Effect of Sintering Conditions on Structure of Manganese Zinc Ferrite Powders

The structures of the Mn-Zn ferrites synthesized under different sintering conditions by the sol-gel method were investigated by the X-ray diffraction （XRD） and the scanning electron microscopy （SEM） with focus on two factors： the pre-sintering treatment and the calcining time. The results show that the sintering conditions have significant effects on the structures and the particle size of the Mn-Zn ferrites. Compared with the products without pre-sintering, those pre-sintered at 500℃ have a single phase and no diffraction peaks of Fe2O3 that could be found. The effects of the pre-sintering temperature on the structures of the ferrites were also studied. As a result, 500℃ proves to be the favorite in the pre-sintering treatment. The XRD patterns of the ferrites calcined at 1 200℃ for 6 h will present diffraction peaks of pure crystallization of spinel phase while those for 2 h or 4 h will show peaks of Fe2O3. The SEM also bears witness to well-grown grains of pure Mn-Zn ferrites if calcined for 6 hours.

Reductive leaching of zinc and indium from industrial zinc ferrite particulates in sulphuric acid media

Zinc ferrite is the principal constituent in zinc neutral-leach residue（NLR） which is commonly treated by hot-acid leaching in electrolytic zinc plants. Reductive leaching of zinc ferrite with sphalerite concentrate as a reducing agent was performed. It was found that leaching of zinc ferrite in the presence of sphalerit concentrate was a viable process that effectively extracted zinc and indium and converted Fe^3＋ into Fe^2＋ at the same time. Reflux leaching tests by two stages were performed to achieve extractions of 98.1% for zinc and 97.5% for indium, and a Fe^2＋/Fe^3＋ molar ratio of 9.6 in leach solution was also obtained. The leaching behaviors of other elements, such as iron, copper and tin were also studied. The results showed that iron and copper were completely leached, whereas tin presented lower extraction values.

Selective reduction process of zinc ferrite and its application in treatment of zinc leaching residues

The traditional zinc hydro-metallurgy generates a large amount of zinc ferrite residue rich in valuable metals. The separation of iron is crucial for resource recycling of valuable metals in zinc ferrite residue. A novel selective reduction roasting？leaching process was proposed to separate zinc and iron from zinc leaching residue which contains zinc ferrite. The thermodynamic analysis was employed to determine the predominant range of Fe3O4 and ZnO during reduction roasting process of zinc ferrite. Based on the result of thermodynamic calculation, we found thatV（CO）/V（CO＋CO2） ratio is a key factor determining the phase composition in the reduction roasting product of zinc ferrite. In the range ofV（CO）/V（CO＋CO2） ratio between 2.68% and 36.18%, zinc ferrite is preferentially decomposed into Fe3O4 and ZnO. Based on thermogravimetric （TG） analysis, the optimal conditions for reduction roasting of zinc ferrite are determined as follows： temperature 700？750 °C, volume fraction of CO 6% and V（CO）/V（CO＋CO2） ratio 30%. Based on the above results, zinc leaching residue rich in zinc ferrite was roasted and the roasted product was leached by acid solution. It is found that zinc extraction rate in zinc leaching residue reaches up to 70% and iron extraction rate is only 18.4%. The result indicates that zinc and iron can be effectively separated from zinc leaching residue.

Thermodynamics and kinetics of carbothermal reduction of zinc ferrite by microwave heating

The kinetics of carbon reduction of ZnFe2O4 in the temperature range of 550-950 °C was investigated in a microwave tank-type reactor. The mechanism of formation of ZnO and Fe3O4/FeO by the decomposition of ZnFe2O4 was detailed using the equilibrium calculations and thermodynamics analysis by HSC chemistry software 6.0. In addition, the effects of decomposition temperature, the C/ZnFe2O4 ratio, the particle size and the microwave power were assessed on the kinetics of decomposition. Zn recovery as high as 97.93%could be achieved at a decomposition temperature of 750 °C with C/ZnFe2O4 ratio of 1：3, particle size of 61-74 μm and microwave power of 1200 W. The kinetics of decomposition was tested with different kinetic models and carbon gasification control mechanism was identified to be the appropriate mechanism. The activation energy for the carbon gasification reaction was estimated to be 38.21 kJ/mol.

