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Process mineralogy of fluorosilicate minerals in ok tedi ores
Miner&
Pergamon
Engineering,
0892-6875(01)00180-7
Vol. 14, No. 12, pp. 1619-1628.2001 0 2001 Elsevier Science Ltd All rights me.rvcd 0892-6875/01/$ - see front matter
PROCESS MINERALOGY OF FLUOROSILICATE MINERALS IN OK TED1 ORES*
L.S. PANGUM!, J.W. GLATTHAAR! and E.V. MANLAPIG’
4[Metallurgy Department, Ok Tedi Mining Ltd, P.O.Box 1, Tabubil, Papua New Guinea 5 Department of Mining, Minerals and Materials Engineering, The University of Queensland, St. Lucia, Qld., Australia Email: Pangum.Lemas.LP @bhp.com.au (Received 9 May 2001; accepted 6 October 2001)
ABSTRACT The impact offluorine in copper flotation was relatively unknown until the introduction of skam ores in the Ok Tedi concentrator. Fluorine in the copper concentrates reports to the gas phase during the smelting stage and forms a corrosive H$O~HCl-HF acid brine mixture which must be neutralised. This work was aimed at studying the mineralogy of the fluorosilicate minerals contained in the various oretypes present in the Ok Tedi porphyry copper deposit. The electron microprobe was used to analyse for fluorine and hence identify the fluorosilicate minerals in each oretype. This study revealed talc, phlogopite, biotite, clays, amphiboles, fluoroapatite and titanite to be the sources of fluorine in the orebody. Laboratory and plant investigations wene conducted to study the flotation response of these minerals. Chemical assaying of the products of these tests was done to determine the bulk assay of fluorine. Using Rietveld analysis, quantitative estimates of the fluorosilicate minerals in these products were generated. Marrying of the bulk assay with the respective mineralogical “assay” enabled the understanding of the flotation behavior of fluorine and it’s associated mineralogy. Talc and phlogopite were found to be the causes of the fluorine problem at Ok Tedi. 0 2001 Elsevier Science Ltd. All rights reserved. Keywords
Froth flotation; ore mineralogy; mineral processing; particle size; sampling
INTRODUCTION
The impact of fluorine in copper flotation was relatively unknown until the introduction of skarn ores in the Ok Tedi concentrator (Lauder, 1994). Fluorine in the copper concentrates reports to the gas phase and forms a corrosive H#Od-HCl-HF acid brine mixture which must be neutral&d (Reist, 1992). The cost * Presented at Applied Mineralogy ‘01, Brisbane, March 2001
1619
1620
L. S. Pangum et ul.
of neutralisation is passed onto contract concentrate suppliers like Ok Tedi in the form of penalty payments. This work was conducted to study two major issues. The first aspect of the work was aimed at assessing the behavior of fluorine (as opposed to fluorine-bearing minerals) during flotation of the different ore types. The second aim was to characterise the fluorine mineralogy of the various oretypes present in the Ok Tedi orebody. This was achieved by examining the concentrates and tails of flotation test products. The results of these examinations enabled the marrying of the bulk fluorine flotation to it’s mineralogy, hence the understanding of flotation process mineralogy of fluorine was possible.
CHARACTERISING THE FLOTATION BEHAVIOUR OF FLUORINE The flotation behaviour of fluorine was studied in a series of laboratory and plant investigations. laboratory study involved flotation testing of different ore types under identical flotation conditions. oretypes that were studied are listed below and results of these investigations are shown in Figure 1. Ore Ore Ore Ore
type type type type
1
High talc bearing magnetite/sulphide skarn Highly altered phlogopite bearing monzonite porphyry Normal monzonite porphyry (weakly altered) Normal monzodiorite porphyry (weakly altered)
1. 2. 3. 4.
Note that subsequent
The The
references to these ore types will be made as “Ore type 1, Ore type 2” etc.
2
3
4
5
6
7
8
9
$0 11 12 13 14 15 16 17 18 19 20 21
Sample Number Fig. 1 Comparison
of fluorine concentration
In Figure 1, the “Sample Number” on the horizontal
in rougher and scavenger concentrates.
scale must be interpreted
as follows:
Sample Numbers 1 to 6 are the rougher (con.1) and scavenger concentrates (con.2) of six flotation tests on the high talc-bearing skarn ore (ore type l), Sample Numbers 7 to 12 are con. 1 and con.2 of six flotation tests on the highly altered monzonite porphyry ore (ore type 2), Sample Numbers 13 to 17 are con.1 and con.2 of five flotation tests on the weakly altered monzonite ore (ore type 3) , Sample Numbers 18 to 21 are con. 1 and con.2 of four flotation tests on the monzodiorite porphyry ore (ore type 4). Figure 1 indicates that oretype 1 concentrates are highly enriched in fluorine than the other oretypes. Unlike other oretypes, this oretype contained talc mineralisation. It also indicates that the scavenger concentrates of all oretypes contain relatively higher amounts of fluorine than the rougher concentrates suggesting that fluorine is contained in both slow and fast floating minerals. This observation is supported by evidence from plant survey as will be discussed later.
