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Improvement of recoveries from copper bearing and copper-activated mineral ores using flex 31
Pergamon
Minerals Engineering, Vol. 9, No. 5, pp. 509-518, 1996 Copyright O 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved PII: S0892-6875(96)00039--8 0892-6875/96 $15.00+0.00
IMPROVEMENT OF RECOVERIES FROM COPPER BEARING AND COPPER-ACTIVATED MINERAL ORES USING FLEX 31
B.G. COUSINS§ and R.S. MACPHAIL? § Tenn~ts Research Technology Applications, Edmonton, Alberta, Canada "~Prospec Chemicals, Weston, Ontario, Canada (Received 29 July 1995; accepted 13 February 1996)
ABSTRACT Many copper-bearing ores use Sodium Isopropyl Xanthate (SIPX) as a flotation agent. In general, SIPX will float to some extent other minerals which may not be desirable, such as pyrite. FLEX 31 is a chemically enhanced SIPX product with many of the same properties as SIPX, but FLEX 31 has the ability to reject mare pyrite from concentrates as well as improves recoveries of copper when using 50% less FLEX 31 than is required if using SIPX. Copper-activated minerals, such as sphalerite and arsenopyrite, show increased recoveries as well using FLEX 31. However, in copper separation from these minerals prior to activation, FLEX 31 performs very similarly to SIPX and does not give the best separation possible with other reagents. Tests have been performed on copper~zinc, arsenopyrite and copper~molybdenum ores.
Keywords Sulphide ores; flotation reagents; flotation kinetics; froth flotation
INTRODUCTION
Sodium Isopropyl Xanthate (SIPX) is one of the most popular flotation chemicals on the market today. Somewhat more specific than amyl xanthates, SIPX is used in a variety of ores such as copper/zinc, lead/zinc, arsenopyrite/pyrite, and many others. An investigation carried out by Teunants Research Technology Applications (TRTA), a division of Charles Tennant & Co. (Canada) Ltd., produced a chemically enhanced S1PX that has shown all the advantages of normal SIPX along with improved recoveries of copper and copper activated minerals. The new product has been named FLEX 31. Currently, FLEX 31 is manufactured at the Prospec Chemicals, another division of Charles Tennant & Co. (Canada) Ltd. Their xanthate plant in Fort Saskatchewan, Alberta, Canada has a capacity of approximately 4500 tons of xanthates per year and is currently undergoing expansion to produce approximately 6000 tons of xanthates per year, making Prospec one of the largest mining chemical producers in the world. The proprietary process for FLEX 31 production is a new addition to plant operations that include the production of xanthate, thionocarbamate and xanthogen formate flotation reagents. Posl~r presentation at M/nera/s Eng/neetqng '95, St. Ives, Cornwall, England, June 1995
509
510
B. G. Cousinsand R. S. MaePhail FLEX 31 CHARACTERISTICS
Xanthate in copper flotation is known to create a dixanthogen on the mineral surface [1]. Copper is the catalyst to the formation. The dixanthogen structure includes a basic hexagonal ring of two carbons and four sulphurs (planar) which is a very stable structure and the increased hydrophobicity explains why copper floats so well with xanthates. Flexanthates were created in an attempt to increase the adsorption of xanthate onto mineral surfaces and enhance flotation. With ordinary xanthate, a large percentage stays soluble in water and does not adsorb. It was theorized that a surfactant that also forms the same type of hexagonal structure with xanthate without actually reacting with it could help in getting more of the xanthate onto the copper surfaces. The copper would help form the complex as it does with dixanthogen. The resultant complex could have the potential to create a higher degree of hydrophobicity than dixanthogen on the copper surface by its organic chemical structure as well as increase adsorption. A number of potential surfactants were tried until the one used to make FLEX 31 was discovered (due to the proprietary nature of flexanthates, the surfactant used cannot be disclosed). The surfactant in effect creates the superior flotation seen with FLEX 31. The proprietary process developed for sodium isopropyl xanthate (SIPX), a standard copper flotation reagent, produced FLEX 31. In extensive flotation studies, not only was it discovered that FLEX 31 had a stronger collecting power for copper and copper-activated minerals, it also had the ability to reject more strongly minerals that SIPX rejects to some degree, such as pyrite. FLEX 31 is produced in a pelleted form. Its appearance is very similar to pelleted SIPX and it has many of the same characteristics. It is totally soluble in a 1% solution with water and colours the solution with the same yellow colour as SIPX. For lab tests, 1% solutions of FLEX 31 in water are recommended. The enhanced activity of FLEX 31 allows for less of the product to be used to achieve better recoveries when compared directly with SIPX. A flotation test that requires 50 g/t of SIPX can still show better recoveries with the addition of only 25 g/t of FLEX 31. Increased pyrite rejection has also been observed with FLEX 31 than with SIPX. The reasons for the higher iron mineral rejection over SIPX is not known at this time. It is possible the surfactant used is capable of creating a high hydrophilic surface with iron minerals on its own. Precious metals associated with sulphides also show increased recoveries as well [2,3]. However, precious metals associated with pyrite tend to get rejected with the pyrite. Free precious metals normally not collected by SIPX will not be collected by FLEX 31 either. TESTWORK Flotation Rate Determinations Some of the data from the testwork was analyzed using first order rate kinetics. Flotation can be described as a process where the ore is ground to a predetermined fineness, and having a given size distribution and distribution of liberated and locked particles of valuable and gangue minerals, the valuable minerals can be separated from the gangue minerals in a flotation circuit. Depending on the prevailing Eh-pH, temperature and solution conditions as well as the presence of various reagents, the feed is split into two products; the concentrate containing the valuable mineral and the tails containing the gangue. This separation is essentially a kinetic process. Work carded out at INCO Research determined that the kinetic process can be described by a first order rate equation [4,5].
