Luanshya Report by Ramoutar Seecharran (Ken) September 2009
LUANSHYA’s RECOMMENDATIONS A visit was made made to Luanshya concentrator concentrator in September 2009. 2009. Observations were made. The author has 16 years experience in the Luanshya plant, 6 years in a senior position, in i n charge of operations and maintenance. maintenance. These recommendations recommendations are based on those observations made and the author’s knowledge of the mine. The synergies derived can be replicated at the Chambishi mine, wherever possible, for the enhanced profitability and efficiency of the group.
RECOMMENDATIONS 1. The installation of a regrind mill should be seriously considered. considered . Regrinding of copper rougher concentrate prior to cleaning will have a three-fold effect, namely: The concentrate will be of a higher grade, approximately 29-31% Cu is anticipated. Entrained cobalt in copper concentrate will be minimized. Most smelters do not pay for cobalt content of copper concentrate, as the contained cobalt is lost in slag. And, Referring to Figure 1, does a plant always strive to operate at the optimum profitability point? Assuming it was budgeted to operate at a concentrate grade of 30% Cu but during a part of the period the plant operated at (<30%). Do plant operators compensate by operating at (>30%) for the remainder of the period so that on average a grade of 30% is achieved. If so, a loss of revenue is incurred during both scenarios. It is best to operate in the oval area. This gives a factor of safety to plant operators. Regrinding of rougher concentrate before final cleaning will guarantee operating in the oval area. A regrind mill is available on on the property, it needs needs refurbishing and and pipe work installation to be able to carry out this function.
REVENUE vs GRADE
Figure 1: Revenue vs Concentrate grade
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u C 31.5 % 31 ( E 30.5 D A 30 R G 29.5 S 29 N O 28.5 C 28 1. 2
1. 25
1. 3
1. 35
REVENUE ($/lb)
2
1. 4
1. 45
2. Utilising forged grinding balls as opposed to cast balls will be more economical. The forging process compresses and strengthens the grinding ball. Very often, a poorly cast ball can end up being porous on the inside, Figure 2. The lines of stress travel from one void to another and such a ball shatters prematurely when compressed in the mill, Figure 3! A shattered ball does not have the kinetic energy to break rock and it sits in the mill taking up useful space and consuming power! If cast balls are to be used, and they are to be sourced from within Zambia, then Zamchin is the best manufacturer in the country. Crasters from Zimbabwe must be avoided at all cost; they produce the most inferior balls. The Chinese forged balls manufacturers are quite consistent in quality, Table 1. If the combined buying power of Luanshya and Chambishi is used as leverage, a more favourable price might be negotiated. THE RULE OF THUMB IN CHOOSING A MILL BALL IS HARDNESS; CHOOSE A BALL WITH ROCKWELL HARDNESS (H RC) IN EXCESS OF 55 OR A BRINELL HARDNESS (H BN) IN EXCESS OF 450. The forging process changes the ball’s microstructure from that resembling pearlitic to martensitic. Compacting the grain structure in the process and densifying the ball at the same time. We then get a ball of uniform hardness, unlike a cast ball which is much softer in the centre, Figure 4.
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Figure 2: Section of a poorly cast mill ball
Figure 3: Shattered mill ball
BRINELL HARDNESS ACROSS BALL
500 450 400 350 300 250 200 150 100 50 0 1
2
3
4
5
6
7
Figure 4: Hardness across a cast mill ball
4
8
Table 1: List of popular mill ball manufacturers, those shaded green are acceptable manufacturers and should be pursued
3. Star rotors on flotation machines should be rotated every year. This will prolong the life of the rotor and even out wear, guaranteeing cell dynamics over a longer period of time. 4. A feed well must be installed in the Baluba and Luanshya 250’ thickeners. Figure 5. The need for this will become evident in the cold season. Pulp entering the thickener could be about 28 o Celsius while ambient temperature at 0300 hours might be as low as 3 degrees. This will set up a convectional circulation in the thickeners and it will bring slimes to the surface, they will then “short circuit” towards the overflow launder, leading to a dirty supernatant overflow. This is often reported by the plant operators as a “SLIMING THICKENER”. A feed well will ensure that the feed solids is fed below the teeter zone, which will act as a filter, and prevent fine slimes from rising to the surface. Conveyor belting bolted to a steel ring can be used.
