Analytical and mineralogical studies of ore and impurities from a chromite mineral using X-ray analysis, electrochemical and microscopy techniques

A wide analytical study of South African chromite ore, material with high interest in ceramic industry, has been carried out. With this purpose, an accurate chemical identification and mineralogical characterization of the mineral and the gangue have been performed using X-ray fluorescence (XRF), voltammetry, X-ray diffraction (XRD), light microscopy (LM), and scanning electron microscopy (SEM/EDX). The elemental composition of the sample (ore and gangue) has been obtained by XRF. The voltammetric analysis has allowed to demonstrate that iron in the sample was as Fe(II). The main compound of the chromite ore was a spinel (magnesiochromite ferroan), identified by XRD from the sample, which constitutes the chromite ore. This technique has also been useful to characterize some silicates as impurities in the chromite ore sample. Light microscopy has allowed the detection of the spinel and the identification of a silicate impurity (chrome chlorite), by means of their colouration. On the other hand, the other silicate impurity was identified as labradorite by means of X-ray microscopy by SEM/EDX. Finally, a strategy was developed to calculate the composition of each mineral in the unknown sample. The obtained results were: chromite spinel 82.89%, chlorite 12.79% and labradorite 4.32%.     

Mössbauer Investigation of Characteristic Distribution of Iron Oxides in Sediments from the Antarctica

Sediments from the Admiralty Bay, King George Island, Antarctica, were investigated by ⁵⁷Fe Mössbauer spectroscopy, X-ray diffractometry, and radiometry. Quartz, feldspar, chlorite, calcite, dolomite, mica, kaolinite, hematite and magnetite were identified as constituent minerals in the sediment samples. The phase composition and the iron distribution among the crystallographic sites of iron-bearing minerals (silicates, magnetite and hematite) of samples from different location have been derived from the complex Mössbauer spectra. At different locations sediments had significant characteristic differences in the mineral composition, in the iron distribution among the crystallographic site of silicates, and in the specific radioactivity of Cs radionuclides. These results indicate differences in the rock formation and alteration by the sediments in this maritime part of Antarctica. There is a much higher amount of iron oxides in the sediments from south part of the geological fault across the Admiralty Bay than in the north part. This can be associated with much more alteration in the rocks in the south part compared to the northern one. This finding can contribute to the question of the history of the formation and alteration of volcanic rocks in the border of Antarctica.     

Thermal characterization of a Spanish red mud

A Spanish red mud was thermally characterized. Chemical and mineralogical composition were determined by XRF and XRD.The thermal events observed in the range from room temperature to 1300°C were related to the sample composition. The first mass loss step was related to free water content, while many of the other processes were related to dehydration processes. It was found that most of the decomposition reactions of hydrohematite, ferrihydrite, aluminogoethite, boehmite, silicates and carbonates were strongly overlapping. It was also explained the formation of silicates and calcium titanate, which presence was confirmed at 1000°C by XRD.     

A total dissolution method for determination of the α-emitting isotopes of uranium and thorium in deep-sea sediments

A method is described for the determination of specific activities of the natural α-emitting isotopes of uranium and thorium in deep-sea marine sediments. Such information is needed primarily for estimation of sediment accumulation rates. The method is based on total dissolution of sample after fusion with potassium fluoride (to dissolve silicates) and with sodium/potassium pyrosulphate (to dissolve other refractory minerals and convert to the sulphate system). Uranium and thorium fractions are purified for electroplating by anion exchange, with elements naturally present used as carriers. Final determinations are made by α-spectrometry by means of isotopic tracers added at the outset of processing. Experience gained with different types of deep-sea sediment is discussed.     

