Karowe Comminution Circuit Upgrade P. Morgan 1 , L. van Niekerk 1 , M. Duddy 1 , G. Underwood 2 and A. Paz 3 1. DRA Global, Johannesburg, No. 3 Inyanga Close, Sunninghill, 2157, South Africa, [email protected], [email protected], [email protected] 2. Minopex, 7 Pinswood Office Park, 33 Riley Rd, Woodmead, 2196, [email protected] 3. Outotec Australia, 40 Kings Park Road, 6005 WA West Perth, Australia, [email protected] Boteti are due to begin treating the significantly more competent (Unit13) kimberlites at their Karowe Diamond plant, Botswana & wish to continue with AG milling as the “heart” of their process flow sheet. Aim: – Assess current performance of the AG mill; – Assess impact of treating harder kimberlites & increased throughput in the new/modified flowsheet; – A Turbo-Pulp Lifter (TPL TM ) system is anticipated to improve upon the original mill grate/pan lifter operation. Interpreted Abrasion Factor, t a Interpreted ta 13 FK S2 S1 y = 2.4x -1 Apparent Dwi (kW/m 3 ) Observed Relative Grinding Rates Relative Grinding Rates & DWi Relationship Relative Hardness (Energy Basis) 13 S1 S2 FK U1 SL New Circuit Design • Outotec will provide their innovative Turbo Pulp Lifter (TPL TM ) system to improve the discharge & grate efficiency; • Two TPL™ designs will be incorporated: • 90mm pebble ports for treatment of fragmented kimberlites (FK); • 115mm pebble ports for hard kimberlites (Unit 13), early 2015. Turbo-Pulp Lifter (TPL™) • DRA used an ‘in-house’ modelling tool to compare against Outotec’s JKSimMet to assess the proposed circuit; • Two surveys (S1 & S2) indicated that grate ports were ‘clogging up’ & pan lifters were ‘retaining material’ that should escape the mill; • Minerals being processed: • Unusually hard for a kimberlite; • Very abrasive, high DMS yields; • Have high crushing strength; • Low amenability to scrubbing; • Large degree of variability (soft sandstones & weathered kimberlites, to more competent kimberlites, mudstones & basalts). • Using this relationship it was possible to simulate the mill-crusher circuit performance when ‘treating’ the harder ores; • Initial design trial simulations indicated that partial pre-crushing, modified grate design & bypass screening was necessary to control the mill overloading; • Less fines were going to be produced, potentially overloading the existing DMS circuit; • High DMS yields are also anticipated on harder ores. Simulation Results Circuit Benefits Back- ground Weathered & soft Bulk Sample Milling plant sampling audit 2 Milling plant sampling audit 1 Fragmented Kimberlite Unit 13 Hard Kimberlite Deeper material is more competent • The fully- autogenous mill: offers flexibility for high variability in the ore; combines crushing & scrubbing steps; • A secondary gyratory crusher will crush a proportion of jaw crusher product for a consistent feed to the AG mill; • Mill discharge screen recycles +60mm directly & combines with -60mm+32mm LDR tails to the existing pebble crusher; • Pebble crusher product can be partially split to bypass mill recycle; • XRT bulk sorting for Large Diamond Recovery (LDR); • -8mm+1.5mm fraction will be treated in the existing DMS; • TPL™ for improved mill capacity & efficiency. Benchmarking showed that the mill would receive material significantly harder in the future (Unit 13) than seen in the past (S1 & S2). Good Attrition Good Impact Slurry Pool Poor Impact Improper Attrition Turbo Pulp Lifter™ Radial Pulp Lifter Sample Population Dwi (kW/m 3 ) Karowe Drop Weight Testwork SMC Karowe Data PopulationDistributionModel FK 13 S2 S1 A significant degree of hardness variation is shown, that prescribes virtually the complete spectrum of DWi values. Published DWi database distribution superimposed PEBBLE CRUSHER MILL FEED STOCKPILE MILL FEED PRE-CRUSHER EXISTING MILL +60mm +1.5x60mm FINES DMS JAW CRUSHER -1.5mm LARGE DIAMOND RECOVERY (LDR) LARGE DIAMOND RECOVERY (LDR) CONCENTRATE PEBBLE BLEED SPLITTER - 32mm +32x60mm +20x32mm LARGE DIAMOND RECOVERY (LDR) MIDDLES BULK SORTER LARGE DIAMOND RECOVERY (LDR) FINES BULK SORTER -20mm +1.5x8mm TERTIARY CRUSHER and DEWATERING +8x14mm +14x32mm 1 7 8 14 15 16 17 12 20 18 +8x60mm 19 4 2 5 6 9 10 11 13 ROM FEED THICKENER FEED GRITS TAILS RECOVERY FEED CONCENTRATE Current Circuit Constraints (-8mm) Legend: T = Tails C = Concentrate T T C C +32mm +1.25x8mm -1.25mm +1.25x8mm BLEED SCREENING T C