GRAVITY CIRCUIT Knelson Performance, Maintenance, Back to Basics Drissa ARAMA, Plant Manager
Morila Mine locality
Data for the record Commissioning Oct 2000 Official opening Feb 2001 First bullion bar poured was gravity gold Highest production record 1,052 koz in 2002 of which 337.4 koz was from gravity Average feed grade in 2002 14.14 g/t Plant upgrade 2004 Randgold took over Morila operation Management in Feb 2008
Metallurgical process Oxide Crusher SAG Mill Ball Mill Classification Thickening Sulphide Crusher Primary & Secondary Recycle Crusher Gravity Recovery BWI 16 kwh/t Throughput 520 tph Avail. 91.8 % Recovery Oxide 96 % Sulphide 92 % CIL Tailings 40% Elution Electrowinning 60% Gravity Gold CIL Gold
Metallurgy - process flow Oxide Gravity Gold 25.4% Oxide CIL Gold 95% Oxide overall Gold 96.6% Oxide Ore 10 g/t Sulphide Ore 4.3 g/t Crushing SAG & Ball Milling & Gravity Carbon in Leach & Elution Tailings Storage Facility Sulphide Gravity Gold 40% Sulphide CIL Gold 87.0% Sulphide overall Gold 92%
Metallurgy - Knelson concentration 3xKnelson Concentrator KC XD48 G5 cone 450 t/hr Crushed Slag NaCN Lime Table Feed Tank By-pass concentrate to ILR Reactor Feed Tank H 2 O 2 Reagent Pot Gemini Table Gold for direct smelting Sump Table middlings & tails Reactor Drum 250 kg/h
Key production statistics Parameters Design data After upgrade Throughput rate 400 tph 520 tph Monthly capacity 250,000 t 350,000 t Head grade - oxide ore 10 g/t Head grade - sulphide ore 4.3 g/t 3.1 g/t Gravity recovery 40% 40% Leach circuit recovery 87% 87% Overall recovery 92% 92%
Production overview Head Grade (Au, g/t) Total Gold Produced (kg) Total Gold Produced (ounce) Gravity Gold (%) Gravity Gold (kg) 2000 * 10.71 4,446 142,942 57.9 2,389 2001 7.44 19,647 631,650 39.05 7,643 2002 14.14 32,746 1,052,816 32.05 10,495 2003 7.98 24,750 795,716 34.16 8,453 2004 5.16 15,896 511,077 24.61 3,912 2005 5.75 20,252 651,117 25.61 5,187 2006 4.18 16,070 516,666 28.45 4,571 2007 3.88 13,991 449,817 21.27 2,975 2008 3.51 8,750 281,319 31.40 2,759
Recovery - Gravity vs Overall 60 95 50 40 30 20 93 91 89 10 2000 2001 2002 2003 2004 2005 2006 2007 Jan-08 Feb-08 Gravity recovery (%) Overall plant recovery (%) 87
BACK TO BASICS MAINTENANCE
Finding and remedial actions KNELSON OPERATION
Operation Knelson feed PARAMETRES PREVIOUS CURRENT Panel screen size Combination of 2.0 and 4.0 mm Panel 2.0 mm N o of cyclone U/F to gravity 03 02 (Targeting 03) N o of KC- on line 03 03 Screen Feed Channeling Spray bars (Water pressure) 20% short-cut in oversize due to eccentric feed 02 x separate bars; 10 % short-cut in oversize 10 % short-cut in oversize due to central feed Equalized pressure: 5 % short-cut in oversize Screen Capacity 3 cyclones to KC 2 cyclones (Planned to Install Double Deck Screen for more cyclone)
Operation steel balls scats in concentrate Chinese Ball! Impact Gold Recovery
Finding and remedial actions MAINTENANCE UNIT STATUS
Maintenance leaking water around holding bolts
Maintenance silt holes
Finding and remedial actions OPERATING PARAMETERS
Machine setpoints flow Parameter Concentration flow Intermediate flow - Low flow Purge flow Setpoint 160 120 USGPM 40 USGPM 200 USGPM Positive pressure 2 psia Incorrect fluidising water pressure = Poor recovery
Machine setpoints timers Parameter Feed off delay Drain time Purge time Positive pressure delay Setpoint 5 seconds 40 seconds 30 seconds 300 seconds Knelson total purge time reduced from 360 sec to 250 sec = increased Knelson running time
Machine setpoints pressure Parameter Operating pressure - Hi alarm Operating pressure - Hi shutdown Operating pressure - Lo alarm Operating pressure - Lo shutdown Setpoint 38 psia 44 psia 14.5 psia 13.8 psia*
Utilisation Utilisation takes motor-off flush time into account, but: Feed off delay = 5 sec Ramp down = 135 sec Drain #1 = 40 sec Purge = 30 sec Drain #2 = 40 sec Total = 250 seconds Then ideally, UTILISATION = ((3600-250)/3600)X100 = 93.05% Daily running time = 22.3hours
Other soft issues TURNED OVER New Engineering staff Alarmed override POOR SUPERVISION & SKILLS LEVEL Inspection/Cleaning Motivation COST SAVING Cone (Heart of the machines) leave for longer period TRAINING ON UNIT MAINTENANCE Back to Basics Reset all Set Points Re-effect passwords TRAINING ON UNIT OPERATION Back to Basics New Supervisor IMMEDIATE REPLACEMENT OF WEAR CONE Interlock between the mills and the Knelson
Performance GRG vs grade % 70 60 50 40 30 20 10 0 GRG (%) Theoritical GRG (%) Plant Head (Au, g/t) High Grade 16 14 12 10 8 6 4 2 0 Au, g/t
Performance GRG vs recovery 70 60 93 50 40 91 30 20 89 10 0 87 Gravity recovery (%) Overall recovery (%)
Basic maintenance LUBRICATION : Correctly and on schedule as per planned maintenance schedule Bearing caps need greasing every 2 days Rotary Union needs greasing every week Bearings need greasing every 6 months Do NOT grease these items randomly and all at once. Only grease them when the rotor is turning and bearings are warm SILT EJECTION HOLES : Check (daily) and clean WATER STRAINER : Check (weekly) and clean CONCENTRATING CONES : Remove and clean as required (regular) REPLACE CONE : as required
Best practice cones cleaning Concentrating cones Monthly concentrating cone schedule by the operation Engineering staff to check and confirm if the cone is cleaned before to reinstall it Regular measurement of the cone wear Cone cleaning process Cleaned concentrating cone
Constraints KNELSON UNITS LOCATED IN CONFINED PLACE WITHIN THE GOLD ROOM Arrange simpler access CONTROL PANEL IS A STAND ALONE UNIT Integrate to SCADA or SEPARATE PC
Conclusion In summary apart from having good Gravity recovery (2000-2003) the Morila Gravity Circuit performance dipped (2004-2008) as a result of: Poor Supervision and Control on the units Poor engineering and operation practice Maintenance not as per KNELSON recommendation New Engineering staff not familiar with the UNITS Lack of training Lack of regular communication between Morila mine and Knelson Gravity Solutions
Continuous improvement BACK TO BASICS Operation & Maintenance TRAINING MODULES for new personnel including refresher training Re-enforce supervision, Zero Tolerance to deviations Technical staff to conduct PTO s on KC units Initiate Auto Flush
Continuous improvement Ensure all SETTINGS are correct Investigate additional FEED to GRAVITY CIRCUIT Overall utilization > 82%, if not investigate Target more >35% GRAVITY RECOVERY
Merci Beaucoup