This equation is:
R = RI[1-exp -kO÷°)]
Recoveriesfrom copperbearing and copper-activatedmineralores
511
where: is is is is is
R RI k t 0
the the the the the
cmnulative recovery after time t maximum theoretical flotation recovery first order rate constant (time - l ) cumulative flotation time time correction factor
The time correction factor is included to allow for such things as air aspirated into the flotation cell during conditioning and some time elapses between the time that air flow is started and the first collection of floated material. The first factor indicates that time should be added whereas the second factor suggests that time should be d¢~lucted. The three parameters to be fitted to the rate equation are k, RI and 0. The equation is rearranged as follows:
RI-R I n ~ RI
= -k(t+0)
A computer program has been developed to fit the data into the above equation. A least square regression is done with this equation with an arbitrary, but adjustable, value of RI. An F test is done with regression mean square in the numerator and the residual mean square in the denominator and if the fit is judged significant at a 99 % level of significance, the values of k and 0 are calculated. If the value of O falls outside a pre-selected range of acceptable values, the data point for the longest flotation time is deducted and the procedure repeated with the truncated data set. Most of the work carried out at this time has been with copper/zinc ores. One ore in particular, a copper/zinc ore (Ore A), has had extensive work carried out on it. Another ore (Ore B) is an arsenopyrite/pyrite gold ore where the arsenopyrite is activated with copper sulphate to get it to float. The third ore is a copper/molybdenum ore (Ore C). Table 1 shows conditions used in all the testwork. There has been a large mnount of data obtained from the testing program studying FLEX 31. For the sake of brevity, not all the data obtained in this testwork is presented here, but other experiments and results are mentioned in the text of this paper. TABLE 1 Testwork conditions Ore Grind Cell
Irpm Frother % solids No. of Roug~ers/Cu cone. float times (min) No. of Scavengers/Zn Cone float times (rain) Primary Collector Secondary Collector Activator pH
•
A -- Cu/Zn
-
B -Arsenopyrite 80% --325 mesh 80% --200 mesh 2L MBM Autoflot 3L Agitar 825 1500 MIBC Dowfroth 250 33 33 3 1
1,2,4 3 1,2,4 SIPX
0 0 3:1 SIPX/PAX
SIPX copper sulphate 10.5/11.0
3:1 SIPX/PAX copper sulphate 8.0
8
C - - Cu/Mo 70% --65 mesh 2L MBM Autoflot 1200 MIBC 33 2 1,2 2 3,3 isobutyl dithiophosphate SIPX 10.6
Copper/Zinc Ore (:Ore A) Ore A was used to investigate the use of FLEX 31 against SIPX. The ore is a complex g-s-C
512
B.G. Cousinsand R. S. MaePhail
chaicopyrite/sphalerite/pyrite mixture requiring 80% passing 200 mesh for good dissemination of the minerals. Gold is present in the ore and is generally associated with the chalcopyrite. A derivative combination normally used on Ore A for copper collection is a xanthogen formate/thionocarbamate mixture at 20 g/t with pH modification using lime (pH = 10.5). After the copper is collected, the sphalerite is activated by copper sulphate and collected using a thionocarbamate at approximately 20 g/t. For comparison of FLEX 31 to SIPX, only SIPX and FLEX 31 were used for both copper and zinc collection. FLEX 31 showed marked improvement over SIPX in copper, zinc and gold recoveries with an improved rejection of iron in the concentrates. However, the copper/zinc separation was similar for both SIPX and FLEX 31. Both reagents gave similar results for zinc recovery in the copper concentrates. Using the xanthate derivative mixture normally used, a better separation is possible. Metallurgical balances are listed in Table 2. The rate curves are shown in Figure 1. TABLE 2 Ore A flotation data
Reagent
Product
wt Cu %
I
Zn %
Aecum Rec. Cu Zn
1
SIPX
Cone 1 2 3 4 5 6 tails total
22.76 22.37 35.16 44.21 51.97 34.68 801.9 1013.05
1.95 2.12 1.45 0.78 0.33 0.21 0.03 0.22
5.67 6.18 4.38 24.54 16.38 4.78 0.54 2.92
19.66 40.67 63.25 78.52 86.12 89.34 100.00
4.37 9.04 14.25 50.95 79.74 85.35 100.00
FLEX 31
1 2 3 4 5 6 tails tOtal
45.00 22.43 24.39 30.46 39.18 30.69 803.3 995.5
1.66 2.18 1.48 0.73 0.33 0.18 0.03 0.23
3.55 5.26 4.46 42.48 20.31 6.14 0.35 2.96
33.28 55.06 71.14 81.04 86.80 89.26 100.00
5.42 9.43 13.12 57.05 84.06 90.46 100.00
1/2 FLEX 31
1 2 3 4 5 6 tails total
45.12 25.07 31.69 30.37 32.96 31.22 800.9 997.3
1.65 2.15 1.16 0.70 0.35 0.18 0.03 0.23
3.59 5.73 4.31 44.02 19.87 5.87 0.37 2.92
32.72 56.40 72.56 81.90 86.97 89.44 100.00
5.56 10.49 15.18 61.06 83.54 89.83 100.00
The data for copper was submitted to the computer program FLOTRATE for analysis. The results of the treatment are listed in Table 3. The data indicates that FLEX 31 increases the rate of flotation for copper (k value). This effect is still evident at one half the dosage of SIPX. Similar data is obtained when zinc is examined in the zinc concentrates. Also note that the maximum theoretical flotation recovery (RI value) for both FLEX 31 and the half dose of FLEX 31 are significantly higher than for SIPX.
