Investigation of the Petrological and Geochemical Characteristics of Siderite in the Early Cretaceous Sandstone of Lacustrine Sedimentary Sequence in the Erlian Basin from Northeastern China

Siderite is a prevalent authigenic mineral in siliciclastic rocks, which usually occurred in eodiagensis period and could be used as an indicator of sedimentary environment. Some siderite precipitated in burial depth with geochemical information of basin fluid evolution. The crystal morphology, geochemical composition, and isotope values are influenced by physical and geochemical environment of precipitation. In this study, samples from the Early Cretaceous of Erlian basin in the northwestern China were collected, and mineralogy, bulk and in-situ geochemistry, C and O isotopes were analyzed to comprehensively investigate the sedimentary and diagenetic environment that the sediments experienced. Six lithofaices with three types of crystal habits were recognized in the siderite-rich sandstone, bundle crystal in spherical forms, blocky rhombs in intergranular pore and cleavage of muscovite, and micro bundle and mosaic crystals aggregates in nodular. The siderite growth proceeds through micro bundle and mosaic crystals to bundle siderite aggregates and then into blocky rhombs. The crystal evolution is also reflected by geochemical composition. The micro bundle and mosaic crystals are Casiderite. The spheritic shaped bundle aggregates are Ca-Mn-siderite. The blocky rhomb siderite shows gray part and bight part with Ca, Mg and Mn varies. Increase of Ca in block rhomb siderite suggests burial and mesodiagenesis, the high content of Mn may have linkage with eogenetic effects. The relatively positive and slightly negative δ13C value indicates meteoric water domination and influence of organic matter evolution in shallow buried time. The narrow ranges negative δ18O value suggest a small span of temperature of siderite formation.

Reaction behavior and non-isothermal kinetics of suspension magnetization roasting of limonite and siderite

In order to develop limonite and decrease CO_(2) emissions,siderite is proposed as a clean reductant for suspension magnetization roasting(SMR) of limonite.An iron concentrate(iron grade:65.92wt%,iron recovery:98.54wt%) was obtained by magnetic separation under the optimum SMR conditions:siderite dosage 40wt%,roasting temperature 700℃,roasting time 10 min.According to the magnetic analysis,SMR achieved the conversion of weak magnetic minerals to strong magnetic minerals,thus enabling the recovery of iron via magnetic separation.Based on the phase transformation analysis,during the SMR process,limonite was first dehydrated and converted to hematite,and then siderite decomposed to generate magnetite and CO,where CO reduced the freshly formed hematite to magnetite.The microstructure evolution analysis indicated that the magnetite particles were loose and porous with a destroyed structure,making them easier to be ground.The non-isothermal kinetic results show that the main reaction between limonite and siderite conformed to the two-dimension diffusion mechanism,suggesting that the diffusion of CO controlled the reaction.These results encourage the application of siderite as a reductant in SMR.

Fluidized magnetization roasting of refractory siderite-containing iron ore via preoxidation-low-temperature reduction

Magnetization roasting is one of the most effective way of utilizing low-grade refractory iron ore.However,the reduction roasting of siderite(FeCO3)generates weakly magnetic wüstite,thus reducing iron recovery via weak magnetic separation.We systematically studied and proposed the fluidized preoxidation-low-temperature reduction magnetization roasting process for siderite.We found that the maghemite generated during the air oxidation roasting of siderite would be further reduced into wüstite at 500 and 550℃due to the unstable intermediate product magnetite(Fe_(3)O_(4)).Stable magnetite can be obtained through maghemite reduction only at low temperature.The optimal fluidized magnetization roasting parameters included preoxidation at 610℃for 2.5 min,followed by reduction at 450℃for 5 min.For roasted ore,weak magnetic separation yielded an iron ore concentrate grade of 62.0wt%and an iron recovery rate of 88.36%.Compared with that of conventional direct reduction magnetization roasting,the iron recovery rate of weak magnetic separation had greatly improved by 34.33%.The proposed fluidized preoxidation-low-temperature reduction magnetization roasting process can realize the efficient magnetization roasting utilization of low-grade refractory siderite-containing iron ore without wüstite generation and is unlimited by the proportion of siderite and hematite in iron ore.

