The dissolution experiments aimed at studying the kinetics of alunite and basaluminite dissolution are ongoing. With these experiments, the dissolution rates of these two important aluminium sulphates will be obtained and their dissolution reactions and mechanisms will be better understood. This will allow improving predictive calculations and modelling of Al release and behaviour in mine environments and in the treatments designed for their remediation.
The batch dissolution experiments are being carried
out in the Wolfson Laboratory of Environmental Geochemistry (University College
of London, London, UK) and in the Laboratory of Environmental Geochemistry at Birkbeck College (London, UK). In these batch
experiments, 100 mg of synthetic pure alunite or basaluminite are placed in glass beakers,
stirred to 400 rpm and kept in contact with 200 mL of different types of
solutions (pH 2, 3 and 4 H2SO4, pH 5.5 MES-buffered, pH 5.5 unbuffered deionized water, pH 8 TRIS-buffered, etc) and
under controlled temperature conditions (4, 20ºC and 40ºC) during reaction times between 24 hours and 2 weeks. These
conditions are intended to be similar to the ones found in environments
affected by acid drainage after contact with sulphide minerals.
During the experiments, 6 ml aliquots are being removed
at regular intervals, filtered using 0.22 mm filters and acidified to 1% HNO3 for
ICP analyses of the dissolved concentrations of Al, S and K, used to monitor
the progress of the dissolution process and to obtain the dissolution rates.
Solution pH and temperature are also monitored during the experiments. All the
experiments are run at least in triplicate.
Mineral samples are also being collected at the beginning and end of the experiments and studied by several mineralogical techniques (X-ray Diffraction, Raman spectroscopy, Scanning Electron Microscopy, X-ray Photoelectron Spectroscopy, etc) to characterize the changes induced by the dissolution process on the surface of the reacting solids.
