Dry separation of particulate iron ore using density-segregation in a gas–solid fluidized bed

A gas–solid fluidized bed has been used to separate particulate iron ore (+250–500 μm in size) by segregating the particles by density. The ore particles were put into a cylindrical column of inner diameter of 100 mm and bed height of 50 mm, and were fluidized at a given air velocity u₀/u_mf = 1.2–3.2 for 10 min. u₀ and u_mf are the superficial air velocity and the minimum fluidization air velocity, respectively. The bulk density of the ore particles after fluidization was measured as a function of height through the bed in 5 mm increments (the 50 mm height was divided into 10 layers) to investigate the density-segregation. The size of the particles in each of the 10 layers was also measured to investigate size-segregation. It was found that both density-segregation and size-segregation occurred as a function of height through the bed after fluidization at u₀/u_mf = 2.0. However, the segregation did not occur near the bottom of the bed for lower u₀/u_mf and did not occur near the top of the bed for larger u₀/u_mf. The origin of the segregation-dependence on the air velocity was discussed considering the air bubbles size and the fluidizing intensity at upper and lower sections of the bed. The Fe content of the 10 layers at u₀/u_mf = 2.0 was measured to calculate the Fe-grade and Fe-recovery. The ore-recovery was also calculated using the weight of ore particles as a function of height through the bed. The feed Fe-grade (before separation) was 52.1 wt%. If the ore particles in the bottom half of the bed were regarded as the product, the Fe-grade was 59.0 wt%, and the Fe-recovery and the ore-recovery were 68.5 wt% and 60.5 wt%, respectively.     

Hydrodynamic behavior of binary mixture of solids in a triple-bed combined circulating fluidized bed with high mass flux

Flow behaviors of binary mixture of silica sand and nylonshot (coal char substitute) were investigated in a triple-bed circulating fluidized bed (TBCFB) as a cold model of coal gasifier. The TBCFB consisted of a downer (ϕ 0.1 m × 6.5 m), a bubbling fluidized bed (0.75 m × 0.27 m × 1.9 m), a riser (ϕ 0.1 m × 16.6 m) and a gas-sealing bed (GSB, ϕ 0.158 m × 5 m). The initial fraction of the nylonshot in the solid mixture (X_nylon,i) was 15.4 and 30% on mass and volume bases, respectively, or otherwise, 30.7 and 50%. The maximum solids mass flux (G_s) at X_nylon,i of 15.4 and 30.7 wt% were 394 and 349 kg/m² s, respectively, when the gas velocity in the riser (U_gr) was 10 m/s. Apparent solids holdups of silica sand and nylonshot were calculated separately from the static pressure gradient across the riser and the downer. The results showed possibility of large-mass-flux circulation of char in the gasifier, which plays a significant role in decomposition of tar from pyrolysis as the primary step of gasification. A newly developed pressure balance model successfully predicted G_s of the binary mixtures in TBCFB.     

Improvement of dry float–sink separation of smaller sized spheres by reducing the fluidized bed height

In this study, the influence of the fluidized bed height on the float–sink of different sized spheres in a gas–solid fluidized bed was investigated. Fluidized beds with heights h = 200, 150, 100 and 50 mm were prepared using a cylindrical column of inner diameter = 290 mm and a mixture of zircon sand and iron powder as the fluidized medium. Float–sink experiments were carried out using density adjusted spheres of diameter D_sp = 40, 30, 20 and 10 mm. It was found that the float–sink performance at D_sp ?20 mm is not affected by the height of the bed, and the sharpness of separation (the density range where spheres neither float nor sink completely) is less than or equal to 200 kg/m³. In the case of D_sp = 10 mm, the sharpness of separation is a larger value (1100 kg/m³ at h = 200 mm), whereas it decreases with decreasing h and is 400 kg/m³ at h = 50 mm. The fluctuation of the surface height of the fluidized bed was visually recorded. The fluctuation is reduced by reducing h. The fluctuation vs. h correlates with the sharpness of separation at D_sp = 10 mm vs. h. These results indicate that the dry float–sink separation of smaller sized spheres is improved as the fluctuation of fluidized bed surface is decreased by reducing the fluidized bed height.     

