Aggregation process of fine hematite particles suspension using xanthan gum in the presence of Fe(III)

Aggregation is an economical and widely existing method to in hematite mineral processing. In order to achieve the aggregation of hematite particles, high-efficiency agents are required. In this work, the xanthan gum (XG) and Fe³⁺ were used to explore its aggregation effect on the fine hematite particles. The settling and adsorption experiments were conducted on hematite with XG in the absence and presence of Fe³⁺. The results show that it is difficult to settle hematite with XG alone, and XG exhibits excellent performance with the mass ratio of 2/1 (XG/ FeCl₃) at pH 2–10 in the presence of Fe³⁺. Zeta potential measurements, Fourier transform infrared (FTIR), Microscope and X-ray photoelectron spectroscopy (XPS) analyses were performed to detect the underlying mechanism. The zeta potential, solution chemistry and FTIR analyses results show that the co-adsorption of XG, Fe(OH)₂⁺, Fe(OH)²⁺ and Fe³⁺ is found on hematite surface through specific and electrostatic adsorption, respectively, and the hematite surface is also covered by Fe(OH)_3(s) precipitation turned by Fe³⁺. XPS spectral investigations and microscope observations provide evidence in support of coordination interaction between ferric ions active sites and XG. In addition, the aggregation model of fine hematite particles suspension using XG in the presence of Fe³⁺ was drawn.     

Formation of palladium precipitate by hydrazine in a simulated high level liquid waste

The formation of precipitates by hydrazine was experimentally examined in the simulated high level liquid waste (HLLW), which was composed of 9 elements (Nd, Fe, Ni, Mo, Zr, Pd, Ru, Cs, Sr). Palladium was precipitated over 90% above 0.05M of hydrazine concentration and at 2M HNO₃, while all of the other elements were hardly precipitated. The elements of Pd and Zr were precipitated 93% and 70% in the simulated solution in which the concentrations of Zr and Mo were decreased from 0.069M to 3.45·10^–3M and 6.9·10^–3M, respectively, and the acid concentration was decreased to about 0.5M after denitration. In a Pd solution of 0.5M and 2M HNO₃, the precipitation yield of Pd increased with hydrazine concentration and reached over 98% at 0.1M. The precipitation yield of Pd at 0.5M HNO₃ was higher than at 2M HNO₃. The Pd precipitate, formed by adding hydrazine to an acidified solution, was an amorphous compound consisting of Pd, hydrazine, nitrate and hydrate.     

Synthesis of multielement ferrites and their silica composites

Ferrites of composition M_0.2Co_0.4Zn_0.4Fe₂O₄ with M = Cu²⁺, Mn²⁺ and Ni²⁺ were prepared by citrate complex method. Later, their composites with silica have also been obtained by a simple route. The citrate complex precursors of multielement ferrites were characterized by FTIR spectroscopy and thermal analysis, been found a similar behavior for the three systems. The thermal treatment (at 400, 600 and 800 °C) of precursors gives, as result, the spinel type cubic ferrite pure when the ions substituted were copper and nickel; when manganese was used an hematite phase was obtained as contaminant at 800 °C. The presence of all ions involved and the particle size was corroborated by EDX analysis and measured from a TEM micrograph, respectively. The magnetic parameters related to magnetic properties, magnetization and coercivity, were different depending of the chemical composition of the ferrite and the thermal treatment temperature, as it was expected. At room temperature, the values obtained were near to those reported for Co-ferrite in bulk. The synthesis route of the composites M_0.2Co_0.4Zn_0.4Fe₂O₄-SiO₂, proposed in this work, gives as result magnetic nanoparticles in an amorphous silica matrix. Their magnetic properties were depending on weight percentage of the magnetic phase in the composite.     

Precipitation of Zirconium and Molybdenum in Simulated High-level Liquid Waste Concentration and Denitration Process

This paper focuses on the precipitation behaviors of zirconium and molybdenum during concentration and denitration by using simulated HLLW. The dependences of precipitates on final acidity of nitric acid, concentration factors and initial mass ratio of Mo/Zr were investigated. As a result, the presence of zirconium molybdate hydrate (ZMH) is confirmed in all experiments by the analysis of X-ray diffraction (XRD), but mass ratio of Mo/Zr in ZMH shows large deviations from the precipitate yield of Mo/Zr in solution. This is considered as a result of the generation of amorphous precipitate of Mo.     

