BAUXITE ORE BODY KNOWLEDGE AND DIGESTION EXTRACTION EFFICIENCY FOR WORSLEY ALUMINA GRANITIC BAUXITE TRANSITION

Worsley has been processing bauxite with Greenstone-type basement (low silica, ferritic-bauxite type) since refinery was built. However, soon, the refinery must prepare for a change in bauxite feed coming from mining areas with Granite-type basement (high silica, granitic-bauxite type). Worsley has begun preparing for this transition to granitic bauxite by investing in detailed ore-body knowledge to better understand and fully optimise Worsley’s processes in mining and alumina refining.
A key data source of this work has been the scanning of all of Worsley legacy drillhole samples by Diffused-Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). Approximately 10% of the samples were also analysed by primary test methods to develop predictive models for mineralogy, wet chemistry, elemental composition, and physical properties. FTIR models were used to predict metrics that are either expensive or are not practical to analyse in large quantities, such as mineralogy by quantitative XRD (>$200/sample) and physical properties (>$1,000/sample). The 4-year program successfully recorded the variability of possible future bauxite sources spatially in terms of mineralogy such as: (1) boehmite, which impacts Worsley refinery’s digestion extraction efficiency (DEE); (2) corundum, which is strongly correlated to Bond work index and Bond abrasion index; (3) goethite to hematite ratio, which impacts mud settling, (4) quartz levels, which are associated with the Bond abrasion index, increased erosion of refinery structures, and a source of increased reactive silica; (5) amorphous aluminous and siliceous phases, which have variable solubility depending on caustic concentrations and digestion conditions impacting DEE.
The characterisation of the potential future bauxite areas has delivered valuable information in decision making for mine planning including blending strategies as well as understanding properties/characteristics to improve processability and optimise costs. Successful mapping and variable visualization of the granite mining areas contribute valuable information in blending strategies aimed to minimize variability in the stockpile feed to refinery for a more sustainable operation.