manganese as the main content. The manganese content of metal phase increases with the xise of temperature. The particle size of the metal phase is within the range from 0. 01 to 0.05 mm. MO2 phase in the stuff is entirely changed into MnO phase and the slag phase is mainly composed of wollastonite and manganese olivine. The stuff reduced is loose and massive as a whole and its porosity is from 30% to 45%. The low softening-melting property and the low density of the stuff impact, to some degree, the solid phase reduction of powder by microwave heating.

Slag/metal Separation Process of Gas-reduced Oolitic High-phosphorus Iron Ore Fines

Slag/metal separation process of the highly reduced oolitic high-phosphorus iron ore fines was investigated. Samples were prepared using the reduced ore fines （metallization rate： 88%） and powder additives of CaO and Na2CO3. Slag/metal separation behavior tests were conducted using a quenching method and the obtained metal parts were subjected to direct observation as well as microstructure examination with SEM and EDS; iron recovery and phosphorus distribution tests were conducted using a Si-Mo high temperature furnace and the obtained metal parts were examined by ICP-AES analysis and mass measurement. Thermodynamic calculation using coexistence theory of slag structure was also performed. Results show that temperature for slag/metal separation must be higher than 1823 K and a satisfying slag/metal separation of the highly reduced ore fines needs at least 4 min; phosphorus con- tent of hot metal is mainly determined by thermodynamics; temperature of 1823-1873 K and Na2CO3 mixing ratio of about 3 % are adequate for controlling phosphorus content to be less than 0.3 mass% in hot metal; temperature, time and Na2CO3 mixing ratio do not have significant effect on iron recovery, and iron recovery rate could be higher than 80% as long as a good slag/metal separation result is obtained.

Effects of pressure and plastic addition on sticking of fine iron ore particles in fluidized bed reduction

The adhesion of fine iron ore particles during fluidized bed reduction was studied using pressurized visible fluidized bed laboratory equipment.The results showed that the optimal operating parameters for pure hydrogen reduction under high pressure were reduction temperature of 1073 K,particle size of 0.18-0.66 mm,pure H_(2) linear velocity of 0.8 m/s,reduction pressure of 200 kPa,and reduction time of 50 min.When plastic particles were mixed into the fluidized bed,the optimal parameters were reduction temperature of 973 K,particle size of 0.18-0.66 mm,pure H_(2) linear velocity of 0.8 m/s,reduction pressure of 100 kPa,mass content of plastic particles of 8%,and reduction time of 65 min.The chemical reaction resistance is much higher than the inner diffusion resistance at the initial stage of the reaction,whereas,in later stage,the inner diffusion resistance exceeds the chemical reaction resistance.The contact area of iron atoms or iron whiskers gradually decreases with the increase in reduction pressure from 0.20 to 0.45 MPa,and the sticking trend gradually decreases.Adding plastic particles in the fluidized reduction process of fine iron ore can effectively inhibit the adhesion among fine iron ore particles.

Reduction Kinetics of Fine Iron Ore Powder in Mixtures of H_2-N_2 and H_2-H_2O-N_2 of Fluidized Bed

Reduction kinetics of fine iron ore powder in different gas mixtures were investigated in high-temperature fluidized bed at a scale of kilograms. Influence of processing parameters, such as particle size, gas flow velocity, height of charge, temperature, compositions of gas mixture, and percentage of inert components, on reduction ki- netics was experimentally determined under the condition of fluidization. The equations for calculating instantaneous and average oxidation rates were deduced. It was found that an increasing H2 O percentage in the gas mixture could obviously decrease the reduction rate because the equilibrium partial pressure of H2 decreased with increasing content of Hz O in the gas mixture and then the driving force of reduction reaction was reduced. When the H2 content was high, .the apparent reaction rate was so rapid when the average size of iron ore fines was less than 1 mm that the re- action temperature can be as low as 750 ℃ ; when the average size of iron ore fines was more than 1 mm, a high re- action temperature of 800 ℃ was required. In addition, it was also found that the content of H2O should be less than 10% for efficient reduction.

Recent status of fluidized bed technologies for producing iron input materials for steelmaking

Today steel is produced by two steelmaking processes, the basic oxygen furnace and the electric arc furnace, Three types of iron input materials for both processes are liquid hot metal or in solidified form as pig iron, direct reduced iron （DRI） and hot briquetted iron （HB1） as well as steel scrap. Hot metal, pig iron, DRI and HBI are virgin iron materials, which have to be produced from iron ore by the so-called ironmaking technologies. New ironmaking processes based on fluidized bed technology have been developed in the last two decades. The main advantage of these technologies is that fine ore can be directly used in the processes and prior treatment such as sintering or pelletizing can be avoided which is required for the established processes. Theoretical aspects for reduction of fine iron oxides in a fluidized bed reactor system will be explained. The fluidized bed reducing technologies utilized in the most advanced new ironmaking processes for direct use of fine ore, FINMET, Circored, FINEX~ and Hismelt will be compared.

Influence of Coating MgO on Sticking and Functional Mechanism during Fluidized Bed Reduction of Vanadium Titano-magnetite

The vanadium titano-magnetite （VTM） iron ore fines of 110--150/xm in diameter were reduced in a trans- parent quartz fluidized bed by 70 %CO-30 % H2 （volume fraction） mixtures. MgO powders served as coating agent to solve sticking problem. Two coating methods were introduced in this experiment： high temperature injection method and briquetting→oxidizing roast→crushing method. According to the experimental results, the minimum effective coating amount of MgO was 0. 1 mass%. The metallization ratio （MR） of the product rose from around 58% to above 90% with the above treatments. To investigate the sticking mechanism of fine ore, the morphology evolution was in- vestigated. Instead of iron whiskers, an interlaced fibrous porous surface formed. The ulvospinel （2FeO ： TiO2 ） in VTM is more difficult to be reduced than FeO according to thermodynamic calculation. XRD results showed that MgO diffused into Fe203 lattice before forming pleonaste （MgO · Fe2O3 ） during oxidizing roast at 1273 K. The melting point of the pleonaste is 1986 K and that made contribution to prevent the sticking problem.