Siderite Particles Research Articles

Adsorption behavior of sodium oleate on iron minerals and its effect on flotation kinetics

This work systematically studied the adsorption behavior of sodium oleate (NaOL) on hematite, limonite, and siderite and their corresponding flotation performance at alkaline pH. The adsorption behavior and conformation of NaOL on mineral surfaces were investigated using zeta potential analysis, Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy spectra (XPS), and atomic force microscopy (AFM) imaging characterization. The effect of NaOL adsorption on the surface wettability and bubble-particle attachment was further analyzed by contact angle measurement, attachment time tests, and wrap angle tests. Finally, batch flotation tests and kinetic analysis were carried out to evaluate three mineral flotation behaviors. The results revealed that NaOL could chemically adsorb on hematite, limonite, and siderite and caused the significant negative mobility in their zeta potentials. It was found that Fe atoms exposed on their surface were the main active centers for the chemisorption of NaOL. Hematite and limonite had more active sites for NaOL adsorption than siderite, and Fe(III) on hematite and limonite surface could interact more strongly with NaOL than Fe(II) on siderite, which resulted in the higher adsorption density and intensity of NaOL on hematite and limonite than that on siderite. This further contributed to the stronger hydrophobicity on their surface than that on siderite surface. The enhancement of hydrophobicity could increase the attachment efficiency of bubble-particle (Ea). Therefore, hematite and limonite particles had more and faster attachment with bubbles than siderite particles. As such, much higher cumulative ultimate recoveries (R∞) and flotation rate constants (k) of hematite and limonite than those of siderite were obtained.

Composition-Structure Relationship and Routes of Formation of Blocklike Ferrospheres Produced by Pulverized Combustion of Two Coal Types.

The composition–structure relationship of blocklike ferrospheres (FSs) isolated from fly ash produced during the combustion of two different types of coal was studied systematically by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. Monoblock globules were shown to consist of large sintered crystallites of Mg, Mn ferrospinel, which are formed from excluded siderite particles containing isomorphic impurities of magnesium and manganese carbonates. The common groups of globules for which the gross composition of polished sections corresponds to the general equations for the relationship of the concentrations SiO2 = f(Al2O3) and CaO = f(SiO2) were highlighted from FSs of two series. These globules are formed during the thermochemical transformation of associates of siderite, quartz, calcite, and anorthite, which have a silicate modulus of SiO2/Al2O3 equal to 1.18, which corresponds to the coefficients in the general equations of the relationship SiO2 = f(Al2O3). SEM analysis of polished cross-sections of the globules of selected FS groups demonstrates that the crystallite size of ferrospinel decreases, while the content of the glass phase increases with the declining FeO concentration in individual globules. The crystallite size and shape are found to depend on the size of the local melt area where the concentration of spinel-forming oxides is >85 wt %. The observed increase in the glass-phase content is attributed to the broadening of the liquation zone in the FeO–Fe2O3–SiO2 system as the oxidative potential increases and to the higher content of [Fe3+O2]− and [Fe3+2O5]4– ferrite complexes in calcium-rich melts.

Aggregation characteristics of fine hematite and siderite particles in aqueous suspension

Siderite-bearing hematite is a type of refractory iron ore, where fine particle aggregation or dispersion behavior is of importance for the separation efficiency. Hence, the aggregation characteristics of fine particles (hematite and siderite) using sodium oleate (NaOl) as a flocculant were investigated through FBRM particle size analysis (a real-time particle characterization tool), zeta potential analysis, adsorption tests, contact angle measurements, and X-DLVO theoretical calculations. The results showed that NaOl could interact with hematite and siderite when the pH value ranged from 5.0 to 9.0, in which the hydrophobic interaction played a leading role in inducing homo-aggregation and hetero-aggregation in the mineral particles. However, in the strong alkaline solution environment (pH = 11.0), NaOl could only interact with siderite and scarcely adsorbed onto the hematite surface, which was mainly covered with ferric hydroxyl compound (Fe-OH). This largely prevented the formation of hematite-hematite and hematite-siderite aggregates in the suspension.

