A Theoretical Treatment of the Precipitation of Doubly Substituted Solid Solutions in Aqueous Solutions

Abstract

International audienceWe present a theoretical formalism, which, for the first time, accounts for nucleation and growth of mineral particles of variable composition involving two independent substitutions, in aqueous solutions. It is based on the classical nucleation theory, on a size-dependent algebraic growth law allowing growth, resorption, and ripening of particles simultaneously, and on conservation laws akin to a thermodynamically closed system. Truly kinetic conditions are provided to determine the composition of the new nuclei which form and the composition of the deposited layers on the particles which were previously formed. Devised for describing the precipitation of a large range of solid solutions with double substitution, it yields the time evolution of all ion activities in the aqueous solution, together with the particle population characteristics: number, size, and composition profile of particles as a function of time and of their time of nucleation. We show that four different scenarios may take place, depending on the number of end-members involved in the chemical mixing (three or four) and depending on the particle aspect ratio, which may imply quasi two-dimensional growth, like in clay minerals, or three-dimensional growth for more compact solids like salts. This theoretical approach, in the line of our previous works made to treat precipitation of minerals of fixed composition or binary solid solutions, provides a major advance with respect to presently available solid solution precipitation models

Nanospectroscopy Captures Nanoscale Compositional Zonation in Barite Solid Solutions

“…Despite the widespread occurrence of solid solutions, their formation is poorly understood. Thermodynamic models have been extensively developed 9 , 19 , 20 , but kinetically controlled processes during precipitation limit the accuracy of thermodynamic predictions 21 – 23 . When kinetic processes are limiting and the reaction has not achieved equilibrium, heterogeneity in the surrounding fluid can occur, which can then lead to spatial heterogeneities within a solid solution 2 , 24 .…”

Interaction of Nonideal, Multicomponent Solid Solutions With Water: A Simple Algorithm to Estimate Final Equilibrium States

“…Aqueous‐solid solution (AQ‐SS) processes can be used in “active” remediation measures to immobilize toxic metals, radionuclides, and other harmful ions generated by human activities. Because structural incorporation is generally a more durable retention mechanism than adsorption or ionic exchange, AQ‐SS systems have attracted increasing attention from environmental scientists and engineers during the last decades (Bruno et al, ; Curti, 1997; Fernández‐González et al, ; Godelitsas & Astilleros, ; Noguera et al, ; Prieto et al, ; Putnis, ; Zhang et al, , and references there in).…”

“…Most experimental studies on the uptake of foreign ions by coprecipitation have been performed using pure samples of the host mineral, which implies considering a solid solution formed by two components, the pure host mineral and the equivalent pure compound of the guest ion. With some exceptions (Noguera et al, ; Vinograd et al, ; Wagner et al, ), geochemical modeling of AQ‐SS processes deals with binary solid solutions and the same occurs with the experimental and atomistic estimation of thermodynamic nonideality parameters. However, in aquifers, soils, and other aquatic environments, the potential host minerals could be binary solid solutions and the study of their interaction with a third dissolved ion would require considering ternary solid solutions (TSS).…”