Recoveries from copper bearing and copper-activated mineral ores
513
Some tests were c~Lrriedout using just FLEX 31 as the zinc collector, using the xanthate derivative mixture for copper collection. As a replacement for Ethyl Isopropyl Thionocarbamate, it was very successful. FLEX 31 showed superior zinc recovery upon activation with copper sulphate. Pyrite rejection was improved as well. Therefore, with copper/zinc ores, FLEX 31 is an excellent activated zinc collector. 100
T
Copper Recovery 2
9"
A lq FLEX31 I
0
so 60
20
I 0
I
200
I
400 600 Time (see)
I
I
800
1000
~ 200
SIPX
Zinc Recovery
I
~
I
I
400
600
800
100O
Time(see)
I00
Corrected Zinc Recovery
4O ---iS-- FLEX 31 ---k-- 1/2 FLEX 31
200
I
I
400
600
Time (see)
Fig. 1 Ore A Recovery Rate Curves
TABLE 3 Rate Data for Ore A (copper) Reagent SIPX FLEX 31 1/2 FLEX 31[
RI 0.87 0.90 0.90
k x 10 -J 5.36 5.91 5.72
0 19.6 26.8 28.0
514
B.G. Cousinsand IL S. MacPhail
Arsenopyrite/Pyrite Ore (Ore B) Many gold ores consist of gold tied up in sulphide mineralization. The mineralization can be pyrite, chalcopyrite, arsenopyrite and a variety of other sulphide minerals. Gold can also exist as free gold in large enough particle sizes to be able to recover very easily. Ore B is such an ore, having gold associated with arsenopyrite. In order to collect the gold, general bulk flotation agents are used. A present collector combination used is a 3:1 ratio of Sodium Isopropyl Xanthate (SIPX) to Potassium Amyl Xanthate (PAX). Tests run were direct comparison tests of SIPX to varying amounts of FLEX 31. SIPX was added to 56 g/t and PAX to 19 g/t for each concentrate. Three tests replaced SIPX with FLEX 31, added to 56 g/t, 47 g/t and 38 g/t with the PAX additions staying set at 19 g/t. Rate data was not obtainable as only one rougher concentrate was collected for each test. Table 4 results show that arsenic recovery using FLEX 31 over SIPX improved in the rougher concentrate. This translated into higher gold recoveries. The arsenic and gold grades are higher as well. This is due to the significantly reduced weight floated in the rougher concentrate. This ore has a significant pyrite concentration which has been rejected by FLEX 31. The net result is significantly improved recoveries of arsenic (+7%) and gold (+4%) with an approximately 17% reduction in the weight of the concentrate. When the dose of FLEX 31 is reduced by one third, the recoveries of arsenic are slightly improved again (+ 1.5 %) while gold showed a slight drop ( - 2 %) with another 6 % drop in concentrate weight. The grades of arsenic show jumps of 29% for a full dose of FLEX 31 and 37% for a 2/3 dose of FLEX 31. Gold grades improve by 33% for a full dose of FLEX 31 and 32% for a 2/3 dose of FLEX 31. TABLE 4 Ore B flotation data
Reagent
Product
wt (g)
SIPX/PAX 3:1
Rough. Tails Head
173.25 827.3 1000.6
Reagent
Product
wt (g)
FLEX/PAX 3:1
Rough. Tails Head
143.15 856.9 1000.1
Reagent
Product
wt (g)
FLEX/PAX 2:1
Rough. Tails Head
132.76 867.1 999.9
As (%) 2.86 0.17 0.64
Assay Au (ppm) 41.4 1.7 8.6
Aecum.Recovery As Au 77.89 83.61
As (%) 3.70 0.12 0.63
Assay Au (ppm) 55.1 1.4 9.1
Accum.Recovery As Au 83.74 86.80
As (%) 3.92 0.13 0.63
Assay Au (ppm) 54.5 1.5 8.5
Accum.Recovery As Au 82.20 84.76
For Ore B, FLEX 31 has proven that it is a stronger collector of the copper-activated arsenopyrite mineral and hence can improve gold recoveries when the gold is associated with arsenopyrite. Improved specificity is also a mark of FLEX 31, being able to improve recoveries by floating less material, hence improving grades greatly.
Copper/Molybdenum Ore (Ore C) Recent work has been carried out against an ethyl dithiophosphate and SIPX on a copper/molybdenum ore. The dithiophosphate was used in a rougher concentrate with the SIPX being used as a scavenger collector. Tests were carried out to replace both with FLEX 31 (Table 5).
Recoveries from copper bearing and copper-activated mineral ores
515
TABLE 5 Ore C flotation data
(g)
Reagent
Cone
wt
Dithio,/SlPX
1 2 3 4 tails total
57.06 21.20 30.35 18.37 832.5 959.5
11.42 6.22 1.60 1.81 0.26 1.13
0.070 0.114 0.054 0.033 0.008 0.016
60.24 72.43 76.92 79.99 100.00
26.08 41.86 52.56 56.52 100.00
FI.,EX
1 2 3 4 tails total
59.41 29.35 18.16 16.71 867.2 990.8
9.74 7.36 5.00 1.59 0.26 1.15
0.073 0.109 0.067 0.030 0.008 0.016
50.87 69.86 77.84 80.18 I00.00
26.78 46.54 54.06 57.15 100.00
1/2 FLEX
1 2 3 4 tails total
48.68 37.05 31.04 18.03 854.3 989.0
12.18 6.04 3.17 1.83 0.22 1.15
0.088 0.095 0.049 0.029 0.007 0.016
52.19 71.89 80.55 83.46 100.00
27.07 49.30 58.91 62.22 100.00
Assay (%) Cu ] Mo
Accum. Recovery Cu Mo
Molybdenum flotation is usually carried out with some sort of oil-based collector as the minerals are generally hydrophobic by themselves and only need some assistance. Reagents used include dithiophosphates, thionocarbamates, straight bunker "C" oil, and a variety of different water insoluble compounds. The water insolubility of these compounds can sometimes inhibit their effectiveness as they cannot disperse through the slurry very well. FLEX 31 has no problem being soluble in water and the proprietary surfactant has been found to be a superior molybdenum collector over the isobutyl dithiophosphate it was tested against. In the rougher concentrates, FLEX 31 did not prove superior in copper flotation. As seen in Figure 2, the dithiophosphate gave a better recovery in the first rougher, but FLEX 31 caught up by the second rougher. FLEX 31 definitely outperformed SIPX in the scavengers. It is interesting to note that the reduced FLEX 31 dosage actually outperformed the full FLEX 31 dosage with this ore. With molybdenum, Figure 2 shows that FLEX 31 outperformed the dithiophosphate with both full and reduced dosages, giving better grades and recoveries. Iron rejection was improved as well with the half dose of FLEX 31, but not the full dose of FLEX 31, where the dithiophosphate was better. The data for copper and molybdenum were submitted to the computer program FLOTRATE for analysis. The results of the treatment are listed in Table 6. Here, it is shown that for copper, the kinetics are significantly slower for FLEX 31 than the dithiophosphate (copper k values), but the theoretical maximum recoveries are slightly higher for FLEX 31 and significantly higher for 1/2 FLEX 31. For molybdenum, the best theoretical recovery also comes with 1/2 dose FLEX 31 and the kinetics are significantly higher as well. It appears that with copper/moly type ores, overdosing with FLEX 31 is possible, creating the slow kinetics for copper observed in the full dose FLEX 31 tests. On ore C, FLEX 31 has proven comparable to a dithiophosphate in copper flotation and superior in molybdenum flotation and pyrite rejection.
