# Effect of calcium minerals reactivity on fatty acids adsorption and flotation

Inna Filippova, Lev Filippov, Zineb Lafhaj, Odile Barres, Daniel Fornasiero

► To cite this version:

Inna Filippova, Lev Filippov, Zineb Lafhaj, Odile Barres, Daniel Fornasiero. Effect of calcium minerals reactivity on fatty acids adsorption and flotation. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018, 545, pp.157-166. 10.1016/j.colSURFA.2018.02.059. hal-02505657

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# Effect of calcium minerals reactivity on fatty acids adsorption and flotation

Inna V. Filippova<fnref n="1" />,<fnref n="2" />, Lev O. Filippov<fnref n="1" />,<fnref n="2" />*, Zineb Lafhaj<fnref n="1" />, Odile Barres<fnref n="1" />, Daniel Fornasiero<fnref n="1" />,<fnref n="3" />

## Graphical Abstract:

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## Highlights:

* Calcite and apatite recovery was related to the amount of fatty acid adsorption.

* Oleate and linoleate adsorption was measured by colorimetric, XPS and IR methods.

* Fatty acid adsorption increases with calcium mineral dissolution at pH 9.

* Magnesium and sulphate impurities may increase calcite dissolution.

* Slightly higher recovery with linoleate than oleate although their adsorption is similar.

<figure><img src="image_3.png" /></figure>

<footnote n="1">¹Université de Lorraine, Laboratoire GeoRessources UMR 7359 CNRS-Cregu</footnote>

<footnote>ENSG, 2 rue du doyen Marcel Roubault, BP10162, F-54505, Vandœuvre-lès-Nancy, France</footnote>

<footnote n="2">²National University of science and technology MISIS, Leninsky Ave 4, 119049 Moscow, Russia</footnote>

<footnote n="3">³Future Industries Institute, University of South Australia, Mawson Lakes SA 5095 Australia</footnote>

<footnote>*Corresponding Author: lev.filippov@univ-lorraine.fr</footnote>
**Abstract**

The separation between calcium minerals such as apatite and calcite by flotation relies on the use of long chain fatty acid collectors. Oleic acid, and its salt, is the main fatty acid collector and many studies have reported on the mechanisms of its interaction with calcium at the mineral surface and in solution, and on the oleic acid species present at the mineral surface. Although collector adsorption and mineral flotation depend mainly on solution pH and collector concentration, other factors such as mineral crystallinity and impurity affect mineral dissolution, influence collector adsorption and may explain the different flotation results reported in the literature on the same minerals. In this study the flotation of two calcites, with different degrees of purity, and one apatite was compared and related to the amount and type of collector adsorbed on the mineral surface, and to the reactivity of these minerals (acid-base interaction and dissolution). The results obtained in this study indicate that calcium dioleate (or dilinoléate) is the species present on the minerals surface at pH 9 and its amount increases with collector addition and calcium mineral dissolution, which results in a higher flotation of the calcium minerals. The influence of calcium site density and impurity in the minerals on flotation was also discussed.

**Keywords:** calcite; apatite; flotation; fatty acids; collector adsorption; mineral dissolution

**1. Introduction**

For the beneficiation of phosphate ores fatty acid collectors are commonly used to float phosphate minerals in alkaline pH conditions while depressants are added to reduce the flotation of gangue minerals. Many studies have been devoted to the study of the adsorption of these fatty acids on apatite and other semi-soluble calcium-bearing minerals, and of the mechanisms of interaction involved (Pugh and Stenius, 1985; Marinakis and Shergold, 1985; Rao et al., 1991a, 1991b; Finkelstein, 1989; Mielczarski et al., 1993; Free and Miller, 1998; Somasundaran and Zhang, 2000). Oleic acid, or its soap sodium oleate, is the best known fatty acid collector; it is a long hydrocarbon chain (18 C) monocarboxylic acid with one double bond. Fatty acids are mainly derived from tall oil but also from other sources such as vegetable oil and animal fat (Sis and Chander, 2003; Guimaraes et al., 2005), which results in various compositions of these fatty acids; for example, fatty acids derived from tall oil contained mainly 59% of oleic acid and 37% of linoleic acid, but only 26% of oleic acid, no

<figure><img src="image_4.png" /></figure>
linoleic acid and 59% of linolenic acid if fatty acids are derived from corn (Guimaraes et al., 2005). Both linoleic and linolenic acids are carboxylic acids with the same number of carbons (18 C) as oleic acid (or stearic acid) but with two double bonds in linoleic acid and three in linolenic acid. These three fatty acids have different collector strengths and therefore one expects variation in flotation performance if they are derived from different sources or have a lower purity. Earlier studies have shown that these three fatty acids (with 18 C) produced similar recoveries of rutile or hematite at pH less than 8 but higher recoveries with oleic (1 C=C) than with linoleic (2 C=C) and linolenic (3 C=C), in that order, at pH larger than 8 (Iwasaki et al., 1960; Purcell and Sun, 1963). It was concluded that fatty acids with a higher degree of unsaturation in the hydrocarbon chain (e.g., linolenic acid) have more interaction with water (their solubility increases) and therefore less surface activity. This was confirmed in the zeta potential measurements of Purcell and Sun (1963) which indicated that less adsorption of linolenic than linoleic and oleic occurs on rutile at pH larger than 8. For apatite, the collecting strength of these fatty acids (>98% purity) at pH larger than 7 was slightly different with oleic the worse collector, linoleic the strongest collector and linolenic in between (Brandao et al, 1994). More recently, the collecting strength of these fatty acids in the flotation of a phosphate ore at pH 9 was compared by Zhang (2008) who showed that oleic produced higher P₂O₅ recovery and grade than linoleic (both collectors with 99% purity) but the situation was reversed (especially the grade) in the presence of sodium silicate depressant. Brandao and co-workers (1994) in the flotation of a phosphate ore at pH 10 found that vegetable oils with higher percentages of linoleic acid produced better P₂O₅ recovery and grade than those with higher percentages of oleic acid (in the presence of corn starch depressant). The better performance of linoleate may be attributed to a slightly more bulky conformation of its hydrocarbon chain at the mineral surface because of the presence of the additional double bond. These fatty acids have both collecting and frothing properties which both increase with their concentration, which makes the comparison of their collector strength in the different studies difficult. In particular, with increasing fatty acid concentration froth quality may be enhanced or depressed, especially if fine particles are present.

Oleic acid is one of the collectors which have received the most attention for the mechanisms of its adsorption at the minerals surface. Although the adsorption results obtained were sometimes different and their interpretation somewhat controversial, it is generally agreed that the carboxylic group of oleic acid, and oleate at pH larger than 8 (Ananthapadmanabhan and Somasundaran, 1988), interacts chemically with metallic cations

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at the mineral surface and in solution. Oleic acid adsorption at the mineral surface proceeds until monolayer coverage is reached when all the surface metal ions have reacted. Oleic acid adsorption is also enhanced by van der Waals interaction between vicinal hydrocarbon chains at the mineral surface but may be reduced by electrostatic repulsion between the negatively charged carboxylate groups. At higher oleic acid concentrations (≥10⁻⁴ M) where the solubility of calcium dioleate is exceeded at the mineral-solution interface or in bulk solution, surface precipitation of calcium dioleate takes place on top of the chemically bonded oleate monolayer (Rao et al, 1981a, 1981b; Thistletwaite et al., 1996; Lu et al., 1998; Somasundaran and Zhang, 2000). On some minerals and at certain pH values, this adsorption proceeds for several layers of adsorbed oleic acid or it is limited to a monolayer. Orientation of the oleic acid molecule above monolayer coverage is critical for flotation; formation of dimers (Ananthapadmanabhan and Somasundaran, 1988) where the carboxylate group of one oleic acid molecule faces the solution should therefore results in decreased surface hydrophobicity and flotation recovery compared to that at monolayer coverage (Yap et al., 1981). Lu and co-workers (1998) found multilayers adsorption of oleic acid on apatite at pH 8.0 but only a monolayer at pH 9.5.

