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Quantifying accidental activation. Part II. Cu activation of pyrite
Minerals Engineering 15 (2002) 573–576 This article is also available online at: www.elsevier.com/locate/mineng
Quantifying accidental activation. Part II. Cu activation of pyrite G. Wong, D. Lascelles, J.A. Finch
*
Department of Mining and Metallurgical Engineering, McGill University, M.H. Wong Building, 3610 University Street, Montreal, Que., Canada H3A 2B2 Received 9 August 2001; accepted 9 May 2002
Abstract As a case study to quantify the flotation response, Cu activation of pyrite was examined. Two particle sizes, 106/150 and 37/74 lm (surface area 304 and 901 cm2 /g), were used. Micro-flotation was performed to determine the rate constant, k, as a function of surface concentration of copper, [Cu]surf . The [Cu]surf was determined by EDTA extraction and controlled by contact with Cu salt solution or with chalcopyrite and chalcocite particles. The rate constant relative to zero copper, kCu =k0 , followed the same trend against [Cu]surf for both particle sizes. Chalcocite gave a surface concentration about 40 times higher than chalcopyrite, corresponding to their relative ion production (the b-values in Part I). An estimate of mineral grade likely to cause activation was made assuming the grade was inversely dependent on b and taking the critical grade of chalcocite as 0.1% (Petruk, 2000). This gave a critical chalcopyrite grade of ca. 2%. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Froth flotation; Flotation activators; Sulphide ores
1. Introduction
2. Experimental
The study of accidental activation involves the release and transfer of metal ions and the subsequent flotation response. In Part I the production of Cu ions from two Cu-minerals, chalcopyrite and chalcocite, was modeled (Lascelles and Finch, 2002). Part II examines the response of pyrite to Cu activation. The interaction mechanism in this system continues to be investigated (Weisener and Gerson, 2000) but the emphasis here is to quantify the flotation response in a way that permits integration with Part I to estimate the grade of Cumineral posing the potential for activation. To quantify flotation for this purpose it would be useful if the measure were independent of machine type and particle size. The experimental and data analysis approach was organized with that in mind.
2.1. Material preparation
* Corresponding author. Tel.: +1-514-398-4755; fax: +1-514-3984492. E-mail address: jim.fi[email protected] (J.A. Finch).
2.1.1. Minerals The pyrite was obtained from Ward’s Natural Science Establishment. The sample was crushed in a ring pulverizer and screened to obtain two size classes, 37/74 and 106/150 lm. The surface area, measured by BET, was 901 and 304 cm2 /g, respectively. The chemical analysis was: Fe 45.64%, Cu 0.04%, Pb 0.01%, Zn 0.01%. Chalcopyrite and chalcocite samples were obtained from Ward’s Natural Science Establishment. Each was crushed in a jaw crusher. Handpicked specimens were ground in the pulverizer and wet-screened to obtain a selected size fraction, 25/37 lm. The minerals were passed on the Mozley Table to remove impurities, washed twice with a dilute hydrochloric acid solution (pH 2), rinsed with acetone and stored under acetone. 2.1.2. Reagents and solutions Table 1 gives the reagents used. The sodium isopropyl xanthate (SIPX) was purified by dissolving in acetone followed by precipitation with petroleum ether (Rao, 1971). Fresh 1 103 M xanthate stock solution was
0892-6875/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 8 9 2 - 6 8 7 5 ( 0 2 ) 0 0 0 8 2 - 1
574
G. Wong et al. / Minerals Engineering 15 (2002) 573–576
Table 1 Reagents employed in test work Chemical
Grade
Supplier
Usage
HCl NaOH CuSO4 5H2 O C3 H7 COS2 Na Acetone Petroleum ether
ACS reagent Analytical reagent ACS reagent Purified ACS reagent Analytical reagent
Fisher Scientific Co. ACP Chemicals Inc. Fisher Scientific Co. Prospec Chemicals BDH Chemicals BDH Chemicals
EDTAa
ACS reagent
Aldrich Chemical Company, Inc.