Effect and mechanism of siderite on reverse anionic flotation of quartz from hematite

Reverse flotation technology is one of the most efficient ways to improve the quality and reduce impurity of iron concentrate. Mineral processors dealing with hematite face a challenge that the flotation results of reverse flotation of hematite are poor in presence of siderite using fatty acid as collector, starch as depressant of iron minerals and calcium ion as activator of quartz at strong alkaline pH. In this work, the effect of siderite on reverse anionic flotation of quartz from hematite was investigated. The effect mechanism of siderite on reverse flotation of hematite was studied by solution chemistry, ultraviolet spectrophotometry(UV) and Fourier transform infrared spectroscopy(FTIR). It was observed that siderite had strong depressive effect on quartz in flotation using sodium oleate as collector, corn starch as depressant of iron minerals and calcium chloride as activator of quartz at strong alkaline pH. The starch was adsorbed onto calcium carbonate by chemical reaction which was formed by CO^(2-)_3 from siderite dissolution and Ca^(2+) from calcium chloride as activator of quartz and precipitated on the surface of quartz, which resulted in improving the hydrophilic ability of quartz.

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.

Siderite pyrolysis in suspension roasting:An in-situ study on kinetics,phase transformation,and product properties

Siderite,as an abundant iron ore,has not been effectively utilized,with a low utilization rate.In this study,the in-situ kinetics and mechanism of siderite during suspension magnetization roasting(SMR)were investigated to improve the selective conversion of siderite to magnetite and CO,enriching the theoretical system of green SMR using siderite as a reductant.According to the gas products analyses,the peak value of the reaction rate increased with increasing temperature,and its curves presented the feature of an early peak and long tail.The mechanism function of the siderite pyrolysis was the contraction sphere model(R_(3)):f(α)=3(1−α)2/3;E_(α)was 46.4653 kJ/mol;A was 0.5938 s^(−1);the kinetics equation was k=0.5938exp[−46.4653/(RT)].The in-situ HT-XRD results indicated that siderite was converted into magnetite and wüstite that exhibited a good crystallinity in SMR under a N_(2) atmosphere.At 620℃,the saturation magnetization(M_(s)),remanence magnetization(Mr),and coercivity(Hc)of the product peaked at 53.63×10^(-3)A·m^(2)/g,10.23×10^(-3)A·m^(2)/g,and 12.40×10^(3)A/m,respectively.Meanwhile,the initial particles with a smooth surface were transformed into particles with a porous and loose structure in the roasting process,which would contribute to reducing the grinding cost.

Kinetics of the Thermal Decomposition of Wangjiatan Siderite

The thermal decomposition processes of Wangjiatan siderite samples were studied in nitrogen by thermogravimetric（TG）analysis.The mechanism of thermal decomposition of the siderite obeyed an F n kinetic law and the n-order was between 1.16 and 1.29.The results from non-isothermal experiments show that the size of particles has an obvious effect on the logarithm of pre-exponential factor in kinetics parameter of the thermal decomposition of Wangjiatan siderite.A linear relationship is shown between the size of particles and the logarithm of pre-exponential factor.An F 1 kinetic model containing size factor describes the thermal decomposition of Wangjiatan siderite well.

Adsorption of Fluoride in Aqueous Solution on Synthetic Siderite

The present article bears in itself the investigation of the authors on the ways of treating high-fluoride containing groundwater by using synthetic siderite. Effects of various physico-chemical parameters such as contact time,initial F^-concentration,temperature and pH of solution,absorbent dose,and coexistence anions on F^-adsorption were studied in terms of batch tests.It was found that,as contact time increased。

An exsitu underground coal gasification experiment with a siderite interlayer:course of the process,production gas,temperatures and energy efficiency

A 72-h ex situ hard coal gasification test in one large block of coal was carried out.The gasifying agent was oxygen with a constant flow rate of 4.5 m^(3)/h.The surroundings of coal were simulated with wet sand with 11%moisture content.A 2-cm interlayer of siderite was placed in the horizontal cut of the coal block.As a result of this process,gas with an average flow rate of 12.46 m^(3)/h was produced.No direct influence of siderite on the gasification process was observed;however,measurements of CO_(2)content in the siderite interlayer before and after the process allow to determine the location of high-temperature zones in the reactor.The greatest influence on the efficiency of the gasification process was exerted by water contained in wet sand.At the high temperature that prevailed in the reactor,this water evaporated and reacted with the incandescent coal,producing hydrogen and carbon monoxide.This reaction contributes to the relatively high calorific value of the resulting process gas,averaging 9.41 MJ/kmol,and to the high energy efficiency of the whole gasification process,which amounts to approximately 70%.

