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Use of “oily bubbles” and dispersants in flotation of molybdenite in fresh and seawater
Minerals Engineering 148 (2020) 106197
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Use of “oily bubbles” and dispersants in flotation of molybdenite in fresh and seawater
T
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Andres Ramireza,b, Leopoldo Gutierreza,b, , Janusz S. Laskowskic a
Department of Metallurgical Engineering, University of Concepcion, Chile Water Research Centre for Agriculture and Mining (CRHIAM), University of Concepcion, Chile c PN.B. Keevil Institute of Mining Engineering, University of British Columbia, Canada b
A R T I C LE I N FO
A B S T R A C T
Keywords: Froth flotation Molybdenite Molybdenite flotation Oily bubbles Dispersants Seawater Sodium hexametaphosphate Sodium silicate
Molybdenite - as all inherently hydrophobic minerals – is floated with the use of water-insoluble oily collectors. Such collectors can be used in flotation either after emulsification in water, but can also be brought to the point of particle-to-bubble attachment on the surface of bubbles (as oily-bubbles). In this paper we are testing the effect of oily-bubbles and the dispersants sodium hexametaphosphate (SHMP) and sodium silicate (SS) on the flotation of moleybdenite in seawater in alkaline environment. The results show that molybdenite recovery increases when kerosene is supplied on the surface of bubbles which was particularly important in the flotation of molybdenite at pH > 9.5 in seawater. SHMP dispersant had a strong positive effect on the recovery of molybdenite at pH > 9.5, the pH range known to cause depression of the molybdenite flotation when pH is raised to depress pyrite and magnesium species precipitate as hydroxo-complexes/hydroxide. The combined effect of the oily bubbles and dispersants allows for the molybdenite recoveries to reach to similar values to those achieved when using fresh water. The results of induction time measurements indicate that the attachment of bubbles to molybdenite is significantly improved when the bubbles are coated with a layer of kerosene.
1. Introduction Molybdenite, along with minerals like talc and graphite, belongs to a group of inherently hydrophobic minerals which are floated with the use of water insoluble collectors. In the flotation processes, water-soluble collectors are applied in the form of aqueous emulsions and the collector, which is needed at the point of the particle-to-bubble attachment, is commonly carried to this point adsorbed on the surface of the mineral particles. Selectivity of the adsorption determines the outcome of the process. In the case of water-insoluble oily collectors (e.g. kerosene, Diesel oil) introduction of the oily compound into the aqueous system is a little more complicated. In such a case, as a result of emulsification, the collector appears in the pulp in the form of droplets which collide with mineral particles as a result of conditioning and can get attached to the hydrophobic mineral particles. Oil droplets can spread at the air/water interface, while oil does not straightforwardly spread on hydrophobic solid surfaces submerged in water (and adheres to such solid surfaces in the form of droplets). Better dispersion of the compound which is insoluble in water and its use as emulsion was shown to be more efficient (Hoover and Malhotra, 1976; Born et al., 1976). The alternative involves the use of
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the so called “oily bubbles” (Masliyah et al., 2004; Tarkan, et al., 2009; Xia and Yang, 2013). The method consists in covering the bubbles with a thin layer of a non-polar collector which benefits the transport of the collector to the surface of the particles improving flotation (Laskowski, 2007, 2010). This methodology has been applied to improve flotation of oxidized coal, and especially to improve fine particle flotation (Xu et al., 2003). Misra and Anazia (1987) compared the results of coal flotation tests carried out with fuel oil, which was either added directly into a Denver flotation cell in an ultrasonically emulsified form or as an aerosol in the stream of air entering the cell. The results indicate that the introduction of collector on the surface of bubbles produces superior results. Misra and Anazia also demonstrated that the induction time needed for the oil-coated bubbles to attach to coal specimens was many times shorter in comparison with the induction time measured for the oil-free bubbles which supports the reported work by Laskowski (2007). Gomez et al. (2008) tested aerosol-enhanced flotation in deinking of recycled paper with the use of silicone oil. They found that oil coated bubbles increased deinking efficiency when oil was used. They reported that gas holdup increased and concluded that this resulted either from smaller bubbles or from their slower movement. The improved flotation efficiency upon injecting oil could also result from
Corresponding author at: Department of Metallurgical Engineering, University of Concepcion, Edmundo Larenas 285, Concepcion 4070371, Chile. E-mail address: [email protected] (L. Gutierrez).
https://doi.org/10.1016/j.mineng.2020.106197 Received 22 May 2019; Received in revised form 2 January 2020; Accepted 9 January 2020 0892-6875/ © 2020 Elsevier Ltd. All rights reserved.
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Table 1 Chemical analyses of molybdenite sample. Chemical analyses Cu(%)
Fe(%)
S(%)
Mo(%)
Ins(%)
0,55
0,49
37,9
55,4
5,3
obtained from a molybdenum concentrate represents better the mineral obtained from porphyry type deposits in which this mineral is found dispersed in a quartz matrix. Additional studies are being conducted to evaluate the effect of oily bubbles in combination with dispersants to improve molybdenite recovery through batch flotation tests using freshly ground Cu-Mo ore feed. Methyl isobutyl carbinol (MIBC) of analytical grade (Merck) was used as frother, extra pure sodium silicate (SS) from Merck, and sodium hexametaphospate (SHMP) 65–70% P2O5 (Sigma Aldrich) were used as dispersants. Kerosene was used as a non-polar collector. Milli-Q water of 18.4 MΩ∙cm at 25 °C was utilized in all the experiments. Seawater samples were taken from the coast of Concepcion, Bio Bio, Chile. The pH was adjusted with sodium hydroxide and/or lime. Fig. 1. Particle size distribution of molybdenite.
2.2. Procedures 2.2.1. Micro-flotation experiments The floatability of molybdenite was evaluated through micro-flotation tests that were carried out in a 150 mL Partridge and Smith glass cell using nitrogen (NR2R) at a flowrate of 80 mL/min to produce bubbles using a porous glass frit (Fig. 2). The flotation feed was prepared by mixing 1 g of molybdenite with 100 mL of solution (0.01 M NaCl or seawater). After 2 min of conditioning at the required pH, MIBC, and emulsified kerosene were added at a concentration of 15 and 100 ppm respectively, and conditioned for 5 more minutes at the previously established pH value. The kerosene used in the micro-flotation tests was emulsified in a 1 L juice blender for 30 s using Mili-Q water, adding 15 ppm of MIBC. Additional solution was then added to make up to 150 mL required for the micro-flotation glass cell and the pH was adjusted for 5 min. The flotation process started when opening the gas valve, and was carried out for a period of time of 2 min with the froth product being removed every 10 s. The pulp level in the micro-flotation cell was kept constant by adding a background solution prepared at the same composition and pH as in the original solution. Finally, the concentrates and tailings were filtered and washed with distilled water to remove solids precipitates, and with acetone to remove collectors, and dried in an oven at 105 °C for 12 h. Then, concentrate yield was calculated as the ratio between the mass of molybdenite in the concentrate and the mass of molybdenite in the concentrate plus tailings. All the experiments were done in duplicate. For the tests with oily bubbles it was necessary to use a modified version of the Partridge and Smith cell which incorporated a section that permitted the contact between gas bubbles and a kerosene emulsion, as shown in Fig. 2. As a result of the interaction between bubbles and the micro-drops of kerosene, the coating of the bubbles with the non-polar collector was promoted just before entering the cell collection zone. In the case of tests performed using oily bubbles, the collector dosage was fixed by adjusting the volume of emulsion used during the 2 min of flotation, and the kerosene concentration in the emulsion in order to achieve the 100 ppm (based on the 150 mL of the cell) of collector needed in the experiments.
