Intensified co-precipitation and ion exchange using an agitated tubular reactor (ATR) for enhanced removal of Cs+ and Sr2+ ions

Abstract

Composite coagulants were synthesised in both a batch system and an agitated tubular reactor (ATR) using natural clinoptilolite with barite (BaSO₄) co-precipitation for the intensified simultaneous removal of Cs⁺ and Sr²⁺ ions. Ideal plug-flow characterisation of ATR was initially assessed under 3 and 5 Hz oscillations, showing pseudo plug-flow behaviour at the higher rate. Composite flocs were characterised by SEM and size analysis, while dewaterability was also studied by sedimentation and pressure filtration. Aggregate sizes were smaller, but denser and more monodisperse from the ATR than in batch. Composite flocs also gave measured specific cake resistances > 10 × smaller than pure BaSO₄. The higher metal removal performance was achieved using the ATR for Cs⁺ (95.7%) and Sr²⁺ (99.9%) at 5 Hz oscillation. A further enhancement for Cs⁺ removal was achieved by introducing Ba²⁺ ions into ATR after Na₂SO₄ addition, achieving > 96% Cs⁺ and > 99.9% Sr²⁺ removal. Overall, this study highlights that composite flocs outperform pure BaSO₄ in Cs⁺ and Sr²⁺ ion removal while achieving greater dewaterability and filterability. Additionally, we show the ATR effectively intensified the co-precipitation process, potentially reducing plant size and cost, making it a suitable process for modular nuclear cleanup and post-management operations.