Process Mineralogy
The rising complexity of ores processed today necessitates more detailed mineralogical characterization than in the past. To ensure that metallurgists have the skills and knowledge required, all students will develop basic skills in reflected microscopy using a virtual polarizing microscope tutorial being prepared as a CD ROM. Importance is on characterization of ore minerals and mill products.
Process mineralogy differs in practice from geological mineralogy in the questions it answers. After characterization of mineral material in rocks the geological mineralogist is principally concerned in questions of petrogenesis. How did these minerals form? What do they tell us about the origin of the rock in which they occur? The process mineralogist characterizes ore minerals and processing products with different questions in mind, such as: How can these minerals are separated? In which minerals are the elements of value? Is there a mineralogical reason for low recovery? Are there surface coatings on particles that are interfering with flotation?
Specialist process mineralogists are few in number and tend to work in technical laboratories of major mining houses, government research agencies, such as CANMET in Canada and Mintek in South Africa, a few universities and consultancies for example, Amtel in London, Ontario. Lots of of the applied mineralogists who have shown the value of mineralogy in metallurgy are nearing the end of their professional careers. Unfortunately, few mineralogists are being trained to take over their work.
The increasing complexity and lower grades of many ores being processed today put further demands on those responsible for the design and operation of metallurgical plants. This will be evident from the following description of problems encountered in the processing of refractory gold ores, ores that show low Au recovery after cyanide leaching, and their resolution through application of mineralogical studies.
The problem with processing of gold ores is that often a large amount of the gold is not present in the ores as the familiar native metal, but rather may be present as gold tellurides, antimony and bismuth compounds, or invisible gold, gold in solid solution within sulphide crystal lattices. Only native gold is easily soluble in alkaline cyanide solution, the usual way of extracting gold, for the other gold minerals more complicated pre-treatment is required like roasting or bacterial oxidation. It is sometimes very difficult for metallurgical test work to determine which of these types of gold are present in ores and the relative proportions of each type. Process mineralogy is essential in understanding these ores. The mineralogist may need to use reflected light microscopy, electron microprobe and or secondary ion mass spectroscopy, SIMS, to fully determine gold deportment in a complex gold ore. In particular, SIMS is usually required to accurately measure invisible gold in sulphides. For example, if an ore contains fine-grained native gold particles locked in pyrite, then fine grinding possibly could be used to liberate the gold. But, if the gold is present as invisible gold in pyrite, then fine grinding is not an option and more expensive techniques must be used. It makes good sense to correctly recognize the deportment of gold prior to designing a plant.