Probing the effect of particle imperfections on the sliming of siderite in carbonate-bearing iron ore

The sliming properties of siderite contained in carbonate-bearing iron ore have an unavoidable, negative impact on the reverse flotation of hematite during the beneficiation process. This leads to the ineffective beneficiation of carbonate-bearing iron ore. The main purpose of this study was to reveal the effect of particle imperfections in siderite and hematite on the inherent sliming mechanism, from the perspectives of local defects in the crystal structures and the pre-existing micropores present in these particles. To this end, an X-ray microscope (XRM) was used to characterize the mesostructure of milled siderite and hematite, revealing their particle size and the pre-existing micropores present in these minerals. Additionally, the microstructures of vacancy defects in the crystals were determined with the aid of density functional theory (DFT). XRM results demonstrated that siderite particles contain a greater density of pre-existing micropores than hematite particles, increasing the sliming properties of siderite when it is milled simultaneously with hematite. DFT calculations suggested that siderite crystals were more susceptible to O-vacancy defects, which contributes to the number of micropores in siderite particles. This study provides an insight into the relationship between the particle structure and sliming properties of siderite and hematite, thereby paving the way for improvements in the beneficiation process of carbonate-bearing iron ore.

Catalytic effect of siderite on H2O2 oxidation of carmine dye: Performance, mechanism and kinetics

The role of siderite in catalyzing the H2O2 degradation of carmine was studied by using batch experiments. The effects of the size of siderite particles, ratio of H2O2 to siderite, initial pH, reaction time, and reaction temperature were examined, and the degradation mechanism and kinetics were discussed. The size of siderite slightly affected the degradation of carmine, and the ratio of H2O2 to siderite significantly influenced degradation; a ratio of 6:1 resulted in maximum carmine degradation. Although the optimal reaction pH was 3, excellent degradation efficiency was also found at pH 4 and 5. In the H2O2/siderite system, the kinetic reaction order is 1.04, and the rate constant is 10.15 min−1; 99.97% of the chroma was removed, and 80.61% of the TOC was degraded when the ratio of H2O2 to siderite was 6:1 with an initial pH of 3. The slow release of Fe2+ in siderite played an important role in the catalytic H2O2 degradation of carmine. Moreover, siderite was cycled eight times without affecting decolorization efficiency. The experimental data illustrated that siderite provided the catalyst for the Fenton process and that siderite has great application value and potential in carmine degradation; this data serves as a foundation for the industrial use of recycled natural mineral materials.

Adsorption of Pregelatinized Starch for Selective Flocculation and Flotation of Fine Siderite.

Pregelatinized starch (PS) was used for the selective flocculation and flotation of fine siderite in a carbonate-containing iron ore. With PS, the flotation of fine siderite was improved. The repulsive forces between fine siderite particles and the attractive forces between siderite and hematite or quartz were decreased after treatment with PS, indicating that the aggregation of siderite was enhanced and the aggregations of mixed minerals were weakened. An analysis of the changes in X-ray photoelectron spectra showed that coordination bonds were formed when PS was adsorbed on siderite and hematite. However, PS could not adsorb on quartz. Moreover, the molecular simulation showed that the main mechanism for PS adsorption on siderite was confirmed as a "tail model" with end -OH coordinated with Fe2+. The bridge connection of PS enhanced the flocculation of fine siderite. The flotation of fine siderite was also enhanced. For hematite treated with PS, the combination of coordination bond and hydrogen bond resulted in the "loop model" and "train model" as the main adsorption mechanisms of PS. The molecules covered the hematite surface and prevented the adsorption of the collector. The flotation of hematite was depressed. As a result, the selective flocculation and flotation of fine siderite were realized.

Elemental affinity for siderite found in a Japanese paddy subsoil

ABSTRACTSiderite (FeCO3), a type of carbonate mineral, is very occasionally recognized as a nodule in anoxic soils and sediments. During siderite formation, elements are expected to be accumulated or excluded between siderite and bulk soil. Therefore, we verified the affinity of 40 elements for siderite found in the gley horizon of a smectite-rich paddy field in northeastern Japan from the elemental concentration of the soil and the siderite dissolved in 2.88 mol L−1 hydrochloric acid (10% HCl). The concentration ratio of the target element of the soil to the siderite was expressed by the product of the dimensionless R0 value and ratio of titanium (Ti) concentration of the soil to the siderite (Csiderite /Csoil) = R0 (Tisiderite /Tisoil). The affinity of each element for the siderite was analyzed by comparing the R0 values. In comparison with Ti used as the reference element, P, Cr, Co and Mo were accumulated (R0 > 1.0), and alkali metals, such as Li, Na and K, and chalcophile elements, such as Cu, Zn, Cd and Pb, tended to be equal or excluded from the siderite (R0 ≦1.0). Of the group 2 elements, Ca, Sr and Ba were accumulated, while Mg was excluded. The affinity of Mn for siderite exceeded that of Fe as the main component of the siderite, which reflects the fact that siderite was formed in a fresh water condition. The siderite size did not influence the elemental affinity. Observation of micromorphology using a scanning electron microscope showed that the siderite nodules were aggregations of siderite particles and clays, suggesting that the siderite grew by taking in clay around it. The rare earth element (REE) distribution pattern showed a tendency not to increase linearly but to increase with forming a concave curve at the intervals of the four elements with the increase of atomic number (i.e. tetrad effects). Although these findings are from the lower horizons of anoxic soils, the elemental affinity for siderite of this study is useful in order to elucidate the complex elemental dynamics in the anoxic environment.