Preparation and characterization of composite microspheres of nano zinc ferrite/poly(D,L-lactide-co-alanine)

Magnetic nano zinc ferrite fliuds were synthesized using an improved liquid phase chemical method, which would be used to replace tradditional iron oxides magnetic material. A novel copolymer （PLAA） with D, L-lactide （D, L-LA） and alanine was synthesized using stannous octoate as initiator. Magnetic polymer microspheres were fabricated with nano zinc ferrite fluid coated with alanine modified poly lactide. These as-prepared zinc ferrite fluids, modified poly lactide and magnetic composites, were characterized with X-ray diffraction diffractometer, FT-IR spectrometer, nuclear magnetic resonance spectrometer, scanning electron microscope, transmission electron microscope, vibrating sample magnetometer, and thermogravimetric analyzer. The results demonstrate that the as-prepared zinc ferrite is spinel type of ZnFe2O4 nano crystals with particle size of 20-45 nm and magnetization of 32×10^-3 A.m2. Alanine is copolymerized with lactide, and the prepared composite magnetic microsphere is coated with the modified polylactide, with mass fraction of 45.5% of PLA, particle size ranging from 80-300 nm, and magnetization of 10.6×10^-3 A·m^2, which suggests ZnFe2O4 enjoys a stable magnetization after being coated by polymer.

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.

Bench-Scale Testing of Zinc Ferrite Sorbent for Hot Gas Clean-up

Advanced integrated gasification combined cycle （IGCC） power generation systems require the development of high-temperature, regenerable desulfurization sorbents, which are capable of removing hydrogen sulfide from coal gasifier gas to very low levels. In this paper, zinc ferrites prepared by co-precipitation were identified as a novel coal gas desulfurization sorbent at high temperature. Preparation of zinc ferrite and effects of binders on pore volume, strength and desulfurization efficiency of zinc ferrite desulfurizer were studied. Moreover, the behavior of zinc ferrite sorbent during desulfurization and regeneration under the temperature range of 350-400 ℃ are investigated. Effects of binders on the pore volume, mechanical strength and desulfurization efficiency of zinc ferrite sorbents indicated that the addition of kaolinite to zinc ferrite desulfurizer seems to be superior to other binders under the experimental conditions.

Effect of Sintering Temperature and Zinc Content on Some Properties of Li-Zn Ferrites

Li-Zn mixed ferrites with composition formula ZnxLi0.5-x/2Fe2.5-x/2O4 (0.2≤x≤0.8) were prepared by the usual ceramic method in 1000~1150℃. The effects of Zn substitution and sintering temperature on the formation, densification, microstructure and a.c. electrical conductivity have been studied. Under the effect of changing the firing temperature and Zn content, high sintered Li-Zn ferrite bodies are achieved. More fine structure bodies having high electrical resistance are obtained at high Zn content

Synthesis and Characterization of Trivalent Al Substituted Zinc Ferrite using Ethylene Diamine (EDA) as Ligand

Nano domain Al substituted Zinc ferrite was prepared by chemical route using Ethylene Diamine as ligand.High purity precursors nitrate salts of Zinc,Fe(3+),Al(3+)were utilized along with citric acid which acts as both fuel and complexing agent.Two different molar ratios of Zn(2+):(Fe3+):Al(3+)is 1:1.5:0.5 and 1:1.25:0.75.After ensuring proper mix of the solution Ethylene diamine was added dropwise to form a gel like mass with proper pH control.Before annealing,thermal analysis was carried to determine the crystallization/phase transition zone.Drying was carried in several stages.Initially,gel like mass was obtained after drying at 40°C while pH was about 7.Drying of gel was carried in oil bath at about 90°C and powdered mass obtained was grinded followed by auto combustion at 150°C for 60 minutes before annealing at 150°C,350°C,650°C,950°C for 2 hours to ensure the phase formation.Crystallite size,lattice strain and lattice parameters were studied from XRD analysis.

Radio-frequency-heating capability of silica-coated manganese ferrite nanoparticles

MnFe204 nanoparticles （NPs） with various sizes and tight size-distribution were synthesized by a chemical solution- phase method. The as-synthesized NPs were coated with a silica shell of 4 nm-5 nm in thickness, enabling the water- solubility and biocompatibility of the NPs. The MnFe204 NPs with a size of less than 18 nm exhibit superparamagnetic behavior with high saturated magnetization. The capacity of the heat production was enhanced by increasing particle sizes and radio frequency （RF） field strengths. MnFe204/SiO2 NPs with 18-nm magnetic cores showed the highest heat- generation ability under an RF field. These MnFe204/SiO2 NPs have great potentiality to cancer treatments, controlled drug releases, and remote controls of single cell functions.

