Yongsheng Sun

Recovery of iron from high phosphorus oolitic iron ore using coal-based reduction followed by magnetic separation

Oolitic iron ore is one of the most important iron resources. This paper reports the recovery of iron from high phosphorus oolitic iron ore using coal-based reduction and magnetic separation. The influences of reduction temperature, reduction time, C/O mole ratio, and CaO content on the metallization degree and iron recovery were investigated in detail. Experimental results show that reduced products with the metallization degree of 95.82% could be produced under the optimal conditions (i.e., reduction temperature, 1250°C; reduction time, 50 min; C/O mole ratio, 2.0; and CaO content, 10wt%). The magnetic concentrate containing 89.63wt% Fe with the iron recovery of 96.21% was obtained. According to the mineralogical and morphologic analysis, the iron minerals had been reduced and iron was mainly enriched into the metallic iron phase embedded in the slag matrix in the form of spherical particles. Apatite was also reduced to phosphorus, which partially migrated into the metallic iron phase.

Coal-based reduction mechanism of low-grade laterite ore

Abstract A low-grade nickel laterite ore was reduced at different reduction temperatures. The morphology of metallic particles was investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Experimental results indicate that the metallic nickel and iron gradually assemble and grow into larger spherical particles with increasing temperature and prolonging time. After reduction, the nickel laterite ore obviously changes into two parts of Fe-Ni metallic particles and slag matrix. An obvious relationship is found between the reduction of iron magnesium olivine and its crystal chemical properties. The nickel and iron oxides are reduced to metallic by reductant, and the lattice of olivine is destroyed. The entire reduction process is comprised of oxide reduction and metallic phase growth.

Distribution behavior of phosphorus in the coal-based reduction of high-phosphorus-content oolitic iron ore

This study focuses on the reduction of phosphorus from high-phosphorus-content oolitic iron ore via coal-based reduction. The distribution behavior of phosphorus (i.e., the phosphorus content and the phosphorus distribution ratio in the metal, slag, and gas phases) during reduction was investigated in detail. Experimental results showed that the distribution behavior of phosphorus was strongly influenced by the reduction temperature, the reduction time, and the C/O molar ratio. A higher temperature and a longer reaction time were more favorable for phosphorus reduction and enrichment in the metal phase. An increase in the C/O ratio improved phosphorus reduction but also hindered the mass transfer of the reduced phosphorus when the C/O ratio exceeded 2.0. According to scanning electron microscopy analysis, the iron ore was transformed from an integral structure to metal and slag fractions during the reduction process. Apatite in the ore was reduced to P, and the reduced P was mainly enriched in the metal phase. These results suggest that the proposed method may enable utilization of high-phosphorus-content oolitic iron ore resources.

Investigation of kinetics of coal based reduction of oolitic iron ore

Abstract An oolitic iron ore was isothermally reduced by coal at 1423–1573 K, and the reduction kinetics was investigated in detail. The degree of reduction and reduction rate increased with increasing temperature and C/O molar ratio to some extent at the same reduction time. In the entire reduction process, the reduction mechanism changes with changing experimental conditions. The degree of reduction under different experimental conditions should be represented by different reduction kinetic models. The reduction rate curves are similar in shape and could be analytically divided into initial, intermediate and final stages. The apparent activation energies of the three stages are 48·26, 69·80 and 127·58 kJ mol−1 respectively. The rate controlling mechanism in the reduction process was determined by analysing the reduction process and apparent activation energy. The rate controlling steps of these stages are combined gas diffusion and interfacial chemical reaction, surface chemical reaction and combined solid state diffusion and boundary reaction.

Size Distribution Behavior of Metallic Iron Particles in Coal-Based Reduction Products of an Oolitic Iron Ore

The size distribution of metallic iron particles is important to better understand the coal-based reduction mechanisms of refractory iron ores. This study was focused on the particle size distribution behavior of metallic iron in coal-based reduction products of an oolitic iron ore. The size of metallic iron particles was measured using image analysis, and the data obtained were analyzed using frequency and cumulative distributions. The curves of the size-frequency distribution and cumulative passing percentage of metallic iron particles exhibited nearly the same trend with respect to particle size. The particle size distribution of metallic iron particles was markedly influenced by both reduction time and temperature. The number of metallic iron particles with large size increased with the reduction time and temperature. Goodness-of-fit tests indicated that the power function and the cumulative distribution function (CDF) of the log-normal distribution best fitted the experimental data of size frequency distribution and cumulative passing percentage of metallic iron particles, respectively.

Separation and recovery of iron from a low-grade carbonate-bearing iron ore using magnetizing roasting followed by magnetic separation

ABSTRACT In this study, a process of magnetizing roasting followed by low-intensity magnetic separation (MR-LMS), which is used to separate and recover iron from a low-grade carbonate-bearing iron ore (containing 34.6 wt.% Fe), was investigated. A magnetic concentrate containing 65.4 wt.% Fe with an iron recovery rate of 92.6 wt.% was obtained under optimal conditions: roasting temperature of 800°C, roasting time of 8 min, bitumite ratio of 10:100, grinding fineness of around 85 wt.% passing 38 µm, and magnetic intensity of 0.12 T. In addition, the phase transformation and magnetic properties were analyzed by X-ray diffraction (XRD) and vibrating sample magnetometry (VSM) to reveal the mechanism.