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Figure 5: Proposed feed well installation on Baluba and Luanshya 250’ tailings thickeners 5. Workers must be sensitized to cost and the cost of production every minute of the day. It is advisable that popular items and their costs be displayed at prominent points so that the workforce can get an understanding of the cost, eg safety boots, 1 kg of grease, a loader tyre. A litre of diesel etc. Production cost in ¢/lb must be displayed at prominent points as and when they are updated. 6. A rapid response team should be found in every section of the company in order to safeguard lives, curtail injuries and protect the company’s assets in the event of an emergency such as fire, flooding, chemical spills, sabotage etc. Such team should hold regular practice sessions and drills. Any member, who misses two consecutive practice sessions, should be replaced. Every member of the team should be paid a bonus to motivate them. They should all be familiar with the geography of their section, the areas posing hazards, emergency switches and isolating valves, emergency telephones etc. 7. The use of synthetic oils in underground loaders must be implemented. They can withstand overheating better than mineral oils. The poor ventilation conditions underground make them susceptible to overheating and subsequent engine seizures. 8. Wherever possible, froth pipes should be changed to open launders. An open launder allows the froth to aerate, Figure 6, so when it enters a pump box, there is no overflowing and pumping efficiency improves. In addition, an open launder provides a gentler flow into the sump and minimises additional air entrainment from a high velocity downward cascade. When overflowing occurs, plant operators instinctively slow down the flotation cells; this leads to a reduction in copper and cobalt recoveries. 6
Figure 6: Open froth launder, allows aeration of froth 9. The use of High Density Poly Ethylene (HDPE) pipes instead of steel pipes for slurry handling applications should be pursued, Figure 7. HDPE pipes have six major advantages, namely: They are cheaper than steel pipes They are easier to fabricate than steel pipes, thermal welding is used, Figure 8. Joining plastic pipes is much faster than arc welding of steel pipes Skilled boilermakers are not required for their fabrication The risk of accidents is greatly reduced Expensive welding rods and gaskets are not required They are highly versatile and can be welded into a shape which a metal pipe cannot be fabricated into, Figure 9.
Figure 7: HDPE pipe used for slurry handling 7
Figure 8: Thermal welding of HDPE pipe
Figure 9: 13 pieces of plastic welded into a triple bend 10.Lime and cyanide, used for cobalt depression, should be added to the feed end of the mills, and not the discharge end, the reasons being: The minerals need to be “coated” with cyanide and lime as soon as they are broken in order to enhance the effect of depression, and
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Using lime in the grinding circuit reduces mill balls and liners consumption. The chemistry being, MOST OF THE IRON IS DISSOLVED AS IRON HYDROXIDE, THIS IN TURN, INTRODUCES HYDROGEN INTO THE PULP FROM THE DECOMPOSITION OF WATER AS HYDROXIDE IS FORMED. PULP ACIDITY, AND ULTIMATELY METAL CONSUMPTION, IS INCREASED FURTHER. The problem is exacerbated when grinding in a pulp of pH below 5.5. 11. A culture of good housekeeping must become an essential part of life in the flotation plant. Spillage, if not immediately cleaned up, starts tarnishing. A tarnished sulphide mineral particle is slower to float and stands a greater chance of reporting as tailings, leading to copper and cobalt losses! 12. The mine should aim to operate between $1.5 and $2.0 per pound of copper produced after cobalt credit. The clear patch shown in the 5-year copper price chart, Figure 10. For a production cost lower than this, a bonus could be paid to everyone employed at the mine; the mechanism of such a bonus will need further calculations. Cobalt credit in the range of $15.00 - $18.00/lb should be used in financial modelling. The clear patch in Figure 11. 13. Reprocessing of 14 Shaft’s surface waste should be seriously considered, Appendix I. This will constitute a variable cost and should be very profitable. Blockage of the tails race has been a regular problem in the past, especially since the closure of the Luanshya concentrator, it is believed that the reduced throughput does not provide enough transport velocity to keep the tailings particles in suspension and sedimentation rapidly follows, especially during periods when the grind coarsens, and plant throughput is reduced. The reprocessing of 14 Shaft’s surface waste will alleviate this problem and utilize the excess capacity available in the plant. The increased throughput through the plant will make the flow of tailings in the “tails race” easier.