1621
F’rocess mineralogy of fluorosilicate minerals in Ok Tedi ores
Additional laboratory testwork was performed on drill hole samples. Results of one such sample is shown in Figure 2, which compares the fluorine head grade against the rougher concentrate assay.
153-
168-
18%
198-
21%
22x-
243.
2S8-
273-
288-
168
183
19x
213
22x
243
2.58
273
288
303.7
Inlrnrl.
rrwh-es
Fig.2 DDH 390: Fluorine variation with depth. It is apparent that the entire interval (153 to 304 m) is consistently higher than 1000 ppm F in feed. The behavior of F in all samples appears to be quite variable. The interval between 153 and 183m shows an acceptably low fluorine in the concentrate despite it’s high content of talc and phlogopite. From 183 to 303 metres, fluorine is massively enriched in the concentrate and high recoveries of fluorine ranging from 10% to 3 1% are observed. Disregarding the slight inconsistency, possibly due to experimental error, high amounts of talc in all the samples result in unacceptably high fluorine recovery and very high fluorine levels in the concentrates. Quantitative 1.
XRD (QXRD) analysis on the above sample reveal the following
TABLE
mineralogy
shown in Table
1 Mass % of Minerals by QXRD of DDH 390 siderite
quartz
CuFeS,
1.2
1.6
1.7
1.2
Cl.0
1.7
1.9
2.1
3.3
3.4
Cl.0
6.0
Cl.0
1.7
4.9
Cl.0
6.7
Cl.0
2.8
3.0
Cl.0
4.4
4.8
4.2
8.9
20.2
6.9
Note that in all such mineralogy tables, the row totals will not always equal 100, because some phases, occur in amounts less than 1 %. The detection limit for Rietveld analysis is between 0.3 to 1.O weight % so any phase below 1 wt. % is recorded as ~1 wt. % (Mandile and Johnson, 1998). The high amounts of magnetite in the entire 150 metre length (depth) of this drillhole indicate that DDH 390 intersects massive magnetite skarn bodies containing significant amounts of pyrite, talc and phlogopite mineralisation.
L. S. Pangum et al.
1622
Table 2 contains QXRD data related to drillhole samples devoid of talc mineralisation. TABLE DDH
RL
2 Summary
1 Interval,
% talc
(meters)
(QXm)
(metres)
of data for skarn with no talc mineralisation %
phlogopite
,(QXW
% amphibole
% garnet,
(Qm)
(Qm)
Head,
F wm
I
1 27-42
1678
1 42-57
1618
1 102-117
1693
12.0
1517
Cl
25.0
1423
1067
0.7
2.5
Cl
1285
809
0.6
Cl
1.6
Cl
1056
840
0.8
Cl
1.4
cl
1093
411
0.4
Cl
1.6
5.1
1387
1018
0.7
2.4
2.8
Cl
1289
620
0.5
5.2
1044
539
0.5
2.5
3.2
850
507
0.6
I
498
589
Cl
Cl
3.9
3.5
1149
375
0.3
Cl
Cl
904
675
0.7
9.1
1891
296
L
576
116
I
1
1678
1 27-45
Cl
1663
45-63
1.6
37.5
2266
240
0.1
1648
63-78
35.4
1327
626
0.5
1633
78-96
‘4
1.1
Cl
79.1
1695
586
0.3
1618
96-l 14
Cl
2.4
64.6
1625
543
0.3
1603
114-128
1.4
52.5
1616
348
0.2
1648
105-120
5.5
1.7
Cl
2345
1237
0.5
1633
120-135
5.5
5.0
2326
1242
0.5
1618
135-150
4.2
2.5
1730
1134
0.7
1603
150-165
4.7
6.5
1934
1025
0.5
1588
165-180
5.1
Cl
2815
823
1573
180-192
Cl
2208
1349
I
1
0.2
0.3 0.6
The flotation behavior of this sample is shown in Figure 3. It is apparent that samples devoid of talc mineralisation yield concentrates which are low in fluorine, a trend which is in direct contrast with those samples containing talc in the feed as shown earlier in Figure 2. In summary, laboratory studies have shown that samples containing of high fluorine concentration.
talc mineralisation
yield concentrates
Process mineralogyof fluorosilicatemineralsin Ok Tedi ores
1623
3000
2500
2000
s Head L
1500
a Cont.
ii
1000
500
0 12345979
9
10
II
#of observations
Fig.3 Fluorine flotation behaviour
in talc-free feed.
