Thermodynamics and kinetics of extracting zinc from zinc oxide ore by the ammonium sulfate roasting method

Thermodynamic analyses and kinetic studies were performed on zinc oxide ore treatment by (NH₄)₂SO₄ roasting technology. The results show that it is theoretically feasible to realize a roasting reaction between the zinc oxide ore and (NH₄)₂SO₄ in a temperature range of 573-723 K. The effects of reaction temperature and particle size on the extraction rate of zinc were also examined. It is found that a surface chemical reaction is the rate-controlling step in roasting kinetics. The calculated activation energy of this process is about 45.57 kJ/mol, and the kinetic model can be expressed as follows:1-(1-α)1/3=30.85 exp(-45.57/RT)·t. An extraction ratio of zinc as high as 92% could be achieved under the optimum conditions.     

Effect of magnesium on the aluminothermic reduction rate of zinc oxide obtained from spent alkaline battery anodes for the preparation of Al–Zn–Mg alloys

The aluminothermic reduction of zinc oxide (ZnO) from alkaline battery anodes using molten Al may be a good option for the elaboration of secondary 7000-series alloys. This process is affected by the initial content of Mg within molten Al, which decreases the surface tension of the molten metal and conversely increases the wettability of ZnO particles. The effect of initial Mg concentration on the aluminothermic reduction rate of ZnO was analyzed at the following values: 0.90wt%, 1.20wt%, 4.00t%, 4.25wt%, and 4.40wt%. The ZnO particles were incorporated by mechanical agitation using a graphite paddle inside a bath of molten Al maintained at a constant temperature of 1123 K and at a constant agitation speed of 250 r/min, the treatment time was 240 min and the ZnO particle size was 450-500 mesh. The results show an increase in Zn concentration in the prepared alloys up to 5.43wt% for the highest initial concentration of Mg. The reaction products obtained were characterized by scanning electron microscopy and X-ray diffraction, and the efficiency of the reaction was measured on the basis of the different concentrations of Mg studied.     

Addition of IrO2 to RuO2+TiO2 coated anodes and its effect on electrochemical performance of anodes in acid media

Ternary mixed metal oxide coatings with the nominal composition IrxRu(0.6-x)Ti0.4O2(x=0, 0.1, 0.2, 0.3) on the titanium substrate were prepared by thermal decomposition of a chloride precursor mixture. Surface morphology and microstructure of the coatings were investigated by Scanning electron microscopy(SEM), Field emission scanning electron microscopy(FE-SEM) and X-ray diffraction(XRD) analysis. Systematic study of electrochemical properties of these coatings was performed by cyclic voltammetry(CV) and polarization measurements. The corrosion behavior of the coatings was evaluated under accelerated conditions(j=2 A cm-2) in acidic electrolyte. The role of iridium oxide admixture in the change of electrocatalytic activity and stability of Ru0.6Ti0.4O2coating was discussed. Small addition of IrO2can improve the stability of the RuO2+TiO2mixed oxide, while the electrocatalytic activity for oxygen evolution reaction(OER) is decreased. The shift of redox potentials for Ru0.6Ti0.4O2electrode that is slightly activated with IrO2and improvement in the stability can be attributed to the synergetic effect of mixed oxide formation.     

Hot-corrosion behavior of Cr2O3-CNT-coated ASTM-SA213-T22 steel in a molten salt environment at 700℃

The present work investigates the hot-corrosion behavior of carbon nanotube (CNT)-reinforced chromium oxide coatings on boiler steel in a molten salt (Na₂SO₄-60wt%V₂O₅) environment at 700℃ under cyclic conditions. The coatings were deposited via the high-velocity oxygen fuel process. The uncoated and coated steel samples were subjected to hot corrosion in a silicon tube furnace at 700℃ for 50 cycles. The kinetics of the corrosion behavior was analyzed through mass-gain measurements after each cycle. The corrosion products were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray analysis techniques. The results revealed that uncoated steel suffered spallation of scale because of the formation of nonprotective Fe₂O₃ scale. The coated steel samples exhibited lower mass gains with better adhesiveness of oxide scale with the steel alloy until the end of exposure. The CNT-reinforced coatings were concluded to provide better corrosion resistance in the hot-corrosion environment because of the uniform dispersion of CNTs in the coating matrix and the formation of protective chromium oxides in the scale.     