Mineral cleaning pH regulator Copper pretreatment Collector Purification of C3 H7 COS2 Na Purification and storage of C3 H7 COS2 Na Complexing agent
a
Ethylenediaminetetraacetate, disodium salt dihydrate.
prepared daily at natural pH, and then diluted to 1 105 M with distilled water at about pH 9.5 for flotation. Stock solutions of copper sulphate, ranging from 100 ppm Cu (1:57 103 M) to 1770 ppm Cu (2:78 102 M), were prepared by dissolving CuSO4 5H2 O crystals in distilled water at natural pH. For the test work, concentrations varying from 1 ppm (1:57 105 M) to 17.7 ppm (2:78 104 M) were generally used.
was computed from Eq. (1) (first-order kinetics batch flotation equation): R ¼ 1 expðktÞ
ð1Þ
The micro-flotation cell was a version of the Partridge and Smith (1972) design. The liquid volume was about 100 ml and the sample size was 1 g. The cell was made of glass to facilitate cleaning and was closed at the bottom by a glass frit of nominal pore size <5 lm. A magnetic stirrer suspended the particles. Air rate was controlled at 16 ml/min.
2.3.3. EDTA extraction––determining surface Cu concentration Samples of pyrite were conditioned in the same manner as for flotation. The solution was decanted, the solids washed and treated with 25 ml 0.05 M EDTA solution for half-an-hour (cf. Part I). The suspension was filtered, and the extract analysed (by atomic absorption spectroscopy) to measure the amount of Cu extracted. This is taken as a measure of Cu on the surface, and knowing the surface area of pyrite gives surface concentration, [Cu]surf , with the units selected as mg/cm2 . Taking the ionic radius of copper as 0.096 nm (Callister, 1994), surface concentration was also expressed in terms of monolayers (1 monolayer 3:7 104 mg/cm2 ).
2.3. Test procedure
3. Results and discussion
2.3.1. Pyrite conditioning For conditioning with solution, a 1 g sample of pyrite was mixed for 10 min on an orbital shaker at 250 rpm in 100 ml of a given Cu concentration at natural pH. The solution was decanted and the solids conditioned in 100 ml of 1 105 M SIPX at pH 9.5 for 10 min. This solution was then decanted and the solids transferred to the flotation cell. For conditioning with Cu-minerals, 1 g 106/150 lm pyrite samples were used and mixed with 0.05 g chalcopyrite or 0.002 g chalcocite for 10 min in 100 ml distilled water at natural pH. The samples were screened at 37 lm to separate the pyrite from the Cu-minerals. The pyrite was then conditioned in SIPX and transferred to the flotation cell in the manner described above.
3.1. Flotation rate constant
2.2. Flotation
2.3.2. Flotation––determining rate constant Flotation was conducted as a function of time up to 8 min for the 37/74 lm size class and up to 2 min for the 106/150 lm size class. All products were dried, weighed, and the cumulative recovery (R) calculated as a function of cumulative time (t). The flotation rate constant, k,
Fig. 1 shows flotation followed first-order kinetics. The pyrite had a flotation response without Cu addition but clearly the rate increased with Cu.
Fig. 1. Specimen flotation data: 37/74 lm pyrite with and without Cu.
G. Wong et al. / Minerals Engineering 15 (2002) 573–576
Fig. 2. Flotation rate constant as a function of the initial Cu concentration of conditioning solution.
Fig. 2 shows the flotation rate constant increased with increasing solution copper concentration. The 106/150 lm pyrite displayed about 10 times the rate of the 37/74 lm particles, a larger dependence on size than reported elsewhere (Jameson et al., 1977). In the tests with chalcopyrite and chalcocite, the flotation rate constant (of the 106/150 lm pyrite particles) was ca. 1.6 and 9.5 min1 , respectively. 3.2. Correlating rate constant and surface Cu concentration Fig. 3 shows the rate constant relative to zero Cu addition, kCu =k0 , as a function of [Cu]surf . The same trend is followed for both particle sizes up to [Cu]surf 0:1 104 mg/cm2 (0.03 monolayer), despite their large difference in absolute rates. The result after
Fig. 3. Relative flotation rate constant of pyrite (i.e., rate with Cu to that without) as a function of surface Cu concentration for the contact with solution and mineral (mixed mineral) tests (Note: Py ¼ pyrite, Cp ¼ chalcopyrite, Cc ¼ chalcocite).
