Surface complexation of neodymium at the rutile-water interface: A potentiometric and modeling study in NaCl media to 250°C

Inner-sphere complexation of cations at the rutile–water interface: A concise surface structural interpretation with the CD and MUSIC model

“…The rutile powder used in this study was from Tioxide Corporation and has been used extensively in previous studies (Machesky et al, 1994(Machesky et al, , 1998Ridley et al, 2002Ridley et al, , 2005. The specific N 2 -BET surface area was 14.4 ± 0.1 m 2 /g (after hydrothermal pretreatment following Machesky et al (1998)), which is slightly lower than the batch used in some of our previous studies (17 ± 2 m 2 /g).…”

“…For all experiments, the initial electrode calibration solution was basic, comprising 5 Â 10 À4 m OH À (see potentiometric titration procedure below), to which an acid calibration solution was added that contained sufficient HCl to attain a calibration point close to 0.002 m H + . These calibration solutions contained sufficient electrolyte to produce the desired ionic strength (Ridley et al, 2002 (Ridley et al, 1999a(Ridley et al, , 2002(Ridley et al, , 2005) the ionic strength of the titrant was slightly higher than the corresponding test solution, making it possible to largely compensate for changes in ionic strength during a titration. Consequently, the ionic strength varied no more than 3% throughout a particular titration.…”

“…Ion adsorption and surface charging have been studied most frequently as a function of pH, at the macroscopic scale Dzombak and Morel, 1990;Boily and Fein, 1996;Boily et al, 2000;Wesolowski et al, 2000;Ridley et al, 2005;Machesky et al, 2006;Stachowicz et al, 2006). The resulting data have typically been rationalized by various surface complexation models (SCM), which combine chemical descriptions of surface protonation and ion adsorption reactions with electrostatic descriptions of the EDL (Westall and Hohl, 1980;Dzombak and Morel, 1990;Venema et al, 1996a).…”

“…Earlier studies have provided significant insights into ion adsorption and the interface domain (for example, Venema et al, 1996b;Bourikas et al, 2001;Rietra et al, 2001;Ridley et al, 2004Ridley et al, , 2005Zhang et al, 2004;Sverjensky, 2005;Boily et al, 2005;Fitts et al, 2005;Hiemstra and Van Riemsdijk, 2006;Machesky et al, 2006). In general, systems with electrolyte ions have been described with rather simple EDL models.…”

“…However, X-ray spectroscopy has revealed that electrolyte cations can form inner-sphere complexes at the (1 1 0) face of rutile (Fenter et al, 2000;Zhang et al, 2004Zhang et al, , 2007. Moreover, the observed structures have been incorporated into a few previous modeling efforts (Zhang et al, 2004;Ridley et al, 2005). In these prior efforts, however, electrolyte cations have been considered as simple point charges.…”