trouble shooting guelb moghrein's concentrator

7/30/2019 Trouble Shooting Guelb Moghrein's Concentrator

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The author was asked to visit our sister plant, Guelb Moghrein, in Mauritania, and adviseon matter pertaining to flotation issues. Guelb had been encountering low concentrategrades with high arsenic content in their final product. A visit was made from 24th to 28thDecember 2008, allowing 3 full days of study. During this period, it was unfortunate thatrefractory material, high graphite content, from the surface stockpile was treated. This isevident by the fact that the use of frother was suspended at 0900 hrs on 25th until the timeof departure, and the physical appearance of the froth still indicated high frother content.

At the time, a polypropylene glycol frother was being used; such frother does not build upin the recycled process water. In the unlikely event of a build up occurring, it would have

taken 20-30 hours to purge the system; here it lasted over 72 hours, proving thedeleterious effect of graphite.

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The copper mineralisation at Guelb is predominantly Chalcopyrite (CuFeS2) comprisingabout 80% and Cubanite (CuFe2S3), making up the remaining 20%. The main sulphidegangue being Pyrrhotite (FeS). The predominant non sulphide gangue is fibrous

Amphibolite, called Anthophyllite, a cousin to the other asbestos mineral, Tremolite.Anthophyllite is highly surface active and it causes severe scaling problems with plantpiping.

Guelb started off as a TORCO (Treatment OfRefractory Copper Ore) plant in 1970 and

closed down in 1977 as a result of technical difficulties and rising oil prices. When it was inoperation, it was the only TORCO plant in the world. The existing plant was added as anappendage to the original Torco plant, and it worked well at lower tonnages and with

favourable mineralogy.As tonnage increased, and mineralogy became more refractory, the weaknesses started to

surface.


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It is evident that some modifications were carried out under stress and panic rather than

judiciously, the highly accurate and thorough plant sampling exercise carried out in May2007 corroborates this assessment.

Overall, although the plant operators, and local supervisors, are not of a high academicstandard, compared to plants like Kansanshi and Frontier, they showed immense capacityand eagerness to learn. Language is not perceived as a problem. However, it could takeanother 6 months or so to get them up to international standards where their own initiative

will come into play, rather than that of the expat shift supervisor. Continuous on-the-jobtraining, round the clock, like that which was implemented at Frontier at start up, in late2007, is called for.

Despite the refractory ore which was treated during the visit, the author is convinced that aconcentrate grade of 23-25% Cu with arsenic below 2500ppm and a tailings grade of

0.18-0.21% Cu can be achieved as the plant norm. The Courier on-stream analyser provedinvaluable here, and this was backed up by plant samples analysed by the lab. This

compares with INTERMETs theoretical metallurgical modelling of 25% Cu in cons and0.20% Cu in tails.

Plant hygiene was not of the highest standard, this was as a result of pump boxesoverflowing, rather than the reluctance of the plant operatives to carry out clean up. Theywere literally being overwhelmed, from hour to hour.

Plant technical personnel are aware of where pumps needed speeding up, or bigger pumpsinstalled, and their mechanical counterparts enthusiastically facilitated the installations,only to find that the equipments have not been installed because of a lack of electricalupgrade. To draw a parallel with Frontier, the electrical upgrade is made prior to the actualinstallation!

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22..11:: The roughing/scavenging bank is running too slow. Scavenger cells 5 and 6 are

running like rougher cells 1 and 2 should run. This invariably leads to lower thananticipated recoveries. Operators are forced to do so because pump, PMP3001Ais unable to cope with the volume. PMP3001B has been upgraded but is awaitingelectrical upgrade prior to commissioning. This should be treated with greaterurgency. In addition, speeding up this bank increases the load to the first

cleaner bank, this results in the tails sump overflowing. Pump PMP3009B hasbeen upgraded and is also awaiting an electrical upgrade.

22..22:: The operators need to be taught the difference between a good and a bad froth.After 4 hours with them, they were able to decipher for themselves the difference,and were engaging in dialogues for future improvements, Figure 3. And 72 hours

later, the remarkable results is shown in Figure 4. Froth crowding often occurs onthe first cell in a bank. Because the froth is thick and viscous, insols get entrained.

The misconception of most plant operators is to instinctively speed up such cells,this only leads to a higher mass pull of insols. It is often best to accommodate thisdistasteful appearance, and use that cell as a conditioner. This practice gives the

hydrophilic particles a chance to get wetted. As a result, there is bettersegregation in the succeeding cells between hydrophilic and hydrophobic particles.Judiciously speeding up the succeeding cells in that bank gives better flotation

grades. The ideal froth is the one shown in Figure 4. Here the bubbles areconstantly breaking and reforming, giving the hydrophilic insols a chance to sinkto the bottom of the flotation cells and report as tailings. The ideal froth is shownin Figure 5.

