Dolomite complexation

Greater adsorption of trace metals is found at higher pH and C02(g) concentrations. Sites available for Zn2+ sorption are less than 10% of the Ca2+ sites on the calcite surface, and Zn adsorption is independent of surface charge. This indicates a surface complex with a covalent character (Zachara et al., 1991). Furthermore, the surface complex remains hydrated and labile because Zn2+ is rapidly exchangeable with Ca2+, Zn2+ and ZnOH. At the dolomite-solution interface, the carbonate(C03)-metal (Ca/Mg) complex dominates surface speciation at pH > 8, but at pH 4-8, hydroxide (OH) -metal (Ca/Mg) dominates surface speciation (Pokrovsky et al., 1999). Calcite has an observed selectivity sequence Cd > Zn > Mn > Co > Ni > Ba = Sr, but their sorption reversibility is correlated with the hydration energies of the metal sorbates. Cadmium and Mn dehydrate soon after adsorption to calcite and form a precipitate, while Zn, Co and Ni form surface complexes, remaining hydrated until the ions are incorporated into the structure by recystallization (Zachara et al., 1991). 

Flow in the Pennsylvanian Fountain formation, a sandstone aquifer that underlies the Lyons and is separated from it by an aquitard complex, was more restricted because the formation grades into less permeable dolomites and evaporites in the deep basin. Groundwater in the Fountain recharged along the Front Range and... 

The geology of Cyprus is dominated by four distinct terranes - the Troodos Ophiolite Complex composed of mafic and ultramafic rocks, the Circum-Troodos Sedimentary Sequence containing calcarenites, siltstones and carbonates, the Mamonia Complex composed of igneous, sedimentary and metamorphic rocks and the Kyrenia Terrain containing a series of allochthonous massive and recrystallised limestones dolomites and marbles. These terranes generate highly varied landscapes (Fig 1). 

The beneficiation of mixed lead zinc sulphide oxide ores is a complex process and is dependent on gangue composition of the ore. There are two basic types of mixed sulphide oxide ores that have been extensively studied. These include (a) ores with dolomitic and... 

The Renison Bell tin mine is a large, but complex, oxide mineral deposit. Renison ore consists largely of pyrrhotite, quartz, dolomite, siderite and dorite. The chemical composition of the iron varies considerably. Some of the ore types are high in copper and silver. Table 21.5 shows the chemical analyses of various ore types. 

The Mountain Pass (USA) operation treats a relatively complex ore. The major REO mineral is bastaenesite with minor amounts of synchisite, parasite and monazite. The major gangue minerals are calcite, barite, silicates, and dolomite. The amount of the individual gangue minerals in this ore are variable and change on a yearly basis. There are two major ore types treated at the Mountain Pass concentrator (a) high calcite ore (35-45% CaO) and (b) a high barite-dolomite ore (so-called brown ore). Barite also contains significant quantities of strontium. 

Figure 7.18. Comparison of experimental and predicted phase equilibria in the system CaC03-MgC03 using CVM in the tetrahedron approximation for a trigonally distorted f.c.c. Ising lattice. Semi-quantitative agreement is achieved for the calcite-dolomite segment but the Mg-rich side of the diagram indicates the need to include a more complex model (Burton and Kikuchi 1984b).

Carter, M. L., Vance, E. R., Mitchell, D. R. G., Hanna, J. V., Zhang, Z. Loi, E. 2002. Fabrication, characterisation, and leach testing of hollandite, (Ba,Cs)(Al,Ti)2Ti6016. Journal of Materials Research, 17, 2578-2589. Chakhmouradian, A. R. Mitciiiill, R. H. 1998. Lueshite, pyrochlore and monazite-(Ce) from apatite-dolomite carbonatite, Lesnaya Varaka complex, Kola Peninsula, Russia. Mineralogical Magazine, 62, 769-782. 

Conclusively, the material is characterized by an N-linked aromate, which, together with additional aliphatic and aromatic structures, and probably under participation of sulfur and phosphorus, composes complex molecules. In the exterior sheath of the microspheres, dolomite is indicated by the lines at 1100, 725 and 300 cm-1. A weak line at 1445 cm-1 might belong either to dolomite or to a C—H deformation (Pflug et al., 1979)117) (Fig. 34). There is scarcely any doubt that the detected organic substances represent decomposed and fossilized remains of cell material. 