improved attachment efficiency of oil-coated bubbles versus clean bubbles. It was recently shown that the depression of molybdenite in seawater over the pH range from pH 9.5 to 10.5, over which it most likely results from the presence of magnesium colloidal species, could be reduced when dispersing agent such as sodium hexametaphosphate (SHMP) is used (Rebolledo et al., 2017). So it is reasonable to think that the combined action of both oily bubbles and dispersants could lead to even better results in the case of molybdenite flotation. The objective of this work is to study the use of oily bubbles as an alternative to improve the flotation of molybdenite in both fresh water and seawater. As part of the work, the use of oily bubbles in the presence of SHMP and sodium silicate dispersants was also studied. 2. Materials and methods 2.1. Samples and reagents The molybdenite sample used in this work was obtained from an industrial molybdenum concentrate which was further purified through 3 stages of flotation without collector. Fig. 1 shows the particle size distributions The samples were washed and cleaned following the procedure described by Uribe et al. (2016) and Rebolledo et al. (2017). The procedure includes 3 stages of washing with sodium hydrosulfide (NaSH) and acetone in order to remove any inorganic and organic reagents such as collectors present in the sample. To evaluate the presence of residual reagents in the molybdenite sample, tests were performed in which 3 g of molybdenite were mixed with 15 mL of Milli-Q water and kept under stirring using a magnetic stirrer for 10 min. After this, the suspension was filtered, and the solution obtained was analyzed for total organic carbon (TOC) in a Shimadzu TOC-L Total Organic Analyzer. These tests were performed at pH 8, 9, 10, and 11 and in all the cases no TOC was detected in the solutions indicating that the molybdenite sample was free from flotation reagents. Table 1 shows the chemical analysis of the sample. In order to reduce molybdenite oxidation, the samples were stored in a freezer in sealed plastic bags previously blown with nitrogen, at a temperature of about 1 °C (Ekmekci and Demirel, 1997; Zhang et al., 1997; Ansari and Pawlik, 2007). It has to be noted that although the use of freshly ground minerals simulates better the real flotation conditions in a concentrator, at this stage of the research program it was considered that molybdenite
2.2.2. Bubble-particle attachment tests The bubble-particle attachment tests were conducted following the procedure described by Castro et al. (2014) and the device built at the University of Alberta was used (Fig. 3A). In this procedure a bubble is contacted with a solution for 1 min (Fig. 3A-1), and then pushed against 2
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Fig. 2. Schematic representation of flotation cell modified for the use of emulsified kerosene.
Fig. 3. (A) No oily bubbles: 1. bubble generation; 2 bubble-particles contact; 3 bubble-particles detachment; (B) With oily bubbles: 1. bubble-kerosene contact; 2. Interaction of bubble with aqueous solution; 3 oily bubble-particles contact; 4 oily bubble-particles detachment (Adapted from Liu et al., 2002). 3
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same procedure as described is followed (Fig. 3B-2; Fig. 3B-3; Fig. 3B4). The particles beds were prepared using 3 g of molybdenite which were dispersed in 30 mLP of solution. Then, the pH is adjusted for 2 min to the required value, and frother and/or dispersants are added and conditioned for additional 10 min, after which the suspension is transferred to a 15 mLP cell in order to start the bubble-attachment measurements. All these experiments were conducted in duplicates thus the results presented in this paper are average values. 3. Results 3.1. Micro-flotation with/without oily bubbles, pH adjusted using NaOH Fig. 4 shows the molybdenite recovery as a function of pH in a 0.01 M NaCl solution, and in seawater, with and without oily bubbles. In these experiments the pH was adjusted using NaOH. The results show that there is a small positive effect of the use of the oily bubbles on molybdenite recovery in both types of aqueous media. The results with a 0.01 M NaCl solution show an increase in molybdenite recovery of 3–7 percentage points at pH > 10, while with seawater the increase is of the order of 5–9 percentage points, in the whole pH range studied. The positive effects of the use of the oily bubbles in all cases are greater than the experimental error, that reached maximum values of the order of 2 percentage points. Fig. 4 demonstrates that the flotation of molybdenite is strongly depressed when the process is carried out in seawater, as previously reported (Rebolledo et al, 2017; Castro, 2012). As it was reported, SHMP and SS are able to disperse precipitating/ coagulating hydroxides from the molybdenite surface and improve its flotation (Rebolledo et al., 2017; Ramirez et al., 2018). Fig. 5 shows molybdenite recovery as a function of pH in seawater, in the absence and presence of SHMP and SS, and without and with oily bubbles. The results indicate that both reagents have a positive effect on the recovery of molybdenite when the process is carried out in seawater at pH > 9.5, which is in agreement with what was reported by Rebolledo et al. (2017). These results demonstrate that SHMP caused the strongest effect. Comparison of the results obtained without and with oily bubbles (Fig. 5a and b) indicate that at pH 10 the combined effect of the oily bubbles and dispersants allows for the molybdenite recoveries to reach similar values to those achieved when using 0.01 M NaCl solution (95–96%).
Fig. 4. Molybdenite recovery as a function of pH in a 0.01 M NaCl solution and in seawater with and without oily bubbles. Conditions: 100 ppm kerosene (total), 15 ppm MIBC, pH adjusted with NaOH.
a bed of particles for a given contact time controlled by the device (Fig. 3A-2). Then the bubble is detached and observed using a microscope to determine if attachment between bubbles and particles took place (Fig. 3A-3). For every contact time, the procedure is repeated 10 times over different positions of the bed of particles and then the percentage of contacts for which particles attached to the bubble is determined. The contact times are varied and the same procedure is repeated. Finally, a plot of percentages of successful contacts (NSC) versus the measured contact time (tc) is generated. The induction time then can be defined as the contact time at which 50% of the contacts were successful. As Fig. 3B shows, in the case of the tests carried out to evaluate the effect of oily bubbles on the attachment with molybdenite particles, the bubble is initially submerged for 1 min in kerosene so that they get coated with the non polar collector (Liu et al., 2002). Then the
Fig. 5. Molybdenite recovery as a function of pH in seawater, in the absence and presence of SHMP and SS, (a) without oily bubbles, and (b) with oily bubbles. Conditions: 100 ppm kerosene (total), 15 ppm MIBC, pH adjusted with NaOH. 4
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explained by the increase in the concentration of calcium ions in solution. Fig. 8 shows molybdenite recovery as a function of pH in seawater, in the absence and presence of SHMP and SS, and without and with oily bubbles. As previously reported, the recovery of molybdenite is strongly depressed in seawater when the pH exceeds pH 9.5 (Castro, 2012). Fig. 8a also reveals a positive effect of the dispersants SHMP and SS on molybdenite recovery, with SHMP being more efficient. These results are in agreement with those previously reported by Rebolledo et al. (2017) and Ramirez et al. (2018). Fig. 8a and b also show that over the pH range from 10 to 10.5 the combined use of SHMP and oily bubbles in seawater allows for molybdenite recoveries that are close to those obtained in fresh water. 3.3. Bubble-particle attachment tests (pH adjusted using lime) Fig. 9 shows the induction times as a function of pH in seawater, in the absence and presence of SHMP and SS, without (Fig. 9a) and with oily bubbles (Fig. 9b). It is observed that the induction time values increase by several orders of magnitude when the pH exceeds 9.5, and that the use of dispersants, in particular SHMP, makes it possible to reduce these values, which agrees with the recovery of molybdenite presented in Figs. 5, 7, and 8. On the other hand, Fig. 9a and b show that the coating of the bubbles by kerosene reduces the induction times by an order of magnitude, and that the combined use of dispersants and oily bubbles has an important synergistic effect. Fig. 10 shows images obtained from the bubble-attachment tests that were carried out in seawater without (left) and with (right) oily bubbles at pH 9. The images reveal formation of a layer of kerosene that covers the bubble. Fig. 11 shows images obtained without (left) and with (right) oily bubbles at pH = 10.5. It can be seen that the presence of a layer of kerosene prevents Mg precipitates from attaching to bubbles.