The amount of fatty acid adsorption on calcium minerals depends on the surface calcium density and crystal structure (Lu et al., 1998; Gao et al., 2018; Jiang et al., 2018). Solution conditions, such as pH, and type of salt and concentration, affect mineral reactivity including dissolution. Mineral crystallinity including ionic substitutions has been shown to influence calcium mineral reactivity and flotation (Rodrigues and Brandão, 1993; Born et al., 1996). For example, carbonate substitution into the apatite structure decreases crystallinity (Baig et al., 1996), which in turn increases the mineral solubility (Papangkorn et al., 2008). Substitution of calcium for magnesium into Ca minerals should result in a stronger metal-oleate interaction according to results of ab initio calculations because of the smaller size of the magnesium ion (Hirva and Tikka, 2002). Moreover, Jiang and co-workers (Jiang et al., 2018) indicated that a shorter Ca bond length (Ca-O, Ca-F, etc) and larger bond dissociative energy should increase the surface Ca reactivity resulting in an increase interaction with collectors; for example the higher dissociative energy of Ca-F bonds in fluorite than Ca-O bonds in calcite was used to explain the higher adsorption of a hydroxamic acid collector on fluorite than on calcite leading to a selective separation of these two Ca minerals (Jiang et al., 2018).
The principal aim of this study is to better understand the flotation behaviour of some calcium minerals in the presence of fatty acid at alkaline pH conditions. For this, two calcites with different degrees of purity and one apatite were selected and their flotation was compared firstly to the amount of fatty acid adsorbed on these minerals using several complementary analytical techniques and secondly to the reactivity of these minerals in solution (acid-base interaction, dissolution). Furthermore, as flotation also depends on the composition and purity of these fatty acids, the collector strength of oleic and linoleic acids, the main constituents of fatty acids, was compared.

## 2. Material and methods

The two calcites were obtained from Mexico and from China (thereafter referred as calcite M and calcite C, respectively in the paper) while the fluorapatite sample was from Madagascar. Their mineralogical composition was determined with a Bruker D8 XRD instrument using CoKα radiation of wavelength 1.78026 Å. The chemical composition was determined using an Inductively Coupled Plasma Optical Emission Spectrometer (Perkin Elmer Elan; Icap 6500). A millivoltmeter Ion 450 MeterLab equipped with a specific electrode was used to analyse fluorine.

The collectors oleic and linoleic acid were obtained from Sigma-Aldrich with a purity >99% and >98.5%, respectively. The structure of these carboxylic acids is similar with the same number of hydrocarbons, except that oleate has one double bond (cis-9) and linoléate has two (cis-9,12). Saponification of these acids with sodium hydroxide produced sodium oleate and linoléate (2 h at 60° C at pH 11.6). To prevent their oxidation they were kept in a refrigerator and prepared just before use.

The following method was used to determine the quantity of collector adsorbed on the minerals. 1 g of mineral (20-38 µm) was conditioned for one hour with 50 ml of solution containing a known concentration of oleate or linoléate at pH 9.0. After centrifugation, the solid was dried in a dessicator at room temperature and analysed by infrared spectroscopy and X-ray photoelectron spectroscopy (XPS). The colorimetric method of Gregory (1966) was used to determine the amount collector (that has not adsorbed on the minerals) in the supernatant. The method relies on the reaction of the carboxylate collector with copper triethylenetetramine in the presence of monoethanolamine followed by extraction with a mixture of isobutanol and cyclohexane. Finally, the copper associated with the carboxylate in the extract is reacted with diethylammonium diethyldithiocarbamate in isobutanol to produce

<figure><img src="image_6.png" /></figure>
a coloured solution where the absorbance at 435 nm is proportional to the concentration of oleate or linoléate that was present in the supernatant. The experiments were repeated twice and the results were averaged. Standard solutions in the range 0 to 8.85×10⁻⁴ mol/L oleate or linoléate were also prepared using the same procedure but without the minerals. The absorbance of the solution was measured at a wavelength of 435 nm and a calibration curve of absorbance versus oleate or linoleate concentration was obtained which shows a good linearity (Figure 1). The experimental procedure was the same for the measurements of calcium dissolution and change of solution pH as a function of time, except that the initial pH before mineral addition was 6.7.

A X-ray photoelectron spectrometer (XPS), XPS Kratos Axis Ultra DLD, with a monochromatic Al Kα X-ray source (1486.7 eV) operated at 120 W was used to measure the species on the mineral surface. A fixed pass energy of 160 eV for wide (or survey) scans or 20 eV for narrow scans was used. The energy scale was calibrated using the Fermi edge and the 4f 7/2 line (BE = 84.0 eV) for gold. The XPS spectra were curve fitted using the CASA program version 2.3.10. The infrared (IR) spectra were measured using a spectrometer Bruker IFS 55 equipped with a broad band mercury-cadmium-telluride liquid-nitrogen-cooled detector. The dried mineral samples were mixed with spectroscopic grade KBr powder in exactly 1:50 ratio for all the tests and placed in a cup of the Harrick diffuse reflectance accessory inside the IR spectrometer. The IR spectra were recorded with a resolution of 2 cm⁻¹. The IR spectrum of the mineral was subtracted from that of the mineral with the collector to produce the final IR spectrum.

Flotation experiments were performed with a 180 ml Minemet flotation machine at 1750 rpm with 3 g of mineral (38-106 µm) in 100 ml of solution. The pH of the pulp solution was adjusted with addition of HCL or NaOH. After 5 min of conditioning, the flotation was performed for 2 min and the flotation products were dried at 40°C and then weighted to determine the mineral recovery. The flotation experiments were repeated twice and the results were averaged.

### 3. Results

#### 3.1 Mineral characterisation and reactivity (acid-base interaction and solubility)

Results of the chemical (Table 1) and XRD (Figure 2) analyses reveal that a small amount of quartz is present in the fluorapatite sample and some magnesium in the calcite samples.

<figure><img src="image_7.png" /></figure>
The infrared and XPS spectra of these samples (not shown) confirm the presence of a small amount of quartz at the fluorapatite surface. Sulphate in calcite M and fluorapatite was also detected by infrared spectroscopy and by XPS (<0.5%). The ratios of percentages of Ca, P and F determined from the chemical analysis of fluorapatite (Table 1), Ca/P=1.79 and Ca/F=5.96, differ from the theoretical stoichiometry of Ca/P=1.67 and Ca/F=5.0, and indicate a deficiency in phosphate and fluorine relative to calcium, which may be due to the substitution in the lattice of phosphate and fluorine by carbonate as it is the case in carbonated fluorapatite (Hsu et al., 1994; Baig et al., 1996; Chhettry et al., 1999, Ren et al. 2014). The loss on ignition (LOI) in Table 1 may also indicate the presence of a small amount of carbonate in the fluorapatite sample. Carbonate in the fluorapatite sample was confirmed by infrared and XPS spectroscopies. The BET surface area for calcite M, calcite C and fluorapatite are 0.5, 0.7 and 0.8 m²/g, respectively.