Simulation experiments on the reaction system of CH_4-MgSO_4-H_2O

H2S-rich gas in carbonate reservoirs is usually attributed to thermochemical sulfate reduction (TSR). In this paper, thermal simulation experiments on the reaction system of CH4-MgSO4-H2O were carried out using autoclave at 425℃―525℃. The threshold temperature for initiating TSR is much lower than our previous studies (550 ℃ ). Properties of the reaction products were analyzed by microcoulometry, gas-chromatography (GC), Fourier transform-infrared spectrometry (FT-IR) and X-ray diffraction (XRD) methods. Thermodynamics and reaction kinetics of TSR processes were investigated on the basis of the experimental data. The results show that thermochemical reduction of magnesium sulfate with methane can proceed spontaneously to produce magnesium oxide, hydrogen sulfur, and carbon diox-ide as the main products, and high temperature is thermodynamically favorable to the reaction. Ac-cording to the reaction model, the calculated activation energy of TSR is 101.894 kJ/mol, which is lower than that by most previous studies. Mg2 may have played a role of catalytic action in the process of TSR. The elementary steps of TSR and reaction mechanism were discussed tentatively. The study can provide important information on the explanation of geochemical depth limit for natural gas and on the generation of high H2S gas in deep carbonates reservoirs.     

Zinc oxide nanostructures and porous films produced by oxidation of zinc precursors in wet-oxygen atmosphere

Wet oxidation can be used to produce high quality zinc oxide(ZnO) nanostructures at moderately high temperatures with low requirements of equipment and experimental conditions.Zn precursor films were prepared by magnetron sputtering and controlled ZnO nanostructures were produced by oxidation of the Zn precursor films in wet O_2.The growth mechanism of the ZnO nanowires and nanobelts in wet oxidation was discussed based on the experimental results.Silver and nitrogen doping were realized in the wet oxida...     

(NH4)2SO4焙烧?浸出法从氧化锌矿石中提取锌

An improved method of (NH₄)₂SO₄ roasting followed by water leaching to utilize zinc oxidized ores was studied. The operating parameters were obtained by investigating the effects of the molar ratio of (NH₄)₂SO₄ to zinc, roasting temperature, and holding time on zinc extraction. The roasting process followed the chemical reaction control mechanism with the apparent activation energy value of 41.74 kJ·mol?1. The transformation of mineral phases in roasting was identified by X-ray diffraction analysis combined with thermogravimetry–differential thermal analysis curves. The water leaching conditions, including the leaching temperature, leaching time, stirring velocity, and liquid-to-solid ratio, were discussed, and the leaching kinetics was studied. The reaction rate was obtained under outer diffusion without product layer control; the values of the apparent activation energy for two stages were 4.12 and 8.19 kJ·mol?1. The maximum zinc extraction ratio reached 96% while the efficiency of iron extraction was approximately 32% under appropriate conditions. This work offers an effective method for the comprehensive use of zinc oxidized ores.     

Thermodynamics and phase transformations in the recovery of zinc from willemite

Willemite is a common component of zinc and lead metallurgical slags that, in the absence of effective utilization methods, cause serious environmental problems. To solve this problem and increase zinc recovery, we proposed a novel extraction method of zinc from willemite by calcified roasting followed by leaching in NH₄Cl-NH₃·H₂O solution. The thermodynamics and phase conversion of Zn₂SiO₄ to zinc oxide (ZnO) during calcified roasting with CaO were investigated. The mechanism of mineralogical phase conversion and the effects of the CaO-to-Zn₂SiO₄ mole ratio (n(CaO)/n(Zn₂SiO₄)), roasting temperature, and the roasting time on zinc-bearing phase conversion were experimentally investigated. The results show that Zn₂SiO₄ was first converted to Ca₂ZnSi₂O₇ and then to ZnO. The critical step in extracting zinc from willemite is the conversion of Zn₂SiO₄ to ZnO. The zinc percent leached in the ammonia leaching system rapidly increased because of the gradual complete phase conversion from willemite to ZnO via the calcified roasting process.     