575
contact with chalcopyrite lies close to the trend line (the error bars indicate greater scatter in these data) and corresponds to [Cu]surf 0:07 104 mg/cm2 . This supports the notion that activation by contact occurs by release and migration of Cu ions. Contact with chalcocite gave a surface concentration of ca. 2–4 104 mg/cm2 (i.e., ca. 1 monolayer), some 40 times that given by chalcopyrite and the kCu =k0 is correspondingly high (30). Variability in the data is evident (the shaded area). Considering flotation response likely maximizes at monolayer coverage, the result after contact with chalcocite also fits the trend. The relative surface concentration generated by chalcocite and chalcopyrite (ca. 40) is of the same order as the relative Cu ion production (i.e., the b-value) of chalcocite and chalcopyrite reported in Part I. 3.3. Relating activation to ore grade The method of presenting the flotation response in Fig. 3 eliminates particle size as a factor in the flotation response (and may be worth exploring in other situations such as flotation modeling). We can at least advance the argument that the method also eliminates the machine factor: the relative rate constant determined in one device should be the same as in another provided the ‘‘chemistry’’ is the same (in this case the surface concentration of Cu). In other words, the relationship in Fig. 3 approaches the criterion of a measure of flotation response independent of machine and particle size. We are now in a position to try to link flotation response to Cu ion production through the surface concentration. If a threshold or ‘‘critical’’ [Cu]surf could be identified at which activation was evident then by cross-reference to Fig. 4 (Part I) the ‘‘critical’’ grade for activation could be estimated. To illustrate, taking kCu =k0 ¼ 5 the corresponding [Cu]surf is ca. 0:08 104 mg/cm2 and the corresponding grade ca. 0.001% for Cc and ca. 0.1% for Cp. The relationship in Fig. 3, however, shows a continuous variation making any choice of a critical surface concentration arbitrary. An alternative approach was thus adopted. Petruk (2000), emphasizing the importance of identifying minerals in an ore which release metal ions, based on the work of McLean (1984), McTavish (1985) and others, noted that accidental Cu activation could occur with grades of secondary Cu-minerals like chalcocite as low as 0.1%. This serves to calibrate the activation effect of other minerals if we make the assumption that the critical grade is inversely dependent on ion production (the higher the production the lower the grade), i.e., the b-value in Part I. The fact that the relative surface Cu concentration derived from the Cc and Cp in Part II is similar to their relative b-values in Part I supports this contention. Table 2 gives the chalcopyrite grade thus calculated for b-values associated with ores.
576
G. Wong et al. / Minerals Engineering 15 (2002) 573–576
Table 2 Estimation of grade for activation Mineral
b
Grade
Chalcocite Chalcopyrite Galena
291 14 100
0.1 2.1 0.3
was inversely dependent on b and calibrating using a reported critical chalcocite grade of 0.1% (Petruk, 2000). 5. Parts I and II both emphasize the significant threat of accidental activation posed by chalcocite compared with chalcopyrite.
Assumption: grade (%) ¼ 1=b, basis: Cc grade ¼ 0:1% (Petruk, 2000).
The Cp grade, ca. 2% (equivalent to 0.75% Cu), is in line with the experience that chalcopyrite ores do not generally pose activation problems compared with those containing chalcocite. The contact tests mirror these grades: the 1 g pyrite sample mixed with 0.002 g Cc and 0.05 g Cp corresponds to ‘‘grades’’ of 0.2% Cc and 5% Cp. Table 2 includes the result when the approach is extended to galena based on the b Pb/Ga value for ore (1 0 0) reported by Sui et al. (1999a). The grade, 0.3%, is higher than that estimated by Sui et al. (1999a) and Rashchi and Finch (in press) (0.1%) but may still be an underestimate. To include in Table 2 as it stands assumes the impact of Pb, ion for ion, is the same as Cu. Sui et al. (1999b) estimated Cu was up to six times as active an activator compared with Pb, which would increase the galena grade in Table 2 to ca. 1.8%. In principle, Table 2 can be extended to other minerals by measuring the bvalue relative to b Cu/Cc and the impact on flotation of the released metal ion relative to that of Cu. In this way the identification of minerals that promote accidental activation can be augmented by some idea of the critical grades of such minerals. This demands an accurate b Cu/ Cc value. As noted in Part I, this already high b-value may still be low as possible galvanic effects were absent in the measurement. If this is the case the critical grade for the other minerals in Table 2 will be higher.