The changes of pH with time of a solution containing calcite or fluorapatite in suspension are shown in Figure 3. Results show that the pH of the solution (6.7) increases very rapidly after addition of the mineral, and reaches a plateau after 1-2 min for calcite M, ~8 min for calcite C and after 15 min for fluorapatite. The change of pH is more pronounced for calcite M than for calcite C and for fluorapatite. These changes in solution pH following mineral addition are well known for semi-soluble minerals, such as calcite, and have been associated with the dissolution of the minerals (Eq. 1) and the hydrolysis of calcium and carbonate ions at the surface or in solution to produce H⁺ and OH⁻, respectively as in Eq. 2 (Somasundaran and Agar, 1967).

$$CaCO_3 + H^+ \rightleftharpoons Ca^{2+} + HCO_3^- \quad (1)$$

$$Ca^{2+} + H_2O \rightleftharpoons CaOH^+ + H^+ \text{ and } CO_3^{2-} + H_2O \rightleftharpoons HCO_3^- + OH^- \quad (2)$$

Somasundaran and Agar (1967) found that the change of solution pH was related to calcite dissolution; as the solution pH increased (consumption of protons as in Eq. 1) with time more calcium and carbonate were found in solution. Also, they observed that the pH increased when the initial solution pH was acidic or neutral and it decreased when the initial solution pH was basic, although these changes of pH invariably converge to the same (equilibrium) pH, at approximately 8.2 which was associated to the point of zero charge of calcite. These trends of pH change (Figure 3) and calcium dissolution (Figure 4) with time observed in this study for the three minerals are in agreement with the results and interpretation of Somasundaran and Agar (1967).

<figure><img src="image_8.png" /></figure>
To demonstrate that the change in solution pH (ΔpH) results from calcium carbonate dissolution, and the proportionality between the change in pH and calcium dissolved, the amount of calcium dissolved was calculated using the various equilibrium constants $pK_{H2CO3}=6.36$ for equation $H_2CO_3 \leftrightarrow H^+ + HCO_3^-$ and $pK_{HCO3^-}=10.33$ for equation $HCO_3^- \leftrightarrow H^+ + CO_3^{2-}$, and solubility product $pK_s=8.34$ for equation $CaCO_3(s) \leftrightarrow Ca^{2+} + CO_3^{2-}$ at atmospheric pressure ($[H_2CO_3]=1.2 \times 10^{-5}$ M) at 25°C (Somasundaran and Agar, 1967). These calculations predict that the presence of $CaCO_3$ should produce a change of solution pH, ΔpH, of 2.62 and a dissolution of $5.1 \times 10^{-4}$ M calcium, which compares favourably to what is observed in Figures 3 and 4 with respectively a ΔpH of 2.7 and a calcium dissolution of $8.0 \times 10^{-4} - 8.7 \times 10^{-4}$ M (32-35 mg/l after 5-60 min in Figure 4) for calcite M.

More importantly, calcium dissolution, and therefore change of solution pH (Figure 3), from calcite M is larger than from calcite C and from fluorapatite (Figure 4). Other studies have reported the link between change of solution pH and calcium dissolution. For example, Pugh and Stenius (1985) found that the change of solution pH and calcium dissolution were higher for calcite than apatite and finally fluorite. The higher dissolution of calcite than apatite is also well predicted by thermodynamic calculation (Somasundaran et al., 1985).

## 3.2 Flotation

Figure 5 shows that the flotation recovery of the minerals increases with oleate and linoleate concentration and the recovery at $5 \times 10^{-5}$ mol/L collector is larger for calcite M than for calcite C and fluorapatite. The recovery of calcite C appears to reach a plateau at collector concentrations above $5 \times 10^{-5}$ mol/L while that of fluorapatite continues to increase past the highest concentration tested. The mineral recoveries using linoleate are slightly higher (within experimental errors) than those with oleate at all the concentrations, which is agreement with results in the literature for calcium-bearing minerals in alkaline pH conditions (Brandao et al, 1994; Zhang, 2008) and may be related to a more bulky conformation of the linoleate hydrocarbon chain with its two double bonds.

## 3.3 Collector adsorption

The amount of fatty acid collector adsorbed on the minerals surface was measured directly using XPS and infrared spectroscopies but was also determined indirectly from the

<figure><img src="image_9.png" /></figure>
measurement of the concentration of fatty acid (non-adsorbed) in solution using the colorimetric method.

### 3.3.1 X-ray photoelectron spectroscopy (XPS) results

XPS is a very surface-sensitive analytical technique and it was used to measure the changes occurring at the mineral surface after addition of the collectors, oleate and linoleate. The results are presented in the form of spectra and atomic concentrations of the various elements on the surface. The XPS survey spectra (not shown) show the major peaks characteristic of the elements present at the mineral surface: carbon, oxygen and calcium, and of phosphorus and fluorine for fluorapatite. Two additional small peaks of Si(2s) at 153 eV and Si(2p) at 103 eV (Wagner, 1990) are present in the XPS spectrum of fluorapatite and are attributed to quartz impurity (see ICP and XRD results in Table 1 and Figure 2). A tiny S(2p) peak (<0.5%) at 168.6 eV attributed to sulphate is also present in the survey spectra of calcite M and fluorapatite (Wagner, 1990). The atomic concentrations of all the elements at the mineral surface together with the binding energy of the corresponding XPS bands are reported in Table 2.

The high resolution spectra of C(1s), O(1s), Ca(2p), P(2p) and F(1s) were measured and only the C(1s) and O(1s) spectra were deconvoluted into individual components to analyse in more details the changes occurring in these XPS spectra after collector addition (Figures 6 and 7). The C(1s) XPS spectra were deconvoluted into four components (Figure 6 for calcite C with linoleate), at 284.6 eV attributed to hydrocarbon (C-C, C-H), at 285.5-286.2 eV attributed to carbonyl (C-O), at 287.3-288.3 eV attributed to carboxyl (O-C=O) and at 289.3-289.5 eV attributed to carbonate (CO₃²⁻) (Wagner, 1990; Smart, 1991; Stipp et al., 1991). The component at 284.6 eV is commonly selected as a reference to calibrate the binding energy scale (Wagner, 1990). The hydrocarbon and carbonyl components are usually attributed to adventitious carbon contamination when the mineral is in contact with air (Wagner, 1990; Smart, 1991) but may also originate from an adsorbed surfactant/collector as in the present study. The carboxyl/carbonate in fluorapatite in the absence of collector may originate from the substitution in the lattice of phosphate and fluorine by carbonate as it is the case in carbonated fluorapatite (Hsu et al., 1994; Baig et al., 1996; Chhetry et al., 1999). Indeed, the Ca/P and Ca/F ratios of 1.8 and 5.3, respectively in Table 3 in the absence of collector (Ca/P=1.8 and Ca/F=6.0 in the bulk from chemical analysis in Table 1) are higher than the theoretical stoichiometries of Ca/P=1.7 and Ca/F=5.0, indicating a deficiency in phosphate and fluorine relative to calcium at the surface which is attributed to the substitution

