Anhydrite Analysis

A laboratory example of the above principle is given by the "strictly-congruent" dissolution experiment of Denis and Michard (14) on a 3.5% Sr-anhydrite. Analysis of their results shows that maximum SIceiestite SI... 

The activity product Q ave corresponding to the averaged analysis (ignoring variation in activity coefficients) equals the equilibrium constant K only when fluids A and B are identical otherwise Qmc exceeds K and anhydrite is reported to be supersaturated. To demonstrate this inequality, we can assume arbitrary values for aCa++ and so4 that satisfy Equations 6.4—6.5 and substitute them into Equation 6.6. 

XRD analysis has revealed the presence of several different types of carbonate minerals in liquefaction residues from a number of coals. Minerals identified included vaterite and calcite (two polymorphs of CaCO,) dolomite (CaMg[C03]2) and in the residue from a high sulfur coal (2.26 db), anhydrite (CaSO,) was identified. The types of mineral deposits formed depend not only on the coal but also on the reaction conditions. Our data indicates that whilst vaterite forms at low temperatures (380°C), as the temperature increases, the vaterite becomes progressively converted to calcite, the more stable form. After further increases in temperature, particularly at long reaction times, dolomite begins to form. 

G.C. Kennedy, suggesting that the quadruple point (gypsum—anhydrite— bassanite—H2O) is near 600 MPa (6 kbar) and 130°C, with the bassanite field widening in temperature at higher pressures. Zen (1965) estimated from thermochemical calculations and chemographic analysis that the quadruple point should be near 900 MPa (9 kbar) and 170°C. Solubility and phase-transformation experiments (Zen, 1965 Kinsman, 1974) indicate that bassanite is metastable at 0.101 MPa (1 atm.) and temperatures of 25—70°C. The conclusion of Goodman (1957) from petrographic examination that... 

The microscope is a great tool to have around a gypsum laboratory. The polarizing microscope in particular is perhaps the fastest and most accurate means for qualitative analysis of gypsum. It can also be put to work doing some quantitative analysis of anhydrite in gypsum. 

Determination of the optimal heat treatment temperature in the reactor is done by differential thermal analysis (DTA) and thermogravimetric analysis (TG) it appears (Fig. 2) that in our experimental procedure, for all the studied granulometries (<25 to 250 gm), a specimen fired at 398 K for 3 h contains no mote gypsum, and a specimen fired at 423 K still contains almost only hemihydrate. Above this temperature anhydrite III appears. The very small amount of anhydrite 111 contained in a specimen fired at 423 K is different from a gypsum variety, but quite stable and characteristic for a variety of gypsum (Fig. 6) fZ]. 

ABSTRACT A rapid and precise X-ray fluorescence method has been developed for the multielement analysis of gypsum and gypsum products. Gypsum specimens are calcined at IOOO°C and then fused with sodium tetraborate flux into flat and transparent disks. The choice of a suitable flux system for the specimen preparation is critical because of a rapid decomposition of anhydrite. CaSO,. in lithium ba fluxes at temperatures above 95O C. This decomposition causes not only visible imperfections in the didi surface but also alters considerably the concentrations of the major elements, calcium and sulfur. The procedure used for a fast setup of ten element analysis of gypsum on the Philips PW-1400 spectrometer utilizing synthetic standards and off-line calculated alpha coefficients is presented. Calibrations carried out with chemically analyzed specimens and their mixtures are compared lo those performed with synthetic standards prepared by blending pure chemicals and anhydrite into the flux. 

The second part of this paper is devoted to the procedure used for a quick setup of ten element analysis of gypsum and gypsum products on the Philips PW-1400 X-ray fluorescence spectrometer, utilizing alpha coefficients. Calibration data obtained with chemically analyzed specimens and their mixtures are compared with those based on synthetic standards prepared by blending pure chemicals with anhydrite. 