La and Co substituted M-type barium ferrites processed by sol–gel combustion synthesis

The flake-like Ba_1−xLa_xCo_xFe_12−xO₁₉ (x = 0.0–0.4) were synthesized using sol–gel combustion synthesis process followed by the thermal insulation process and heating treatment. The synthesis process was investigated and the structure details, morphology, and magnetic properties were evaluated. TG/DTA was used to investigate the formation mechanism and to identify the thermal insulation temperature at 400 °C followed by the heat treatment temperature at 1200 °C. XRD patterns demonstrated that the unit cell volume and particle size decreased with the increase of the substitution content. The typical particles size was in the range of 1–2 μm in the planar dimension whilst the thickness was in the range of 200–500 nm. It was found from the VSM graphs that the saturation magnetizations M_s reached a maximum of 68.15 emu g⁻¹ at x = 0.3 and then decreases to 64.72 emu g⁻¹ at x = 0.3 whilst the coercivity H_c sustained decreases from 2190.70 to 1181.07 Oe g⁻¹ with substitution content increased from 0 to 0.4.     

Investigation on resistance to attrition of coated particles by response surface methodology

The purpose of the present study is to obtain better understanding of the influence of the coating thickness, h, coating formulation, T_g, and fluid bed temperature, T_bed, variables on the resistance to attrition of the coated sodium benzoate reference particles. Three reference coating materials (T_g = 50 – 125 – 150 °C) have been sprayed by using top spray fluid bed coater. Per each coating formulation three different coating levels (h = 1% – 5% – 9% w/w) have been obtained. The coating processes were performed at three different fluid bed temperatures (T_bed = 40 – 55 – 70 °C). The experiments have been designed according to the response surface methodology (RSM). Both single effects and interactions between single effects on the resistance to attrition (response variable) calculated by means of repeated impact tester were evaluated. From statistical analysis, the coating quantity appears to have a predominant effect on the resistance to attrition of the coated particle in these studied ranges of variables. This relationship is linear and positive, which means that an increasing quantity leads to more resistance to attrition. The interaction coating thickness – coating formulation, the interaction between the fluid bed temperature and the coating formulation and the coating formulation as well as the interaction costing thickness – fluid bed temperature were found to be very significant. On the contrary, no direct effect of the fluid bed temperature on the resistance to attrition is detected.     

Agglomerating vibro-fluidization behavior of nano-particles

An experiment study of agglomerating fluidization behavior of three kinds of nano-particles (SiO₂, TiO₂, ZnO) in vibro-fluidized bed (VFB) has been performed. At certain amplitude (3 mm) of vibrations applied, the minimum fluidization velocity decreases, whilst the equilibrium pressure drop increases with increase in the vibration frequency. The minimum fluidization velocity is nearly independent of the vibration amplitude at almost constant frequency of about 40 Hz, whilst the equilibrium pressure increases. Using the linear regression, the Richardson–Zaki exponents of three kinds of nano-particles have been calculated. R–Z analyses indicate that the particulate fluidization degree of cohesive particles can be greatly improved by vibration force.     

Influence of air bubble size on float–sink of spheres in a gas–solid fluidized bed

The float–sink of density adjusted spheres of different diameter (10–40 mm) in a gas–solid fluidized bed was investigated at various bed heights (50–200 mm). The maximum density of floating spheres (ρ_float) and the minimum density of sinking spheres (ρ_sink) were determined by the float–sink experiments. The fluidized bed density (ρ_fb) was measured using the height and cross section of the fluidized bed and total weight of the fluidized media. The diameter of air bubbles at the bed surface was measured at each bed height, and was normalized by the sphere diameter. It was found that the value of ρ_fb–ρ_float approaches zero as the normalized bubble diameter decreases from 4 to 0.5 regardless of the sphere diameter. The value of ρ_sink–ρ_fb for sphere diameter = 10 mm approaches zero as the normalized bubble diameter decreases from 4 to 1.5, whereas the value for sphere diameter = 20–40 mm rises from zero as the normalized bubble diameter decreases from 1.5 to 0.5. The float and sink of spheres basically tend to follow the fluidized bed density with decreasing the normalized bubble diameter. However, relatively larger spheres do not sink based on the density difference as the normalized bubble diameter decreases, which may be due to that the fluidized bed viscosity becomes larger as the normalized bed diameter decreases.     

The synthesis of nanocrystalline YIG in an ammonium nitrate melt

Yttrium iron garnet particles were synthesized in two different ways: first, in an ammonium nitrate melt (ANM) and second, via a solid-state reaction (SSR) route. The structural and magnetic properties of the samples were compared using XRD, SEM and dc magnetization measurements. It was observed for the ANM technique that the phase formation of YIG starts at 1000 °C and then develops with increasing temperature and sintering times. The saturation magnetization, M_s, increases sharply with increasing annealing temperature and then saturates at around 23 emu g^?1 above 1100 °C, while the coercivity decreases due to the increasing particle size. An almost single-phase sample was obtained through ANM route by annealing for 2 h at 1300 °C, after which the YIG fraction in the SSR sample was only 0.34, with M_s = 7.08 emu g^?1. The average particle sizes of the ANM samples were calculated using experimentally determined M_s values. It appeared that they vary from the sub-micron to the micron range, depending on the sintering temperature, and this coincides with the values determined from the SEM micrographs. These samples have homogeneous structures, small grains, good magnetic properties, and do not contain massive agglomerates. Therefore, the synthesis of YIG via the ANM technique represents another alternative to the SSR route.     

