Solid/liquid interface, mineral processing

Many theories have been advanced concerning the mechanisms involved in surfacing the mineral particles so as to create a hydrophobic hydrocarbon film on the mineral surface, and many investigations have been carried out to define these mechanisms. When firoth flotation is used in an aqueous medium that carries the solids to be separated (together with dispersed air bubbles and possibly an organic liquid) a three- or possibly a four-phase system must be considered. In most froth flotation processes, the solid particles are initially completely water-wetted, and the solid-liquid interface must be replaced by... 

Applications of redox reactions on mineral surfaces in areas such as water treatment have been reviewed by Segal and Sellers (1984) Voudrias and Reinhard (1986) discussed the organic transformations at the solid-liquid interface. Here the discussion is confined to selected inorganic redox reactions. Table 1 lists some of the more important heterogeneous processes of inorganic... 

In mineral-reagent systems, surface precipitation has been proposed as another mechanism for chemisorption. The solubility product for precipitation and the activities of the species at the solid-liquid interface determine the surface precipitation process. Under appropriate electrochemical conditions, the activity of certain species can be higher in the interfacial region than that in the bulk solution and such a redistribution can lead to many reactions. For example, the sharp increase in adsorption of the calcium species on silica around pH 11 has been shown to be due to surface precipitation (Somasundaran and Anan-thapadmanabhan, 1985 Xiao, 1990). Similar correlations have been obtained for cobalt-silica, alumina-dodecylsulfonate, calcite/apatite/dolomite-fatty acid, francolite-oleate and tenorite-salicylaldoxime systems. The chemical state of the surfactant in the solution can also affect adsorption (Somasundaran and Ananthapadmanabhan, 1985). 

Another example of the usefulness of microcalorimetry to study the solid-liquid interface has been reported by Draoui et al. [118]. They analyzed the adsorption of Paraquat on different minerals, which are part of the soil, to study the retention process of this pesticide by soils. In the particular case of silica they concluded that the main driving force for adsorption is electrostatic. They found a linear decrease of the adsorption enthalpy in the range of -25 to -20 kJ/mol. Nevertheless, the Paraquat molecule has two charges the heat evolved during adsorption is of the same order as in the case of other single-charged molecules. This fact is explained assuming that the... 

An understanding of the acid-base properties of solid surfaces is extremely important in almost all fields of science and engineering. For example, the solid/ gas interface intervenes when solid acids (or bases) are used as heterogeneous catalysts in the oil refining and chemical industries. The solid/liquid interface between rocks, minerals, and soils and natural waters is continuously transformed by weathering processes that result in the geohydrochemical circuit of elements. These are only two examples in which the primary reactivity factor is determined by the acid-base chemistry at solid interfaces, usually confined to molecule-sized spaces. 

Oxides, especially those of Al, Si, Fe, and Mg, are essential components of the earth s minerals their surface sites may have either Bronsted or Lewis acid-base properties. The weathering of rocks and the formation of soils are processes at the solid/liquid interface between minerals and natural waters or solutes from the medium in which solid phases are either formed, altered, or dissolved. Dissolution of solid minerals is controlled by slow surface reactions rather than... 

The surfaces of oxide colloidal particles or silicate minerals in contact with aqueous solutions are charged positively or negatively by adsorption or desorption of H+ ions. An electrical double layer at solid/liquid interface is formed by adsorbing counterions from the aqueous solution to its surface (Sen and Khilar, 2009). The charge developing process on the surfaces can be represented as follows (Cornell and Schwertmann, 1998) ... 

The adsorption of ionic surfactants on several different kinds of natural solid materials (e.g., ores, minerals, clays) is of great practical importance. Therefore, a vast and ever-expanding literature is published on this subject. Because of the complexity of interactions involved in the accumulation of ionic surfactant at solid/liquid interface from dilute aqueous solution, no single and unifying model of adsorption process for a range of solid-surfae-tant combinations has yet emerged [1, 2]. 

Solid/liquid separation is usually required at the interface of the primary and secondary stages to allow optional upgrading of the crude coal liquids of the primary liquefaction stage, by removing mineral matter, unreacted coal, heavy products, and catalysts (111, 112). Distillation, anti-solvent extraction, and centrifugation have been conventionally employed in liquefaction processes (113, 114). 

The structure electrical double layer at the silica-aqueous electrolyte interface was one of the earlier examined of the oxide systems. At the beginning the investigations were performed with application of electrokinetic methods next, with potentiometric titrations. The properties of this system were very important for flotation in mineral processing. Measurements proved that pHpZC and pHiep are equal to 3, but presence of some alkaline or acidic contaminants may change the position of these points on pH scale. Few examples, concerning edl parameters are shown in Table 3. Presented data concern a group of systems of different composition of the liquid phase and solid of a different origin. The latest measurements of this system takes into account the kinetics of the silica dissolution [152], and at zeta measurements, also the porosity of dispersed solid [155]. 

This paper reviews the work of the author and that of other users of flow microcalorimetry (FMC). which led to discoveries of new phenomena at solid-liquid and solid-gas interfaces [7, 8] including the behaviour of adsorbates at different surface coverages [9, 10], and many, previously unknown, interactions of surfaces of metals, metal oxides, graphites [11], active carbons, zeolites, clays, and other minerals with organic and inorganic adsorptives. The work led to development of new selective adsorption processes [12], prediction of the performance of liquid lubricants and its components [13], surface reactions [14, 15], dispersion technology [16] and determinations of specific areas of surface sites with different chemical properties [17, 18]. 

In the froth flotation process, air is bubbled through a water suspension containing the crushed minerals to form a foam or froth. The wetted particles (those that are hydrophilic) remain in the water suspension, whereas hydrophobic particles collect at the air bubble/water interface and can be removed from the liquid. Various agents, such as amino acids (having a high molecular weight), can be used to enhance the relative wettability of the solids in a... 

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