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The effect of frother type and dosage on flotation performance in the presence of high depressant concentrations
Minerals Engineering 36–38 (2012) 204–210
Contents lists available at SciVerse ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
The effect of frother type and dosage on flotation performance in the presence of high depressant concentrations Jenny Wiese ⇑, Peter Harris Centre for Minerals Research, University of Cape Town, South Africa
a r t i c l e
i n f o
Article history: Available online 20 April 2012 Keywords: Precious metal ores Froth flotation Flotation depressants Flotation frothers
a b s t r a c t The use of high dosages of polysaccharide depressants in order to depress the undesired naturally floatable gangue (NFG) present in ores beneficiated from the Bushveld Complex, South Africa, results in a significant decrease in the stability of flotation froths. These unstable froths can result in restricted mass pull and decreased valuable mineral recovery. Previous work using a single polyglycol ether type frother, DOW 200, has shown that an increase in frother dosage could be used to overcome the destabilisation of the froth to a certain extent and improve valuable mineral recovery. This resulted in an increase in water recovery and dilution of the concentrate by entrained material. This work extends this study to examine the effect of using a stronger frother, DOW 250, on the recovery of sulphide minerals and floatable gangue from a Merensky ore at different dosages of guar gum and CMC, which are typically used as depressants in the processing of Merensky ore. Results indicate that an increase in the strength of the frother resulted in a more robust froth. Depressant type also had an influence on results obtained. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction The presence of naturally floating gangue (NFG) in ores mined from the Bushveld Complex, South Africa, can result in negative effects during the flotation process. The presence of NFG, which consists mainly of pyroxene associated with talcaceous minerals, results in the stabilisation of the froth and although present in small amounts (0.5–5% by mass in the ore) can cause these unwanted effects. That these minerals are naturally floatable is due to the presence of talc along pyroxene grain boundaries (Becker et al., 2006; Jasieniak and Smart, 2009). Increasingly, concentrators processing ores containing significant quantities of NFG are making use of high depressant dosages to minimise the recovery of these undesirable minerals and to increase the grade of the concentrate. The two polysaccharide depressants most widely used in PGM flotation are guar gum and carboxymethyl cellulose (CMC). The CMC molecule has a high negative charge density, and when used at high concentration results in a strong negative charge as it adsorbs on particles resulting in significant dispersion. The guar gum molecule has a very low charge density and does not result in dispersed pulps particularly in the presence of the high ionic strength waters found in concentrators. Steenberg and Harris (1984), by conducting comparative adsorption studies of CMC, guar gum and starch depressants on talc showed that starch and guar gum produced a higher level of adsorption on talc than did ⇑ Corresponding author. Tel.: +27 21 650 2517; fax: +27 21 650 5501. E-mail address: [email protected] (J. Wiese). 0892-6875/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mineng.2012.03.028
CMC for any equilibrium concentration. Parolis et al. (2008) showed that the adsorption of CMC on talc was enhanced by the presence of Ca++, Mg++ and K+, commonly found in the recycle process water of Merensky flotation circuits. The use of high depressant dosages invariably results in a marked decrease in froth stability due to the depression of froth stabilising NFG (Bradshaw et al., 2005; Martinovic et al., 2005; Wiese, 2009). This could restrict solids recovery and result in decreased valuable mineral recovery. Low mass pulls may be overcome by an increase in frother dosage (Wiese et al., 2010), but could result in problems further downstream. Valuable mineral grade and recovery are strongly dependent on the stability of the froth since the recovery of entrained gangue is directly proportional to the amount of water recovered (Engelbrecht and Woodburn, 1975; Zheng et al., 2006a,b; Neethling and Cilliers, 2002). A froth stability which is too low can, however, result in a loss in the recovery of valuable minerals and the inability to transport material for further processing. The polyglycol ether range of frothers has strong surface activity, and their molecular weight (MW) and carbon chain-length determine their strength and performance (Bulatovic, 2007), with an increase in MW resulting in increased frothability, but lower selectivity. Wiese et al. (2010) using a single polyglycol frother, showed that an increase in frother dosage resulted in enhanced valuable mineral recovery. This work extends that study to include the use of a stronger frother, DOW 250, to determine whether its use would result in better management of the froth under high depressant dosages.
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J. Wiese, P. Harris / Minerals Engineering 36–38 (2012) 204–210
For this work a Merensky ore containing a significant amount of NFG (Becker et al., 2006; Wiese, 2009) was selected and since the PGE in this type of ore are strongly associated with the sulphide minerals the effect of the increased frother dosages on the recovery of copper and nickel representing the sulphide minerals, chalcopyrite and pentlandite may be assessed. The investigation into the effects on PGE recovery is beyond the scope of the current paper.
