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Germany| The aim of the project is to develop and test
a new cost-effective technology to remediate uranium mill tailings. The
technology will be based on processes similar to natural occurring precipitation
and crystallisation phenomena. Artificially induced crystallisation processes
within the tailings shall be used to immobilise heavy metals and radionuclides
or to seal porous zones in order to prevent the migration of contaminants.
This can be realised by the treatment of contaminated areas with solutions
leading to the formation of slightly soluble minerals such as sulfates,
carbonates or hydroxides. For example, grouts producing gypsum precipitates
can be prepared by mixing solutions containing Ca2+ ions with
sulfate containing solutions in the presence of precipitation inhibitors.
The inhibitors prevent spontaneous precipitation during the mixing of the
solutions, however, they are only temporary stable. The course of gypsum
precipitation can be adjusted by the composition of the inhibitor, its
concentration, temperature and solution composition. It is possible to
prepare grouts leading to gypsum crystallization between few and more than
100 hours. Solutions resulting in BaSO4 precipitation can be
synthesised by mixing of Ba(OH)2 solutions and diluted H2SO4.
Apart from the inhibitor the resulting grout contains only Ba2+
and SO42- ions and no further components are brought
into the formation has to be sealed. The maximum achievable BaSO4
supersaturation lies between 200 and 400 mg/l, depending on the inhibitor
concentration and the composition of fresh water used in preparation. Due
to the extremely low solubility of 10-10 mol2 l-2
long time stable layers protecting reactive mineral surfaces are formed.
Solutions allowing the in situ formation of carbonates offer a wide range
of applications for the in situ construction of reactive barriers. An increase
of the puffer capacity of polluted areas as well as directed immobilisation
of heavy metals can be achieved by grouts leading to hydroxide precipitation.
The grouts are clear solutions containing the minerals that will be formed
in a dissolved form. Interactions with pore water present in the formations
are not necessary to produce the sealing or immobilisation.
The following tasks will be in the centre of the project: · Determination of the immobilisation and/or sealing capacity of differently composed grouts leading to the formation of slightly soluble sulfates, carbonates or hydroxides such as Gypsum, BaSO4, CaCO3 or Al(OH)3. · Characterisation of the course of permeability reduction during treatment of different types of tailings with mineral forming solutions. · Proof of the long time stability of the immobilisation. · Characterisation of the development of pH value and redox potential in soils treated with mineral forming solutions. · Characterisation of secondarily formed layers on reactive mineral surfaces by means of XRD and SEM. · Determination of the immobilising and sealing capacity of the grouts. In co-operation with WISMUT GmbH (Chemnitz, Germany) the large scale application of grouts leading to BaSO4 precipitation will be tested in the former Uranium mine Königstein. The immobilisation will be proved by a characterisation of the solution composition after passing the sandstone formation. |
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