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 CaCO3 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.

The first find of biogenic nanosiderite in oxidized ferrous quartzite of the Lebedinsk deposit, Kursk Magnetic Anomaly

The first data on biogenic nanosiderite originally discovered in oxidized Fe-quartzites from the Lebedinsk deposit of the Kursk Magnetic Anomaly (KMA) are reported. Two generations of siderite with radically different morphology and crystal-chemical and physical properties were identified. The biogenic origin is substantiated for the late generation (nanosized siderite particles). We suggest that the early ores were transformed as a result of the evolution of the atmosphere and biosphere in the area of the KMA in the Phanerozoic. Such significant differences in the properties of biogenic nanosiderite and early rhombohedral siderite may provide evidence for their different origins. The early generation of siderite was most likely formed during an abiogenic process.

Hematite reactivity with supercritical CO 2 and aqueous sulfide

Hematite nanoparticles were reacted in a solution containing sulfide in contact with supercritical CO 2, to simulate conditions relevant to carbon dioxide sequestration in the Earth's subsurface. X-ray diffraction was used to identify reaction products. Rietveld analysis of the X-ray diffractograms and thermogravimetric analysis were used to estimate the amounts of reaction product formed. Under the experimental conditions used (70 °C), a near equimolar amount of siderite (FeCO 3) and pyrite (FeS 2) formed. The equimolar amounts of pyrite and siderite products were consistent with the stoichiometry associated with the following overall reaction, 2Fe 3+ + 2S 2− + CO 3 2– → FeS 2 + FeCO 3. In situ infrared spectroscopy suggested that the conversion of the hematite was rapid and largely occurred within 4 h at 70 °C. Analysis of the reaction product with electron microscopy showed the presence of framboidal pyrite and rhombohedral siderite particles that were micron-sized. The observed morphologies suggest that the transformation from hematite to siderite occurred via a dissolution–reprecipitation reaction.

XAFS Investigation of the Interactions of UVI with Secondary Mineralization Products from the Bioreduction of FeIII Oxides

Biogenic Fe(II) phases (magnetite, green rust, siderite, vivianite, etc.) provide a reservoir of reducing capacity in many subsurface environments that may contribute to the reduction of contaminants such as U(VI). We have examined the uptake and reduction of U(VI) in the presence of biogenic green rust (BioGR), magnetite (BioMAG), and siderite (BioSID) formed during the reduction of Fe(III) oxides by Shewanella putrefaciens CN32. Within 48 h, total solution-phase U(VI) concentrations decreased from 500 microM to 1.5 microM, 392 microM, and 472 microM in the U-BioGR, U-BioMAG, and U-BioSID systems, respectively. Analysis of the samples by U L(III) extended X-ray absorption fine structure spectroscopy (EXAFS) indicated that despite a stoichiometric excess of Fe(II), no more than 6% of U(VI) was reduced to U(IV) in the U-BioSID system, and no more than 22% of U(VI) was reduced in the U-BioMAG system. For comparison, in the U-BioGR system, >99% of U(VI) was reduced to U(IV). Uptake of U(VI) by BioGR and BioMAG was accompanied by formation of nanoparticulate uraninite. The U EXAFS data for the U-BioSID system were consistent with partial U(VI)/U(IV) substitution for Fe(II) in the surface layer of siderite particles and adsorption of U(IV).