Plant investigations The behavior of fluorine and it’s associated mineralogy in the Ok Tedi flotation plant has been studied in a survey of the circuit. The flotation circuit at Ok Tedi consists of typical rougher, scavenger and cleaner operations to produce a copper concentrate assaying typically 28% to 32% Cu. Figure 4 depicts the stage behaviour of fluorine and it’s associated mineralogy. This graph shows that increasing amounts of F, talc and phlogopite are recovered as flotation proceeds down the cells with the maximum being recovered in the scavenger banks (Cells IO-15 cont.). The final concentrate represents overall plant recovery of F, talc and phlogopite and is indicative of the plant’s ability to reject fluorine. Fluorine recovery appears to be sympathetic to talc recovery. This relationship suggests that fluorine recovery is a function of fluorosilicate mineral recovery. In fact, fluorine recovery is in direct proportion to talc recovery as depicted in Figure 5. The influence of entrainment on fluorine recovery was examined by plotting the water recovery in the rougher and scavenger stages of flotation. This is shown in Figure 6 and indicates that fluorosilicate mineral flotation in the roughers is influenced more by natural flotation than by entrainment. However, the
1624
L.S.Pangum etal.
predominant mechanism for fluorine flotation in the scavengers indicates that the fluorosilicate minerals are slow floating.
can be attributed
to entrainment.
It also
Fig.4 Stage recovery of fluorine, talc and phlogopite.
10.0
.
9.0 I SO -7.0 .g
.60 . .
i
so--
5 I k
4.0 -.
l
3.0 -. 2.0 -. 1.0 . .
l
. 0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
TskRecovery
Fig.5 Talc versus Fluorine recovery at various stages of flotation. The four data points in Figure 6 represent rougher stages (l-3) and (4-9), the scavenger stage (10-15) and a weighted average point. The absence of data points in the region between the lower and upper ends is due to the fixed number of flotation stages (i.e., there are only three stages of flotation in the circuit at Ok Tedi).
1625
Process mineralogyof fluorosilicate minerals in Ok Tedi ores
2oJ LO.
a0
:
2ao
Fig.6 Water recovery versus fluorine recovery at various stages of flotation. Such relationships were also noted by Smith and Warren (1989) to describe recovery of water and hydrophobic particles. They noted that hydrophobic mineral flotation consists of two parts; namely inherent flotation and entrained flotation. In the present case, inherent flotation (ideally zero water recovery) yields 1 % recovery of fluorine predominantly in talc. Levels above 1% recovery represent entrained talc and phlogopite. High talc and fluorine recovery observed in Figure 5 is due to high levels of water recovery in the scavenger cells. Partitioning of mass and material distributions of a given ore or concentrate sample into different size fractions is a useful metallurgical technique. Typically, such analysis shows the deportment of the elements of interest (Cu and F in this case) into the various size fractions. Such data are useful for determination of the influence of particle size on flotation performance. These streams as they appear on the above graph are: 10-15 concentrate (scavenger concentrate (rougher stage 1 concentrate), 4-9 concentrate (rougher stage 2 concentrate), feed, final concentrate, cleaner tail and final tails.
concentrate), l-3 new feed, recycle
Figure 7 shows that, in all flotation streams, the deportment of fluorine in the -12.7 micron fraction is higher than in the coarse fractions. Of particular note is the scavenger concentrate (10-15 cont.) in which more than 40% of the fluorine is deported in the minus 12 micron fraction. These data suggest that fluorine is contained in a fine, slow floating species, confirming the observations of the laboratory testwork. In summary, this work confirms the laboratory observations that scavenger concentrate is more enriched in fluorine than rougher concentrate due to higher recoveries of talc and phlogopite. The predominant mechanism for the flotation of these minerals is entrainment.
1626
L. S. Pangum et al.
45.040.0. 35.0&z 30.0*i 25.0c .E m.OCI lz. SO10.0SO-
212
150
‘Is
38
31
219
149
12.7
-12.7
gmtidea&llGcnlm
Fig. 7 Fluorine distribution
by size in Ok Tedi flotation streams.
