Activation of hematite photoanode synthesized at low temperature by W doping

1.Introduction Solar water splitting offers a promising approach for green hydrogen production[1].There are many ways to achieve solar water splitting,such as photocatalytic(PC)water splitting,photoelectrochemical(PEC)water splitting,and photovoltaicelectrocatalytic(PV-EC)water splitting[2].

The role of titanium at the interface of hematite photoanode in multisite mechanism:Reactive site or cocatalyst site?

Hematite(α-Fe_(2)O_(3))constitutes one of the most promising photoanode materials for oxygen evolution reaction(OER).Recent research on Fe_(2)O_(3) have found a fast OER rate dependence on surface hole density,suggesting a multisite reaction pathway.However,the effect of heteroatom in Fe_(2)O_(3) on the multisite mechanism is still poorly understood.Herein we synthesized Fe_(2)O_(3) on Ti substrates(Fe_(2)O_(3)/Ti)to study the oxygen intermediates of OER by light-dark electrochemical scans.We identified the Fe-OH species disappeared and Ti-OH intermediates appeared on Fe_(2)O_(3)/Ti when pH=11‒14,which significantly improved the OER performance of Fe_(2)O_(3)/Ti.Combined with the density functional theory calculations,we propose that Ti atom acts as cocatalyst site and captures proton from neighboring Fe-OH species under highly alkaline condition,thereby promoting the coupling of Fe=O and reducing the energy barrier of the non-electrochemical step.Our work provides a new insight into the role of heteroatom in OER multisite mechanism based on clarifying the reaction intermediates.

Novel polyhydroxy cationic collector N-(2,3-propanediol)-Ndodecylamine: Synthesis and flotation performance to hematite and quartz

To enhance the performance of traditional cationic collector,a novel polyhydroxy amine collector N-(2,3-Propanediol)-N-dodecylamine(PDDA)was designed by introducing one propylene glycol group into dodecylamine(DDA).It was prepared by a nucleophilic substitution reaction,which showed better solubility and hydrophobicity than DDA and was firstly employed as the collector for the separation of hematite and quartz.Flotation tests showed that PDDA had an excellent flotation performance and significantly better selectivity than DDA.In addition,the flotation performance and adsorption mechanism of PDDA on hematite and quartz surfaces were studied using Fourier transform infrared spectroscopy(FTIR),zeta potential and X-ray photoelectron spectroscopy(XPS)tests.These results demonstrated that the interaction between PDDA and the minerals’surfaces was mainly electrostatic adsorption and hydrogen bond,while PDDA tended to adsorb on the surfaces of quartz more than that of hematite.Performance optimization of amine collectors by introducing hydroxyl was also verified,which was of great meaning to the design,development,and application of the polyhydroxy cationic collector.In conclusion,PDDA could be used as a potential collector in the flotation separation of quartz and hematite.

Adsorption of sodium oleate at the microfine hematite/aqueous solution interface and its consequences for flotation

The adsorption of sodium oleate(NaOL)at the microfine hematite/aqueous solution interface was investigated in this paper.Experimental research indicated that negative effects stemmed from the dissolution of the microfine hematite(D50=19.21μm)could be effectively eliminated via the appropriate dosage of NaOL at alkali pH conditions.Solution chemistry calculation and adsorption test results indicated that RCOO
and(RCOO)_(2)^(2-) ions were responsible for microfine hematite flotation at pH 8.2.Zeta potential and FTIR measurements confirmed the co-adsorption of molecular and ionic oleate species occurred at pH 8.2.X-ray photoelectron spectroscopy(XPS)results further indicated that oleate species interacted with hematite surfaces mainly through chemisorption,giving rise to molecule/colloid formation of oleate and Fe―OL complex compound.Time-of-flight secondary ion mass spectrometry(ToF-SIMS)results demonstrated that oleate species adsorbed onto the hematite surfaces with a thickness of a few nanometers.Furthermore,the normalized peak intensity of C4H7+ions on the hematite sample at pH 8.2 increased remarkably comparing with corresponding result of hematite sample at pH 6.8.The new findings of the present study well revealed the dissolution of microfine hematite and the pH effects on the hematite flotation,as well as the adsorption characteristics of oleate species.