4. Conclusions 1. For two particle sizes, the rate constant of pyrite with and without Cu (kCu =k0 ) showed the same dependence on surface concentration of Cu ([Cu]surf ) regardless whether Cu was introduced from solution or contact with Cu-minerals. 2. Presenting the flotation response in this manner reduces the dependence on machine and particle size. 3. The relative surface Cu concentration derived from chalcocite and chalcopyrite, ca. 40, was of the same order as their relative b-values measured in Part I. 4. An estimate of mineral grade with potential to cause accidental activation was made assuming the grade
Acknowledgements The authors acknowledge the financial support of the Canadian Mining Industry Research Organization, CAMIRO (representing Rio Algom, Hudson Bay Mining and Smelting, Les Mines Selbaie, Mine Louvicourt, Noranda, Westmin Resources, Breakwater Resources, and Agnico-Eagle) and the Natural Sciences and Engineering Research Council of Canada (NSERC) under the NSERC Collaborative Research and Development program.
References Callister, W., 1994. In: Materials Science and Engineering, third ed. John Wiley & Sons Inc. Jameson, G.J., Nam, S., Moo-Young, M., 1977. Physical factors affecting recovery rates in flotation. Minerals Science and Engineering 9, 103–118. Lascelles, D., Finch, J.A., 2002. Quantifying accidental activation: Part I. Cu ion production. Minerals Engineering 15 (8), 567–571. McLean, D.C., 1984. Upgrading of copper concentrates by chalcocite de-rimming of pyrite with cyanide. Process Mineralogy III AIME/ SME, 3–13. McTavish, S., 1985. Goldstream concentrator design and operation. Proceedings of the 17th Annual Meeting of the Canadian Mineral Processors (division of CIM), paper 3, 20 pp. Partridge, A.C., Smith, G.W., 1972. Technical note, Small-sample flotation testing: a new cell. Trans. Inst. Min. Metall. Sec. C 80, C199–C200. Petruk, W., 2000. In: Applied Mineralogy in the Mining Industry. Elsevier, Amsterdam, pp. 5–7. Rao, S.R., 1971. In: Xanthates and Related Compounds. Marcel Dekker, New York, pp. 15–17. Rashchi, F., Finch, J.A., in press. Sphalerite activation and surface Pb ion concentration. Int. J. Miner. Process. Sui, C., Grimmelt, J.C., Rashchi, F., Rao, S.R., Finch, J.A., 1999a. Lead ion production and sphalerite recovery in copper rougher flotation. In: Hancock, B.A., Pon, M.R.L. (Eds.), Proceedings of Copper 99–Cobre 99 International Environment Conference, vol. 2. Mineral Processing Environment, pp. 145–157. Sui, C., Lee, D., Casuge, A., Finch, J.A., 1999b. Comparison of the activation of sphalerite by copper and lead. Minerals and Metallurgical Processing 16 (2), 53–61. Weisener, C., Gerson, A., 2000. An investigation of the Cu(II) adsorption mechanism on pyrite by ARXPS and SIMS. Minerals Engineering 30, 454–458.
Quantifying accidental activation. Part II. Cu activation of pyrite G. Wong, D. Lascelles, J.A. Finch
*
Department of Mining and Metallurgical Engineering, McGill University, M.H. Wong Building, 3610 University Street, Montreal, Que., Canada H3A 2B2 Received 9 August 2001; accepted 9 May 2002
Abstract As a case study to quantify the flotation response, Cu activation of pyrite was examined. Two particle sizes, 106/150 and 37/74 lm (surface area 304 and 901 cm2 /g), were used. Micro-flotation was performed to determine the rate constant, k, as a function of surface concentration of copper, [Cu]surf . The [Cu]surf was determined by EDTA extraction and controlled by contact with Cu salt solution or with chalcopyrite and chalcocite particles. The rate constant relative to zero copper, kCu =k0 , followed the same trend against [Cu]surf for both particle sizes. Chalcocite gave a surface concentration about 40 times higher than chalcopyrite, corresponding to their relative ion production (the b-values in Part I). An estimate of mineral grade likely to cause activation was made assuming the grade was inversely dependent on b and taking the critical grade of chalcocite as 0.1% (Petruk, 2000). This gave a critical chalcopyrite grade of ca. 2%. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Froth flotation; Flotation activators; Sulphide ores
1. Introduction
2. Experimental
The study of accidental activation involves the release and transfer of metal ions and the subsequent flotation response. In Part I the production of Cu ions from two Cu-minerals, chalcopyrite and chalcocite, was modeled (Lascelles and Finch, 2002). Part II examines the response of pyrite to Cu activation. The interaction mechanism in this system continues to be investigated (Weisener and Gerson, 2000) but the emphasis here is to quantify the flotation response in a way that permits integration with Part I to estimate the grade of Cumineral posing the potential for activation. To quantify flotation for this purpose it would be useful if the measure were independent of machine type and particle size. The experimental and data analysis approach was organized with that in mind.