Table 1 Properties of the frothers used in this study. Frother
Description
Molecular weight
Supplier
Dowfroth 200 Dowfroth 250
Polypropylene glycol methyl ether Tri-polypropylene glycol methyl ether
205
Betachem
260
Betachem
2. Experimental details An ore from the southern section of the Merensky Reef in the Bushveld Igneous Complex, South Africa was prepared at UCT (Wiese et al., 2007) for use in batch flotation tests. The mean copper (Cu), nickel (Ni) and sulphur (S) values for the ore were calculated using the concentrate and tailings values obtained from all the batch flotation tests and are as follows: Cu 0.087 wt.%, Ni 0.247 wt.%, S 0.367 wt.%. The NFG content of the ore sample was approximately 8%. All batch flotation tests were conducted using synthetic plant water, whereby distilled water is modified by the addition of various chemical salts to contain total dissolved solids of 1023 ppm (Wiese, 2009). Batch flotation tests were conducted using a method developed at UCT (Wiese, 2009). 1 kg portions of the ore sample were milled at 66% solids in synthetic plant water to achieve a grind of 60% passing 75 lm using a laboratory scale stainless steel rod mill. The milled slurry was transferred to a modified 3 L Leeds flotation cell. The volume in the cell was made up to produce 35% solids using synthetic plant water. The flotation cell was fitted with a variable speed drive and the pulp level was controlled manually by the addition of synthetic plant water. The impeller speed was set at 1200 rpm. The frothers, Dowfroth 200 (DOW 200) and Dowfroth 250 (DOW 250), supplied by Betachem were added at dosages of 40, 50 and 60 g/t. The collector, sodium isobutyl xanthate (SIBX), supplied by Senmin was added to the mill prior to grinding at a dosage of 150 g/t. The polymeric depressants used in the batch flotation tests were Depramin 267, a carboxymethylcellulose (CMC) supplied by AKZO Nobel Functional Chemicals and Stypres 504, a modified guar gum supplied by Chemquest. The MW of Depramin 267 used in this study was 325,000 g/mol, and that of Stypres 504 was 230,000 g/mol. The depressants were added at dosages of 250 and 500 g/t. Depressants were made up every second day at dosages corrected for active content. Tests were also conducted in the absence of a depressant. The chemical salts used in making up the synthetic plant water were obtained from Merck. (see Table 1). The general formula for DOW 200 is CH3(C3H6O)3OH, and that of DOW 250 is CH3(C3H6O)4OH. Both frothers are totally soluble in water. The air supply to the flotation cell was maintained at a flow rate of 7 L/min in all tests and the froth height was kept constant at 2 cm throughout. Four concentrates were collected at 2, 6, 12 and 20 min of flotation time by scraping the froth into a collecting pan every 15 s. A feed sample was taken before and a tailings sample was taken after each test. Water recoveries were measured for each test. Feeds, concentrates and tails were filtered, dried and weighed before analysis. All batch flotation tests were conducted in duplicate. Error bars showing standard error between duplicate tests are included in figures. Copper and total nickel analysis of all samples was done using a Bruker S4 Explorer XRF spectrophotometer. Sulphur analysis was carried out using a LECO S 632 sulphur analyser. 3. Results and discussion In order to determine the effect of the presence/absence of NFG on the frothing behaviour upon increases in frother dosage, tests
were conducted in the absence of depressant where NFG was present. All NFG was depressed at a depressant dosage of 500 g/t (Wiese, 2009) and this allows for the determination of gangue recovered by entrainment. At a depressant dosage of 250 g/t it has been determined (Wiese et al., 2010) that the amount of NFG recovered in the concentrate is of the same order as that of entrained gangue reporting to the concentrate. Two phase batch flotation tests i.e. water and air only, were conducted using DOW 200 and DOW 250 at the same dosages as were used in the three phase tests (water, air and solids). The results of these tests are shown in Fig. 1. Greater amounts of water were recovered from tests using DOW 250 than from tests using DOW 200 as the frother indicating that DOW 250 is the stronger frother of the two. The volume of froth obtained in these tests, as indicated by the water recovery, was substantially greater than that obtained from tests conducted in the presence of solids. This is as a result of the destabilising effects of the solids even in the absence of a depressant where the maximum amount of froth stabilising NFG was present or possibly the adsorption of frother onto the solids (Lotter et al., 2003). Results for total mass and water recovered for the various conditions using DOW 200 and DOW 250 at increasing dosages in the presence of guar gum at dosages of 0, 250 and 500 g/t are presented in Fig. 2. Care should be taken in assessing the recovery of solids as their recovery is dependent on the amount of water recovered. In the absence of a depressant the amount of water recovered by both frothers was similar and the amounts of solids recovered may thus be compared. Greater amounts of solids were recovered from tests using DOW 200 than from equivalent tests using DOW 250. This may be associated with the influence of the frother on NFG. The system was dominated by the presence of large amounts of NFG and the destabilising effects of the sulphide minerals were overridden. Guar gum addition at a dosage of 250 g/ t resulted in differences in the amount of water recovered, in that for equivalent dosages, DOW 250 always achieved higher water recoveries than DOW 200. At a guar gum dosage of 500 g/t, gangue reporting to the concentrate was via entrainment alone as all NFG was depressed at this dosage. For all conditions an increase in frother dosage resulted in an increase in the stability of the froth as indicated by increased water recovery. DOW 200 at a dosage of 60 g/t achieved similar water recoveries to DOW 250 at a dosage of 50 g/t. For the Merensky ore used in this study the changes in water recovery on increased guar gum dosage were not large when compared to tests conducted in the absence of a depressant. However, the mass of solids reporting to the concentrate was reduced when guar gum dosage was increased from 250 to 500 g/t. Statistical analysis using t tests of the data presented in Fig. 2 at the 10% significance level determined that the increases in the amounts of mass and water recovered when the frother dosage was increased from 40 to 60 g/t at all depressant dosages for both frothers were significant. Differences in the recovery of solids between the two frothers were significant only in the absence of a depressant, whereas differences in water recoveries were significant at depressant dosages of 250 and 500 g/t. Fig. 3 presents the results obtained for total mass and water recovered for the various conditions using DOW 200 and DOW
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J. Wiese, P. Harris / Minerals Engineering 36–38 (2012) 204–210 1600 DOW 200 DOW 250
Cumulative water, g
1400 1200 1000 800 600 400 200 0
40
50
60
Frother dosage, g/t Fig. 1. Cumulative water recovered for DOW 200 and DOW 250 from batch flotation tests conducted in the absence of solids.
Fig. 2. Final mass and water recovered for guar gum at dosages of 0, 250 and 500 g/t in the presence of DOW 200 and DOW 250 at dosages of 40, 50 and 60 g/t.
Fig. 3. Final mass and water recovered for CMC at dosages of 0, 250 and 500 g/t in the presence of DOW 200 and DOW 250 at dosages of 40, 50 and 60 g/t.