Fig. 6. Molybdenite recovery as a function of pH in a 0.01 M NaCl solution and seawater with and without oily bubbles. Conditions: 100 ppm kerosene (total), 15 ppm MIBC, pH adjusted with lime.
3.2. Micro-flotation with/without oily bubbles, pH adjusted using lime Fig. 6 shows the results of molybdenite recovery as a function of pH in a 0.01 M NaCl solution, and seawater, with and without oily bubbles. Lime was used in these exeriments to adjust pH. The results indicate that the recovery of molybdenite is much more affected when the pH is adjusted with lime in the absence of oily bubbles. These results also indicate that the depressing effect of seawater in the flotation of molybdenite is strongly mitigated when oily-collector is supplied in the form of oily-bubbles, which can increase recovery by up to 35 percentage. Fig. 7 shows molybdenite recovery as a function of pH (adjusted with lime) in a 0.01 M NaCl solution, in the absence and presence of SHMP and SS, and without and with oily bubbles. The results indicate a slight depressing effect of pH on the recovery of molybdenite, which is
4. Discussion In the conventional flotation process, flotation reagents are supplied as aqueous solutions and as these reagents are needed at the point of particle-to-bubble attachment, they are brought to this point partially adsorbed on mineral particles (mostly collectors) and partially on the surface of bubbles (frothers). Theoretical analysis of the process
Fig. 7. Molybdenite recovery as a function of pH in a 0.01 M NaCl solution, in the absence and presence of SHMP and SS, (a) without oily bubbles, and (b) with oily bubbles. Conditions: 100 ppm kerosene (total), 15 ppm MIBC, pH adjusted with lime (CaO). 5
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Fig. 8. Molybdenite recovery as a function of pH in seawater, in the absence and presence of SHMP and SS, (a) without oily bubbles, and (b) with oily bubbles. Conditions: 100 ppm kerosene (total), 15 ppm MIBC, pH adjusted with lime (CaO).
Fig. 9. Induction time as a function of pH in seawater, and in the absence and presence of SHMP and SS, (a) without oily bubbles, and (b) with oily bubbles. pH adjusted with lime (CaO).
of Ca(OH)P+P leads to precipitation of calcium hydroxide on molybdenite faces, which can be explained by the presence of nano-edges and nano-faces covering the molybdenite basal planes on which this precipitation can take place (Lopez-Valdivieso et al., 2012). The results shown in Fig. 6 indicate that the depressing effect of lime (calcium) on the flotation of molybdenite could be reduced when oily bubbles are utilized. It is now well established that molybdenite flotation is strongly affected in seawater when pH is increased with lime to depress pyrite, and that responsible for the depressing effect are the MgP2+P hydrolysis products which accumulate on the molybdenite surface (Castro, 2012; Castro et al., 2012, Castro et al., 2014). Previous studies also showed that the hydrolysis products of magnesium ions can accumulate on the surface of bubbles, generating a hydrophilic coating that prevents the bubbles from interacting directly with the minerals, which induces a strong depression of flotation (Li and Somasundaran, 1991). The results presented in Fig. 6 demonstrate that the depressing effect of
indicates that bringing the reagents on the surface of bubbles is much more efficient (Laskowski, 2007). Supply of the flotation reagents on the surface of bubbles is particularly advantageous when these reagents are water-insoluble such as oily collectors as it is in the flotation of molybdenite. The results obtained in fresh water presented in Figs. 4–8 validate this hypothesis and show that molybdenite recovery increases when bubbles are coated with kerosene. Fig. 4, for example, shows that in the experiments in which the pH was adjusted using NaOH, molybdenite recovery increases between 3 and 7 percentage points at pH > 10, the range that is larger than the experimental error. The results of molybdenite flotation obtained using lime to adjust pH presented in Fig. 6 indicate a positive effect of the use of oily bubbles on molybdenite recovery, even in this case which is known to be more adverse for molybdenite. Chander and Fuerstenau (1972) proposed that in the alkaline pH range (pH > 8) molybdenite flotation is strongly depressed by the chemical adsorption of Ca(OH)P+P compounds and the subsequent formation of calcium molybdate. Successive adsorption 6
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Fig. 10. Images obtained from bubble-attachement tests in seawater without (left) and with (right) oily bubbles at pH = 9.
Fig. 11. Images obtained from bubble-attachement tests in seawater without (left) and with (right) oily bubbles at pH = 10.5. 7
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seawater on flotation of molybdenite is strongly reduced when oil is supplied on the surface of bubbles. These results can be explained by the fact that the bubbles coated by films of oil get protected to some extent from the coating by Mg hydrolysis products leading to the molybdenite flotation improvement. Images shown in Fig. 11 supports this hypothesis that the presence of a layer of kerosene on bubbles makes the presence of Mg precipitates on the bubbles surface less likely. The reason that explains why magnesium hydroxo complexes attach to bubbles but not to oily bubbles in the process of flotation in seawater is still unknown and deserves further research. Li and Somasundaran (1991) proposed that the modification of the surface properties of bubbles in magnesium solutions at alkaline pH values is explained by the precipitation of Mg(OH)2(s) at the air-liquid interface which occurs after adsorption of positively charged Mg(OH)+ on the negatively charged bubbles. Thus, the magnesium concentration at the air-liquid interface increases and exceeds the values necessary to form Mg (OH)2(s). However, in the process of flotation using seawater the ionic strength is high (~0.7 M) and the surface charge of bubbles, particles and kerosene is expected to be suppressed, and the mechanisms of interactions between the hydroxo complexes of magnesium should be different which at this stage of our research remains unknown. The use of dispersants to remove precipitating/coagulating magnesium hydroxides from the molybdenite surface was tested and the results were reported in the paper by Rebolledo et al. (2017). It was shown that the use of sodium hexametaphosphate (SHMP) restores molybdenite flotation over the alkaline pH range. These results open new alternatives for processing Cu-Mo sulfide ores. The previous paper also showed that pyrite flotation is depressed at pH > 10.5 and that the floatability of pyrite over this pH range is not restored by SHMP. The results presented in Figs. 5 and 8 show that in seawater at pH 10, and in the absence of SHMP the use of oily bubbles allows molybdenite recovery to be increased by about 10 and 25 percentage when the pH is adjusted with NaOH and lime, respectively. On the other hand, Figs. 5a and 8)a show that the use of SHMP alone results in an increased of recovery of 15 and 45 percentage points with the use of NaOH and lime, respectively. Additionally, when comparing the results of the effect of oily bubbles in the presence of SHMP, it can be observed that a recovery increase of 7 percentage points can be achieved using NaOH to adjust pH (Fig. 6); no effect is observed with lime (Fig. 8). In summary, the data show that the effect of the SHMP dispersant is stronger than that of the oily bubbles, which is probably due to the fact that this compound disperses the magnesium hydroxo complexes on both, the molybdenite and bubble surfaces, while oil coates only bubbles. In general, the experimental data indicate that the combined action of oily bubbles and SHMP increases molybdenite recovery to levels similar to those achieved using fresh water (95–96%). All these results are also in line with the induction time data presented in Fig. 9. As was previously cited, Gomez et al. (2008) tested aerosol-enhanced flotation in deinking of recycled paper and found that the positive effect of the oil coated bubbles correlated with the increase of gas holdup probably associated to smaller bubbles sizes. It is likely that in the experiments carried out in this study, oil spreading on the surface of bubbles also affects the bubble size which, however, was not measured. The results of induction time measurements indicate that the attachment of bubbles to molybdenite is significantly improved when the bubbles are coated with a layer of kerosene which demonstrates the benefits of transport of the collector to the surface of the particles in the process of flotation (Laskowski, 2007).
