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Mining, Metallurgy & Exploration

, Volume 36, Issue 1, pp 89–98 | Cite as

Flotation in Seawater

  • J. S. LaskowskiEmail author
  • S. Castro
  • L. Gutierrez
Review
  • 45 Downloads

Abstract

A classification of flotation processes carried out in concentrated electrolyte solutions, e.g., seawater, is proposed using the most obvious features of these processes: low or high content of Mg2+ and Ca2+ ions, pulp ionic strength, and pH. The first distinguishable group is the processes carried out in NaCl/KCl solutions, about 0.5 M in the case of salt flotation of inherently hydrophobic minerals, and at concentrations about 10 times higher in the flotation of potash ores. In the flotation of sulfide ores, such as nickel or copper ores, with xanthate-like collectors, the xanthate collector is apparently not affected by pulp ionic strength and only adjustment of frother may be required. Content of Mg2+ and Ca2+ ions in seawater is the main difference between such systems and fresh water. The presence of these metallic ions can adversely affect flotation in the pH ranges over which these ions hydrolyse. The successful flotation of Cu-Mo ores typically requires depression of pyrite at high pH values achieved with the use of lime. However, in seawater, flotation of Cu-Mo ores requires removal of the hydrolysis products of the Mg2+ and Ca2+ ions or the use of a pyrite depressant that can be effective over the pH ranges that are much below the pH of hydrolysis. Mg2+ and Ca2+ ions also affect flotation of phosphate ores with fatty acids. In this case, the depression mechanism is not caused by precipitating magnesium hydroxides on the mineral surface but by precipitation of collector insoluble salts, and the same ions are responsible for depression in both cases. In the seawater flotation of Cu-Mo sulfide ores and phosphate ores, the practical solution involves either removal of Mg2+ and Ca2+ ions prior to the flotation or complexation with other reagents.

Keywords

Seawater Flotation Cu-Mo sulfide ores Phosphate ores Electrolyte concentration 

1 Introduction

According to Gleick [10], 97.5% of the total water resources on Earth is in the oceans and ice caps, and thus, only about 2.5% is fresh water. Fresh water is typically used by the mining industry, and this is a very important issue as it is generally believed that the use of fresh water in flotation critically determines the outcome of the process. It should also be noted that mining operations are often located in arid areas with very limited access to fresh water. The demand for and shortage of water in certain parts of the world (e.g., the Atacama Desert in Chile) makes the use of seawater by the mining industry the only sustainable solution.

Flotation in highly concentrated electrolyte solutions was studied more than 70 years ago by Klassen [14] who reported that hydrophobic, bituminous coals could float in salt solutions (e.g., 0.3–0.5 M NaCl) without addition of any other flotation agents. The process is referred to as salt flotation. Other inherently hyhrophobic minerals (e.g., talc, graphite, sulfur) were shown by Klassen and Mokrousov [15] to behave similarly.

2 Salt Flotation

In Klassen’s monograph [14], coal salt flotation was tested using various inorganic salts (Na2SO4, NaCl and NaNO3). While some differences between the tested salts (explained by different foaming properties of these solutions) were detected, all the tests indicated that coals that are hydrophobic float very well in concentrated electrolyte solutions. Such a flotation process in which the solid particles are inherently hydrophobic and do not have to be made hydrophobic by adsorbing collector provides a unique opportunity to study the effect of electrolyte concentration on flotation. This eliminates the effect of the electrolyte on the collector and frother and makes interpretation of the results much simpler.

To avoid the effect of foamability of electrolyte solutions, tests carried out 40 years ago by Fuerstenau et al. [8] at the University of California Berkeley were all conducted in 0.5 M NaCl using various coals from different mines.

The wettability of the coal samples was characterized by equilibrium moisture content, which is known to be very low for very hydrophobic bituminous coals. These results, shown in Fig. 1, demonstrated that coals with a very low equilibrium moisture content, that is, very hydrophobic coal samples, floated very well in 0.5 M NaCl solutions, and these results also explain why only inherently hydrophobic minerals (e.g., talc, graphite, sulfur) float well under such conditions. To study the mechanism of salt flotation, Laskowski and Iskra [17] used methylated hydrophobic quartz as a model hydrophobic solid. The tests revealed that while increasing concentration of salt (KCl) did not change wettability (contact angle) of the hydrophobic methylated silica, it sharply reduced the induction time and improved floatability. Since particles of the hydrophobic methylated quartz carry negative electrical charge [16], this builds up the energy barrier opposing attachment of bubbles; compression of the double layer improves flotation by reducing the energy barrier. The relationship between the energy barrier and flotation kinetics was later demonstrated by Laskowski et al. [18].
Fig. 1