250 at increasing dosages in the presence of CMC at dosages of 0, 250 and 500 g/t. The addition of CMC resulted in a decrease in
the stability of the froth in comparison to the results obtained for guar gum. High dosages of CMC result in dispersed pulps and at
J. Wiese, P. Harris / Minerals Engineering 36–38 (2012) 204–210
a dosage of 250 g/t it is be expected that some degree of dispersion would be present. At this dosage slightly more froth was obtained from tests using DOW 250 than from DOW 200, which is evidence of it being a stronger frother. The destabilising effects of CMC are more evident at the fully dispersive conditions at a dosage of 500 g/t where tests conducted in the presence of DOW 200 resulted in very low froth stability. A procedure developed at UCT to evaluate the coagulative/dispersive nature of a mineral pulp was used to determine the extent to which particle aggregates were formed in a suspension of pulp at the depressant types and dosages evaluated. The procedure utilised an image analysis technique to measure the transmission of light through a mineral slurry with the same characteristics as the pulp phase used in the batch flotation tests i.e. 35% solids and a particle size distribution of 60% passing 75 lm. In the absence of depressant there was an almost immediate settling of suspended particles as indicated by the transmission of light through the suspension. In the presence of Stypres 504 at both dosages evaluated there was a steady increase in the transmission of light through the suspension during the course of the experiment. This was indicative of aggregation of particles. In the presence of Depramin 267 full dispersion of the pulp over the course if the experiment was indicated by zero transmission of light through the suspension for both dosages evaluated in this study. The increase in dosage of DOW 200 was not sufficient to develop a robust froth whereas DOW 250 was strong enough to overcome the destabilising conditions created by the high dosage of CMC. The use of DOW 200 at a dosage of 60 g/t yielded lower water recoveries than DOW 250 at a dosage of 40 g/t. At higher dosages of CMC the destabilising conditions are probably as a result of the slime-cleaning properties of CMC which would result in sulphide particles with enhanced hydrophobicity. Statistical analysis using t tests of the data presented in Fig. 3 at the 10% significance level determined that the increase in the amounts of mass and water recovered from tests in which frother dosage was increased from 40 to 60 g/t for tests conducted in the absence of depressant and at 250 g/t using both frothers was significant. At a depressant dosage of 500 g/t this was only true when DOW 250 was used as the frother, and for water only. Differences in the recovery of solids between the two frothers were significant only in the absence of a depressant. Differences in the recovery of water between the two frothers were significant only at a depressant dosage of 500 g/t. The amounts of total gangue recovered as a function of water recovered are compared in Fig. 4 for DOW 200 and DOW 250. The values shown on the figure are for all tests conducted at 500 g/t depressant dosage irrespective of frother dosage. The gradient of the line is equivalent to the entrainment factor and is equal to the amount of entrained material reporting to the concentrate per unit water recovered. The values obtained for both frothers are shown in Table 2. More gangue was recovered by entrainment when using DOW 250 (3.19 g per 100 ml water) than when using DOW 200 (2.92 g per 100 ml water). Values obtained for DOW 250 are slightly higher than for DOW 200 for guar gum and CMC. The values obtained for CMC are slightly higher than for guar gum, most probably due to full dispersion at the high CMC dosages. These differences in the entrainment values would, however, result in very small differences in the recovery of solids. Fig. 5 compares the amount of NFG reporting to the concentrate as a function of water recovered for DOW 200 and DOW 250 at all dosages evaluated. The amount of NFG reporting to the concentrate in each case was determined using the entrainment factors as shown in Table 2. Greater amounts of NFG were recovered in tests using DOW 200 than from tests using DOW 250. This is particularly evident in the absence of a depressant, but the same trend was seen at a depressant dosage of 250 g/t. This suggests that there
207
may have been some interaction of DOW 250 with NFG in that the increase in frother chain-length has led to an adsorption of the frother onto NFG which may have resulted in some NFG depression. In testwork conducted by Lotter et al. (2003) it was shown using ToF-SIMS (time of flight secondary ion mass spectrometry) that DOW 250 had an affinity for Mg silicates in that these particles were covered by a surface layer of DOW 250. Surrounding sulphide mineral particles were unaffected. NFG recovery for DOW 200 from a feed mass of 1 kg ranged from 50 to 80 g depending on the frother dosage and that for DOW 250 from 45 to 70 g. The figure illustrates that at a depressant dosage of 500 g/t there was, by definition, total depression of NFG. An attempt was made to measure the residual concentration of frother in solution, but the results obtained were inconsistent. The analysis of the response of the sulphide minerals to frother type and dosage in this study was determined by following the recovery of copper and nickel. Some of the nickel present in Merensky ore is associated with gangue minerals and total nickel recoveries obtained are lower than the sulphide nickel recoveries would be expected to be. In this work total nickel recoveries were sufficient to monitor pentlandite behaviour (Brough, 2008; Wiese, 2009). Fig. 6 presents final copper recoveries and grades for all dosages of DOW 200 and DOW 250 in the presence of all dosages of guar gum. Upon observation of the figure it is evident that copper recoveries were at their maximum in the absence of a depressant with similar copper recoveries being obtained for both frothers under all conditions. Depressant addition resulted in a decrease in copper recovery probably due to the loss of partially liberated copper minerals. There was, however, little difference in the recovery of copper when guar gum dosage was increased from 250 to 500 g/t. The copper grades obtained in the absence of a depressant were low as a result of dilution by NFG. For all dosages of guar gum for both frothers, copper recoveries increased with an increase in frother dosage. This was accompanied by a decrease in copper grade due to the dilution of the concentrate by gangue. The highest copper grades were obtained at depressant dosages of 500 g/t where there is no expectation of NFG recovery to dilute the grade. For all conditions, in the presence of guar gum, higher copper grades were obtained for DOW 200 than for DOW 250. This has been attributed to greater dilution of the concentrate grade by entrained gangue as a result of the increased recovery of water in these tests. The slight differences in recovery obtained between DOW 200 and DOW may be within experimental error as it is not expected that frother type would influence copper recovery. Final copper recoveries and grades for all dosages of DOW 200 and DOW 250 in the presence of all dosages of CMC are presented in Fig. 7. The results obtained are similar to those obtained for equivalent tests conducted using guar gum in that an increase in frother dosage resulted in increased copper recovery with a reduction in copper grade. The recovery of copper on CMC addition did not decrease as much as in the presence of gaur gum when compared to tests conducted in the absence of a depressant. This is due to CMC not being as strong a depressant as guar gum with improved flotation of the partially liberated copper minerals (Wiese et al., 2007). Copper recovery was not impaired even at the lowest froth stability conditions i.e. DOW 200 in the presence of CMC at a dosage of 500 g/t. The highest copper grades were obtained for DOW 200 at a CMC dosage of 500 g/t. This is due to the strong destabilisation of the froth when using DOW 200 (see Fig. 2) and the full depression of NFG. Final recoveries and grades obtained for nickel for both frothers at all dosages in the presence of guar gum at dosages of 0, 250 and 500 g/t are presented in Fig. 8. As observed with copper the highest nickel recoveries accompanied by the lowest nickel grades were
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J. Wiese, P. Harris / Minerals Engineering 36–38 (2012) 204–210 25 y = 0.0319x
Total gangue, g
20
15 y = 0.0292x 10
5
0
0
100
200
300
400
500
600
700
800
Water, g Dow 200
Dow 250
Fig. 4. Total gangue versus water recovered for all tests conducted at increasing dosages of DOW 200 and DOW 250.
