Lace Diamond Mine DMS Commissioning

Transcription

1 Lace Diamond Mine DMS Commissioning Derek Lahee Consulmet (Pty) Limited ABSTRACT This paper addresses the Lace Diamond Mine 100tph Fines DMS and 65tph Coarse DMS commissioning. Emphasis has been placed on practical applications versus previous published papers, specifically Hendriena van der Walt and Dr. Kurt Petersen s DMS CYCLONE SIZE VS. CYCLONE EFFICIENCY: THE DE BEERS PERSPECTIVE, and current industry trends. This paper is based on practical experience during operating and commissioning and the observations are open to debate. 1. INTRODUCTION Lace Diamond Mine Phase 1 processing plant was commissioned in August and September The Phase 1 scope was designed for kimberlite tailings re-treatment and the Phase 2 expansion will include for treatment of competent kimberlite from the open pit. The following process difficulties were expected and addressed in the design: 1. Extremely weathered kimberlite tailings with high clay content, therefore feed preparation was a priority. 2. Water recovery: Extensive testwork was done until a flocculent and coagulant was selected for ideal water recovery and clarity conditions. 3. Fine Diamond Recovery was critical due to the nature of the deposit (kimberlite tailings) and the stone size distribution curve, therefore: Importance of DMS Efficiency Re-crush Efficiency Final Recovery Efficiency We will be concentrating on the DMS aspect of the plant.

2 Process Flow Block Diagram 220 TPH ROM VIBRATING GRIZZLY 15 TPH +100MM 205 TPH -100MM SCRUBBER 1 & DOUBLE SKIN TROMMEL 4 TPH +100MM 143 TPH MM 198 TPH MM SCRUBBER 2 & PRIMARY SCREEN 100 TPH DMS FEED 100TPH FINES DMS MM 65 TPH DMS FEED 65TPH COARSE DMS MM 1 TPH SINKS 63 TPH FLOATS 2 TPH SINKS 2 TPH +28MM 3 TPH SINKS 97 TPH -6MM FLOATS COARSE STOCKPILE FINAL RECOVERY (GREASE) FLOATS STOCKPILE 45 TPH -28+6MM 55 TPH -6+1MM 108 TPH FEED RECRUSH (WF CONE CRUSHER) 58 TPH -1MM 31 TPH -1MM 1 TPH -1MM 1 TPH -1MM 8 TPH -1MM 99 TPH -1MM EFFLUENT THICKENER CIRCUIT LACE DIAMOND MINE 220 TPH KIMBERLITE BLOCK FLOW DIAGRAM (PTY) LTD CONSULMET 2. LACE DMS PROCESS The mass balance indicated a 100tph Fines (-8+1.0mm) DMS requirement and 65tph Coarse (-28+8mm) DMS requirement. The Consulmet Standard 100tph module has 2-off 420mm cyclones and the 65tph has a 510mm cyclone. Process bottlenecking was anticipated on the -8+1mm fraction with the 65tph Coarse DMS having a high probability of under-utilisation. A by-pass was designed into the fines bin, enabling feed to the 510mm cyclone plant.

3 DMS Feed Surge Bin This process requirement allowed us the luxury to compare fines recovery efficiencies from both the 420mm cyclones and the 510mm cyclone. DMS Parameters 100tph DMS 65tph DMS Cyclone Feed Pressure 185kPa (17D) 170kPa (13D) C.M. Density FeSi 270D 270D Our general rule of thumb on FeSi selection is as follows: Cyclone 200mm 250mm 300mm 350mm 420mm 510mm 620mm FeSi Cyclone 60 Cyclone D 270D 270D 270D 150D 100D Finer FeSi Coarse FeSi

4 The client requested, if possible, 1-off FeSi selection. From experience, we have had major stability problems using 150D on 420mm cyclones; therefore we selected 270D for both plants, and monitored the viscosity closely on the 510mm plant. The 270D proved to be suitable, in this process case, for the 510 plant. One must take into account the very clean, competent material feed into the DMS due to good feed preparation. Preliminary Tracer Test Results: 2mm tracers were used. Plant D50 EPM 2 x 420mm mm ACTUAL RESULTS We were able to run -8+1mm through the 510mm cyclone for extended periods of time (48 hours +) during commissioning, with two important observations: 1. Diamond recovery (grade in cpht) remained consistent. 2. Diamond size distribution remained consistent. This is important in this case as there were large amounts of mm stones. Actual stone count remained consistent whether feeding through the 420mm cyclones or the 510 cyclone. 4. OBSERVATIONS 1. Y shaped pulp distributor Our 420mm cyclone circuit was considerably improved by the introduction of a Multotec Y shaped pulp distributor. We were the first company to install the prototype and it is a significant development with regard to feed of multiple cyclones. We have had considerable problems with T shaped distributors in the past. These problems have included turbulence, high wear and unequal distribution to the cyclones.