Effect of coal surface wettability (expressed by coal inherent moisture content) on the salt flotation rate (in 0.5 M NaCl). Capital letters stand for different western US coals (after ref. [8] with permission of Elsevier)

Dispersion of gas into fine bubbles is a central component of the flotation process. In a conventional flotation process, the size of bubbles is determined by bubble coalescence, which can be entirely prevented by a frother [5, 6].

As Fig. 2 reveals, the critical coalescence concentration (CCC) values for DF-250 (0.042 mmol/L) are much smaller than for MIBC (0.089 mmol/L). The CCC for NaCl solutions is around 0.78 M. The critical coalescence concentration of MIBC in water is about 7 ppm. At higher concentrations, the bubbles generated in MIBC solutions are stable and do not coalesce. Bubble coalescence can also be prevented by increasing electrolyte concentration.
Fig. 2

Bubble size as a function of frother concentration for MIBC and DF-250 (in distilled water), and as a function of NaCl concentration in a separate experiment (adapted from Ref. [3])

The salt flotation then meets all the flotation process requirements:
  1. (i)

    The solid particles are hydrophobic;

     
  2. (ii)

    In the environment of high ionic strength, the energy barrier opposing attachment of the hydrophobic particles to bubbles is reduced making attachment possible;

     
  3. (iii)

    At the same time, fine bubbles are generated under such conditions.

     

3 Effect of Electrolytes on Behavior of Flotation Reagents

The case of salt flotation is an example of a very “clean” system in which only the effect of electrolytes on surface properties of mineral particles, and on foaming, is to be studied. In all other cases in which collectors are also utilized, the effect of electrolyte concentration on properties of these agents has to be considered as well.

For the sake of discussion in this paper, flotation surfactants will be classified in three groups: (i) thio compounds (collectors for sulfides), (ii) non-thio ionizable surfactants (collectors), and (iii) weakly surface-active agents used as frothers.

As shown in Fig. 3, short-chain xanthates do not affect surface tension, frothers (see alcohols) are weakly surface active, micelle-forming surfactants are strongly surface active, and inorganic salts are generally classified as surface-inactive. The effect of inorganic salts on surface tension is thus totally different from the effect the other compounds have on surface tension, and this is shown in Fig. 3. It results from a negative adsorption of inorganic ions at the water/air interface. The negative adsorption means that the concentration of the ions is lower in the surface layer than in the bulk. For the surface-active compounds, the concentration of these compounds in the surface layer is higher than in the bulk. The question that arises is how the environment of inorganic salts might affect the properties of the flotation agents, or in other words, how the surface-active flotation agents might behave in the inorganic salt solutions. Following Traube [29] who postulated that the surface-active substances are displaced from their solutions by substances that increase the surface tension of water, the answer to the question can also be found in Fig. 3.
Fig. 3

Schematic relationship between surface tension and concentration for solutions of inorganic salts, short-chain xanthates, alcohols, and surfactants

Fig. 4 from Lekki [22] shows the effect of NaCl concentration on surface tension of aqueous solutions of α-terpineol (the main component of pine oil, which was a prominent frother in use at that time).
Fig. 4

Surface tension of aqueous solutions of α-terpineol at various concentrations of NaCl. Curve 1, no NaCl; curve 2, 100 g/L of NaCl; curve 3, 200 g/L of NaCl (after ref. [22])

More recent tests with MIBC and DF-250 by Castro et al. [2], as shown in Figs. 5 and 6, confirm the trend observed in Fig. 4 (schematically depicted in Fig. 7).
Fig. 5

Effect of MIBC concentration on surface tension of aqueous solutions of NaCl (after ref. [3] with permission of Elsevier)

Fig. 6

Effect of DF-250 concentration on surface tension of NaCl aqueous solutions (after ref. [3] with permission of Elsevier)

Fig. 7

Schematic representation of the surface tension changes in aqueous solutions of flotation frothers with varying electrolyte concentration (after ref. [3] with permission of Elsevier)

Figure 7 summarizes the data for the three tested frothers in a general fashion and indicates that the surface properties of frother solutions are modified with increasing ionic strength of the solution. The plot allows for the determination of the intersection point termed “surface tension switched point” (STSP). In the area to the left side of this point, the solution properties are dominated by inorganic electrolyte, while to the right side, the properties are dominated by the frother. The STSP values were determined to be around 120 ppm for MIBC, 40 ppm for α-terpineol, and around 1.2 ppm for DF-250. This implies that the frothing properties of DF-250 are only affected by inorganic salts at extremely low concentrations of this frother in solution. This frother exhibits very powerful foaming properties in seawater.

