Geometallurgical approach to understand how the variability in mineralogy at Zinkgruvan orebodies affects the need for copper activation in the bulk rougher- scavenger flotation Ivan Belo Fernandes Geosciences, master's level (120 credits) 2017 Luleå University of Technology Department of Civil, Environmental and Natural Resources Engineering ABSTRACT Zinkgruvan is a Pb-Zn-Ag deposit located in south-central Sweden, owned and operated by Lundin Mining. The ore is beneficiated by a collective-selective flotation circuit, recovering both galena and sphalerite in a bulk rougher-scavenger flotation stage and later on separating them into two final products. Opportunities for increase in zinc recovery in the bulk rougher-scavenger flotation stage have been identified as the plant is relying on natural Pb-activation to process the ore. Process mineralogical tools were used to characterize four different orebodies from Zinkgruvan (Burkland, Borta Bakom, Nygruvan and Sävsjön) and evaluate the metallurgical performance for flotation and magnetic separation, following a geometallurgical approach to better understand and predict the behavior of such ore types in processing plant. The first hypothesis in this thesis is that by addition of copper sulfate and increased collector dosage, Zn recovery will be improved without being detrimental to galena flotation. Results demonstrated that there is a significant increase in Zn recovery by further increasing collector dosage and copper- activating the flotation pulp in the scavenger stage. For instance, an increase in zinc recovery up to 16% has been achieved after addition of copper sulfate. Galena is readily floatable while sphalerite takes longer to be recovered. In addition, iron sulfides take longer to be recovered and, after addition of copper sulfate, there was an increase in iron sulfide recovery. The amount of iron sulfides reporting to the concentrate should still not be a problem to the plant. Most of the Fe in the concentrate is still coming from the sphalerite lattice. However, it might be that some orebodies coming into production in the near future have higher amounts of pyrrhotite, which might be a problem. Therefore, magnetic separation methods have been tested to remove pyrrhotite from the bulk ore. The second hypothesis is that the high Fe content in the concentrate might be due to the presence of iron sulfides, in which case they could be selectively removed by magnetic separation. XRD analyses demonstrated that Sävsjön is a highly variable orebody, and that its high Fe content varies with the location inside the orebody, being caused by either iron sulfide or iron oxide minerals. Both monoclinic and hexagonal pyrrhotite have been observed. Davis Tube could remove monoclinic pyrrhotite but it was very inefficient when dealing with hexagonal pyrrhotite. WHIMS, on the other hand, performed well for both types of pyrrhotite. When applying Davis Tube on Sävsjön OLD feed, a concentrate with up to 52.3% pyrrhotite is achieved, at a recovery of 35.32%. However, sphalerite is also reporting to the magnetic concentrate, which would generate Zn losses for the overall process. Zinc losses were up to 15.3% when the highest field strength was applied. Therefore, the applicability of magnetic separation for Zinkgruvan ore must be further evaluated. Keywords: Geometallurgy, Zinkgruvan, Zn-Pb flotation, ore variability, mineral chemistry, pyrrhotite, magnetic separation i ABBREVIATIONS PSD: Particle size distribution LA-ICP-MS: Laser ablation inductively coupled plasma mass spectrometry EMC: Element-to-mineral conversion XRD: X-ray diffraction WHIMS: Wet high intensity magnetic separator (Jones separator) Bu: Burkland orebody Sä: Sävsjön orebody Ny: Nygruvan orebody BB: Borta Bakom orebody ii TABLE OF CONTENTS ABSTRACT ......................................................................................................................................... i ABBREVIATIONS ............................................................................................................................. ii 1. INTRODUCTION ...................................................................................................................... 1 2. HYPOTHESIS AND OBJECTIVES OF STUDY ..................................................................... 1 3. LITERATURE REVIEW ........................................................................................................... 3 3.1. The geometallurgical approach ........................................................................................... 3 3.2. Lead-Zinc sulfide flotation .................................................................................................. 5 3.3. Froth flotation ...................................................................................................................... 6 3.3.1. Reagents ...................................................................................................................... 7 3.3.2. Mineral surfaces activation ......................................................................................... 9 3.3.3. Zinc and lead sulfide minerals properties .................................................................. 14 3.4. Mineral chemistry ............................................................................................................. 15 3.5. Iron sulfides separation ..................................................................................................... 17 3.5.1. Pyrrhotite reactivEness, oxidation and effects over its flotation ............................... 17 3.5.2. Pyrrhotite characterization under optical microscope and XRD ............................... 19 3.5.3. Magnetic separation .................................................................................................. 20 3.6. The Zinkgruvan operation ................................................................................................. 21 3.6.1. Geology ..................................................................................................................... 22 3.6.2. Mining operations and beneficiation process ............................................................ 23 3.7. Gaps identified for development of a master thesis .......................................................... 25 4. METHODOLOGY ................................................................................................................... 26 4.1. Sampling and preparation .................................................................................................. 26 4.2. Flotation ............................................................................................................................ 27 4.3. Magnetic separation .......................................................................................................... 29 4.3.1. Davis tube .................................................................................................................. 29 4.3.2. Wet Hight intensity magnetic separation (WHIMS) ................................................. 30 4.4. Process mineralogy ........................................................................................................... 30 4.4.1. Chemical assays ........................................................................................................ 31 4.4.2. X-Ray Diffraction ..................................................................................................... 32 4.4.3. Optical Microscopy ................................................................................................... 32 iii 4.4.4. Laser ablation Inductively coupled Mass Spectrometry ........................................... 33 4.5. Post-processing ................................................................................................................. 33 4.5.1. Element-to-Mineral conversion (EMC) .................................................................... 33 4.5.2. Mineral liberation analysis ........................................................................................ 34 4.5.3. Updated mineralogical composition .......................................................................... 34 5. RESULTS ................................................................................................................................. 36 5.1. Metallurgical performance – Flotation .............................................................................. 36 5.1.1. Density and Particle size distribution measurements ................................................ 36 5.1.2. Flotation experiments ................................................................................................ 37 5.1.3. Sphalerite mineral chemistry ..................................................................................... 46 5.1.4. X-Ray Diffraction (XRD) results for Burkland C1 ................................................... 51 5.2. Mineral liberation analyses ............................................................................................... 51 5.3. Metallurgical performance - Magnetic separation ............................................................ 53 5.3.1. Davis tube .................................................................................................................. 53 5.3.2. X-Ray Diffraction (XRD) results on Davis Tube...................................................... 54 5.3.3. Wet High Intensity Magnetic Separation (WHIMS)