Chemical and spectroscopic investigation on the plaster of a Byzantine church

The discovery of a Byzantine church under the floor of one of the oldest churches of Salerno (Italy) has given us the opportunity to investigate the fine composition of the plaster through chemical and spectroscopic methods. In particular, considering that plasters are generally formed by a carbonate phase (carbonates) and an inert phase (silicates), the characterization, performed on the carbonate phase by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA), has revealed the presence of dolomite minerals. This information indicates that, during the building process, some accessory minerals of marble were added in the mortar to be used like fillers. The carbonate phase makes too difficult the spectroscopic characterization of the inert phase. Only by acid attack of the plaster the inert phase has been isolated and its characterization, by XRD and optical microscopy, has indicated the presence of olivine minerals and other typical silicates of river sands.     

Study of mineralogical speciation of arsenic in soils using X ray microfluorescence and scanning electronic microscopy

In this paper we studied the As content in natural contaminated soils, classified as Dystric Leptosol, Chromic Luvisol, Eutric Cambisol and Mollic Leptosol. In soil samples, sieved (<2 mm), total As was determined by XRF and chemical speciation by sequential extraction. As-bearing minerals were concentrated from fine sand fraction of soil (200-20 μm) using heavy liquid. In this fraction, mineralogical speciation was studied by X-ray microfluorescence, XRD with Göbbel mirror and SEM-BEI-EDX. Total As contents ranging from 61.00 to 131.00 mg kg⁻¹. The results of the sequential extraction showed that As was, mainly, in the residual fraction (52.51-98.76 mg kg⁻¹) and in the fraction bound to iron oxyhydroxides (0-36.5 mg kg⁻¹). Mapping of As with X-ray microfluorescence show strongly relationship between Fe and As. Iron (III) oxyhydroxides (FeOHs) (lepidocrocite and goethite), scorodite, angelellite, schultenite and dussertite were identified by XRD analysis as most likely mineral phases. The contents of As, Fe, Pb and Ba obtained with EDX-microprobe, confirmed the results of XRD. The results of sequential extraction and X-ray microfluorescence indicate that As is strongly bound to the soils because the identified As-bearing mineral phases are very stable at the pH conditions of studied soils. Consequently, a low mobility of As can be assumed in these soils.     

选择性萃取对沉积物非残渣态、粘土矿物结构及吸附特性的影响

用NH2OH·HCl, (NH4)2C2O4和H2O2对表层沉积物中非残渣态的Mn氧化物、Fe/Mn氧化物和有机质进行选择性化学萃取, 同时提取粘土矿物, 并对提取前后的表层沉积物样品进行了比表面积、FTIR、ESEM和XRD等分析. 结果表明, 萃取后沉积物的比表面积显著增大, 沉积物颗粒的分散度随之增大, 晶体边缘逐渐清晰, 棱角逐渐分明, 但沉积物的XRD和FTIR谱图变化不大, 原因在于XRD和FTIR谱图中的特征峰主要是由矿物组分产生的. 萃取后随着沉积物分散度的增大, 晶体颗粒表面粗糙度减弱, 沉积物的吸附能力降低, 表明颗粒表面特征对重金属的吸附起到一定作用; 而沉积物的比表面积与沉积物吸附能力之间的反比关系说明沉积物主要吸附组分对其吸附的贡献远远大于沉积物表面与孔隙结构的贡献.     

Analysis of major and trace elements by INAA to predict the thousands year old sediment deposition environment in the Meghna river delta

Major, trace and rare earth elements have been measured in sediments of different layers to determine the controls of constituent minerals on the distribution of elements and sediment deposition environment in the Meghna river delta. The geochemical composition of sediments was enriched in SiO₂, Ca, Mg and Ba and depleted in Al, Fe, Ti, Mn, and Sr relative to PAAS (Post-Archaen Average Shale) value. The X-ray diffraction and elemental analyses demonstrate the dominant presence of quartz, micas, feldspar, chlorite, amphibole and clay minerals in sediments. The very low contents of trace elements suggest that the oxic condition was more prevalent during sediment deposition of Pleistocene-Holocene period and reflect the massive chemical weathering by biogeochemical reactions. The enrichment of light rare earth elements and La/Yb ratio reflect the intense silicate weathering of crustal materials and the high sediment depositional rate in the Meghna river delta.     