This is further illustrated in Fig. 8 that shows the results obtained while working with seawater. It is quite obvious that bubbles do not coalesce in seawater and thus fine bubbles can be produced in seawater without addition of a frother.
Fig. 8

Effect of the frother MIBC on bubble size in seawater (after ref. [3] with permission of Elsevier)

4 Classification of Flotation in Concentrated Electrolyte Solutions

This paper is an attempt at classification of the flotation operations carried out in process waters that are concentrated electrolyte solutions. In the development of such a classification system, the first question that is to be considered is which parameters to select in classifying such processes. The classification of the flotation processes carried out in concentrated electrolyte solutions is based on the following observations: (i) in simple solutions (e.g., NaCl) inherently hydrophobic minerals float very well (salt flotation) and in NaCl-KCl saturated brine potash ores are floated. (These cases do not require any pH adjustment.) (ii) Flotation of sulfides with xanthate-like collectors in concentrated electrolyte solutions may require adjustment of frothers; (iii) Cu-Mo sulfide ores commonly contain pyrite and its depression is achieved with the use of lime. This increases pH values, and in seawater in the pH range of 9.5–10, magnesium hydrolysis products (magnesium hydroxy-complexes, magnesium hydroxide) start appearing and depress molybdenite flotation. This harmful effect can be alleviated either by removal of the Mg2+ ions [1], or by floating the ore at a pH value well below the magnesium ions hydrolysis range (this requires a different pyrite depressant). Alternatively, when lime is applied it might be possible to disperse the magnesium hydrolysis products from the molybdenite surface; (iv) Fatty acids used in the flotation of phosphate ores form insoluble salts with Ca2+ and Mg2+ ions. Improvement of flotation in seawater can be achieved either by precipitating Ca/Mg ions prior to the flotation or by complexation of these ions with dispersing agents (e.g., water glass, hexametaphosphate).

In the left portion of the diagram shown in Fig. 9, just below salt flotation, is the flotation process carried out in a saturated NaCl-KCl brine (about 6–7 mol/L). This is the flotation of potash ores (sylvinite ores). In the brine with electrolyte concentration about ten times higher than in seawater, the salt concentration affects the Krafft point of the long-chain amines used as a collector to float sylvite, and this further reduces solubility of these compounds in the brine. The pH in this process is not adjusted and hydrolysis of divalent cations is not an issue. More details on this process have been reported by Laskowski [20].
Fig. 9

Classification of flotation processes carried out in concentrated electrolyte solutions

The graphical form of the classification of the flotation processes carried out in concentrated electrolyte solutions is shown in Fig. 9.

In the diagram shown in Fig. 9, the diagonal line divides the figure into two areas:
  1. 1.

    The zone on the left includes flotation pulps containing mostly NaCl and KCl salts, and natural pH ranges that are not specifically adjusted.

     
  2. 2.

    The zone on the right covers systems with considerable concentrations of Mg2+ and Ca2+ that may also require pH adjustment (this also includes seawater that will be treated here as 0.6 M NaCl solution with 1.3 g of Mg2+ and 0.4 g/L of Ca2+).

     

5 Effect of Electrolytes on Flotation

Short-chain alkali xanthates are highly soluble in water. Poling [26] reports the solubilities of sodium or potassium xanthates at 20 °C as varying from 8 M for ethyl xanthate to 2 M for hexyl xanthate. Due to their short hydrocarbon chains and to the high aqueous solubilities, these collectors do not adsorb at the air/liquid interface. That is, ethyl xanthate has a negligible effect on the surface tension of water [21]. The most visible difference between commercially utilized xanthates and other flotation surfactants is that only short-chain xanthates are utilized by industry while the ionic collectors used in the flotation of a large variety of minerals have alkyl chains of at least C12. These differences result from the fact that xanthate ions interact with mineral surfaces by forming dixanthogen and heavy-metal xanthates, while for long-chain surfactants, the most likely mechanism of adsorption proceeds via hemi-micelle formation on the mineral surface [12]. Thus, it is obvious that while concentration of NaCl/KCl does not affect adsorption of xanthates onto sulfides, it does affect very strongly micellization of long-chain surfactants and consequently their adsorption. At high electrolyte concentration, the Krafft point of the surfactant is also affected, as it is in potash ore flotation [19, 20].