Preparation and Microstructure of Spinel Zinc Ferrite ZnFe_2O_4 by Co-precipitation Method

Spinel zinc ferrites ZnFe2O4, prepared by co-precipitation method using the zinc nitrate Zn（NO3）2·6H2O and ferric nitrate Fe（NO3）3·2H2O as the raw materials, were characterized by the thermo gravimetric analysis （TG） and differential scanning calorimeter （DSC）, X-ray diffraction （XRD） and scanning electron microscope （SEM）. The influence of synthesis conditions, such as Zn/Fe molar ratio, pH value, the sintering temperature and time, on the microstructures was detailedly investigated. The relationships between the microstructures and the synthesis conditions were discussed. The results show that the pure spinel zinc ferrites ZnFe2O4 are formed when the Zn/Fe molar ratio is 1.05∶2 at pH=8.5 or Zn/Fe molar ratio is 1∶2 at Ph=9-10, and the precursors are sintered at 1100 ℃ for 4 h. Especially no other phases are observed when the Zn/Fe molar ratio is 1∶2 at pH=10 and the precursor is sintered above 700 ℃ for 4 h. The higher sintering temperature and longer sintering time contribute to grain growth.

Preparation, characterization and photocatalytic properties of nanometer zinc ferrite

A combustion synthesis method was adapted for the efficient preparation ofpure zinc ferrite particles (ZnFe_2O_4). It is based on the exothermic reaction of the correspondingmetal nitrates with a reducing agent, to produce extremely fine-grained ashes that readily convertinto pure ZnFe_2O_4 with treating thermally. The composition and microstructure of the so-obtainedsamples were studied by XRD (X-ray powder diffraction), TEM (Transmission Electron Microscopy) andAFM (Atomic Force Microscopy). These results showed that the range of particle size of ZnFe_2O_4 isabout 15-25 nm. Photocatalytic activities of nanometer ZnFe_2O_4 were also evaluated by degradationof the curcumin solution.

Surfactant-assisted synthesis and magnetic properties of monodispersed manganese ferrite nanocrystals

Monodispersed manganese ferrite （MnFe2O4） nanocrystals could be successfully synthesized in large quantities via a facile synthetic technique based on the pyrolysis of organometallic compound precursor, in which octadecene was used as solvent, and oleic acid and oleylamine were used as capping ligands. MnFe204 nanocrystals were obtained with size in a tunable range of 4- 15 nm and their morphologies could be tuned from spherical to triangle-shaped by varying the surfactants. The phase structure, morphology, and size of the products were characterized in detail by X-ray diffraction （XRD） and transmission electron microscopy （TEM）. Magnetic properties of MnFe2O4 nanocrystals with different morphologies were measured using a superconducting quantum interference device （SQUID）. Both monodisperse MnFe204 nanocrystals with spherical and triangle-shapes are superparamagnetic at room temperature while ferromagnetic at 2 K. The pyrolysis method may provide an effective route to synthesize other spinel ferrites or metal oxides nanocrystals.

Effect of chemical activation process on adsorption of As(V) ion from aqueous solution by mechano-thermally synthesized zinc ferrite nanopowder

Nanostructured ZnFe2O4 was synthesized by the heat treatment of a mechanically activated mixture of ZnO/α-Fe2O3.X-ray diffraction(XRD)and differential thermal analysis(DTA)results demonstrated that,after 5 h of the mechanical activation of the mixture,ZnFe2O4 was formed by heat treatment at 750°C for 2 h.To improve the characteristics of ZnFe2O4 for adsorption applications,the chemical activation process was performed.The 2 h chemical activation with 1 mol·L?1 HNO3 and co-precipitation of 52%?57%dissolved ZnFe2O4 led to an increase in the saturated magnetization from 2.0 to 7.5 emu·g?1 and in the specific surface area from 5 to 198 m2·g?1.In addition,the observed particle size reduction of chemically activated ZnFe2O4 in field emission scanning electron microscopy(FESEM)micrographs was in agreement with the specific surface area increase.These improvements in ZnFe2O4 characteristics considerably affected the adsorption performance of this adsorbent.Adsorption results revealed that mechano-thermally synthesized ZnFe2O4 had the maximum arsenic adsorption of 38%with the adsorption capacity of 0.995 mg·g?1 in a 130 mg·L?1 solution of As(V)after 30 min of agitation.However,chemically activated ZnFe2O4 showed the maximum arsenic adsorption of approximately 99%with the adsorption capacity of 21.460 mg·g?1 under the same conditions.These results showed that the weak adsorption performance of mechano-thermally synthesized ZnFe2O4 was improved by the chemical activation process.

