Sulphate phases

Two calcium sulphate phases coexist In the crystallizer, the hemlhydrate fed In and the gypsum being formed. Figure 4 shows the solubility of these two phases as a function of temperature for one particular acid liquor. The two solubility lines cross at the transition tenq[>erature (75 C in this case). Above this temperature, the hemlhydrate Is the stable phase (has the lower solubility) and below, gypsum. 

Mars 1.5 78.3 6,796 280 0.01 Mafic silicates in daik regions, pyroxenes detected locally, olivine suspected Fe3t phases in bright regions probably include nanophase hematite and sulphate phases these and clay silicates in global dust are oxidative weathering products HjO (frost) condensates ice at north pole dry ice (C02) at south pole. 

Very recent studies have examined the possibility of using 33S MAS spectroscopy in the study of some structural problems in cementitious materials107 108 and in sulphur speciation in silicate melts.109 Several processes of the deterioration of cements and more generally lapideous materials can be correlated to the stability of sulphate, to changes in the sulphate phase and to the interaction of sulphate ions with water molecules and hydrates.108 Since sulphate anion is one of the species that can be studied more easily by 33S NMR solid-state spectroscopy, this technique can be a valuable tool in studying... 

For most normal clinker compositions, the major sulphate phase will be aphthitalite with its maximum K/Na ratio of 3.0, with minor amounts of KS or C2KS3 or both only with unusually low values of K/Na in the clinker would one expect NS to be formed. It is only possible to estimate a maximum value for the content of anhydrite, based on the amount of SO3 that is not water soluble this will often be zero, as in the example given above. Anhydrite may, however, be determined by QXDA (Section 4.3.2). Rarely, the amount of water-soluble SO3 is insufficient to balance that of water-soluble alkalis this has been attributed to the presence of traces of alkali carbonates (P2), or of potassium oxide and potassium aluminate (KA) (F4). 

The analysis must be corrected for any of the four major components not present in the four major phases. This is routinely done for free lime, but CaO may also be present in sulphate phases, and, assuming modern analytical methods (e.g. XRF) to have been used, some of the Si02 and Al Oj will normally be present in an acid-insoluble residue. 

Free lime, 0.6% insoluble residue, 0.3% main analysis by XRF. 4.4.3 Estimation of sulphate phases... 

The procedure given below provides an estimate of the amounts of KjO, NajO, CaO and SO3 present in sulphate phases. It is based on the results of Pollitt and Brown (P2) (Section 3.5.6), and more specifically on the curves in... 

If the contents of water-soluble K2O and Na20 are known, it is necessary only to calculate AT, and TV, from them, and R, and then to carry out stages 2 and 4. From AT, TV, and C the quantities of individual sulphate phases may be estimated as described in Section 3.5.6. In the example given, the calculation indicates that the sulphate phases account for all the SO3, 0.07% of Na20, 0.28% of KjO and 0.04% of CaO. These probably occur as aphthitalite (0.6%) and calcium langbeinite (0.1%). 

Table 6.5 Crystal and optical data for hydrated sulphate phases... 

Unless otherwise stated, this chapter relates to ordinary Portland cements hydrated in pastes at 15-25°C and w/c ratios of 0.45-0.65. XRD powder studies on such pastes have been reported by many investigators (e.g. C38,M67). The rates of disappearance of the phases present in the unreacted cement are considered more fully in Section 7.2.1. Gypsum and other calcium sulphate phases are no longer detectable after, at most, 24 h, and tbe clinker phases are consumed at differing rates, alite and aluminate phase reacting more quickly than belite and ferrite. The ratio of belite to alite thus increases steadily, and after about 90 days at most, little or no alite or aluminate phase is normally detectable. 

To this purpose, isotopic data presented in this paper were obtained from several selected Gorleben groundwaters as part of the colloid characterisation programme. The contents of major and minor ions, light isotopes ( H, H, and and the U/Th isotopes were measured. Radiocarbon and were measured in dissolved inorganic carbon (DIG), ion the humic acid (HA-colloids) and fulvic acid (FA-solution) fractions of dissolved organic caibon (DOC). The and were also determined in dissolved sulphate phase. The U/Th isotope measurements were carried out on total and surface solid phases, colloid fraction (1-1000 nm particle size, HA) and solution (<1.5 nm, FA). 

The distribution of the flame volatile sodium between the ash silicate and sulphate phases is markedly influenced by the temperature and residence time of the ash particles in the flame. 

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