Table 2 Entrainment values determined for DOW 200 and DOW 250 in the presence of guar gum and CMC at dosages of 500 g/t. Frother type
Guar gum
CMC
DOW 200 DOW 250
0.0292 0.0319
0.0334 0.0356
obtained in the absence of a depressant. An increase in depressant dosage resulted in a decrease in nickel recovery. Nickel recoveries were more susceptible to depressant addition than the recoveries of copper. This decrease in nickel recovery was accompanied by an increase in nickel grade. Once again an increase in frother dosage always led to an increase in recovery. As with copper under the same conditions the highest grades were obtained using DOW 200 as the frother. The results obtained for nickel recoveries and grades in the presence of CMC are presented in Fig. 9. At a CMC dosage of 250 g/t there was very little difference in nickel recoveries and
grades for the two frothers. At a CMC dosage of 500 g/t in the presence of DOW 200 the recovery of nickel was impaired by froth crowding under highly destabilised conditions. In these tests there was a reversal of the grade, in that the grade increased with an increase in frother dosage which is the complete opposite trend to that obtained for both copper and nickel under all conditions evaluated. This condition yielded the lowest froths as indicated by the lowest water recovery (see Fig. 2). This has resulted in competitive adsorption between copper and nickel in the highly unstable froth, with copper floating at the expense of nickel. Under the same conditions DOW 250 yielded higher grades and recoveries by overcoming the destabilising effects of the sulphide minerals as a result of slime-cleaning. The phenomenon of slime coating removal from sulphide surfaces by CMC is known (Nagaraj and Ravisahnkar, 2007). In the absence of a depressant where there is NFG present, similar results were obtained for the two frothers. This testwork was carried out using an ore containing NFG in the form of partial talc rims along pyroxene grain boundaries. Further work should include the evaluation of an ore with different NFG mineralogy i.e. liberated talc to determine whether this results in differences in the mechanism of froth stabilisation.
90 80
Floating gangue, g
70 60 50 40 30 20 10 0
0
200
400
600
800
1000
1200
Water, g DOW 200 - No depressant
DOW 200 - 250 g/t Depressant
DOW 200 - 500g/t Depressant
DOW 250 - No depressant
DOW 250 - 250 g/t Depressant
DOW 250 - 500 g/t Depressant
Fig. 5. Floating gangue versus water recovered for all tests conducted using DOW 200 and DOW 250 at dosages of 40, 50 and 60 g/t.
J. Wiese, P. Harris / Minerals Engineering 36–38 (2012) 204–210
Fig. 6. Final copper grades and recoveries for all dosages of DOW 200 and DOW 250 in the presence of guar gum.
Fig. 7. Final copper grades and recoveries for all dosages of DOW 200 and DOW 250 in the presence of CMC.
Fig. 8. Final nickel grades and recoveries for all dosages of DOW 200 and DOW 250 in the presence of guar gum.
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J. Wiese, P. Harris / Minerals Engineering 36–38 (2012) 204–210
Fig. 9. Final nickel grades and recoveries for all dosages of DOW 200 and DOW 250 in the presence of CMC. The reversal of grade obtained using DOW 200 at a CMC dosage of 500 g/t is highlighted.
4. Conclusions Increased frother dosage, from 40 to 60 g/t, resulted in increased froth stability (as indicated by water recovery) for all conditions evaluated. The highly destabilised froths obtained using DOW 200 in the presence of high dosages of CMC depressant resulted in froth crowding with nickel competing with copper for adsorption. The increased strength of DOW 250 overcame this effect. Under destabilising conditions DOW 250 showed improved performance over that of DOW 200, but under conditions with maximum NFG presence there was little difference in their performance. An increase in frother dosage resulted in slightly improved copper recoveries, with a more marked improvement in the recovery of nickel, but at the expense of grade. Higher amounts of NFG were recovered from tests using DOW 200 than equivalent tests using DOW 250 in the absence of a depressant. This may be due to the adsorption of DOW 250 on NFG particles. It should be noted that an increase in frother dosage in a rougher circuit could affect downstream circuits. Acknowledgement The members of the UCT Reagent Research Group are thanked for providing the financial support for this study. References Becker, M., Harris, P., Wiese, J., Bradshaw, D. 2006. The use of quantitative mineralogical data to interpret the behaviour of gangue minerals in the flotation of Merensky Reef ores. In: Proceedings of Automated Mineralogy 06 Brisbane Australia. Bradshaw, D.J., Harris, P.J., O’Connor, C.T. 2005. The effect of collectors and their interactions with depressants on the behaviour of the froth phase in flotation. In: Proceedings of Centenary of Flotation Symposium Brisbane, 2005.
Brough, C. 2008 An investigation into the process mineralogy of the Merensky Reef at Northam Platinum Limited. MSc Thesis. Faculty of Engineering and the Built Environment, University of Cape Town. Bulatovic, S.M., 2007. Handbook of flotation reagents. Chemistry, Theory and Practice, Flotation of Sulfide ores, vol. 1. Elsevier. Engelbrecht, J.A., Woodburn, E.T., 1975. The effects of froth height, aeration rate and gas precipitation of flotation. Journal of South African Institute of Mining and Metallurgy, 125–132. Jasieniak, M., Smart, R.St.C., 2009. Collectorless flotation of pyroxene in Merensky ore: residual layer identification using statistical ToF-SIMS analysis. International Journal of Mineral Processing 92, 169–176. Lotter, N.O., Kowal, D.L., Tuzun, M.A., Whittaker, P.J., Kormos, L., 2003. Sampling and flotation testing of sudbury basin drill core for process mineralogy modelling. Minerals Engineering 16, 857–864. Martinovic, J., Bradshaw, D.J., Harris, P.J., 2005. Investigation of surface properties of gangue minerals in platinum bearing ores. Journal of the South African Institute of Mining and Metallurgy 105, 1–7. Nagaraj, D.R., Ravisahnkar, S.A., 2007. Flotation reagents – a critical overview from an industry perspective. In: Fuerstenau, M.C., Jameson, G., Yoon, R.H. (Eds.), Froth Flotation – A Century of Innovation. SME Littleton, Colorado, USA. Neethling, S.J., Cilliers, J.J., 2002. The entrainment of gangue into a flotation froth. International Journal of Mineral Processing 64, 123–134. Parolis, L.A.S., van der Merwe, R., Groenmeyer, G., Harris, P.J., 2008. The influence of metal cations on carboxymethylcelluloses as talc depressants. Journal of Colloids and Surfaces, A: Physiochemical and Engineering Aspects 317 (1–3), 109–115. Steenberg, E., Harris, P.J., 1984. Adsorption of carboxymethyl cellulose, guar gum and starch onto talc, sulphides, oxides and salt type minerals. South African Journal of Chemistry 37 (3). Wiese, J. 2009. Investigating depressant behaviour in the flotation of selected Merensky ores. MSc Thesis. Faculty of Engineering and the Built Environment, University of Cape Town. Wiese, J., Harris, P., Bradshaw, D., 2007. The response of sulphide and gangue minerals in selected Merensky ores to increased depressant dosages. Minerals Engineering 20, 986–995. Wiese, J., Harris, P., Bradshaw, D., 2010. The effect of increased frother dosage on froth stability at high depressant dosages. Minerals Engineering 23, 1010– 1017. Zheng, X., Franzidis, J.P., Johnson, N.W., 2006a. An evaluation of different models of water recovery in flotation. Minerals Engineering 19, 871–882. Zheng, X., Johnson, N.W., Franzidis, J.P., 2006b. Modelling of entrainment in industrial flotation cells: water recovery and degree of entrainment. Minerals Engineering 19, 1191–1203.
