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Effect of fineness of grind on semi-batch flotation test results
Minerals Engineering 18 (2005) 367–370
Technical Note
This article is also available online at: www.elsevier.com/locate/mineng
Effect of fineness of grind on semi-batch flotation test results Claude Bazin a
a,*
, Carole Fortin b, Daniel Hodouin a, Jean Cayouette
c
Department of Mining, Metallurgical and Materials Engineering, Laval University, Quebec, QC, Canada G1K 7P4 b Brunswick Mining and Smelting, Mining Division, Bathurst, New-Brunswick, Canada E2A 3Z8 c Les Ressources Aur, Mine Louvicourt, Val-d’Or, Que´bec, Canada J6P 6V2 Received 31 January 2004; accepted 4 June 2004
Abstract Laboratory semi-batch flotation tests were conducted with two different sulphide ore samples using various degrees of size reduction. The selectivity curves show that some minerals are more sensitive to particle size reduction than other ones suggesting that preferential associations of minerals may exist in the ore. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Grinding; Froth flotation; Liberation; Particle size; Sulphide ores
1. Introduction The grinding and flotation processes are intimately linked together. Grinding liberates mineral grains, while flotation separates them into valuable minerals and gangue. The paper analyzes the effect of the fineness of grind through the results of semi-batch flotation tests conducted using two different ore samples. The first section describes the ore samples and the test procedure and the second section analyzes the results. 2. Experimental procedure The ore samples used for the tests were provided by Brunswick Mining and Mines Louvicourt. The Brunswick Mining ore is a complex sulphide consisting of galena (3–5% PbS), marmatite (12–17% Zn(Fe)S), chalcopyrite (0.7–1.5% CuFeS2), pyrite (50–70% FeS2) and a non-sulphide gangue of silica and chlorite (Petruk and Schnarr, 1981). The sample from Louvicourt is a Cu–Zn ore containing copper sulphides (4–6%), sphaler-
ite (1–4% ZnS) and pyrite (15–25% FeS2) in a silica gangue (Duchesne et al., 2001). The Brunswick Mining ore sample was crushed to 1.2 mm and separated into 2 kg batches. The batches were ground for various times in a rod mill with soda ash and water. The ground material was aerated and conditioned with xanthate prior to the flotation of 6 concentrate samples. The slurry density for the flotation was 50% w/w solids. The pulp conditions are adjusted to promote the flotation of lead and copper minerals, and to reject marmatite, pyrite and non-sulphide gangue. Table 1 summarizes the test conditions. The Louvicourt Cu–Zn ore sample was crushed to 1.2 mm and separated into 1 kg batches. The batches were ground for various times and process to float 4 copper concentrate samples. Each flotation test was repeated three times and results are presented as averages of the repeated tests. The detailed procedures for both series of flotation tests are given elsewhere (Bazin et al., in preparation). 3. Analysis of the results
*
Corresponding author. Tel.: +1 418 656 5914; fax: +1 418 656 5343. E-mail address: [email protected] (C. Bazin). 0892-6875/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2004.06.008
The results of the flotation tests are analyzed here using the rate and grade–recovery curves and will
368
C. Bazin et al. / Minerals Engineering 18 (2005) 367–370
mineral target recovery. This raises the idea of rebalancing the energy between primary and regrinding mills to have a coarser grind in the primary grinding and a more intense action in the regrinding circuits which could lead to reduction of the overall energy required for mineral processing. Fig. 2 compresses the previous results at 75% Pb recovery (see Fig. 1). The time required to achieve 75% Pb recovery shows a possible trend with fineness of grind as grinding probably redistributes galena between slow floating coarse and fine particles. Except for chalcopyrite whose flotation is promoted by finer grinding, the recovery of marmatite, pyrite and non-sulphide minerals shows a significant decrease with fineness of grind. Hydraulic entrainment that is favourable to the recovery of fine particles is probably in the order of 5%, the ultimate recovery of fine non-sulphide gangue. Natural activation is probably not a dominant factor for the recovery of marmatite and pyrite as a finer grind should be favourable to the release of ions into solution. A redistribution of these minerals into size intervals of lower floatability is not sufficient to explain the observed behaviour (Bazin et al., 2001). The increase liberation of galena with fineness of grind is likely to be responsible for the results of Fig. 2. The slopes of the marmatite, pyrite and non-sulphide minerals recovery are respectively 0.43, 0.23 and 0.13 %/%–0.038 mm. This may indicate that middlings of galena–marmatite are more efficiently liberated than galena–pyrite or galena non-sulphide minerals middlings. This sensitivity for galena–marmatite is somewhat surprising as the low concentration of these minerals in the ore should be less favourable to the production of their middlings (Petruk and Schnarr, 1981; Lane and Richmond, 1993) unless there are preferential associations between these minerals in the ore.
