The effect of pH on chlorite dissolution rates at 25 degrees C
2003 (English)In: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXVI, 2003, Vol. 757, 649-655 p.Conference paper (Refereed)
The Swedish nuclear industry is planing to dispose spent nuclear fuel encapsulated in copper canisters in granitic bedrock at a depth of approx. 500 m. The reducing capacity of the geosphere is important for canister corrosion and radionuclide migration. The main inorganic reductants are Fe(II)-containing minerals: biotite in the bedrock, and pyrite and chlorite in the fracture filling minerals as well as in the buffer and backfill. As a consequence, the dissolution of chlorite is an important parameter when considering the reducing capacity available to groundwaters around the repository. The weathering rates of a chlorite sample from Taberg in central Sweden has been studied in 0.01 M NaCl media at (25+/-1)degreesC in the pH region 2-12. The chlorite was characterized before and after grinding and sieving, and was found to have a relatively low Fe-content, with the formula ((Mg9.44Fe0.72Al1.68)-Al-II)(Si6.47Al1.40Fe0.13III)O-20(OH)(16). Kinetic experiments were performed using a thin-film continuous flow-through technique with flow rates of 5 mL/h or 2.7 mL/h. Ibis technique prevents the precipitation of secondary phases such as iron(III) hydroxides. Solution samples were taken after a reaction time of 0-30 days. The contents of released Al, Fe, Mg and Si were analyzed using an Inductively Coupled Plasma emission spectroscopy (ICP-AES) technique and then normalized to the Brunauer-Emmet-Teller (BET) surface area and flow-rate in order to obtain rates of dissolution. The dissolution rate of the chlorite studied was pH-dependent, and a minimum was observed in the neutral pH region. The dissolution rate (based on Si data) decreased from 7x10(-11) mol/(m(2) s) at pH=2 to 4x10(-13) mol/(m(2) s) at pHapproximate to7 and then increased to 3x10(-12) mol/(m(2) s) at pH=12.
Place, publisher, year, edition, pages
2003. Vol. 757, 649-655 p.
, Materials research society symposium proceedings, ISSN 0272-9172
precipitation kinetics; biotite dissolution; minerals; 80-degrees-c; temperature; dependence; kaolinite; iron; fuel
IdentifiersURN: urn:nbn:se:kth:diva-24159ISI: 000186634300088ISBN: 1-55899-694-XOAI: oai:DiVA.org:kth-24159DiVA: diva2:344361
26th Symposium on the Scientific Basis for Nuclear Waste Management held at the 2002 MRS Fall Meeting BOSTON, MA, DEC 02-05, 2002
QC 201008192010-08-192010-08-192010-08-19Bibliographically approved