such circumstances. The depressing effect of seawater in the flotation of molybdenite at pH > 9.5 is reduced when oily-collector is supplied on the surface of bubbles. This can be explained by the fact that the bubbles coated by films of oil get protected from the coating by Mg hydrolysis products and this improves molybdenite flotation. SHMP dispersant has a strong positive effect on the recovery of molybdenite at pH > 9.5, which agrees with that reported by Rebolledo et al. (2017), and the combined effect of the oily bubbles and dispersant allows for the molybdenite recoveries to reach to similar values to those achieved when using fresh water (95–96%). Practical application of the “oily-bubble” technology will need some better engineering solutions which will allow for broad application of this technology. CRediT authorship contribution statement Andres Ramirez: Writing - original draft, Investigation. Leopoldo Gutierrez: Conceptualization, Writing - original draft. Janusz S. Laskowski: Conceptualization, Writing - review & editing. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors wish to thank CRHIAM for financing this work through CONICYT/FONDAP/15130015, Andres Ramirez would like to acknowledge the financial support provided through CONICYT/FONDAP/ 15130015 scholarship during his PhD study. References Ansari, A., Pawlik, M., 2007. Floatability of chalcopyrite and molybdenite in the presence of lignosulfonates Part I. Adsorption studies. Miner. Eng. 20 (6), 600–608. Born, C.A., Bender, F.N., Kiehn, O.A., 1976. Molybdenite flotation reagent development at Climax, Colorado. In: Flotation. Am. Inst. Min. Metall. Pet. Eng., New York, pp. 1147–1184. Castro, S., 2012. Challenges in flotation of Cu-Mo sulfide ores in seawater. In: Drelich, J. (ed.), Water in Mineral Processing, SME, pp. 29–40. Castro, S., Uribe, L., Laskowski, J.S., 2014. Depression of inherently hydrophobic minerals by hydrolysable metal cations: molybdenite depression in seawater. In: XXVII International Mineral Processing Congress-IMPC 2014, Flotation Chemistry Chapter, Santiago, Chile, October 20–24, 2012, pp. 207–217. Chander, S., Fuerstenau, D.W., 1972. On the natural floatability of molybdenite. Trans. AIME 252, 62–69. Ekmekci, Z., Demirel, H., 1997. Effects of galvanic interaction on collectorless flotation behaviour of chalcopyrite and pyrite. Int. J. Miner. Process. 52, 31–48. Gomez, C.O., Acuna, C., Finch, J.A., Pelton, R., 2008. Aerosol-enhaced flotation deiniking of recycled paper. Pulp Paper Canada 102 (10), 28–30. Hoover, M.R., Malhotra, D. (1976). Emulsion flotation of molybdenite. In: Fuerstenau, M. C., Flotation, A.M. (Eds.), Gaudin Memorial, vol. 1. AIME, pp. 485–505. Laskowski, J.S., 2007. Flotation thermodynamics: can we learn anything from it? Can. Metall. Q. 46 (3), 251–258. Laskowski, J.S., 2010. A new approach to classification o flotation collectors. Can. Metalurg. Quart. 49, 397–404. Li, C., Somasundaran, P., 1991. Reversal of bubble charge in multivalent inorganic salt solutions – effect of magnesium. J. Colloid Interface. Sci. 146, 215–218. Liu, J., Mak, T., Zhou, Z., Xu, Z., 2002. Fundamental study of reactive oily-bubble flotation. Miner. Eng. 15 (9), 667–676. Lopez-Valdivieso, A., Madrid-Ortega, I., Valdez-Pérez, D., Yang, B., Song, S., 2012. The heterogeneity of the basal plane of molybdenite: its effect on molybdenitefloatability and calcium ion adsorption. In: Proceedings of the 9th International Mineral Processing Conference, pp. 288–296. Masliyah, J., Zhou, Z.J., Xu, Z., Czarnecki, J., Hamza, H., 2004. Understanding waterbased bitumen extraction from Athabasca oil sands. Can. J. Chem. Eng. 82 (4), 628–654. Misra, M., Anazia, I., 1987. Ultrafine coal flotation by gas phase transport of atomized reagents. Miner. Mineral. Process. 4, 233–236. Ramirez, A., Rojas, A., Gutierrez, L., Laskowski, J.S., 2018. Sodium hexametaphosphate and sodium silicate as dispersants to reduce the negative effect of kaolinite on the flotation of chalcopyrite in seawater. Miner. Eng. 125, 10–14.
5. Conclusions The hypothesis that the supply of the reagents on the surface of bubbles is much more efficient when water-insoluble oily collectors are utilized, is validated for the molybdenite flotation. The results of molybdenite flotation obtained using lime to adjust pH also indicate a positive effect of the use of oily bubbles on molybdenite recovery under 8
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Xia, W., Yang, J., 2013. Experimental design of oily bubbles in oxidized coal flotation. Gospod. Surowcami Miner.-Mine. Resour. Manage. 29 (4), 129–136. Xu, Z., Liu, J., Kennedy, C., 2003. Fundamental study of reactive oily bubbles in sulfide flotation. In: 35th Annul Meeting of Canadian Mineral Processors, pp. 607–619. Zhang, Q., Xu, Z., Bozkurt, V., Finch, J.A., 1997. Pyrite flotation in the presence of metal ions and sphalerite. Int. J. Miner. Process. 52 (2–3), 187–201.
Rebolledo, E., Laskowski, J.S., Gutierrez, L., Castro, S., 2017. Use of dispersants in flotation of molybdenite in seawater. Miner. Eng. 100, 71–74. Tarkan, H.M., Bayliss, D.K., Finch, J.A., 2009. Investigation on foaming properties of some organics for oily bubble bitumen flotation. Int. J. Miner. Process. 90 (1), 90–96. Uribe, L., Gutierrez, L., Jerez, O., 2016. The depressing effect of clay minerals on the floatability of chalcopyrite. Miner. Process. Extr. Metall. Rev. 37 (4), 227–235.