516
B . G . Cousins and 1~ S. MacPhail
9O 70
60 50 40
! 30 20 0
I
..
Copper Recovery 1
I 100
0
I 200
I 300
400
Time (see)
+ 100
Dithio/SIPX
---IS-- FLEX 31
so
,~,
I 600
500
1/2 FLEX 31
Copper Recovery/Grade Curve
40 < ~
20 0 4
I
I
t
I
I
5
6
7
8
9
I
I
I
I
I
I
10 11 12 13 14 15
Acctmt Grade (%)
70
~,--
~
5O 40
o/SIPX
' ~ 30
ml~
20 10 0
~
0
Molybdenum Recovery
-'-M'-- FLEX 31
I
I
I
I
100
200
300
400
1/2 FLEX31 -
I
-
I
500
600
Time (sec)
70 6O
50
Molybdenum Recovery/Grade Curve
Dithio/SIPX
~ 3o
- - I I - - FLEX 31 - - N - - 1/2 FLEX 31
10
0.03
I
I
I
I
I
I
I
0.04
0.05
0.06
0.07
0.08
0.09
0.10
Aecum
Grade (%)
Fig.2 Ore C Recovery Rate Curves and Recovery/Grade Curves
Recoveriesfromcopperbearingand copper-activatedmineralores
517
TABLE 6 Rate data for ore C Copper Reagent DTP/SIPX FLEX 31 1/2 FLEX 31
RI 0.806 0.809 0.845
k x 10 -3 0 9.29 119.8 7.94 64.6 7.45 68.9
Molybdenum Reagent DTP/SIPX FLEX 31 I/2 FLEX 31
RI 0.594 0.580 0.633
k x 10 -3 5.31 7.59 7.45
# 48.9 21.2 14.7
FLEXANTHATES IN PLANT TRIALS Currently, FLEX :31 is being tested at copper/zinc mines in Northern Quebec as a zinc collector. Plant scale tests are being carded out at the Louvincourt Mine and at Les Mines Selbaie in their respective zinc circuits. Results were not available at the time of writing, but indications are that FLEX 31 performed very well at both Louvincourt and Les Mines Selbaie. Other mines in the area are in the process of evaluating FLEX 31 for their copper/zinc operations. Another flexanthate product, FLEX 20 (chemically enhanced potassium ethyl xanthate) was developed along the same lines as FLEX 31 and tested at Zinc Corp. of America's zinc mine near Grosveneur, New York. The Zinc Corp. operation is highly automated with on-line analyzers where reagent evaluations can be carried out quickly in the mill. At the time of the plant trial, Zinc Corp. was using a mixture of potassium ethyl xanthate and isobutyl dithiophosphate. Neither of these reagents was able to perform properly on its own. FLEX 20 was found to be capable of replacing both reagents and working by itself in the mill. FLEX 20 also gave improved grades and recoveries. FLEX 20 solutioned well and was handled as easily as the potassium ethyl xanthate. Zinc Corp. has now switched over to FLEX 20 as their reagent of choice. The plant trials have shown that flexanthates are as easily handled as their respective regular xanthates and produce superior results with a much lower dosage. More plant trials are pending at mines in Northern Quebec and Arizona.
CONCLUSION The surfactant used in FLEX 31 has shown that it has the ability to increase adsorption of xanthate onto copper and copper activated mineral surfaces. The increased adsorption gives it marked improvement over SIPX in many flotation situations and comparable results with xanthate derivative and dithiophosphate reagents. With both copper-bearing and copper-activated minerals, FLEX 31 can produce higher grade concentrates, better overall recoveries and improved pyrite rejection than SIPX. When precious metals are well associated with the copper and copper-activated minerals, their recovery can also be improved. Plant trials with F]iexanthates have shown that the improved results obtained in the laboratory testing programs have tran,dated well to operating fotation mills, with FLEX 20 now being the reagent of choice at Zinc Corp., and FLEX 31 at Louvincourt. Future work will involve testing a chemically enhanced potassium isobutyl xanthate (FLEX 41).
518
B.G. Cousins and R. S. MacPhaii
ACKNOWLEDGEMENTS The authors would like to thank Prospec Chemicals and Charles Tennant & Co. (Canada) Ltd. for funding the work involved in testing FLEX 31. The authors would also like to thank Natalie Duszezyszyn for her work with the microflot cell and the Zinc Corporation of America, Aur Louvineourt and Les Mines Selbaie for carrying out their plant trials on FLEX 20 and FLEX 31
REFERENCES
°
2.
.
4. 5.
Finkelstein, N.P. & Poling, G.W., The Role of Dithiolates in the Flotation of Sulphide Minerals. Mineral Science Engineering, 9, 177 (1977). Melis, L.A., Armstrong, K.C., Cron, A.B. & MacPhail, R.S., Metallurgy of the Mount Milligan Porphyry Copper/Gold Deposit. Proc. 23rd Annual Meeting of the Canadian Mineral Processors, CIM, Paper No. 13. (1991). MacPhall, R.S. & Cousins, B.G., Improvement of Recoveries from Copper-Bearing and CopperActivated Mineral Ores Using FLEX 31. Proc. Randol Gold Forum, 73 (1995). Agar, G.E., Mineral Process Flowsheet Synthesis. Challenges in Mineral Processing, SME 1989 678-693 (1989). Agar, G.E. & Barrett, J.J., The Use of Flotation Rate Data to Evaluate Reagents. CIM Bulletin, 76, No. 851, 157 (1983).
