Structure barite

The possibility of Cr emission may be excluded because octahedral coordination is absent in barite structure. Luminescence of Fe is crystallographi-cally possible because tetrahedral surrounding presents in barite structure but Fe -S substitution is very difficult to suppose. The iron presence in ICP data is evidently connected with micro-impurities of iron minerals, which is usual for natural barite. Other ions, such as Ti and Ni with possible red luminescence, have ionic radii of 81 and 83 pm, respectively, which are small compared to the 156 ppm of Ba " ". ICP data confirm the absence of Ni in barite, while the minor quantities of Ti maybe connected to Ti" ". ... 

Figure 4.31 A clinographic view of the barite structure. The density for barite is about 4.5 g/cc.

A reproduction of a Laue photograph through (001) of barite has been published by Wyckoff. The Structure of Crystals, The Chemical Catalog Co., New York, 1924, p. 110. 

Other inorganic crystals studied by Mark and his collaborators, sometimes leading to complete structure determinations, include strontium chloride, zinc hydroxide, tin tetraiodide, potassium chlorate, potassium permanganage, and ammonium ferrocyanide. Minerals investigated by them include CaSO (anhydrite), BaSO (barite), PbSO, Fe2TiO[j (pseudobrookite), and three forms of Al2Si05 (cyanite, andalusite, and sillimanite). 

Free energy variations with temperature can also be used to estimate reaction enthalpies. However, few studies devoted to the temperature dependence of adsorption phenomena have been published. In one such study of potassium octyl hydroxamate adsorption on barite, calcite and bastnaesite, it was observed that adsorption increased markedly with temperature, which suggested the enthalpies were endothermic (26). The resulting large positive entropies were attributed to loosening of ordered water structure, both at the mineral surface and in the solvent surrounding octyl hydroxamate ions during the adsorption process, as well as hydrophobic chain association effects. 

Other resolubilized trace metals precipitate as replacement ions in existing solids such as fecal pellets and bone. Examples of these fiassilized materials include barite, phosphorite, and glauconite. These precipitates contain small amounts of a variety of trace metals as well as other elements. As a result, their chemical composition is variable and their structure is usually amorphous, making it difficult to assign them an empirical formifia. 

Fig. 3.27 data of structurally substituted sulfur in carbonate and in barite vs time (Prokoph et al. 2008)... 

Barite is a barium sulfate, BaS04, with orthorhombic structure 2jm2jm2jm) where the sulfur is situated in tetrahedral coordination with oxygen, and barium in twelve-fold coordination with oxygen. The mineral barite is one of the first luminescent materials from which the famous Bologna stone was obtained. Nevertheless, up to today understanding of natural barite luminescence... 

The structure of celestine is similar to that of barites, with Sr taking the place of Ba. 

The spectra of the green laser-induced luminescence represented in Fig. 4.4a, together with their decay time, also allows its association with These luminescence spectra strongly differ from the spectral parameters of all known uranyl minerals. For this reason it is not possible to connect this type of green luminescence with finely dissipated uranyl phases. On the other hand, this luminescence is very similar in such different host minerals as sedimentary apatites, opalites, chalcedony, chert, quartz and barites. Luminescence independence from the minerals structure evidences that it may be connected with uranyl adsorption on the minerals surface, supposedly in the form of (UO2 X nH20)2+. 

At 77 K the relative intensity of the band at 605 nm with an even longer decay time of 25 ms is much stronger. Such bands are usually connected with Mn +, but Mn " " in barite has different luminescence. Mn " in anhydrite CaS04 is characterized by a narrow band peaking at 505 nm. Thus such a band in barite may be connected with Ca impurity and anhydrite type local structure. 

Buick R., Dunlop J. S. R., and Groves D. I. (1981) Stromatolite recognition in ancient rocks an appraisal of irregularly laminated structures in an Early Archean chert-barite unit from North Pole, Western Australia. Alcheringa 5, 161-181. 

Where undiluted hydrothermal fluids mix with cold seawater at and near the seafloor, minerals precipitate out of solution to form chimney structures and other deposits. These deposits are mineralogically complex, containing sulphides (e.g. pyrite, marcasite, chalcopyrite, sphalerite, wurtzite, galena), sulphates (e.g. anhydrite, barite), silica and oxyhydroxides (e.g. Hannington etal., 1995 ... 

High-resolution in situ X-ray reflectivity studies of mineral/water interfaces have been published, to date, for calcite, barite, corundum, orthoclase, mica, and quartz. These studies have led to general insights on the extent of relaxation and reconstruction at mineral/water interfaces as well as the structure of interfacial water and other adsorbates (discussed in a subsequent portion of this chapter and in the chapter by Fenter in this volume). 

Fenter P, Geissbuhler P, DiMasi E, Srajer E, Sorensen LB, Sturchio NC (2000a) Surface speciation of calcite observed in situ by high-resolution X-ray reflectivity. Geochim Cosmochim Acta 64 1221-1228 Fenter P, McBride MT, Srajer G, Sturchio NC, Bosbach D (2001b) Structure of barite (001) - and (210) -water interfaces. JPhys ChemB 105 8112-8119... 

Fenter P, McBride MT, Srajer G, Sturchio NC, Bosbach D (2001) Structure of barite(OOl) and (210)-water interfaces. JPhys ChemB 105 8112-8119... 

Flotation has been used for more than 100 years to separate sulphides, oxides and other salts from ores, as well as to obtain phosphates, barite, chromite and other materials. Up to 90% of copper, lead, nickel, zinc are extracted using flotation in the USA [152 - 153]. In Russia, flotation is widely used to additionally obtain apatite, barite and phosphates. Flotation of iron oxides is not used in practise yet, but the number of experiments carried out in this direction is rather large. The main physicochemical principles of flotation have been discussed above [59 -74]. Here, only some practical problems will be discussed. In [153], requirements are pointed out which apply to three-phase flotation foams, and the main components of the process are defined, i.e. surfactant - collector surfactant - frother activator, depressants, colligend, gangue. The peculiarities of flotation and foam separation in batch and continuous modes are outlined as well as the structure and properties of the main types of flotation agents described. As surfaces of the majority of mineral particles are hydrophilic in nature, hydrophobisation of particles is necessary for a selective separation. 

We continue our investigation of the affect of the anion on structure with several sulfates— anhydrite (CaS04) and barite (BaS04). The tetrahedral sulfate ion is shown in Figure 71 (a) sitting on its base (a face) and oriented on an edge in Figure 71 (b). 

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