Gravity Circuit Project (Apr Jul 2008)

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1 Gravity Circuit Project (Apr Jul 2008) Summary The recent focus on the gravity circuit has resulted in an increase in gravity recovery and improved circuit availability. The main reasons for these improvements include; Increased knelson efficiency by installing a new knelson bowl Installation of high tensile bolts for the scalping screen motors Regular inspections of the gravity circuit and knelson bowl cleaning Gravity recovery is highly dependant on the circuit availability and as there is a relationship between gravity recovery and the CIL residue grade it is important to maintain high availability. Therefore regular inspections of the circuit and monitoring of availability must continue to happen and any circuit issues must be addressed as soon as possible. It has been shown that if the circuit can consistently run at >90% availability gravity recoveries above 10% are achievable. Main Works Completed A new G5 knelson bowl was installed in KC2 on the 8 th of May to replace the existing flex flo bowl. When the flex flo bowl was inspected it was found that the top strips were missing and that several holding bolts for the bowl were also missing. This meant that the bowl would not have been fluidising and flushing correctly during operation and the efficiency would have been low. This was illustrated in gravity recovery from April to May (Figure 2) where the overall circuit availability was similar however the gravity recovery was much improved. High tensile bolts for the scalping screen motors were installed in late June. After an initial problem of the bolts coming loose on scalping screen 2 these bolts have performed well and the availability of the scalping screens is greatly improved. This is the main reason for the increase in gravity circuit availability during July as indicated in Figures 2 & 3. Daily and weekly inspection checklists for the gravity circuit were made for the plant met to monitor the circuit performance and availability. These checklists are located in Metallurgy 2:\Log sheet\kc. Regular inspections need to be continued to ensure that the focus on the circuit s availability and overall recovery continues. Of particular importance is monitoring the knelson s bowl pressures, scalping screen condition and also a weekly inspection of the bowls interior. The pinch valve for KC1 was found to be closing too slowly which meant that the gravity cyclone underflow box would regularly overflow. The rate at which this valve closed was sped up to stop this overflow issue. New lids and locks have been installed on both Knelsons to replace the corroded old ones. This will allow better security and also allow the plant met better access to inspect the interior of the knelson bowls. Fluidization and silt holes on the knelson bowls have been cleaned numerous times and this will need to continue to be done on a routine basis (ideally every 2 weeks). The fluidising water filters and seals were replaced on both Knelsons. Several surveys were done to assess the performance of the acacia reactor. Cyanide levels, ph, leach curves and overall recoveries were investigated. Overall the operating conditions were good with recoveries being >98%. Acacia reactor solution diffusion screen was cleaned.

2 Gravity Circuit Performance Figure 1 highlights the improvement in gravity recovery in May July in comparison to previous months. The main reasons for this improvements include; The installation of the new bowl in KC2, as mentioned earlier Regular inspections of circuit and cleaning of knelson bowls Improved availability of gravity circuit, in particular the scalping screens Figure 1 also highlights the relationship between the CIL residue grade and gravity recovery over the last 12 months. Thus, it is important to get the highest gravity recovery possible. Figure 1 Gravity Recovery vs CIL Residue Grade 9.0% % 5.0% 3.0% Gravity Recovery CIL Residue Grade CIL Residue Grade (g/t) 1.0% 0.1 Jun 07 Jul 07 Aug 07 Sep 07 Oct 07 Nov 07Dec 07 Jan 08 Feb 08 Mar 08 Apr 08 May 08 Jun 08 Jul 08 0 Figure 2 shows the relationship between gravity recovery and circuit availability for Apr July 08. Two things are highlighted here. Firstly, the improvement from Apr to May resulted from increased knelson efficiency due to the new bowl being installed, as the circuit availability was the same for both months. Secondly, from May July the gravity recovery is strongly correlated to the circuit availability. During June a Knelson was offline for the majority of the month due to the scalping screen not being available. Thus the gravity recovery dropped significantly. When the new high tensile bolts for the screen motor were installed availability increased during July resulting in the increase in gravity recovery. Figure 2. Gravity Recovery vs Circuit Availability 9.0% % 5.0% 3.0% 1.0% Gravity Reco very Circuit A vailability Circuit Availability (%) Apr 08 May 08 Jun 08 Jul 08 4