Bioprocess-inspired Actin Biomineralized Hematite Mesocrystals for Energy Storage

Biomineralization is a biological process of synthesizing inorganic minerals within organisms.It has been found that intracellular proteins are involved in the room temperature synthesis process of anatase Ti O2in living mussels.Here,we used intracellular actin to synthesize hematite by biomineralization.Biomineralized hematite has a nano spindle structure with a particle size of approximately 150 nm.The microstructure indicates that the prepared hematite is a mesocrystals composed of ordered arrangement and assembly of primary nanoparticles.In addition,hematite mesocrystals exhibit good lithium storage performance as electrode materials for lithium batteries.The discharge specific capacity of the battery remained at 560.7 m Ah·g^(-1)after 130 cycles at a current density of 200 m A·g^(-1).This work expands the synthesis methods of hematite by biomineralization,and provides a new strategy for preparing inorganic materials by intracellular proteins.

Synthesis and Characterization of Gadolinium Oxide-Hematite Magnetic Ceramic Nanostructures

Mixed-oxide nanostructures of the type xGd2O3-(1-x)α-Fe2O3 (x=0.1, 0.3, 0.5 and 0.7) were synthesized by mechanochemical activation for ball milling times of 0, 2, 4, 8 and 12 hours. The systems were subsequently analyzed by Mӧssbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflectance spectroscopy. The magnetic hyperfine field was studied as function of ball milling time for all sextets involved and found to be consistent with the formation of a limited solid solution in the systems investigated. The end-product was the gadolinium perovskite, represented by a doublet whose abundance was derived as function of the milling time. The XRPD patterns recorded for the equimolar composition were dominated by the diffraction peaks of GdFeO3 after 12 hours of milling. The hysteresis loops were recorded at 300 and 5 K in an applied magnetic field of 5 T and were interpreted as a superposition of paramagnetic behavior of gadolinium oxide and weak ferromagnetic behavior of hematite and gadolinium perovskite. The Morin transition of hematite was inferred from zero-field-cooling-field-cooling (ZFC-FC) curves measured with a magnetic field of 200 Oe in the 5-300 K temperature range and was found to depend on the ball milling time. Optical diffuse reflectance spectra showed that the compounds were semiconductors with an optical band gap of 2.1 eV.

Shear hydrophobic flocculation and flotation of ultrafine Anshan hematite using sodium oleate

Effects of stirring speed and time, pH and sodium oleate concentration on the shear hydrophobic flocculation of ultrafine Anshan hematite with sodium oleate as the surfactant were discussed. The results show that these parameters significantly affect the shear hydrophobic flocculation of ultrafine hematite. The optimum conditions for the flocculation are： stirring speed 1 400 r/min, flocculation time 20 min, pH 9 and sodium oleate concentration 3.94×10-4 mol/L; the flotation recovery of hematite flocs is remarkably high compared with non flocculated ultrafine hematite. According to the extended DLVO theory, the total interaction potential of Anshan ultrafine hematite was determined. The calculation results indicate that the hydrophobic flocculation state of the ultrafine hematite-sodium oleate system is mainly dominated by electric double layer repulsive interaction potential and hydrophobic interaction potential. A mechanical agitation is required to impart particles a kinetic energy to overcome potential barrier between them due to the existence of electric double layer repulsive interaction potential. Those particles further approach to form flocs due to the significant increase of the hydrophobic interaction potential.