Contents lists available at SciVerse ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
The effect of frother type and dosage on flotation performance in the presence of high depressant concentrations Jenny Wiese ⇑, Peter Harris Centre for Minerals Research, University of Cape Town, South Africa
a r t i c l e
i n f o
Article history: Available online 20 April 2012 Keywords: Precious metal ores Froth flotation Flotation depressants Flotation frothers
a b s t r a c t The use of high dosages of polysaccharide depressants in order to depress the undesired naturally floatable gangue (NFG) present in ores beneficiated from the Bushveld Complex, South Africa, results in a significant decrease in the stability of flotation froths. These unstable froths can result in restricted mass pull and decreased valuable mineral recovery. Previous work using a single polyglycol ether type frother, DOW 200, has shown that an increase in frother dosage could be used to overcome the destabilisation of the froth to a certain extent and improve valuable mineral recovery. This resulted in an increase in water recovery and dilution of the concentrate by entrained material. This work extends this study to examine the effect of using a stronger frother, DOW 250, on the recovery of sulphide minerals and floatable gangue from a Merensky ore at different dosages of guar gum and CMC, which are typically used as depressants in the processing of Merensky ore. Results indicate that an increase in the strength of the frother resulted in a more robust froth. Depressant type also had an influence on results obtained. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction The presence of naturally floating gangue (NFG) in ores mined from the Bushveld Complex, South Africa, can result in negative effects during the flotation process. The presence of NFG, which consists mainly of pyroxene associated with talcaceous minerals, results in the stabilisation of the froth and although present in small amounts (0.5–5% by mass in the ore) can cause these unwanted effects. That these minerals are naturally floatable is due to the presence of talc along pyroxene grain boundaries (Becker et al., 2006; Jasieniak and Smart, 2009). Increasingly, concentrators processing ores containing significant quantities of NFG are making use of high depressant dosages to minimise the recovery of these undesirable minerals and to increase the grade of the concentrate. The two polysaccharide depressants most widely used in PGM flotation are guar gum and carboxymethyl cellulose (CMC). The CMC molecule has a high negative charge density, and when used at high concentration results in a strong negative charge as it adsorbs on particles resulting in significant dispersion. The guar gum molecule has a very low charge density and does not result in dispersed pulps particularly in the presence of the high ionic strength waters found in concentrators. Steenberg and Harris (1984), by conducting comparative adsorption studies of CMC, guar gum and starch depressants on talc showed that starch and guar gum produced a higher level of adsorption on talc than did ⇑ Corresponding author. Tel.: +27 21 650 2517; fax: +27 21 650 5501. E-mail address: [email protected] (J. Wiese). 0892-6875/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mineng.2012.03.028
CMC for any equilibrium concentration. Parolis et al. (2008) showed that the adsorption of CMC on talc was enhanced by the presence of Ca++, Mg++ and K+, commonly found in the recycle process water of Merensky flotation circuits. The use of high depressant dosages invariably results in a marked decrease in froth stability due to the depression of froth stabilising NFG (Bradshaw et al., 2005; Martinovic et al., 2005; Wiese, 2009). This could restrict solids recovery and result in decreased valuable mineral recovery. Low mass pulls may be overcome by an increase in frother dosage (Wiese et al., 2010), but could result in problems further downstream. Valuable mineral grade and recovery are strongly dependent on the stability of the froth since the recovery of entrained gangue is directly proportional to the amount of water recovered (Engelbrecht and Woodburn, 1975; Zheng et al., 2006a,b; Neethling and Cilliers, 2002). A froth stability which is too low can, however, result in a loss in the recovery of valuable minerals and the inability to transport material for further processing. The polyglycol ether range of frothers has strong surface activity, and their molecular weight (MW) and carbon chain-length determine their strength and performance (Bulatovic, 2007), with an increase in MW resulting in increased frothability, but lower selectivity. Wiese et al. (2010) using a single polyglycol frother, showed that an increase in frother dosage resulted in enhanced valuable mineral recovery. This work extends that study to include the use of a stronger frother, DOW 250, to determine whether its use would result in better management of the froth under high depressant dosages.
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For this work a Merensky ore containing a significant amount of NFG (Becker et al., 2006; Wiese, 2009) was selected and since the PGE in this type of ore are strongly associated with the sulphide minerals the effect of the increased frother dosages on the recovery of copper and nickel representing the sulphide minerals, chalcopyrite and pentlandite may be assessed. The investigation into the effects on PGE recovery is beyond the scope of the current paper.
Table 1 Properties of the frothers used in this study. Frother
Description
Molecular weight
Supplier
Dowfroth 200 Dowfroth 250
Polypropylene glycol methyl ether Tri-polypropylene glycol methyl ether
205
Betachem
260
Betachem