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Use of “oily bubbles” and dispersants in flotation of molybdenite in fresh and seawater
T
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Andres Ramireza,b, Leopoldo Gutierreza,b, , Janusz S. Laskowskic a
Department of Metallurgical Engineering, University of Concepcion, Chile Water Research Centre for Agriculture and Mining (CRHIAM), University of Concepcion, Chile c PN.B. Keevil Institute of Mining Engineering, University of British Columbia, Canada b
A R T I C LE I N FO
A B S T R A C T
Keywords: Froth flotation Molybdenite Molybdenite flotation Oily bubbles Dispersants Seawater Sodium hexametaphosphate Sodium silicate
Molybdenite - as all inherently hydrophobic minerals – is floated with the use of water-insoluble oily collectors. Such collectors can be used in flotation either after emulsification in water, but can also be brought to the point of particle-to-bubble attachment on the surface of bubbles (as oily-bubbles). In this paper we are testing the effect of oily-bubbles and the dispersants sodium hexametaphosphate (SHMP) and sodium silicate (SS) on the flotation of moleybdenite in seawater in alkaline environment. The results show that molybdenite recovery increases when kerosene is supplied on the surface of bubbles which was particularly important in the flotation of molybdenite at pH > 9.5 in seawater. SHMP dispersant had a strong positive effect on the recovery of molybdenite at pH > 9.5, the pH range known to cause depression of the molybdenite flotation when pH is raised to depress pyrite and magnesium species precipitate as hydroxo-complexes/hydroxide. The combined effect of the oily bubbles and dispersants allows for the molybdenite recoveries to reach to similar values to those achieved when using fresh water. The results of induction time measurements indicate that the attachment of bubbles to molybdenite is significantly improved when the bubbles are coated with a layer of kerosene.
1. Introduction Molybdenite, along with minerals like talc and graphite, belongs to a group of inherently hydrophobic minerals which are floated with the use of water insoluble collectors. In the flotation processes, water-soluble collectors are applied in the form of aqueous emulsions and the collector, which is needed at the point of the particle-to-bubble attachment, is commonly carried to this point adsorbed on the surface of the mineral particles. Selectivity of the adsorption determines the outcome of the process. In the case of water-insoluble oily collectors (e.g. kerosene, Diesel oil) introduction of the oily compound into the aqueous system is a little more complicated. In such a case, as a result of emulsification, the collector appears in the pulp in the form of droplets which collide with mineral particles as a result of conditioning and can get attached to the hydrophobic mineral particles. Oil droplets can spread at the air/water interface, while oil does not straightforwardly spread on hydrophobic solid surfaces submerged in water (and adheres to such solid surfaces in the form of droplets). Better dispersion of the compound which is insoluble in water and its use as emulsion was shown to be more efficient (Hoover and Malhotra, 1976; Born et al., 1976). The alternative involves the use of
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the so called “oily bubbles” (Masliyah et al., 2004; Tarkan, et al., 2009; Xia and Yang, 2013). The method consists in covering the bubbles with a thin layer of a non-polar collector which benefits the transport of the collector to the surface of the particles improving flotation (Laskowski, 2007, 2010). This methodology has been applied to improve flotation of oxidized coal, and especially to improve fine particle flotation (Xu et al., 2003). Misra and Anazia (1987) compared the results of coal flotation tests carried out with fuel oil, which was either added directly into a Denver flotation cell in an ultrasonically emulsified form or as an aerosol in the stream of air entering the cell. The results indicate that the introduction of collector on the surface of bubbles produces superior results. Misra and Anazia also demonstrated that the induction time needed for the oil-coated bubbles to attach to coal specimens was many times shorter in comparison with the induction time measured for the oil-free bubbles which supports the reported work by Laskowski (2007). Gomez et al. (2008) tested aerosol-enhanced flotation in deinking of recycled paper with the use of silicone oil. They found that oil coated bubbles increased deinking efficiency when oil was used. They reported that gas holdup increased and concluded that this resulted either from smaller bubbles or from their slower movement. The improved flotation efficiency upon injecting oil could also result from
Corresponding author at: Department of Metallurgical Engineering, University of Concepcion, Edmundo Larenas 285, Concepcion 4070371, Chile. E-mail address: [email protected] (L. Gutierrez).
https://doi.org/10.1016/j.mineng.2020.106197 Received 22 May 2019; Received in revised form 2 January 2020; Accepted 9 January 2020 0892-6875/ © 2020 Elsevier Ltd. All rights reserved.
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Table 1 Chemical analyses of molybdenite sample. Chemical analyses Cu(%)
Fe(%)
S(%)
Mo(%)
Ins(%)
0,55
0,49
37,9
55,4
5,3
obtained from a molybdenum concentrate represents better the mineral obtained from porphyry type deposits in which this mineral is found dispersed in a quartz matrix. Additional studies are being conducted to evaluate the effect of oily bubbles in combination with dispersants to improve molybdenite recovery through batch flotation tests using freshly ground Cu-Mo ore feed. Methyl isobutyl carbinol (MIBC) of analytical grade (Merck) was used as frother, extra pure sodium silicate (SS) from Merck, and sodium hexametaphospate (SHMP) 65–70% P2O5 (Sigma Aldrich) were used as dispersants. Kerosene was used as a non-polar collector. Milli-Q water of 18.4 MΩ∙cm at 25 °C was utilized in all the experiments. Seawater samples were taken from the coast of Concepcion, Bio Bio, Chile. The pH was adjusted with sodium hydroxide and/or lime. Fig. 1. Particle size distribution of molybdenite.
2.2. Procedures 2.2.1. Micro-flotation experiments The floatability of molybdenite was evaluated through micro-flotation tests that were carried out in a 150 mL Partridge and Smith glass cell using nitrogen (NR2R) at a flowrate of 80 mL/min to produce bubbles using a porous glass frit (Fig. 2). The flotation feed was prepared by mixing 1 g of molybdenite with 100 mL of solution (0.01 M NaCl or seawater). After 2 min of conditioning at the required pH, MIBC, and emulsified kerosene were added at a concentration of 15 and 100 ppm respectively, and conditioned for 5 more minutes at the previously established pH value. The kerosene used in the micro-flotation tests was emulsified in a 1 L juice blender for 30 s using Mili-Q water, adding 15 ppm of MIBC. Additional solution was then added to make up to 150 mL required for the micro-flotation glass cell and the pH was adjusted for 5 min. The flotation process started when opening the gas valve, and was carried out for a period of time of 2 min with the froth product being removed every 10 s. The pulp level in the micro-flotation cell was kept constant by adding a background solution prepared at the same composition and pH as in the original solution. Finally, the concentrates and tailings were filtered and washed with distilled water to remove solids precipitates, and with acetone to remove collectors, and dried in an oven at 105 °C for 12 h. Then, concentrate yield was calculated as the ratio between the mass of molybdenite in the concentrate and the mass of molybdenite in the concentrate plus tailings. All the experiments were done in duplicate. For the tests with oily bubbles it was necessary to use a modified version of the Partridge and Smith cell which incorporated a section that permitted the contact between gas bubbles and a kerosene emulsion, as shown in Fig. 2. As a result of the interaction between bubbles and the micro-drops of kerosene, the coating of the bubbles with the non-polar collector was promoted just before entering the cell collection zone. In the case of tests performed using oily bubbles, the collector dosage was fixed by adjusting the volume of emulsion used during the 2 min of flotation, and the kerosene concentration in the emulsion in order to achieve the 100 ppm (based on the 150 mL of the cell) of collector needed in the experiments.