MICROPROBE ANALYSIS The products from the flotation testwork were analysed by the electron microprobe to determine the fluorine content of the different minerals. Those minerals which registered a fluorine assay were then classified as fluorine-bearing, and those which did not show a fluorine value were classified as non fluorine-bearing. The minerals which were identified as fluorine-bearing include talc, phlogopite, biotite, amphiboles, clay, apatite and titanite. Talc and phlogopite were detected in the skam samples while the other minerals including phlogopite were detected in the porphyry samples. In all these minerals, the fluorine content exhibited significant variability, typical of the type of cation/anion substitution observed in silicates. Classifying these minerals in order of increasing fluorine weight %, the order is: TABLE 3 Order of increasing fluorine content in minerals
Fluorine-bearing
mineral
Average fluorine content, wt. % I
clay (illite and kaolinite)
I
amphibole(actinolite
& tremolite)
1.20
talc
I I
from normal monzonite
phlogopite
1.72 porphyry
from normal monzodiorite fluoro-apatite
phlogopite
from highly altered monzonite phlogopite from skam
1
0.50
biotite phlogopite
0.35 0.47
titanite (sphene)
1
2.15
I
2.53 3.20
porphyry
3.46 3.56
Examining the order of increasing fluorine content above, the presence of apatite in the concentrate may appear to render high fluorine concentration. However, apatite was detected mainly in the tailings while
1627
Process mineralogyof fluorosilicate minerals in Ok Tedi ores
only talc and phlogopite with minor amounts of the other minerals were present in the concentrate. Phlogopite originating from the skarn ore has been observed to contain higher amounts of fluorine than the other oretypes. This observation has direct implications for the quality of the final concentrate, in that fluorine from skam-derived phlogopite, in combination with talc-derived fluorine can lead to elevated levels of fluorine in the concentrates. In order to determine the nature of the fluorosilicate minerals appearing in the plant final concentrate, a number of monthly composites were examined for the mineral and fluorine contents. The relative proportions of fluorosilicate minerals that were detected in these samples are listed in Table 4. TABLE
4 Fluorine
mineralogy
in final concentrate
Mass % of Fluorosilicate Mineral
Fluorine,
%
in final concentrate
MiIliIllum
Average
Maximum
talc
1.75
0.8
2.3
4.7
phlogopite
3.10
0.2
0.5
0.6
biotite
1.36
0.2
0.4
0.6
clay
0.32
0.2
0.5
1.3
amphibole
0.52
0.2
0.4
0.5
It is noteworthy that, for example, the mass % of talc ranges from 0.8 to 4.7, indicating variability in either the content of talc in the mill feed, variability in the performance of the plant or both. It must also be pointed out that the proportion (mass %) of talc in the concentrates is significantly (4-8 times) higher than the other fluorine-bearing species. Using these data, the fluorine contribution by each fluorosilicate mineral to final concentrate fluorine was cakulated according to Equation 1 and tabulated in Table 5. In all calculations, the mass percentage of each mineral has been varied while the weight % F is kept constant. This approach reflects the fact that fluorosilicate response to flotation is not dependent on fluorine abundance but is entirely dependent on the efficiency of the flotation circuit to maximise rejection of fluorosilicate minerals, as confirmed by the results. Fpp,,,= Mass % of mineral x % Fluorine content of mineral x 100
(1)
On average, talc is the major contributor (64 %> to the fluorine content, by virtue of its relatively high mass percent and high unit fluorine content. Talc’s natural hydrophobic character enables it to float unaided, resulting in relatively high amounts of this mineral in the concentrate. Phlogopite accounts for 22 % (average) of the fluorine and the balance is distributed amongst the other minerals shown. Phlogopite has been found to occur in all ore types (skarn and porphyry), as discussed earlier, whereas talc is restricted to the skarn ores. Hence, one would expect phlogopite to impact significantly on the levels of fluorine in the final concentrate. The results of this work indicate that despite widespread occurrence in the various ore types, phlogopite is not recovered in the flotation process in significant amounts.
1628
L. S. Pangum et al.
TABLE 5 Fluorine distribution in final concentrate
CONCLUSION
Examination of the various flotation feed and products revealed talc to be the major cause of the fluorine problem. Phlogopite, despite it’s low amounts in the final concentrate also impacted on the fluorine content of the final concentrate, due to it’s high unit fluorine content. Entrainment was found to be the major mechanism of flotation of talc and other fluorosilicate minerals although some talc was found to be floating due to natural hydrophobicity. The bulk of the fluorine was recovered in the scavenger concentrate and up to 40% of the fluorine was deported in the - 12.7 micron fraction, signifying that it was contained in fine and slow-floating minerals. All in all, appropriate choice of diagnostic tools enabled characterisation of the full suite of fluorosilicate minerals in the Ok Tedi orebody and their response to flotation processing of copper ores.
ACKNOWLEDGEMENT The authors wish to acknowledge publish this paper.