<figure><img src="image_10.png" /></figure>
of phosphate and fluorine by carbonate. The O(1s) spectra (Figure 7) have been divided into three components. The highest binding energy component at around 532.9-533.4 eV is clearly attributed to adsorbed water (Wagner, 1990). The lowest binding energy component at around 531.0-531.2 eV is attributed to hydroxide (Wagner, 1990), such as in Ca-OH. The middle band at 531.9-532.2 eV may be attributed to the oxygen belonging to the adventitious carbon contamination, carbonate or phosphate. The Ca(2p) spectrum (Figure 7) is composed of a doublet characteristic of that element with the first band for Ca(2p3/2) at 347.2-347.3 eV in fluorapatite or 346.6-346.9 eV in calcites, and a second one 3.5 eV higher for Ca(2p1/2), with the intensity of the first band double that of the second (Wagner, 1990; Stipp et al., 1991). We note that the binding energy for the Ca(2p) bands in fluorapatite is ~0.5 eV higher than that for calcite, in agreement with the Ca(2p) binding energy in calcium phosphate (Chusuei et al, 1999; Ni and Ratner, 2008). Gopinah and co-workers (2002) also reported variations of 0.5 eV in the Ca(2p3/2) binding energies for the calcium carbonate minerals of calcite, aragonite, vaterite and dolomite that could be related to their different crystal structures. For fluorapatite, only one component is observed in the P(2p) and F(1s) spectra (Figure 7), at 133.1-133.3 eV attributed to phosphate and at 684.3-684.4 eV attributed to fluorine, respectively (Wagner, 1990; Nelson et al., 2004; Vlacic et al., 2008).

The major observation from results in Table 2 (a, b and c) is that only the concentration of carbon (C-C) increased (Δ values are positive) with collector (oleate and linoleate) concentration while that of all the other elements (O, CO3, Ca and P, F and Si for fluorapatite) decreased (Δ values are negative). Indeed, after addition of 5×10-4 M collector, the C-C atomic concentration increased by ~60% (positive Δ values in Table 2) on fluorapatite, ~100% on calcite C and by more 150% on calcite M while that of O and Ca decreased by ~22% on fluorapatite, ~27% on calcite C and ~40% on calcite M (negative Δ values in Table 2). As a result, the C-C/Ca ratio nearly doubles on fluorapatite, triples on calcite C and quadruples on calcite M (Table 3), which indicates that more collector adsorbs on calcite M than on calcite C and fluorapatite. The increase and decrease in concentration of these elements on the minerals surface is similar for linoleate and oleate. Table 3 shows that although the concentrations of Ca, CO3 and P decrease with increasing collector concentration, the ratio Ca/P for fluorapatite stays constant at 1.7-1.8 and so is the ratio Ca/CO3 for calcites C and M, 0.8-0.9. We note however that the Ca/F ratio for fluorapatite increased, which is the result of a larger decrease in the concentration of fluorine than calcium at the surface (Δ values of 25-36% for F compared to only 16-22% for Ca, respectively in Table 2) after collector adsorption; no explanation can be provided for this

<figure><img src="image_11.png" /></figure>
trend. Considering the high surface-sensitivity of XPS, these changes observed in Tables 2 and 3 can be simply explained by the coverage of the mineral surface by the collector, ‘masking’ the elements underneath, especially if its long hydrocarbon chain (18 carbons) stands perpendicular to the surface in a monolayer or in multilayers (see Figure 8). These results also indicate that there is a similar amount of oleate and linoléate at the minerals surface at the highest collector concentration used but more oleate is adsorbed than linoleate at the lower collector concentration of 5×10⁻⁵ M.

### 3.3.2 Results from the colorimetric analysis

The concentration of collectors adsorbed on the minerals determined with the Gregory (1966) colorimetric method and the calibration curves in Figure 1 are shown in Figure 8. The results in Figure 8 show that first the collectors adsorb on the mineral surface more or less linearly with the concentration of collector added, up to at least 5×10⁻⁴ M; secondly more collector adsorbs on calcite M than on calcite C and on fluorapatite, and finally oleate and linoléate adsorb to the same extent (within experimental errors), in agreement with the XPS results. For example, at a collector concentration of 4.6×10⁻⁵ mol/L, 4.1×10⁻⁵ mol/m² Li and 4.4×10⁻⁵ mol/m² Ol adsorb on calcite M, 3.1×10⁻⁵ mol/m² Li and 3.2×10⁻⁵ mol/m² Ol adsorb on calcite C, and 2.4×10⁻⁵ mol/m² Li and 2.7×10⁻⁵ mol/m² Ol adsorb on fluorapatite. Moreover, the collectors adsorb in multilayers at the minerals surface as the maximum concentration of oleate or linoléate required to form a monolayer is only 5.5×10⁻⁶ mol/m² or 8.3×10⁻⁶ mol/m² if the area per molecule of oleate is 30 Å²/molecule or 20 Å²/molecule, respectively (Ananthapadmanabhan and Somasundaran, 1988; Rao et al, 1990). As no real plateau in collector adsorption is observed in Figure 8, we can conclude that the strength of collector adsorption in the monolayer or the multilayer is similar.

### 3.3.3 Infrared spectroscopy results

The advantage of infrared spectroscopy is that it provides more direct information than XPS on the nature of the adsorbed species. The IR spectra of oleate and linoléate adsorbed on the minerals are very similar in relation to the position of the IR main peaks and their relative intensity. Figure 9 shows an example of IR spectra of oleate adsorbed on fluorapatite. For oleate or linoléate, there are two regions of interest in the IR spectrum. The 3010-2750 cm⁻¹ region, characteristic of C-H vibrations, shows four peaks at 3005-3007 cm⁻¹, 2954-2957 cm⁻¹, 2921-2926 cm⁻¹ and 2851-2854 cm⁻¹ attributed respectively to v<sub>as</sub>(-CH=), v<sub>as</sub>(CH<sub>3</sub>), v<sub>as</sub>(CH<sub>2</sub>) and v<sub>s</sub>(CH<sub>2</sub>) (Gong et al, 1991; Thistletwaite et al, 1996). The 1750-1300 cm⁻¹

<figure><img src="image_12.png" /></figure>
region shows two main peaks at 1573 and 1537 cm⁻¹ attributed to v<sub>as</sub>(COO⁻) and a third one at 1475 cm⁻¹ attributed to CH₂ deformation. One can also distinguish in Figure 9 among the noise two other peaks of weaker intensity at 1430 and 1405 cm⁻¹ only at the highest collector concentrations and for fluorapatite. Calcite has a strong and broad IR peak at around 1425 cm⁻¹ due to v<sub>3</sub>(CO₃) (Ren et al., 2014) which after subtraction of its contribution produces a very noisy IR spectrum at wavenumbers below 1500 cm⁻¹. No IR peaks were observed at wavenumbers in the region 1600-1750 cm⁻¹, which therefore excludes the presence of oleic or linoleic acid at the mineral surface (v(C=O), ~1710 cm⁻¹), as expected at pH 9 where the oleate species dominates (Ananthapadmanabhan and Somasundaran, 1988). The peak at 1405 cm⁻¹ may be attributed to v<sub>s</sub>(COO⁻) rather than to a C-O-H vibration (Thistletwaite et al., 1996). The weak 1430 cm⁻¹ peak has also been observed in the IR spectrum of oleate adsorbed on apatite (Gong et al., 1991) and may be attributed to calcium dioleate (Rao and co-workers (1991a) reported a peak at 1427 cm⁻¹ for calcium dioleate). The two peaks at 1573 and 1537 cm⁻¹ (v<sub>as</sub>(COO⁻)) are also present in the IR spectrum of calcium dioleate. These two peaks have been the subject of most debates in the literature as to their origin (Gong et al., 1992; Mielczarski et al., 1993; Miller and al., 1995; Thistletwaite et al., 1996). Results in the literature (Free and Miller, 1998; Lu et al., 1998) showed that at oleate concentrations up to monolayer coverage on the apatite surface a single IR peak at 1554 cm⁻¹ is present, attributed to chemisorbed oleate, but at higher oleate concentrations a doublet at 1573 and 1538 cm⁻¹ is observed which they attributed to physically adsorbed/precipitated calcium dioleate. Indeed, the only IR spectrum in Figure 9 at an oleate concentration, 3.54×10⁻⁵ M, lower than that corresponding to monolayer coverage (see Figure 8), does not show the presence of this characteristic doublet or of any single peak around 1550 cm⁻¹ among the noise.