Removal of nitric acid from a simulated high level liquid waste by a safe chemical denitration

The heat and off-gas generation behavior was experimentally examined during a safe chemical denitration, pre- and mild-denitration, of simulated HLLW with a nitric acid concentration of 2 to 7.5 M. The maximum heat and off-gas generation were no more than 100 cal/s·1 and about 0.8 l/min, respectively. The solution temperature does not reach boiling temperature and no solution was squirted out from the denitration vessel. The pre-and mild-denitration technique could be considered as one of safe methods for removing nitric acid from the HLLW with various nitric acid concentrations. The pre- and mild-denitration also has an advantage to improve the filtration characteristics of precipitates produced by the denitration of simulated HLLW. The denitration of HLLW with 7.5M nitric acid concentration induced formation of “very easy-to-filter” solid. Moreover, a good filter cake washing is possible.     

“Protein‐Like” Copolymers: Effect of Polymer Architecture on the Performance in Bioseparation Process

Recently, a new class of copolymers, so‐called protein‐like copolymers has been predicted theoretically by computer simulation. In these copolymers, the conformation of the copolymer determines the exposure of certain comonomer units to the outer solution. Depending on the conformation, copolymer molecules with essentially the same comonomer composition could have pronouncedly different properties. The authors demonstrated experimentally such behavior in case of poly[(N‐vinylcaprolactam)‐co‐(N‐vinylimidazole)] (Dokl. Chem. 2001 , 375, 637). One more group of copolymers with protein‐like behavior is copolymers of N‐isopropylacrylamide with N‐vinylimidazole. Poly[(N‐isopropylacrylamide)‐co‐(N‐vinylimidazole)] was synthesized by radical polymerization and separated into two fractions using immobilized metal affinity chromatography on Cu²⁺‐loaded iminodiacetic acid sepharose CL 6B (Cu²⁺‐IDA‐sepharose). The unbound fraction which passed through the column and bound fraction eluted with Ethylenediaminetetraacetic acid, disodium salt (EDTA) solution differed significantly in molecular weight, 1.4×10⁶ and 1.35×10⁵, respectively but were very close in comonomer composition, 7.8 and 9.1 mol‐% of imidazole, respectively. The composition of bound fraction was confirmed by titration of imidazole groups. Despite close chemical composition, the bound and unbound fraction behaved differently with respect to temperature‐induced phase separation at different pH values, the dependence of hydrodynamic diameter on pH and concentration of Cu²⁺‐ions, and the coprecipitation of soybean trypsin inhibitor with the copolymer in the presence of Cu²⁺‐ions. The differences in the behavior of copolymer fractions are rationalized assuming that the bound fraction presents a protein‐like copolymer.     

Hydrolytic precipitation of magnesium polyvanadates in vanadium (IV, V) solutions

The phase and chemical composition of precipitates formed in Mg(VO₃)₂-VOSO4-H₂O system at initial pH from 1 to 7 and temperature from 80 to 90°C was studied. Polyvanadates of variable composition Mg _x V _y ⁴⁺V_12-y ⁵⁺¹O_31–δ · nH₂O (0.7 ≤ x ≤ 1.3, 1.2 ≤ y ≤ 2.4, 0.7 ≤ δ = 1.4) were formed at pH from 1 to 4 and V⁴⁺/V⁵⁺ ratio from 0.43 to 9. Compounds with the general formula Mg _x V _y ⁴⁺V_6-y ⁵⁺O_16-δ · nH₂O (0.7 ≤ x ≤ 0.65, y = 1.0, 0.8 ≤ δ ≤ 0.85) were formed at pH from 6.0 to 7.0 and V⁴⁺/V⁵⁺ ratios from 0.11 to 0.25. The maximum V⁴⁺ concentration (y = 2.4) in the precipitates was achieved at the VV⁴⁺/V⁵⁺ solution ratio of 1.0 and pH = 3. The precipitates in solutions with pH 3 were formed only upon addition of VO²⁺ ions with the maximum rate at a V⁴⁺/V⁵⁺ ratio of 0.33. These processes were limited by second-order reactions on the surface of polyvanadates.     

