Mineral processing surface characterization techniques

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... 

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. 

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-... 

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... 

Finally, new methods of analysis have recently been developed that may allow characterization of single atoms on surfaces such as atomic force microscopy.9 In certain cases, in situ experiments can be done such as the study of electrodes, enzymes, minerals and biomolecules. It has even been shown that one atom from a tip can be selectively placed on a desired surface.10 Such processes may one day be used to prepare catalysts that may enhance selectivity. Other methods that show promise as regards detection of surface catalytic intermediates are temperature programmed desorption techniques.11 Selective poisoning of some surface intermediates with monitoring via temperature programming methods may also allow the preparation of more selective catalysts. 

In the 1960s, carbon blacks were mainly prepared by channel processes, and their acidic functions were present at about 10 eq/g, which allows relatively easy determinations but now, with furnace blacks, the surface acidic functions are generally of about 10 eq/g, and specific techniques (Bertrand and Weng, 1998) or drastic reaction conditions must be used (Custodero et al., 1992). Obviously, such delicate determination must be conducted on previously extracted black, in order to eliminate basic mineral impurities that would hinder any characterization of the rare acidic groups present on carbon black. 

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