2.1. Material preparation
* Corresponding author. Tel.: +1-514-398-4755; fax: +1-514-3984492. E-mail address: jim.fi[email protected] (J.A. Finch).
2.1.1. Minerals The pyrite was obtained from Ward’s Natural Science Establishment. The sample was crushed in a ring pulverizer and screened to obtain two size classes, 37/74 and 106/150 lm. The surface area, measured by BET, was 901 and 304 cm2 /g, respectively. The chemical analysis was: Fe 45.64%, Cu 0.04%, Pb 0.01%, Zn 0.01%. Chalcopyrite and chalcocite samples were obtained from Ward’s Natural Science Establishment. Each was crushed in a jaw crusher. Handpicked specimens were ground in the pulverizer and wet-screened to obtain a selected size fraction, 25/37 lm. The minerals were passed on the Mozley Table to remove impurities, washed twice with a dilute hydrochloric acid solution (pH 2), rinsed with acetone and stored under acetone. 2.1.2. Reagents and solutions Table 1 gives the reagents used. The sodium isopropyl xanthate (SIPX) was purified by dissolving in acetone followed by precipitation with petroleum ether (Rao, 1971). Fresh 1 103 M xanthate stock solution was
0892-6875/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 8 9 2 - 6 8 7 5 ( 0 2 ) 0 0 0 8 2 - 1
574
G. Wong et al. / Minerals Engineering 15 (2002) 573–576
Table 1 Reagents employed in test work Chemical
Grade
Supplier
Usage
HCl NaOH CuSO4 5H2 O C3 H7 COS2 Na Acetone Petroleum ether
ACS reagent Analytical reagent ACS reagent Purified ACS reagent Analytical reagent
Fisher Scientific Co. ACP Chemicals Inc. Fisher Scientific Co. Prospec Chemicals BDH Chemicals BDH Chemicals
EDTAa
ACS reagent
Aldrich Chemical Company, Inc.
Mineral cleaning pH regulator Copper pretreatment Collector Purification of C3 H7 COS2 Na Purification and storage of C3 H7 COS2 Na Complexing agent
a
Ethylenediaminetetraacetate, disodium salt dihydrate.
prepared daily at natural pH, and then diluted to 1 105 M with distilled water at about pH 9.5 for flotation. Stock solutions of copper sulphate, ranging from 100 ppm Cu (1:57 103 M) to 1770 ppm Cu (2:78 102 M), were prepared by dissolving CuSO4 5H2 O crystals in distilled water at natural pH. For the test work, concentrations varying from 1 ppm (1:57 105 M) to 17.7 ppm (2:78 104 M) were generally used.
was computed from Eq. (1) (first-order kinetics batch flotation equation): R ¼ 1 expðktÞ
ð1Þ
The micro-flotation cell was a version of the Partridge and Smith (1972) design. The liquid volume was about 100 ml and the sample size was 1 g. The cell was made of glass to facilitate cleaning and was closed at the bottom by a glass frit of nominal pore size <5 lm. A magnetic stirrer suspended the particles. Air rate was controlled at 16 ml/min.