Mechanism of phosphorus removal in beneficiation of high phosphorous oolitic hematite by direct reduction roasting with dephosphorization agent

High phosphorous oolitic hematite ore is one of typical intractable iron ores in China, and the conventional beneficiation methods are found to be impracticable to , remove phosphorus from the ore effectively. Better beneficiation index were gotten by direct reduction roasting with dephosphorization agent followed by two stages of grinding and magnetic separation. P content decreases from 0.82% in the raw ore to 0.06% in the magnetic concentrate, and the total iron grade increases from 43.65% to 90.23%, the recovery of iron can reach 87%. Mechanisms of phosphorus removal in the beneficiation of high phosphorous oolitic hematite ore by direct reduction roasting with dephosphorization agent were studied using XRD, SEM and EPMA. The results showed that about 20% of the apatite in the raw ore transferred into phosphorus and volatilized with the gas in the process of reduction roasting, while the rest 80% apatite was not involved in the reaction of generation of phosphorus, and remained as apatite in the roasted products, which was removed to tailings by grinding and magnetic separation. A small amount of phosphorus existed in the magnetic concentrate as apatite. The oolitic texture of raw ore was partly changed during roasting, resulting in the formation of nepheline in the reaction between the dephosphorization agent, SiO2 and Al2O3 in the raw ore, which greatly improved the liberation degree of minerals in the roasted products, and it was beneficial to the subsequent grinding and magnetic separation.

Separation behavior and mechanism of hematite and collophane in the presence of collector RFP-138

The reverse flotation separation performance and mechanism of hematite and cellophane in the presence of RFP-138, a newly synthesized dephosphorization collector, were studied. Reverse flotation tests on monominerals and artificially mixed minerals of hematite and collophanite show that, this anionic collector performs excellently in reducing the phosphorus content in hematite. It can decrease the content of P in artificially mixed minerals from 1.05% to 0.12% and achieve the TFe recovery rate of 91.30%. The chemical behavior of solution and infrared spectra of RFP-138 were investigated to explore the selective collecting mechanism of RFP-138 to these two minerals.

FT-IR, XPS, and DFT Study of Adsorption Mechanism of Sodium Acetohydroxamate onto Goethite or Hematite

The adsorption of sodium acetohydroxamate on the goethite or hematite surface was investi- gated by Fourier transform infrared spectroscopy （FT-IR）, X-ray photoemission spectroscopy and periodic plane-wave density functional theory （DFT） calculations. The core-level shifts and charge transfers of the adsorbed surface iron sites calculated by DFT with periodic in- terfacial structures were confronted to the X-ray photoemission experiments. FT-IR results reveal that the interracial structure of sodium acetohydroxamate adsorbed on the goethite or hematite surface may be assigned to a five-membered ring complex. In agreement with the adsorption energies determined by the DFT calculations, a five-membered ring complex is formed via bonding of one surface iron atom of goethite （101） or （100） to both oxygen atoms of hydroxamate group, and these two oxygen atoms of the hydroxamate group correspond- ingly attach to two neighboring iron atoms of the goethite surface. But a five-membered ring complex between two oxygen atoms of the hydroxamate group and one surface iron atom of hematite （001） is formed without any extra attachments. The calculated core-level shifts of Fe2p for the interracial structures are correspondingly in good agreement with the experimental observed one, which confirmed the reliability of the calculated results.

Effect of sodium alginate on reverse flotation of hematite and its mechanism

Given the gradual increase in the chlorite content of hematite ores, pulp properties seriously deteriorate during flotation. The traditional anion reverse flotation of hematite cannot effectively eliminate the effects of chlorite, leading to a significant decrease in the total Fe(TFe) grade of the concentrate. In this work, the effect of sodium alginate on the reverse flotation of hematite was systematically investigated. Flotation tests of artificially mixed ores were conducted, and the results showed that sodium alginate can significantly improve the removal rates of quartz and chlorite. The adsorption measurements, infrared spectroscopy, and contact angle tests demonstrated that sodium alginate adsorbs on the quartz surface by chelating with calcium ions, thereby weakening the steric hindrance of oleate ions and increasing the adsorption capacity of sodium oleate to ultimately improve the removal rate of quartz. Furthermore, owing to its lower density and fine particle size, chlorite is easily entrained into the foam layer. Sodium alginate dramatically increases the liquid-to-gas ratio of the foam layer by increasing pulp viscosity, thereby increasing the entrainment rate of chlorite and finally improving its removal rate. The core content of this thesis bears significance in improving the Fe grade in the reverse flotation of chlorite-containing hematite.