Table 1 Flotation test conditions P0.074 (%)
P0.038 (%)
P0.016 (%)
Brunswick ore sample 20 89 27 97 30 98 40 99 50 99 60 99 70 100 80 100
60 66 70 86 93 97 98 99
23 23 25 28 34 39 43 45
Louvicourt ore sampleb 5.5 63 7.5 78 9.5 94 11.5 97 13.5 99 15.5 99 17.5 100
44 52 59 67 73 80 88
17 18 19 21 25 29 37
Grinding (min) a
Pxxx: % finer than size xxx in mm. a Flotation machine: Denver––4 l bowl; aeration rate: 5–7 l/min; reagents: collector––Isoprophyl xanthate: 55 g/t; frother––MIBC 6 g/t; pH modifier––soda ash (pH: 9.7); flotation feed: 2 kg of ore at 35% w/ w solids––2.94%Pb, 7.35%Zn, 0.38%Cu, 23.7%Fe. b Flotation machine: Denver––2.5 l bowl; aeration rate: 5–7 l/min; reagents: collector––3418-A 25 g/t; frother––MIBC 7 g/t; pH modifier––lime (pH: 10.5); flotation feed: 1 kg of ore at 30% w/w solids–– 2.93%Cu, 0.91%Zn, 24.03%Fe.
subsequently be used to build a simulator that includes hydraulic entrainment, mineral recovery by size (Trahar, 1981) and liberation data (Sutherland, 1989). 3.1. Brunswick ore sample Fig. 1 shows the effect of fineness of grind on the rate of flotation of Pb and Zn minerals and Pb grade–recovery curves for the Brunswick Mining ore. Results show that increasing fineness of grind from 60% to 99% finer than 0.038 mm (see Table 1) has little impact on the rate of flotation of galena but affects the recovery of marmatite. Grade recovery curves show that any gain in selectivity due to fineness of grind is offset by a high Pb
3.2. Louvicourt Cu–Zn ore Results for the Louvicourt ore sample are presented in Fig. 3. The Louvicourt sample is conditioned to float selectively the copper minerals from sphalerite, pyrite 40 97
Pb
80
Pb grade (%)
Recovery (%)
100
60 60% < 0. 038 mm
40 99% < 0.038 mm
Zn
20
30 60
99 86
20
69
10
Pb grade at 75% Pb recovery
Fineness increases
0
% passing 0.038mm 95
0
0
2
4
Flotation time (min)
6
8
30
50
70
Pb recovery (%)
Fig. 1. Brunswick ore sample rate and grade–recovery curves.
90
C. Bazin et al. / Minerals Engineering 18 (2005) 367–370 25
Slow floating coarse particles
Slow floating fine particles
Pb grade at Pb75
Time for Pb75 (min)
3
369
2
1
20
15
10 50
60
70
80
90
100
50
60
% finer than 0.038 mm
70
80
90
100
% finer than 0.038 mm 30
75
Recovery at Pb75
Cu recovery at Pb75
25
70
65
Zn sulphide 20 15
Fe sulphide
10 5
60
Non-sulphide
0
50
60
70
80
90
50
100
60
70
80
90
100
% finer than 0.038 mm
% finer than 0.038 mm
Fig. 2. Brunswick flotation results at 75% Pb recovery.
