Carbonate dissolution precipitation kinetics

Morse JW (1983) The kinetics of caldum carbonate dissolution and precipitation. Rev Mineral 11 227-264 Muller W, Aerden D, Halliday AN (2000) Isotopic dating of strain fringe increments Duration and rates of deformation in shear zones. Science 288 2195-2198... 

Carbonate minerals are among the most chemically reactive common minerals under Earth surface conditions. Many important features of carbonate mineral behavior in sediments and during diagenesis are a result of their unique kinetics of dissolution and precipitation. Although the reaction kinetics of several carbonate minerals have been investigated, the vast majority of studies have focused on calcite and aragonite. Before examining data and models for calcium carbonate dissolution and precipitation reactions in aqueous solutions, a brief summary of the major concepts involved will be presented. Here we will not deal with the details of proposed reaction mechanisms and the associated complex rate equations. These have been examined in extensive review articles (e.g., Plummer et al., 1979 Morse, 1983) and where appropriate will be developed in later chapters. 

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... 

Morse J.W. (1983) The kinetics of calcium carbonate dissolution and precipitation. In Reviews in Mineralogy Carbonates - Mineralogy and Chemistry (ed. R. J. Reeder), pp. 227-264. Mineralogical Society of America. Bookcrafters, Inc., Chelse, MI. 

Morse J. W. (1979) The kinetics of calcium carbonate dissolution and precipitation, 227. 

The phenomena of surface precipitation and isomorphic substitutions described above and in Chapters 3.5, 6.5 and 6.6 are hampered because equilibrium is seldom established. The initial surface reaction, e.g., the surface complex formation on the surface of an oxide or carbonate fulfills many criteria of a reversible equilibrium. If we form on the outer layer of the solid phase a coprecipitate (isomorphic substitutions) we may still ideally have a metastable equilibrium. The extent of incipient adsorption, e.g., of HPOjj on FeOOH(s) or of Cd2+ on caicite is certainly dependent on the surface charge of the sorbing solid, and thus on pH of the solution etc. even the kinetics of the reaction will be influenced by the surface charge but the final solid solution, if it were in equilibrium, would not depend on the surface charge and the solution variables which influence the adsorption process i.e., the extent of isomorphic substitution for the ideal solid solution is given by the equilibrium that describes the formation of the solid solution (and not by the rates by which these compositions are formed). Many surface phenomena that are encountered in laboratory studies and in field observations are characterized by partial, or metastable equilibrium or by non-equilibrium relations. Reversibility of the apparent equilibrium or congruence in dissolution or precipitation can often not be assumed. 

To convert calciiun carbonate to dolomite, some of the calcium must have been replaced by magnesiiun, requiring the partial dissolution of the carbonate. This process is promoted by contact with acidic pore water, such as occurs in organic-rich sediments because remineralization produces carbon dioxide. This is probably why dolomites are presently forming in detrital algal mats buried beneath sabkhat. The restricted extent of these modern dolomites reflects a kinetic hindrance to precipitation. Apparently dolomite precipitation in this setting is too slow to form substantial deposits when sea level is rapidly fluctuating. 

The kinetics of calcium carbonate precipitation in simple solutions have received less attention than those of dissolution reactions. This perhaps reflects the fact that most sedimentary carbonates are initially formed biogenically and that the primary interest in carbonate precipitation reactions has been directed at reaction... 

Model the carbonate precipitation in this carbonate channel by means of a Id transport with 40 cells of 10 m length each. Dispersivity is assumed with lm. Use the key words KINETICS and RATES and the BASIC program for calcite from the data set PHREEQC.dat describing the kinetics for both the calcite dissolution and the calcite precipitation. How much calcite precipitates each year within the channel s first 400 meter after the discharge How much C02 degasses at the same time ... 

The second example is for the precipitation of calcium carbonate from Ca(HC03)2 solutions. The mechanistic model was derived by Plummer et al. [40] from a kinetic study of the dissolution of Iceland spar crystals. The approach has more recently been extended to the interpretation of crystal growth [41]. The model is based upon the reaction between a partially dehydrated [Ca-HC03]+ complex or ion-pair and possible anionic reaction... 

Many investigators have reported use of hydroxyapatite for stabilizing Pb [20,40, 46-54]. Among these extensive studies, the work of Zang et al. [47] reports on pH-dependent experiments to study the kinetics of stabilization. These investigators treated Pb carbonate (cerussite) with hydroxyapatite and found that both cerussite and hydroxyapatite dissolved in the solution at low pH, and a less-soluble chloropyromorphite [Pb5(P04)3Cl] precipitated, leading to pH stabilization. The following dissolution reactions were responsible for this precipitation ... 

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