Minerals Engineering, Vol. 9, No. 5, pp. 509-518, 1996 Copyright O 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved PII: S0892-6875(96)00039--8 0892-6875/96 $15.00+0.00
IMPROVEMENT OF RECOVERIES FROM COPPER BEARING AND COPPER-ACTIVATED MINERAL ORES USING FLEX 31
B.G. COUSINS§ and R.S. MACPHAIL? § Tenn~ts Research Technology Applications, Edmonton, Alberta, Canada "~Prospec Chemicals, Weston, Ontario, Canada (Received 29 July 1995; accepted 13 February 1996)
ABSTRACT Many copper-bearing ores use Sodium Isopropyl Xanthate (SIPX) as a flotation agent. In general, SIPX will float to some extent other minerals which may not be desirable, such as pyrite. FLEX 31 is a chemically enhanced SIPX product with many of the same properties as SIPX, but FLEX 31 has the ability to reject mare pyrite from concentrates as well as improves recoveries of copper when using 50% less FLEX 31 than is required if using SIPX. Copper-activated minerals, such as sphalerite and arsenopyrite, show increased recoveries as well using FLEX 31. However, in copper separation from these minerals prior to activation, FLEX 31 performs very similarly to SIPX and does not give the best separation possible with other reagents. Tests have been performed on copper~zinc, arsenopyrite and copper~molybdenum ores.
Keywords Sulphide ores; flotation reagents; flotation kinetics; froth flotation
INTRODUCTION
Sodium Isopropyl Xanthate (SIPX) is one of the most popular flotation chemicals on the market today. Somewhat more specific than amyl xanthates, SIPX is used in a variety of ores such as copper/zinc, lead/zinc, arsenopyrite/pyrite, and many others. An investigation carried out by Teunants Research Technology Applications (TRTA), a division of Charles Tennant & Co. (Canada) Ltd., produced a chemically enhanced S1PX that has shown all the advantages of normal SIPX along with improved recoveries of copper and copper activated minerals. The new product has been named FLEX 31. Currently, FLEX 31 is manufactured at the Prospec Chemicals, another division of Charles Tennant & Co. (Canada) Ltd. Their xanthate plant in Fort Saskatchewan, Alberta, Canada has a capacity of approximately 4500 tons of xanthates per year and is currently undergoing expansion to produce approximately 6000 tons of xanthates per year, making Prospec one of the largest mining chemical producers in the world. The proprietary process for FLEX 31 production is a new addition to plant operations that include the production of xanthate, thionocarbamate and xanthogen formate flotation reagents. Posl~r presentation at M/nera/s Eng/neetqng '95, St. Ives, Cornwall, England, June 1995
509
510
B. G. Cousinsand R. S. MaePhail FLEX 31 CHARACTERISTICS
Xanthate in copper flotation is known to create a dixanthogen on the mineral surface [1]. Copper is the catalyst to the formation. The dixanthogen structure includes a basic hexagonal ring of two carbons and four sulphurs (planar) which is a very stable structure and the increased hydrophobicity explains why copper floats so well with xanthates. Flexanthates were created in an attempt to increase the adsorption of xanthate onto mineral surfaces and enhance flotation. With ordinary xanthate, a large percentage stays soluble in water and does not adsorb. It was theorized that a surfactant that also forms the same type of hexagonal structure with xanthate without actually reacting with it could help in getting more of the xanthate onto the copper surfaces. The copper would help form the complex as it does with dixanthogen. The resultant complex could have the potential to create a higher degree of hydrophobicity than dixanthogen on the copper surface by its organic chemical structure as well as increase adsorption. A number of potential surfactants were tried until the one used to make FLEX 31 was discovered (due to the proprietary nature of flexanthates, the surfactant used cannot be disclosed). The surfactant in effect creates the superior flotation seen with FLEX 31. The proprietary process developed for sodium isopropyl xanthate (SIPX), a standard copper flotation reagent, produced FLEX 31. In extensive flotation studies, not only was it discovered that FLEX 31 had a stronger collecting power for copper and copper-activated minerals, it also had the ability to reject more strongly minerals that SIPX rejects to some degree, such as pyrite. FLEX 31 is produced in a pelleted form. Its appearance is very similar to pelleted SIPX and it has many of the same characteristics. It is totally soluble in a 1% solution with water and colours the solution with the same yellow colour as SIPX. For lab tests, 1% solutions of FLEX 31 in water are recommended. The enhanced activity of FLEX 31 allows for less of the product to be used to achieve better recoveries when compared directly with SIPX. A flotation test that requires 50 g/t of SIPX can still show better recoveries with the addition of only 25 g/t of FLEX 31. Increased pyrite rejection has also been observed with FLEX 31 than with SIPX. The reasons for the higher iron mineral rejection over SIPX is not known at this time. It is possible the surfactant used is capable of creating a high hydrophilic surface with iron minerals on its own. Precious metals associated with sulphides also show increased recoveries as well [2,3]. However, precious metals associated with pyrite tend to get rejected with the pyrite. Free precious metals normally not collected by SIPX will not be collected by FLEX 31 either. TESTWORK Flotation Rate Determinations Some of the data from the testwork was analyzed using first order rate kinetics. Flotation can be described as a process where the ore is ground to a predetermined fineness, and having a given size distribution and distribution of liberated and locked particles of valuable and gangue minerals, the valuable minerals can be separated from the gangue minerals in a flotation circuit. Depending on the prevailing Eh-pH, temperature and solution conditions as well as the presence of various reagents, the feed is split into two products; the concentrate containing the valuable mineral and the tails containing the gangue. This separation is essentially a kinetic process. Work carded out at INCO Research determined that the kinetic process can be described by a first order rate equation [4,5].
