UNIVERSITÀ DEGLI STUDI DI MILANO Dottorato di Ricerca in Scienze della Terra Ciclo XVIII A flow-sheet approach to the issue of sulfide-rich tailings The beneficiation process as a key to the environmental management of copper mines Ph.D. Thesis Irene Fantone Matricola R10113 Tutor Academic Year Coordinator Prof. Giovanni Grieco 2014-2015 Prof. Elisabetta Erba Nothing is to be thrown away Abstract The present work is meant to evaluate the effect of separation of pyrite-rich fractions of tailings for both economic and environmental benefit. The project was focused on two tailing dumps in the former mining and processing site of Reps (Northern Albania). In-situ and laboratory investigations were conducted (i) to outline the main environmental characters of the selected dumps with an emphasis on heterogeneities within and between dumps and (ii) to evaluate the concentration potential of commodities, namely pyrite, from the waste materials. Mineralogical and geochemical data were collected and the Acid-Base account procedure was performed in order to evaluate the Acid Drainage (AD) potential of the selected tailing dumps. A quantitative flowsheet was devised in order to relate quantitatively the available information on processing and the collected data. Gravity separation tests were performed by a water shaking table method and the re-processing potential was evaluated through mineralogical and geochemical analyses. The site is subject to long-lasting (103 years) AD processes with significant release of Potentially Toxic Elements into the local environment. Two different classes of tailings have been recognized, based on the sulfide S content. The high- sulfide (S>10%) content material (hS) accounts for about 82% of the total potential H2SO4 production, despite it represents less than 20% of the whole tailing discard. On the contrary, the remnant low- sulfide (S<3%) content material (lS) is the most abundant fraction, yet responsible of a much lower environmental footprint. The two types of tailings are interpreted as by-products of two different mineral processing chains. A single-stage flotation stream yielded to discard lS+hS tailings. On the other hand, a double-stage flotation chain, when active, included a secondary flotation of the tailings produced by the primary Cu flotation. The latter flowsheet yielded to obtain a pyrite concentrate and to discard lS materials. The S content of tailings was thus reduced by over 50%. Re-processing via gravity concentration is an effective method for pyrite recovery from tailings. Tabling tests recovered 29 to 52% of the total sulfide S of the R2 dump, the hS material reworking being the most cost-effective procedure. The final concentrate may also become a sealable product and the gold content may increase the value of pyritic concentrates, given a measured selection of the separation input and parameters. Separation can therefore be used to both confer value to wastes and create smaller sulfide-rich dumps, with lower reclamation costs. Summary CHAPTER 1 .......................................................................................................................................... Introduction ........................................................................................................................................ 1 1.1 Aims and novelties ..................................................................................................................... 1 1.2 Mining impact and regulation: the Albanian case ..................................................................... 1 1.3 Issues related to processing tailings ........................................................................................... 3 1.4 Reuse and recycling ................................................................................................................... 8 CHAPTER 2 .......................................................................................................................................... The study area .................................................................................................................................. 11 2.1 Overview of the study area ...................................................................................................... 11 2.2 Geographic setting ................................................................................................................... 11 2.3 Geological setting .................................................................................................................... 13 2.4 Copper industry in Northern Albania ....................................................................................... 15 2.5 Environmental issues related to waste piles ............................................................................. 17 CHAPTER 3 .......................................................................................................................................... Effects of pyrite separation on the environmental impact of Cu-processing tailings: a case- study at Reps, Mirdita District, Albania ........................................................................................ 19 3.1 Quantitative Flowsheet approach to the tailing management .................................................. 19 3.2 Reps site ................................................................................................................................... 20 3.3 Materials and methods ............................................................................................................. 22 3.4 Results ...................................................................................................................................... 24 3.5 Heterogeneous features and Acid Drainage ............................................................................. 28 3.6 Quantitative Flowsheet: effects of single and double flotation ................................................ 30 3.7 Conclusions .............................................................................................................................. 32 CHAPTER 4 .......................................................................................................................................... Evaluation of heterogeneous sulfide – rich tailings as secondary raw materials. Reps case- study .................................................................................................................................................. 33 4.1 Pyrite market and potential tailing recycling market ............................................................... 33 4.2 Gravity separation applied to recycling ................................................................................... 34 4.3 Materials and methods ............................................................................................................. 34 4.4. Results ..................................................................................................................................... 36 4.5 Discussion ................................................................................................................................ 37 4.6 Conclusions .............................................................................................................................. 42 CHAPTER 5 .......................................................................................................................................... General conclusions ..................................................................................................................... 43 Acknowledgments ........................................................................................................................ 45 List of references .......................................................................................................................... 47 APPENDIX A ................................................................................................................................ 55 APPENDIX B ................................................................................................................................ 57 APPENDIX C ................................................................................................................................ 58 APPENDIX D ................................................................................................................................ 60 APPENDIX E ................................................................................................................................ 64 CHAPTER 1 Introduction 1.1 Aims and novelties The aim of this work is to provide a contribution to the characterization and management of tailing dumps. In particular, the overall study is meant to evaluate the separation of pyrite-rich fractions of tailings with either economic or environmental purposes. The project was focused on former mining districts of Northern Albania, where few mining activities are currently operative. This choice is motivated by the socio-political and economical transition that Albania is going through. The study takes shape from an overview of six dump sites, conducted in order to select target sites and materials. Among others, a tailing dump site of the Mirdita District was selected. In-situ and laboratory investigations were thus conducted with the following objectives: - To outline the main characters of the selected dumps, including the estimation