Secondary particle size determining sedimentation and adsorption kinetics of titanate-based materials for ammonia nitrogen and methylene blue removal

The effect of the main size distribution of particles on the adsorption process for adsorbent materials has been well-recognized; however, the impact of secondary particle size (agglomerated, aggregated or hydrated ones) on adsorbent properties and performance was rarely reported so far. In this study, a series of sodium titanates (STs) and peroxide modified sodium titanates (PSTs) with different primary particle sizes, and secondary sizes are synthesized by controlling synthesis conditions and subsequently applied to batch adsorption experiment. By employing scanning electron microscopes and Laser particle size analyzers, the particle sizes of STs and PSTs are found to be closely correlated with synthesis conditions. The surface morphology and specific surface area of titanates are size-dependent, while the components of all the samples maintained constant. The sedimentation experiment and CFD simulation demonstrated that particles with larger secondary sizes tended to settle more quickly than those with a bigger size. PSTs or STs particles with smaller secondary sizes could reach equilibrium more rapidly than those with the bigger size. The fitting results from Elovich and Weber-Morris models demonstrated that the particle sizes affect kinetics mainly through the liquid film diffusion process within the initial stages.