Minerals aqueous surface chemistry

Parks, G. A. (1967), "Aqueous Surface Chemistry of Oxides and Complex Oxide Minerals Isoelectric Point and Zero Point of Charge," in Equilibrium Concepts in Natural Water Systems, Advances in Chemistry Series, No. 67, American Chemical Society, Washington, DC. 

Aqueous Surface Chemistry of Oxides and Complex Oxide Minerals... 

Parks, G.A. 1967. Aqueous surface chemistry of oxides and complex oxide minerals Isoelectric point and zero point of charge, p. 121-160. In R.F. Gould (ed.) Equilibrium concepts in natural water systems. Vol. 67. Advances in Chemistry Series, ACS, Washington, DC. 

D.T. Ray and R. Hogg, Bonding of Ceramics Using Polymers at Low Concentration Levels in Innovations in Materials Processing Using Aqueous, Colloid Surface Chemistry, F.M. Doyle, S. Raghavan, P. Somasundaran and G.W. Warren (eds.). The Minerals, Metals Materials Soeiety, Warrendale PA, 1989, pp. 165-180. 

This paper is devoted to the sorption of uranyl, which exhibits a complex aqueous and surface chemistry. We review briefly the sorption behaviour of An in the environment, and illustrate the variety of environmental processes using published data of uranyl sorption in the Ban-gombe natural reactor zone. After summarizing the general findings of the mechanisms of An sorption, we then focus particularly on the current knowledge of the mechanisms of uranyl sorption. A major area of research is the influence of the aqueous uranyl speciation on the uranyl surface species. Spectroscopic data of U(VI) sorbed onto silica and alumina minerals are examined and used to discuss the role of aqueous uranyl polynuclear species, U02(0H)2 colloids and uranyl-carbonate complexes. The influence of the mineral surface properties on the mechanisms of sorption is also discussed. 

SE Friberg, CC Yang. In FM Doyle, S Raghavan, P Soinasundaran, GW Warren, eds. Innovations in Materials Processing Using Aqueous, Colloid and Surface Chemistry. Warrendale, PA Minerals, Metals Materials Society, 1988, pp 181-191. 

We begin with a discussion of the most common minerals present in Earth s crust, soils, and troposphere, as well as some less common minerals that contain common environmental contaminants. Following this is (1) a discussion of the nature of environmentally important solid surfaces before and after reaction with aqueous solutions, including their charging behavior as a function of solution pH (2) the nature of the electrical double layer and how it is altered by changes in the type of solid present and the ionic strength and pH of the solution in contact with the solid and (3) dissolution, precipitation, and sorption processes relevant to environmental interfacial chemistry. We finish with a discussion of some of the factors affecting chemical reactivity at mineral/aqueous solution interfaces. 

Davis J. and Kent D. (1990) Surface complexation modeling in aqueous geochemistry. In Mineral-Water Interface Chemistry, Reviews in Mineralogy 23 (eds. M. Hochella and A. White). Mineralogical Society of America, Washington, DC, pp. 177-260. 

Friberg, S. E. Yang, C. C. In Innovations in Materials Processing Using Aqueous, Colloid and Surface Chemistry Doyle, F. M. Raghavan, S. Somasun-daran, P. Warren, G. W., Eds. Minerals, Metals, and Materials Society Warrendale, PA, 1988 p 181. 

Over the past several decades the equations and resultant codes have evolved greatly. Many of the codes that today serve as the foundations for geochemical calculations have increased in complexity both as a result of new theories in aqueous chemistry and the technical issues which needed to be resolved. The technical issues currently being addressed are often more complex in scope than originally imagined, and as a result the limits of application and the inadequacies are revealed. Researchers have evaluated the models under a wide variety of circumstances including the adequacy of the aqueous theory, usefulness for a broad range of applications, and the impact of solution-solid interactions such as is affected by mineral surface chemistry. 

Various methods in computational chemistry have been applied to study clay minerals since the early 1970s. The molecular modeling of clay mineral structure and surface chemistry that we will discuss here is mainly about computational chemistry applied to the clay mineral alone or in contact with a specific aqueous solution. 

