Ure, Alexander David
(2017)
Understanding the influence of mineralogy and microwave energy input on the microwave treatment of copper ores.
PhD thesis, University of Nottingham.
Abstract
Ore comminution is an energy intensive and inefficient process in which new innovative technologies could potentially deliver great benefits. Over the past two decades, the high power microwave treatment of ores has shown the potential of being a novel step-changing comminution technology. The ability of microwaves to rapidly and selectively heat certain minerals within an ore, and generate and propagate intergranular fractures at grain boundaries, has been shown to be an innovative process for reducing ore strength and enhancing mineral liberation. A review of the literature has identified that, while the understanding of the process has developed significantly over recent years, fundamental knowledge of how mineralogical characteristics of different ores influences their amenability to microwave treatment is still limited. Previous work in this field has also been primarily concerned with assessing the downstream mineral processing benefits achievable, rather than directly measuring the impact of the treatment on ore fracturing.
The aim of this experimental investigation has been to make an original and distinct contribution towards the current state of knowledge, through the application of innovative microwave treatment processes and conventional and novel analytical methods. Three copper ore samples, termed MZ, QZ and QX, were assessed following a series of microwave treatments at unprecedented conditions, for changes in Cu-sulphide mineral liberation using automated mineralogy, and changes in ore comminution using JK GeM Crushing Index and Bond Ball Mill Work Index testing methods. A novel fracture analysis and quantification method was also developed and applied for the first time to the assessment of microwave treated ores.
MZ and QZ ores achieved similar improvements in Cu-sulphide mineral liberation and comminution performance following microwave treatment, as it has been shown from coarse ore characterisation that both ores possess characteristics that render them highly amenable to beneficial microwave treatment outcomes. This finding validates ore amenability characteristics proposed by previous researchers. Fracture analysis results have quantifiably shown for the first time that microwave treatments can induce additional beneficial fracturing in amenable ores. An additional original contribution to the field is that beneficial fracture outcomes were shown to correspond with benefits achieved in Cu-sulphide liberation, and ore comminution testing.
Investigations were also conducted to determine the minimum microwave energy input threshold at which measurable benefits in ore comminution and mineral liberation are achievable. Following an additional series of unprecedentedly low dose microwave treatments of MZ ore, it was observed that benefits in Cu-sulphide mineral liberation can be achieved from microwave treatment with a power density of 2.0x106W/m3 and a total microwave energy input of 0.3kWh/t, at an applicator residence duration of ~0.25 seconds. Treatment conditions for total microwave energy input at which benefits have been shown to be achievable, are lower than conditions previously reported in the literature for any ore type. This outcome indicates that scale-up of the process to industrially relevant throughputs (i.e. >10,000 t/h) could potentially be achieved using existing microwave generator technology, eliminating the need for the development of higher power generators producing over 100kW of microwave power.
Conclusions from this experimental investigation have provided an original contribution to the fundamental knowledge of the microwave treatment of copper ores, and have advanced the understanding of the application of the process to enhancing mineral liberation and ore comminution. Further investigations of a range of amenable copper ores, or ores of different commodities, at low microwave treatment doses of 0.3-0.7kWh/t would allow for an assessment of whether this newly determined minimum energy threshold at which mineral processing benefits have been shown, also applies to ores with different mineralogical and textural characteristics.
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