TY  - JOUR
A1  - Lippold, Holger
A1  - Eidner, Sascha
A1  - Kumke, Michael Uwe
A1  - Lippmann-Pipke, Johanna
T1  - Diffusion, degradation or on-site stabilisation - identifying causes of kinetic processes involved in metal-humate complexation
JF  - Applied geochemistry : journal of the International Association of Geochemistry and Cosmochemistry
N2  - The applicability of equilibrium models for humic-bound transport of toxic or radioactive metals is affected by kinetic processes leading to an increasing inertness of metal-humic complexes. The chemical background is not yet understood. It is widely believed that bound metals undergo an in-diffusion process within the humic colloids, changing from weaker to stronger binding sites. This work is focussed on the competition effect of Al(III) on complexation of Tb(III) or Eu(III) as analogues of trivalent actinides. By using ion exchange and spectroscopic methods, their bound fractions were determined for solutions of Al and humic acid that had been pre-equilibrated for different periods of time. Whilst the amount of bound Al remained unchanged, its blocking effect was found to increase over a time frame of 2 days, which corresponds to the kinetics of the increase in complex inertness reported in most pertinent studies. Thus, the derived "diffusion theory'' turned out to be inapplicable, since it cannot explain an increase in competition for the "initial'' sites. A delayed degradation of polynuclear species (as found for Fe) does not occur. Consequently, the temporal changes must be based on structural rearrangements in the vicinity of bound Al, complicating the exchange or access. Time-dependent studies by laser fluorescence spectroscopy (steady-state and time-resolved) yielded evidence of substantial alterations, which were, however, immediately induced and did not show any significant trend on the time scale of interest, suggesting that the stabilisation process is based on comparatively moderate changes.
Y1  - 2012
U6  - https://doi.org/10.1016/j.apgeochem.2011.11.001
SN  - 0883-2927
VL  - 27
IS  - 1
SP  - 250
EP  - 256
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Schäfer, Thorsten
A1  - Huber, Florian
A1  - Seher, Holger
A1  - Missana, Tiziana
A1  - Alonso, Ursula
A1  - Kumke, Michael Uwe
A1  - Eidner, Sascha
A1  - Claret, Francis
A1  - Enzmann, Frieder
T1  - Nanoparticles and their influence on radionuclide mobility in deep geological formations
JF  - Applied geochemistry : journal of the International Association of Geochemistry and Cosmochemistry
N2  - This article gives an overview of the current status of knowledge concerning the role of nanoparticles (inorganic and organic) in deep geological host rocks and the potential influence of these nanoparticles on radionuclide migration in far-field systems. The manuscript is not intended to be a full review paper or overview paper concerning nanoparticles, here the intention is to refer to recent publications but to highlight the progress made in the 6th framework project IP FUNMIG (Fundamental processes of radionuclide migration) and the open literature over the past 5 a concerning the process understanding of nanoparticle related issues in the three host rock formations investigated, namely: claystones, crystalline rocks and salt rock overburden. The results show inter alia that the inorganic nanoparticle concentration in deep groundwaters of advection dominated systems rarely exceeds 1 mg L (1) and is expected to be in the ng L (1) range in diffusion controlled systems. For organic nanoparticles DOC concentrations up to tens of milligrams in diffusion-controlled indurated clays with molecular sizes mostly <500 Da have been found. Fulvic acid type organics have been identified in crystalline environments and plastic Clay formations (Boom Clay) with molecular sizes <= 300 kDa. Additional sources of inorganic nanoparticles from the repository near-field (compacted bentonite) were identified and the initial erosion rates were determined. The results indicate under stagnant conditions similar to 38 mg cm (2) a (1) for bi-distilled water, similar to 20 mg cm (2) a (1) for glacial melt water (Grimsel groundwater) and very low rates similar to 0.02 mg cm (2) a (1) for 5 mM CaCl2 contact water. The low critical coagulation concentration (CCC) indicative for purely diffusion controlled coagulation of 1 mM L (1) Ca2+ found in bentonite nanoparticle stability analysis matches the low nanoparticle mobilization from compacted bentonite found in these systems.
Y1  - 2012
U6  - https://doi.org/10.1016/j.apgeochem.2011.09.009
SN  - 0883-2927
VL  - 27
IS  - 2
SP  - 390
EP  - 403
PB  - Elsevier
CY  - Oxford
ER  -