Yuexin Han

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.

Preparation of homogeneous ZnO nanoparticles via precipitation-pyrolysis with Zn5(CO3)2(OH)6 as precursor

Abstract ZnO nanoparticles were synthesized via precipitation-pyrolysis (P&P), where the precursor zinc hydroxide carbonate (Zn5(CO3)2(OH)6) was obtained and then pyrolyzed. The results of TEM indicate that pyrolysis temperature is the predominant factor for controlling mean sizes of nanoparticles, ranging from 8 nm to 80 nm. Increasing the pyrolysis temperature enhances the mean size. The results of XRD show that nanoparticles are all of crystalline zincite. The mean size observed by TEM is in agreement with that calculated from the specific surface area(SSA) and the crystalline size calculated from the XRD patterns, indicating that the primary particles are rather uniform in size and have single crystals. The growth behaviors of epitaxy along the C-axis are responsible for the morphology of ZnO changing from sphere to rod-like shape, and then to reticulation. Compared with other synthesis approaches, P&P can get fairly good product with a relatively low cost.

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.

Effect of serpentine and sodium hexametaphosphate on ascharite flotation

Abstract Sodium hexametaphosphate (SHMP) was used to minimize the adverse effect of serpentine for improving ascharite recovery. The effects of particle size and content of SHMP, and serpentine on ascharite flotation process were investigated through flotation, zeta potential tests, FT-IR analysis, XPS analysis and DLVO theory. Particles interaction and mechanism of SHMP were also discussed. It was found that aggregation between serpentine and ascharite particles easily happened, and the particle size of serpentine had a profound impact on the ascharite recovery. In particular, the fine serpentine with size less than 38 μm had the greatest contribution to the deterioration of ascharite flotation performance. After SHMP treatment, the adverse effect of serpentine was significantly reduced. The mechanism of SHMP showed that it could alter the surface charges of serpentine and ascharite to prevent severe interparticle aggregation, which resulted in a well-dispersed pulp and benefited ascharite flotation process. The adsorption of SHMP on serpentine was due to hydrogen bonding and chemical adsorption, resulting in the formation of complex on serpentine surface to decrease its floatability.

Recovery of boron from high-boron iron concentrate using reduction roasting and magnetic separation

The comprehensive utilization of abundant high-boron iron concentrate is of particular significance to China, and the high-boron iron concentrate has not yet been utilized as a source for boron at an industrial scale due to its complex mineralogy and fine mineral dissemination. An innovative method was proposed for recovery of boron and iron from high-boron iron concentrate by reduction roasting and magnetic separation. The effects of reduction temperature and roasting time were investigated and their optimum conditions were determined. The mineralogical changes during roasting were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the pyrrhotite (FeS) contained in the high-boron iron concentrate and the new-formed FeS-Fe solid solution softened or melted at high temperatures owing to their low melting points, and then decreased the metallic iron ratio and accelerated the growth of metallic iron particles. Meanwhile, the magnetite and szaibelyite were converted into metallic iron and suanite, respectively. Consequently, boron was readily enriched into the non-magnetic product and the metallic iron was aggregated to the magnetic concentrate by magnetic separation. Boron recovery of 88.6% with corresponding B2O3 content of 14.5% and iron recovery of 95.1% with an iron grade of 92.7% were achieved when high-boron iron concentrate was reduced at 1125 °C for 150 min. Besides, the boron reactivity of the boron-rich non-magnetic product was up to 80.8%.

Flotation behaviors and mechanisms of chalcopyrite and galena after cyanide treatment

Abstract Adsorbing tests between CN − and chalcopyrite or galena were conducted firstly, and then flotation tests of the two cyaniding minerals were investigated in butyl xanthate (BX) system. Results showed that the interaction between CN − and the two mineral surfaces were both chemical adsorption and can be described by the Langmuir adsorption isotherm model. In the optimum condition of pH 6.5 and 4.0 mg/L BX, the recovery of cyaniding chalcopyrite and galena reached 82.1% and 63.9%, respectively. BX improved the hydrophobicity of the surfaces of the two minerals, although CN − reduced the contact angle on the surface of minerals. The inhibitory effect of CN − on chalcopyrite far outweighed galena. Electrostatic adsorption exists in the interaction between BX and the surface of galena after cyanide treatment in the pH range of 4.2–8.4, while the interactions between BX and the surface of chalcopyrite after cyanide treatment is chemical adsorption.