Size distribution of FEBEX bentonite colloids upon fast disaggregation in low-ionic strength water

Abstract

Bentonite colloids generated from the backfill barrier in nuclear waste repositories may act as radionuclide carriers, if they are stable and mobile. Repository scenarios with highly saline groundwater inhibit colloid stability as particles tend to aggregate but, in the time frame of repositories, groundwater conditions may evolve, promoting particle disaggregation and stabilization. The disaggregation of FEBEX bentonite colloids by fast dilution to lower ionic strength was analysed in this study. Time-resolved dynamic light-scattering experiments were carried out to evaluate the kinetics of bentonite colloid aggregation and disaggregation processes in Na+ and Na+-Ca2+ mixed electrolytes of low ionic strength. Attachment and detachment efficiencies were determined.Aggregation is promoted by increasing ionic strength, being more efficient in the presence of divalent cations. Once bentonite colloids are aggregated, a decrease in ionic strength facilitates disaggregation, but the process is not fully reversible as the initial size of the stable bentonite colloids at low ionic strength is not fully recovered. Particle-size distribution and concentration in suspension were analysed on disaggregated samples by single particle-counting measurements. Small colloids were measured in the disaggregated samples but their population was smaller than in the initial stable sample, especially in the presence of Ca2+.

Bentonite Nanoparticle Stability and the Effect of Fulvic Acids: Experiments and Modelling

“…The mean bentonite colloid, as determined by PCS, had a diameter of 185 nm with a half-width of 90 nm, recalculated from the polydispersity index of 0.24. That made it smaller than the FEBEX bentonite colloids prepared in NaClO 4 with a particle size of 340 ± 10 nm by Mayordomo et al [21].…”

“…This transition is also observed for the stability ratio where W transitions from higher values to 1. The dynamic light scattering technique (photon correlation spectroscopy; PCS) is frequently used to determine the coagulation rate and CCC of various clay colloid suspensions [17,18,[20][21][22].…”

Stability of Artificial Nano‐Hydroxyapatite in the Presence of Natural Colloids: Influence of Steric Forces and Chargeability

“…Aggregation influences the stability of particles and consequently their transport and fate (Chowdhury et al, 2011). The characteristic and stability of nanoparticles depend greatly on environmental conditions such as pH, ionic strength, ion composition, cation valence, and temperature (García-García et al, 2009;Mayordomo et al, 2016), and also on coexisting organic and inorganic colloids (Erhayem and Sohn, 2014;Siliveru et al, 2018). Soil colloids have a high potential to interact with nanoparticles.…”