Magnetizing Roasting Mechanism and Effective Ore Dressing Process for Oolitic Hematite Ore

Magnetizing roasting of oolitic hematite ore from western Hubei Province was investigated.The mechanism for reduction roasting of oolitic hematite ore was discussed and analyzed.It is found that flash magnetizing roasting-magnetic separation process is a promising approach for the processing of oolitic hematite ore from western Hubei Province.

Magnetic and flotation studies of banded hematite quartzite (BHQ) ore for the production of pellet grade concentrate

To identify and establish beneficiation techniques for banded hematite quartzite （BHQ） iron ore, a comprehensive research on BHQ ore treatment was carried out. The BHQ ore was assayed as 38.9wt% Fe, 42.5wt% SiO2, and 1.0wt% Al2O3. In this ore, hematite and quartz are present as the major mineral phases where goethite, martite, and magnetite are present in small amounts. The liberation of hematite particles can be enhanced to about 82% by reducing the particle size to below 63 μm. The rejection of silica particles can be obtained by magnetic and flotation separation techniques. Overall, the BHQ ore can be enriched to 65.3wt% Fe at 61.9% iron recovery. A flowsheet has been suggested for the commercial exploitation of the BHQ ore.

Study on the strength of cold-bonded high-phosphorus oolitic hematite-coal composite briquettes

Composite briquettes containing high-phosphorus oolitic hematite and coal were produced with a twin-roller briquette machine using sodium carboxymethyl cellulose, molasses, starch, sodium silicate, and bentonite as binders. The effect of these binders on the strength of the composite briquettes, including cold strength and high-temperature strength, was investigated by drop testing and compression testing. It was found the addition of Ca（OH）2 and Na2CO3 not only improved the reduction of iron oxides and promoted dephosphorization during the reduction-separation process but also provided strength to the composite briquettes during the briquetting process; a compressive strength of 152.8 N per briquette was obtained when no binders were used. On this basis, the addition of molasses, sodium silicate, starch, and ben- tonite improved the cold strength of the composite briquettes, and a maximum compressive strength of 404.6 N per briquette was obtained by using starch. When subjected to a thermal treatment at 1200~C, all of the composite briquettes suffered from a sharp decrease in compressive strength during the initial reduction process. This decrease in strength was related to an increase in porosity of the composite briquettes. X-ray diffraction （XRD） and scanning electron microscopy （SEM） analyses showed that the decrease in strength of the composite briquettes could be caused by four factors： decomposition of bonding materials, gasification of coal, transportation of byproduct gases in the composite briquettes, and thermal stress.

Optimization of flotation variables for the recovery of hematite particles from BHQ ore

The technology for beneficiation of banded iron ores containing low iron value is a challenging task due to increasing demand of quality iron ore in India. A flotation process has been developed to treat one such ore, namely banded hematite quartzite （BHQ） containing 41.8wt% Fe and 41.5wt% SiO2,by using oleic acid, methyl isobutyl carbinol （MIBC）, and sodium silicate as the collector, frother, and dispersant, respectively. The relative effects of these variables have been evaluated in half-normal plots and Pareto charts using central composite rotatable design. A quadratic response model has been developed for both Fe grade and recovery and optimized within the experimental range. The optimum reagent dosages are found to be as follows： collector concentration of 243.58 g/t, dispersant concentration of 195.67 g/t, pH 8.69, and conditioning time of 4.8 min to achieve the maximum Fe grade of 64.25% with 67.33% recovery. The predictions of the model with regard to iron grade and recovery are in good agreement with the experimental results.