Determination of laminar and turbulent flow ranges through vertical packed beds in terms of particle friction factors

Despite the presence of a variety of studies dealing with the magnitude of particle Reynolds number, Re_p defining transition from laminar to turbulent regime for flow through packed beds, the manner is still one of the unknowns. An approach based on the experimental data concerning upward airflow through fixed cylindrical packed beds is presented in this paper. The utilized packed beds had the following ranges of; sphericity, Φ, 0.55 ? Φ ? 1.00, packing material diameter to bed length ratio, D_p/L, 0.04 ? D_p/L ? 0.72, and bed porosity, ε, 0.36 ? ε ? 0.56. The test cases covered the ranges of particle Reynolds number, Re_p 708 ? Re_p ? 7772 and particle Froude number; Fr_p 2.86 ? Fr_p ? 10.39. The measurements of pressure drop through packed bed; ΔP_Bed and superficial mean exit velocity; U are used to determine bed frictional effects in reference to the available literature on particle friction factors, f_p. The magnitude of Re_p defining transition is assumed to be 2000 with particular emphasis to the flow dynamics. The definitions of Bird et al. [R.B. Bird, W.E. Stewart, E.N. Lightfoot, Transport Phenomena, John Wiley and Sons, NY, 1960] are used to calculate f_p. The calculated f_p for the covered test cases are given as a function of pressure coefficient, ΔP* and Re_p, Fr_p, Φ, ε, D_p/L in the approximate ranges of laminar and turbulent flow for Re_p < 2000 and Re_p > 2000, respectively. The proposed separate equations of f_p = f_p(ΔP*, Re_p, Fr_p, Φ, ε, D_p/L) are satisfied for laminar and turbulent flows with corresponding average error margins of ±7.6% and ±18%. Furthermore ranges of transitional and fully rough flow through packed beds are estimated as 2000 ? Re_p ? 4000 and Re_p > 5000 with an analogy to the well-known Moody Chart in pipe flows.     

Dry dense medium separation of iron ore using a gas–solid fluidized bed

The dry dense medium separation of iron ore based on floating and sinking of ore particles in a gas–solid fluidized bed was investigated using zircon sand as the fluidized medium. The float-sink of ore particles with mean size D_ave = 23.6 mm was investigated as the fluidizing air velocity and the float-sink time were varied. It was found that gangue with density less than 2850 kg/m³ which float is able to be separated from valuable ore with density greater than 2850 km/m³ which sink. The set point (density where half the particles float and half the particles sink) decreases with increasing the air velocity, and that the float-sink separation is completed within 2 min. The influence of different sized ore particles in the float-sink experiments was also investigated. As a result, the iron ore with D_ave ? 17.6 mm are successfully separated. As D_ave decreases below 17.6 mm, the ore particles with density near the set point tend to scatter in the fluidized bed without floating or sinking, resulting in separation efficiency which decreases with decreasing D_ave. This indicates that the size of the ore particles is one of the major factors to achieve high separation efficiency.     

Nanocrystalline ruthenium oxide of fine mesoporosity prepared by templating for electrochemical capacitor applications

Hydrous ruthenium-oxide (RuO_xH_y) particles composed of nanocrystallites of ～5 nm in size were prepared, using hexagonal self-ordered mesoporous SiO₂ (SBA-15) as a template and RuCl₃ as the ruthenium precursor. The material has a highly mesoporous structure with a sharp distribution of fine pores of size around 3–4 nm. A high specific capacitance of 954 F g^?1 for the RuO_xH_y in 1 M H₂SO₄(aq) and a high energy density of 118.9 J g^?1 (or 32.7 W h kg^?1) were obtained from an electrochemical capacitor made with the material. Rectangular shape of the cyclic voltammetry was observed even increasing the scan rate to about 100 mV s^?1.     