Figure 9 shows that the intensity of the peaks attributed to C-H (3010-2750 cm⁻¹ region), CH₂ (1475 cm⁻¹) and COO⁻ (1573 and 1537 cm⁻¹) vibrations increases with the amount of oleate added to fluorapatite. The same is true for the IR spectra of oleate and linoléate adsorbed on calcite M, Calcite C and fluorapatite.

Figure 10 shows the IR spectra of oleate adsorbed on calcite M and calcite C only in the 3010-2750 cm⁻¹ region because, for calcite, noise dominates the 1750-1300 cm⁻¹ region, as explained earlier. These figures show clearly that the position and relative intensity of the peaks remain the same but their intensity increases with collector concentration.

<figure><img src="image_13.png" /></figure>
The intensity of the strongest IR peak at 2921 cm⁻¹ is plotted in Figure 11 at a collector concentration of 4.6×10⁻⁴ M. These IR results confirm the trend observed with the other two analytical methods where more collector adsorbs on calcite M than on calcite C and on fluorapatite (except for oleate where its adsorption on fluorapatite measured by IR is slightly higher than that on calcite C), and the adsorption of oleate on these minerals is stronger than that of linoléate.

**4. Discussion**

A good agreement was found in the trends observed with the three analytical methods used for the adsorption of the two fatty acids on the three minerals. All the results of oleate and linoléate adsorption at pH 9.0 in this study have clearly shown that more collector adsorbs on calcite M than on calcite C and on fluorapatite (XPS, colorimetric and IR studies), which can well explain the same trend obtained for the flotation of these minerals in Figure 5. Fatty acid collectors are well known to interact strongly with calcium ions at the mineral surface and in solution. At pH 9, the oleate ion is the major species in solution (Pugh and Stenius, 1985; Somasundaran, P. and Zhang, L., 2000) and it reacts with calcium species at the mineral surface to form a monolayer followed by the precipitation of calcium dioleate (formed close to the surface or in solution) in multilayers at higher collector concentrations. Most of the collector concentrations used in this study were well above that required for monolayer coverage (Figure 8), and therefore we can conclude that calcium dioleate (or dilinoleate) is the oleate species at the outermost mineral surface responsible for the high flotation of these minerals observed in this study.

Formation of calcium dioleate only occurs if sufficient dissolution of the minerals exists at pH 9 and its precipitation is expected if the solubility product of calcium dioleate is exceeded such as at high collector concentrations (Thistletwaite et al, 1996). Calcium dissolved from calcite at pH 9 is approximately 35 mg/L (Figure 4) or 8.75×10⁻⁴ M, which after reaction with oleate to form calcium dioleate, should start to precipitate at an oleate concentration of 2.1×10⁻⁵ M in solution (solubility product of calcium dioleate is 12.4; Somasundaran and Zhang, 2000). This oleate concentration for calcium dioleate precipitation is above that necessary for the formation of an oleate monolayer on the minerals surface (Figure 8). The AFM study of Paiva and co-workers (Paiva et al., 2011) has clearly shown that at pH 8 and calcium and oleate concentrations of 2×10⁻⁴ M and 4×10⁻³ M, respectively, calcium dioleate forms and precipitates in the form of agglomerates on the surface of an apatite crystal. In the

<figure><img src="image_14.png" /></figure>
present study at pH 9, more calcium is found in solution with the calcites than with fluorapatite in agreement with results in the literature (Pugh and Stenius, 1985; Somasundaran et al., 1985), which should result in more calcium ions interacting with the collectors at the mineral-solution interface and in solution. At high collector concentrations, well above that for monolayer coverage, Pugh and Stenius (1985) observed a higher oleate adsorption density on calcite than fluorite and apatite and this was related to the amount of calcium dissolution from these minerals; calcium concentrations in solution measured and calculated were higher for calcite than fluorite and apatite (Lu et al., 1998). The higher dissolution of calcite than apatite can also be related to the higher calcium surface site density on calcite (Lu et al., 1998).

As the oleate or linoleate adsorption density seems to be related to mineral solubility, the next question is why calcium dissolution from calcite M is higher than on calcite C? The only mineralogical difference between these two calcites (Table 1) is the higher amount of magnesium in calcite M (%MgO=1.2) than in calcite C (%MgO=0.3) and the presence of sulphate on calcite M detected by infrared and XPS analyses. The concentration of magnesium detected in solution is relatively low, 4.2 mg/L for calcite M and 2.9 mg/L for calcite C after 5 min, which reflects the magnesium content in these two calcites. Oleate is known to also interact with magnesium at the mineral surface or in solution; the solubility product of magnesium dioleate is 10.8 compared to 12.4 for calcium dioleate (Somasundaran and Zhang, 2000). Several studies have reported on the effect of the presence of magnesium and sulphate ions on the formation of calcium carbonate and its dissolution (e.g., Berner, R., 1967; Loste et al., 2003). More importantly for the present study, the results of Akin and Lagerwerff (1965), which have been later confirmed by Dabb (1971), have shown that the solubility of calcium carbonate increases in the presence of magnesium and sulphate ions. They claimed that the substitution of magnesium ions for calcium ions modifies the calcite lattice into one of higher energy and solubility. It is also possible that the presence of magnesium and its substitution favour the formation of a more amorphous phase of calcite, and therefore more soluble. Besides, calculations of interaction energies for oleate with magnesium and calcium ions (Hirva and Tikka, 2002) revealed that oleate interacts more strongly with magnesium ions than with calcium ions because of the smaller size of the magnesium ion, which can provide another explanation for the higher collector adsorption on (and higher flotation of) calcite M (with a higher Mg content) than on calcite C. Another factor which was not investigated in the present paper is the influence of mineral crystallinity

<figure><img src="image_15.png" /></figure>
on calcite and apatite dissolution (Baig et al., 1996; Papangkorn et al., 2008) and their flotation with oleic acid (Rodrigues and Brandao, 1993; Born et al., 1996).

The other topic in this study was the comparison between oleate and linoléate. For each mineral, all the results show that the amount of oleate adsorbed is slightly higher than that of linoléate, which can be related to the lower solubility of oleate, and the higher stability of calcium dioleate than calcium dilinoleate with solubility products, pKs, of 11.6 and 10.1, respectively (Beneventi et al., 2016). However, slightly higher mineral recoveries were observed with linoléate than oleate, which indicates that for the same amount of collector adsorbed, linoléate provides a higher hydrophobicity at the mineral surface (because of the conformation of its hydrocarbon chain) than oleate or generates a more stable froth.

