Simulation of the nucleation and growth of binary solid solutions in aqueous solutions

Simulation of the nucleation and growth of simple clay minerals in weathering processes: The NANOKIN code

“…We have not tried to do so, because the present code does not allow to describe phases of variable composition. This is an extension presently under progress in our group (Amal, 2008;Noguera et al, 2008). We have thus stopped the simulation when the dynamics enters the Ca-montmorillonite stability field, at a maximum time of the order of a few 10 7 s. It is interesting to point out that the maximum size of the particles then is of the order of 1 lm, which is the right order of magnitude expected for kaolinite or halloysite, under the conditions that we have chosen.…”

Simulation of the nucleation and growth of clay minerals coupled with cation exchange

“…When surface energies depend upon composition, it is necessary to add another surface term in Eq. (27), involving algebraic excess quantities n A y=n Ms and n B y=m Ms of A y=n M and B y=m M formula units at the surface of the nucleus (Noguera et al, 2010). However, knowledge of clay surface energies is very poor, especially when lateral surface energies r lat are concerned, so we will assume the same values for A y=n M; B y=m M and Clayðx; yÞ surface energies.…”

“…In order to express the interfacial activities with respect to the bulk activities, the condition of mass balance at the surface of the particle must be expressed. As in our previous work (Noguera et al, 2010), we assume that, due to their smaller size, cation diffusion in the aqueous solution is much faster than anion diffusion, which allows to write:…”

“…The formalism to describe growth is similar to that developed for minerals with variable composition in their framework (Noguera et al, 2010). The Gibbs' free energy during growth is formally identical to the Gibbs' free energy for nucleation, but interfacial ionic activities have to be used to evaluate the interfacial saturation state I i .…”

“…It represents a new step in a long term project, which aims at providing a theoretical and numerical framework for the description of clay precipitation in the natural environment. In past studies, we have developed a framework for the precipitation of minerals of fixed composition (Noguera et al, 2006a,b; and the precipitation of minerals with substitution in their framework Noguera et al, 2010). The present study focuses on the treatment of the cation exchange capacity of clays (CEC) in contact with an aqueous solution, during precipitation.…”