improved attachment efficiency of oil-coated bubbles versus clean bubbles. It was recently shown that the depression of molybdenite in seawater over the pH range from pH 9.5 to 10.5, over which it most likely results from the presence of magnesium colloidal species, could be reduced when dispersing agent such as sodium hexametaphosphate (SHMP) is used (Rebolledo et al., 2017). So it is reasonable to think that the combined action of both oily bubbles and dispersants could lead to even better results in the case of molybdenite flotation. The objective of this work is to study the use of oily bubbles as an alternative to improve the flotation of molybdenite in both fresh water and seawater. As part of the work, the use of oily bubbles in the presence of SHMP and sodium silicate dispersants was also studied. 2. Materials and methods 2.1. Samples and reagents The molybdenite sample used in this work was obtained from an industrial molybdenum concentrate which was further purified through 3 stages of flotation without collector. Fig. 1 shows the particle size distributions The samples were washed and cleaned following the procedure described by Uribe et al. (2016) and Rebolledo et al. (2017). The procedure includes 3 stages of washing with sodium hydrosulfide (NaSH) and acetone in order to remove any inorganic and organic reagents such as collectors present in the sample. To evaluate the presence of residual reagents in the molybdenite sample, tests were performed in which 3 g of molybdenite were mixed with 15 mL of Milli-Q water and kept under stirring using a magnetic stirrer for 10 min. After this, the suspension was filtered, and the solution obtained was analyzed for total organic carbon (TOC) in a Shimadzu TOC-L Total Organic Analyzer. These tests were performed at pH 8, 9, 10, and 11 and in all the cases no TOC was detected in the solutions indicating that the molybdenite sample was free from flotation reagents. Table 1 shows the chemical analysis of the sample. In order to reduce molybdenite oxidation, the samples were stored in a freezer in sealed plastic bags previously blown with nitrogen, at a temperature of about 1 °C (Ekmekci and Demirel, 1997; Zhang et al., 1997; Ansari and Pawlik, 2007). It has to be noted that although the use of freshly ground minerals simulates better the real flotation conditions in a concentrator, at this stage of the research program it was considered that molybdenite
2.2.2. Bubble-particle attachment tests The bubble-particle attachment tests were conducted following the procedure described by Castro et al. (2014) and the device built at the University of Alberta was used (Fig. 3A). In this procedure a bubble is contacted with a solution for 1 min (Fig. 3A-1), and then pushed against 2
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Fig. 2. Schematic representation of flotation cell modified for the use of emulsified kerosene.
Fig. 3. (A) No oily bubbles: 1. bubble generation; 2 bubble-particles contact; 3 bubble-particles detachment; (B) With oily bubbles: 1. bubble-kerosene contact; 2. Interaction of bubble with aqueous solution; 3 oily bubble-particles contact; 4 oily bubble-particles detachment (Adapted from Liu et al., 2002). 3
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same procedure as described is followed (Fig. 3B-2; Fig. 3B-3; Fig. 3B4). The particles beds were prepared using 3 g of molybdenite which were dispersed in 30 mLP of solution. Then, the pH is adjusted for 2 min to the required value, and frother and/or dispersants are added and conditioned for additional 10 min, after which the suspension is transferred to a 15 mLP cell in order to start the bubble-attachment measurements. All these experiments were conducted in duplicates thus the results presented in this paper are average values. 3. Results 3.1. Micro-flotation with/without oily bubbles, pH adjusted using NaOH Fig. 4 shows the molybdenite recovery as a function of pH in a 0.01 M NaCl solution, and in seawater, with and without oily bubbles. In these experiments the pH was adjusted using NaOH. The results show that there is a small positive effect of the use of the oily bubbles on molybdenite recovery in both types of aqueous media. The results with a 0.01 M NaCl solution show an increase in molybdenite recovery of 3–7 percentage points at pH > 10, while with seawater the increase is of the order of 5–9 percentage points, in the whole pH range studied. The positive effects of the use of the oily bubbles in all cases are greater than the experimental error, that reached maximum values of the order of 2 percentage points. Fig. 4 demonstrates that the flotation of molybdenite is strongly depressed when the process is carried out in seawater, as previously reported (Rebolledo et al, 2017; Castro, 2012). As it was reported, SHMP and SS are able to disperse precipitating/ coagulating hydroxides from the molybdenite surface and improve its flotation (Rebolledo et al., 2017; Ramirez et al., 2018). Fig. 5 shows molybdenite recovery as a function of pH in seawater, in the absence and presence of SHMP and SS, and without and with oily bubbles. The results indicate that both reagents have a positive effect on the recovery of molybdenite when the process is carried out in seawater at pH > 9.5, which is in agreement with what was reported by Rebolledo et al. (2017). These results demonstrate that SHMP caused the strongest effect. Comparison of the results obtained without and with oily bubbles (Fig. 5a and b) indicate that at pH 10 the combined effect of the oily bubbles and dispersants allows for the molybdenite recoveries to reach similar values to those achieved when using 0.01 M NaCl solution (95–96%).
Fig. 4. Molybdenite recovery as a function of pH in a 0.01 M NaCl solution and in seawater with and without oily bubbles. Conditions: 100 ppm kerosene (total), 15 ppm MIBC, pH adjusted with NaOH.
a bed of particles for a given contact time controlled by the device (Fig. 3A-2). Then the bubble is detached and observed using a microscope to determine if attachment between bubbles and particles took place (Fig. 3A-3). For every contact time, the procedure is repeated 10 times over different positions of the bed of particles and then the percentage of contacts for which particles attached to the bubble is determined. The contact times are varied and the same procedure is repeated. Finally, a plot of percentages of successful contacts (NSC) versus the measured contact time (tc) is generated. The induction time then can be defined as the contact time at which 50% of the contacts were successful. As Fig. 3B shows, in the case of the tests carried out to evaluate the effect of oily bubbles on the attachment with molybdenite particles, the bubble is initially submerged for 1 min in kerosene so that they get coated with the non polar collector (Liu et al., 2002). Then the
Fig. 5. Molybdenite recovery as a function of pH in seawater, in the absence and presence of SHMP and SS, (a) without oily bubbles, and (b) with oily bubbles. Conditions: 100 ppm kerosene (total), 15 ppm MIBC, pH adjusted with NaOH. 4
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explained by the increase in the concentration of calcium ions in solution. Fig. 8 shows molybdenite recovery as a function of pH in seawater, in the absence and presence of SHMP and SS, and without and with oily bubbles. As previously reported, the recovery of molybdenite is strongly depressed in seawater when the pH exceeds pH 9.5 (Castro, 2012). Fig. 8a also reveals a positive effect of the dispersants SHMP and SS on molybdenite recovery, with SHMP being more efficient. These results are in agreement with those previously reported by Rebolledo et al. (2017) and Ramirez et al. (2018). Fig. 8a and b also show that over the pH range from 10 to 10.5 the combined use of SHMP and oily bubbles in seawater allows for molybdenite recoveries that are close to those obtained in fresh water. 3.3. Bubble-particle attachment tests (pH adjusted using lime) Fig. 9 shows the induction times as a function of pH in seawater, in the absence and presence of SHMP and SS, without (Fig. 9a) and with oily bubbles (Fig. 9b). It is observed that the induction time values increase by several orders of magnitude when the pH exceeds 9.5, and that the use of dispersants, in particular SHMP, makes it possible to reduce these values, which agrees with the recovery of molybdenite presented in Figs. 5, 7, and 8. On the other hand, Fig. 9a and b show that the coating of the bubbles by kerosene reduces the induction times by an order of magnitude, and that the combined use of dispersants and oily bubbles has an important synergistic effect. Fig. 10 shows images obtained from the bubble-attachment tests that were carried out in seawater without (left) and with (right) oily bubbles at pH 9. The images reveal formation of a layer of kerosene that covers the bubble. Fig. 11 shows images obtained without (left) and with (right) oily bubbles at pH = 10.5. It can be seen that the presence of a layer of kerosene prevents Mg precipitates from attaching to bubbles.