Structural and Electrical Conductivity Studies in Nickel-Zinc Ferrite

The magnetic particles of nickel-zinc ferrite with chemical composition Ni1-xZnxFe2O4 were synthesized successfully by citrate precursor auto-combustion method using high purity nitrates and citric acid as chelating agent. The prepared powder of nickel-zinc ferrites was sintered at 1000℃ for 1 hr to obtain good crystalline phase and was used for further study. The X-ray diffraction technique was employed to confirm the single phase formation of nickel ferrite. The X-ray diffraction pattern shows the Bragg’s peak which belongs to cubic spinel structure. The values of lattice constant, X-ray density, bulk density, and porosity were calculated. The temperature dependence of the electrical conductivity plot shows the kink, which can be attributed to ferromagnetic-paramagnetic transition. The activation energy obtained from resistivity plots in paramagnetic region is found to be more than that in ferrimagnetic region. The conduction mechanism in nickel-zinc ferrite particles has been discussed on the basis of hopping of electrons.

Decolorization of Disperse Dyes Using Immobilized Laccase Enzyme on Nano Zinc Ferrite from Single and Binary Systems

In this paper, immobilized laccase enzyme on nano zinc ferrite was used in order to decolorize disperse dyes from single and binary systems. In this case, disperse dyes such as Disperse red 60 (DR60), Disperse blue 56 (DB56) and Disperse yellow 54 (DY54) were selected as model dyes. Several parameters such as enzyme concentration, pH and dye concentration and their effect on decolorization of dyes from single and binary systems were studied. According to the experimental results, the optimized immobilized laccase enzyme concentration, reaction time and pH for decolorization of DR60, DB56 and DY54 from single and binary systems were 500 mg/L (for DR60 and DY54) and 400 mg/L (for DB56), 20 min and 3, respectively. Moreover, Dye decolorization kinetics followed Michaelis-Menten Model. Finally, the results showed that enzymatic process using immobilized laccase enzyme on nano zinc ferrite was effective method to decolorize disperse dyes from single and binary systems.

Influence of pH on properties of Mn-Zn ferrites synthesized from low-grade manganese ore

Mn-Zn ferrite powders were produced from low-grade manganese ore(LMO) via the chemical coprecipitation method combined with the ceramic method,after the LMO was leached in sulfuric acid and the obtained solution was purified.The effect of the pH on the magnetic properties of Mn-Zn ferrite was investigated by the varying pH of the co-precipitation system.The crystal structure and phases of the samples were characterized by X-ray diffraction and infrared spectrum,respectively.The magnetic measurements were carried out on a vibrating sample magnetometer.The optimal sample was obtained with a saturation magnetization of 55.02 emu/g,a coercivity of 8.20 G and a remanent magnetization of1.71 emu/g when pH is 7.5.

Preparation and Characterization of La Doped Ferrite Using Marine Manganese Nodules as Raw Materials

A kind of La doped ferrite was prepared with marine manganese nodules derived from East Pacific sea-bottom as raw material, NaOH as fluxing reagent, La(NO3)3 as doping agent, by calcination at 1000 ℃ for 5 h. XRD analysis showed that the ferrite products were of a spinel structure, and that its molecular formula could be expressed as MnFe2-xRxO4. SEM images proved that these ferrites showed octahedral and cubic aspects. It was found that there is some relationship between the La doping amount and the magnetic property of the ferrite. When the La doping amount was 0.03, the susceptibility of the ferrite was maximal. The as-prepared La doped ferrite is a kind of soft magnetic material that is easy to be magnetized with rather weak coercive force.

Nano crystalline powders of NiCu ferrite and NiCuZn ferrite prepared from citrate gel method： Synthesis and cnaracterzation

Nano size nickel copper ferrite powders （NiCuFe204） and nickel copper zinc ferrite powders have been prepared by a citrate gel precursor method. The resulting powders were characterized by X-ray diffraction （XRD） and scanning electron microscope （SEM）. The results showed that nickel copper ferrites and nickel copper zinc ferrites were also in the nanosaele. The NiCu ferrite powders showed extensive XRD fine broadening and sizes of crystals were calculated （from the XRD line broadening） as 26 run-44 run over the temperature range is 200-800℃. The NiCuZn ferrite powders showed XRD line broadening and sizes of of crystals were calculated 46-65 nm over 200-800℃.