Original Froth Improved Froth

Figure 3: Original and Improved froth at Guelb, after 4 hours of training


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22..33:: From the grind vs grade regression graph shown in Figure 6, and to avoid

the question of fineness of grind being raised in the future, it should beplaced on record that a grind of 67-70% passing 75microns be adhered to.More often than not, the plant has operated within this envelope.


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GRADE vs GRIND REGRESSION

22.5

23.0

23.5

24.0

24.5

25.0

25.5

64.5 65.5 66.5 67.5 68.5 69.5

GRIND % -75um

GRADE%Cu

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22..44:: Concentrate from Rougher cell 6 should be isolated and pumped back tothe head of flotation. It bears a close resemblance in grind and coppercontent to flotation feed, as shown in Figure 7. Such a move will have adouble pronged effect, firstly, that cell can then be run as a conventionalscavenger, and secondly, that reagents associated with such a froth might makethe froth in the first two cells more brittle, thus giving better control over grade.The feed box to cell 1 already has ports to accommodate this material, Figure 8.

Float Feed Rougher Cell 6 Cons

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Size - m Weight % Dist Cu Dis t As Dist Au

+106 7.30 14.0 0.0 10.6

+75 12.59 11.2 0.0 7.1

+53 16.14 10.2 4.1 10.8

+45 6.07 3.0 2.4 3.9

-45 57.90 61.6 93.4 67.6

Total Grade 1.70 1283 3.30

Total P80 (m) 74.84

Rougher Cell 6 ConcentrateSize - m Weight % Dist Cu Di st As Dist Au

+212 1.87 1.0 0.6 1.2

+180 1.84 1.0 0.2 2.2

+150 2.76 1.5 0.0 3.0

+106 9.60 6.9 5.2 9.0

+75 12.87 12.4 9.4 13.5

+53 12.07 12.8 15.4 14.2

+45 5.35 6.0 6.3 7.5

-45 53.63 58.4 62.8 49.4

Total Grade 1.62 638 1.99

Total P80 (m) 96.54

Float Feed


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22..55:: At least 40% of the copper lost in tailings is in the minus 53 microns sizefaction, as shown in Figure 9. Clariant, the reagent manufacturer doesproduce a frother reputed for generation of small bubbles. Such a frother,if used on the gold scavenger flotation circuit, might float most of thatcopper in the first 2 cells of that bank. A plant trial is highly recommended.This concentrate can probably then join that of the rougher/scavenger

bank.

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22..66:: Flotation cell level control is an art which has been mastered by the mostexperienced operators. The less experienced ones do so by trial and error.

Size - m Weight % Dist Cu Dist As Dist Au

+212 2.54 9.6 0.0 3.4

+180 2.22 6.7 1.6 4.3

+150 3.28 6.8 0.0 7.6

+106 10.76 16.5 0.1 13.1

+75 13.24 13.1 0.1 14.3

+53 12.78 6.6 4.0 12.3

+45 4.63 2.0 5.3 4.3

-45 50.55 38.9 88.8 40.8

Total Grade 0.12 256 0.96

Total P80 (m) 103.20

Rougher Tail


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The tail end of each group of cells is controlled by two valves, one manual

and the other automatic. At low flows there is no problem, but at highflows, the manual valve has to be partially opened so that the auto valve

does the controlling. It is recommended that actuators be procured tomake both valves automatic. The cell level measuring device is state of theart!

22..77:: Note the similarity between 1st cleaners cell 7 (or cleaner scavenger cell 4)

cons grade and that of 2nd cleaners (or recleaners, at the time of sampling)tails. Figure 10. Those two should follow the same route. Re-examinationof the rerouting of these streams ties in with the reevaluation of theregrind circuit operation.

