Surface characterization mineral processing

In mineral processing, surface characterization techniques are used primarily to study mechanisms of various subprocesses. These studies are carried out mostly in research laboratories using model systems so as to keep the system simple and amenable to interpretation by known laws of physics and chemistry. For these very reasons, some of the newer surface characterization techniques have been used to investigate pure solids, often single crystals. In mineral processing operations, one necessarily deals with particles of complex ores with an objective to recover the valuable minerals contained in the ore. Experience, both in industry and laboratory, shows that complex ore particles behave differently from simple solids in many ways. In process evaluation and in optimization of operating plants, it is necessary to characterize the ore particles as they undergo various treatments. In recent years ESCA has been found to be a useful technique for... 

Surface and interfacial phenomena of importance in mineral processing are reviewed. Examples of a fundamental and an applied nature are taken from the recent literature to illustrate how the use of several different surface characterization techniques makes it possible to delineate a detailed molecular-scale picture of interfaces. Lack of... 

In mineral processing, there are numerous systems in which postulates have been made to suggest adsorption of surface active molecules on specific surface sites. Most of the postulates are based on inference from a variety of observations and direct evidence has been lacking. It should now be possible to use Raman spectroscopy to characterize solid/aqueous solution interfaces. 

Understanding of the structure of the adsorbed surfactant and polymer layers at a molecular level is helpful for improving various interfacial processes by manipulating the adsorbed layers for optimum configurational characteristics. Until recently, methods of surface characterization were limited to the measurement of macroscopic properties like adsorption density, zeta-potential and wettability. Such studies, while being helpful to provide an insight into the mechanisms, could not yield any direct information on the nanoscopic characteristics of the adsorbed species. Recently, a number of spectroscopic techniques such as fluorescence, electron spin resonance, infrared and Raman have been successfully applied to probe the microstructure of the adsorbed layers of surfactants and polymers at mineral-solution interfaces. 

These equations provide an opportunity to view all complex compoimds on the surface as interconnected and express their concentration on the surface through base components in solutions composition. This assumption makes it possible to study surface complexation together with homogeneous processes but also taking in consideration the electrostatic effect of the mineral s surface. In a closed system the complexation process runs with the preservation of mass and molar constancy of the base components in the solution as a whole. For this reason in equation (2.229) should be added a summand characterizing the molarity of component i in the composition of surface complexes ... 

Electron spectroscopy in its several modes has proved to be particularly powerful for determining the nature of species present on solid surfaces. These methods have been applied extensively to the characterization of SAMs, and they are finding an increasing application to mineral processing systems. Of the various available techniques. X-ray photoelectron spectroscopy (XPS) is particularly appropriate for the study of mineral surfaces because a knowledge of the chemical environment of atoms, in addition to elemental composition, is usually required. Such information is important in identifying surface thiol species on sulfide minerals be-... 

As was mentioned in the introduction to this chapter "diffusion-controlled dissolution" may occur because a thin layer either in the liquid film surrounding the mineral or on the surface of the solid phase (that is depleted in certain cations) limits transport as a consequence of this, the dissolution reaction becomes incongruent (i.e., the constituents released are characterized by stoichiometric relations different from those of the mineral. The objective of this section is to illustrate briefly, that even if the dissolution reaction of a mineral is initially incongruent, it is often a surface reaction which will eventually control the overall dissolution rate of this mineral. This has been shown by Chou and Wollast (1984). On the basis of these arguments we may conclude that in natural environments, the steady-state surface-controlled dissolution step is the main process controlling the weathering of most oxides and silicates. 

Zeitner, W. A., E. C. Yost, M. L. Machesky, M. I. Tejedor-Tejedor, and M. A. Anderson (1986), "Characterization of Anion Binding on Goethite Using Titration Calorimetry and Cylindrical Internal Reflec-tion-Fourier Transform Infrared Spectroscopy", in J. A. Davis and K. F. Hayes, Eds., Geochemical Processes at Mineral Surfaces, Am. Chem. Soc., Washington, 142-161. 

Sorption processes are influenced not just by the natures of the absorbate ion(s) and the mineral surface, but also by the solution pH and the concentrations of the various components in the solution. Even apparently simple absorption reactions may involve a series of chemical equilibria, especially in natural systems. Thus in only a comparatively small number of cases has an understanding been achieved of either the precise chemical form(s) of the adsorbed species or of the exact nature of the adsorption sites. The difficulties of such characterization arise from (i) the number of sites for adsorption on the mineral surface that are present because of the isomorphous substitutions and structural defects that commonly occur in aluminosilicate minerals, and (ii) the difference in the chemistry of solutions in contact with a solid surface as compound to bulk solution. Much of our present understanding is derived from experiments using spectroscopic techniques which are able to produce information at the molecular level. Although individual methods may often be applicable to only special situations, significant advances in our knowledge have been made... 

Sherman, D.M. (1985) Electronic structures of Ee " coordination sites in iron oxides application to spectra, bonding and magnetism. Phys. Chem. Min. 12 161-175 Sherman, D.M. (1987). Molecular orbital (SCF-Xa-SW) theory of metal-metal charge transfer processes in minerals I. Application to the Fe vpe charge transfer and electron delocalization in mixed-valenced iron oxides and si-licates.Phys Chem Min 70 1262-1269 Sherman, D.M. (1990) Crystal chemistry, electronic structure and spectra of Fe sites in clay minerals. Applications to photochemistry and electron transport. In Coyne, L.M. McKeever, S.W.S. Blake, D.F. (eds.) Spectroscopic characterization of minerals and their surfaces. A.C.S. Symposium Series 415, 284-309... 

Zeltner,W.A. Yost, E.C. Machesky M.L. Teje-dor-Tejedor, M.I. Anderson, M.A. (1986) Characterization of anion adsorption on goethite using titration calorimetry and CIR-ETIR. In Davis, J.A. Hayes, K.E. (eds.) Geochemical processes at mineral surfaces. 

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