Assessment of powder flow characteristics in incoherent soup concentrates

Soup mixtures represent specific flow characteristics while particles of different sizes and properties form a homogeneous mixture. In such mixtures, particle–particle interactions differ with addition of different fat types. This study was done to present a characterization and comparison of the cohesion index, powder flow speed dependency and caking properties of four different aggregates of fat particles with three different moisture contents, used in various compositions of powdered soup concentrates. ESEM micrographs have shown that different fat types bind particles differently. The moisture content of cream soup concentrates has a significant influence on cake height ratio of all cycles – more moisture causes higher cake height ratios (from r_s = 0.86 to r_s = 0.76; p < 0.05). Cream soup concentrates cake strength values are also significantly influenced by the mixtures moisture content – higher moisture content samples showed higher cake strength values (r_s = 0.73, p < 0.05). There is a significant correlation between compaction coefficients of all speeds and cake height ratios of all cycles for the cream soup concentrates. Combination of measuring techniques (Powder Flow Analyzer, ESEM and Mastersizer) together with Spearman’s Rank Order Correlation, as a method of non-parametric statistics, provides parturient results in characterization of extremely non-homogenous powder mixtures.     

Synthesis and characterization of a new p-phenylenediammonium dihydrogenmonophosphate [p-NH3C6H4NH3][H2PO4]2

Chemical preparation, crystal structure and NMR spectroscopy of a new organic cation p-phenylenediammonium monophosphate [p-NH₃C₆H₄NH₃][H₂PO₄]₂ are presented. This new compound crystallizes in the orthorhombic system, with the space group Pnma and the following parameters: a = 7.970 (2) Å; b = 22.770 (7) Å; c = 7.000 (7) Å, V = 1270.3 (11) Å³, Z = 4 and D_x = 1.590 g cm⁻³. The crystal structure has been determined and refined to R = 0.043 and R_(w) = 0.057 using 2623 independent reflections. The structural arrangement can be described as inorganic layers of (H₈P₄O₁₆)⁴⁻ units, parallel to (a, c) planes. The organic groups (p-H₃NC₆H₄NH₃)²⁺are anchored between the phosphoric layers to form a three-dimensional infinite network. This compound is also investigated by IR and solid-state ¹H, ¹³C and ³¹P MAS NMR spectroscopies. The ab initio method is used in the calculation of chemical shifts.     

Preparation,magnetic and optical properties of layered oxychalcogenides SmCuOCh (Ch = S or Se)

This paper reports on the synthesis and the electrical, magnetic and optical properties of SmCuOS and SmCuOSe. The magnetic properties reveal that Sm is in its 3+ oxidation state (μ^theo = g√J(J + 1) = 0.85 μ_B; g = 2/7) with a large Van Vleck contribution, and exclude the possibility of a divalent oxidation state for samarium (Sm²⁺; ⁷F₀ state, g = J = 0, μ_eff = 0).Optical properties were studied by means of diffuse reflectance and photoluminescence spectra in the UV–vis range. The electrical measurements show that the two samarium copper oxychalcogenides, SmCuOSe and SmCuOS are semiconductors with optical band gap (E_g) values of 2.60 and 2.90 eV, respectively.     

Unidirectional solidification of a Zn-rich Zn–2.17 wt%Cu hypo-peritectic alloy

Unidirectional solidification of a Zn-rich Zn–2.17 wt%Cu hypo-peritectic alloy has been carried out to investigate the microstructure evolution over the growth velocity range 0.02–4.82 mm/s at a temperature gradient of 15 K/mm by means of the Bridgman technique. Regular and plate-like two-phase cellular structures were observed in samples grown at growth velocities V above 0.48 and 2.64 mm/s, respectively. The dominant microstructure in samples grown below 0.22 mm/s was dendrites of primary ε in a matrix of secondary η. Intercellular spacing Λ decreased with increasing growth velocity V such that ΛV^1/2 is a constant of 316±55 μm^3/2/s^1/2. Secondary dendrite arm spacing λ₂ of primary ε decreased with increasing V such that λ₂V^1/3 is a constant of 14.9±0.9 μm^4/3/s^1/3. The observed transition from regular cells to plate-like cells of η is discussed on the basis of competitive growth and crystallographic effect.     

Crystal structure,thermal analysis and IR spectrometric investigation of l-tyrosine hydrazide diphosphate monohydrate

The monoclinic crystal structure of (C₉H₁₅N₃O₂)₂P₂O₇·H₂O denoted DLTHDP [a = 14.626(1), b = 6.1990(2), c = 14.562(1) Å, β = 97.289(3)°, Z = 2, monoclinic P2₁, D_cal = 1.508, D_mes = 1.49 g cm⁻³] has been solved using direct methods and refined to a reliability factor R = 4.37% for 2079 independent reflections. The DLTHDP structure can be described by infinite polyanions [P₂O₇·H₂O]_n⁴ⁿ⁻ organized in chains parallel to the b-direction and located at z = 1/2, alternating with organic cations associated in ribbons spreading along the a-direction. Multiple hydrogen bonds originating from amine, hydroxyl groups and water molecules donors [NH…O(N) and O(W)H…O] connect the different components of the lattice. The IR data of DLTHDP is reported and discussed according to the theoretical group analysis and by comparison with IR results of similar compounds. The coupled thermogravimetric analysis (TGA)–differential thermal analysis (DTA) thermal study shows the departure of one water molecule, confirming the hydrated character of this compound.     

