Mobilization of colloidal ferrihydrite particles in porous media—An inner-sphere complexation approach

Do Goethite Surfaces Really Control the Transport and Retention of Multi-Walled Carbon Nanotubes in Chemically Heterogeneous Porous Media?

“…This result is expected because the electrostatic interaction between the negatively charged MWCNTs (i.e., carboxylate groups, −COO − ) and the positively charged GQS (Fe−OH 2+ ) is attractive, whereas it is repulsive for the negatively charged QS. 60,61 Figure S2 also confirms that statement and demonstrates that the significant amounts of roughness shown in Figure S1 will decrease and increase the MWCNT adhesive interaction between GQS and QS, respectively. The value of K D also dramatically increased with a decrease in the grain size of the GQS because of a corresponding increase in the specific surface area (Table S1).…”

Reactive transport of gentisic acid in a hematite-coated sand column: Experimental study and modeling

“…Thus Fe in the effluent may not be solely due to dissolution. Part of it could be related to mobilization of the hematite nano-particles while GA is adsorbing, as previously reported for ferrihydrite particles (Liang et al, 2000;Hofmann and Liang, 2007). In this case, the pattern of the iron curve suggests that GA is accessing the intra-aggregate sites progressively, provoking a tiny but constant rate of particle dispersion.…”

“…They may be accessed progressively, thereby inducing some mobilization of nano-particles. In a system of ferrihydrite-coated sand, Hofmann and Liang (2007) showed that citrate adsorption could induce sufficient repulsive force to disperse individual ferrihydrite colloids and release them in solution. Also, Hofmann et al (2005) showed for ferrihydrite aggregates that intra-aggregate diffusion in nanometric pores could account for an earlier breakthrough of the sorbate.…”

Effect of citrate on the local Fe coordination in ferrihydrite, arsenate binding, and ternary arsenate complex formation

“…Despite the high ionic strength of roughly 0.45 M, more than 60% of Fe remained in the supernatant when the initial citrate/Fe ratio was greater than 5 mol% (Table 2), which was due to both Fe complexation by citrate and electrostatic stabilization of Fh particles by adsorbed citrate (Hofmann and Liang, 2007). As a consequence, more than 60% of total As(V) remained in the supernatants (Table 2).…”

“…Examples of direct and indirect mechanisms leading to an increased mobility of As(V) in the environment include (i) adsorption competition (Grafe et al, 2002;Martin et al, 2009), (ii) the inhibition of Fh precipitation or the dissolution of Fh through Fe complexation (e.g., Ford et al, 2006), (iii) the inhibition of As surface precipitate formation, or (iv) the electrostatic stabilization of Fh particles in solution, which facilitates the colloidal transport of As(V) (Hofmann and Liang, 2007). In addition, the surface speciation of As(V) on Fh may be significantly affected by a decrease in crystallinity and crystal size.…”