Università degli Studi di Milano Facoltà di Scienze Matematiche, Fisiche e Naturali Dipartimento di Scienze della Terra “Ardito Desio” Scuola di Dottorato “Terra, Ambiente e Biodiversità” Dottorato di Ricerca in Scienze della Terra Ciclo XXV – Raggruppamento disciplinare GEO/09 Chromite: from the mineral to the commodity PhD Thesis Maria Pedrotti Matr. N. R08693 Tutore Anno Accademico Coordinatore Prof. Giovanni Grieco 2011-2012 Prof. Elisabetta Erba A chi mi vuole bene, mi stima e crede in me Index Index CHAPTER 1: CHROMITE: HISTORY, GEOLOGY, USES AND REPORT OF CHROMIUM MARKET .... 1 1.1 INTRODUCTION ......................................................................................................................................................................... 1 1.2 HISTORY ...................................................................................................................................................................................... 1 1.3 GEOLOGY ................................................................................................................................................................................... 1 1.3.1 Mineralogy .......................................................................................................................................................................... 1 1.3.2 Chromite ore deposit types .............................................................................................................................................. 2 1.3.3 Stratiform chromite ........................................................................................................................................................... 3 1.3.4 Podiform chromite ............................................................................................................................................................ 4 1.4 DISTRIBUTION OF MAJOR CHROMITE DEPOSITS ................................................................................................................. 5 1.5 CHROMITE USES ......................................................................................................................................................................... 6 1.6 METALLURGICAL INDUSTRY ................................................................................................................................................... 7 1.6.1 High-carbon ferrochromium ........................................................................................................................................... 7 1.6.2 Low-carbon ferrochromium ............................................................................................................................................ 7 1.6.3 Steels .................................................................................................................................................................................... 7 1.6.4 Chromium metal ................................................................................................................................................................ 8 1.6.5 Nonferrous alloys .............................................................................................................................................................. 8 1.7 CHEMICAL INDUSTRY ............................................................................................................................................................... 9 1.7.1 Pigments .............................................................................................................................................................................. 9 1.7.2 Tannings .............................................................................................................................................................................. 9 1.7.3 Surface treatments ............................................................................................................................................................. 9 1.7 REFRACTORY INDUSTRY .......................................................................................................................................................... 9 1.7 FOUNDRY SAND ....................................................................................................................................................................... 10 1.8 REPORT ANALYSES FOR CHROMIUM MARKET ................................................................................................................... 10 CHAPTER 2: CHROMITE: ENRICHMENT PROCESSES ........................................................................... 13 2.1 MINERAL PROCESSING CONCEPT ......................................................................................................................................... 13 2.2 MINERAL PROCESSING METHODS ........................................................................................................................................ 14 2.3 CHROMITE ORE BENEFICIATION AND PROCESSING ........................................................................................................ 15 2.4 COMMINUTION ........................................................................................................................................................................ 15 2.4.1 Crushers ............................................................................................................................................................................ 16 2.4.2 Grinding mills................................................................................................................................................................... 16 2.5 GRAVITY CONCENTRATION .................................................................................................................................................. 17 2.5.1 Jigs ...................................................................................................................................................................................... 18 2.5.2 Spirals................................................................................................................................................................................. 18 2.5.2 Shaking tables ................................................................................................................................................................... 19 2.6 EFFICIENCY OF MINERAL PROCESSING OPERATIONS ...................................................................................................... 21 2.6.1 Liberation .......................................................................................................................................................................... 21 2.6.2 Concentration ................................................................................................................................................................... 22 CHAPTER 3: MADAGASCAR CHROMITE ORE DEPOSITS: STUDY AND SELECTION ....................... 25 3.1 INTRODUCTION ....................................................................................................................................................................... 25 3.2 GEOLOGY OF MADAGASCAR ................................................................................................................................................ 26 3.3 LOCAL GEOLOGY, TEXTURE AND MINERAL CHEMISTRY ................................................................................................ 28 3.3.1 Andriamena ...................................................................................................................................................................... 29 3.3.2 North Befandriana ........................................................................................................................................................... 30 3.3.3 North Toamasina ............................................................................................................................................................. 30 3.3.4 Antanimbary ..................................................................................................................................................................... 31 Index 3.3.5 North Belobaka ................................................................................................................................................................ 32 3.4 DISCUSSION .............................................................................................................................................................................. 33 3.5 CONCLUSIONS .......................................................................................................................................................................... 39 CHAPTER 4: EVALUATION OF GEOLOGICAL PARAMETERS AFFECTING CHROMITE ENRICHMENT PROCESSES ........................................................................................................................... 41 4.1 INTRODUCTION ....................................................................................................................................................................... 41 4.2 MATERIALS AND METHODS ................................................................................................................................................... 42 4.3 RESULTS