**5. Conclusions**

Several analytical methods were used to measure directly (X-ray photoelectron spectroscopy, infrared spectroscopy) and indirectly (colorimetric method) the amount of fatty acid collectors, oleate and linoléate, adsorbed on two calcites and one apatite at pH 9. The collector adsorbed amount was related to the reactivity (acid-base interaction and solubility) of these minerals in order to explain flotation performance.

The results obtained in this study indicate that the amount of calcium dioleate or dilinoléate adsorbed/precipitated on the minerals surface increases with collector addition and calcium mineral dissolution, which results in a higher flotation of these minerals. The degree of calcium dissolution was related to different calcium site densities in calcite and apatite, to a difference in crystallinity between the two calcites and/or to the presence of impurity/substitution in the mineral lattice, such as with magnesium and sulphate ions that were present in one of the calcites.

For all the minerals tested, linoleate provided a slightly higher mineral flotation than oleate although more oleate was adsorbed at the mineral surface. It is possible that linoleate provides a higher surface hydrophobicity because of the different conformation of its hydrocarbon chain or it generates a more stable froth.

**Acknowledgements**

The financial support from the European Union's Horizon 2020 research and innovation programme under grant agreement No 641650 for the FAME project is gratefully

<figure><img src="image_16.png" /></figure>
acknowledged. D. Fornasiero acknowledges the financial support provided by the Région Lorraine (FEDER) and EU's EMERALD program.

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<figure><img src="image_21.png" /></figure>
Figures Captions

**Fig. 1.** Calibration curves of absorbance at 435 nm versus concentration of oleate (left) and linoléate (right) in solution using the colorimetric method.

**Fig. 2.** XRD pattern of calcite M (top), calcite C (middle) and fluorapatite (bottom). The vertical lines refer to calcite or fluorapatite and ‘Q’ refers to quartz impurity.

**Fig. 3.** Change of pH with time after addition of the minerals to a solution of pH 6.7 (particle size <20 µm).

**Fig. 4.** Calcium dissolution from calcite M, calcite C and fluorapatite as a function of time (particle size <20 µm).

**Fig. 5.** Recovery of minerals versus concentration of oleate (left) and linoléate (right) after 3 min of flotation (the lines are shown simply to guide the eye). The reproducibility in recoveries was +/-2%.

**Fig. 6.** XPS C(1s) spectra of calcite C as a function of linoleate concentration (the intensities are different in the three figures).

**Fig. 7.** XPS spectra of fluorapatite with $5×10^{-4}$ M oleate (the intensities are different in the five figures).

**Fig. 8.** Concentration of oleate (left) and linoléate (right) adsorbed on the minerals as a function of collector (total) concentration. The reproducibility in collector adsorbed was estimated at $\pm3×10^{-6}$ mol/m$^2$. The dashed horizontal lines represent monolayer coverage calculated for an oleate area of 30 Å$^2$/molecule ($5.5×10^{-6}$ mol/m$^2$) or 20 Å$^2$/molecule ($8.3×10^{-6}$ mol/m$^2$).

**Fig. 9.** Infrared spectra of oleate adsorbed on fluorapatite as a function of oleate concentration of $3.54×10^{-5}$, $1.06×10^{-4}$, $1.77×10^{-4}$, $3.54×10^{-4}$ and $4.61×10^{-4}$ M with increasing IR intensity.

**Fig. 10.** Infrared spectra of oleate adsorbed on (left) calcite M and (right) calcite C as a function of oleate concentration of $3.54×10^{-5}$, $1.06×10^{-4}$, $1.77×10^{-4}$, $2.83×10^{-4}$, $3.54×10^{-4}$ and $4.61×10^{-4}$ M with increasing IR intensity.

<figure><img src="image_22.png" /></figure>
**Fig. 11.** Intensity of the 2931 cm⁻¹ IR peak of oleate and linoleate adsorbed on calcite M, calcite C and fluorapatite at a collector concentration of 4.61×10⁻⁴ M.

<figure><img src="image_23.png" /></figure>
Figures:

<figure><img src="image_24.png" /><figcaption>**Fig. 1.** Calibration curves of absorbance at 435 nm versus concentration of oleate (left) and linoleate (right) in solution using the colorimetric method.</figcaption></figure>

<figure><img src="image_25.png" /></figure>
<figure><img src="image_26.png" /><figcaption>**Fig. 2.** XRD pattern of calcite M (top), calcite C (middle) and fluorapatite (bottom). The vertical lines refer to calcite or fluorapatite and ‘Q’ refers to quartz impurity.</figcaption></figure>

<figure><img src="image_27.png" /></figure>
<figure><img src="image_28.png" /><figcaption>**Fig. 3.** Change of pH with time after addition of the minerals to a solution of pH 6.7 (particle size <20 µm).</figcaption></figure>

<figure><img src="image_29.png" /></figure>
<figure><img src="image_30.png" /><figcaption>**Fig. 4.** Calcium dissolution from calcite M, calcite C and fluorapatite as a function of time (particle size <20 µm).</figcaption></figure>
<figure><img src="image_31.png" /><figcaption>**Fig. 5.** Recovery of minerals versus concentration of oleate (left) and linoleate (right) after 3 min of flotation (the lines are shown simply to guide the eye). The reproducibility in recoveries was +/-2%.</figcaption></figure>
<figure><img src="image_32.png" /><figcaption>**Fig. 6.** XPS C(1s) spectra of calcite C as a function of linoleate concentration (the intensities are different in the three figures).</figcaption></figure>

<figure><img src="image_33.png" /></figure>
<figure><img src="image_34.png" /><figcaption>Fig. 7. XPS spectra of fluorapatite with 5×10⁻⁴ M oleate (the intensities are different in the five figures).</figcaption></figure>

<figure><img src="image_35.png" /></figure>
<figure><img src="image_36.png" /><figcaption>**Fig. 8.** Concentration of oleate (left) and linoleate (right) adsorbed on the minerals as a function of collector (total) concentration. The reproducibility in collector adsorbed was estimated at $+/-3 \times 10^{-6}$ mol/m². The dashed horizontal lines represent monolayer coverage calculated for an oleate area of 30 Å²/molecule ($5.5 \times 10^{-6}$ mol/m²) or 20 Å²/molecule ($8.3 \times 10^{-6}$ mol/m²).</figcaption></figure>
<figure><img src="image_37.png" /><figcaption>**Fig. 9.** Infrared spectra of oleate adsorbed on fluorapatite as a function of oleate concentration of 3.54×10⁻⁵, 1.06×10⁻⁴, 1.77×10⁻⁴, 3.54×10⁻⁴ and 4.61×10⁻⁴ M with increasing IR intensity.</figcaption></figure>
<figure><img src="image_38.png" /><figcaption>**Fig. 10.** Infrared spectra of oleate adsorbed on (left) calcite M and (right) calcite C as a function of oleate concentration of 3.54×10⁻⁵, 1.06×10⁻⁴, 1.77×10⁻⁴, 2.83×10⁻⁴, 3.54×10⁻⁴ and 4.61×10⁻⁴ M with increasing IR intensity.</figcaption></figure>
<figure><img src="image_39.png" /><figcaption>**Fig. 11.** Intensity of the 2931 cm⁻¹ IR peak of oleate and linoleate adsorbed on calcite M, calcite C and fluorapatite at a collector concentration of 4.61×10⁻⁴ M.</figcaption></figure>

<figure><img src="image_40.png" /></figure>
Tables:

<caption>**Table 1**</caption>

Chemical analysis of the minerals (ICP-OES).