In order to model clay mineral structure and understand its surface chemistry, it is important to understand some of the basic features of clay mineral structures. We are dealing with the simulation of a system where solid clay mineral structure is interfaced with an aqueous system. Therefore it is essential to understand the structure of the clay mineral itself and its hydrates before any computer modeling effort. 

Because the crystal structure of clay minerals plays a very large role in determining the way a clay will interact with aqueous solutions, a review of clay mineral surface chemistry must, by necessity, begin with a brief outline of the chemical origins of clay mineral structures. From this basis we will outline the role of edge-site chemical interactions and, subsequently, the controls on ion exchange. This overview of clay chemistry will conclude with a survey outlining how the various site interactions determine the macroscopic behavior of a number of elays in natural systems. 

Casey WH (1991) On the relative dissolution rates of some oxide and orthosilicate minerals. J Colloid Interface Sci 146 586-589 Casey WH, Westrich HR (1992) Control of dissolution rates of orthosilicate minerals by local metal-oxygen bonds. Nature 355 157-159 Casey WH, Carr MJ, Graham RA (1988a) Crystal defects and the dissolution kinetics of rutile. Geochim Cosmochim Acta, 52 1545-1556 Casey WH, Westrich HR, Arnold GW (1988b) The surface chemistry of labradorite feldspar reacted with aqueous solutions at pH = 2, 3 and 12. Geochim Cosmochim Acta 52 2795-2807... 

This interface is critically important in many applications, as well as in biological systems. For example, the movement of pollutants tln-ough the enviromnent involves a series of chemical reactions of aqueous groundwater solutions with mineral surfaces. Although the liquid-solid interface has been studied for many years, it is only recently that the tools have been developed for interrogating this interface at the atomic level. This interface is particularly complex, as the interactions of ions dissolved in solution with a surface are affected not only by the surface structure, but also by the solution chemistry and by the effects of the electrical double layer [31]. It has been found, for example, that some surface reconstructions present in UHV persist under solution, while others do not. 

Even though the vacuum-oriented surface techniques yield much useful information about the chemistry of a surface, their use is not totally without problems. Hydrated surfaces, for example, are susceptible to dehydration due to the vacuum and localized sample heating induced by x-ray and electron beams. Still, successful studies have been conducted on aquated inorganic salts (3), water on metals (3), and hydrated iron oxide minerals (4). Even aqueous solutions themselves have been studied by x-ray photoelectron spectroscopy (j>). The reader should also remember that even dry samples can sometimes undergo deterioration under the proper circumstances. In most cases, however, alterations in the sample surface can be detected by monitoring the spectra as a function of time of x-ray or electron beam exposure and by a careful, visual inspection of the sample. 

In the present paper the chemistry of plutonium is reviewed, with particular reference to the ambient conditions likely to be encountered in natural waters. In addition, experimental work is presented concerning the effects of such variables as pH, plutonium concentration, ionic strength, and the presence of complexing agents on the particle size distributions of aqueous plutonium. In subsequent papers it will be shown that these variables, as they influence the particle size distribution of the aqueous plutonium, greatly affect its interaction with mineral surfaces. The orientation of these studies is the understanding of the likely behavior and fate of plutonium in environmental waters, particularly as related to its interaction with suspended and bottom sediments. 

Zero point of charge (ZPC) The zero point of charge of a mineral or another solid substance is the pH of an aqueous solution in contact and equilibrium with the solid when the solid has a net surface charge of zero. The ZPC depends on the composition of the solid and the concentration and chemistry of the electrolytes in the aqueous solution. In situations where the net surface charge of the solid is only controlled by the adsorption of OH- or H+, the zero point of charge is the isoelectric point. 

The above processes involve separation based either on bulk properties (for example, size, density, shape, etc.) directly or by subtle control of the chemistry of the narrow interfacial region between the mineral particle and the aqueous solution in which it is suspended. In the processing of certain ores, such as those of uranium, gold or oxidized copper, chemical alteration of the minerals may be required to recover the valuable metals. These techniques are not discussed here, except to include those aspects which are directly related to surfaces and interfaces. 

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