Natural siderite derivatives activated peroxydisulfate toward oxidation of organic contaminant: A green soil remediation strategy

Natural siderite(FeCO_(3)),simulated synthetic siderite and nZVI/FeCO_(3) composite were used as green and easily available iron-based catalysts in peroxydisulfate activation for remediating 2-chlorophenol as the target contaminant and this technique can effectively degrade organic pollutants in the soil.The key reaction parameters such as catalysts dosage,oxidant concentration and pH,were investigated to evaluate the catalytic performance of different materials in catalytic systems.The buffering property of natural soil conduced satisfactory degradation performance in a wide pH range(3-10).Both the main non-radical of ^(1)O_(2) and free radicals of SO_(4)^(-) and OH·were evidenced by quenching experiment and electron paramagnetic resonance.The reduction of nZVI on FFC surface not only has the advantage for electronic transfer to promote the circulation of Fe(Ⅲ)to Fe(Ⅱ),but also can directly dechlorinate.Furthermore,the intermediates were comprehensively analyzed by GC-MS and a potential removal mechanism of three oxidant system for 2-CP soil degradation was obtained.Briefly,this research provides a new perspective for organic contaminate soil treatment using natural siderite or simulated synthetic siderite as efficient and environmental catalytic material.

Mesoproterozoic biomineralization:Cyanobacterium-like filamentous siderite sheaths~1.4 Ga

Biomineralization was a key development in a wide variety of organisms,yet its history prior to the Ediacaran remains poorly understood.In this paper,we describe~1420-1330 million year old microscopic tubes preserved as siderite(FeCO_(3)).In size and shape these tubes closely resemble cyanobacterial sheaths forming mineralized mats.We consider two competing explanations for their formation.First,the tubes and associated sediment were originally composed of Ca-carbonate that was subsequently replaced by siderite.In this case,siderite mineralization was early,but post-mortem,as in early silicification,and preferentially preserved the more resilient sheath.However,no relict calcite is observed.Second,the Fe-carbonate mineralogy of the tubes and sediment is synsedimentary.In this case,photosynthetic oxygen may have precipitated Fe-oxyhydroxide that was promptly converted to siderite by dissimilatory iron reduction(DIR).Primary siderite mineralization of cyanobacteria has not been described before.Both explanations link photosynthetic processes to preferential sheath mineralization during the life of the cyanobacteria,as observed in present-day calcified cyanobacteria.This process might include CO_(2)-concentrating mechanisms(CCMs)linked to relatively low levels of atmospheric CO_(2),consistent with empirical estimates of mid-Proterozoic CO_(2)levels based on paleosols and weathering rinds.In either case,these cyanobacterium-like fossils preserved in siderite provide an early example of biomineralization and suggest the interactive in-fluences of both metabolic processes and ambient seawater chemistry.

Catalytic performance and reaction mechanisms of NO removal with NH_(3) at low and medium temperatures on Mn-W-Sb modified siderite catalysts

Iron-based catalysts have been explored for selective catalytic reduction(SCR)of NO due to environmentally benign characters and good SCR activity.Mn-W-Sb modified siderite catalysts were prepared by impregnation method based on siderite ore,and SCR perfor-mance of the catalysts was investigated.The catalysts were analyzed by X-ray diffrac-tion,H_(2)-temperature-programmed reduction,Brunauer-Emmett-Teller,Thermogravimetry-derivative thermogravimetry and in-situ diffused reflectance infrared Fourier transform spectroscopy(DRIFTS).The modified siderite catalysts calcined at 450℃ mainly consist of Fe_(2)O_(3),and added Mn,W and Sb species are amorphous.3Mn-5W-1.5Sb-siderite catalyst has a wide temperature window of 180-360℃ and good N_(2) selectivity at low temperatures.In-situ DRIFTS results show NH_(4)^(+),coordinated NH_(3),NH_(2),NO_(3)^(-)species(bidentate),NO_(2)-species(nitro,nitro-nitrito,monodentate),and adsorbed NO_(2) can be discovered on the sur-face of Mn-W-Sb modified siderite catalysts,and doping of Mn will enhance adsorbed NO_(2) formation by synergistic catalysis with Fe^(3+).In addition,the addition of Sb can inhibit sulfates formation on the surface of the catalyst in the presence of SO_(2) and H_(2)O.Time-dependent in-situ DRIFTS studies also indicate that both of Lewis and Br?nsted acid sites play a role in SCR of NO by ammonia at low temperatures.The mechanism of NO removal on the 3Mn-5W-1.5Sb-siderite catalyst can be discovered as a combination of Eley-Rideal and Langmuir-Hinshelwood mechanisms with three reaction pathways.The mechanism of NO,oxidized by synergistic catalysis of Fe^(3+)and Mn^(4+/3+)to form NO_(2) among three pathways,reveals the reason of high NO_(x) conversion of the catalyst at medium and low temperatures.