2. Experimental details An ore from the southern section of the Merensky Reef in the Bushveld Igneous Complex, South Africa was prepared at UCT (Wiese et al., 2007) for use in batch flotation tests. The mean copper (Cu), nickel (Ni) and sulphur (S) values for the ore were calculated using the concentrate and tailings values obtained from all the batch flotation tests and are as follows: Cu 0.087 wt.%, Ni 0.247 wt.%, S 0.367 wt.%. The NFG content of the ore sample was approximately 8%. All batch flotation tests were conducted using synthetic plant water, whereby distilled water is modified by the addition of various chemical salts to contain total dissolved solids of 1023 ppm (Wiese, 2009). Batch flotation tests were conducted using a method developed at UCT (Wiese, 2009). 1 kg portions of the ore sample were milled at 66% solids in synthetic plant water to achieve a grind of 60% passing 75 lm using a laboratory scale stainless steel rod mill. The milled slurry was transferred to a modified 3 L Leeds flotation cell. The volume in the cell was made up to produce 35% solids using synthetic plant water. The flotation cell was fitted with a variable speed drive and the pulp level was controlled manually by the addition of synthetic plant water. The impeller speed was set at 1200 rpm. The frothers, Dowfroth 200 (DOW 200) and Dowfroth 250 (DOW 250), supplied by Betachem were added at dosages of 40, 50 and 60 g/t. The collector, sodium isobutyl xanthate (SIBX), supplied by Senmin was added to the mill prior to grinding at a dosage of 150 g/t. The polymeric depressants used in the batch flotation tests were Depramin 267, a carboxymethylcellulose (CMC) supplied by AKZO Nobel Functional Chemicals and Stypres 504, a modified guar gum supplied by Chemquest. The MW of Depramin 267 used in this study was 325,000 g/mol, and that of Stypres 504 was 230,000 g/mol. The depressants were added at dosages of 250 and 500 g/t. Depressants were made up every second day at dosages corrected for active content. Tests were also conducted in the absence of a depressant. The chemical salts used in making up the synthetic plant water were obtained from Merck. (see Table 1). The general formula for DOW 200 is CH3(C3H6O)3OH, and that of DOW 250 is CH3(C3H6O)4OH. Both frothers are totally soluble in water. The air supply to the flotation cell was maintained at a flow rate of 7 L/min in all tests and the froth height was kept constant at 2 cm throughout. Four concentrates were collected at 2, 6, 12 and 20 min of flotation time by scraping the froth into a collecting pan every 15 s. A feed sample was taken before and a tailings sample was taken after each test. Water recoveries were measured for each test. Feeds, concentrates and tails were filtered, dried and weighed before analysis. All batch flotation tests were conducted in duplicate. Error bars showing standard error between duplicate tests are included in figures. Copper and total nickel analysis of all samples was done using a Bruker S4 Explorer XRF spectrophotometer. Sulphur analysis was carried out using a LECO S 632 sulphur analyser. 3. Results and discussion In order to determine the effect of the presence/absence of NFG on the frothing behaviour upon increases in frother dosage, tests
were conducted in the absence of depressant where NFG was present. All NFG was depressed at a depressant dosage of 500 g/t (Wiese, 2009) and this allows for the determination of gangue recovered by entrainment. At a depressant dosage of 250 g/t it has been determined (Wiese et al., 2010) that the amount of NFG recovered in the concentrate is of the same order as that of entrained gangue reporting to the concentrate. Two phase batch flotation tests i.e. water and air only, were conducted using DOW 200 and DOW 250 at the same dosages as were used in the three phase tests (water, air and solids). The results of these tests are shown in Fig. 1. Greater amounts of water were recovered from tests using DOW 250 than from tests using DOW 200 as the frother indicating that DOW 250 is the stronger frother of the two. The volume of froth obtained in these tests, as indicated by the water recovery, was substantially greater than that obtained from tests conducted in the presence of solids. This is as a result of the destabilising effects of the solids even in the absence of a depressant where the maximum amount of froth stabilising NFG was present or possibly the adsorption of frother onto the solids (Lotter et al., 2003). Results for total mass and water recovered for the various conditions using DOW 200 and DOW 250 at increasing dosages in the presence of guar gum at dosages of 0, 250 and 500 g/t are presented in Fig. 2. Care should be taken in assessing the recovery of solids as their recovery is dependent on the amount of water recovered. In the absence of a depressant the amount of water recovered by both frothers was similar and the amounts of solids recovered may thus be compared. Greater amounts of solids were recovered from tests using DOW 200 than from equivalent tests using DOW 250. This may be associated with the influence of the frother on NFG. The system was dominated by the presence of large amounts of NFG and the destabilising effects of the sulphide minerals were overridden. Guar gum addition at a dosage of 250 g/ t resulted in differences in the amount of water recovered, in that for equivalent dosages, DOW 250 always achieved higher water recoveries than DOW 200. At a guar gum dosage of 500 g/t, gangue reporting to the concentrate was via entrainment alone as all NFG was depressed at this dosage. For all conditions an increase in frother dosage resulted in an increase in the stability of the froth as indicated by increased water recovery. DOW 200 at a dosage of 60 g/t achieved similar water recoveries to DOW 250 at a dosage of 50 g/t. For the Merensky ore used in this study the changes in water recovery on increased guar gum dosage were not large when compared to tests conducted in the absence of a depressant. However, the mass of solids reporting to the concentrate was reduced when guar gum dosage was increased from 250 to 500 g/t. Statistical analysis using t tests of the data presented in Fig. 2 at the 10% significance level determined that the increases in the amounts of mass and water recovered when the frother dosage was increased from 40 to 60 g/t at all depressant dosages for both frothers were significant. Differences in the recovery of solids between the two frothers were significant only in the absence of a depressant, whereas differences in water recoveries were significant at depressant dosages of 250 and 500 g/t. Fig. 3 presents the results obtained for total mass and water recovered for the various conditions using DOW 200 and DOW
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J. Wiese, P. Harris / Minerals Engineering 36–38 (2012) 204–210 1600 DOW 200 DOW 250
Cumulative water, g
1400 1200 1000 800 600 400 200 0
40
50
60
Frother dosage, g/t Fig. 1. Cumulative water recovered for DOW 200 and DOW 250 from batch flotation tests conducted in the absence of solids.
Fig. 2. Final mass and water recovered for guar gum at dosages of 0, 250 and 500 g/t in the presence of DOW 200 and DOW 250 at dosages of 40, 50 and 60 g/t.
Fig. 3. Final mass and water recovered for CMC at dosages of 0, 250 and 500 g/t in the presence of DOW 200 and DOW 250 at dosages of 40, 50 and 60 g/t.