sult is probably related to the redistribution of copper minerals into size intervals of faster flotation rate and the higher copper content of the floated particles. The recovery of sphalerite at 90% copper recovery decreases with fineness of grind, while the recovery of iron sulphide minerals exhibits a rapid fall and stabilizes at 5% which could be used to approximate the hydraulic entrainment contribution although it is probably less since there could be iron sulphide flotation. The different behaviours of sphalerite and iron sulphide minerals may be an indication that pyrite–chalcopyrite are liberated more efficiently by grinding than chalcopyrite–sphalerite middlings. On the other hand, if liberation is responsible for the sphalerite flotation there should be preferential associations between chalcopyrite and sphalerite in the ore
and non-sulphide minerals. Except for the coarsest grind, an increase from 52% to 88% finer than 0.038 mm has very little effect on the rate of copper mineral flotation but has a significant effect on the rate of recovery of sphalerite. As observed for the Brunswick ore good recovery of copper minerals could be achieved at coarse grind leading to the idea that a coarser grind in the primary grinding circuit followed by a more intense regrinding of the rougher/scavenger concentrate could reduce the overall energy consumption. The effect of the fineness of grind for the Louvicourt ore is shown in Fig. 4 using 90% copper recovery as the reference condition for the data compression. The time required to achieve 90% copper recovery shows a slight decrease with increasing fineness of grind. This re-
30
100
73/80/88
Cu 25
Cu content (%)
Recovery (%)
80 60 Zn
40 20
59 & 67
20
52
% <0.038mm
15
44
10 5
Fineness increases
0
0
0
1
2 3 Flotation time (min)
4
5
50
60
70
80
Cu recovery (%)
Fig. 3. Rate and grade–recovery curves for the Louvicourt ore.
90
100
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C. Bazin et al. / Minerals Engineering 18 (2005) 367–370 25
Cu grade at Cu90
Time for Cu90 (min)
3.0
2.0
1.0
20
15
10
0.0 40
60
80
40
100
80
100
% finer than 0.038 mm
40
40
Pyrite recovery at Cu90
Sphalerite recovery at Cu90
% finer than 0.038 mm
60
35 30 25 20
30 20 10 0
40
60
80
100
40
% finer than 0.038 mm
60
80
100
% finer than 0.038 mm
Fig. 4. Louvicourt ore flotation results at 90% copper recovery.
because the two minerals are in low concentration which is not favourable to the production of their middlings.
4. Conclusion Semi-batch flotation tests were conducted with Cu–Pb–Zn and Cu–Zn sulphide ores with various size distributions. Results show a possible advantage of rebalancing the energy between the primary grinding mills and the regrinding units and may provide useful information for an indirect estimation of the mineral liberation and ore texture.
Acknowledgements The authors acknowledge the support of Brunswick Mining and Smelting and Mines Louvicourt for providing the samples for the flotation tests.
References Bazin, C., Hodouin, D., Cooper, M., 2001. Interaction between grinding and flotation. In: J.A. Finch (Ed.), Presented at the Interactions in Mineral Processing Symposium, 40th Annual Conference of Metallurgist, CIM, Toronto, August, pp. 3–16. Bazin, C., Fortin, C., Hodouin, D., Cayouette, J., in preparation. Modelling the effect of particle size distribution on the flotation response. Duchesne, S., Cayouette, J., Dallaire, B., 2001. Installation of Flash Flotation units at the Louvicourt Concentrator. In: Proceedings of the 33rd Annual Meeting of the Canadian Mineral Processors, Ottawa, January, pp. 285–302. Lane, G.S., Richmond, G.D., 1993. Improving fine particle flotation selectivity at Hellyer, XVIII International Mineral Processing Congress, Sydney, May 23–28, pp. 897–904. Petruk, W., Schnarr, J.R., 1981. An evaluation of the recovery of free and unliberated mineral grains, metals and trace elements in the concentrator of Brunswick Mining and Smelting Corp. Ltd. CIM Bull. 74 (833), 132–159. Sutherland, D.N., 1989. Batch flotation behaviour of composite particles. Miner. Eng. 2 (3), 351–367. Trahar, W.J., 1981. A rational interpretation of the role of particle size in flotation. Int. J. Miner. Process 8, 280–327.
