Analysis and Modelling of Mineral and Element Composition in Compression Breakage

Licentiate thesis, 2018

The outstanding properties of tungsten and tantalum make them valuable metals and, in some cases, irreplaceable in applications. The growing interest due to the high economic importance and the limited supply places these metals in the critical metals risk list. As a consequence of the increasing global demand for these metals, there is also a need to develop more efficient extraction processes. Coarse comminution processes are commonly assessed by the size reduction of particles, however, liberation and mineralogy are not taken into consideration.

The main hypothesis of this research is that critical metals are not evenly distributed in the different size fractions during coarse comminution processes since the breakage of particles will be affected by the mineralogy and texture. Further, to demonstrate the significant impact that mineralogy understanding has during breakage and develop a test procedure to include the concentration of the critical metals which will increase the resolution of coarse comminution models.

This thesis focuses on finding an experimental methodology to analyse the rock properties and its general characteristics, followed by defining a multicomponent model that combines size reduction and concentration for critical metals. In this research, the work is divided into 3 stages. The first main stage is the rock materials characterisation which consists of two parts: mechanical and mineralogical analyses. The second stage is the modelling and the third stage is theoretic implementation.

The mechanical characterisation includes compressive breakage through the use of interparticle breakage. Mineralogical characterisation was evaluated through the assessment of size fractions with a scanning electron microscopy (SEM) and geochemical analysis. Results from these tests give information about breakage, mineral composition and element concentration.

The second main stage corresponds to modelling. The first modelling part was the methodology of fitting measured data into a size reduction model. The second part corresponds developing a model capable of predicting the rare metal concentration as a function of the particle size distribution after a cycle of the compression crushing process. The model was developed by selecting a bimodal Weibull distribution for calibration which is shown to be capable of simulating critical metal concentration as a function of the compression ratio.

The third stage is a simulation. The aim of this section is to demonstrate a theoretical case where the concentration model allows to make well based estimations of how a plant should be designed. Evaluations have shown that by considering the information of the ore and its behaviour in terms of concentration and performance of the crushing, the process could be improved by changing machine parameters, i.e. closed side setting and adding a pre-screening before the milling process.

The work shows that considering the effect of mineralogy and element concentration in the coarse comminution models, it is possible to achieve better performance in terms of cone crusher and plant design.