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Process mineralogy in the mining industry Jacques Eksteen Consulting MetallurgiMarch 2011. Factors to investigate during process development. The mineralogical microstructure of the ore body
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Process mineralogy in the mining industry Jacques Eksteen Consulting MetallurgiMarch 2011
Factors to investigate during process development • The mineralogical microstructure of the ore body • Not only the minerals / metals of interest, but specifically the minerals associated with the mineral / metal of interest. • The degree of dispersion of the valuable mineral within the matrix of less valuable minerals. • The morphology (size, shape, crystallinity and texture) of the minerals • One ore high in a valuable mineral / metal grade may still not necessarily be economical to extract compared to one of a lower grade, due to a difference in associated minerals or the level of dispersion and intergrowth patterns.
Techniques to characterize ore mineralogy • X-Ray Fluorescence (XRF): Technique which can be used to determine the quantities of elements present…usually reported as their oxides. It is a quantitative method. • X-Ray Diffraction (XRD): Identifies minerals based on the effect their different crystallographies have on the diffraction of X-rays. Used in conjunction with Rietveld refinement it becomes semiquantitative. Amorphous solid phases and glasses are not easily quantifiable. • Inductively coupled plasma (ICP): A quantitative method to determine the quantities of elements present after a samples has been dissolved. • It is normally couples to MS or OES depending on the concentrations of the species to be measured. • Laser ablation ICP – MS: Solid state ICP-MS • Scanning electron microscopy with energy dispersive system (SEM-EDS): Used to identify intergrown minerals, relative quantities, mineral chemistries i.t.o. their elements. • Optical Microscopy: Mineral identification using transmitted or reflected light • Liberation analysis and diagnostic leaching: Grinding and wet chemical analysis to analyze mineral associations.
Mineral Shape & Porosity • Shape can be isometric, plate-like, irregular, fibrous, etc. • Shape influence behaviour in process • Shape deviations (from the spherical particle form) may cause difficulties when screening, floating, or transporting mineral slurries • Porous ores are easier to leach or roast than dense ones, as the lixiviant or roasting gas can enter via the pores in the ore to gain access to the mineral to be transformed.
Mineral associations may vary as one mines deeper into an ore body • As a mineral reef are characterized by a certain assemblage of valuable and associated gangue minerals, mining into a different reef would result in a different combination of valuable and gangue minerals. • Example: Merensky reef, Plat reef and UG2 reef found in the Bushveld Igneous Complex • Example: Reef outcrops tend to show weathering (oxidation and effect of carboxylated water and humic acids) which change their mill & float behaviour, leaching behaviour and smelting behaviour. • Different reefs within the same mine might require an adaptation of existing technologies, e.g. platinum mines used to mine the more accessible and easier-to-process Merensky Reef, but due to the reef becoming scarcer, they have to adapt their processes to handle the chrome-rich UG2 layer, which is more difficult to obtain a low chromite flotation concentrate and causes significant problems when conventional smelting and converting operations are used.
General remarks • UG2 often has an inherently higher PGM value than Merensky, however: • UG2 reef has much PGMs associated with silicates and chromites (or on their grain boundaries), and requires energy intensive ultrafine grinding to liberate. • Complete rejection of the chromite is nearly impossible as flotation separation between gangue and valuable particles become more difficult as the particles becomes finer (especially below 20 micron).
General remarks (continued) • UG2 concentrates are high in altered silicates such as talc, which can relaase significant water during heating in a furnace. Halogen (F, Cl) ions in the crystal latice, together with water released during smelting cause severe corrosion. • the fineness of grind to liberate the PGMs from the host minerals, leads to significant dusts losses in the furnace. • The fine particle size contribute significantly to the loss of concentate bed porosity in a furnace leading to overheating of the liquid bae meta sulphide (matte).
