Kinetics and Equilibrium of the Ion Exchange of Cd2+at Na-montmorillonite: Analysis of Heterogeneity by Means of the Regularization Technique CONTIN
✍ Scribed by Sabina Haber-Pohlmeier; Andreas Pohlmeier
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 219 KB
- Volume
- 188
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
surface. Structural details are given in Refs. (1,. The Kinetics and equilibrium of the ion exchange of Cd 2/ at Nabinding properties of the ion exchange sites are not uniform. montmorillonite are investigated and analyzed for the first time Their affinity and accessibility for metal ions may vary due by kinetic and affinity spectra. To obtain these distribution functo (i) the different charge density inside the layer (3), (ii) tions an inverse integral transformation is performed numerically the location of binding sites on the outer surface and in the by the program CONTIN with the integral adsorption equation.
interlayer space (1, 2), and (iii) the irregular shape of the It employs the constrained regularization technique with a smoothclay platelets (see also Fig. ). These properties give rise ing regularizor favoring parsimony of the solution and an autoto a heterogeneity of the surface influencing their binding matic adjustment of the regularization strength by the statistical properties with respect to metal ions.
F test. A Langmuir equation as local isotherm is additionally built in the code for the first time so that CONTIN is now a very
In the past years it became obvious that the classical deconvenient and handy tool for the calculation of model indepenscription of the exchange process by single, discrete coeffident kinetic and affinity spectra. Bimodal kinetic spectra are obcients like rate constants and ion exchange constants is not served where the main process (80%) is the binding of Cd 2/ at satisfactory; the heterogeneity must be taken into account the outer surface. The mean rate coefficient k mean is 11 s 01 at 25ЊC and introduced into reaction models. A convenient way of and the HWHH of the distribution function of about 0.1 log k doing this is by introducing distribution functions of the units proves the considerable degree of heterogeneity. An inner Gibbs free enthalpy (DG j ) leading to an affinity spectrum sphere complex is formed that is controlled by the ion exchange and of the rate coefficient k, leading to a kinetic spectrum reaction itself, not by diffusion, as proven by temperature depen-(4). The experimentally observable quantity f (u), i.e., the dent measurements. The more heterogeneous slow process is amount of bound heavy metal ions, is related to the spectra caused by aggregation of the platelets and intercalation of Cd 2/ by the integral adsorption equation, into the interlayer space. A broad monomodal affinity spectrum is found with a mean value of log K ex,mean Å 0.5 and an asymmetry to the low affinity side. ᭧ 1997 Academic Press f (u) Å ͐ ϱ g Å0 S(g)k(g, u)dg / w, [1]