Linking the Characterisation of Cobalt-Bearing Copper Ore to Comminution Properties: Using a Geometallurgical Approach

The metal cobalt is essential in creating a sustainable society, as it is an important component in lithium- ion batteries and wind energy turbines. About half of the Earth’s land-based cobalt reserves can be found in the Democratic Republic of Congo (DRC). This study focusses on characterising cobalt-bearing copper ore from a DRC based mining operation and linking characteristic ore properties to the comminution behaviour. Portable X-ray Fluorescence (pXRF) is used to determine the geochemistry, while QEMSCAN, CT scan and InfraRed (IR) spectroscopy are used to assess mineralogy on different length scales. In terms of geotechnical properties, the surface hardness of the ore is determined using a rebound hardness tester. The comminution behaviour is assessed by crushing selected ore samples below 3.35 mm and by grinding the crushed samples for 21 minutes using a ball mill. The energy consumption required for different ore types is quantified using the crushing and sieving simulation package Bruno. The chemical characterisation of ore samples showed significant variation in cobalt content, as the cobalt grade measured in the samples using pXRF varied from 0% to 33.5%. By applying QEMSCAN analysis to samples coming from different locations within the deposit, two different mineralogical zones have been identified: a weathered, and a sulphide zone, with large differences in modal mineralogy. In the weathered zone kolwezite and heterogenite are the principal cobalt bearing minerals, in the sulphide zone carrollite is the only mineral containing cobalt. The CT scan confirmed the unique mineralogy of certain samples, as the mineralogy of pure carrollite nodules found using QEMSCAN showed to continue in 3D. Both QEMSCAN and CT scan were able to detect differences in mineral texture of the studied samples. In terms of geotechnical properties, differences between surface hardness of the samples were observed using the rebound hardness tester. An empirical formula has been derived to adjust the measured surface hardness of drill core samples with a mass below 300 grams. This formula aided in identifying the differences in surface hardness for the distinct mineral textures of the sulphide zone. Influence of mineralogy on the sur- face hardness has been observed, as areas containing only carrollite showed to have a lower surface hardness than areas with a mixture of Mg silicates, quartz and carrollite. Fourier Transformed IR (FTIR) spectroscopy was used to identify a range of gangue minerals within the samples. Carrollite could be identified if it was present in significant proportions and no other IR active minerals were present. FTIR spectroscopy also allowed to refine mineralogical data, as it was possible to differentiate between talc or serpentine and muscovite or illite in the studied samples, which was not possible using QEMSCAN. In total 8 minerals were identified using IR spectroscopy. The relative proportions of the modal mineralogy showed to be in agreement with the mineralogy found through QEMSCAN. The comminution experiments led to the identification of three different comminution classes. These three classes can again be linked to the identified mineral texture types. The surface hardness showed to be correlated to the p80 of samples with the same mineral texture. After 21 minutes of milling, the samples with a higher surface hardness had a coarser p80. Simulation showed that the crushing energy requirements differ up to a maximum of 27% for different comminution classes. This research provides a foundation towards identification of geometallurgical domains in the sulphide section of the investigated cobalt-bearing copper deposit. This MSc thesis was carried out at Camborne School of Mines (University of Exeter) as part of the NERC funded Cobalt: Geology, Geomicrobiology and Geometallurgy (CoG3) project.