Iron speciation related to color of Jurassic sedimentary rocks in Turpan Basin, northwest China

Mesozoic-Cenozoic reddish and green beds are widely distributed in northwest China. Mössbauer spectroscopy revealed that the composition of iron species varies with color in the middle-upper Jurassic sedimentary rocks from the Turpan Basin. Three main kinds of iron species were identified: (1) ferric iron of hematite (hem-Fe³⁺), (2) paramagnetic ferric iron (para-Fe³⁺), and (3) paramagnetic ferrous iron (para-Fe²⁺). Pyrite iron (pyr-Fe²⁺) was revealed only in a few samples. In general, there is a direct correlation between rock color, iron species and total iron content, however, in detail, this relationship is more complicated. The reddish rocks contain higher contents of total iron and hem-Fe³⁺, whereas the gray rocks contain much more para-Fe²⁺. However, relatively low hematite content cannot give red color to rocks, probably due to suppression by other pigments such as organic matter in black or chlorite in green. The dark or green rocks normally contain either only paramagnetic Fe²⁺ and paramagnetic Fe³⁺ species or these two species associated with hematite Fe³⁺, but the relative content of hematite species is lower. The variations of different iron species control lithological properties such as color and also may reflect the sedimentary conditions. Moreover, iron speciation in these rocks is one of the main factors, which result the color features of rocks in remote sensing imagery.This revised version was published online in November 2005 with corrections to the Cover Date.     

Archaeological pottery from Nasca culture studied by Raman and Mössbauer spectroscopy combined with X-ray diffraction

In the present paper, we report on a study of archaeological fragments from Nasca ceramics using Raman and Mössbauer spectroscopy combined with X-ray diffraction (XRD). By combining results obtained by these methods it is possible to quantitatively determine the paints composition, temperature and environment during the firing. The samples were collected from the Ceremonial Centre of Cahuachi in Southern coast of Peru. Raman spectroscopy allows us to determine the composition of the different pigments used in the preparation of Nasca ceramic. The results show that the composition of the white pigments is formed by rutile and anatase while the black and red pigments are formed by amorphous carbon and hematite, respectively. The Mössbauer spectra were measured at room temperature (RT) and show the presence of components associated with Fe³⁺ indicating an oxidizing environment during the manufacturing process of the ceramic. The analysis is complemented by data obtained by X-ray diffraction suggesting firing temperatures around 950 °C, in agreement with Raman measurements.     

Hematite Surface Activation by Chemical Addition of Tin Oxide Layer

In this study, the effect of tin (Sn⁴⁺) modification on the surface of hematite electrodes synthesized by an aqueous solution route at different times (2, 5, 10, 18, and 24 h) is investigated. As confirmed from X‐ray diffraction results, the as‐synthesized electrode exhibits an oxyhydroxide phase, which is converted into a pure hematite phase after being subjected to additional thermal treatment at 750 °C for 30 min. The tin‐modified hematite electrode is prepared by depositing a solution of Sn⁴⁺ precursor on the as‐synthesized electrode, followed by thermal treatment under the same abovementioned conditions. This modification results in an enhancement of the photocurrent response for all hematite electrodes investigated and attains the highest values of around 1.62 and 2.3 mA cm^?2 at 1.23 and 1.4 V versus RHE, respectively, for electrodes obtained in short synthesis times (2 h). Contact angle measurements suggest that the deposition of Sn⁴⁺ on the hematite electrode provides a more hydrophilic surface, which favors a chemical reaction at the interface between the electrode and electrolyte. This result generates new perspectives for understanding the deposition of Sn⁴⁺ on the hematite electrode surface, which is in contrast with several studies previously reported; these studies state that the enhancement in photocurrent density is related to either the induction of an increased donor charge density or shift in the flat‐band potential, which favors charge separation.     

Regularities of Lewis site formation upon the microwave irradiation of gibbsite-γ-Al(OH)3

Spatially separated Lewis acidic and basic sites can be formed upon the microwave irradiation of gibbsite. This is demonstrated by IR spectroscopy and indicates the possibility of the selective activation of chemical bonds of different nature within the initial crystals of Al³⁺ hydroxide. A scheme for the formation of spatially separated Lewis acidic and basic sites is proposed. It is shown that water as a product of the micro-wave activation of gibbsite is adsorbed on these Lewis acidic sites in molecular form (without subsequent dissociation) and is desorbed at calcination temperatures no higher than 100–110°C. During standard (contact) thermal treatment of Al³⁺ hydroxides and oxides, dehydroxylation and water removal take place at 350–550°C to form the acid-base pair-Al^δ+-O^δ?-. The microwave activation of gibbsite results in the formation of an amorphous component believed to consist of small -Al-O- complexes closely packed in the solid phase. It is established that the fraction of Al³⁺ atoms accessible for the low-temperature adsorption of CO in microwave-activated (for 10 min) gibbsite is 4.5 at % of the total number of Al³⁺ atoms present in the amorphous component of this material.     

