Aluminosilicate Mineralogy and the Sorption of Organic Cations: Interplay between Electrostatic Barriers and Compound...

Area of Science:

• Environmental Chemistry
• Geochemistry
• Materials Science

Background:

• Current organic cation sorption models assume uniform interactions with mineral sites.
• Aluminosilicate structure and charge distribution are key factors in mineral-surface interactions.

Purpose of the Study:

• To investigate how aluminosilicate mineralogy influences organic cation sorption.
• To determine if variations in clay structure and electrostatic potential affect sorption behavior.

Main Methods:

• Studied seven smectites with varying isomorphic substitution and interlayer presence.
• Collected sorption coefficients for 14 benzylamine derivatives and 9 pharmaceutical compounds.
• Employed stochastic molecular modeling and electrostatic potential mapping.

Main Results:

• Organic cation sorption coefficients (K_CEC) varied by up to one order of magnitude between hectorite and nontronite.
• Tetrahedral charge in aluminosilicates created electrostatic barriers, penalizing larger organic cations.
• Octahedral charge resulted in lower barriers, reducing sorption penalties for quaternary amines.
• Mineralogy-driven electrostatic potentials explained sorption trends not predicted by basic theories.

Conclusions:

• Aluminosilicate mineralogy exerts a significant influence (0.5-1 order of magnitude) on organic cation sorption.
• Electrostatic potential mapping provides crucial insights into sorption mechanisms.
• Predictive models must account for mineral-specific electrostatic properties for accurate sorption estimations.