This equation is:
R = RI[1-exp -kO÷°)]
Recoveriesfrom copperbearing and copper-activatedmineralores
511
where: is is is is is
R RI k t 0
the the the the the
cmnulative recovery after time t maximum theoretical flotation recovery first order rate constant (time - l ) cumulative flotation time time correction factor
The time correction factor is included to allow for such things as air aspirated into the flotation cell during conditioning and some time elapses between the time that air flow is started and the first collection of floated material. The first factor indicates that time should be added whereas the second factor suggests that time should be d¢~lucted. The three parameters to be fitted to the rate equation are k, RI and 0. The equation is rearranged as follows:
RI-R I n ~ RI
= -k(t+0)
A computer program has been developed to fit the data into the above equation. A least square regression is done with this equation with an arbitrary, but adjustable, value of RI. An F test is done with regression mean square in the numerator and the residual mean square in the denominator and if the fit is judged significant at a 99 % level of significance, the values of k and 0 are calculated. If the value of O falls outside a pre-selected range of acceptable values, the data point for the longest flotation time is deducted and the procedure repeated with the truncated data set. Most of the work carried out at this time has been with copper/zinc ores. One ore in particular, a copper/zinc ore (Ore A), has had extensive work carried out on it. Another ore (Ore B) is an arsenopyrite/pyrite gold ore where the arsenopyrite is activated with copper sulphate to get it to float. The third ore is a copper/molybdenum ore (Ore C). Table 1 shows conditions used in all the testwork. There has been a large mnount of data obtained from the testing program studying FLEX 31. For the sake of brevity, not all the data obtained in this testwork is presented here, but other experiments and results are mentioned in the text of this paper. TABLE 1 Testwork conditions Ore Grind Cell
Irpm Frother % solids No. of Roug~ers/Cu cone. float times (min) No. of Scavengers/Zn Cone float times (rain) Primary Collector Secondary Collector Activator pH
•
A -- Cu/Zn
-
B -Arsenopyrite 80% --325 mesh 80% --200 mesh 2L MBM Autoflot 3L Agitar 825 1500 MIBC Dowfroth 250 33 33 3 1
1,2,4 3 1,2,4 SIPX
0 0 3:1 SIPX/PAX
SIPX copper sulphate 10.5/11.0
3:1 SIPX/PAX copper sulphate 8.0
8
C - - Cu/Mo 70% --65 mesh 2L MBM Autoflot 1200 MIBC 33 2 1,2 2 3,3 isobutyl dithiophosphate SIPX 10.6
Copper/Zinc Ore (:Ore A) Ore A was used to investigate the use of FLEX 31 against SIPX. The ore is a complex g-s-C
512
B.G. Cousinsand R. S. MaePhail
chaicopyrite/sphalerite/pyrite mixture requiring 80% passing 200 mesh for good dissemination of the minerals. Gold is present in the ore and is generally associated with the chalcopyrite. A derivative combination normally used on Ore A for copper collection is a xanthogen formate/thionocarbamate mixture at 20 g/t with pH modification using lime (pH = 10.5). After the copper is collected, the sphalerite is activated by copper sulphate and collected using a thionocarbamate at approximately 20 g/t. For comparison of FLEX 31 to SIPX, only SIPX and FLEX 31 were used for both copper and zinc collection. FLEX 31 showed marked improvement over SIPX in copper, zinc and gold recoveries with an improved rejection of iron in the concentrates. However, the copper/zinc separation was similar for both SIPX and FLEX 31. Both reagents gave similar results for zinc recovery in the copper concentrates. Using the xanthate derivative mixture normally used, a better separation is possible. Metallurgical balances are listed in Table 2. The rate curves are shown in Figure 1. TABLE 2 Ore A flotation data
Reagent
Product
wt Cu %
I
Zn %
Aecum Rec. Cu Zn
1
SIPX
Cone 1 2 3 4 5 6 tails total
22.76 22.37 35.16 44.21 51.97 34.68 801.9 1013.05
1.95 2.12 1.45 0.78 0.33 0.21 0.03 0.22
5.67 6.18 4.38 24.54 16.38 4.78 0.54 2.92
19.66 40.67 63.25 78.52 86.12 89.34 100.00
4.37 9.04 14.25 50.95 79.74 85.35 100.00
FLEX 31
1 2 3 4 5 6 tails tOtal
45.00 22.43 24.39 30.46 39.18 30.69 803.3 995.5
1.66 2.18 1.48 0.73 0.33 0.18 0.03 0.23
3.55 5.26 4.46 42.48 20.31 6.14 0.35 2.96
33.28 55.06 71.14 81.04 86.80 89.26 100.00
5.42 9.43 13.12 57.05 84.06 90.46 100.00
1/2 FLEX 31
1 2 3 4 5 6 tails total
45.12 25.07 31.69 30.37 32.96 31.22 800.9 997.3
1.65 2.15 1.16 0.70 0.35 0.18 0.03 0.23
3.59 5.73 4.31 44.02 19.87 5.87 0.37 2.92
32.72 56.40 72.56 81.90 86.97 89.44 100.00
5.56 10.49 15.18 61.06 83.54 89.83 100.00
The data for copper was submitted to the computer program FLOTRATE for analysis. The results of the treatment are listed in Table 3. The data indicates that FLEX 31 increases the rate of flotation for copper (k value). This effect is still evident at one half the dosage of SIPX. Similar data is obtained when zinc is examined in the zinc concentrates. Also note that the maximum theoretical flotation recovery (RI value) for both FLEX 31 and the half dose of FLEX 31 are significantly higher than for SIPX.
