DETERMINATION OF QUARTZ CONCENTRATIONS IN BAUXITE VIA HF-FREE ACID DIGEST AND DIFFERENTIAL SCANNING CALORIMETRY
Quartz concentrations in bauxite contribute to process soda and alumina losses via binding with the mineral residue in red mud. Queensland Alumina Limited plant samples were historically analysed for quartz using a multi-stage wet chemistry digestion method that included several additions of hydrofluoric acid to clarify the final quartz product. Continual safety concerns with the handling and management of hydrofluoric acid led to the development of an alternative method to determine quartz concentrations in bauxite and red mud via differential scanning calorimetry (DSC).
Natural quartz in bauxite and mud undergoes an alpha/beta phase transformation in the region of 560 – 575oC, however the DSC thermogram is generally difficult to see in a raw bauxite sample due to the much larger boehmite peak at 510 – 540oC. A digestion method was developed to concentrate the quartz content so it was suitable for DSC scanning.
Samples were digested in a heated mixed acid solution, filtered, charred and then ignited. DSC analysis of the digest residue could then successfully resolve the quartz peak, where it was compared to known standard calibration curve, and back calculated to give percentage of quartz in bauxite and mud.