Because of the suspected decomposition of anhydrite, CaSO4, in lithium-based tetraborate flux systems at elevated temperatures, it was decided to study their behavior by means of thennal analysis (TGA, DTA). Thermal scans were performed on the Mettler TA-2 thermoanalyzer equipped with a DTA-20 macroholder. Platinum crucibles were filled with 200 mg of specimen flux mixtures and balanced by equal portions of alumina as the reference material. All specimens were heated at a rate of 10 C/min in an oxidation atmosphere (stream of air). 

After calcination, the stuccos were cooled to room temperature with constant stirring to remove all entrained water vapor. The residual gypsum content and soluble anhydrite content as determined by phase analysis 9] were always less than 4.0 and 2.0%, respectively. 

For anions, there was the best linear correlation between TDS and the concentration of S04 (R = 0.996) and the concentration of S04 had the fastest increase. The concentration of CL also increased, but it was a little slower, and in general the concentration of HCO, decreased (Fig. 5). The main minerals of Ordovician aquifer are cal-cite, dolomite, gypsum and pyrite. These indicate that more minerals containing Ca and SO42- dissolved. Considering the analysis of SI of gypsum and anhydrite, gypsum or anhydrite is the main sources of Ca + and SO/. Mg may derive from the dissolution of dolomite, and from the reduc-... 

FTIR characterization. The FTIR spectra (Fig. 6) of unmodified and modified cement pastes are compared after 4 days of hydration. Analysis of pristine PVA and nanoclay was also made. In the range between 3100-3700 cm the H2O and OH stretching bands appear [29]. They are also present in the spectrum of the anhydrite paste, because of the hygroscopicity of the cement. A small increase of the OH band, associated with the Ca(OH)2 molecules, is recorded at -3643 cm when compared to the anhydrite paste. The cement samples have a higher peak than the paste with PVA and PVA/clay. A cement paste hydrated for 28 days has a higher peak than the peak hydrated for only 4 days. 

This classification is not perfect, unlike the other classifications for example the calcareous fly ash is not distinguished regarding the differences of anhydrite content (SO3). As it results from the analysis presented in Table 7.3, the fly ash from Belchatow could be even used in the production of CEM n/B-V cement, after CaO transformation into the calcium hydroxide, while the fly ash from Konin only in a limited range, because of the SO3 content. The transition of CaO to Ca(OH)2 is necessary, because in the PN-EN 197-1 standard the reactive CaO content in fly ash is restricted to 10%. The aforementioned classification rates Polish fly ash from the hard coal combustion to the siliceous ash and that from the brown coal combustion in Turoszow coal-field— to the aluminous ones respectively. 

Analysis of subterranean karst forms revealed that their generation mainly timed to gypsum, anhydrite and limestone. Single cavities were fixed in the thickness of dolomite. 

Klaproth found that precipitated alumina is soluble in caustic potash(i789). He proved by analysis that anhydrite (then called muriacite) is calcium sulphate free from water and that calcite and aragonite are two different crystalline forms of calcium carbonate and confirmed that bitter spar (dolomite) is a compound of calcium and magnesium carbonates. 

The analysis of the primary minerals remains constituting the impurities in the secondary crystals enables determination of the diagenetic processes taking place in the evaporite deposits (including the mineral precursor for the secondary crystal), and the direction and cause of diagenetic transformations (e.g. anhydrite gypsification piitnaiy mineral -anhydrite, cause - presence of fresh or low-mineralized water in the deposit, e.g. as a result of tectonic uplift and exposition to the activity of shallow underground water). 

The decomposition of the ore sample by leaching and the liberation of rare earth elements to the leach liquor depends mainly on leaching temperatures as well as sulfuric acid concentration. Performing the leaching experiments at room temperature dissolve only 50% of the rare earth contents at 5M and 15M acid concentrations. The XRD analysis of the residue showed that relatively equal amounts of anhydrite and yttrium-fluorite were identified at 5M H2SO4. Increasing the acid concentration to 15M enhanced the formation of anhydrite to be double that of the yttrium fluorite in the sepai ated residue. This indicates that the reaction was not sufficient for complete decomposition of the ore sample. 

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