One-pot synthesis and optical properties of In-and Sn-doped ZnO nanoparticles

Colloidal indium-doped zinc oxide (IZO) and tin-doped zinc oxide (ZTO) nanoparticles were successfully prepared in organic solution,with metal acetylacetonate as the precursor and oleylamine as the solvent.The crystal and optical properties were characterized by X-ray diffraction,UV-visible spectrophotometry,and fluorescence spectroscopy,respectively;the surface and structure morphologies were observed by scanning electron microscopy and transmission electron microscopy.The XRD patterns of the IZO and ZTO nanoparticles all exhibited similar diffraction peaks consistent with the standard XRD pattern of ZnO,although the diffraction peaks of the IZO and ZTO nanoparticles were slightly shifted with increasing dopant concentration.With increasing dopant concentration,the fluorescent emission peaks of the IZO nanoparticles exhibited an obvious red shift because of the difference in atomic radii of indium and zinc,whereas those of the ZTO nanoparticles exhibited almost no shift because of the similarity in atomic radii of tin and zinc.Furthermore,the sizes of the IZO and ZTO nanoparticles distributed in the ranges 20-40 and 20-25 nm,respectively,which is attributed to the difference in ionic radii of indium and tin.     

Thermodynamic analysis on the formation mechanism of MgO·Al_2O_3 spinel type inclusions in casing steel

MgO·Al2O3 spinel type inclusions in casing steel were analyzed by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS).The results show that there are three forms.One is pure MgO·Al2O3 spinel,another is the composite oxide of the Mg-Al-Ca-Si-O system,and the third is the complex with oxide as a core covered by sulfide.The formation mechanisms were studied.The influences of slag basicity and vacuum degree on the magnesium content during the vacuum treatment of molten steel and furnace lining in molten steel were calculated with the coexistence theory of slag structure.The results show that the magnesium content increases with the increase in slag basicity and aluminum content in molten steel,and decreases with the increase in CO partial pressure.     

Mechanism of Cathode Process of B(Ⅲ) in LiF-NaF-KBF4 Melt by Electrochemical Titration Technique

The mechanism of cathode process of B(Ⅲ) at molybdenum and platinum electrodes in LiF-NaF-KBF₄ melt was studied and the transferred electron number of the reaction was calculated by means of cyclic voltammetry.The effect of adsorption of electroactive component on the electrochemical response (e.g., the voltammetric i─E curves) was analyzed and discussed. The "electrochemical spectra" for linear sweep voltammetry was used to elucidate the electrode reaction accompanied by a following transform process. The results show that the reduction of B(Ⅲ) to B(0) proceeds in reversible one step three-electron reaction and the cathode process of B(Ⅲ) is affected by product adsorbed strongly at the electrode surface. It is assumed that the reduction and deposition of B(Ⅲ) at molybdenum and platinum electrodes proceed in two kinds of mechanism: (1) B(Ⅲ)+ 3e = B_ads→ B (surface diffusion deposition mechanism) and (2) B(Ⅲ) + 3e = B (direct deposition mechanism).     

铁酸锌焙烧后的还原行为及氨浸特性

A novel method for recovering zinc from zinc ferrite by reduction roasting–ammonia leaching was studied in this paper. The reduction thermodynamic of zinc ferrite by CO was analyzed. The effects of roasting parameters on the phase transformation and conversion rate of zinc ferrite, and the leaching behavior of zinc from the reductive roasted samples by ammonia leaching, were experimentally investigated. The mineralogical phase compositions and chemical compositions of the samples were characterized by X-ray diffraction and chemical titration methods, respectively. The results showed that most of the zinc ferrite was transformed to zinc oxide and magnetite after weak reduction roasting. 86.43% of the zinc ferrite was transformed to zinc oxide under the optimum conditions: CO partial pressure of 25%, roasting temperature of 750°C, and roasting duration of 45 min. Finally, under the optimal leaching conditions, 78.12% of zinc was leached into the solution from the roasted zinc ferrite while all iron-bearing materials were kept in the leaching residue. The leaching conditions are listed as follows: leaching duration of 90 min, ammonia solution with 6 mol/L concentration, leaching temperature of 50°C, solid-to-liquid ratio of 40 g/L, and stirring speed of 200 r/min.     

