A Study of Specific Sorption of Neptunium(V) on Smectite in Low pH Solution

Abstract

The "specific sorption" of neptunium(V) on smectite, in other words, a strong sorption undesorbable by 1 M KCl, is studied with a combination of batch type sorption and desorption experiments over a pH range of 2 to 5. Six types of homoionic smectite (Li-, Na-, Κ-, Cs-, Mg-, and Ca-smectite) are used in this study. Distribution coefficients (K d ) of neptunium for smectite vary over a wide pH range; the maximum K d value of ~300 cm 3 · g _1 at around pH 2 for Li-and Na-smectite and the minimum value of ~2cm 3 · g"' for Cs-smectite. The specific sorption of neptunium depends on pH and on the affinity of the exchangeable cation for smectite; the lower the pH of solution or the affinity, the larger the specific sorption. The neptunium-smectite association varies with the elapse of contact time. Within the first day of the neptunium-smectite contact the neptunium sorbed on Nasmectite at low pH is desorbable by 1 M KCl solution, and on the passage of time most of the neptunium sorbed becomes undesorbable by KCl (the specific sorption). Hydronium ion in solution is sorbed on smectite at low pH and dissociates the exchangeable cation from smectite into solution, and the specific sorption of neptunium increases with increasing the exchangeable cation that is dissociated from smectite.

Characterization of Fe-montmorillonite: A Simulant of Buffer Materials Accommodating Overpack Corrosion Product

“…The preparation of homoionic Na + -montmorillonite (Na-montmorillonite) and Ca 2+ -montmorillonite (Ca-montmorillonite) is described elsewhere. 4) For comparison, synthetic α-FeOOH (Junsei Chemical Co. Ltd.) was also used.…”

“…5) A Se(VI) solution was prepared by dissolving sodium selenate (Na 2 SeO 4 ) in 1×10 −2 M NaClO 4 to yield a working solution having a selenium concentration of 6×10 −4 M. The batch type sorption experiments of Se(VI) were carried out in a similar way as is described elsewhere. 4) The sorption experiments for Fe-montmorillonite were performed in an Ar-gas glove box to avoid the oxidation of Fe(II) until the introduction of Fe-montmorillonite to solution. The Se(VI) solution was not degassed to keep the oxidation state of Se(VI).…”

Distribution coefficients for the sorption of Th, U, Np, Pu, and Am on Opalinus Clay

“…However, up to now no sorption data for americium and plutonium on OPA have been published. More sorption studies have been reported for the uptake of actinides by pure clay minerals, that are the main constituents of OPA (e. g., montmorillonite [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33], illite [32][33][34][35][36][37][38][39][40], kaolinite [31,[41][42][43][44][45][46][47][48][49][50][51] , the cation exchange capacity was equal to 10 ± 4 meq/100 g for both powders [9,11]. The mineral composition and the content of the trace elements of the used OPA measured by X-ray fluorescence analysis are given elsewhere [11].…”

Pu(IV) Intrinsic Colloid Stability in the Presence of Montmorillonite at 25 & 80 C

“…Among the most ubiquitous inorganic colloids are aluminosilicate clays that are commonly observed as mobile colloids due to their inherently small particle size and prevalence as alteration minerals from original host rock material (Kersting et al, 1999). Clays are known to sorb Pu Keeney-Kennicutt and Morse, 1985;Kozai et al, 1996;Kozai et al, 1993;Lujaniene et al, 2007;Powell et al, 2004Powell et al, , 2005Powell et al, 2008;Sabodina et al, 2006;Sanchez et al, 1985;Turner et al, 1998). In addition, the proposed use of bentonite within some engineered barrier systems scenarios for high-level nuclear waste repositories provides additional importance to understanding Pu interaction with smectite aluminosilicate clays (Sabodina et al, 2006).…”