Magnetic–hydrophobic coagulation of paramagnetic minerals: a correlation of theory with experiments

A simple theoretical model of magnetic–hydrophobic coagulation considering the total interaction potential energy between two spheres exposed to an external magnetic field as a sum of the van der Waals, electrostatic, magnetic, and hydrophobic components is proposed. The model was used to interpret experiments on coagulation of fine siderite particles in distilled water and 10 −2 M KCl, hydrophobized by sodium oleate. In the experiments, a relative extent of the coagulation/stability equilibrium of the siderite suspension was evaluated photoelectrically. To estimate the model parameters, the ζ-potential and hydrophobicity of siderite particles were measured. A qualitative agreement was obtained between the model predictions (energy maximum and secondary minimum) and the experimental results (voltage changes after a selected interval of sedimentation) of the siderite suspensions. Moreover, a statistically significant correlation was found between the experimental voltages and the calculated energy maximum (a crucial factor of theories on the fine particle coagulation kinetics), which can be represented by a linear regression equation with the correlation coefficient of 0.979.

Investigation of the High-Temperature Behavior of Excluded Siderite Grains during Pulverized Fuel Combustion

An investigation of the behavior of excluded siderite samples derived from both pure mineral species and by density separation of pulverized coal samples was conducted at combustion temperatures of 1100 and 1600 °C. Analysis of quenched combustion residues collected from the combustion gases under oxidizing conditions was obtained via scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and X-ray fluorescence (XRF) spectroscopy. The FeO−MgO−CaO ternary phase diagram was used to predict the behavior of excluded siderite grains under combustion conditions and indicated that the siderite is unlikely to form sticky or completely melted particles at 1600 °C unless MgO 60wt %. The extent of melting observed for collected particles having different compositions agreed with this prediction. By comparison with published work for excluded pyrite particles, residues from excluded siderite particles are found to be sticky at higher temperatures (1380...

Investigation of microbial—mineral interactions by Mössbauer spectroscopy

Mossbauer spectroscopy was used to investigate the reactions of microbes with iron minerals in aqueous solutions and as components of rocks in banded iron formations and granite. A microbial biofilm that formed on a wall of an excavated granite vault in a deep underground laboratory initiated this research. At the aerobic face of the biofilm, iron was found in a form of ferrihydrite; in the anaerobic face against the rock, iron was found as very small siderite particles. Laboratory incubations of the biofilm microbial consortium showed different mineral species could be formed. When the microbial consortium from the biofilm was incubated with magnetite grains, up to about 10% of the iron was altered in three weeks to hematite. The ability of the consortium to precipitate iron both as Fe2+ and Fe3+ in close proximity may have a bearing on the deposition of banded iron formations. These reactions could also be important in microbially induced corrosion.

The behaviour of coal mineral carbonates in a simulated coal flame

The flame behaviour of the most important carbonates in European import coals has been investigated. The flame tests were performed in a laboratory facility in which the environment of a coal burner was simulated. For the tests the coal minerals were separated from the coal by float-sink separation. Electron microscopy was used to determine the size and morphology of the particles sampled from the flame. The viscosity of the particles was derived from tests of their adherence to refractory deposit plates placed in the flame. Calcite (CaCO 3) particles of 60 μm, a typical size in pulverized coal, broke up into fragments approximately ten times smaller. The time taken for complete fragmentation corresponded to the time calculated for the decomposition of the calcite. None of the ‘siderite’ samples tested showed fragmentation. Detailed analyses with TGA MS (thermogravimetry coupled with mass spectrometry) were performed to determine the actual fraction of FeCO 3 in the ‘siderite’ samples. Flame products of siderite proper had high viscosity. Siderite particles with embedded silicates had flame products of low viscosity. Ankerite (CaFe(CO 3) 2) did not fragment and the flame product was fluid.

Simultaneous Hydrophobic and Magnetic Flocculation of Fine Paramagnetic Mineral Particles inAqueous Suspension

Flocculation of fine paramagnetic particles rendered hydrophobic by absorption of surfactants in external magnetic field in aqueous suspension, called simultaneous hydrophobic and magnetic flocculation (SHMF), has been studied through a theoretical approach and experiments. All interactions between fine paramagnetic particles in the case of SHMF are being discussed in this paper. Through extension of the classical DLVO theory, the theory of stability of fine particles in aqueous suspension in the case of SHMF is proposed. Potential energies of interaction between fine rhodochrosite particles rendered hydrophobic by absorption of sodium oleate in external magnetic field have been calculated from the theory. Experimental results of SHMF of fine rhodochrosite and siderite particles showed that SHMF exhibits much stronger and faster aggregation then either hydrophobic or magnetic flocculation alone. Two examples of SHMF applied to fine particle processing are given.