Cleaner cell 7 cons 2nd Cleaner tails

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22nndd CClleeaanneerr TTaaiillss ((1166//0055//22000077))

22..88:: The regrind mill is operating in open circuit. This is highly unconventional.But it is assumed that the results shown in Figure 11 precipitated such amove. It is felt that a more critical look at the classification circuit wouldhave led to a more plausible solution. Krebs engineering are capable ofrunning a highly accurate simulation of the circuit. It is strongly felt that

such an avenue should be pursued. Without classification, how do we knowthat the regrind circuit is effective? However, in the interim, the operationof the mill should be optimized, especially by ensuring that the ball load is

approximately 15-20% by volume. The plant survey of 16 May 2007indicates that the material being fed to the regrind mill does not requirefurther comminution, as shown below:

Cleaner scavenger cell 4 p80 60.0 micronsCleaner scavenger cell 5 p80 65.3 micronsCleaner scavenger cell 6 p80 47.5 micronsCleaner scavenger cell 7 p80 51.5 microns


+150 1.19 1.8 1.0 1.9

+106 3.93 5.7 3.7 5.9

+75 6.32 8.7 6.6 10.6

+53 7.96 8.3 7.6 9.9

+45 3.25 2.5 4.3 3.4

-45 77.35 73.1 76.8 68.3

Total Grade 7.43 1968 8.23

Total P80 (m) 51.52

Cleaner Cell 7 Concentrate

Size - m We ight % Dist Cu Dist As Dist Au

+75 5.03 8.3 4.3 19.3

+53 6.14 9.1 12.3 22.3

+45 3.44 3.9 5.8 11.5

-45 85.40 78.8 77.6 47.0

Total Grade 8.84 1829 5.67

Total P80 (m) 42.16

ReCleaner Tail


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Mill Feed Mill Discharge Classifier Product

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((1166//0055//22000077))

22..99::At present, approximately 50% of Sodium Ethyl Xanthate (SEX) is added tothe mill discharge sump, 25% to rougher cell 3 and the remaining 25% torougher cell 5. This is a good practice, however, the 50% added to milldischarge sump could be replaced with one of the sodium dithiophospates(DTP) with an addition rate of 3-5gt-1. This could prove to be useful againstthe flotation of arsenopyrite. It is used successfully at Grasberg inIndonesia, where they also have a problem with high arsenic. However theGrasberg deposit is a skarn type and does not contain graphite and

anthophyllite. In the early 1990s, Grasbergs concentrate, then calledErtsberg concentrate, was renowned as the concentrate with the highest

arsenic content in the world. Grasberg produces a 28% Cu concentrate ata recovery of 86%. Instead of the mill discharge at Guelb, the DTP shouldbe added to mill feed.

22..1100::The thickeners should operate with a slight bed, up to 30%. The cone atthe bottom of the feed wells on thickeners of this type diverts the feedinto such a bed which then acts as a trap. This is synonymous to theteeter bed on the old fashion thickeners. This ensures that a clearsupernatant is achieved. A bed level indicator is installed but needsrefurbishing. The current system of using a dipstick to measure and

maintain a bed level of about 1 metre seems to work and should continue.


+106 3.43 3.5 5.6 4.4

+75 6.83 7.9 11.5 9.8

+53 10.41 11.3 17.3 12.4

+45 4.82 5.5 7.0 4.6

-45 74.51 71.9 58.6 68.9

Total Grade 18.83 2988 16.64

Total P80 (m) 54.42

Regrind Mill Feed (Cleaner Concentrate)


+75 1.55 2.6 1.3 6.9

+53 4.52 6.9 9.1 18.9

+45 4.57 5.3 7.8 17.5

-45 89.36 85.1 81.8 56.7

Total Grade 8.56 1816 4.92

Total P80 (m) 40.29

Regrind Mill Cyclone O/FSize - m Weight % Dist Cu Dist As Dist Au

+106 2.78 2.7 1.4 9.5

+75 6.16 7.7 5.2 20.3

+53 11.43 12.8 11.7 19.6

+45 6.31 6.6 7.7 7.3

-45 73.33 70.1 74.0 43.2

Total Grade 7.59 2272 11.61

Total P80 (m) 53.70

Regrind Mill Cyclone Feed


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Fresh Feed

ClearSupernatant

Thickened Underflow

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22..1111:: A froth retaining ring, Figure 14, needs to be fitted to contain the frothwithin the thickeners. This invention came into being after these

thickeners were constructed. Figure 13.

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33:: AAcckknnoowwlleeddggeemmeennttss

The author is indebted to the management of Frontier mine for releasing him toconduct this study. The efficiency with which Diana and Merlin handled visa and

travel arrangements was beyond belief. Silas gave full freedom of the plant. Steve,acting as General Manager, gave continuous encouragement, be it in the car park,at lunch or in the club. The entire metallurgical team was receptive. It was an

honour to interact with such professional people. The close knit family at Guelb will

continue to be the bright jewel in the larger First Quantum crown.

trouble shooting guelb moghrein's concentrator

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