success with arsenopyrite treatment at guelb moghrein mine in mauritania

8/3/2019 Success with Arsenopyrite treatment at Guelb Moghrein Mine in Mauritania

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AARRSSEENNIICC::

1. Arsenic in feed (Jul+Aug 2009) is up at 51%, higher than 30 months average (Jan2007June2009), 1 153ppm vs 765ppm.

2. Arsenic in cons is down at 59% of the corresponding value for identical periods in 1above, i.e. 1 449ppm vs 2 473ppm….August is running at 1 029ppm, the lowestever in the history of the plant, first time sub 1 000ppm was achieved on 20 th and21st, month to date!!!!! Figure 1. Rejection of arsenopyrite is definitely taking place atthe cleaning stage because rougher concentrate is still running with a tenor of about3 650ppm arsenic.

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3. We are definitely recovering less arsenic in cons compared to before, 8.2% vs 23.9%

for the corresponding periods shown in 1 above. Figure 2.

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FFiigguurree 22:: AArrsseenniicc rreeccoovveerreedd iinn ccoonncceennttrraattee ssiinnccee JJaannuuaarryy 22000077

4. On the job training continues to get the operators to recognise forth texture, sheen andcolour and its implications on the quality of the concentrate produced.Figures 3, 4 and 5.

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5. Starting last Tuesday, we are critically looking at collector (SEX) dosage. Preliminary

work concentrated on the physical aspects of flotation, we are now going to focus onthe more difficult, chemical aspects. It will be refined as data is acquired and will formthe backbone of a process control system, linking collector dosage to feed grade andtonnage. We expect:

•

Steadier operation • Better concentrate quality

• Results consistent with plant observations, i.e., fewer surprises from lab results!!

GGRRAAPPHHIITTEE

After arsenic contamination of the concentrate, high graphite content of the ore and itsassociated treatment problems has been the second biggest problem at the mine. It is felt thatsince the arsenic problem has been solved, attention should now be focused on the graphiteproblem, as follows:

It is proposed that a Davcra type flotation cell (Figure 7) be used to clean the rougherconcentrate and skim graphite, prior to cleaning of the scavenger concentrate in the currentcleaner circuits. By its hydrophobic nature, most of the graphite should be floating in the first twocells on the rougher/scavenger bank, i.e. the roughers.Sending this graphitic concentrate to the conventional cleaner banks, as we do currently, isinviting disaster, for the following reasons:

• It is a viscous froth, so cleaning efficiency will deteriorate rapidly as a result, mainlybecause of entrained insols. A viscous froth does not offer selectivity, so arsenopyriteentrainment could also be a problem.

• Such froth, if mechanically agitated, becomes “whipped”, like cream. So it is besttreated in a cell with a more quiescent regime, like a column cell, a Davcra cell, or to a

lesser extent, the Jameson or Maxwell cells.• The surface active fine sulphides, Table 1, and finer graphite combine using van der

Walls adhesion to form a strong unbreakable froth which water sprays fail to break. Itis such froth which builds up in the pump sumps and forces us to reduce tonnage,Figure 6.

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• A column type cell generates finer bubbles, 300-500 microns approximately,compared to 1 000 microns for an agitated cells. The operators floating talc,oxides and molybdenum have found these types of cells to be extremely useful. Intheory, smaller bubbles generate less turbulence behind a rising air bubble, so thefine mineral particles (graphite/talc/molybdenite) can get attached to that bubble,or, cannot get dislodged easily in its greatly reduced wake.

1. On the other hand, skimming material from rougher cells 1 and 2 to a directcleaning section should also help the froth texture produced by scavengerconcentrate in the existing cleaner cells and total plant recovery, for the followingreasons:

2. The concentrate from cells 3 to 6 is different in granulometry, significantly coarserthan the concentrate from cells 1 and 2, as shown in Table 1 below for p80 size inmicrons. This should lead to a more brittle froth. Such froth should not build up inpump sumps, and the process of breaking and reforming should be beneficial alsoto concentrate grade, as insols and the slower floating sulphides (pyrite,arsenopyrite and pyrrhotite) will be given a chance to report as tailings during thefroth collapse phase. Leading to copper enhancement and arsenic reduction.

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Cell 1 Cell 2 Cell 3 Cell 4 Cell 5 Cell 6 Sample

62.1 55.1 83.6 82.6 73.7 74.9 24th April

57.8 57.9 70.4 67.7 70.1 74.8 16th May

3. Since pump sumps will not be overflowing, and with an enhanced concentrategrade obtained, operators will be able to pull the scavenger cells harder, asscavengers should be run. This practice will lead to higher copper and goldrecoveries.

• Use a tank cell to remove the faster floating fines. Referring to the comprehensiveplant survey conducted on 16th May 2007, almost 64% of float feed is -53 microns,Picture 1, leaving the conventional cleaner cells to cope with the slower floatingfine sulphides. These fines should float early; Picture 2 confirms this, p80 approx58 microns from a floatn feed of 96.5, while the last cell in the bank, cell 6, floatedthe slower floating coarser sulphides and locked middlings. Picture 3, p80 of almost75 microns! This was the material which needed regrinding, or in the case of theold circuit, one stage of upgrading and that concentrate sent for regrinding.

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PPiiccttuurree 11:: FFllooaatt ffeeeedd pp8800 9966 mmiiccrroonnss PPiiccttuurree 22:: FFiirrsstt rroouugghheerr cceellll pp8800 5588 mmiiccrroonnss

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• In addition, with the imminent commissioning of the ball mill and the anticipatedconcomitant increase in throughput, removal material early to the concentratethickener will soon become an imperative. My prognosis is that the proposedinstalled Davcra cell will be used full time, even during the treatment of lessrefractory low graphitic feed!

• Skimming graphite off as early as possible to the filter plant will also havedownstream benefit in the CIL circuit, the amount of graphite present to act as“preg robber” will be greatly reduced thus enhancing gold recovery.

Size -

nn

µm Weight % Dist Cu Dist 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 P (µm) 74.8480

Rougher Cell 6 Concentrate

Size - µm Weight % Dist Cu Dist As Dist Au

+106 3.93 4.0 4.8 2.4

+75 7.79 9.1 17.3 1.3

+53 10.60 12.9 25.8 9.0

+45 5.11 5.6 12.1 7.5

-45 72.57 68.4 39.9 79.9

Total Grade 20.95 3737 14.26

Total P80 (µm) 57.82

Rougher Cell 1 ConcentrateSize - µm Weight % Dist Cu Dist 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 (µm) 96.54

Float Feed

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The Davcra cell is non-agitated, so maintenance cost is minimal, on average the feed nozzle ischanged every 4-6 weeks. Instrumentation is basic, level controller (often a DP cell, tails autovalve, air flow meter and a small control panel to link these).

The major cost to be associated with this project will be the pump required to pump theconcentrate to the cons thickener. Tailings will gravity flow into the 1st cleaner tails sump.

A mains compressed air pressure of 6 bars minimum is required for the air sparger.

There is no need to rubber line the tank.

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Plant Superintendent24 August 2009

RAMOUTAR SEECHARRAN

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success with arsenopyrite treatment at guelb moghrein mine in mauritania

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