5 Y-shaped Distributor The disadvantage of the unit is the relative large size of the distributor and high cost as compared to a conventional distributor, but the process benefits are significant: Turbulence is eliminated Wear is eliminated Significantly stable inlet pressures Equal distribution to cyclones Although the unit is large, the design allows for reductions in platework on the overflow and underflow chute work. We would recommend this unit for all future applications of a similar nature.

6 100tph DMS and 65tph DMS Modules 2. Correct Medium Densification vs Dilute Medium Densification Due to plant layout requirements becoming more compact and movable, Correct Medium (CM) densification with tube densifiers has increasingly become a standard. Consulmet, during numerous plant audits over the last two years, has noticed a trend where clients with Correct Medium tube densification circuits have had problems with medium viscosity. In the past, where Bottom Cut-off Size has been higher ( 1.6mm), this has not had any major impact. With BC0S s dropping to 1.2mm, 1.0mm and even 0.8mm, this viscosity is causing recovery problems. One has to look at the old DMS plants from the 1960 s and early 1970 s to see correct medium tube densifiers installed on DMS modules. Dilute Medium (DM) Densification was subsequently introduced for a reason.

7 From our point of view and practical experience, there is no question that the medium quality provided by a DM circuit is better than a correct medium circuit. With regard to modular, mobile DMS units for alluvial diamond deposits, CM densification is still the way to go for practical purposes. If the DMS unit is to be installed into a permanent location, we would recommend DM densification. This observation was highlighted because the viscosity sensitivity has been particularly evident in 420mm cyclones on various plants. 3. Breakaway Size-Practical Overview We feel that breakaway size is highly dependent on various factors including particle feed size range and FeSi selection and quality with regard to viscosity and stability. A recent plant audit on 2-off 610mm cyclone plants (Fines and Coarse) found the following: ROM throughput and power problems caused the decommissioning of the Fines DMS Module. In conjunction with this the client had dropped the BC0S from the original specification of 1.6mm to 0.8mm. The client had noticed a drop in recovery of up to 10% following the above changes. The plant audit found the following: Entire size range ( mm) through a 610mm cyclone 270D FeSi on the 610mm cyclone. Density differentials indicated viscosity issues Worn vortex finder. A tracer test showed the following anomaly (Highlighted in red below), although still producing a good tromp curve:

8 Tromp Curve Data Sheet 4mm SG No. Added No. in sinks No. in floats Total No.lost % in sinks Cyclone Pressure Kpa Cyclone Size (m) 0.63 Density 2.65 D Achieved D Required % Variance G 9.81 Colour SG % in sinks SG = Cut point Black SG Lime SG Yellow EP value Lilac Blue Buff Green Olive Cinnamon Brown Pink Orange

9 TROMP CURVE 4mm (Density = 2.65 Pressure = 300Kpa) % IN SINKS DENSITY The Fines DMS was recommissioned and the mm classified into mm and mm; The FeSi was changed to 150D; The vortex finder was replaced. Unfortunately all three changes were made at once, but recovery improved by 10%. It is of our opinion that if particle size range differential is kept to a minimum and the FeSi specified not only to the size of the cyclone but to the quality of the feed material, breakaway size as per the Multotec chart is not as critical. A larger diameter cyclone can thus be selected for smaller size fractions.

10 5. CONCLUDING REMARKS 1. Following on H van der Walt and Dr K Petersen s paper DMS CYCLONE SIZE vs CYCLONE FFICIENCY, we have had the opportunity to prove that a 510mm cyclone, under the correct operating parameters, can produce equal or better recoveries as compared to a 420mm cyclone. The same will probably apply to cyclones with a larger diameter than the 510mm cyclone. 2. From our experience in the field, we have found the 420mm cyclone to be more sensitive to operating parameters than the 510mm cyclone. 6. REFERENCES 1. H van der Walt and Dr K Petersen s paper DMS CYCLONE SIZE vs CYCLONE FFICIENCY: THE DE BEERS PERSPECTIVE 2. Multotec Cyclone Division D T Lahee May 2008