2.3.3. EDTA extraction––determining surface Cu concentration Samples of pyrite were conditioned in the same manner as for flotation. The solution was decanted, the solids washed and treated with 25 ml 0.05 M EDTA solution for half-an-hour (cf. Part I). The suspension was filtered, and the extract analysed (by atomic absorption spectroscopy) to measure the amount of Cu extracted. This is taken as a measure of Cu on the surface, and knowing the surface area of pyrite gives surface concentration, [Cu]surf , with the units selected as mg/cm2 . Taking the ionic radius of copper as 0.096 nm (Callister, 1994), surface concentration was also expressed in terms of monolayers (1 monolayer 3:7 104 mg/cm2 ).
2.3. Test procedure
3. Results and discussion
2.3.1. Pyrite conditioning For conditioning with solution, a 1 g sample of pyrite was mixed for 10 min on an orbital shaker at 250 rpm in 100 ml of a given Cu concentration at natural pH. The solution was decanted and the solids conditioned in 100 ml of 1 105 M SIPX at pH 9.5 for 10 min. This solution was then decanted and the solids transferred to the flotation cell. For conditioning with Cu-minerals, 1 g 106/150 lm pyrite samples were used and mixed with 0.05 g chalcopyrite or 0.002 g chalcocite for 10 min in 100 ml distilled water at natural pH. The samples were screened at 37 lm to separate the pyrite from the Cu-minerals. The pyrite was then conditioned in SIPX and transferred to the flotation cell in the manner described above.
3.1. Flotation rate constant
2.2. Flotation
2.3.2. Flotation––determining rate constant Flotation was conducted as a function of time up to 8 min for the 37/74 lm size class and up to 2 min for the 106/150 lm size class. All products were dried, weighed, and the cumulative recovery (R) calculated as a function of cumulative time (t). The flotation rate constant, k,
Fig. 1 shows flotation followed first-order kinetics. The pyrite had a flotation response without Cu addition but clearly the rate increased with Cu.
Fig. 1. Specimen flotation data: 37/74 lm pyrite with and without Cu.
G. Wong et al. / Minerals Engineering 15 (2002) 573–576
Fig. 2. Flotation rate constant as a function of the initial Cu concentration of conditioning solution.
Fig. 2 shows the flotation rate constant increased with increasing solution copper concentration. The 106/150 lm pyrite displayed about 10 times the rate of the 37/74 lm particles, a larger dependence on size than reported elsewhere (Jameson et al., 1977). In the tests with chalcopyrite and chalcocite, the flotation rate constant (of the 106/150 lm pyrite particles) was ca. 1.6 and 9.5 min1 , respectively. 3.2. Correlating rate constant and surface Cu concentration Fig. 3 shows the rate constant relative to zero Cu addition, kCu =k0 , as a function of [Cu]surf . The same trend is followed for both particle sizes up to [Cu]surf 0:1 104 mg/cm2 (0.03 monolayer), despite their large difference in absolute rates. The result after
Fig. 3. Relative flotation rate constant of pyrite (i.e., rate with Cu to that without) as a function of surface Cu concentration for the contact with solution and mineral (mixed mineral) tests (Note: Py ¼ pyrite, Cp ¼ chalcopyrite, Cc ¼ chalcocite).