Characteristics of the reduction behavior of zinc ferrite and ammonia leaching after roasting

A novel method for recovering zinc from zinc ferrite by reduction roasting–ammonia leaching was studied in this paper. The reduction thermodynamic of zinc ferrite by CO was analyzed. The effects of roasting parameters on the phase transformation and conversion rate of zinc ferrite, and the leaching behavior of zinc from the reductive roasted samples by ammonia leaching, were experimentally investigated. The mineralogical phase compositions and chemical compositions of the samples were characterized by X-ray diffraction and chemical titration methods, respectively. The results showed that most of the zinc ferrite was transformed to zinc oxide and magnetite after weak reduction roasting. 86.43% of the zinc ferrite was transformed to zinc oxide under the optimum conditions: CO partial pressure of 25%, roasting temperature of 750°C, and roasting duration of 45 min. Finally, under the optimal leaching conditions, 78.12% of zinc was leached into the solution from the roasted zinc ferrite while all iron-bearing materials were kept in the leaching residue. The leaching conditions are listed as follows: leaching duration of 90 min,ammonia solution with 6 mol/L concentration, leaching temperature of 50°C, solid-to-liquid ratio of 40 g/L, and stirring speed of 200 r/min.     

Characterization of mechanothermally processed nanostructured ZnO

In this paper, the Taguchi method with an L₉(34) orthogonal array was used as experimental design to determine the optimum conditions for preparing ZnO nanoparticles via a mechanothermal route. ZnSO₄·H₂O and Na₂CO₃ were used as starting materials. The effects of milling time, Na₂CO₃/ZnSO₄·H₂O molar ratio, and ball-to-powder mass ratio (BPR) on the bandgap (E_g) of ZnO nanoparticles were investigated. The ranges of the investigated experimental conditions were 5–15 h for the milling time (t), 1.0–1.2 for the Na₂CO₃/ZnSO₄·H₂O molar ratio (M), and 10–30 for BPR. The milling time and BPR exhibited significant effects; an increase in milling time reduced the bandgap. The optimum conditions from this study were t₃ = 15 h, M₁ = 1, and BPR₂ = 20. Only two significant factors (t₃, 15 h; BPR₂, 20) were used to estimate the performance at the optimum conditions. The calculated bandgap was 3.12 eV, in reasonable agreement with the experimental results obtained under the optimized conditions.     

The v-v energy transfer of highly vibrationally excitedstates (Ⅱ)──Vibrational quenching of CO(v) by H_2O

The vibrational energy transfer from highly vibrationally excited CO to H 2O molecules is studied by time-resolved Fourier transform infrared emission spectroscopy (TR FTIR). Following the 193 nm laser photolysis of CHBr 3 and O 2 the secondary reactions generate CO(v). The infrared emission of CO(v→v-1) is detected by TR FTIR. The excitation of H 2O molecules is not observed. By the method of the spectral simulation and the differential technique, 8 rate constants for CO(v)/H 2O system are obtained: (1.7±0.1), (3.4±0.2), (6.2±0.4), (8.0±1.0), (9.0±2.0), (12±3), (16±4) and (18±7) (10 -13cm 3·molecule -1·s -1). At least two reasons lead to the efficient energy transfer. One is the contributions of the rotational energy to the vibational energy defect and the other is the result of the complex collision. With the SSH and ab initio calculations, the quenching mechanism of CO(v) by H 2O is suggested.     

Influence of nanometric CeO_2 coating on high temperature oxidation of Cr

Isothermal and cyclic oxidation behavior of chromium and its superficially applied nanometric CeO2 samples were studied at 900℃in air. Scanning electronic microscopy (SEM), transmission electronic microscopy (TEM) and high resolution electronic microscopy (HREM) were used to examine the morphology and micro-structure of oxide films. It was found that ceria addition greatly improved the anti-oxidation ability of Cr both in isothermal and cyclic oxidizing experiments. Acoustic emission (AE) technique was used in situ to monitor the cracking and spalling of oxide films, and AE signals were analyzed in time-domain and number-domain according to the related oxide fracture model. Laser Raman spectrometer was also used to study the stress status of oxide films formed on Cr with and without ceria. The main reason for the improvement in anti-oxidation of chromium was that ceria greatly reduced the growing speed and grain size of Cr2O3. This fine-grained Cr2O3 oxide film might have better high temperature plasticity and could relieve parts of compressive stress by means of creeping, and maintained the ridge character and relatively low internal stress level. Meanwhile, ceria application reduced the size and the number of interfacial defects, while remarkably enhanced the adhesive property of Cr2O3 oxide scale formed on Cr substrate.     