Performance evaluation for selectivity of the flocculant on hematite in selective flocculation

Increased demand for iron ore necessitates the utilization of low-grade iron ore fines, slimes, and existing tailings. Selective flocculation can be an alternative physico-chemical process for utilizing these low-grade fines, slimes, and tailings. In selective fiocculation, the most critical objective is the selection of proper reagents that will make fioc of desired minerals. In present study, selective flocculation was applied to ultra-fine synthetic mixtures of hematite and kaolinite, and the Fe value was upgraded up to 65.78% with the reduction of Al2O3 and SiO2 values to 2.65% and 3.6670, respectively. Here, degraded wheat starch was used as a flocculant.In this process, separation occurs on the basis of the selectivity of the flocculant. The selectivity of the fiocculant can be quantified in terms of separation efficiency. Here, an attempt was also made to develop a correlation between separation efficiency and major operating parameters such as flocculent dose, pH value, and solid concentration to predict the separation performance.

Interaction of humic substances and hematite:FTIR study

The present work extended the knowledge on the binding and complexation of humic substances(humic acid or fulvic acid) and hematite by Fourier transform infrared spectroscopy(FTIR). The FTIR data gained gave the consist evidences by two different sampling preparation methods that the interaction mechanism between humic substances and hematite was mainly conform to the ligand exchange involving carboxylic functional groups of humic substances and the surfaces sites of hematite. The present method, although associated with some uncertainties, provided an opportunity to increase the knowledge in this field.

Phase transformation in suspension roasting of oolitic hematite ore

Suspension roasting followed by magnetic separation is a promising method to upgrade oolitic hematite ore.An oolitic hematite ore was roasted using suspension roasting technology at different temperatures.The phase transformation for iron minerals was investigated by XRD and Mossbauer spectrum,and the characteristics of roasted product were analyzed by VSM and SEM-EDS.Results indicate that the magnetic concentrate is of 58.73% Fe with iron recovery of 83.96% at 650 °C.The hematite is rapidly transformed into magnetite during the roasting with transformation ratio of 92.75% at 650 °C.Roasting temperature has a significant influence on the phase transformation of hematite to magnetite.The transformation ratio increases with increased temperature.After roasting,the magnetic susceptibility is significantly improved,while iron ore microstructure is not altered significantly.

Effect and mechanism of siderite on reverse flotation of hematite

The effects of siderite on reverse flotation of hematite were investigated using micro flotation, adsorption tests, and Fourier transform infrared spectroscopy. The flotation results show that interactions between siderite and quartz are the main reasons that siderite significantly influences the floatability. The interactions are attributed to dissolved siderite species and fine siderite particles. The interaction due to the dissolved species is, however, dominant. Derjaguin-Landau-Verwey-Overbeek（DLVO） theoretical calculations reveal that adhesion on quartz increases when the siderite particle size decreases and that fine particles partly influence quartz floatability. Chemical solution calculations indicate that the dissolved species of siderite might convert the surface of active quartz to CaCO_3 precipitates that can be depressed by starch. The theoretical calculations are in good agreement with the results of adsorption tests and FTIR spectroscopy and explain the reasons why siderite significantly influences reverse flotation of hematite.

Facile Synthesis of Uniform Hollow Hematite Sub-micro Spheres with Controllable Shell Thickness

A simple method was developed to prepare the uniform hematite hollow submicro-spheres with controllable structure and different diameter based on monodisperse poly（styrene-co-acrylic acid） [P（St-co-AA）] particles. The structure and formation mechanism of the hollow spheres were investigated in detail. The control mechanism of shell thickness was also discussed. The results indicated that the shell thickness and coarseness of the synthesized core-shell hematite hollow spheres could be tuned simply by the surface carboxyl content of the P（St-co-AA） particles. This method provided a new approach for the structure control in the preparation of hollow spheres. A Brunauer-Emmett-Teller （BET） test shows that the prepared hollow spheres have large surface areas which were decreased along with the increase of the diameter. The magnetic properties of the as-obtained hematite hollow spheres were investigated. The result showed that the coercivity and saturated magnetization were increased along with the increase of the shell thickness, and the remanent magnetization was increased along with the decrease of the diameter.