575
contact with chalcopyrite lies close to the trend line (the error bars indicate greater scatter in these data) and corresponds to [Cu]surf 0:07 104 mg/cm2 . This supports the notion that activation by contact occurs by release and migration of Cu ions. Contact with chalcocite gave a surface concentration of ca. 2–4 104 mg/cm2 (i.e., ca. 1 monolayer), some 40 times that given by chalcopyrite and the kCu =k0 is correspondingly high (30). Variability in the data is evident (the shaded area). Considering flotation response likely maximizes at monolayer coverage, the result after contact with chalcocite also fits the trend. The relative surface concentration generated by chalcocite and chalcopyrite (ca. 40) is of the same order as the relative Cu ion production (i.e., the b-value) of chalcocite and chalcopyrite reported in Part I. 3.3. Relating activation to ore grade The method of presenting the flotation response in Fig. 3 eliminates particle size as a factor in the flotation response (and may be worth exploring in other situations such as flotation modeling). We can at least advance the argument that the method also eliminates the machine factor: the relative rate constant determined in one device should be the same as in another provided the ‘‘chemistry’’ is the same (in this case the surface concentration of Cu). In other words, the relationship in Fig. 3 approaches the criterion of a measure of flotation response independent of machine and particle size. We are now in a position to try to link flotation response to Cu ion production through the surface concentration. If a threshold or ‘‘critical’’ [Cu]surf could be identified at which activation was evident then by cross-reference to Fig. 4 (Part I) the ‘‘critical’’ grade for activation could be estimated. To illustrate, taking kCu =k0 ¼ 5 the corresponding [Cu]surf is ca. 0:08 104 mg/cm2 and the corresponding grade ca. 0.001% for Cc and ca. 0.1% for Cp. The relationship in Fig. 3, however, shows a continuous variation making any choice of a critical surface concentration arbitrary. An alternative approach was thus adopted. Petruk (2000), emphasizing the importance of identifying minerals in an ore which release metal ions, based on the work of McLean (1984), McTavish (1985) and others, noted that accidental Cu activation could occur with grades of secondary Cu-minerals like chalcocite as low as 0.1%. This serves to calibrate the activation effect of other minerals if we make the assumption that the critical grade is inversely dependent on ion production (the higher the production the lower the grade), i.e., the b-value in Part I. The fact that the relative surface Cu concentration derived from the Cc and Cp in Part II is similar to their relative b-values in Part I supports this contention. Table 2 gives the chalcopyrite grade thus calculated for b-values associated with ores.
576
G. Wong et al. / Minerals Engineering 15 (2002) 573–576
Table 2 Estimation of grade for activation Mineral
b
Grade
Chalcocite Chalcopyrite Galena
291 14 100
0.1 2.1 0.3
was inversely dependent on b and calibrating using a reported critical chalcocite grade of 0.1% (Petruk, 2000). 5. Parts I and II both emphasize the significant threat of accidental activation posed by chalcocite compared with chalcopyrite.
Assumption: grade (%) ¼ 1=b, basis: Cc grade ¼ 0:1% (Petruk, 2000).
The Cp grade, ca. 2% (equivalent to 0.75% Cu), is in line with the experience that chalcopyrite ores do not generally pose activation problems compared with those containing chalcocite. The contact tests mirror these grades: the 1 g pyrite sample mixed with 0.002 g Cc and 0.05 g Cp corresponds to ‘‘grades’’ of 0.2% Cc and 5% Cp. Table 2 includes the result when the approach is extended to galena based on the b Pb/Ga value for ore (1 0 0) reported by Sui et al. (1999a). The grade, 0.3%, is higher than that estimated by Sui et al. (1999a) and Rashchi and Finch (in press) (0.1%) but may still be an underestimate. To include in Table 2 as it stands assumes the impact of Pb, ion for ion, is the same as Cu. Sui et al. (1999b) estimated Cu was up to six times as active an activator compared with Pb, which would increase the galena grade in Table 2 to ca. 1.8%. In principle, Table 2 can be extended to other minerals by measuring the bvalue relative to b Cu/Cc and the impact on flotation of the released metal ion relative to that of Cu. In this way the identification of minerals that promote accidental activation can be augmented by some idea of the critical grades of such minerals. This demands an accurate b Cu/ Cc value. As noted in Part I, this already high b-value may still be low as possible galvanic effects were absent in the measurement. If this is the case the critical grade for the other minerals in Table 2 will be higher.
4. Conclusions 1. For two particle sizes, the rate constant of pyrite with and without Cu (kCu =k0 ) showed the same dependence on surface concentration of Cu ([Cu]surf ) regardless whether Cu was introduced from solution or contact with Cu-minerals. 2. Presenting the flotation response in this manner reduces the dependence on machine and particle size. 3. The relative surface Cu concentration derived from chalcocite and chalcopyrite, ca. 40, was of the same order as their relative b-values measured in Part I. 4. An estimate of mineral grade with potential to cause accidental activation was made assuming the grade
Acknowledgements The authors acknowledge the financial support of the Canadian Mining Industry Research Organization, CAMIRO (representing Rio Algom, Hudson Bay Mining and Smelting, Les Mines Selbaie, Mine Louvicourt, Noranda, Westmin Resources, Breakwater Resources, and Agnico-Eagle) and the Natural Sciences and Engineering Research Council of Canada (NSERC) under the NSERC Collaborative Research and Development program.
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