高温下煤中矿物质对气化反应的影响

利用XRD对1100℃~1500℃高温下矿物质在弱还原气氛中的变化进行考察,并利用RIR对矿物质进行半定量分析,发现随着温度的升高莫来石含量增大,而SiO₂含量下降,符合SiO₂-Al₂O₃二元相图的变化。高温下部分无定形矿物质发生熔融,主要为硅铝酸盐。在煤焦二氧化碳气化过程中,熔融的硅铝酸盐与煤焦表面接触阻碍气化反应进行。利用FT-IR测定了硅铝酸盐结构的变化,说明高温下矿物质对气化反应的影响与硅铝酸盐的聚合程度存在一定的关系。     

不同灰化温度下生物质混煤灰的烧结特性研究

选取晋城无烟煤和麦秆作为研究对象,利用压差法烧结温度测定装置测量不同灰化温度下煤和麦秆混合灰的烧结温度,再利用SEM-EDS以及XRD对灰样进行烧结特性分析。结果表明,不论灰化温度高低,随着麦秆的添加,煤和麦秆混合灰的烧结温度都呈现降低趋势,其降低幅度略有差别。灰化温度较低时,煤和麦秆混合灰的烧结温度低于灰化温度较高情况下混合灰的烧结温度。SEM-EDS分析表明,低温灰化得到的样品中出现较多不规则的纤维结构;较高温度下获得的灰样中出现较多致密的球状颗粒,这表明矿物质发生熔融形成球状颗粒。XRD分析表明,低温灰化烧结后的煤和麦秆混合灰样中因含有较多的含钾等碱金属系助融矿物质,导致混合灰样的烧结温度降低。然而,像钙长石等含钙矿物质本身具有较高的熔点,因此,在1 100℃时混合灰样具有较高的烧结温度。     

Solid-state NMR study of geopolymer prepared by sol-gel chemistry

Geopolymers are a new class of materials formed by the condensation of aluminosilicates and silicates obtained from natural minerals or industrial wastes. In this work, the sol-gel method is used to synthesize precursor materials for the preparation of geopolymers. The geopolymer samples prepared by our synthetic route have been characterized by a series of physical techniques, including Fourier-transform infrared, X-ray diffraction, and multinuclear solid-state NMR. The results are very similar to those obtained for the geopolymers prepared from natural kaolinite. We believe that our synthetic approach can offer a good opportunity for the medical applications of geopolymer.     

Synthesis and characterization of silica gel from siliceous sands of southern Tunisia

The present work aimed to achieve valorization of Albian sands for the preparation of sodium silicates that are commonly used as a precursor to prepare silica gel. A siliceous sand sample was mixed with sodium carbonate and heated at a high temperature (1060 °C) to prepare sodium silicates. The sodium silicates were dissolved in distilled water to obtain high quality sodium silicate solution. Hydrochloric acid was then slowly added to the hydrated sodium silicates to obtain silica gel. The collected raw siliceous sands, as well as the prepared silica gels, were characterized by different techniques, such as X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis (DSC). XRF confirmed that the detrital sand deposits of southern Tunisia contain high amounts of silica, with content ranging from 88.8% to 97.5%. The internal porosity varied between 17% and 22%, and the specific surface area was less than 5 m²/g. After the treatment described above, it was observed that the porosity of the obtained silica gel reached 57% and the specific surface area exceeded 340 m²/g. Nitrogen adsorption isotherms showed that the prepared silica gels are microporous and mesoporous materials with high adsorption capacities. These results suggest that the obtained silica gels are promising materials for numerous environmental applications.     

