Determination of Percentage Total Sulphur in Pyritic Building Aggregate using Inductively Coupled Plasma-Optical Emission Spectrometry, X-Ray Fluorescence and X-Ray Diffraction

Abstract

Pyritic heave in subfloor aggregates is caused by the oxidation of pyrite, which produces sulphuric acid that reacts with calcite to form gypsum. The construction materials standard (I.S. 398-1:2013) specifies analyses of total sulphur (TS) by either a microwave digestion method followed by ICP-OES analysis or by a high temperature combustion method. This thesis comprised four investigations: 1) Develop a method of digestion method for ICP-OES analysis of TS and test the suitability of ED-XRF analysis for TS; 2) Characterize samples and evaluate the link between mineralogy and TS bulk XRD Rietveld analysis; 3) Assessment of reactive lithologies within the bulk samples by petrographic analysis, followed by XRD analysis to determine the reactivity of each lithology; 4) Investigation of the relationship between particle size and mineralogy by XRD analysis of each fraction. The results found the best agreement between the in-house ICP-OES data and the data from one of the XRF instruments (NEX QC+) but lesser agreement with the data from the accredited laboratory. The XRD results, when plotted in a ternary diagram with the data broken down based on % TS groups, demonstrated overlaps in mineralogical composition within the 0.2-0.3% TS range, the 0.3-1% TS and >1% TS range. Petrographic analysis revealed that bulk samples deemed indeterminate with regard to reactivity (I.S. 398-1:2013) show clean, potentially unreactive lithologies accompanied by a single pyrite-bearing deleterious component lithology. These samples would otherwise pass the standard without problem. The particle size analysis demonstrated an increase in deleterious material with decreasing particle size.