Calcite, analysis mixture

Figure 5.12 shows the DTA trace of the base glass composition of the most coarse particle size (125-250 /j,m) as well as the DTA traces of several binary pairs, a soda ash-calcite-silica mixture, and soda ash alone, all of particle size 90-125 /jm. The soda ash, binary, and ternary mixtures were used in order to determine (by comparison) the constituents in the base glass batch which were the significant contributors to various endothermic features along the DTA trace. The carrots along the trace correspond to the points of quench for x-ray diffraction analysis. 

With time, however, the company encountered problems, including caving of the formation into the wellbore and the loss of permeability in zones that had accepted fluid. In June 1987, a number of sidewall cores were taken from the formation (Mehnert et al., 1990). Mineralogic analysis by x-ray diffraction showed that significant amounts of calcite (CaCCb) and brucite [Mg(OH)2], as well as some amorphous matter, had formed from the original dolomite. In some samples, the dolomite was completely consumed and the rock was found to be composed entirely of a mixture of brucite and calcite. 

Once the pure mineral powders characterized, 3 mixtures were manually prepared and named ML1, ML2 and ML3. They contain each of the 8 minerals in different proportions reproducing 3 mine tailings falling in the uncertainty zone of the static test used. The 3 synthetic tailings were characterized with the same techniques as for the pure minerals. Cp and Sp weight fractions were evaluated from their chemical element tracers (respectively Cu and Zn) obtained from ICP-AES analysis. Qz, Dol, and Sid samples are considered pure and their percentages in the mixtures are not corrected. Table 1 presents the fraction of each mineral in the three mixtures before and after correction taking into consideration the contamination of Po sample by pyrite and calcite, as previously determined. The corrected mineral proportions are used for calculation of the static test parameters based on... 

This method of analysis is particularly valuable when chemical methods are inadequate or inapplicable. For instance, for complex mixtures where the different elements or ions may be associated in many different ways, all compatible with the analytical figures or for mixtures of polymorphous forms of the same substance, such as the three crystalline forms of CaC03 (calcite, aragonite, and vaterite) or the three crystalline forms of FeO(OH) (goethite, lepidocrocite, and P FeO(OH)—see Bunn, 1941)—mixtures for which chemical analytical methods are irrelevant. 

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. 

Stable carbon and oxygen isotopes of the different diagenetic carbonates were determined in 22 sandstone samples, which were selected after careful optical and cathodoluminescence examination. Samples in which contamination caused by allo-chems or mixtures of different textural types of calcite (both easily recognized by optical petrography and cathodoluminescence) were not considered for isotopic analysis. The Kiel system for calcite sample preparation was used, and calcite was reacted with anhydrous phosphoric acid at 25°C under vacuum for 2 h, the produced COj was... 

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