Crystal chemistry of clay minerals in bottom sediments of the Sea of Okhotsk as a paleoclimatic indicator

X-ray diffraction and infrared spectroscopy were used to study the mineral composition of bottom sediments of the Sea of Okhotsk with ages ranging from Holocene (10 My ago) to Pleistocene (10 to ～74 My ago). The concentrations of nonlayered minerals (quartz, plagioclase, carbonates, and biogenic silica) were determined from IR spectra, which made it possible to estimate the actual abundance of the clay component in test samples. Calibration curves used in the calculation were plots of the optical density in the maximum of the analytical absorption band of the analyzed component versus its concentration in the sample. These curves were constructed for standard mixtures of known compositions. The crystal-chemical parameters and quantitative ratios of clay minerals were elucidated by the computer simulation of X-ray diffraction profiles; clear correlations were found between these parameters and paleoclimatic changes. Our results show that the clay minerals from the bottom sediments of the Sea of Okhotsk can serve to search for paleoclimatic events in the North-Eastern Asia.     

Application of differential thermal analysis in mineralogy

In mineralogical research differential thermal analysis can be applied as either a single or a combined method for three purposes:

1. for the qualitative identification of minerals and the (semi-)quantitative determination of the components of rocks and soils,
2. for the characterization of crystal-physical and crystal-chemical properties, including the study of kinetics and the determination of thermodynamic data, phase and reaction equilibria,
3. for special petrogenetic investigations concerning the interrelation of mineralogical properties with the formation, decomposition or recrystallization of minerals.

The presented results were obtained under strongly standardized and reproducible conditions of analysis and by means of some methods recently developed by the author. They include the construction of key diagrams ofΔT versus peak temperatures to identify unknown minerals; the dependence of dehydration and decomposition peak temperatures on the partial pressure of gaseous reaction products (= PA curves); the determination of chemical and crystal-chemical parameters of minerals by using the dependence of dehydroxylation peak temperatures on solid solution (chlorites, smectites) or by using the interrelation between the peak temperatures of structural transformations and crystal-chemical substitutions (sulfides, carbonates, phosphates, silicates); the determination of the degree of disorder of minerals formed in sedimentary environments by using the dehydration or inversion peak temperature and peak shape dependence on the defect character of these crystal structures (clay minerals, quartz, cristobalite, hydroxides); the subdivision of mineral groups by using the interrelation of crystal chemistry and dehydration behaviour (zeolites, mixed-layer clay minerals); the characterization of ferromagnetic minerals by studying the Curie temperatures as a function of the chemical composition; the development of a DTA method to measure the degree of weathering of granitic rocks, etc. Data of 150 minerals are given.     

Characterization of some boron minerals against neutron shielding and 12 year performance of neutron permeability

In this study, the nuclear radiation permeability properties of various boron minerals are evaluated because of their high neutron absorption and lowest transmission properties. Because of these properties boron minerals can be used at the area of neutron shielding. X-ray diffraction (XRD) analyses are done for the identification of the minerals, and then their B₂O₃ contents are determined experimentally. In addition, X-ray florescence (XRF) analyses are made for quantitative determination of calcium, iron, zinc and arsenic contents. The methods of Differential Thermal Analysis, Thermal Gravimetry (TG/DTA) and Differential Scanning Calorimeter (DSC) are used for obtaining the enthalpy and weight changes with temperature. Additionally, neutron permeability experiments are conducted. From the experimental results, the highest boron oxide content was found in clay containing colemanite. Iron, zinc and arsenic contents were not affecting the neutron shielding. The lowest permeability is provided by the kurnakovite mineral. Also it is observed that all of the minerals show an increase in their permeability in 12 years. It can be stated that boron minerals, specifically kurnakovite, is determined to yield the lowest neutron permeability value and therefore, the use of these materials for neutron shielding would be suitable.     