There are several reports on the effect of electrolyte concentration in process water on flotation of sulfide ores. Lekki [22] studied the effect of NaCl concentration on flotation of copper ores. The effect of α-terpineol and NaCl concentration on surface tensions was shown in Fig. 4, while the foamability of α-terpineol–NaCl aqueous solutions is shown in Fig. 10. The sulfide ore used in these experiments was from the sedimentary deposits in SW Poland. This ore consists of three lithological layers: easy-upgradable sandstone ore, fairly-upgradable carbonate ore, and poorly upgradable clay-dolomitic-bituminous black shale. While the host rock for the copper sulfides is very different in these three ores, copper appears in all of them as mainly chalcocite and bornite. A mixture of these three totally different lithological types is processed in the KGHM plants.
Fig. 10

Effect of α-terpineol concentration on the maximum foam thickness at different concentrations of NaCl: curve 1, no NaCl; curve 2, 25 g/L of NaCl; curve 3, 50 g/L of NaCl; curve 4, 100 g/L of NaCl; curve 5, 150 g/L of NaCl (atter ref. [22])

.

The results of laboratory batch flotation tests for the sandstone ore are shown in Fig. 11. The experiments were carried out at 150 g/t of ethyl xanthate with varying doses of α-terpineol (frother). At that time, the use of pine oil as a frother was quite common, and α-terpineol is the main component of pine oil.
Fig. 11

Effect of α-terpineol dosage on flotation of the copper sandstone ore in tap water (1) and process water that contains 14 g/L of NaCl. Dosage of ethyl xanthate 150 g/t and flotation time 8 min (after ref. [22])

The tests carried out with all three types of copper sulfide ores, processed in the KGHM plants, gave very similar results to those shown in Fig. 11. Lekki [22] concluded that NaCl concentration in the process water does not affect copper recovery in the flotation of copper sulfide ores. In the flotation with high content of salts in process water, frother dosage can be reduced; it was also found that at higher concentrations of α-terpineol and NaCl reduced foamability could affect Cu recovery.

The results reported by Quinn et al. [27] agree well with Lekki’s findings. While studying the flotation of Cu-Ni sulfide ore at the Raglan plant in Quebec carried out at 0.4 M NaCl, they concluded that the plant could be operated without a frother.

The effect of ionic strength on flotation of Cu-Ni sulfide ore (platinum bearing ore) was studied by Corin et al. [7]. They concluded that increased ionic strength of the pulp resulted in increased froth stability and water recoveries and that the increase in ionic strength had no apparent effect on the recovery of sulfide minerals.

Of special interest to the proposed classification system described in this paper is that these three publications, which came from different countries and were conducted with different sulfide ores, provide similar conclusions. The studies conclude that the ionic strength of the pulp in the flotation of sulfide (Cu, Ni) ores with xanthate-like collectors does not affect recovery of the valuable metal, but that frothability of these systems is affected so that the dosage of frother has to be reduced. In the group of flotation processes of sulfide ores with xanthate-like collectors carried out in the plant waters with elevated salt concentration, it is important to note that these process waters do not contain considerable amounts of Mg2+ and Ca2+ ions and pulp pH is far from being close to the hydrolysis pH for these ions. With these limitations, the dominant factor in this group of processes is ionic strength of the pulp.

6 Flotation Processes in Plant Waters with Considerable Content of Mg2+ and Ca2+ Ions

In the diagram shown in Fig. 9, the diagonal line divides the whole figure into two areas. The zone on the left covers NaCl and KCl solutions at natural pH values that are not specifically adjusted. The zone on the right is applied to considerable concentrations of Mg2+ and Ca2+ ions and alkaline pH ranges.

