Sorption specificity and desorption hysteresis of gibberellic acid on ferrihydrite compared to goethite, hematite, montmorillonite, and kaolinite

Abstract

The pesticide gibberellic acid (GA₃) is a potential endocrine disruptor and environmental toxin; therefore, research into its environmental fate is warranted. Batch studies were conducted to investigate the sorption and desorption characteristics of GA₃ on aquifer media. The results demonstrated special sorption characteristic of GA₃ on ferrihydrite compared to goethite, hematite, montmorillonite, and kaolinite, where the sorption kinetics of GA₃ on ferrihydrite was fitted well with the pseudo-second-order, Elovich, and intra-particle diffusion models. The sorption kinetics of GA₃ on ferrihydrite indicated an initial high sorption rate followed by a slow reaction process. The initial high GA₃ sorption rate may be related to electrostatic sorption and surface complexation reactions on the outer surfaces and at the macropore entrances of ferrihydrite. While the slow step was controlled by GA₃ diffusion into mesopore of ferrihydrite. Analysis of the desorption hysteresis indicated a high hysteresis index (HI) ranging from 0.68 to 17.32, and a low desorption percentage ranging from 18 to 48%. After sufficient desorption, the calculated maximum residual GA₃ quantity due to surface complexation reactions with the ferrihydrite coordinated unsaturated sites was 9.05 ± 0.12 mg g⁻¹. The calculated maximum quantity of GA₃ trapped within the mesopore was 16.23 ± 0.91 mg g⁻¹.

Graphical Abstract

Schematic overview of GA₃ sorption and desorption on five minerals in groundwater

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