Recoveries from copper bearing and copper-activated mineral ores
513
Some tests were c~Lrriedout using just FLEX 31 as the zinc collector, using the xanthate derivative mixture for copper collection. As a replacement for Ethyl Isopropyl Thionocarbamate, it was very successful. FLEX 31 showed superior zinc recovery upon activation with copper sulphate. Pyrite rejection was improved as well. Therefore, with copper/zinc ores, FLEX 31 is an excellent activated zinc collector. 100
T
Copper Recovery 2
9"
A lq FLEX31 I
0
so 60
20
I 0
I
200
I
400 600 Time (see)
I
I
800
1000
~ 200
SIPX
Zinc Recovery
I
~
I
I
400
600
800
100O
Time(see)
I00
Corrected Zinc Recovery
4O ---iS-- FLEX 31 ---k-- 1/2 FLEX 31
200
I
I
400
600
Time (see)
Fig. 1 Ore A Recovery Rate Curves
TABLE 3 Rate Data for Ore A (copper) Reagent SIPX FLEX 31 1/2 FLEX 31[
RI 0.87 0.90 0.90
k x 10 -J 5.36 5.91 5.72
0 19.6 26.8 28.0
514
B.G. Cousinsand IL S. MacPhail
Arsenopyrite/Pyrite Ore (Ore B) Many gold ores consist of gold tied up in sulphide mineralization. The mineralization can be pyrite, chalcopyrite, arsenopyrite and a variety of other sulphide minerals. Gold can also exist as free gold in large enough particle sizes to be able to recover very easily. Ore B is such an ore, having gold associated with arsenopyrite. In order to collect the gold, general bulk flotation agents are used. A present collector combination used is a 3:1 ratio of Sodium Isopropyl Xanthate (SIPX) to Potassium Amyl Xanthate (PAX). Tests run were direct comparison tests of SIPX to varying amounts of FLEX 31. SIPX was added to 56 g/t and PAX to 19 g/t for each concentrate. Three tests replaced SIPX with FLEX 31, added to 56 g/t, 47 g/t and 38 g/t with the PAX additions staying set at 19 g/t. Rate data was not obtainable as only one rougher concentrate was collected for each test. Table 4 results show that arsenic recovery using FLEX 31 over SIPX improved in the rougher concentrate. This translated into higher gold recoveries. The arsenic and gold grades are higher as well. This is due to the significantly reduced weight floated in the rougher concentrate. This ore has a significant pyrite concentration which has been rejected by FLEX 31. The net result is significantly improved recoveries of arsenic (+7%) and gold (+4%) with an approximately 17% reduction in the weight of the concentrate. When the dose of FLEX 31 is reduced by one third, the recoveries of arsenic are slightly improved again (+ 1.5 %) while gold showed a slight drop ( - 2 %) with another 6 % drop in concentrate weight. The grades of arsenic show jumps of 29% for a full dose of FLEX 31 and 37% for a 2/3 dose of FLEX 31. Gold grades improve by 33% for a full dose of FLEX 31 and 32% for a 2/3 dose of FLEX 31. TABLE 4 Ore B flotation data
Reagent
Product
wt (g)
SIPX/PAX 3:1
Rough. Tails Head
173.25 827.3 1000.6
Reagent
Product
wt (g)
FLEX/PAX 3:1
Rough. Tails Head
143.15 856.9 1000.1
Reagent
Product
wt (g)
FLEX/PAX 2:1
Rough. Tails Head
132.76 867.1 999.9
As (%) 2.86 0.17 0.64
Assay Au (ppm) 41.4 1.7 8.6
Aecum.Recovery As Au 77.89 83.61
As (%) 3.70 0.12 0.63
Assay Au (ppm) 55.1 1.4 9.1
Accum.Recovery As Au 83.74 86.80
As (%) 3.92 0.13 0.63
Assay Au (ppm) 54.5 1.5 8.5
Accum.Recovery As Au 82.20 84.76
For Ore B, FLEX 31 has proven that it is a stronger collector of the copper-activated arsenopyrite mineral and hence can improve gold recoveries when the gold is associated with arsenopyrite. Improved specificity is also a mark of FLEX 31, being able to improve recoveries by floating less material, hence improving grades greatly.
Copper/Molybdenum Ore (Ore C) Recent work has been carried out against an ethyl dithiophosphate and SIPX on a copper/molybdenum ore. The dithiophosphate was used in a rougher concentrate with the SIPX being used as a scavenger collector. Tests were carried out to replace both with FLEX 31 (Table 5).
Recoveries from copper bearing and copper-activated mineral ores
515
TABLE 5 Ore C flotation data
(g)
Reagent
Cone
wt
Dithio,/SlPX
1 2 3 4 tails total
57.06 21.20 30.35 18.37 832.5 959.5
11.42 6.22 1.60 1.81 0.26 1.13
0.070 0.114 0.054 0.033 0.008 0.016
60.24 72.43 76.92 79.99 100.00
26.08 41.86 52.56 56.52 100.00
FI.,EX
1 2 3 4 tails total
59.41 29.35 18.16 16.71 867.2 990.8
9.74 7.36 5.00 1.59 0.26 1.15
0.073 0.109 0.067 0.030 0.008 0.016
50.87 69.86 77.84 80.18 I00.00
26.78 46.54 54.06 57.15 100.00
1/2 FLEX
1 2 3 4 tails total
48.68 37.05 31.04 18.03 854.3 989.0
12.18 6.04 3.17 1.83 0.22 1.15
0.088 0.095 0.049 0.029 0.007 0.016
52.19 71.89 80.55 83.46 100.00
27.07 49.30 58.91 62.22 100.00
Assay (%) Cu ] Mo
Accum. Recovery Cu Mo
Molybdenum flotation is usually carried out with some sort of oil-based collector as the minerals are generally hydrophobic by themselves and only need some assistance. Reagents used include dithiophosphates, thionocarbamates, straight bunker "C" oil, and a variety of different water insoluble compounds. The water insolubility of these compounds can sometimes inhibit their effectiveness as they cannot disperse through the slurry very well. FLEX 31 has no problem being soluble in water and the proprietary surfactant has been found to be a superior molybdenum collector over the isobutyl dithiophosphate it was tested against. In the rougher concentrates, FLEX 31 did not prove superior in copper flotation. As seen in Figure 2, the dithiophosphate gave a better recovery in the first rougher, but FLEX 31 caught up by the second rougher. FLEX 31 definitely outperformed SIPX in the scavengers. It is interesting to note that the reduced FLEX 31 dosage actually outperformed the full FLEX 31 dosage with this ore. With molybdenum, Figure 2 shows that FLEX 31 outperformed the dithiophosphate with both full and reduced dosages, giving better grades and recoveries. Iron rejection was improved as well with the half dose of FLEX 31, but not the full dose of FLEX 31, where the dithiophosphate was better. The data for copper and molybdenum were submitted to the computer program FLOTRATE for analysis. The results of the treatment are listed in Table 6. Here, it is shown that for copper, the kinetics are significantly slower for FLEX 31 than the dithiophosphate (copper k values), but the theoretical maximum recoveries are slightly higher for FLEX 31 and significantly higher for 1/2 FLEX 31. For molybdenum, the best theoretical recovery also comes with 1/2 dose FLEX 31 and the kinetics are significantly higher as well. It appears that with copper/moly type ores, overdosing with FLEX 31 is possible, creating the slow kinetics for copper observed in the full dose FLEX 31 tests. On ore C, FLEX 31 has proven comparable to a dithiophosphate in copper flotation and superior in molybdenum flotation and pyrite rejection.