Importance of H2 gas for growth of hot-wire CVD nanocrystalline 3C-SiC from SiH4/CH4/H2

Silicon carbide (SiC) thin films were prepared by hot-wire chemical vapor deposition from SiH₄/CH₄/H₂ and the influence of H₂ gas flow rate (F(H₂)) on the film properties was investigated. The SiH₄ gas flow rate was 1 sccm. At the CH₄ gas flow rate (F(CH₄)) of 1 sccm, nanocrystalline cubic SiC (nc-3C-SiC) grew even without H₂. On the other hand, at F(CH₄) = 2 sccm, amorphous SiC grew without H₂ and nc-3C-SiC grew above F(H₂) = 50 sccm. As F(H₂) was increased, the crystallinity improved both at F(CH₄) = 1 and 2 sccm. However, the mean crystallite size decreased at F(CH₄) = 1 sccm and increased at F(CH₄) = 2 sccm. We discuss growth mechanisms of nc-3C-SiC.     

Characterization of M(H2PO4)2·2H2O (M = Mn,Co, Ni) and their in situ thermal decomposition by magnetic measurements

It has been established that M(H₂PO₄)₂·2H₂O (M = Mn, Co, Ni) are paramagnetics between 173 and 353 K with weak antiferromagnetic exchange interaction between the metal ions. In situ magnetic measurements during the thermal decomposition of the salts show that the oxidation state and the octahedral coordination of M²⁺ are preserved. From the data obtained it could be supposed that in M(H₂PO₄)₂·2H₂O (M = Co, Ni) this process is topotactic with no long-range diffusion transport. In Mn(H₂PO₄)₂·2H₂O, the formation of the large variety of intermediate products probably requires more drastic rearrangement and diffusion of the manganese ions during the complex transformations, which reflect on both the value and the sign of the θ constants. M₂P₄O₁₂ (M = Mn, Co, Ni), which are the final decomposition products of the corresponding dihydrogen phosphates are paramagnetics in the temperature range of 295–573 K with antiferomagnetic interactions between the metal ions. The lattice parameters of Ni(H₂PO₄)₂·2H₂O have been calculated. It crystallizes in the monoclinic system with a = 7.228(1) Å; b = 9.778(1) Å; c = 5.306(1) Å; β = 94.50(1)°, SG P2₁/n with Z = 2.     

Ferrocene adsorbed into the porous octakis(hydridodimethylsiloxy)silsesquioxane after thermolysis in tetrahydrofuran media: An applied surface for ascorbic acid determination

Octakis(hydridodimethylsiloxi)silsesquioxane (Q₈M₈^H) was synthesized and Ferrocene was adsorbed in a polymeric net through electrostatic interactions, with anion forming after the cleavage of any siloxy groups (ESFc). The nanostructured materials (Q₈M₈^H and EsFc) were characterized by Fourier transform infrared spectra (FT-IR), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), Thermogravimetric analyses and Voltammetric technique The cyclic voltammograms of the graphite paste electrode modified with ESFc showed one redox couple with E⁰′ = 0.320 V (1.0 mol L^?1 NaCl, v = 50 mV s^?1), with a diffusion-controlled process and the redox process shows electrocatalytic activity for the oxidation of ascorbic acid.     

Shock propagation in a tape wrapped carbon fibre composite

The use of carbon fibre composites has become more prevalent in recent years. As such, detailed knowledge of the material behaviour over a range of conditions is needed. In particular, knowledge of the high strain rate response is desirable. The shock response of a tape wrapped carbon fibre composite of density 1.46 g cm^?3 has been determined using both lateral and longitudinal Manganin stress gauges. The U_S ? u_p Hugoniot was found to be U_S = 3.69 + 0.59u_p. Deviation from the Hugoniot was observed in the P–V/V₀ plane for impact stresses above 5 GPa. Further, use of lateral gauges allowed the Hugoniot elastic limit to be estimated; this was found to be approximately 1.53 GPa, comparable to other composite materials. In addition, oscillations were observed in multiple traces, and found to be a function of the thickness of the carbon fibre weave.