Technical Note
This article is also available online at: www.elsevier.com/locate/mineng
Effect of fineness of grind on semi-batch flotation test results Claude Bazin a
a,*
, Carole Fortin b, Daniel Hodouin a, Jean Cayouette
c
Department of Mining, Metallurgical and Materials Engineering, Laval University, Quebec, QC, Canada G1K 7P4 b Brunswick Mining and Smelting, Mining Division, Bathurst, New-Brunswick, Canada E2A 3Z8 c Les Ressources Aur, Mine Louvicourt, Val-d’Or, Que´bec, Canada J6P 6V2 Received 31 January 2004; accepted 4 June 2004
Abstract Laboratory semi-batch flotation tests were conducted with two different sulphide ore samples using various degrees of size reduction. The selectivity curves show that some minerals are more sensitive to particle size reduction than other ones suggesting that preferential associations of minerals may exist in the ore. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Grinding; Froth flotation; Liberation; Particle size; Sulphide ores
1. Introduction The grinding and flotation processes are intimately linked together. Grinding liberates mineral grains, while flotation separates them into valuable minerals and gangue. The paper analyzes the effect of the fineness of grind through the results of semi-batch flotation tests conducted using two different ore samples. The first section describes the ore samples and the test procedure and the second section analyzes the results. 2. Experimental procedure The ore samples used for the tests were provided by Brunswick Mining and Mines Louvicourt. The Brunswick Mining ore is a complex sulphide consisting of galena (3–5% PbS), marmatite (12–17% Zn(Fe)S), chalcopyrite (0.7–1.5% CuFeS2), pyrite (50–70% FeS2) and a non-sulphide gangue of silica and chlorite (Petruk and Schnarr, 1981). The sample from Louvicourt is a Cu–Zn ore containing copper sulphides (4–6%), sphaler-
ite (1–4% ZnS) and pyrite (15–25% FeS2) in a silica gangue (Duchesne et al., 2001). The Brunswick Mining ore sample was crushed to 1.2 mm and separated into 2 kg batches. The batches were ground for various times in a rod mill with soda ash and water. The ground material was aerated and conditioned with xanthate prior to the flotation of 6 concentrate samples. The slurry density for the flotation was 50% w/w solids. The pulp conditions are adjusted to promote the flotation of lead and copper minerals, and to reject marmatite, pyrite and non-sulphide gangue. Table 1 summarizes the test conditions. The Louvicourt Cu–Zn ore sample was crushed to 1.2 mm and separated into 1 kg batches. The batches were ground for various times and process to float 4 copper concentrate samples. Each flotation test was repeated three times and results are presented as averages of the repeated tests. The detailed procedures for both series of flotation tests are given elsewhere (Bazin et al., in preparation). 3. Analysis of the results
*
Corresponding author. Tel.: +1 418 656 5914; fax: +1 418 656 5343. E-mail address: [email protected] (C. Bazin). 0892-6875/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2004.06.008
The results of the flotation tests are analyzed here using the rate and grade–recovery curves and will
368
C. Bazin et al. / Minerals Engineering 18 (2005) 367–370
mineral target recovery. This raises the idea of rebalancing the energy between primary and regrinding mills to have a coarser grind in the primary grinding and a more intense action in the regrinding circuits which could lead to reduction of the overall energy required for mineral processing. Fig. 2 compresses the previous results at 75% Pb recovery (see Fig. 1). The time required to achieve 75% Pb recovery shows a possible trend with fineness of grind as grinding probably redistributes galena between slow floating coarse and fine particles. Except for chalcopyrite whose flotation is promoted by finer grinding, the recovery of marmatite, pyrite and non-sulphide minerals shows a significant decrease with fineness of grind. Hydraulic entrainment that is favourable to the recovery of fine particles is probably in the order of 5%, the ultimate recovery of fine non-sulphide gangue. Natural activation is probably not a dominant factor for the recovery of marmatite and pyrite as a finer grind should be favourable to the release of ions into solution. A redistribution of these minerals into size intervals of lower floatability is not sufficient to explain the observed behaviour (Bazin et al., 2001). The increase liberation of galena with fineness of grind is likely to be responsible for the results of Fig. 2. The slopes of the marmatite, pyrite and non-sulphide minerals recovery are respectively 0.43, 0.23 and 0.13 %/%–0.038 mm. This may indicate that middlings of galena–marmatite are more efficiently liberated than galena–pyrite or galena non-sulphide minerals middlings. This sensitivity for galena–marmatite is somewhat surprising as the low concentration of these minerals in the ore should be less favourable to the production of their middlings (Petruk and Schnarr, 1981; Lane and Richmond, 1993) unless there are preferential associations between these minerals in the ore.
