An Investigation of the Affinity of Inorganic Ions for Desilication Product, Using First Principle Quantum Mechanical Calculations
Desilication product (DSP) is an important by-product of alumina refining, which generates export earnings for Australia of approximately A$5 billion per annum. DSP is paradoxically both useful, for removing inorganic impurities from the recycled Bayer liquors, and problematic, since it builds up on the surfaces of heat exchanger pipes. The aim of this project is to investigate the molecular-scale interactions between inorganic impurity anions and DSP. This will increase understanding of the impurity removal process, and may lead to increased control and efficiency of this process, which would have both environmental and economic benefits. The understanding of these interactions may also be of use in determining the mechanisms involved in the build-up of scale on heat exchanger pipes. Computer modelling of these interactions is a critical part of our study, since experimental investigation is extremely challenging in Bayer-like systems.
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Principal Investigator Andrew RohlNanochemistry Research Institute Curtin University of Technology |
Project f45 |
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Co-Investigator Jennifer LoweNanochemistry Research Institute/Applied Chemistry Curtin University of Technology |
RFCD Codes 250603 |
Significant Achievements, Anticipated Outcomes and Future Work
Specific research aims of this project are to determine the affinities of various inorganic anions for the DSP bulk and surface structures. Initial calculations completed using the APAC National Facility SC have determined the structures of sodalites containing chloride, sulfate, carbonate, hydroxide and aluminate anions. These calculations have been used to validate and improve our previously developed interatomic potential forcefield, and have been compared to literature structures. Our computational results have also been compared to the affinities of each ion for inclusion within sodalite, as observed in our laboratory results. This represented a significant development in our research, since physical data available to validate our interatomic forcefield calculations was quite limited. We have now commenced molecular dynamics calculations on the SC, which will better establish the behaviour of the anions within the sodalite cage over time and at the temperature that has been used in our lab-based experimental studies. Results from the molecular dynamics calculations will be directly compared to our experimental results.
Computational Techniques Used
All DFT calculations were performed using the first principles program SIESTA. Initial simulations typically involved 50-70 atoms. Calculations were typically performed on 4 processors, requiring approximately 1-2 GB of RAM. For the parallelisation of SIESTA, a distributed memory approach has been taken with communication via MPI. When using matrix diagonalisation to solve the SCF procedure, then the Scalapack library has been utilised. The orbitals are distributed over the processors in a 1-D block cyclic fashion, while for evaluation of the Hartree and Exchange-Correlation potentials on the real space mesh a 2-D block-cyclic distribution of grid points is utilised. Molecular dynamics calculations are been performed utilising GULP, which is developed at our laboratory and has been parallelised by its author, Prof J. Gale. Ability to access the APAC National Facility has ensured that this project was feasible, since the in-house processing capability at Curtin University of Technology was unable to allow calculations of this nature to be completed within a reasonable timeframe.
Publications, Awards and External Funding
External Funding and Awards
IVEC postgraduate scholarship
AJ Parker CRC for Hydrometallurgy postgraduate scholarship
Australian Postgraduate Award scholarship
AINSE postgraduate scholarship
Publications
None