<table><caption>**Table 2a**</caption><thead><tr><th></th><th>CaO</th><th>P<sub>2</sub>O<sub>5</sub></th><th>MgO</th><th>SiO<sub>2</sub></th><th>K<sub>2</sub>O</th><th>Na<sub>2</sub>O</th><th>F</th><th>LOI</th><th>Total</th></tr></thead><tbody><tr><td>Fluorapatite</td><td>53.45</td><td>37.73</td><td>-</td><td>3.89</td><td>-</td><td>0.05</td><td>3.04</td><td>0.61</td><td>98.77</td></tr><tr><td>Calcite C</td><td>55.44</td><td>-</td><td>0.27</td><td>0.06</td><td>-</td><td>-</td><td>-</td><td>43.54</td><td>99.31</td></tr><tr><td>Calcite M</td><td>54.05</td><td>-</td><td>1.23</td><td>0.07</td><td>0.01</td><td>0.14</td><td>-</td><td>43.32</td><td>98.82</td></tr></tbody></table>

Concentration (atomic %) of the elements measured by XPS at the surface of fluorapatite as a function of oleate (Ol) or linoleate (Li) concentration. BE is the binding energy (eV) for each element/species and Δ is the change in atomic % for each element after collector addition*.

<table><thead><tr><th colspan="13">Fluorapatite</th></tr><tr><th rowspan="2">Elements</th><th colspan="3">No collector</th><th colspan="3">5×10<sup>-5</sup> M Ol</th><th colspan="3">5×10<sup>-4</sup> M Ol</th><th colspan="3">5×10<sup>-5</sup> M Li</th><th colspan="3">5×10<sup>-4</sup> M Li</th></tr><tr><th>BE</th><th>at%</th><th>Δ</th><th>BE</th><th>at%</th><th>Δ</th><th>BE</th><th>at%</th><th>Δ</th><th>BE</th><th>at%</th><th>Δ</th><th>BE</th><th>at%</th><th>Δ</th></tr></thead><tbody><tr><td>C(1s)</td><td></td><td>27.5</td><td></td><td></td><td>35.5</td><td>+29</td><td></td><td>42.2</td><td>+54</td><td></td><td>33.8</td><td>+23</td><td></td><td>43.1</td><td>+57</td></tr><tr><td>O(1s)</td><td></td><td>45.4</td><td></td><td></td><td>40.2</td><td>-11</td><td></td><td>35.3</td><td>-22</td><td></td><td>42.1</td><td>-7</td><td></td><td>36.2</td><td>-20</td></tr><tr><td>Ca(2p)</td><td>347.3</td><td>14.2</td><td></td><td>347.3</td><td>12.2</td><td>-14</td><td>347.3</td><td>11.9</td><td>-16</td><td>347.2</td><td>12.3</td><td>-13</td><td>347.3</td><td>11.0</td><td>-22</td></tr><tr><td>P(2p)</td><td>133.3</td><td>7.7</td><td></td><td>133.1</td><td>7.3</td><td>-6</td><td>133.2</td><td>6.6</td><td>-15</td><td>133.1</td><td>7.2</td><td>-7</td><td>133.2</td><td>6.3</td><td>-19</td></tr><tr><td>F(1s)</td><td>684.3</td><td>2.7</td><td></td><td>684.4</td><td>2.1</td><td>-23</td><td>684.3</td><td>2.0</td><td>-25</td><td>684.3</td><td>2.1</td><td>-19</td><td>684.4</td><td>1.7</td><td>-36</td></tr><tr><td>Si(2p)</td><td>103.1</td><td>2.4</td><td></td><td>103.0</td><td>2.7</td><td>+10</td><td>102.9</td><td>2.0</td><td>-19</td><td>102.8</td><td>2.4</td><td>-1</td><td>102.8</td><td>1.7</td><td>-32</td></tr><tr><td>Total</td><td></td><td>100</td><td></td><td></td><td>100</td><td></td><td></td><td>100</td><td></td><td></td><td>100</td><td></td><td></td><td>100</td><td></td></tr><tr><td>C species</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>C-C,C-H</td><td>284.6</td><td>22.3</td><td></td><td>284.6</td><td>25.8</td><td>+16</td><td>284.6</td><td>36.8</td><td>+65</td><td>284.6</td><td>23.7</td><td>+6</td><td>284.6</td><td>33.6</td><td>+51</td></tr><tr><td>C-O</td><td>286.0</td><td>3.4</td><td></td><td>285.6</td><td>6.2</td><td>+81</td><td>285.5</td><td>4.1</td><td>+20</td><td>285.9</td><td>6.5</td><td>+91</td><td>285.8</td><td>6.4</td><td>+86</td></tr><tr><td>CO<sub>3</sub></td><td>288.9</td><td>1.8</td><td></td><td>288.1</td><td>3.5</td><td>+95</td><td>288.5</td><td>1.3</td><td>-28</td><td>288.1</td><td>3.6</td><td>+96</td><td>288.0</td><td>3.1</td><td>+73</td></tr><tr><td>O species</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>O-H</td><td>531.1</td><td>33.5</td><td></td><td>531.0</td><td>27.7</td><td>-17</td><td>531.2</td><td>25.7</td><td>-23</td><td>531.1</td><td>29.1</td><td>-13</td><td>531.1</td><td>23.4</td><td>-30</td></tr><tr><td>O-C,O-P</td><td>532.2</td><td>9.5</td><td></td><td>532.0</td><td>9.3</td><td>-2</td><td>532.0</td><td>7.6</td><td>-20</td><td>532.2</td><td>9.8</td><td>+4</td><td>532.0</td><td>9.9</td><td>+4</td></tr><tr><td>H<sub>2</sub>O</td><td>533.2</td><td>2.5</td><td></td><td>532.9</td><td>3.3</td><td>+32</td><td>533.1</td><td>2.0</td><td>-19</td><td>533.2</td><td>3.2</td><td>+29</td><td>533.0</td><td>2.9</td><td>+17</td></tr></tbody></table>

<figure><img src="image_41.png" /></figure>

<footnote>* Δ= 100×(at%(with collector) - at%(no collector)) / at%(no collector)</footnote>
**Table 2b**

Same as in Table 2a, but for calcite C.