and thank the management
of Ok Tedi Mining Ltd for the permission
to
REFERENCES Lauder, D.W.,. Review of fluorine in Ok Tedi concentrates, Technical Memorandum, Ok Tedi Mining Ltd, Tabubil, Papua New Guinea, 1994. Mandile, A.J. and Johnson, N.W., Quantitative mineral analysis of ores and minerals processing products using X-ray Diffraction, AusIMM ‘The Mining Cycle, Mt. Isa, 1998, pp. 271 - 276. Reist, M.A.,. Fluorine behavior and control in copper smelting., ,BHP Minerals Inc. Internal Memorandum, 1992. Smith, P.G and Warren, L.J., Entrainment of particles into flotation pulps, Mineral Processing and Extractive Metallurgy Review, 5, 1989, pp. 123-145
Correspondence on papers published bwills @min-eng.com
in Minerals
Engineering
is invited by e-mail to
Pergamon
Engineering,
0892-6875(01)00180-7
Vol. 14, No. 12, pp. 1619-1628.2001 0 2001 Elsevier Science Ltd All rights me.rvcd 0892-6875/01/$ - see front matter
PROCESS MINERALOGY OF FLUOROSILICATE MINERALS IN OK TED1 ORES*
L.S. PANGUM!, J.W. GLATTHAAR! and E.V. MANLAPIG’
4[Metallurgy Department, Ok Tedi Mining Ltd, P.O.Box 1, Tabubil, Papua New Guinea 5 Department of Mining, Minerals and Materials Engineering, The University of Queensland, St. Lucia, Qld., Australia Email: Pangum.Lemas.LP @bhp.com.au (Received 9 May 2001; accepted 6 October 2001)
ABSTRACT The impact offluorine in copper flotation was relatively unknown until the introduction of skam ores in the Ok Tedi concentrator. Fluorine in the copper concentrates reports to the gas phase during the smelting stage and forms a corrosive H$O~HCl-HF acid brine mixture which must be neutralised. This work was aimed at studying the mineralogy of the fluorosilicate minerals contained in the various oretypes present in the Ok Tedi porphyry copper deposit. The electron microprobe was used to analyse for fluorine and hence identify the fluorosilicate minerals in each oretype. This study revealed talc, phlogopite, biotite, clays, amphiboles, fluoroapatite and titanite to be the sources of fluorine in the orebody. Laboratory and plant investigations wene conducted to study the flotation response of these minerals. Chemical assaying of the products of these tests was done to determine the bulk assay of fluorine. Using Rietveld analysis, quantitative estimates of the fluorosilicate minerals in these products were generated. Marrying of the bulk assay with the respective mineralogical “assay” enabled the understanding of the flotation behavior of fluorine and it’s associated mineralogy. Talc and phlogopite were found to be the causes of the fluorine problem at Ok Tedi. 0 2001 Elsevier Science Ltd. All rights reserved. Keywords
Froth flotation; ore mineralogy; mineral processing; particle size; sampling
INTRODUCTION
The impact of fluorine in copper flotation was relatively unknown until the introduction of skarn ores in the Ok Tedi concentrator (Lauder, 1994). Fluorine in the copper concentrates reports to the gas phase and forms a corrosive H#Od-HCl-HF acid brine mixture which must be neutral&d (Reist, 1992). The cost * Presented at Applied Mineralogy ‘01, Brisbane, March 2001
1619
1620
L. S. Pangum et ul.
of neutralisation is passed onto contract concentrate suppliers like Ok Tedi in the form of penalty payments. This work was conducted to study two major issues. The first aspect of the work was aimed at assessing the behavior of fluorine (as opposed to fluorine-bearing minerals) during flotation of the different ore types. The second aim was to characterise the fluorine mineralogy of the various oretypes present in the Ok Tedi orebody. This was achieved by examining the concentrates and tails of flotation test products. The results of these examinations enabled the marrying of the bulk fluorine flotation to it’s mineralogy, hence the understanding of flotation process mineralogy of fluorine was possible.
CHARACTERISING THE FLOTATION BEHAVIOUR OF FLUORINE The flotation behaviour of fluorine was studied in a series of laboratory and plant investigations. laboratory study involved flotation testing of different ore types under identical flotation conditions. oretypes that were studied are listed below and results of these investigations are shown in Figure 1. Ore Ore Ore Ore
type type type type
1
High talc bearing magnetite/sulphide skarn Highly altered phlogopite bearing monzonite porphyry Normal monzonite porphyry (weakly altered) Normal monzodiorite porphyry (weakly altered)
1. 2. 3. 4.
Note that subsequent
The The
references to these ore types will be made as “Ore type 1, Ore type 2” etc.
2
3
4
5
6
7
8
9
$0 11 12 13 14 15 16 17 18 19 20 21
Sample Number Fig. 1 Comparison
of fluorine concentration
In Figure 1, the “Sample Number” on the horizontal
in rougher and scavenger concentrates.
scale must be interpreted
as follows:
Sample Numbers 1 to 6 are the rougher (con.1) and scavenger concentrates (con.2) of six flotation tests on the high talc-bearing skarn ore (ore type l), Sample Numbers 7 to 12 are con. 1 and con.2 of six flotation tests on the highly altered monzonite porphyry ore (ore type 2), Sample Numbers 13 to 17 are con.1 and con.2 of five flotation tests on the weakly altered monzonite ore (ore type 3) , Sample Numbers 18 to 21 are con. 1 and con.2 of four flotation tests on the monzodiorite porphyry ore (ore type 4). Figure 1 indicates that oretype 1 concentrates are highly enriched in fluorine than the other oretypes. Unlike other oretypes, this oretype contained talc mineralisation. It also indicates that the scavenger concentrates of all oretypes contain relatively higher amounts of fluorine than the rougher concentrates suggesting that fluorine is contained in both slow and fast floating minerals. This observation is supported by evidence from plant survey as will be discussed later.