Mineralogical alteration of thermally treated siderite in air: Mossbauer spectroscopy results

Mineralogical alternation of thermally treated siderite in air atmosphere has been systematically analyzed by Mossbauer effects. It was preliminarily estimated from the area of sub-spectra that 4% , 39% and 62% of magnetite were formed at 410℃, 490℃ and 510℃ respectively. After being incrementally heated at 530℃ the spectra consist of two sextets of Fe3O4. Sextet of γ-Fe2O3 with hyperfine field of 50T was observed at 550℃. Spectra at 580℃

Chemico-viscous remanent magnetization in the oxidation of siderite and its implications in paleomagnetism

Studies have been done of the secondary chemico-viscous remanent magnetization (CVRM) produced in the oxidization and decomposition of high-purity crystal siderite specimens collected from Dalizi Deposit, Jilin Province, The CVRM intensity increases to a peak value at an annealing temperature of 490*^0 . The direction of CVRM is always parallel to the applied field , and no self- reversal behavior has been observed in the transformation of maghemite to hematite . It is suggested that the phase transition of magnetic minerals can make great contribution to secondary magnetization. Results of successive heating at low temperature indicate that the crystal mineral siderite is basically stable. Finally , the paleomagnetic significance of CVRM is discussed.

Mechanism of improved magnetizing roasting of siderite–hematite iron ore using a synergistic CO–H2 mixture

A fluidized-bed magnetizing roasting-magnetic separation process was selected to treat this type of material.Phase transformations and microstructural changes in the product resulting from magnetizing roasting under different reducing gases(CO,H2,CO+H2)were clarified by vibrating sample magnetometry,X-ray diffraction,scanning electron microscopy,and energy-dispersive X-ray spectroscopy.The results indicated that the conversion ratio and saturation magnetization of samples roasted in a mixed gas of CO and H2 were higher than those of samples produced under CO or H2 alone.This indicated that synergy of the combined CO and H2 gas had a positive effect on the fluidized-bed magnetizing roasting process.The mechanism and kinetics of the improved magnetizing roasting of a siderite-hematite iron ore mixture under this synergistic CO-H2 system were investigated under isothermal conditions.The results indicated that the apparent activation energies of the reactions of the iron oxides decreased from 37.7 and 17.9 to 15.9 kJ/moI when the roasting atmosphere was changed from pure H2 or CO to a gas mixture of CO and H2,respectively.The mixed CO-H2 gas promoted the conversion ratio of hematite and siderite to magnetite,thereby improving the conversion ratio in the fluidized-bed magnetizing roasting process.

Mechanism of high temperature reduction on iron carbide preparation with low-grade siderite

The carburization roasting followed by magnetic separation is a feasible method to utilize low-grade siderite ore.In order to enhance the carburization efficiency and separation effciency,high temperature reduction was carried out,and its mechanism was demonstrated by measuring carburization index,phase change,and microstructure under a carbon-sulfur infrared analyzer,an X-ray diffractometer,and a metallurgical microscope.The results show that both the carburization effciency of siderite pellet and the separation efficiency of iron carbide from gangue are very low.However,high temperature reduction is a useful way to enhance the carburization efficiency,as it can accelerate the reduction reaction rate and carburization reaction rate.Furthermore,high temperature reduction can improve the growth of iron carbide particle,promote the carburization efficiency,and strengthen the sodium modification reactions,thereby greatly accelerating the separation efficiency of iron carbide and gangue.When the siderite pellets were reduced at 1050℃ for 90 min and carburized at 650℃ for 120 min,the carburization index of carburized pellets reached 36.06.After magnetic separation treatment,an electric furnace burden assaying 83.12 wt.%Fe and 6.96 wt.%C was prepared,and the corresponding iron recovery rate was 95.43%.The high temperature reduction is promisingly adopted to promote the utilization of low-grade siderite ores using carburization-magnetic separation technology.