250 at increasing dosages in the presence of CMC at dosages of 0, 250 and 500 g/t. The addition of CMC resulted in a decrease in
the stability of the froth in comparison to the results obtained for guar gum. High dosages of CMC result in dispersed pulps and at
J. Wiese, P. Harris / Minerals Engineering 36–38 (2012) 204–210
a dosage of 250 g/t it is be expected that some degree of dispersion would be present. At this dosage slightly more froth was obtained from tests using DOW 250 than from DOW 200, which is evidence of it being a stronger frother. The destabilising effects of CMC are more evident at the fully dispersive conditions at a dosage of 500 g/t where tests conducted in the presence of DOW 200 resulted in very low froth stability. A procedure developed at UCT to evaluate the coagulative/dispersive nature of a mineral pulp was used to determine the extent to which particle aggregates were formed in a suspension of pulp at the depressant types and dosages evaluated. The procedure utilised an image analysis technique to measure the transmission of light through a mineral slurry with the same characteristics as the pulp phase used in the batch flotation tests i.e. 35% solids and a particle size distribution of 60% passing 75 lm. In the absence of depressant there was an almost immediate settling of suspended particles as indicated by the transmission of light through the suspension. In the presence of Stypres 504 at both dosages evaluated there was a steady increase in the transmission of light through the suspension during the course of the experiment. This was indicative of aggregation of particles. In the presence of Depramin 267 full dispersion of the pulp over the course if the experiment was indicated by zero transmission of light through the suspension for both dosages evaluated in this study. The increase in dosage of DOW 200 was not sufficient to develop a robust froth whereas DOW 250 was strong enough to overcome the destabilising conditions created by the high dosage of CMC. The use of DOW 200 at a dosage of 60 g/t yielded lower water recoveries than DOW 250 at a dosage of 40 g/t. At higher dosages of CMC the destabilising conditions are probably as a result of the slime-cleaning properties of CMC which would result in sulphide particles with enhanced hydrophobicity. Statistical analysis using t tests of the data presented in Fig. 3 at the 10% significance level determined that the increase in the amounts of mass and water recovered from tests in which frother dosage was increased from 40 to 60 g/t for tests conducted in the absence of depressant and at 250 g/t using both frothers was significant. At a depressant dosage of 500 g/t this was only true when DOW 250 was used as the frother, and for water only. Differences in the recovery of solids between the two frothers were significant only in the absence of a depressant. Differences in the recovery of water between the two frothers were significant only at a depressant dosage of 500 g/t. The amounts of total gangue recovered as a function of water recovered are compared in Fig. 4 for DOW 200 and DOW 250. The values shown on the figure are for all tests conducted at 500 g/t depressant dosage irrespective of frother dosage. The gradient of the line is equivalent to the entrainment factor and is equal to the amount of entrained material reporting to the concentrate per unit water recovered. The values obtained for both frothers are shown in Table 2. More gangue was recovered by entrainment when using DOW 250 (3.19 g per 100 ml water) than when using DOW 200 (2.92 g per 100 ml water). Values obtained for DOW 250 are slightly higher than for DOW 200 for guar gum and CMC. The values obtained for CMC are slightly higher than for guar gum, most probably due to full dispersion at the high CMC dosages. These differences in the entrainment values would, however, result in very small differences in the recovery of solids. Fig. 5 compares the amount of NFG reporting to the concentrate as a function of water recovered for DOW 200 and DOW 250 at all dosages evaluated. The amount of NFG reporting to the concentrate in each case was determined using the entrainment factors as shown in Table 2. Greater amounts of NFG were recovered in tests using DOW 200 than from tests using DOW 250. This is particularly evident in the absence of a depressant, but the same trend was seen at a depressant dosage of 250 g/t. This suggests that there
207
may have been some interaction of DOW 250 with NFG in that the increase in frother chain-length has led to an adsorption of the frother onto NFG which may have resulted in some NFG depression. In testwork conducted by Lotter et al. (2003) it was shown using ToF-SIMS (time of flight secondary ion mass spectrometry) that DOW 250 had an affinity for Mg silicates in that these particles were covered by a surface layer of DOW 250. Surrounding sulphide mineral particles were unaffected. NFG recovery for DOW 200 from a feed mass of 1 kg ranged from 50 to 80 g depending on the frother dosage and that for DOW 250 from 45 to 70 g. The figure illustrates that at a depressant dosage of 500 g/t there was, by definition, total depression of NFG. An attempt was made to measure the residual concentration of frother in solution, but the results obtained were inconsistent. The analysis of the response of the sulphide minerals to frother type and dosage in this study was determined by following the recovery of copper and nickel. Some of the nickel present in Merensky ore is associated with gangue minerals and total nickel recoveries obtained are lower than the sulphide nickel recoveries would be expected to be. In this work total nickel recoveries were sufficient to monitor pentlandite behaviour (Brough, 2008; Wiese, 2009). Fig. 6 presents final copper recoveries and grades for all dosages of DOW 200 and DOW 250 in the presence of all dosages of guar gum. Upon observation of the figure it is evident that copper recoveries were at their maximum in the absence of a depressant with similar copper recoveries being obtained for both frothers under all conditions. Depressant addition resulted in a decrease in copper recovery probably due to the loss of partially liberated copper minerals. There was, however, little difference in the recovery of copper when guar gum dosage was increased from 250 to 500 g/t. The copper grades obtained in the absence of a depressant were low as a result of dilution by NFG. For all dosages of guar gum for both frothers, copper recoveries increased with an increase in frother dosage. This was accompanied by a decrease in copper grade due to the dilution of the concentrate by gangue. The highest copper grades were obtained at depressant dosages of 500 g/t where there is no expectation of NFG recovery to dilute the grade. For all conditions, in the presence of guar gum, higher copper grades were obtained for DOW 200 than for DOW 250. This has been attributed to greater dilution of the concentrate grade by entrained gangue as a result of the increased recovery of water in these tests. The slight differences in recovery obtained between DOW 200 and DOW may be within experimental error as it is not expected that frother type would influence copper recovery. Final copper recoveries and grades for all dosages of DOW 200 and DOW 250 in the presence of all dosages of CMC are presented in Fig. 7. The results obtained are similar to those obtained for equivalent tests conducted using guar gum in that an increase in frother dosage resulted in increased copper recovery with a reduction in copper grade. The recovery of copper on CMC addition did not decrease as much as in the presence of gaur gum when compared to tests conducted in the absence of a depressant. This is due to CMC not being as strong a depressant as guar gum with improved flotation of the partially liberated copper minerals (Wiese et al., 2007). Copper recovery was not impaired even at the lowest froth stability conditions i.e. DOW 200 in the presence of CMC at a dosage of 500 g/t. The highest copper grades were obtained for DOW 200 at a CMC dosage of 500 g/t. This is due to the strong destabilisation of the froth when using DOW 200 (see Fig. 2) and the full depression of NFG. Final recoveries and grades obtained for nickel for both frothers at all dosages in the presence of guar gum at dosages of 0, 250 and 500 g/t are presented in Fig. 8. As observed with copper the highest nickel recoveries accompanied by the lowest nickel grades were
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J. Wiese, P. Harris / Minerals Engineering 36–38 (2012) 204–210 25 y = 0.0319x
Total gangue, g
20
15 y = 0.0292x 10
5
0
0
100
200
300
400
500
600
700
800
Water, g Dow 200
Dow 250
Fig. 4. Total gangue versus water recovered for all tests conducted at increasing dosages of DOW 200 and DOW 250.