Fig. 6. Molybdenite recovery as a function of pH in a 0.01 M NaCl solution and seawater with and without oily bubbles. Conditions: 100 ppm kerosene (total), 15 ppm MIBC, pH adjusted with lime.
3.2. Micro-flotation with/without oily bubbles, pH adjusted using lime Fig. 6 shows the results of molybdenite recovery as a function of pH in a 0.01 M NaCl solution, and seawater, with and without oily bubbles. Lime was used in these exeriments to adjust pH. The results indicate that the recovery of molybdenite is much more affected when the pH is adjusted with lime in the absence of oily bubbles. These results also indicate that the depressing effect of seawater in the flotation of molybdenite is strongly mitigated when oily-collector is supplied in the form of oily-bubbles, which can increase recovery by up to 35 percentage. Fig. 7 shows molybdenite recovery as a function of pH (adjusted with lime) in a 0.01 M NaCl solution, in the absence and presence of SHMP and SS, and without and with oily bubbles. The results indicate a slight depressing effect of pH on the recovery of molybdenite, which is
4. Discussion In the conventional flotation process, flotation reagents are supplied as aqueous solutions and as these reagents are needed at the point of particle-to-bubble attachment, they are brought to this point partially adsorbed on mineral particles (mostly collectors) and partially on the surface of bubbles (frothers). Theoretical analysis of the process
Fig. 7. Molybdenite recovery as a function of pH in a 0.01 M NaCl solution, in the absence and presence of SHMP and SS, (a) without oily bubbles, and (b) with oily bubbles. Conditions: 100 ppm kerosene (total), 15 ppm MIBC, pH adjusted with lime (CaO). 5
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Fig. 8. Molybdenite recovery as a function of pH in seawater, in the absence and presence of SHMP and SS, (a) without oily bubbles, and (b) with oily bubbles. Conditions: 100 ppm kerosene (total), 15 ppm MIBC, pH adjusted with lime (CaO).
Fig. 9. Induction time as a function of pH in seawater, and in the absence and presence of SHMP and SS, (a) without oily bubbles, and (b) with oily bubbles. pH adjusted with lime (CaO).
of Ca(OH)P+P leads to precipitation of calcium hydroxide on molybdenite faces, which can be explained by the presence of nano-edges and nano-faces covering the molybdenite basal planes on which this precipitation can take place (Lopez-Valdivieso et al., 2012). The results shown in Fig. 6 indicate that the depressing effect of lime (calcium) on the flotation of molybdenite could be reduced when oily bubbles are utilized. It is now well established that molybdenite flotation is strongly affected in seawater when pH is increased with lime to depress pyrite, and that responsible for the depressing effect are the MgP2+P hydrolysis products which accumulate on the molybdenite surface (Castro, 2012; Castro et al., 2012, Castro et al., 2014). Previous studies also showed that the hydrolysis products of magnesium ions can accumulate on the surface of bubbles, generating a hydrophilic coating that prevents the bubbles from interacting directly with the minerals, which induces a strong depression of flotation (Li and Somasundaran, 1991). The results presented in Fig. 6 demonstrate that the depressing effect of
indicates that bringing the reagents on the surface of bubbles is much more efficient (Laskowski, 2007). Supply of the flotation reagents on the surface of bubbles is particularly advantageous when these reagents are water-insoluble such as oily collectors as it is in the flotation of molybdenite. The results obtained in fresh water presented in Figs. 4–8 validate this hypothesis and show that molybdenite recovery increases when bubbles are coated with kerosene. Fig. 4, for example, shows that in the experiments in which the pH was adjusted using NaOH, molybdenite recovery increases between 3 and 7 percentage points at pH > 10, the range that is larger than the experimental error. The results of molybdenite flotation obtained using lime to adjust pH presented in Fig. 6 indicate a positive effect of the use of oily bubbles on molybdenite recovery, even in this case which is known to be more adverse for molybdenite. Chander and Fuerstenau (1972) proposed that in the alkaline pH range (pH > 8) molybdenite flotation is strongly depressed by the chemical adsorption of Ca(OH)P+P compounds and the subsequent formation of calcium molybdate. Successive adsorption 6
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Fig. 10. Images obtained from bubble-attachement tests in seawater without (left) and with (right) oily bubbles at pH = 9.
Fig. 11. Images obtained from bubble-attachement tests in seawater without (left) and with (right) oily bubbles at pH = 10.5. 7
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seawater on flotation of molybdenite is strongly reduced when oil is supplied on the surface of bubbles. These results can be explained by the fact that the bubbles coated by films of oil get protected to some extent from the coating by Mg hydrolysis products leading to the molybdenite flotation improvement. Images shown in Fig. 11 supports this hypothesis that the presence of a layer of kerosene on bubbles makes the presence of Mg precipitates on the bubbles surface less likely. The reason that explains why magnesium hydroxo complexes attach to bubbles but not to oily bubbles in the process of flotation in seawater is still unknown and deserves further research. Li and Somasundaran (1991) proposed that the modification of the surface properties of bubbles in magnesium solutions at alkaline pH values is explained by the precipitation of Mg(OH)2(s) at the air-liquid interface which occurs after adsorption of positively charged Mg(OH)+ on the negatively charged bubbles. Thus, the magnesium concentration at the air-liquid interface increases and exceeds the values necessary to form Mg (OH)2(s). However, in the process of flotation using seawater the ionic strength is high (~0.7 M) and the surface charge of bubbles, particles and kerosene is expected to be suppressed, and the mechanisms of interactions between the hydroxo complexes of magnesium should be different which at this stage of our research remains unknown. The use of dispersants to remove precipitating/coagulating magnesium hydroxides from the molybdenite surface was tested and the results were reported in the paper by Rebolledo et al. (2017). It was shown that the use of sodium hexametaphosphate (SHMP) restores molybdenite flotation over the alkaline pH range. These results open new alternatives for processing Cu-Mo sulfide ores. The previous paper also showed that pyrite flotation is depressed at pH > 10.5 and that the floatability of pyrite over this pH range is not restored by SHMP. The results presented in Figs. 5 and 8 show that in seawater at pH 10, and in the absence of SHMP the use of oily bubbles allows molybdenite recovery to be increased by about 10 and 25 percentage when the pH is adjusted with NaOH and lime, respectively. On the other hand, Figs. 5a and 8)a show that the use of SHMP alone results in an increased of recovery of 15 and 45 percentage points with the use of NaOH and lime, respectively. Additionally, when comparing the results of the effect of oily bubbles in the presence of SHMP, it can be observed that a recovery increase of 7 percentage points can be achieved using NaOH to adjust pH (Fig. 6); no effect is observed with lime (Fig. 8). In summary, the data show that the effect of the SHMP dispersant is stronger than that of the oily bubbles, which is probably due to the fact that this compound disperses the magnesium hydroxo complexes on both, the molybdenite and bubble surfaces, while oil coates only bubbles. In general, the experimental data indicate that the combined action of oily bubbles and SHMP increases molybdenite recovery to levels similar to those achieved using fresh water (95–96%). All these results are also in line with the induction time data presented in Fig. 9. As was previously cited, Gomez et al. (2008) tested aerosol-enhanced flotation in deinking of recycled paper and found that the positive effect of the oil coated bubbles correlated with the increase of gas holdup probably associated to smaller bubbles sizes. It is likely that in the experiments carried out in this study, oil spreading on the surface of bubbles also affects the bubble size which, however, was not measured. The results of induction time measurements indicate that the attachment of bubbles to molybdenite is significantly improved when the bubbles are coated with a layer of kerosene which demonstrates the benefits of transport of the collector to the surface of the particles in the process of flotation (Laskowski, 2007).
