Sorption and desorption kinetics of Np(V) on magnetite and hematite

Abstract

Sorption kinetics of Np(V) on magnetite and hematite were investigated, and a sequential desorption method was applied to investigate changes in the chemical form of Np sorbed according to the amount of time they were in contact with the Np solution. It was found that the sorption process consists of fast sorption and slow sorption which reaches equilibrium in 1 h. According to the desorption results, it was conjectured (i) that fast sorption is attributable to sorption on/into the surface and non-crystalline phases of iron oxides for magnetite and hematite in both acidic and alkaline solutions, (ii) that sorption on/into the crystalline phase also contributes to fast sorption for hematite in an alkaline solution, and (iii) that slow sorption represents sorption into the crystalline phase of magnetite in both acidic and alkaline solutions and that of hematite in an acidic solution. From the results of sorption and desorption kinetics, it was concluded that the equilibrium between various chemical forms of sorbed Np was achieved in about 1 week, although the amount of sorbed Np reached an equilibrium in only 1 h.

Neptunium redox behavior and sorption onto goethite and hematite in the presence of humic acids with different hydroquinone content

“…It was established that Np(V) sorption by ␣-Fe 2 O 3 and ␣-FeOOH is described by two-steps process: rapid sorption on external surface of the colloids and the slow diffusion to internal micropores. These results are consistent with previously reported data [19,20].…”

Sorption coefficients and molecular mechanisms of Pu, U, Np, Am and Tc to Fe (hydr)oxides: A review

“…The dominant aqueous NpO 2 + sorbed onto ferrihydrite surface to form NpO 2 (OH) 0 surface complex. Recent studies on the sorption of Np(V) onto hematite [110][111][112][113], goethite [112] and magnetite [113] are in agreement with the previous results for ferrihydrite. The sorption behavior of Np(V) to hematite under aerobic and anaerobic conditions was not noticeably different, because the Np(V) species onto hematite was not reduced [110].…”

Kinetics of neptunium(V) sorption and desorption on goethite: An experimental and modeling study

“…Results from previous Np(V)-iron (oxyhydr)oxide sorption studies under aerobic conditions indicate a fast initial metal uptake in the order of minutes to hours followed by slower metal sorption rates over days to weeks (Nakayama and Sakamoto, 1991;Kohler et al, 1999;Nakata et al, 2000;Jerden and Kropf, 2007). Neptunium desorption experiments with Fe-(oxyhydr)oxides have been performed at the same chemical solution conditions as during adsorption (Keeney-Kennicutt and Morse, 1984), after controlled changes in solution pH (Nakayama and Sakamoto, 1991;Jerden and Kropf, 2007), or with various types of extraction solutions (Keeney-Kennicutt and Morse, 1984;Nakata et al, 2000;Nakata et al, 2002).…”

“…Neptunium desorption experiments with Fe-(oxyhydr)oxides have been performed at the same chemical solution conditions as during adsorption (Keeney-Kennicutt and Morse, 1984), after controlled changes in solution pH (Nakayama and Sakamoto, 1991;Jerden and Kropf, 2007), or with various types of extraction solutions (Keeney-Kennicutt and Morse, 1984;Nakata et al, 2000;Nakata et al, 2002). Nakata et al (2000) found that after Np was sorbed to hematite over one week, 24% remained sorbed after sequential desorption steps with 1 M KCl and 0.1 M K 2 C 2 O 4 . Keeney-Kennicutt and Morse (1984) observed a Np fraction of approximately 66% desorbed from goethite in deionized water and natural seawater solutions after two hours.…”

“…Chemical solution conditions during the (ad)sorption step, such as redox conditions and salt composition, affect the extent of metal desorption (Nakata et al, 2002;Jerden and Kropf, 2007). Furthermore, extended (ad)sorption times appear to decrease the reversibility of Np sorption reactions (Nakata et al, 2000).…”