Dissolution-Precipitation Kinetics

The quantitative role of 12 in dissolution-precipitation kinetics can be sharpened by a rate-law analysis of the reaction in Eq. 3.1. The rate of increase in the concentration of M""(aq) can be postulated to be equal to the difference... 

The selection of solvents for the treatment trains is based on the thermodynamics and dissolution/precipitation kinetics of polymer-solvent pairs as well as the toxicity, cost, and solvent recovery feasibility. By selecting solvents which are optimal for each polymer stream, cross-contamination is minimized and expenses reduced. In this way, polymer/solvent compatibility is achieved by solvent selection rather than elevated pressures and temperatures. 

Silica concentration in deep ground water in the granitic rock area (e.g., Kamaishi, Japan) is in equilibrium with SiOz mineral (chalcedony) (Fig. 1.27). Based on a coupled fluid flow-dissolution-precipitation kinetics model the relationship between residence time of deep ground water and A/M was derived, and the reasonable values of x is estimated to be more than 40 years (Shikazono and Fujimoto 2001). 

Much work is needed to elucidate the effects on metamorphic differentiation of rock plastic flow and fluid infiltration (see section on skarns below). Reaction rates and diffusion coefficiently are largely unknown for geological systems under metamorphic conditions (see Brady [46]). Experimental generation of mineral bands out of initially uniform aggregates of two or more kinds of crystals (even if these are not rock-forming minerals but substances with faster dissolution/precipitation kinetics) should be attempted. 

The physical chemist is very interested in kinetics—in the mechanisms of chemical reactions, the rates of adsorption, dissolution or evaporation, and generally, in time as a variable. As may be imagined, there is a wide spectrum of rate phenomena and in the sophistication achieved in dealing wifli them. In some cases changes in area or in amounts of phases are involved, as in rates of evaporation, condensation, dissolution, precipitation, flocculation, and adsorption and desorption. In other cases surface composition is changing as with reaction in monolayers. The field of catalysis is focused largely on the study of surface reaction mechanisms. Thus, throughout this book, the kinetic aspects of interfacial phenomena are discussed in concert with the associated thermodynamic properties. 

Nagy, K. L. (1995). Dissolution and precipitation kinetics of sheef silicates. In "Chemical Weathering Rates of Silicate Minerals" (A. F. White and S. L. Brantley, eds), Mineralogical Society of America, Washington, DC, Reviews in Mineralogy 31, 173-233. 

Little is known about the kinetics of dissolution, precipitation, and oxidation-reduction reactions in the natural environment. Consequently, simulating the kinetics of even more complicated injection- zone chemistry is very difficult. 

Muller, B., 2004, ChemEQL V3.0, A program to calculate chemical speciation equilibria, titrations, dissolution, precipitation, adsorption, kinetics, pX-pY diagrams, solubility diagrams. Limnological Research Center EAWAG/ETH, Kastanienbaum, Switzerland. 

Nagy, K. L., 1995, Dissolution and precipitation kinetics of sheet silicates. Reviews in Mineralogy 31, 173-233. 

The principle we have applied here is called microscopic reversibility or principle of detailed balancing. It shows that there is a link between kinetic rate constants and thermodynamic equilibrium constants. Obviously, equilibrium is not characterized by the cessation of processes at equilibrium the rates of forward and reverse microscopic processes are equal for every elementary reaction step. The microscopic reversibility (which is routinely used in homogeneous solution kinetics) applies also to heterogeneous reactions (adsorption, desorption dissolution, precipitation). 

We can generally group the rate laws adopted to describe dissolution and precipitation kinetics into three main categories (Delany et al., 1986) ... 

The kinetic mass transfer model developed to take into consideration the geochemical evolution of the Cigar Lake ore deposit was mainly done by simulating the evolution of the Al-Si system in the Cigar Lake ore deposit system. To this aim the system formed by kaoli-nite, gibbsite and illite as main aluminosilicate solid phases was considered and kinetics for the dissolution-precipitation processes were taken from the open scientific literature (Nagy et al. 

Nagy, K. L. Blum, A. E. Lasaga, A. C. 1991. Dissolution and precipitation kinetics of kaolinite at 80°C and pH 3. The dependence on solution saturation state. American Journal of Science, 291, 649-686. 

In natural systems, carbonates react with a variety of solutions at different pressures and temperatures. The processes involved in these reactions are complex, but depend significantly on the solubilities of the carbonate minerals, their surface chemistries, and dissolution and precipitation kinetics. In this chapter, we have... 

Together with acid-base reactions, where a proton transfer occurs (pH-dependent dissolution/ precipitation, sorption, complexation) redox reactions play an important role for all interaction processes in aqueous systems. Redox reactions consist of two partial reactions, oxidation and reduction, and can be characterized by oxygen or electron transfer. Many redox reactions in natural aqueous systems can actually not be described by thermodynamic equilibrium equations, since they have slow kinetics. If a redox reaction is considered as a transfer of electrons, the following general reaction can be derived ... 

Solute movement through soil is a complex process. It depends on convective-dispersive properties as influenced by pore size, shape, continuity, and a number of physicochemical reactions such as sorption-desorption, diffusion, exclusion, stagnant and/or double-layer water, interlayer water, activation energies, kinetics, equilibrium constants, and dissolution-precipitation. Miscible displacement is one of the best approaches for determining the factors in a given soil responsible for the transport behavior of any given solute. 

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