516
B . G . Cousins and 1~ S. MacPhail
9O 70
60 50 40
! 30 20 0
I
..
Copper Recovery 1
I 100
0
I 200
I 300
400
Time (see)
+ 100
Dithio/SIPX
---IS-- FLEX 31
so
,~,
I 600
500
1/2 FLEX 31
Copper Recovery/Grade Curve
40 < ~
20 0 4
I
I
t
I
I
5
6
7
8
9
I
I
I
I
I
I
10 11 12 13 14 15
Acctmt Grade (%)
70
~,--
~
5O 40
o/SIPX
' ~ 30
ml~
20 10 0
~
0
Molybdenum Recovery
-'-M'-- FLEX 31
I
I
I
I
100
200
300
400
1/2 FLEX31 -
I
-
I
500
600
Time (sec)
70 6O
50
Molybdenum Recovery/Grade Curve
Dithio/SIPX
~ 3o
- - I I - - FLEX 31 - - N - - 1/2 FLEX 31
10
0.03
I
I
I
I
I
I
I
0.04
0.05
0.06
0.07
0.08
0.09
0.10
Aecum
Grade (%)
Fig.2 Ore C Recovery Rate Curves and Recovery/Grade Curves
Recoveriesfromcopperbearingand copper-activatedmineralores
517
TABLE 6 Rate data for ore C Copper Reagent DTP/SIPX FLEX 31 1/2 FLEX 31
RI 0.806 0.809 0.845
k x 10 -3 0 9.29 119.8 7.94 64.6 7.45 68.9
Molybdenum Reagent DTP/SIPX FLEX 31 I/2 FLEX 31
RI 0.594 0.580 0.633
k x 10 -3 5.31 7.59 7.45
# 48.9 21.2 14.7
FLEXANTHATES IN PLANT TRIALS Currently, FLEX :31 is being tested at copper/zinc mines in Northern Quebec as a zinc collector. Plant scale tests are being carded out at the Louvincourt Mine and at Les Mines Selbaie in their respective zinc circuits. Results were not available at the time of writing, but indications are that FLEX 31 performed very well at both Louvincourt and Les Mines Selbaie. Other mines in the area are in the process of evaluating FLEX 31 for their copper/zinc operations. Another flexanthate product, FLEX 20 (chemically enhanced potassium ethyl xanthate) was developed along the same lines as FLEX 31 and tested at Zinc Corp. of America's zinc mine near Grosveneur, New York. The Zinc Corp. operation is highly automated with on-line analyzers where reagent evaluations can be carried out quickly in the mill. At the time of the plant trial, Zinc Corp. was using a mixture of potassium ethyl xanthate and isobutyl dithiophosphate. Neither of these reagents was able to perform properly on its own. FLEX 20 was found to be capable of replacing both reagents and working by itself in the mill. FLEX 20 also gave improved grades and recoveries. FLEX 20 solutioned well and was handled as easily as the potassium ethyl xanthate. Zinc Corp. has now switched over to FLEX 20 as their reagent of choice. The plant trials have shown that flexanthates are as easily handled as their respective regular xanthates and produce superior results with a much lower dosage. More plant trials are pending at mines in Northern Quebec and Arizona.
CONCLUSION The surfactant used in FLEX 31 has shown that it has the ability to increase adsorption of xanthate onto copper and copper activated mineral surfaces. The increased adsorption gives it marked improvement over SIPX in many flotation situations and comparable results with xanthate derivative and dithiophosphate reagents. With both copper-bearing and copper-activated minerals, FLEX 31 can produce higher grade concentrates, better overall recoveries and improved pyrite rejection than SIPX. When precious metals are well associated with the copper and copper-activated minerals, their recovery can also be improved. Plant trials with F]iexanthates have shown that the improved results obtained in the laboratory testing programs have tran,dated well to operating fotation mills, with FLEX 20 now being the reagent of choice at Zinc Corp., and FLEX 31 at Louvincourt. Future work will involve testing a chemically enhanced potassium isobutyl xanthate (FLEX 41).
518
B.G. Cousins and R. S. MacPhaii
ACKNOWLEDGEMENTS The authors would like to thank Prospec Chemicals and Charles Tennant & Co. (Canada) Ltd. for funding the work involved in testing FLEX 31. The authors would also like to thank Natalie Duszezyszyn for her work with the microflot cell and the Zinc Corporation of America, Aur Louvineourt and Les Mines Selbaie for carrying out their plant trials on FLEX 20 and FLEX 31
REFERENCES
°
2.
.
4. 5.
Finkelstein, N.P. & Poling, G.W., The Role of Dithiolates in the Flotation of Sulphide Minerals. Mineral Science Engineering, 9, 177 (1977). Melis, L.A., Armstrong, K.C., Cron, A.B. & MacPhail, R.S., Metallurgy of the Mount Milligan Porphyry Copper/Gold Deposit. Proc. 23rd Annual Meeting of the Canadian Mineral Processors, CIM, Paper No. 13. (1991). MacPhall, R.S. & Cousins, B.G., Improvement of Recoveries from Copper-Bearing and CopperActivated Mineral Ores Using FLEX 31. Proc. Randol Gold Forum, 73 (1995). Agar, G.E., Mineral Process Flowsheet Synthesis. Challenges in Mineral Processing, SME 1989 678-693 (1989). Agar, G.E. & Barrett, J.J., The Use of Flotation Rate Data to Evaluate Reagents. CIM Bulletin, 76, No. 851, 157 (1983).