The coordination chemistry of weathering: III. A generalization on the dissolution rates of minerals
The coordination chemistry of weathering: III. A generalization on the dissolution rates of minerals
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DOI：
10.1016/0016-7037(88)90178-0
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发表时间：
1988-08
影响因子：
5
通讯作者：
E. Wieland;B. Wehrli;W. Stumm
中科院分区：
文献类型：
--
作者：
E. Wieland;B. Wehrli;W. Stumm
A general rate law on the surface-controlled dissolution of oxides and silicates is discussed. Combining concepts of surface coordination chemistry with established models of lattice statistics and activated complex theory we propose a general rate law for the acid- and ligand-promoted dissolution of minerals:R=kxa,PjSwhereRis the proton- or ligand-promoted dissolution rate [moles m−2s−1],kstands for the appropriate rate constant [s−1],xadenotes the mole fraction of dissolution active sites [−],Pjrepresents the probability to find a specific site in the coordinative arrangement of the precursor complex [−] andSis the surface concentration of sites [mol m−2]. Surface complexes (surface chelates and metal proton complexes) are precursors in the rate-limiting detachment of a central metal ion from the surface into the solution.We develop a mechanistic model, which clarifies the pH-dependence of dissolution rates. First appropriate surface protonation isotherms are derived. The surface protonation equilibria of different minerals at constant ionic strength match a single Freundlich isotherm with a slope ofca. 0.2. This result explains the frequently reported fractional pH-dependence of dissolution rat`es. Based on the Bragg-Williams approximation a lattice statistical procedure is outlined which permits the calculation of the probabilityPjof the precursor complex. The consistency of reported experimental dissolution rates and activation energy is tested and, as a consequence, different possibilities to correlate reaction rates (kinetic rate constants [s−1] are not reported) or apparent activation energies with thermodynamic data in the form of free linear energy relations are explored. We postulate that the site energy (Madelung energy) of the most stable lattice constituent (generally a metal cation at a surface site) or the ion formation energy of the solid—characteristic of the free energy needed to break the essential bonds in the lattice—are suitable free energy parameters to be correlated with the dissolution rates (logRHat pH 5).
