Atomistic computer simulations to understand alunite dissolution

Atomistic computer simulations are being carried out within the framework of the EC-funded RASMIM project and in collaboration with Dr. Julian Gale and Dr. Kate Wright, from the Department of Chemistry of the University of Curtin (Perth, Western Australia) . 

The bulk and surface structure of alunite have been modelled and the effect of solvation (attachment of water molecules) on different types of alunite surfaces have been explored. This has allowed observing and quantifying some of the initial effects that dissolution may have on this mineral, such as surface relaxation and reordering of molecules at the interface solid-solution.

The ongoing work will help understand the results obtained in alunite dissolution experiments, shedding light on the behaviour of this key mineral in mining environments.

Morphology obtained for non solvated (top) and solvated (bottom) alunite crystal by means of atomistic computer simulations (visualization using GDIS). The more preferential development of the (003) surface in the solvated specimen can be clearly observed.

Preliminary alunite dissolution results presented at SEM Conference 2014

Some of the preliminary results obtained about the dissolution rates and mechanisms of alunite dissolution have been presented in the 34th Annual Meeting of the Spanish Mineralogical Society, held in Granada (Spain) between the 1st and the 4th of July 2014.

Dr Karen Hudson-Edwards and Dr Patricia Acero awarded NERC grant

Dr Karen Hudson Edwards and Dr Patricia Acero have received a NERC grant for the project Characterisation of Nanometre-Sized Aluminium Sulphates: Implications for Mobility of Aluminium from Mine Wastes. The grant will allow accessing the Facility for Environmental  Nanoparticle Analysis and Characterisation (FENAC) at the University of Birmingham and will contribute to better achieve the objectives of the RASMIM project.

For further information, read this related post in the News section from Birkbeck College.

Alunite and Basaluminite kinetic dissolution experiments

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 H₂SO_4, 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.