Figure 10 5-year copper price chart, clear patch denotes target 9
Figure 11: 4-year cobalt price chart, clear patch indicates selling price to be used in financial modelling 14. It is cheaper to crush than to mill ore. As a result, the crushing plant must produce the finest product which will not restrict throughput. In so doing: Milling rate will increase Grinding media consumption will reduce, and Milling power consumption will also reduce The last two items comprising the most expensive part of the grinding process. 15. Good environmental stewardship must be on the mind of every employee at the mine at all times. Luanshya is the last of the Copperbelt mine along the Kafue River’s catchment area and the unpolluted integrity of the river, Figure 12, must be maintained.
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Figure 12: The Kafue River in the vicinity of Luanshya 16. Multiskilling of operators must continue throughout the year. This will allow plant management to: Select the best operators for a particular section, leading to improved plant efficiency and encourage a culture of continuous improvement Assist in the smooth running of the plant during periods of absenteeism, illness or leave, compassionate or planned. 17. A culture of zero tolerance must pervade the entire mine. Thefts, dishonesty, alcoholism, drug abuse and similar misdemeanors should not be tolerated! 18. Depending on the price of cobalt, a special section in the mine can be set up to extract cobalt ore from the closed (back) draw points if the economics make it feasible. This must be kept separate from normal operations, or else, mine grade will drop. At Baluba, it is common for cobalt mineralization to extend about 1.5m into the hanging and foot walls beyond the copper contact, Figure 13. Here again, extracting and processing such material constitutes a variable cost component, as the fixed costs have already been incurred.
Figure 13: Sketch showing extension of cobalt mineralization into hanging and foot walls of the Baluba orebody 19. Managers in all Departments must be proactive about safety and lead from the front. They must personally conduct the Departmental safety audits. 20. All managers must develop a culture of continuous improvement and must inculcate such attributes in their subordinates. Targets set and achievements must be reported in their monthly reports. 21. To encourage the workers to think of continuous improvement, a suggestion scheme should be introduced. 25% of the anticipated annual savings should be paid to the worker who promoted the suggestion, at a well-publicised public event. 22. One crusher, and its ancillary equipment (oil pump, screen, grizzley, 11
electrics etc.), is to be maintained each day of the week . There are five crushers installed, two Standards and three Short heads. This will ensure that the crushers are in perfect condition to execute Item 14 above. Being a job that is carried out every week on similar equipment, the quality of workmanship and the time of carrying out such tasks, will improve with time as mechanical proficiency improves. 23. A froth ring should be installed in the concentrate thickeners Figure 14, to prevent froth reporting to the settling ponds, Figure 15. The method involved is very simple, Figure 16. This froth ring should be concentric with the overflow launder of the thickener. At the best of times, settlement in the settling ponds in inefficient, and if material does settle there, Copper and Cobalt could be tied up for as long as three months, affecting cash flow. When the ponds are excavated and the wet concentrate is drying in the sun, it acts as a bait for thieves! In the past, thieves have been known to set up camp on the old tailings dam, opposite the concentrate drying pad, just waiting for an opportune time to pounce!
