Major oxide minerals

A very large number of theoretical studies have been performed on MgO and AI2O3. Only some of the early studies and some of the most recent will be described here, in order to give some idea of the extent of progress over the past two decades. Important advances have recently been made in the application of ionic models to such materials as well as in band-theory studies and embedded-cluster studies. After reviewing the early work, contemporary studies of structure, stability, phase relations, and dynamic properties will be described, followed by recent studies of spectral properties and characteristics of the electron-density distribution for each of these materials. Attention is then turned to Si02, the silica polymorphs, and various compounds and clusters that may be used to model tetrahedrally coordinated Si in silica and the silicates. 

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Volume 2 of the Flotation Reagents Handbook is a continuation of Volume 1, and presents fundamental and practical knowledge on flotation of gold, platinum group minerals and the major oxide minerals, as well as rare earths. 

Attention will then be turned to the major oxide minerals MgO, AljOj, and SiOj and the binary transition-metal oxides of Ti, Mn, and Fe, with some brief discussion of the series of transition-metal monoxides (MnO, FeO, CoO, NiO) and complex oxides (FeCr204, FeTiOj, etc.), and of the problem of the calculation of Mossbauer parameters in iron oxides (and other compounds). 

Flotation is certainly the major separation method based on the surface chemistry of mineral particles. It is, however, not the only method. Selective flocculation and agglomeration may be mentioned as other methods used commercially to a limited extent. The former is for hematite, while the latter is for coal and finely divided metallic oxide minerals. Both processes use the same principles as described for flotation to obtain selectivity. In selective flocculation, polymeric flocculants are used. The flocculants selectively adsorb on the hematite, and the hematite floes form and settle readily. Thereby separation from the sili-... 

Literature on flotation of gold, PGMs, rare earths and various oxides is rather limited, compared to literature on treatment of sulphide-bearing ores. As mentioned earlier, the main problem arises from the presence of gangue minerals in the ore, which have flotation properties similar to those of valuable minerals. These minerals have a greater floatability than that of pyrochlore or columbite. In the beneficiation of oxide minerals, finding a selectivity solution is a major task. 

This volume of the Handbook is devoted to the beneficiation of gold, platinum group minerals and, most important, oxide minerals. The book contains details on flotation properties of the major minerals. The fundamental research carried out by a number of research organizations over the past several decades is also contained in this book. Commercial plant practices for most oxide minerals are also presented. 

Mixed copper sulphide oxide ores. These contain varieties of both sulphide and oxide minerals, and are the most complex copper-bearing ores from a beneficiation point of view. The major copper minerals present in this ore type include bomite, chalcocite, covellite, malachite, cuprite and chrysocolla. In some cases, significant amounts of cobalt minerals are also present in this ore. 

The mixed willemite-smithsonite ore has the simplest mineral composition of the three basic ore types. The silicate, goethite and barite are the principal gangue minerals. Will-emite is a major zinc oxide mineral present as free crystals ranging from 50 to 500 pm in size. Smithsonite is usually stained with Fe-hydroxides and sometimes is associated with silicate as inclusion and/or attachments. The barite content of the ore may vary from several percent up to 12%. A few deposits of this ore type are found in Mexico and South America. 

Flotation of the lead oxide minerals is a difficult problem not least because there are no known direct acting collectors. Normally, during oxide lead flotation, a sulphidization method is used with xanthate as a collector. In the majority of cases, the ore is pretreated using a desliming process, especially if the ore contains clay and Fe-hydroxides. Another method includes the preconcentration using heavy liquid. 

There are only few operations treating mixed lead zinc sulphide oxide ores that contain barite-calcite gangue minerals. A typical example of such an operation is the Tynagh oxide complex in Ireland [11]. In this deposit, the oxide ores are generally located at the bottom and at the ends of the sulphide mud ores. The major gangue mineral is barite (large quantities) and minor amounts of clay. This ore assays 8.5% Pb(total), 6% Pb(oxide), 6.8% Zn(total) and 5% ZnO. 

Tab. 4.1 Morphological characteristics of major iron oxide minerals...

Ore samples identified as oxides are highly oxidized or gossan ores in which the major lead mineral is also galena. 