1621
F’rocess mineralogy of fluorosilicate minerals in Ok Tedi ores
Additional laboratory testwork was performed on drill hole samples. Results of one such sample is shown in Figure 2, which compares the fluorine head grade against the rougher concentrate assay.
153-
168-
18%
198-
21%
22x-
243.
2S8-
273-
288-
168
183
19x
213
22x
243
2.58
273
288
303.7
Inlrnrl.
rrwh-es
Fig.2 DDH 390: Fluorine variation with depth. It is apparent that the entire interval (153 to 304 m) is consistently higher than 1000 ppm F in feed. The behavior of F in all samples appears to be quite variable. The interval between 153 and 183m shows an acceptably low fluorine in the concentrate despite it’s high content of talc and phlogopite. From 183 to 303 metres, fluorine is massively enriched in the concentrate and high recoveries of fluorine ranging from 10% to 3 1% are observed. Disregarding the slight inconsistency, possibly due to experimental error, high amounts of talc in all the samples result in unacceptably high fluorine recovery and very high fluorine levels in the concentrates. Quantitative 1.
XRD (QXRD) analysis on the above sample reveal the following
TABLE
mineralogy
shown in Table
1 Mass % of Minerals by QXRD of DDH 390 siderite
quartz
CuFeS,
1.2
1.6
1.7
1.2
Cl.0
1.7
1.9
2.1
3.3
3.4
Cl.0
6.0
Cl.0
1.7
4.9
Cl.0
6.7
Cl.0
2.8
3.0
Cl.0
4.4
4.8
4.2
8.9
20.2
6.9
Note that in all such mineralogy tables, the row totals will not always equal 100, because some phases, occur in amounts less than 1 %. The detection limit for Rietveld analysis is between 0.3 to 1.O weight % so any phase below 1 wt. % is recorded as ~1 wt. % (Mandile and Johnson, 1998). The high amounts of magnetite in the entire 150 metre length (depth) of this drillhole indicate that DDH 390 intersects massive magnetite skarn bodies containing significant amounts of pyrite, talc and phlogopite mineralisation.
L. S. Pangum et al.
1622
Table 2 contains QXRD data related to drillhole samples devoid of talc mineralisation. TABLE DDH
RL
2 Summary
1 Interval,
% talc
(meters)
(QXm)
(metres)
of data for skarn with no talc mineralisation %
phlogopite
,(QXW
% amphibole
% garnet,
(Qm)
(Qm)
Head,
F wm
I
1 27-42
1678
1 42-57
1618
1 102-117
1693
12.0
1517
Cl
25.0
1423
1067
0.7
2.5
Cl
1285
809
0.6
Cl
1.6
Cl
1056
840
0.8
Cl
1.4
cl
1093
411
0.4
Cl
1.6
5.1
1387
1018
0.7
2.4
2.8
Cl
1289
620
0.5
5.2
1044
539
0.5
2.5
3.2
850
507
0.6
I
498
589
Cl
Cl
3.9
3.5
1149
375
0.3
Cl
Cl
904
675
0.7
9.1
1891
296
L
576
116
I
1
1678
1 27-45
Cl
1663
45-63
1.6
37.5
2266
240
0.1
1648
63-78
35.4
1327
626
0.5
1633
78-96
‘4
1.1
Cl
79.1
1695
586
0.3
1618
96-l 14
Cl
2.4
64.6
1625
543
0.3
1603
114-128
1.4
52.5
1616
348
0.2
1648
105-120
5.5
1.7
Cl
2345
1237
0.5
1633
120-135
5.5
5.0
2326
1242
0.5
1618
135-150
4.2
2.5
1730
1134
0.7
1603
150-165
4.7
6.5
1934
1025
0.5
1588
165-180
5.1
Cl
2815
823
1573
180-192
Cl
2208
1349
I
1
0.2
0.3 0.6
The flotation behavior of this sample is shown in Figure 3. It is apparent that samples devoid of talc mineralisation yield concentrates which are low in fluorine, a trend which is in direct contrast with those samples containing talc in the feed as shown earlier in Figure 2. In summary, laboratory studies have shown that samples containing of high fluorine concentration.
talc mineralisation
yield concentrates
Process mineralogyof fluorosilicatemineralsin Ok Tedi ores
1623
3000
2500
2000
s Head L
1500
a Cont.
ii
1000
500
0 12345979
9
10
II
#of observations
Fig.3 Fluorine flotation behaviour
in talc-free feed.
