Understanding the Dissolution of Zeolites

Abstract

Scientific knowledge of how zeolites, a unique classification of microporous aluminosilicates, undergo dissolution in aqueous hydrochloric acid solutions is limited. Understanding the dissolution of zeolites is fundamental to a number of processes occurring in nature and throughout industry. To better understand the dissolution process, experiments were carried out establishing that the Si-to-Al ratio controls zeolite framework dissolution, by which the selective removal of aluminum constrains the removal of silicon. Stoichiometric dissolution is observed for Type 4A zeolite in HCl where the Si-to-Al ratio is equal to 1.0. Framework silicon dissolves completely during Type 4A dissolution and is followed by silicate precipitation. However, for the zeolite analcime which has a Si-to-Al ratio of 2.0 dissolves non-stoichiometrically as the selective removal of aluminum results in partially dissolved silicate particles followed by silicate precipitation. In Type Y zeolite, exhibiting a Si-to-Al ratio of 3.0, there is insufficient aluminum to weaken the structure and cause silicon to dissolve in HCl. Thus, little or no precipitation is observed, and amorphous undissolvable silicate particles remain intact. The initial dissolution rates of Type Y and 4A zeolites demonstrate that dissolution is constrained by the number of available reaction sites, and a selective removal rate parameter is applied to delineate the mechanism of particle dissolution by demonstrating the kinetic influence of the Si-to-Al ratio. Zeolite framework models are constructed and used to undergird the basic dissolution mechanism. The framework models, scanning electron micrographs of partially dissolved crystals, and experimentally measured dissolution rates all demonstrate that a zeolite's Si-to-Al framework ratio plays a universal role in the dissolution mechanism, independent of framework type. Consequently, the unique mechanism of zeolite dissolution has general implications on how petroleum reservoir stimulation treatments should be designed.

Degree of reaction and phase content of silica-based one-part geopolymers investigated using chemical and NMR spectroscopic methods

“…Refs. [36,37]). While 29 Si MAS NMR measures only silicon atoms in the samples, the results of the dissolution method are based on the accuracy of the measurements of the insoluble residue, and the assumption that the insoluble residue contains only remaining silica but no reaction products.…”

Dissipation Potentials for Reaction-Diffusion Systems

“…16,18,26 Although these involve phase change associated with nonconvexity of thermodynamic potentials, this does not rule out convex dissipation potentials.…”

Mesoporous aluminosilicates assembled from dissolved LTA zeolite and triblock copolymer in the presence of tetramethylammonium hydroxide

“…The pure silica framework suggests a dealumination from the dissolved zeolite precursor and absence of interaction between the aluminum species and the nonionic surfactant in a strongly acidic aqueous solution. Hartman and Fogler reported that dealumination from Na-A zeolite occurs during the dissolution in acid solutions [16]. They indicated that the random and selective removal of aluminum from LTA structure results in the release of silicon and then complete crystal disintegration.…”