Elemental iron, the major element in Earth s core, is the fourth most abundant element in Earth s crust (about 5.0% by mass overall, 0.5%-5% in soils, and approximately 2.5 parts per billion in seawater.) In the crust, iron is found mainly as the oxide minerals hematite, Fe203, and magnetite, Fe304. Other common mineral forms are siderite, FeC03, and various forms of FeO(OH). Iron is an essential element in almost all living organisms. In the human body, its concentration ranges between 3 and 380 parts per million (ppm) in bone, 380-450 ppm in blood, and 20-1,400 ppm in tissue. 

A review of the literature shows that there is a vast amount of crystal field spectral data for iron, the major transition metal in silicate and oxide minerals. The focus of this chapter, therefore, is mainly on ferromagnesian silicates. However, there is also a significant amount of information for chromium-, vanadium- and manganese-bearing minerals. The data are more sporadic for other cations. The optical spectra of the transition metal-bearing minerals enable semi-quantitative estimates to be made of the relative CFSE s of Fe2+, Cr3+, Mn3+, V3+, Ti3+, Ni2+ and Co2+ in many mineral structures. Note, however, that Mn2+ and Fe3+ in high-spin states acquire zero CFSE in oxides and silicates. The crystal field spectra of Mn(II) and Fe(III) minerals are described separately later in the chapter ( 5.10.6 and 5.10.7). 

Most of the Mn(IV) oxide minerals listed in table 8.3 occur in weathered continental rocks, and often constitute important manganese ore deposits. However, several of the minerals, notably todorokite, bimessite, vemadite and, perhaps, buserite and asbolane, are major constituents of seafloor hydrothermal crusts near spreading centres and in manganese nodule deposits. 

Vaughan, D. J. Tossell, J. A. (1978) Major transition metal oxide minerals Their electronic structures and interpretations of mineralogical properties. Canad. Mineral., 16, 159-68. 

Rare earth and yttrium contents of major source minerals [5] (percent of total rare earth oxide). 

It can still be seen in mineralogical museums how Berzelius classified many compounds as adducts of oxides, as when alum is written K20 A1203 4 S03 24 H20 whereas it was later written KA1(S04)2 12 H20 and the crystal structure indicates only half of the water molecule oxygen atoms directly connected to aluminum K[A1(0H2)6](S04)2(0H2)6. Actually, the large majority of minerals are mixed oxides (and though these formulae derive from the precursor ideas of electrovalent bonding, considering calcium sulfate as an adduct CaO S03, they have the undoubted... 

Uranous ion (U ) and its aqueous complexes predominate in groundwaters of low Eh. U(IV) is the major oxidation state in the most common uranium ore minerals uraninite [U02(c)]—pitchblende is roughly U02(am)—and coffinite (USi04). The U(IV) concentrations in groundwater at low... 

While coal ash is a complex mixture of mineral components the crystallization behaviour of homogeneous ash melts has been shown to be governed by the major oxide components. The equilibrium system CaO-FeO-Al2O2-SiO2 has been shown to be able to model the initial crystallization behaviour of ash melts. Furthermore the system also appears to govern the crystallization of boiler deposits to a significant extent. The applicability of the use of phase equilibria data to the phenomena of boiler deposits has been indicated. 

Various chemical surface complexation models have been developed to describe potentiometric titration and metal adsorption data at the oxide—mineral solution interface. Surface complexation models provide molecular descriptions of metal adsorption using an equilibrium approach that defines surface species, chemical reactions, mass balances, and charge balances. Thermodynamic properties such as solid-phase activity coefficients and equilibrium constants are calculated mathematically. The major advancement of the chemical surface complexation models is consideration of charge on both the adsorbate metal ion and the adsorbent surface. In addition, these models can provide insight into the stoichiometry and reactivity of adsorbed species. Application of these models to reference oxide minerals has been extensive, but their use in describing ion adsorption by clay minerals, organic materials, and soils has been more limited. 

Aluminum forms many mixed oxides of which the aluminosilicates are major constituents of minerals (see Topic J2) In these compounds aluminum sometimes replaces a portion of the silicon present as corner-sharing Si04 groups (see, e g. zeolites, Topic D5). The mixed oxide mineral spinel... 

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