Plant investigations The behavior of fluorine and it’s associated mineralogy in the Ok Tedi flotation plant has been studied in a survey of the circuit. The flotation circuit at Ok Tedi consists of typical rougher, scavenger and cleaner operations to produce a copper concentrate assaying typically 28% to 32% Cu. Figure 4 depicts the stage behaviour of fluorine and it’s associated mineralogy. This graph shows that increasing amounts of F, talc and phlogopite are recovered as flotation proceeds down the cells with the maximum being recovered in the scavenger banks (Cells IO-15 cont.). The final concentrate represents overall plant recovery of F, talc and phlogopite and is indicative of the plant’s ability to reject fluorine. Fluorine recovery appears to be sympathetic to talc recovery. This relationship suggests that fluorine recovery is a function of fluorosilicate mineral recovery. In fact, fluorine recovery is in direct proportion to talc recovery as depicted in Figure 5. The influence of entrainment on fluorine recovery was examined by plotting the water recovery in the rougher and scavenger stages of flotation. This is shown in Figure 6 and indicates that fluorosilicate mineral flotation in the roughers is influenced more by natural flotation than by entrainment. However, the
1624
L.S.Pangum etal.
predominant mechanism for fluorine flotation in the scavengers indicates that the fluorosilicate minerals are slow floating.
can be attributed
to entrainment.
It also
Fig.4 Stage recovery of fluorine, talc and phlogopite.
10.0
.
9.0 I SO -7.0 .g
.60 . .
i
so--
5 I k
4.0 -.
l
3.0 -. 2.0 -. 1.0 . .
l
. 0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
TskRecovery
Fig.5 Talc versus Fluorine recovery at various stages of flotation. The four data points in Figure 6 represent rougher stages (l-3) and (4-9), the scavenger stage (10-15) and a weighted average point. The absence of data points in the region between the lower and upper ends is due to the fixed number of flotation stages (i.e., there are only three stages of flotation in the circuit at Ok Tedi).
1625
Process mineralogyof fluorosilicate minerals in Ok Tedi ores
2oJ LO.
a0
:
2ao
Fig.6 Water recovery versus fluorine recovery at various stages of flotation. Such relationships were also noted by Smith and Warren (1989) to describe recovery of water and hydrophobic particles. They noted that hydrophobic mineral flotation consists of two parts; namely inherent flotation and entrained flotation. In the present case, inherent flotation (ideally zero water recovery) yields 1 % recovery of fluorine predominantly in talc. Levels above 1% recovery represent entrained talc and phlogopite. High talc and fluorine recovery observed in Figure 5 is due to high levels of water recovery in the scavenger cells. Partitioning of mass and material distributions of a given ore or concentrate sample into different size fractions is a useful metallurgical technique. Typically, such analysis shows the deportment of the elements of interest (Cu and F in this case) into the various size fractions. Such data are useful for determination of the influence of particle size on flotation performance. These streams as they appear on the above graph are: 10-15 concentrate (scavenger concentrate (rougher stage 1 concentrate), 4-9 concentrate (rougher stage 2 concentrate), feed, final concentrate, cleaner tail and final tails.
concentrate), l-3 new feed, recycle
Figure 7 shows that, in all flotation streams, the deportment of fluorine in the -12.7 micron fraction is higher than in the coarse fractions. Of particular note is the scavenger concentrate (10-15 cont.) in which more than 40% of the fluorine is deported in the minus 12 micron fraction. These data suggest that fluorine is contained in a fine, slow floating species, confirming the observations of the laboratory testwork. In summary, this work confirms the laboratory observations that scavenger concentrate is more enriched in fluorine than rougher concentrate due to higher recoveries of talc and phlogopite. The predominant mechanism for the flotation of these minerals is entrainment.
1626
L. S. Pangum et al.
45.040.0. 35.0&z 30.0*i 25.0c .E m.OCI lz. SO10.0SO-
212
150
‘Is
38
31
219
149
12.7
-12.7
gmtidea&llGcnlm
Fig. 7 Fluorine distribution
by size in Ok Tedi flotation streams.