Figure 14: Froth ring required in concentrate thickeners
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Figure 15: Concentrate thickener without froth ring
Figure 16: Installation of froth retaining ring on concentrate thickener 24. Operators should be trained to recognise the copper and cobalt minerals. The sheen and texture of the froth can be used as a guide. Based on this knowledge, they should then be taught how to cut the froth layer to maximize copper to copper concentrate and cobalt to cobalt concentrate. Figure 17.
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Figure 17: Methodology of cutting flotation froth
ACKNOWLEDGEMENTS The author wishes to express profound gratitude to the management and staff of CNMC Luanshya for offering him the opportunity to conduct this study. The hospitality was heartening and made the homecoming a warm and memorable one. The support of Mauritanian Copper Mines for making this trip possible at such short notice is also acknowledged. It is hoped that the links established will enhance the entente cordiale between the two companies to enhance their efforts in efficiency enhancement.
RAMOUTAR SEECHARRAN Plant Superintendent
APPENDIX I SUPPLEMENTING PLANT FEED WITH SURFACE WASTE
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This report, explains in details the costing and logistical implications which were involved in treating waste rock from 14 Shaft and it contains proposals for utilizing excess plant capacity to continue the exercise. SINCE THIS PRACTICE CONSTITUTES A VARIABLE COST COMPONENT, IT WILL HELP IN DILUTING THE EFFECTS OF FIXED COSTS, AND MAKE THE OPERATION MORE PROFITABLE. In addition, taking up the surges in tonnage supply from the mine will guarantee better plant control. 1: Assumptions:
The plant will process up to 3 000 tonnes of waste per day, working 24 hours per day, this equates to 10 trucks of 15 tonnes capacity per hour. Tipping of the ore will be done on the Cable Belt transfer conveyor, TB1, feed end. Tipping will be carried out North and South, thus allowing two trucks to tip simultaneously, in a safe manner.
Figure 18: TB1 conveyor, waste to be dumped at tail end
Loading of trucks will take place at two points on the waste dump, this well ease congestion, and facilitate the smooth flow of traffic. Since the waste was primary crushed before being tipped, there will be no need for blasting. Large rocks will be shifted aside and manual labour used to break them before loading. Since the waste is predominantly copper bearing, the chemical reagents associated with cobalt processing (lime, cyanide and dithiophosphate) will not be required, contributing to significant cost savings.
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Figure 19: Baluba’s milling section 2: Calculations:
3 000 tonnes per day. Feed grade 0.55% Cu, for average case scenario, 0.45% Cu for worst case scenario, and 0.40% Cu for extreme worst case scenario. Plant recovery 65% total Cu, although higher recoveries can be expected as shown below at the Frontier mine 50kms away, part of the same geological formation called the Lufilian Arc.
W ASTE
ROCK
TREATMENT
91.0
86.0
) % ( Y R 81.0 E V O C E R 76.0
71.0
66.0 0.14
0.24
0.34 GRADE %
0.44
0.54
Cu
Figure 20: Average grade waste rock treatment at Frontier mine 16
WASTE ROCK TREATMENT LOW GRADE
90.0
85.0 ) % ( Y R E V O C E R
80.0
75.0
70.0
65.0
60.0 0.14
0.24
0.34
0.44
GRADE ( %Cu)
Figure 21: Low grade waste rock treatment at Frontier mine
Smelter/refinery combined recoveries 95%. Processing cost 7¢/lb recoverable copper for average case scenario, 8¢/lb for worst case scenario and 10¢/lb for extreme worst case scenario due to increased mill balls usage. Mining and transporting cost to plant, max 5kms, 5¢/lb recoverable copper for average case scenario, 7¢/lb for worst case scenario and 9¢/lb for extreme worst case scenario, because of the larger volume of barren rock at the lower grade to be transported. Overheads and contingencies, 3¢/lb recoverable copper for average case scenario, 4¢/lb for worst case scenario and 5¢/lb for extreme worst case scenario. LME selling price of copper $1.10/lb, for average case scenario $1.00/lb for worst case scenario and $0.90/lb for extreme worst case scenario. Figure 22.