Phase composition and magnetic properties of niobium-iron codoped TiO2 nanoparticles synthesized in Ar/O2 radio-frequency thermal plasma

Nanoparticles of Nb⁵⁺-Fe³⁺ codoped TiO₂ with various Nb⁵⁺ concentrations (Nb/(Ti+Fe+Nb)=0-10.0 at%) and Fe³⁺ (Fe/(Ti+Fe+Nb)=0-2.0 at%) were synthesized using Ar/O₂ thermal plasma. Dopant content, chemical valence, phase identification, morphology and magnetic properties were determined using several characterization techniques, including inductively coupled plasma-optical emission spectrometer, X-ray photoelectron spectroscopy, X-ray diffraction, UV-vis diffuse reflectance spectrometer, field-emission scanning electron microscopy, transmission electron microscopy and SQUID commercial instrument. The XRD revealed that all the plasma-synthesized powders were exclusively composed of anatase as major phase and rutile. The rutile weight fraction was increased by the substitution of Fe³⁺ for Ti⁴⁺ whereas it was reduced by the Nb⁵⁺ doping. The plasma-synthesized Nb⁵⁺-Fe³⁺ codoped TiO₂ powders had intrinsic magnetic properties of strongly paramagnetic and feebly ferromagnetic at room temperature. The ferromagnetic properties gradually deteriorated as the Fe³⁺ concentration was decreased, suggesting that the ferromagnetism was predominated by the phase composition as a carrier-mediated exchange.     

Influence of the composition on the electronegativity and on the oxygen charge distribution in a binary hydrotalcite-like by modified Sanderson method

An intuitive and computationally non-intensive model for the classification of Hydrotalcite-like compounds (HTLCs) based simply on the chemical composition using the Sanderson Method led to good prediction of basicity and different basic sites (oxygen atoms with different charge). That model was evaluated at different M³⁺ /(M²⁺+M³⁺) ratio and with different divalent and trivalent metallic cations.AMS subject classification: 92E10     

Influence of Amines on Formation and Texture of Uniform Hematite Particles

The structure and properties of hematite particles obtained by hydrolysis of ferric chloride solution doped with various kinds of amines were examined by TEM, XRD, TG-DTA, N₂and H₂O adsorption, and zeta potential measurements. The shape of precipitates was concentration dependent; they changed from large spheres (diameter: ca. 820 nm) to cubes (edge length: ca. 400 nm) via double-spheres (long axis length: ca. 600 nm) with increasing monoamine concentrations. This effect was enhanced by increasing their pK_avalues. Much pronounced effects of di- and triamines on the particle formation were observed; cubic and double-spherical particles were obtained at a much lower concentration of di- and triamines and small spherical (diameter: ca. 100 nm) and diamond-like (long axis length: ca. 100 nm) particles were further produced at higher concentration. It was suggested that the acceleration of the rate of phase transformation from β-FeOOH to hematite induced by amines plays an important role for producing fairly uniform hematite particles with different shape and size. The hematite particles produced with amines contained small amounts of OH⁻ions in the lattice but were confirmed to be nearly single crystal.     

Thermo‐oxidative degradation of HDPE as a function of its crystalline content

The composition, the thermal properties, and the kinetics of the thermo‐oxidative degradation of high‐density polyethylene (HDPE) were studied as a function of the increasing crystalline fraction, which resulted from the selective extraction of the amorphous part, through digestion by immersion in fuming nitric acid (HNO₃) for different periods of time. The chemical and thermodynamic changes in HDPE, brought about by digestion in nitric acid for different periods of time, are discussed. Changes in the chemistry and microstructure of the HDPE, as a function of acid treatment for different periods of time, were studied using infra‐red spectroscopy (FTIR), gel permeation chromatography (GPC), and thermal analysis (DSC and TGA), as well as scanning electron microscopy (SEM). These studies were carried out as a function of the extracted amorphous fraction of HDPE samples via digestion in HNO₃. These studies showed that in the first stages of the acid chemical attack, the amorphous part first undergoes a chemical modification and then dissolves into the strong acid medium. The total crystalline fraction apparently decreases during the first stages of the chemical attack and then increases as the amorphous part is extracted. TGA results show that as the selective extraction of the amorphous part occurs, there is a displacement of the thermo‐oxidative degradation toward higher temperatures. The kinetics of the thermo‐oxidative degradation as a function of the extraction of the amorphous part was followed according to the Horowitz‐Metzger method, and it was found that as the concentration of the crystalline fraction increases, the activation energy for the thermo‐oxidative degradation increases. SEM studies show that the extraction of the amorphous part does not affect the size of the crystalline lamellar thickness of HDPE. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1906–1915, 2009     