Synthesis and Optical Property Study on ZnO Nanostructures Via Vapor Phase Growth

Nanostructural zinc oxide films have been synthesized via vapor phase growth by heating pure zinc powder. Scanning electron microscopy (SEM) images and X-ray diffraction (XRD) results showed that four kinds of morphologies ZnO nanostructures namely nanowires, well-aligned nanorods, nanofeathers and hexagonal nanorods were formed and all of wurtzite structural crystals. The results indicated that the temperature and substrate play an important role in the formation of different morphologies of ZnO nanostructures. The photoluminescence (PL) measurement was carried out for the wellaligned nanorods ZnO sample and blue emission peaks at 420 and 444 nm have been observed at room temperature. And the blue emission mechanism is discussed.     

Enhanced deposition of ZnO films by Li doping using radio frequency reactive magnetron sputtering

Radio frequency (RF) reactive magnetron sputtering was utilized to deposit Li-doped and undoped zinc oxide (ZnO) films on silicon wafers. Various Ar/O₂ gas ratios by volume and sputtering powers were selected for each deposition process. The results demonstrate that the enhanced ZnO films are obtained via Li doping. The average deposition rate for doped ZnO films is twice more than that of the undoped films. Both atomic force microscopy and scanning electron microscopy studies indicate that Li doping significantly contributes to the higher degree of crystallinity of wurtzite–ZnO. X-ray diffraction analysis demonstrates that Li doping promotes the (002) preferential orientation in Li-doped ZnO films. However, an increase in the ZnO lattice constant, broadening of the (002) peak and a decrease in the peak integral area are observed in some Li-doped samples, especially as the form of Li₂O. This implies that doping with Li expands the crystal structure and thus induces the additional strain in the crystal lattice. The oriented-growth Li-doped ZnO will make significant applications in future surface acoustic wave devices.     

Hot-corrosion behavior of Cr_2O_3–CNT-coated ASTM-SA213-T22 steel in a molten salt environment at 700°C

The present work investigates the hot-corrosion behavior of carbon nanotube(CNT)-reinforced chromium oxide coatings on boiler steel in a molten salt(Na_2SO_4–60 wt%V_2O_5) environment at 700°C under cyclic conditions. The coatings were deposited via the high-velocity oxygen fuel process. The uncoated and coated steel samples were subjected to hot corrosion in a silicon tube furnace at 700°C for 50 cycles. The kinetics of the corrosion behavior was analyzed through mass-gain measurements after each cycle. The corrosion products were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray analysis techniques. The results revealed that uncoated steel suffered spallation of scale because of the formation of nonprotective Fe_2O_3 scale. The coated steel samples exhibited lower mass gains with better adhesiveness of oxide scale with the steel alloy until the end of exposure. The CNT-reinforced coatings were concluded to provide better corrosion resistance in the hot-corrosion environment because of the uniform dispersion of CNTs in the coating matrix and the formation of protective chromium oxides in the scale.     

Crystal structure and hydrogen storage properties of (La,Ce)Ni5-xMx (M=Al,Fe, or Co) alloys

The effects of partial substitution of La by Ce and Ni by Al, Fe, or Co in LaNi₅-based alloys on hydrogen storage performance were systematically studied. All samples were prepared using vacuum arc melting in an argon atmosphere. The results showed that for La-Ni_5-xM_x (M=Al, Fe, or Co) alloys, the lattice constants and unit cell volumes increased with an increasing amount of Al and Fe. On the other hand, these parameters decreased upon partial substitution of La by Ce. In addition, the lattice constant remained almost constant in the La_0.6Ce_0.4Ni_5-xCo_x alloys regardless of the value of x (x=0.3, 0.6, or 0.9), as Ce might enhance the homogeneity of the CaCu₅-type phase in Co-containing alloys. The hydrogen storage properties of the alloys were investigated using pressure, composition, and temperature isotherms. The experimental results showed that the plateau pressure decreased with an increasing content of Al, Fe, or Co, but it increased with Ce addition. Furthermore, the plateau pressures of all Co-containing alloys were almost identical upon substitution with Ce. Finally, the enthalpy (ΔH) and entropy (ΔS) values for all alloys were calculated using van't Hoff plots. The relationship between the lattice parameters and enthalpy changes for hydrogenation will be discussed.