<table><caption>Calcite C</caption><thead><tr><th rowspan="2">Elements</th><th colspan="3">No collector</th><th colspan="3">5×10<sup>-5</sup> M Ol</th><th colspan="3">5×10<sup>-4</sup> M Ol</th><th colspan="3">5×10<sup>-5</sup> M Li</th><th colspan="3">5×10<sup>-4</sup> M Li</th></tr><tr><th>BE</th><th>at%</th><th>BE</th><th>at%</th><th>Δ</th><th>BE</th><th>at%</th><th>Δ</th><th>BE</th><th>at%</th><th>Δ</th><th>BE</th><th>at%</th><th>Δ</th></tr></thead><tbody><tr><td>C(1s)</td><td></td><td>39.1</td><td></td><td>53.3</td><td>+36</td><td></td><td>54.9</td><td>+40</td><td></td><td>43.6</td><td>+11</td><td></td><td>57.4</td><td>+47</td></tr><tr><td>O(1s)</td><td></td><td>46.9</td><td></td><td>35.5</td><td>-24</td><td></td><td>34.3</td><td>-27</td><td></td><td>43.3</td><td>-8</td><td></td><td>32.4</td><td>-31</td></tr><tr><td>Ca(2p)</td><td>346.6</td><td>14.0</td><td>346.9</td><td>11.3</td><td>-20</td><td>346.9</td><td>10.9</td><td>-23</td><td>346.7</td><td>13.1</td><td>-7</td><td>346.8</td><td>10.2</td><td>-27</td></tr><tr><td>Total</td><td></td><td>100</td><td></td><td>100</td><td></td><td></td><td>100</td><td></td><td></td><td>100</td><td></td><td></td><td>100</td><td></td></tr><tr><td>C species</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>C-C,C-H</td><td>284.6</td><td>19.1</td><td>284.6</td><td>33.9</td><td>+74</td><td>284.6</td><td>38.5</td><td>+98</td><td>284.6</td><td>20.8</td><td>+7</td><td>284.6</td><td>40.9</td><td>+110</td></tr><tr><td>C-O</td><td>286.2</td><td>2.3</td><td>285.5</td><td>4.7</td><td>+101</td><td>285.8</td><td>2.6</td><td>+10</td><td>285.7</td><td>5.0</td><td>+114</td><td>285.9</td><td>2.9</td><td>+23</td></tr><tr><td>CO<sub>2</sub></td><td>288.1</td><td>1.0</td><td>287.8</td><td>1.0</td><td>+4</td><td>288.0</td><td>1.2</td><td>+25</td><td>287.3</td><td>1.8</td><td>+82</td><td>288.0</td><td>1.6</td><td>+67</td></tr><tr><td>CO<sub>3</sub></td><td>289.3</td><td>16.3</td><td>289.4</td><td>13.7</td><td>-16</td><td>289.5</td><td>12.6</td><td>-23</td><td>289.3</td><td>16.0</td><td>-2</td><td>289.4</td><td>12.0</td><td>-27</td></tr><tr><td>O species</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>O-H</td><td>531.0</td><td>37.5</td><td>531.2</td><td>29.4</td><td>-22</td><td>531.2</td><td>28.9</td><td>-23</td><td>531.0</td><td>31.8</td><td>-15</td><td>531.2</td><td>26.6</td><td>-29</td></tr><tr><td>O-C</td><td>532.1</td><td>7.7</td><td>532.0</td><td>5.1</td><td>-34</td><td>532.1</td><td>3.8</td><td>-50</td><td>531.9</td><td>8.4</td><td>+9</td><td>532.0</td><td>4.6</td><td>-40</td></tr><tr><td>H<sub>2</sub>O</td><td>533.2</td><td>1.6</td><td>533.2</td><td>1.0</td><td>-36</td><td>532.9</td><td>1.5</td><td>-9</td><td>533.0</td><td>3.2</td><td>+94</td><td>533.0</td><td>1.2</td><td>-23</td></tr></tbody></table>

**Table 2c**

Same as in Table 2a, but for calcite M.

<table><caption>Calcite M</caption><thead><tr><th rowspan="2">Elements</th><th colspan="3">No collector</th><th colspan="3">5×10<sup>-4</sup> M Ol</th><th colspan="3">5×10<sup>-4</sup> M Li</th></tr><tr><th>BE</th><th>at%</th><th>BE</th><th>at%</th><th>Δ</th><th>BE</th><th>at%</th><th>Δ</th></tr></thead><tbody><tr><td>C(1s)</td><td></td><td>38.8</td><td></td><td>62.5</td><td>+61</td><td></td><td>62.7</td><td>+62</td></tr><tr><td>O(1s)</td><td></td><td>47.5</td><td></td><td>28.6</td><td>-40</td><td></td><td>29.2</td><td>-39</td></tr><tr><td>Ca(2p)</td><td>346.7</td><td>13.6</td><td>346.9</td><td>8.9</td><td>-35</td><td>346.9</td><td>8.1</td><td>-40</td></tr><tr><td>Total</td><td></td><td>100</td><td></td><td>100</td><td></td><td></td><td>100</td><td></td></tr><tr><td>C species</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>C-C,C-H</td><td>284.6</td><td>18.2</td><td>284.6</td><td>48.9</td><td>+168</td><td>284.6</td><td>45.6</td><td>+150</td></tr><tr><td>C-O</td><td>286.0</td><td>3.1</td><td>285.7</td><td>2.8</td><td>-11</td><td>285.9</td><td>5.5</td><td>+74</td></tr><tr><td>CO<sub>2</sub></td><td>287.4</td><td>0.9</td><td>288.3</td><td>1.4</td><td>+58</td><td>287.8</td><td>2.6</td><td>+191</td></tr><tr><td>CO<sub>3</sub></td><td>289.3</td><td>16.6</td><td>289.4</td><td>9.4</td><td>-43</td><td>289.4</td><td>9.0</td><td>-45</td></tr><tr><td>O species</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>O-H</td><td>531.1</td><td>36.3</td><td>531.2</td><td>24.1</td><td>-34</td><td>531.2</td><td>22.1</td><td>-39</td></tr><tr><td>O-C</td><td>532.1</td><td>8.2</td><td>532.0</td><td>3.5</td><td>-57</td><td>532.2</td><td>5.4</td><td>-34</td></tr><tr><td>H<sub>2</sub>O</td><td>533.1</td><td>3.1</td><td>533.1</td><td>1.0</td><td>-68</td><td>533.2</td><td>1.7</td><td>-46</td></tr></tbody></table>

<figure><img src="image_42.png" /></figure>
**Table 3**

Ratio of atomic concentration of the elements measured by XPS at the surface of minerals as a function of oleate (Ol) or linoleate (Li) concentration.

<table><thead><tr><th colspan="6">Fluorapatite</th></tr><tr><th></th><th>No collector</th><th>5×10<sup>-5</sup> M Ol</th><th>5×10<sup>-4</sup> M Ol</th><th>5×10<sup>-5</sup> M Li</th><th>5×10<sup>-4</sup> M Li</th></tr></thead><tbody><tr><th>Ca/P</th><td>1.8</td><td>1.7</td><td>1.8</td><td>1.7</td><td>1.8</td></tr><tr><th>Ca/F</th><td>5.3</td><td>5.9</td><td>6.0</td><td>5.7</td><td>6.5</td></tr><tr><th>C-C/Ca</th><td>1.6</td><td>2.1</td><td>3.1</td><td>1.9</td><td>3.0</td></tr></tbody></table>

<table><thead><tr><th colspan="6">Calcite C</th></tr><tr><th></th><th>No collector</th><th>5×10<sup>-5</sup> M Ol</th><th>5×10<sup>-4</sup> M Ol</th><th>5×10<sup>-5</sup> M Li</th><th>5×10<sup>-4</sup> M Li</th></tr></thead><tbody><tr><th>Ca/CO<sub>3</sub></th><td>0.9</td><td>0.8</td><td>0.9</td><td>0.8</td><td>0.9</td></tr><tr><th>C-C/Ca</th><td>1.4</td><td>3.0</td><td>3.5</td><td>1.6</td><td>4.0</td></tr></tbody></table>

<table><thead><tr><th colspan="4">Calcite M</th></tr><tr><th></th><th>No collector</th><th>5×10<sup>-4</sup> M Ol</th><th>5×10<sup>-4</sup> M Li</th></tr></thead><tbody><tr><th>Ca/CO<sub>3</sub></th><td>0.8</td><td>0.9</td><td>0.9</td></tr><tr><th>C-C/Ca</th><td>1.3</td><td>5.5</td><td>5.6</td></tr></tbody></table>