Chemical reduction of hematite with starch

Chemical reduction of hematite with starch in air at elevated temperature was investigated using X-ray powder diffraction, FT-IR and ⁵⁷Fe Mössbauer spectroscopies. On heating the starting mixture for 0.5 and 2 hours at 300 °C, magnetite and a small fraction of hematite were identified by XRD. With the heating time prolonged up to 24 hours, magnetite reoxidized and hematite was obtained again. The formation of magnetite was observed even at 580 °C. However, the magnetite formed at this temperature was substoichiometric, as shown by XRD and Mössbauer spectroscopy. Characteristic IR bands of oxide phases were monitored by FT-IR spectroscopy. Chemical reduction of hematite with starch into a Fe⁰ state was not observed in any sample.     

The calculation of the thermodynamic equilibrium in Fe3+/MoO 4 2− /H+(OH−)/H2O system and determination of reasonable conditions for iron molybdate deposition

The thermodynamic data on the Fe³⁺/MoO₄ ^2?/H⁺(OH^?)/H₂O system were analyzed. The iron(III) molybdate precipitates were studied by the X-ray phase analysis and electron probe microanalysis. It was shown that the content of the iron(III) oxide impurity in the precipitates depends on method and conditions of mixing of an iron precursor solution and an molybdenum precursor solution.     

The electrodeposition and properties of Zn-Ni + Ni composite coatings

The Zn-Ni+Ni coatings were deposited under galvanostatic conditions at the current density range from 20 to 60 mA cm^?2. The influence of deposition current density on surface morphology, chemical and phase composition and corrosion resistance of obtained coatings, was investigated. Structural investigations were conducted by X-ray diffraction method. Surface morphology and surface chemical composition of the obtained coatings were determined by a scanning electron microscope. Studies of electrochemical corrosion resistance were carried out in the 5% NaCl solution, using potentiodynamic and Scanning Kelvin Probe (SKP) methods. A possibility of incorporation of nickel powder from a suspension bath to the Zn-Ni matrix, during galvanostatic deposition was demonstrated. The results of chemical composition analysis show that the Zn-Ni + Ni coatings contain approximately 15?C18% at Ni. It was found that surface morphology, surface chemical and phase composition of Zn-Ni + Ni coatings depend in small degree on deposition current density. However, the current density influences distribution of nickel powder on the surface of these coatings. The optimal values of current density on account of corrosion resistance, are found to be j = 40?C50 mA cm^?2.     

Abiotic Hydrolysis of Poly[(R)-3-hydroxybutyrate] in Acidic and Alkaline Media

Poly[(R)-3-hydroxybutyrate)], P(3HB), is the most common member of polyhydroxyalkanoates, the natural biopolyesters of intrinsic biodegradability and biocompatibility. Abiotic hydrolysis of P(3HB) was investigated in acid and base media by monitoring the formation of two monomer products, 3-hydroxybutyric acid (3HB) and crotonic acid (CA), from three types of P(3HB) samples, amorphous granules, irregular precipitates and solvent cast films. The soluble monomeric products were not detected in acid solutions (0.1 to 4 N H⁺), but measured as the major hydrolytic products in base solutions (0.1 to 4 N OH⁻). Unlike the protons as catalyst in both hydrolysis and esterification, hydroxyl anions were consumed during formation of carboxylate anions. The amorphous granules of P(3HB) were decomposed 80- to 100-fold faster than the precipitates and solvent cast films. The latter two had around 71% crystallinity. The hydrolysis of amorphous grannules exhibited a quasi 0^th-order reaction rate and the activation energy of saponification was 82.2 kJ/mol, silimar to those of the biotic hydrolysis of P(3HB) by enzymes and living cells.     

Sorption Properties of Hematite for Copper Ions

Sorption properties of commercial hematite (α-Fe₂O₃) for divalent copper ions were studied. This was done with a model solution of copper(II) sulfate additionally containing 400 mg L^–1 of sodium sulfate. It was shown that the hematite sample under study is a good sorbent for removal of divalent copper ions from aqueous solutions. The process of Cu²⁺ sorption is described by the Langmuir equation. The parameters of this equation were determined at various pH values of the model solution and compared with similar published parameters for other hematite samples.