Seawater conditions occupy a special position. Seawater will be treated here as a 0.6 M solution of NaCl that also contains about 1.3 g of Mg2+ per liter, and 0.4 g of Ca2+ per liter. For this content of magnesium in seawater (1.3 g/L, equivalent of 5.3 × 10−2 mol/L) and using the solubility product for magnesium hydroxide as Ksp = 1.2 × 10−11, the concentration of OH ions at which magnesium hydroxide will start precipitating in seawater can be calculated as

$$ {K}_{sp}=\left[M{g}^{2+}\right]{\left[O{H}^{-}\right]}^2=1.2x{10}^{-11} $$
(1)
Then,
$$ \left[O{H}^{-}\right]=1.5x{10}^{-5}\ \mathrm{mol}/\mathrm{L} $$
(2)
This indicates that the critical concentration of OH ions will be exceeded somewhere between pH 9 and 10 and Mg(OH)2 will start precipitating. Since surface activity of cations dramatically depends on hydrolysis of these ions [13], this is a very important conclusion. It is especially important for Cu-Mo ores, since these ores usually contain pyrite and in present day practice lime is used to depress pyrite. As reported by Castro et al. [2, 4], when the process is conducted in seawater and the pH is raised up to about 10 with the use of lime, magnesium hydroxy-complexes and magnesium hydroxide appear in the pulp and strongly depress molybdenite flotation (see Fig. 12).
Fig. 12

Effect of pH, adjusted with lime, on Mo recovery in the flotation Cu-Mo sulfide ore (after ref. [2])

The observed molybdenite depression was shown to result from the hydrolysis of Mg2+ ions. The solubility product of magnesium hydroxide (1.2 × 10−11) is much lower than the solubility product of calcium hydroxide (5.5 × 10−6); therefore, the addition of lime to seawater must cause precipitation of magnesium hydroxide (as shown in Fig. 13).
Fig. 13

Effect of addition of lime on concentration of Ca2+ and Mg2+ ions in seawater

If molybdenite depression is caused by the hydrolysis products of Mg2+ ions, then the obvious solution of the problem would be the removal of these ions from the flotation pulp prior to flotation. Such processes of water purification, for instance by reverse osmosis, are well known. A much simpler (and less expensive) method is outlined in the University of Concepcion patent [1] in which seawater is treated with lime. The settling colloidal precipitate is removed, and the supernatant, i.e., the process seawater, is used in flotation (Fig. 14).
Fig. 14

Visual appearance of seawater after addition of lime

6.1 Dispersion of the Colloidal Precipitates to Prevent Molybdenite Depression

Dispersing agents that can prevent molybdenite depression caused by precipitating magnesium colloidal species have been studied. Rebolledo et al. [28] found that the depression of molybdenite flotation in seawater, caused by magnesium colloidal species in the pH range from 9.5 to 10.5, can be prevented with the use of sodium hexametaphosphate dispersant (Fig. 15).
Fig. 15

Flotation recovery of molybdenite in seawater as a function of pH at various dosages of sodium hexametaphopsphate (after ref. [28] with persmission of Elsevier)

6.2 Flotation without the Use of Lime

A highly alkaline pH achieved by lime addition is frequently used to depress pyrite in the flotation process. The depression of molybdenite caused by hydrolysis products of magnesium ions when the flotation process is carried out in seawater can be prevented by removal of Mg2+ and Ca2+ ions from seawater prior to flotation or by flotation of the ore at a pH that is much lower than the hydrolysis range of these ions. Lower pH values for flotation requires a new technology in which pyrite is depressed at natural pH values.

A patented process has been developed to replace lime and cyanide in the depression of pyrite and is called the AMBS (air-metabisulfite) flotation process [11]. The key feature of this operation is an aeration process applied after regrinding of rougher concentrates along with recycled cleaning circuit streams followed by staged addition of sodium metabisulfite without the need for any pH adjustment. In this process, sodium metabisulfite, a reducing agent, is applied in a very unusual way after aeration. A most important aspect is that the process works well around neutral pH, which allows Mg2+ hydrolysis to be avoided.

6.3 Flotation with Fatty Acids

Solubility of calcium and magnesium salts of fatty acids is very low (the solubility product of magnesium oleate is about four orders of magnitude smaller than for magnesium hydroxide [9]) and thus “hard” water, that is, water with a high content of Ca2+ and Mg2+ is not a good medium for flotation with fatty acids as collectors.