Table 1 Flotation test conditions P0.074 (%)
P0.038 (%)
P0.016 (%)
Brunswick ore sample 20 89 27 97 30 98 40 99 50 99 60 99 70 100 80 100
60 66 70 86 93 97 98 99
23 23 25 28 34 39 43 45
Louvicourt ore sampleb 5.5 63 7.5 78 9.5 94 11.5 97 13.5 99 15.5 99 17.5 100
44 52 59 67 73 80 88
17 18 19 21 25 29 37
Grinding (min) a
Pxxx: % finer than size xxx in mm. a Flotation machine: Denver––4 l bowl; aeration rate: 5–7 l/min; reagents: collector––Isoprophyl xanthate: 55 g/t; frother––MIBC 6 g/t; pH modifier––soda ash (pH: 9.7); flotation feed: 2 kg of ore at 35% w/ w solids––2.94%Pb, 7.35%Zn, 0.38%Cu, 23.7%Fe. b Flotation machine: Denver––2.5 l bowl; aeration rate: 5–7 l/min; reagents: collector––3418-A 25 g/t; frother––MIBC 7 g/t; pH modifier––lime (pH: 10.5); flotation feed: 1 kg of ore at 30% w/w solids–– 2.93%Cu, 0.91%Zn, 24.03%Fe.
subsequently be used to build a simulator that includes hydraulic entrainment, mineral recovery by size (Trahar, 1981) and liberation data (Sutherland, 1989). 3.1. Brunswick ore sample Fig. 1 shows the effect of fineness of grind on the rate of flotation of Pb and Zn minerals and Pb grade–recovery curves for the Brunswick Mining ore. Results show that increasing fineness of grind from 60% to 99% finer than 0.038 mm (see Table 1) has little impact on the rate of flotation of galena but affects the recovery of marmatite. Grade recovery curves show that any gain in selectivity due to fineness of grind is offset by a high Pb
3.2. Louvicourt Cu–Zn ore Results for the Louvicourt ore sample are presented in Fig. 3. The Louvicourt sample is conditioned to float selectively the copper minerals from sphalerite, pyrite 40 97
Pb
80
Pb grade (%)
Recovery (%)
100
60 60% < 0. 038 mm
40 99% < 0.038 mm
Zn
20
30 60
99 86
20
69
10
Pb grade at 75% Pb recovery
Fineness increases
0
% passing 0.038mm 95
0
0
2
4
Flotation time (min)
6
8
30
50
70
Pb recovery (%)
Fig. 1. Brunswick ore sample rate and grade–recovery curves.
90
C. Bazin et al. / Minerals Engineering 18 (2005) 367–370 25
Slow floating coarse particles
Slow floating fine particles
Pb grade at Pb75
Time for Pb75 (min)
3
369
2
1
20
15
10 50
60
70
80
90
100
50
60
% finer than 0.038 mm
70
80
90
100
% finer than 0.038 mm 30
75
Recovery at Pb75
Cu recovery at Pb75
25
70
65
Zn sulphide 20 15
Fe sulphide
10 5
60
Non-sulphide
0
50
60
70
80
90
50
100
60
70
80
90
100
% finer than 0.038 mm
% finer than 0.038 mm
Fig. 2. Brunswick flotation results at 75% Pb recovery.
