Interfacial reactions minerals

Solid-liquid PTC conditions in which the nucleophilic salts (organic or mineral) are transferred from the solid state (as they are insoluble) to the organic phase by means of a phase-transfer agent. Most often the organic nucleophilic species can be formed by reaction of their conjugated acids with solid bases (sodium or potassium hydroxides, or potassium carbonate) (Scheme 5.1 path b). Another proposed mechanism suggests that interfacial reactions occur as a result of absorption of the liquid phase on the surface of the solid. 

Scherer, H.W. Zhang, Y. (1999) Studies on the mechanisms of fixation and release of ammonium in paddy soils after flooding. 1. Effect of iron oxides on ammonium fixation. J. Plant Nutr. Soil Sci. 162 593-597 Scherer, M.M. Balko, B.B. Tratnyek, P.G. (1998) The role of oxides in reduction reactions at the metal-water interface In Sparks, D.L. Gmndl.T.J. (eds.) Mineral-Water Interfacial Reactions, Kinetics and Mechanisms ACS Smposium Series 715, Am. Chem. Soc., 301-322... 

Scherer MM, Balko BA, Tratnyek PG. The role of oxides in reduction reactions at the metal-water interface. In Sparks DL, Grundl TJ, eds. Mineral-Water Interfacial Reactions Kinetics and Mechanisms. Washington, DC American Chemical Society, 1998 ACS Symp. Ser. 715 301-322. 

Under geological conditions the substances dissolved in aqueous solutions are sorbed on the surface of the mineral and humic substances. The sorption processes are influenced by the composition of the solution, the stable chemical species. At pH = 6-8, characteristic of the geological environment, some cations have hydrolytic tendencies, and hydroxides and oxides can precipitate. When studying the interfacial reaction of rocks and soils, hydrolysis has to be avoided. 

Before discussing the interfacial reactions of montmorillonite, we have to define what we call montmorillonite in practice. As known, most minerals are not found in pure forms they are present in rocks together with other minerals. Montmorillonite is the main component of bentonite rocks, so bentonites with high montmorillonite content are frequently called montmorillonite. For scientific studies, we use bentonite with high montmorillonite content in natural form after purification with sedimentation. Usually, the fraction <2 pm is the clay fraction containing montmorillonite. 

Sparks, D.L. et al., Kinetics and mechanisms of metal sorption at the mineral-water interface, in Mineral-Water Interfacial Reactions Kinetics and Mechanisms, in Sparks, D.L. and Grundl, T.J., Eds., American Chemical Society, Washington, D.C., 1998, p. 108. 

Tebo B. M. and He L. M. (1999) MicrobiaUy mediated oxidation precipitation reactions. In Mineral-Water Interfacial Reactions (eds. D. L. Sparks and T. J. Grundl). American Chemical Society, Washington, DC, pp. 393—414. 

Spectroscopic techniques (particularly infrared, x-ray photoelectron, and x-ray absorption spectroscopy) have been applied to fill the information gap about chemical speciation and interfacial reactions of As in model and natural materials. They have been used to determine the stmcture of x-ray amorphous particles involved in interfacial reactions, to identify the types of sorption reactions occurring in simplified model systems containing As and one or more phases, and to identify the valence and speciation of predominant As species present in natural, heterogeneous materials. This chapter summarizes much of the recent spectroscopic information on arsenic speciation in minerals and other solid phases that are analogous to phases present in aquifer sediments. These data are primarily derived from analysis of synthetic samples or natural model compounds. 

Suarez, D. L, Goldberg, S., and Su, C., 1999, Evaluation of oxyanion adsorption mechanisms on oxides using FTIR spectroscopy and electrophoretic mobility in Sparks, D. L., and Grundl, T. J., eds., Mineral-Water Interfacial Reactions, American Chemical Society, p. 137-178. 

Like RO membranes, many NF membranes are polyamide thin film composite membranes. These membranes can be prepared by interfacial reaction of piperazine with 1,3,5-benzenetricarbonyl trichloride and/or isophthaloyl dichloride, or by treating polyamide thin film composite RO membranes with compounds such as mineral acids, to increase their flux and lower their salt rejection. A few ceramic NF membranes have also been developed. New methods... 

The most important class of interfacial reactions affecting the environment involves aqueous solutions reacting with mineral surfaces in the earth s outer crust (Stumm et al. 

Fendorf SE, Jardine PM, Taylor DL, Brooks SC, Rochette EA (1998) Auto-inhibition of oxide mineral reductive capacity toward Co(II)EDTA. ACS Symp Ser 715 (Mineral-Water Interfacial Reactions), American Chemical Society, Washington, DC, p 358-371... 

Measurement of mineral-water interface structure during surface reactions provides direct insight into mineral reactivity and is a powerful approach for understanding complex interfacial reactions. It is currently not possible to provide a complete structural measurement with a temporal resolution of a few minutes. It is, however, possible to measure representative changes in real time in a way that provides important constraints on the dissolution process. Such measurements can also be coupled with high-resolution measurements of previously reacted surfaces to provide snapshots of the reacted surface. 

Sparks DL, Grundl TJ (1998) Mineral-water interfacial reactions Kinetics and mechanisms. Am Chem Soc, Washington DC... 

Recently, significant advances have been realized in the employment of kinetic methods and molecular-scale spectroscopic and microscopic techniques to study mineral-water interfacial reactions in-situ. In the past decade, researchers have coupled the detailed understanding of surface structure derived from molecular-scale studies with experimental and modeling studies of macroscopic surface behavior. This synergism has resulted in a dramatic increase in the ability to decipher and predict both the kinetics and mechanisms of mineral-water interfacial reactions. It is these important aspects that form the central theme of this book. 

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