2.1 Average Case Scenario 1. Production, volume and cost: 17
(3 000X0.55X0.65X0.95)*2 205/100 22 466 lbs of copper per day…….@ $1.10/lb $24 712 per day in revenue, say $24 500 2. Operating Cost: 22 466*(7+5+3)/100 $3 370, say $3 500 in expenses 3. Profit: Daily profit is expected to be $24 500 - $3 500 = $21 000 Operating 350 days per year gives $7.3m, or $0.61m per month profit 2.2 Worst Case Scenario 1. Production, volume and cost: (3 000X0.45X0.65X0.95)* 2 205/100 18 381 lbs of copper per day…….@ $1.00/lb $18 380 per day in revenue, say $18 000 2. Operating Cost: 18 381*(8+7+4)/100 $3 492, say $3 500 in expenses 3. Profit: Daily profit is expected to be $18 000 - $3 500 = $14 500 Operating 350 days per year gives $5.07m, or $0.42m per month profit
2.3 Extreme Worst Case Scenario 1. Production, volume and cost: (3 000X0.40X0.65X0.95)*2 205/100 16 339 lbs of copper per day…….@$0.90/lb $14 705 per day in revenue, say $14 500 2. Operating Cost: 16 339*(10+9+5)/100 $3 921, say $4 000 in expenses 3. Profit: Daily profit is expected to be $14 500 - $4 000 = $10 500 Operating 350 days per year gives $3.67m, or $0.30m per month profit 2.4 Extreme Worst Case Scenario, with doubled cost 1. Production, volume and cost: (3 000X0.40X.65X.95)*2 205/100 16 339 lbs of copper per day…….@$0.90/lb $14 705 per day in revenue, say $14 500 2. Operating Cost: 16 339*(20+18+10) $7 842 say 18
$8 000 in expenses 3. Profit: Daily profit is expected to be $14 500 - $8 000 = $6 500 Operating 350 days per year gives $ $2.27m, or $0.19m per month profit
3: Conclusions:
The above presentation shows conclusively that the surface waste from the defunct Luanshya mine could be reprocessed profitably. The copper price used is extremely low, current and long term selling price is expected at least double of what was used in this financial model, Figure 23. The plant recovery used is very low, as the circuit is optimized; at least 75% recovery is expected. Frontier mine 50kms away achieved in excess of 80% recovery, Figures 20 and 21! The costs expected to be incurred will definitely be lower, they will just be incremental costs, as excess plant capacity will be utilized with the same equipment and labour force. The model assumed that waste would have been treated by itself . Considering the three points just made, above, the economics sways well in favour of treating mine waste. The mine manager could have a financial model on his computer, as the LME price increases; he will calculate when 18 Shaft’s and 28 Shaft’s waste can be trucked into the plant from Mpatamatu. While 14 Shaft’s waste is being processed, unemployed youths will be placed on the two Mpatamatu waste dumps to hand pick “copper rocks”, they will be paid according to the copper content of such ore. This will enhance community participation in the operation of the mine. This could become a model for the rest of the Copperbelt to follow, utilising the vast tonnages mine waste discarded on surface, at every copperbelt mine. But as the connotations which go with the name, this material is often overlooked. This project will prove that with innovation, experience and ingenuity, such waste can be converted to a valuable resource to benefit the country, and reflect the proactive approach of the company. The surface waste which is seen as an environmental “eye sore” will be processed and the ensuing waste deposited in the tailings dams in a responsible manner. The concentrate produced is deemed to be “sweet” for smelting. This is attributed to the high pyrite content which makes it exothermic (gives off heat, and saving on smelting fuel). In addition, it contributes to a low viscosity slag, thus improving smelter recovery. Figure 22.
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Figure 22: “Sweet” flotation concentrate, cherished by all smelters
Figure 23: 15-year copper price graph,………..clear patch shows the very conservative price band used in this financial model
RAMOUTAR SEECHARRAN (KEN)
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