The effect of microwave heating on ore sorting

Abstract

Today the Mining industry is being challenged to develop methodologies and technology to process the lower grade and mineralogically complex ore types using ore sorting. The potential of microwave driven selective heating as an excitation tool to underpin sorting is possibly not well known in the mining and mineral industries due to very few applications and lack of awareness of the potential users. This thesis investigates the conditions under which this process is technically effective and can be utilised. A detailed investigation was conducted to understand the reasons for selective heating of specific mineral phases and how infrared sensing can be used as an identification technique to discriminate certain particles from others. This thesis also quantifies the impact of other important factors on the sorting process including; particle shape and size, mineral composition and most importantly the textures of the mineral bearing particles which have a tendency to heat quickly when exposed to microwave energy.An extensive assembly of analytical techniques such as optical microscopy, high-resolution X-ray computed tomography and XL Scanning Electron Microscopy (used by the Mineral Liberation Analyser) were utilised to obtain a mineralogical characterisation of the tested ores. The choice of microwave applicators enabled heating to be carried out in multimode and single mode types of cavity. By engineering synthetic samples a more comprehensive investigation was carried out which enabled some focusing questions from the thesis hypothesis to be addressed. The synthetic samples were used to experimentally validate an adopted theoretical approach of investigating the influence of mineral texture upon selective heating.The supplied ore from the Bingham Canyon Mine, USA (operated by Rio Tinto's Kennecott Utah Copper Corporation) was experimentally tested in two steps of investigations. The first step involved the approach of an "ideal", theoretical sorter for which rock particles had to be destroyed (necessary to perform assaying analysis). The temperature threshold for economically ii justifiable sorting was determined from a temperature difference and assayed metal content of heated particles. In the second step, samples were analysed by heating them in two applicators and the temperature threshold was determined as a function of mineral texture which caused selective heating as in contrast to assayed metal content.The results showed from the exposure of synthetic particles (with designed textures of microwave more responsive minerals) that it is advantageous to use both multimode and single mode cavities for better understanding of microwave heating of the ore. It was also shown that the texture of microwave responsive minerals has a significant effect on the formation of the temperature profiles which are used to evaluate selectivity and potential for the separation as opposed to only mineral composition of the ore particles. It was demonstrated that the types of ores studied in this work, will respond to ...

Microwave Processing of Materials

“…Thus, their temperature was higher than the bulk solution leading to more rapid dissolution [12]. Further work was performed to determine the impact of microwave assistance on other leaching systems, including making clear recommendations for the scale up of the technology [15,16,20].…”

Microwave infrared ore sorting of screen rejected rocks based on their content of iron and copper sulfide in Sarcheshmeh copper complex, Iran, Kerman

“…Today the mining industry is being challenged to develop methodologies and technologies for processing lower grade and complex mineral ore types employing ore sorting (Rizmanoski 2012). Low grade ores fed into mineral processing plants means more barren ores, more energy for comminuting, more water and chemical consumption as well as more waste production.…”

The Impact of Microwave Pre-Treatment on the Liberation of Nb/Ta Minerals from a Tin Oxide Ore

“…Although microwave energy hasn't been applied extensively in the metallurgical processes, it has the following advantages: rapid completion of the heat processes, high yields, low operating and capital costs and environmental benefits. Apart from that, use of microwaves can induce micro fractures in ores containing hydrated minerals thereby weakening the ore and reduce the comminution energy [1]. Macro and micro fractures are induced in ore segments where good heaters of microwave energy are located, such as metal oxides and sulphides.…”

“…Global Ta demand in recent years has been driven up specifically by use of Ta capacitors in portable electronic devices including mobile phones and this demand is expected to increase [4]. Currently Nb/Ta metals are produced by gravity concentration, magnetic separation, electrostatic and some flotation [5,6,7]. The success of all these processes depend on the liberation of Nb/Ta minerals, hence comminution plays a very important role.…”