MICROPROBE ANALYSIS The products from the flotation testwork were analysed by the electron microprobe to determine the fluorine content of the different minerals. Those minerals which registered a fluorine assay were then classified as fluorine-bearing, and those which did not show a fluorine value were classified as non fluorine-bearing. The minerals which were identified as fluorine-bearing include talc, phlogopite, biotite, amphiboles, clay, apatite and titanite. Talc and phlogopite were detected in the skam samples while the other minerals including phlogopite were detected in the porphyry samples. In all these minerals, the fluorine content exhibited significant variability, typical of the type of cation/anion substitution observed in silicates. Classifying these minerals in order of increasing fluorine weight %, the order is: TABLE 3 Order of increasing fluorine content in minerals
Fluorine-bearing
mineral
Average fluorine content, wt. % I
clay (illite and kaolinite)
I
amphibole(actinolite
& tremolite)
1.20
talc
I I
from normal monzonite
phlogopite
1.72 porphyry
from normal monzodiorite fluoro-apatite
phlogopite
from highly altered monzonite phlogopite from skam
1
0.50
biotite phlogopite
0.35 0.47
titanite (sphene)
1
2.15
I
2.53 3.20
porphyry
3.46 3.56
Examining the order of increasing fluorine content above, the presence of apatite in the concentrate may appear to render high fluorine concentration. However, apatite was detected mainly in the tailings while
1627
Process mineralogyof fluorosilicate minerals in Ok Tedi ores
only talc and phlogopite with minor amounts of the other minerals were present in the concentrate. Phlogopite originating from the skarn ore has been observed to contain higher amounts of fluorine than the other oretypes. This observation has direct implications for the quality of the final concentrate, in that fluorine from skam-derived phlogopite, in combination with talc-derived fluorine can lead to elevated levels of fluorine in the concentrates. In order to determine the nature of the fluorosilicate minerals appearing in the plant final concentrate, a number of monthly composites were examined for the mineral and fluorine contents. The relative proportions of fluorosilicate minerals that were detected in these samples are listed in Table 4. TABLE
4 Fluorine
mineralogy
in final concentrate
Mass % of Fluorosilicate Mineral
Fluorine,
%
in final concentrate
MiIliIllum
Average
Maximum
talc
1.75
0.8
2.3
4.7
phlogopite
3.10
0.2
0.5
0.6
biotite
1.36
0.2
0.4
0.6
clay
0.32
0.2
0.5
1.3
amphibole
0.52
0.2
0.4
0.5
It is noteworthy that, for example, the mass % of talc ranges from 0.8 to 4.7, indicating variability in either the content of talc in the mill feed, variability in the performance of the plant or both. It must also be pointed out that the proportion (mass %) of talc in the concentrates is significantly (4-8 times) higher than the other fluorine-bearing species. Using these data, the fluorine contribution by each fluorosilicate mineral to final concentrate fluorine was cakulated according to Equation 1 and tabulated in Table 5. In all calculations, the mass percentage of each mineral has been varied while the weight % F is kept constant. This approach reflects the fact that fluorosilicate response to flotation is not dependent on fluorine abundance but is entirely dependent on the efficiency of the flotation circuit to maximise rejection of fluorosilicate minerals, as confirmed by the results. Fpp,,,= Mass % of mineral x % Fluorine content of mineral x 100
(1)
On average, talc is the major contributor (64 %> to the fluorine content, by virtue of its relatively high mass percent and high unit fluorine content. Talc’s natural hydrophobic character enables it to float unaided, resulting in relatively high amounts of this mineral in the concentrate. Phlogopite accounts for 22 % (average) of the fluorine and the balance is distributed amongst the other minerals shown. Phlogopite has been found to occur in all ore types (skarn and porphyry), as discussed earlier, whereas talc is restricted to the skarn ores. Hence, one would expect phlogopite to impact significantly on the levels of fluorine in the final concentrate. The results of this work indicate that despite widespread occurrence in the various ore types, phlogopite is not recovered in the flotation process in significant amounts.
1628
L. S. Pangum et al.
TABLE 5 Fluorine distribution in final concentrate
CONCLUSION
Examination of the various flotation feed and products revealed talc to be the major cause of the fluorine problem. Phlogopite, despite it’s low amounts in the final concentrate also impacted on the fluorine content of the final concentrate, due to it’s high unit fluorine content. Entrainment was found to be the major mechanism of flotation of talc and other fluorosilicate minerals although some talc was found to be floating due to natural hydrophobicity. The bulk of the fluorine was recovered in the scavenger concentrate and up to 40% of the fluorine was deported in the - 12.7 micron fraction, signifying that it was contained in fine and slow-floating minerals. All in all, appropriate choice of diagnostic tools enabled characterisation of the full suite of fluorosilicate minerals in the Ok Tedi orebody and their response to flotation processing of copper ores.
ACKNOWLEDGEMENT The authors wish to acknowledge publish this paper.
and thank the management
of Ok Tedi Mining Ltd for the permission
to
REFERENCES Lauder, D.W.,. Review of fluorine in Ok Tedi concentrates, Technical Memorandum, Ok Tedi Mining Ltd, Tabubil, Papua New Guinea, 1994. Mandile, A.J. and Johnson, N.W., Quantitative mineral analysis of ores and minerals processing products using X-ray Diffraction, AusIMM ‘The Mining Cycle, Mt. Isa, 1998, pp. 271 - 276. Reist, M.A.,. Fluorine behavior and control in copper smelting., ,BHP Minerals Inc. Internal Memorandum, 1992. Smith, P.G and Warren, L.J., Entrainment of particles into flotation pulps, Mineral Processing and Extractive Metallurgy Review, 5, 1989, pp. 123-145
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