The Trouble With Tailings: How Alteration Mineralogy can Hinder Quantitative Phase Analysis of Mineral Waste
Quantitative phase analysis, using the Rietveld method and X-ray powder-diffraction data, has become a standard technique for analysis of mineral waste from mining operations. This method relies upon the availability of well defined crystal structures for all detectable mineral phases in a sample. An even more basic assumption, central to quantitative mineralogy, is that all significant mineral phases can be detected from X-ray diffraction data. This is not always the case, because X-ray amorphous and nanocrystalline mineral phases can develop within geological samples as a result of chemical weathering. The extent of mineral-water interaction to which mine tailings are exposed, during processing and storage, makes these materials particularly susceptible to weathering and alteration. We have used the Rietveld method and X-ray powder-diffraction data to quantify the uptake of atmospheric CO2 into secondary carbonate minerals at two operating mines: the Diavik Diamond Mine, Northwest Territories, Canada, and the Mount Keith Nickel Mine, Western Australia, Australia. At Diavik, nominally anhydrous minerals in kimberlitic mine tailings have been found to contain X-ray amorphous material and hydroxyl groups detectable by Raman spectroscopy. A series of weighed mixtures, prepared to simulate kimberlite mine tailings, has been used to assess the effects of X-ray amorphous material on quantitative phase analysis of Diavik tailings. At Mount Keith, hydrated sulphate minerals and halide minerals develop efflorescent crusts at the surface of the tailings storage facility. Hydrated sulphate minerals in these mine tailings commonly decompose to amorphous substances rather than dehydrating to produce minerals detectable from X-ray powder-diffraction patterns. Nanocrystalline and X-ray amorphous material in mine tailings can affect the accuracy of quantitative determinations of CO2 trapping and abundances of sulphur-bearing minerals associated with redox reactions. Here we assess the impact of amorphous material on quantitative X-ray diffraction results with particular reference to CO2 sequestration and suggest strategies for detection and analysis.
Cation Disorder in Columbite-Group Minerals by FTIR Analysis
Columbite-group minerals are economically important oxide minerals that form in granitic pegmatites. Past studies have quantified cation disorder in these minerals using XRD data and focusing on lattice dimensions. This previous work has also shown a correlation between cation disorder and transmittance spectra from Fourier Transform Infrared Spectroscopy. Using FTIR we studied a suite of columbite-group mineral samples from the Yellowknife pegmatite field. Both ATR and KBr methods were implemented in order to better quantify cation disorder. Potential for interstitial hydrous phases was also investigated.
Changes in tin smelting efficiency seen through the eyes of UK slag.