“华光礁Ⅰ号”沉船出水青白瓷表面沉积物的分析

为探讨"华光礁Ⅰ号"沉船出水陶瓷器表面沉积物的成分及物相,以青白瓷为例,利用扫描电镜(SEM)和能谱仪(EDS)联用、X射线荧光(XRF)、X射线衍射分析(XRD)三种分析方法,对青白瓷表面不同颜色的沉积物进行了结构和化学组成的测试.结果表明,沉积物主要以碳酸盐类的文石、方解石以及含铁类的磁铁矿、针铁矿为主.本研究可为南海海域出水陶瓷器的保护提供参考和借鉴.     

Validation of the Tessier scheme for speciation of metals in soil using the Bland and Altman test

The Tessier extraction method was used for speciation of Cu, Pb, Zn, As, Fe and Mn in a large concentration range in contaminated soil with various mineralogical compositions. The results were compared by X-ray fluorescence spectrometry (XRF) as a reference method using the Bland and Altman test. A sum of five fractions (exchangeable, bound to carbonates, Fe-Mn oxides, organic matter and residual forms) was compared with the total content determined on solid matrix by the reference method. A good agreement between the methods in the whole concentration range was found for Cu, Zn, As, and Fe. For Mn and Pb, XRF was found suitable to verify the sequential extraction only for concentrations above 250 mg kg⁻¹. This was a consequence of a poorer reproducibility of Pb extraction using the Tessier scheme due to a great difference in the mineralogical composition and the diversity of the Pb species identified in soil. The poorer result of Mn was attributed to the spectral interference of Fe in XRF. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Thermal behavior of selected Czech marble samples

The definition as well as prediction of rock thermal behavior seems to be a quite difficult problem significantly effected by rock composition and structure. Temperature increase causes various changes of rock material (such as decomposition, oxidation, phase and polymorphic transformation, etc.). These changes are connected to thermal expansion with following appearance of tensions and cracks in minerals and rock structure. After consequential temperature decrease, developed tensions and cracks still influence the process. This study presents the application of thermogravimetric analysis, differential thermal analysis and thermomechanical analysis in characterization of selected marble thermal behavior. The texture and morphological orientation of calcite grains for marble samples was determined by optical microscopy. FTIR spectroscopy application along with X-ray diffraction (XRD) extended data about mineralogical composition. According to optical microscopy, the calcite grains show marked morphological anisotropy in one direction for some samples. Therefore, the thermal expansion had to be measured in three different (perpendicular to each other) directions. It is evident, that the effect of temperature on the final marble properties depends not only on mineralogical composition, but also on structure, texture and morphological orientation of grains. All these facts significantly influence the interpretation of differences in various marble thermal behavior.     

Mineralogical analysis with the firing temperature of limestone and clay mixture from Dominican Republic using Mössbauer spectroscopy and X-ray powder diffractometry

The study of a limestone and clay mixture using Mössbauer spectroscopy, and X-ray powder spectrometry (XRD) for different firing temperatures are presented. This type of mixture is used in raw minerals in order to obtain industrial clinker. This study permits to know the changes of the iron present during the clinkerization process, its mineralogical transformation with the temperature, and the minimal temperature necessary to obtain a good quality clinker.     

Synthesis and characterisation of cobalt hydroxy carbonate Co2CO3(OH)2 nanomaterials

In an attempt to make nanofibres based upon cobalt oxides, a novel compound hydrated cobalt hydroxy carbonate was formed. This compound is related to the minerals of the rosasite mineral group. X-ray diffraction (XRD) showed that the formed compound was a cobalt hydroxy carbonate, and scanning electron microscopy (SEM) displayed bundles of fibres on the micron scale in length and nanoscale in width. The morphology was compared with that of the rosasite mineral group. X-ray photoelectron spectroscopy (XPS) proved two bond energies for cobalt and three for oxygen in the compound. The compound was characterised by vibrational spectroscopy and the spectra related to minerals of the rosasite mineral group. The stability of the synthetic mineral was limited to temperatures below 200°C.