3 A closer look at the relationship between gravity recovery and circuit availability (after the new bowl was installed) shows the potential gravity recovery if high circuit availability is maintained. Figure 3 shows that when the availability is consistently above 90% the gravity recovery is above 8% and often well above 10%. Figure 3. Gravity Recovery vs Circuit Availability 100% 90% 80% Circuit A vailability Gravity Reco very Circuit Availability (%) 70% 60% 50% 40% 30% 20% 10% % 1 May 8 May 15 May 22 May 29 May 5 Jun 12 Jun 19 Jun 26 Jun 3 Jul 10 Jul 17 Jul 24 Jul 31 Jul * Availability refers to downtime for the gravity circuit only and does not account for downtime caused by the whole plant being down Ongoing Issues The gravity circuit availability is dependant on having two High Pressure water pumps running to ensure that there is sufficient water to stop the scalping screen discharge chute from choking. Currently Pumps 650 and 680 are running but the spare pump 649 is not operable. Once the parts arrive for this pump it should be repaired so that there is some redundancy when pump 650 or 680 are down. The 4mm x 4mm scalping screen panels that Godwin ordered have arrived onsite and should be installed at the next available time to eliminate the coarser material that goes to the acacia reactor. The next mill shutdown would probably be the best time for this. Circuit Spares 2 x new rotary unions were ordered and are now onsite as spares as there were previously none onsite. Attached below is a list of some of the major spare items for the gravity circuit. Current items on order are; 2 x Spare G5 Knelson bowls 4 x Deflector pads for the Knelson bowls Tim Fielding Senior Metallurgist AngloGold Ashanti

4 Appendix A. Gravity Circuit Spares Equipment Item Item Code Item Description Current Stock On Order Scalping Screens Screen Panels Screen panel type being changed, new stock ordered 4mm x 4mm appature 65 Screen Motors 5192 MOTOR, VIBRATOR, 7.5KW IN,,6KW OUT, 50HZ, CLASS F, IP66, CENTRICAL FORCE 85 MODEL MSV1 10/9000/S90 ITALVIBRAS G.SILINGARDI Screen Motor Bolts Not a current stock item, Bolts to be added as store stock item if they perform ok 40 0 Screen Feed & Bypass Valves 8199 BLADE, GATE KNIFE TYPE 8'',LARKSON, 7490 SUIT CLARKSON KDG8 AC N2V2Z/N2S3Z VALVE 5 1 Knelson G5 Knelson Bowl WEAR CONE 300 TPH XD Concentrators UNC Cone Holding Bolts 1422 BOLT, HEXAGON HEAD STAINLESSS,TEEL GRADE 316 UNC SERIES 5/8IN DIA X 1 1/2IN LG C/W LOCKWASHER 7 Deflector Pad 1436 DEFLECTOR PAD, ROTOR KNELSON, Bowl Cleaning Tool 1417 Rotary Union Assembly 1418 Bearing Lower 1405 Bearing Deflector Lower 1406 Bearing Upper 1407 Bearing Deflector Upper 1408 Drive Belt 1409 Fluidising Water Filter Screen 1410 FLUIDISATION HOLE PROBE, C/W 2,BITS MACHINE #1 S/NO. XD AUTO PIPING S/NO. XD48AP MACHINE #2 S/NO. XD AUTO PIPING S/NO. XD48AP UNION, ROTARY ROTOR ASSEMBLYM,ACHINE #1 S/NO. XD ROTOR S/NO. XD48R MACHINE #2 S/NO. XD ROTOR S/NO. BEARING UNIT, ROLLER PILLOW B,LOCK LOWER, FREE ROTOR ASSEMBLY MACHINE #1 S/NO. DEFLECTOR, DIRT & LIQUID FLING,ER LOWER BEARING ROTOR ASSEMBLY MACHINE #1 S/NO. BEARING UNIT, ROLLER PILLOW B,LOCK UPPER, FIXED ROTOR ASSEMBLY MACHINE #1 S/NO. DEFLECTOR, DIRT & LIQUID FLING,ER UPPER BEARING ROTOR ASSEMBLY MACHINE #1 S/NO BELT, FLAT HIGH TORQUE DRIVEH,TD M MACHINE #1 S/NO.XD CONC CONE S/NO. XD48G MACHINE #2S/NO. XD CONC CONE S/NO. XD48G FILTER, SCREEN, PARTICLE SIZIN,G FILTER 30 MESH, KNELSON, 74351, MACHINE #1 S/NO. XD AUTO PIPING S/NO. XD48AP MACHINE #2 S/NO. XD AUTO PIPING S/NO. XD48AP Fluidising Water Filter Collar 9055 COLLAR, FILTER SCREEN KC XD48,WATER FILTER 6 0

5 Fluidising Water Filter Upper Gland Fluidising Water Filter Spin Plate Fluidising Water Control Valve 5215 GLAND, UPPER RUBBER WATER F,ILTER MACHINE #1 S/NO. XD AUTO PIPING S/NO. XD48AP MACHINE #2 S/NO. XD AUTO PIPING S/NO. XD48AP PLATE, FILTER SPIN MACHINE #,1 S/NO. XD AUTO PIPING S/NO. XD48AP MACHINE #2 S/NO. XD AUTO PIPING S/NO. XD48AP VALVE, CONTROL C/W I/P ACTUA,TOR & POSITIONER NELESNE7295/US Fluidising Water Flowmeter 5214 METER, FLOW YOKOGAWA AE210MN, ART LSA1DH 1 0