Enrichment of phosphorus in reduced iron during coal based reduction of high phosphorus-containing oolitic hematite ore

With the objective of phosphorus enrichment in the metallic iron during coal based reduction, high phosphorus oolitic hematite ore was reduced in the presence of coal with the coal/ore molar ratio (C/O, the molar ratio of fixed carbon in coal to oxygen in iron oxides of ore) varying from 1·0 to 2·5 at temperatures ranging from 1473 to 1548 K. The metallic iron was beneficiated from reduction products by magnetic separation. The results showed that the enrichment of phosphorus in the metallic iron improved with increasing temperature and C/O molar ratio. The phosphorus content and the phosphorus enrichment could reach 2·5 and 77·5%, respectively, with a C/O molar ratio of 2·5 at 1548 K and after 60 min reduction. The high phosphorus-containing metallic iron so obtained could then be converted to steel and high phosphorus steelmaking slag that can be used as a phosphate fertiliser. Kinetic analysis demonstrated that the process of phosphorus enrichment in the metallic iron could be divided into two stages, early and late, described by phase boundary controlled reaction and diffusion controlled, respectively. At the early stage, the apparent activation energy and pre-exponential factor of phosphorus enrichment decreased from 182·12 kJ mol−1 and 9509·06 min−1 to 132·60 kJ mol−1 and 395·44 min−1, respectively, when the C/O molar ratio was increased from 1·0 to 2·5. At the later stage, the apparent activation energy and pre-exponential factor were 245·87 kJ mol−1 and 172 818·99 min−1 at a C/O molar ratio of 1·0, respectively, whilst those were reduced to 210·73 kJ mol−1 and 13 930·28 min−1 at a C/O molar ratio of 2·5.

Reduction behavior of hematite in the presence of coke

The reduction kinetics of hematite in the presence of coke as a reductant was studied via isothermal and non-isothermal thermodynamic analyses. The isothermal reduction of hematite was conducted at a pre-determined temperature ranging from 1423 to 1573 K. The results indicated that a higher reduction temperature led to an increased reduction degree and an increased reduction rate. The non-isothermal reduction of hematite was carried out from room temperature to 1573 K at various heating rates from 5 to 15 K·min−1. A greater heating rate gave a greater reduction rate but decreased reduction degree. With an increase in temperature, both the reduction rate and the reduction degree increased at a smaller rate when the temperature was less than 1150 K, and they increased at a higher rate when the temperature was greater than 1150 K before completion of the reduction reaction. Both the isothermal and the non-isothermal reduction behaviors of hematite were described by the Avrami–Erofeev model. For the isothermal reduction, the apparent activation energy and pre-exponential factor were 171.25 kJ·mol−1 and 1.80 × 105 min−1, respectively. In the case of non-isothermal reduction, however, the apparent activation energy and pre-exponential factor were correlated with the heating rate.

Reduction behaviour of apatite in oolitic haematite ore using coal as a reductant

An oolitic haematite ore containing 1.31% P was reduced in the presence of coal at temperatures ranging from 1473 to 1548 K. The reduction behaviour of apatite, which is the only P-containing mineral in the ore, was studied at different reduction conditions based on the thermodynamic analysis. Thermodynamic calculation showed that the SiO2, Al2O3 or SiO2–Al2O3 could decrease the standard Gibbs free energy and initial temperature of the apatite reduction significantly. The initial temperature of the apatite reduction decreased from above 1650 K to 1497, 1541 and 1419 K in the presence of SiO2, Al2O3 and SiO2–Al2O3, respectively. Experimental results indicated that the reduction conditions obviously affected the reduction behaviour of apatite. A higher reduction temperature, C/O molar ratio and a longer reduction time were favourable for the apatite reduction. The reduction degree of apatite reached 83.62% at 1548 K with a C/O molar ratio of 2.5 and after 60 min reduction. In addition, the reduction kinetics of apatite was investigated by common order reactions, and the corresponding kinetic parameters were computed according to the Arrhenius function. The results demonstrated that the most suitable mechanism for the apatite reduction was first-order reaction, and the apparent reaction rate of apatite reduction increased with increasing reduction temperature and C/O molar ratio. Furthermore, both the apparent activation energy and pre-exponential factor of apatite reduction decreased slightly with increasing C/O molar ratio.

Formation and characterization of metallic iron grains in coal-based reduction of oolitic iron ore

To reveal the formation and characteristics of metallic iron grains in coal-based reduction, oolitic iron ore was isothermally reduced in various reduction times at various reduction temperatures. The microstructure and size of the metallic iron phase were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and a Bgrimm process mineralogy analyzer. In the results, the reduced Fe separates from the ore and forms metallic iron protuberances, and then the subsequent reduced Fe diffuses to the protuberances and grows into metallic iron grains. Most of the metallic iron grains exist in the quasi-spherical shape and inlaid in the slag matrix. The cumulative frequency of metallic iron grain size is markedly influenced by both reduction time and temperature. With increasing reduction temperature and time, the grain size of metallic iron obviously increases. According to the classical grain growth equation, the growth kinetic parameters, i.e., time exponent, growth activation energy, and pre-exponential constant, are estimated to be 1.3759 ± 0.0374, 103.18 kJ·mol−1, and 922.05, respectively. Using these calculated parameters, a growth model is established to describe the growth behavior of metallic iron grains.