Aluminosilicate nanominerals are reactive soil components and have high potential value in industrial and technological applications, however it remains unclear what factors control their formation in nature and in the lab. This work investigated the complex system of physical and chemical conditions that influence the multi-stage formation of imogolite and proto-imogolite (a.k.a., allophane), as well as several impurity phases. Samples were synthesized and analyzed by powder x-ray diffraction, <i>in situ </i>and <i>ex situ</i> small angle x-ray scattering, and high-resolution transmission electron microscopy. Multivariate linear regression analysis combined with linear combination fitting of diffraction data was used to model the influence of different synthesis conditions including concentration, hydrolysis ratio and rate, and aluminum-to-silicon elemental ratio on the particle size of the initial precipitate and on the phase abundances of the final products. The developed models describe how imogolite formation is maximized within a finite range of initial Al:Si ratio, hydrolysis ratio, and concentration of starting reagents. The data also show how larger initial particle sizes result in more rapid formation and growth of imogolite, which likely proceeds by nanoparticle aggregation followed by a combination of nonclassical oriented attachment and classical monomer addition. It was determined from the models that hydrolysis ratio and aluminum concentration are the strongest controls on imogolite formation. These results demonstrated the ability to use this approach to understand complex geochemical systems with competing influences, as well as provided insight into the formation of imogolite and proto-imogolite, which are precursors to hydrous smectite and other more crystalline clay minerals.

Multivariate linear regression analysis of factors regulating the formation of aluminosilicate nanominerals

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