Table 2 Entrainment values determined for DOW 200 and DOW 250 in the presence of guar gum and CMC at dosages of 500 g/t. Frother type
Guar gum
CMC
DOW 200 DOW 250
0.0292 0.0319
0.0334 0.0356
obtained in the absence of a depressant. An increase in depressant dosage resulted in a decrease in nickel recovery. Nickel recoveries were more susceptible to depressant addition than the recoveries of copper. This decrease in nickel recovery was accompanied by an increase in nickel grade. Once again an increase in frother dosage always led to an increase in recovery. As with copper under the same conditions the highest grades were obtained using DOW 200 as the frother. The results obtained for nickel recoveries and grades in the presence of CMC are presented in Fig. 9. At a CMC dosage of 250 g/t there was very little difference in nickel recoveries and
grades for the two frothers. At a CMC dosage of 500 g/t in the presence of DOW 200 the recovery of nickel was impaired by froth crowding under highly destabilised conditions. In these tests there was a reversal of the grade, in that the grade increased with an increase in frother dosage which is the complete opposite trend to that obtained for both copper and nickel under all conditions evaluated. This condition yielded the lowest froths as indicated by the lowest water recovery (see Fig. 2). This has resulted in competitive adsorption between copper and nickel in the highly unstable froth, with copper floating at the expense of nickel. Under the same conditions DOW 250 yielded higher grades and recoveries by overcoming the destabilising effects of the sulphide minerals as a result of slime-cleaning. The phenomenon of slime coating removal from sulphide surfaces by CMC is known (Nagaraj and Ravisahnkar, 2007). In the absence of a depressant where there is NFG present, similar results were obtained for the two frothers. This testwork was carried out using an ore containing NFG in the form of partial talc rims along pyroxene grain boundaries. Further work should include the evaluation of an ore with different NFG mineralogy i.e. liberated talc to determine whether this results in differences in the mechanism of froth stabilisation.
90 80
Floating gangue, g
70 60 50 40 30 20 10 0
0
200
400
600
800
1000
1200
Water, g DOW 200 - No depressant
DOW 200 - 250 g/t Depressant
DOW 200 - 500g/t Depressant
DOW 250 - No depressant
DOW 250 - 250 g/t Depressant
DOW 250 - 500 g/t Depressant
Fig. 5. Floating gangue versus water recovered for all tests conducted using DOW 200 and DOW 250 at dosages of 40, 50 and 60 g/t.
J. Wiese, P. Harris / Minerals Engineering 36–38 (2012) 204–210
Fig. 6. Final copper grades and recoveries for all dosages of DOW 200 and DOW 250 in the presence of guar gum.
Fig. 7. Final copper grades and recoveries for all dosages of DOW 200 and DOW 250 in the presence of CMC.
Fig. 8. Final nickel grades and recoveries for all dosages of DOW 200 and DOW 250 in the presence of guar gum.
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Fig. 9. Final nickel grades and recoveries for all dosages of DOW 200 and DOW 250 in the presence of CMC. The reversal of grade obtained using DOW 200 at a CMC dosage of 500 g/t is highlighted.
4. Conclusions Increased frother dosage, from 40 to 60 g/t, resulted in increased froth stability (as indicated by water recovery) for all conditions evaluated. The highly destabilised froths obtained using DOW 200 in the presence of high dosages of CMC depressant resulted in froth crowding with nickel competing with copper for adsorption. The increased strength of DOW 250 overcame this effect. Under destabilising conditions DOW 250 showed improved performance over that of DOW 200, but under conditions with maximum NFG presence there was little difference in their performance. An increase in frother dosage resulted in slightly improved copper recoveries, with a more marked improvement in the recovery of nickel, but at the expense of grade. Higher amounts of NFG were recovered from tests using DOW 200 than equivalent tests using DOW 250 in the absence of a depressant. This may be due to the adsorption of DOW 250 on NFG particles. It should be noted that an increase in frother dosage in a rougher circuit could affect downstream circuits. Acknowledgement The members of the UCT Reagent Research Group are thanked for providing the financial support for this study. References Becker, M., Harris, P., Wiese, J., Bradshaw, D. 2006. The use of quantitative mineralogical data to interpret the behaviour of gangue minerals in the flotation of Merensky Reef ores. In: Proceedings of Automated Mineralogy 06 Brisbane Australia. Bradshaw, D.J., Harris, P.J., O’Connor, C.T. 2005. The effect of collectors and their interactions with depressants on the behaviour of the froth phase in flotation. In: Proceedings of Centenary of Flotation Symposium Brisbane, 2005.
Brough, C. 2008 An investigation into the process mineralogy of the Merensky Reef at Northam Platinum Limited. MSc Thesis. Faculty of Engineering and the Built Environment, University of Cape Town. Bulatovic, S.M., 2007. Handbook of flotation reagents. Chemistry, Theory and Practice, Flotation of Sulfide ores, vol. 1. Elsevier. Engelbrecht, J.A., Woodburn, E.T., 1975. The effects of froth height, aeration rate and gas precipitation of flotation. Journal of South African Institute of Mining and Metallurgy, 125–132. Jasieniak, M., Smart, R.St.C., 2009. Collectorless flotation of pyroxene in Merensky ore: residual layer identification using statistical ToF-SIMS analysis. International Journal of Mineral Processing 92, 169–176. Lotter, N.O., Kowal, D.L., Tuzun, M.A., Whittaker, P.J., Kormos, L., 2003. Sampling and flotation testing of sudbury basin drill core for process mineralogy modelling. Minerals Engineering 16, 857–864. Martinovic, J., Bradshaw, D.J., Harris, P.J., 2005. Investigation of surface properties of gangue minerals in platinum bearing ores. Journal of the South African Institute of Mining and Metallurgy 105, 1–7. Nagaraj, D.R., Ravisahnkar, S.A., 2007. Flotation reagents – a critical overview from an industry perspective. In: Fuerstenau, M.C., Jameson, G., Yoon, R.H. (Eds.), Froth Flotation – A Century of Innovation. SME Littleton, Colorado, USA. Neethling, S.J., Cilliers, J.J., 2002. The entrainment of gangue into a flotation froth. International Journal of Mineral Processing 64, 123–134. Parolis, L.A.S., van der Merwe, R., Groenmeyer, G., Harris, P.J., 2008. The influence of metal cations on carboxymethylcelluloses as talc depressants. Journal of Colloids and Surfaces, A: Physiochemical and Engineering Aspects 317 (1–3), 109–115. Steenberg, E., Harris, P.J., 1984. Adsorption of carboxymethyl cellulose, guar gum and starch onto talc, sulphides, oxides and salt type minerals. South African Journal of Chemistry 37 (3). Wiese, J. 2009. Investigating depressant behaviour in the flotation of selected Merensky ores. MSc Thesis. Faculty of Engineering and the Built Environment, University of Cape Town. Wiese, J., Harris, P., Bradshaw, D., 2007. The response of sulphide and gangue minerals in selected Merensky ores to increased depressant dosages. Minerals Engineering 20, 986–995. Wiese, J., Harris, P., Bradshaw, D., 2010. The effect of increased frother dosage on froth stability at high depressant dosages. Minerals Engineering 23, 1010– 1017. Zheng, X., Franzidis, J.P., Johnson, N.W., 2006a. An evaluation of different models of water recovery in flotation. Minerals Engineering 19, 871–882. Zheng, X., Johnson, N.W., Franzidis, J.P., 2006b. Modelling of entrainment in industrial flotation cells: water recovery and degree of entrainment. Minerals Engineering 19, 1191–1203.