Magnetic susceptibility variation and AMS exchange related to thermal treatment of siderite

Siderite is one of the common iron-bearing carbonates in deposits. Its magnetic properties are usually neglected due to its paramagnetic property at room temperature. It was shown that the magnetic susceptibility changes with temperature variation. Also it was revealed that the maximum axis (K1) of AMS ellipsoid exchange position gradually with the minimum axis (K3) during thermal treatment, and thus, AMS ellipsoids of samples change from initial prolate to oblate. It was concluded that such changes resulted from the decomposition and oxidation of siderite during heating in which siderite was transformed into magnetite, maghemite, and finally to hematite.

Sorption mechanisms of diphenylarsinic acid on natural magnetite and siderite:Evidence from sorption kinetics,sequential extraction and extended X-ray absorption fine-structure spectroscopy analysis

Diphenylarsinic acid(DPAA)is both the prime starting material and major metabolite of chemical weapons(CWs).Because of its toxicity and the widespread distribution of abandoned CWs in burial site,DPAA sorption by natural Fe minerals is of considerable interest.Here we report the first study on DPAA sorption by natural magnetite and siderite using macroscopic sorption kinetics,sequential extraction procedure(SEP)and microscopic extended X-ray absorption fine-structure spectroscopy(EXAFS).Our results show that the sorption pseudo-equilibrated in 60 minutes and that close to 50%and 20%–30%removal can be achieved for magnetite and siderite,respectively,at the initial DPAA concentrations of 4–100 mg/L.DPAA sorption followed pseudo-secondary and intra-particle diffusion kinetics models,and the whole process was mainly governed by intra-particle diffusion and chemical bonding.SEP and EXAFS results revealed that DPAA mainly formed inner-sphere complexes on magnetite(>80%),while on siderite it simultaneously resulted in outer-sphere and inner-sphere complexes.EXAFS analysis further confirmed the formation of inner-sphere bidentate binuclear corner-sharing complexes(^(2)C)for DPAA.Comparison of these results with previous studies suggests that phenyl groups are likely to impact the sorption capacity and structure of DPAA by increasing steric hindrance or affecting the way the central arsenic(As)atom maintains charge balance.These results improve our knowledge of DPAA interactions with Fe minerals,which will help to develop remediation technology and predict the fate of DPAA in soil-water environments.

Microstructure Characteristic and Phase Evolution of Refractory Siderite Ore during Sodium-carbonate-added Catalyzing Carbothermic Reduction

Thermodynamic analysis of refractory siderite ore during carbothermic reduction was conducted. Micro- structure characteristics and phase transformation of siderite ore during sodium-carbonate-added catalyzing carboth- ermic reduction were investigated. X-ray diffraction （XRD）, scanning electron microscopy and energy-dispersive analysis of X rays were used to characterize the reduced samples. Results indicate that the solid reaction between FeO and SiO2 is inevitable during carbothermic reduction and the formation of fayalite is the main hindrance to the rapid reduction of siderite. The phase transformation of present siderite ore can be described as： siderite-magnetite-metallic iron, complying with the formation of abundant fayalite. Improving the reduction temperature （-1050 -C ） and duration is helpful for the formation and aggregation of metallic iron. The iron particle size in the reduced ore was below 20 l-m, and fayalite was abundant in the absence of sodium carbonate. With 5% Na2CO3 addition, the iron particle size in the reduced ore was generally above 50μm, and the diffraction intensity associated with metallic iron in the XRD pattern increased. The Na2O formed from the dissociation of Na2 CO3 can catalyze the carbothermie reduction of the siderite. This catalytic activity may be mainly caused by an increase in the reducing reaction activity of FeO.

Characterization and kinetic study on ammonia leaching of complex copper ore

Ammonia leaching kinetics of a complex Cu-ore assaying 8.8% Cu and 36.1% Fe was examined. Mineralogical characterization indicated that the major phase of the ore was siderite with chalcopyrite as the major sulfide mineral. The effects of parameters such as agitation, temperature, NH3 concentration, particle size and oxygen partial pressure （Po2） were investigated. Under the standard leaching conditions of 125-212 μm particle size, 120 ℃, 1.29 mol/L NH3 and 202 kPa ofpo2, about 83% Cu could be selectively extracted in 2.5 h. However, when using higher NH3 concentration and lower particle size, more than 95% extraction was achieved. The leaching process was found to be surface reaction controlling. The estimated activation energy was （37.6±1.9） kJ/mol and empirical orders of reaction with respect topos and [NH3] were about 0.2 and 1, respectively.