Precipitation of insoluble salts of fatty acids dramatically increases the required dosage of the fatty acid collector, as is shown in Fig. 16. In the flotation tests reported by Youzef et al. [30], apatite could be floated in seawater only at oleic acid dosage 100 times greater than that required in the soft water. The flotation process with the use of fatty acids requires soft water or the use of sequestering agents that complex divalent cations.
Fig. 16

Flotation of apatite in both soft water and seawater in the absence and presence of Na2CO3 (after ref. [30])

Flotation of the phosphate ore at the Kapuskasing Phosphate Operation in Ontario was studied by Nanthakumar et al. [25]. While the ore from their current operation was relatively easy to upgrade by flotation, the marginal ore, that is, the ore which was stockpiled at the site for about 2 years, turned out to be extremely difficult to process. In the flotation of the marginal ore, it was reported that the process water contained more than 1000 ppm Ca2+, and it was demonstrated that by using soda ash (1800 g/t) in the desliming circuit it was possible to drastically improve flotation recovery of P2O5 and concentrate grades.

As shown in Fig. 17, there is a minimum soda ash dosage below which there was no apatite flotation at all. In this particular case, the critical dosage of soda ash that determines the transition point between poor and good flotation was found to be 1800 g/t.
Fig. 17

Grades and recoveries of P2O5 as a function of soda ash dosage after 5 min of flotation; collector: 800 g/t of saponified tall oil (after ref. [25] with permission of Elsevier)

The findings of Lopez-Valdivieso et al. [24] are significant, as they reported that in the absence of calcium and magnesium ions, apatite floatability was improved with increasing ionic strength from 0.05 to 1.0 mol/L. At 0.7 mol/L ionic strength, magnesium and calcium ions activated apatite floatability at concentrations below that in seawater. In flotation with fatty acid collectors, it is then possible to either precipitate and remove Ca2+ and Mg2+ ions from the flotation system, or complex these two-valent cations with the use of sequestrating agents. Nanthakumar et al. [25] introduced the first option at the Agrium Kapuskasing Phosphate Operations plant (see Fig. 18).
Fig. 18

Schematic diagram of the Agrium Kapuskasing Phosphate Operations plant in Ontario; the point marked X indicates position of the soda ash addition ahead of the desliming stage (adapted from ref. [25] with permission of Elsevier)

The results of flotation tests with phosphate ore from the El-Hamrawein locality, Eastern Desert, Egypt, are shown in Fig. 19 [30]. The ore assays 25.3% P2O5, 9.4% MgO, 6.4% SiO2, 12% CO2, and 43.1% CaO. As illustrated in this figure, flotation of the phosphate ore in seawater was quite possible when a combination of soda ash (1.5 kg/t) and sodium silicate (0.6 kg/t) was used. The results of Yousef et al. [30] demonstrate how soda ash, or soda ash along with water glass, can be utilized to solve the problem related to the use of hard water in fatty acid flotation. The affinity of sodium silicate to remove calcium and magnesium ions from process water was shown by Li et al. [23].
Fig. 19

Effect of sodium oleate on phosphate flotation (after ref. [30])

7 Summary

The Atacama Desert in Chile is an obvious example of an arid area with a large concentration of mining industry. Use of seawater in flotation is believed to be a sustainable solution in such cases. Research studies have identified magnesium ion hydrolysis products as a main culprit responsible for depression of molybdenite flotation when the process is carried out in seawater. The presence of Mg2+ and Ca2+ ions in plant water is also responsible for poor flotation of phosphate ores. In general, problems in flotation separations appear when fatty acid collectors are applied in hard water, and seawater is just an example of extremely hard water. While the reasons for depression in these two cases are not identical, precipitating magnesium hydro-complexes and hydroxides depresses molybdenite by the “slime coating mechanism,” and in the flotation of apatite, depression results from the precipitation of the collector with Mg2+ and Ca2+ ions. Our attempt at analyzing these two systems, Cu-Mo sulfide ore flotation in seawater and phosphate ore flotation in seawater, is presented in this paper. The classification of such flotation processes allows for better understanding of the accompanying phenomena and better selection of the most promising process modifications.

Notes

Funding Information

This study received financial support from CRHIAM provided via CONICYT/FONDAP-15130015 project.

Compliance with Ethical Standards

Conflict of Interest

The authors declare that they have no conflict of interest.

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Copyright information

© The Society for Mining, Metallurgy & Exploration 2018

Authors and Affiliations

  1. 1.N.B. Keevil Institute of Mining EngineeringUniversity of British ColumbiaVancouverCanada
  2. 2.Min-Flot Research Center for Mineral FlotationSantiagoChile
  3. 3.Department of Metallurgical EngineeringUniversity of ConcepcionConcepcionChile

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