Suspended solid surfaces (particles or colloids) in waters play a prominent role in controlling the concentration of dissolved trace elements. Most of these elements are eliminated by sedimentation after incorporation on to or into particles, generally by complexation with the surface sites. The most common inorganic particles and colloids are non-clay silicates (quartz, potash feldspar, plagioclase, opaline silica (diatoms)) clays (illite, smectite) carbonates (calcite, dolomite) Fe-Mn oxides (goethite, magnetite) phosphates (apatite) sulfides (mackinawite). Particles and colloids in a water body may be classified as a function of their origin ... 

Microbial metabolic activity in general is known both to accelerate transitions to stable equilibria and to produce metastable intermediate dissolved species and mineral precipitates that otherwise would not exist or would not be abundant. In general, most metabolic schemes that intervene in the existence and abundance of one anionic species or complex will do so with others, too, and this also has a big effect on the evaporitic and freezing chemistry dealt with by FREZCHEM. For example, dolomite formation is linked to sulfate reduction in one biogeochemical scheme. Lacking microbial activity,... 

Dolomite Dolomite is one of the most abundant sedimentary carbonate minerals, yet after years of intense study its mode of formation remains controversial, and its properties under Earth surface conditions are less well known than for most other carbonate minerals. The primary reason for this seems to be that its formation is kinetically hindered by its complex and well-ordered structure. Another problem in understanding dolomite may be as Lynton Land says "there are dolomites and dolomites and dolomites". The topic of dolomite genesis will be dealt with in several later sections of this book. 

Land (e.g., 198S) has stressed the chemical and structural variations associated with natural dolomites, and has gone so far as to suggest that the name "dolomite" be used in the same way that the mineral name "feldspar" is used. The fact that dolomite is relatively unreactive compared to most other sedimentary carbonate minerals has severely limited experimental studies under temperature and pressure conditions that exist during shallow burial. Consequently, most information on the chemical behavior of dolomite must be obtained from observations of complex natural systems. Such observations are all too often open to multiple interpretations. 

The subsurface situation, however, with respect to dolomitization is more complex, as shown by the work of Land and Prezbindowski (1981). It appears that in the Cenozoic Gulf Coast basin of the United States, subsurface, Ca-rich saline formation waters may be undersaturated with respect to dolomite, and as the brine moves updip, and is progressively diluted by shallow subsurface waters, the brine may cause dedolomitization of carbonates encountered in the subsurface. 

Pressure solution can cause major alterations in carbonate rock structures on megascopic to microscopic scales. Numerous papers and reviews deal with this topic (e.g., Bathurst, 1975 Choquette and James, 1987). We feel that one of the best attempts to bring an orderly picture out of the many complex features that are observed was that by Wanless (1979), who also emphasized the importance of pressure solution for subsurface dolomitization (see next section). Figure 8.12 presents his general model for the characteristics and controls on pressure solution types in limestones. The primary variables that Wanless considered were the clay content of the limestone, the concentration of structurally resistant elements, and variations between different units or beds. Temperature, pressure and fluid composition are also likely to play an important role in determining the timing and extent of pressure solution. 

Voluminous research on the "dolomite problem" (Chapters 7 and 8) has shown that the reasons for the high magnesium content of carbonates are diverse and complex. Some dolomitic rocks are primary precipitates others were deposited as CaCC>3 and then converted entirely or partially to dolomite before deposition of a succeeding layer still others were dolomitized by migrating underground waters tens or hundreds of millions of years after deposition. However, the observation that the magnesium content of pelagic limestones that have not been uplifted, or... 

ABSTRACT As a step in the application of the cracking of tar in fuel gas amelioration the characteristics of the endothermic reaction potential of tar was studied experimentally and theoretically. In this context, however, due to the structural complexity of tar and/or tany constituents in fuel gas well defined hydrocarbons as tar model compounds were applied with inexpensive and readily available materials (dolomites, dolomitic magnesium oxide [MgO], quicklime [CaO]). The effects of operation condition on extent of hydrocarbon conversion, gas product composition, and corresponding endotherai of the reaction potential have been explored. The results obtained in this work provide a basis for ture considerations of catalytic tar cracking. 

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