Mineral phase identification

In addition, the TRW samples were analyzed by the SEM-AIA technique described previously (13). The SEM-AIA data on the mineral phase identification and distribution between the size fractions are presented in Table VI for all three samples of raw and treated coal. The SEM-AIA data show the nearly complete removal of many minerals and a reduction of more than 90X in the overall content of the coal as a result of treatment by the TRW Gravimelt Process. No major changes in particle size distribution were observed, although the pyrite distribution shifted somewhat towards the coarse fraction after processing. 

Table 6.1 Mineral phase identification by JCPDS data files and quantification by Rietveld refinement method...

Applications The general applications of XRD comprise routine phase identification, quantitative analysis, compositional studies of crystalline solid compounds, texture and residual stress analysis, high-and low-temperature studies, low-angle analysis, films, etc. Single-crystal X-ray diffraction has been used for detailed structural analysis of many pure polymer additives (antioxidants, flame retardants, plasticisers, fillers, pigments and dyes, etc.) and for conformational analysis. A variety of analytical techniques are used to identify and classify different crystal polymorphs, notably XRD, microscopy, DSC, FTIR and NIRS. A comprehensive review of the analytical techniques employed for the analysis of polymorphs has been compiled [324]. The Rietveld method has been used to model a mineral-filled PPS compound [325]. 

The SEM-AIA results contain very detailed information for the composite coal/mineral particles and their component parts (i.e., information on size, phase identification, and associations) which can be presented in a number of ways. Tables can be prepared to show the distribution of the sample as a function of particle size and to show the coal-mineral association in terms of bulk properties or in terms of surface properties. For bulk properties, the distribution of coal and minerals is prepared as a function of the total mineral content of the individual particles which can be related to particle density. For surface properties, coal and mineral data are tabulated as a function of the fraction of particle surface covered by mineral matter which can be used to predict the surface properties of the particles and their behavior during surface-based cleaning. Examples of these distributions are given below. 

Techniques of transmission electron microscopy have proved valuable in many areas of solid state science. Use of electron diffraction permits identification of crystal types, determination of unit cell sizes and characterization of crystal defects in the phases. Measurement of Energy Dispersive X-ray (EDS) line intensity allows calculation of the elemental composition of the phases. It is difficult to overestimate the value of such applications to metallic alloys, ceramic materials and electron-device alloys (T-4V Applications to coal and other fuels are far fewer, but the studies also show promise, both in characterization of mineral phases and in determination of organic constituents (5-9. This paper reports measurements on a particular feature of coal, the spatial variation of the organic sulfur concentration. 

Minerals, electrochemistry of — Many minerals, esp. the ore minerals (e.g., metal sulfides, oxides, selenides, arsenides) are either metallic conductors or semiconductors. Because of this they are prone to undergo electrochemical reactions at solid solution interfaces, and many industrially important processes, e.g., mineral leaching and flotation involve electrochemical steps [i-ii]. Electrochemical techniques can be also used in quantitative mineral analysis and phase identification [iii]. Generally, the surface of minerals (and also of glasses) when in contact with solutions can be charged due to ion-transfer processes. Thus mineral surfaces also have a specific point of zero charge depending on their sur-... 

Single crystal structure X-ray diffraction analyses and structural classification of synthetic and natural mineral phases have revealed interesting actinide coordination chemistry. " This approach has led to the identification of in CaU(U02)2(C03)04(0H)(H20)7, the mineral wyartite. The structure contains three unique U positions. Two of these are uranyl ions with the typical pentagonal-bipyramidal coordination. The third is also seven-coordinate, but does not contain -yL oxygens and polyhedral geometry and electroneutrality requirements indicate that this site contains U. ... 

X-ray phase analysis is used for identification of mineral phases of rocks, soils, clays, or mineral industrial material. The phase analysis of clays is particularly difficult because these materials generally consist of a mixture of different phases, like mixed and individual clay minerals, and associated minerals, such as calcite and quartz. Placon and Drits proposed an expert system for the identification of clays based on x-ray diffraction (XRD) data [45]. This expert system is capable of identifying associated minerals, individual clay minerals, and mixed-layer minerals. It can further approximate structural characterization of the mixed-layer minerals and can perform a structural determination of the mixed-layer minerals by comparison of experimental x-ray diffraction patterns with calculated patterns for different models. The phase analysis is based on the comparison of XRD patterns recorded for three states of the sample dried at room temperature, dried at 350°C, and solvated with ethylene glycol. 

X-Ray Phase Analysis an analytical technique for identification of mineral phases in rocks, soils, clays, or mineral industrial material based on XRD. 

An algorithm for an automatic identification of each mineral phases has been developed to process images of sections in hydrothermalized granite in order to quantify the granulometry of each phase (Riss et al., 2001). Percentages for each mineral phase are presented in the Table 1. For the quartz vein, having no specific information, it has been considered as completely monomineral with a heterogeneous radii distribution. 

Figure 1. Quantitative analysis of the hydrothermalized granite, a original sample b sample reconstructed after automatic identification of each mineral phases c sample reconstructed for PFC model from statistical analysis of original samples...

XRD may be applied to a wide variety of ceramic problems such as simple phase identifications, crystallite size measurements, and determination of crystal lattice parameters. The mineral assemblages produced during firing or in different service environments can be readily studied. Techniques are now available for micro XRD, in which an intense X-ray beam is collimated or focused onto a specific feature in the sample in order to characterize the crystal structure. 

In this chapter, the aim is to identify and quantify the iron mineral phases present in South African coal fractions by the use of Mossbauer spectroscopy, in conjunction with various other analytical techniques. Because the atomic weight of the carbon content in coal is low, Mossbauer spectroscopy is a convenient, and to a certain degree unique, analytical tool in the identification of iron-bearing minerals in coal with iron contents as low as 1%. With an understanding of the iron mineral phases present in the as-mined coal, the fete of these minerals during transportation, weathering, oxidation, and combustion or gasification can be better understood. 

The spectral-kinetic parameters of the green laser-induced luminescence of the sedimentary apatites allow its association with 1102 " emission. The spectra presented in Fig. 4.5b, c are typical for uranyl minerals and it is possible to suppose that we are dealing with separate uranyl mineral phase on the apatite surface. Comparison with known uranyl minerals laser-induced luminescence shows that the most similar spectral-kinetic parameters have minerals andersonite Na2Ca (U02)(C03)3 X 6H2O and liebigite Na2(U02)(C03)3.10H20, but this identification is ambiguous. 

Thus, the identification of the chemical form of P-bearing mineral phases is much easier than with a single-beam spectrometer. 

In addition to the identification of the important sorbing mineral phases, defocused ion-beam techniques can be used to provide depth profiles for strongly sorbing radionuclides that have short penetration depths. These profiles can be used to derive diffusion data and sorption coefficients, subject to assumptions regarding access to porespace within the sample. 

Published experimental studies of mineral/cal-cium hydroxide reactions show that at low temperatures (below 110°C), the chief reaction products are calcium silicate hydrate (CSH) gels, while zeolites and feldspars are formed at higher temperatures and in the presence of alkalis NaOH and KOH. The phase identifications have however often been made by low resolution or bulk methods, neither of which are ideal for such material. Published results of numerical simulations are in broad agreement with those of experimental studies of cement/ rock interaction. These models predict that CSH gels will be replaced by zeolites and maybe feldspars as plume chemistry evolves. 

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