such circumstances. The depressing effect of seawater in the flotation of molybdenite at pH > 9.5 is reduced when oily-collector is supplied on the surface of bubbles. This can be explained by the fact that the bubbles coated by films of oil get protected from the coating by Mg hydrolysis products and this improves molybdenite flotation. SHMP dispersant has a strong positive effect on the recovery of molybdenite at pH > 9.5, which agrees with that reported by Rebolledo et al. (2017), and the combined effect of the oily bubbles and dispersant allows for the molybdenite recoveries to reach to similar values to those achieved when using fresh water (95–96%). Practical application of the “oily-bubble” technology will need some better engineering solutions which will allow for broad application of this technology. CRediT authorship contribution statement Andres Ramirez: Writing - original draft, Investigation. Leopoldo Gutierrez: Conceptualization, Writing - original draft. Janusz S. Laskowski: Conceptualization, Writing - review & editing. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors wish to thank CRHIAM for financing this work through CONICYT/FONDAP/15130015, Andres Ramirez would like to acknowledge the financial support provided through CONICYT/FONDAP/ 15130015 scholarship during his PhD study. References Ansari, A., Pawlik, M., 2007. Floatability of chalcopyrite and molybdenite in the presence of lignosulfonates Part I. Adsorption studies. Miner. Eng. 20 (6), 600–608. Born, C.A., Bender, F.N., Kiehn, O.A., 1976. Molybdenite flotation reagent development at Climax, Colorado. In: Flotation. Am. Inst. Min. Metall. Pet. Eng., New York, pp. 1147–1184. Castro, S., 2012. Challenges in flotation of Cu-Mo sulfide ores in seawater. In: Drelich, J. (ed.), Water in Mineral Processing, SME, pp. 29–40. Castro, S., Uribe, L., Laskowski, J.S., 2014. Depression of inherently hydrophobic minerals by hydrolysable metal cations: molybdenite depression in seawater. In: XXVII International Mineral Processing Congress-IMPC 2014, Flotation Chemistry Chapter, Santiago, Chile, October 20–24, 2012, pp. 207–217. Chander, S., Fuerstenau, D.W., 1972. On the natural floatability of molybdenite. Trans. AIME 252, 62–69. Ekmekci, Z., Demirel, H., 1997. Effects of galvanic interaction on collectorless flotation behaviour of chalcopyrite and pyrite. Int. J. Miner. Process. 52, 31–48. Gomez, C.O., Acuna, C., Finch, J.A., Pelton, R., 2008. Aerosol-enhaced flotation deiniking of recycled paper. Pulp Paper Canada 102 (10), 28–30. Hoover, M.R., Malhotra, D. (1976). Emulsion flotation of molybdenite. In: Fuerstenau, M. C., Flotation, A.M. (Eds.), Gaudin Memorial, vol. 1. AIME, pp. 485–505. Laskowski, J.S., 2007. Flotation thermodynamics: can we learn anything from it? Can. Metall. Q. 46 (3), 251–258. Laskowski, J.S., 2010. A new approach to classification o flotation collectors. Can. Metalurg. Quart. 49, 397–404. Li, C., Somasundaran, P., 1991. Reversal of bubble charge in multivalent inorganic salt solutions – effect of magnesium. J. Colloid Interface. Sci. 146, 215–218. Liu, J., Mak, T., Zhou, Z., Xu, Z., 2002. Fundamental study of reactive oily-bubble flotation. Miner. Eng. 15 (9), 667–676. Lopez-Valdivieso, A., Madrid-Ortega, I., Valdez-Pérez, D., Yang, B., Song, S., 2012. The heterogeneity of the basal plane of molybdenite: its effect on molybdenitefloatability and calcium ion adsorption. In: Proceedings of the 9th International Mineral Processing Conference, pp. 288–296. Masliyah, J., Zhou, Z.J., Xu, Z., Czarnecki, J., Hamza, H., 2004. Understanding waterbased bitumen extraction from Athabasca oil sands. Can. J. Chem. Eng. 82 (4), 628–654. Misra, M., Anazia, I., 1987. Ultrafine coal flotation by gas phase transport of atomized reagents. Miner. Mineral. Process. 4, 233–236. Ramirez, A., Rojas, A., Gutierrez, L., Laskowski, J.S., 2018. Sodium hexametaphosphate and sodium silicate as dispersants to reduce the negative effect of kaolinite on the flotation of chalcopyrite in seawater. Miner. Eng. 125, 10–14.
5. Conclusions The hypothesis that the supply of the reagents on the surface of bubbles is much more efficient when water-insoluble oily collectors are utilized, is validated for the molybdenite flotation. The results of molybdenite flotation obtained using lime to adjust pH also indicate a positive effect of the use of oily bubbles on molybdenite recovery under 8
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Xia, W., Yang, J., 2013. Experimental design of oily bubbles in oxidized coal flotation. Gospod. Surowcami Miner.-Mine. Resour. Manage. 29 (4), 129–136. Xu, Z., Liu, J., Kennedy, C., 2003. Fundamental study of reactive oily bubbles in sulfide flotation. In: 35th Annul Meeting of Canadian Mineral Processors, pp. 607–619. Zhang, Q., Xu, Z., Bozkurt, V., Finch, J.A., 1997. Pyrite flotation in the presence of metal ions and sphalerite. Int. J. Miner. Process. 52 (2–3), 187–201.
Rebolledo, E., Laskowski, J.S., Gutierrez, L., Castro, S., 2017. Use of dispersants in flotation of molybdenite in seawater. Miner. Eng. 100, 71–74. Tarkan, H.M., Bayliss, D.K., Finch, J.A., 2009. Investigation on foaming properties of some organics for oily bubble bitumen flotation. Int. J. Miner. Process. 90 (1), 90–96. Uribe, L., Gutierrez, L., Jerez, O., 2016. The depressing effect of clay minerals on the floatability of chalcopyrite. Miner. Process. Extr. Metall. Rev. 37 (4), 227–235.
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