sult is probably related to the redistribution of copper minerals into size intervals of faster flotation rate and the higher copper content of the floated particles. The recovery of sphalerite at 90% copper recovery decreases with fineness of grind, while the recovery of iron sulphide minerals exhibits a rapid fall and stabilizes at 5% which could be used to approximate the hydraulic entrainment contribution although it is probably less since there could be iron sulphide flotation. The different behaviours of sphalerite and iron sulphide minerals may be an indication that pyrite–chalcopyrite are liberated more efficiently by grinding than chalcopyrite–sphalerite middlings. On the other hand, if liberation is responsible for the sphalerite flotation there should be preferential associations between chalcopyrite and sphalerite in the ore
and non-sulphide minerals. Except for the coarsest grind, an increase from 52% to 88% finer than 0.038 mm has very little effect on the rate of copper mineral flotation but has a significant effect on the rate of recovery of sphalerite. As observed for the Brunswick ore good recovery of copper minerals could be achieved at coarse grind leading to the idea that a coarser grind in the primary grinding circuit followed by a more intense regrinding of the rougher/scavenger concentrate could reduce the overall energy consumption. The effect of the fineness of grind for the Louvicourt ore is shown in Fig. 4 using 90% copper recovery as the reference condition for the data compression. The time required to achieve 90% copper recovery shows a slight decrease with increasing fineness of grind. This re-
30
100
73/80/88
Cu 25
Cu content (%)
Recovery (%)
80 60 Zn
40 20
59 & 67
20
52
% <0.038mm
15
44
10 5
Fineness increases
0
0
0
1
2 3 Flotation time (min)
4
5
50
60
70
80
Cu recovery (%)
Fig. 3. Rate and grade–recovery curves for the Louvicourt ore.
90
100
370
C. Bazin et al. / Minerals Engineering 18 (2005) 367–370 25
Cu grade at Cu90
Time for Cu90 (min)
3.0
2.0
1.0
20
15
10
0.0 40
60
80
40
100
80
100
% finer than 0.038 mm
40
40
Pyrite recovery at Cu90
Sphalerite recovery at Cu90
% finer than 0.038 mm
60
35 30 25 20
30 20 10 0
40
60
80
100
40
% finer than 0.038 mm
60
80
100
% finer than 0.038 mm
Fig. 4. Louvicourt ore flotation results at 90% copper recovery.
because the two minerals are in low concentration which is not favourable to the production of their middlings.
4. Conclusion Semi-batch flotation tests were conducted with Cu–Pb–Zn and Cu–Zn sulphide ores with various size distributions. Results show a possible advantage of rebalancing the energy between the primary grinding mills and the regrinding units and may provide useful information for an indirect estimation of the mineral liberation and ore texture.
Acknowledgements The authors acknowledge the support of Brunswick Mining and Smelting and Mines Louvicourt for providing the samples for the flotation tests.
References Bazin, C., Hodouin, D., Cooper, M., 2001. Interaction between grinding and flotation. In: J.A. Finch (Ed.), Presented at the Interactions in Mineral Processing Symposium, 40th Annual Conference of Metallurgist, CIM, Toronto, August, pp. 3–16. Bazin, C., Fortin, C., Hodouin, D., Cayouette, J., in preparation. Modelling the effect of particle size distribution on the flotation response. Duchesne, S., Cayouette, J., Dallaire, B., 2001. Installation of Flash Flotation units at the Louvicourt Concentrator. In: Proceedings of the 33rd Annual Meeting of the Canadian Mineral Processors, Ottawa, January, pp. 285–302. Lane, G.S., Richmond, G.D., 1993. Improving fine particle flotation selectivity at Hellyer, XVIII International Mineral Processing Congress, Sydney, May 23–28, pp. 897–904. Petruk, W., Schnarr, J.R., 1981. An evaluation of the recovery of free and unliberated mineral grains, metals and trace elements in the concentrator of Brunswick Mining and Smelting Corp. Ltd. CIM Bull. 74 (833), 132–159. Sutherland, D.N., 1989. Batch flotation behaviour of composite particles. Miner. Eng. 2 (3), 351–367. Trahar, W.J., 1981. A rational interpretation of the role of particle size in flotation. Int. J. Miner. Process 8, 280–327.