Minerals Engineering 155 (2020) 106456

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Minerals Engineering
journal homepage: www.elsevier.com/locate/mineng

Flotation studies of galena (PbS), cerussite (PbCO3) and anglesite (PbSO4) T

with hydroxamic acids as collectors
⁎
Martha Araceli Elizondo-Álvarez , Alejandro Uribe-Salas, Fabiola Nava-Alonso
Department of Metallurgical Engineering, CINVESTAV-IPN, Unidad Saltillo, 25900 Ramos Arizpe, Coahuila, Mexico

A R T I C LE I N FO A B S T R A C T

Keywords: Currently, the mineral processing industry faces major challenges in the development and implementation of
Hydroxamates strategies and new processes for the recovery of lead from low-grade oxidized minerals, such as cerussite
Adsorption (PbCO3) and anglesite (PbSO4). In this study, the behavior of the individual flotation of galena (PbS), cerussite
Flotation (PbCO3) and anglesite (PbSO4), without sulfidation, was investigated using benzohydroxamic acid (BHA) and
Cerussite
octanohydroxamic acid (OHA) as collectors. Spectroscopy UV/Vis measurements were carried out to investigate
Anglesite
the effect of pH on the adsorption of both collectors on the surface of these minerals. Likewise, contact angle
measurements were conducted to evaluate the hydrophobicity imparted to the minerals. Furthermore, the se-
lectivity of both collectors towards quartz (SiO2) and pyrite (FeS2), mineral species commonly found as gangue,
was evaluated. Overall, microflotation tests showed higher recoveries of galena, cerussite and anglesite using
OHA. Anglesite proved to be the most challenging mineral to float, probably because it is the most soluble of the
three lead minerals tested. It requires higher dosages of OHA and the presence of sulfate (e.g., to reduce its
solubility) to show good recoveries under slightly acidic conditions. Also, the recoveries of cerussite and an-
glesite were affected under alkaline conditions. Thermodynamic modeling suggests that the observed behavior is
due to the presence of hydrocerussite (Pb3(CO3)2(OH)2), of hydrophilic nature, on the mineral surfaces. OHA
proved to be the most effective collector; nevertheless, it also showed significant loss of selectivity against pyrite,
although not against quartz, so its use will depend on the nature of the gangue present in the ore to be treated.
BHA neither floats quartz nor pyrite. Therefore, BHA could be considered a potential candidate for the flotation
of galena and cerussite due to its high selectivity. In summary, the use of hydroxamates would mitigate the
impact on health and the environment that results from the use of xanthates.

1. Introduction practice results in a much less hydrophilic surface, due to the chemical
adsorption of the sulfide ion (Castro et al., 1974), which does not in-
The beneficiation of oxidized ores is receiving increasing interest teract with the water molecules, that is, it does not form bonds with
because many copper and lead sulfides mines around the world have hydrogen, so the sulfurized surface is less hydrated than sulfated or
significant reserves of oxidized minerals, associated with the main de- carbonated surfaces. The reagents usually used in this process are so-
posit of primary sulfide (Lee et al., 2009). However, one of the sig- dium sulfide (Na2S), sodium hydrosulfide (NaSH) and ammonium sul-
nificant limitations in its processing is the inadequate response they fide ((NH4)2S) (Wu et al., 2017); these are added before the collector,
show to xanthates, collectors most commonly used in sulfides flotation usually xanthate. In practice, the dose of sulfurizing agent greatly
(Parker et al., 2012). For this reason, oxidized minerals require sulfi- varies, but will generally fall between 500 and 2500 g/t (Önal et al.,
dation before being conditioned with the collector. 2005).
There is a large number of works published about the sulfidation Marabini and Cozza (1988) demonstrated by infrared spectroscopy
process (Fleming, 1952, 1953; Rey, 1958; Rey et al., 1950, 1954; Rey with Fourier transform (FTIR) that the xanthate is adsorbed on the
and Formanek, 1960), which is the traditional method of floating oxi- sulfurized cerussite, while there is no xanthate adsorption when the
dized minerals using xanthates. The main objective of the sulfidation is cerussite is not treated with Na2S before collector conditioning. In ad-
to convert the oxidized minerals’ surface into lead sulfides because they dition, it is worth emphasizing that there are many disadvantages and
respond better to xanthate than do the sulfates or carbonates. This little benefit of using a slug sulfidization, which uses a single slug dose.

⁎
Corresponding author.
E-mail address: martha.elizondo.a@gmail.com (M.A. Elizondo-Álvarez).

https://doi.org/10.1016/j.mineng.2020.106456
Received 12 November 2019; Received in revised form 1 May 2020; Accepted 13 May 2020
0892-6875/ © 2020 Elsevier Ltd. All rights reserved.
M.A. Elizondo-Álvarez, et al. Minerals Engineering 155 (2020) 106456

Several studies have shown that strict and rigorous control of sulfur- SHA. Likewise, Yao et al. (2019) demonstrated by FTIR that SHA is
izing agents is required (Castro et al., 1974; Herrera-Urbina et al., 1999; chemically adsorbed on the surface of the anglesite.
Park et al., 2016). Unfortunately, insufficient reagent addition causes Based on these previous studies, the present research analyzes the
poor recoveries (Lee et al., 2009), while excessive addition causes de- effect of pH on the recovery of galena (PbS), cerussite (PbCO3) and
pression of oxidized minerals during flotation with xanthates (Park anglesite (PbSO4) using benzohydroxamic acid (BHA) and octanohy-
et al., 2016). In this regard, Controlled Potential Sulfidization (CPS) to a droxamic acid (OHA). It is important to note that, to date, there is little
known Es potential is preferred over slug sulfidization to sulfidize information reported in the literature on the use of hydroxamates as
oxidized sulfide minerals (Corin et al., 2017; Jones and Woodcock, direct collectors in the flotation of sulfides and oxidized lead minerals,
1979). this being the main objective for the development of this research work.
Chelating agents have received particular attention in the search for Likewise, the reason for this work is justified by the need to look for
reagents to improve the flotation separation of oxidized minerals alternative collectors to xanthates, which offer superior performance
without prior sulfidation (Herrera-Urbina, 2003; Liu et al., 2019; (without the need for a previous sulfidation stage) and do not present
Nagaraj and Farinato, 2016). According to the literature, some studies risks to health and the environment.
have been carried out on the use of unconventional collectors in the
direct flotation of oxidized lead minerals. Among them are 8-hydro- 2. Materials and methods
xyquinoline (Rinelli and Marabini, 1973), Alamine 26-D (Herrera-
Urbina, 1980), whose chemical composition consists of primary amines 2.1. Materials
with hydrocarbon chains of different lengths, mercaptobenzothiazole
(Marabini et al., 1989) and diphenyl α-(3-phenylthioureido) hex- The collector adsorption, microflotation and contact angle experi-
ylphosphonate (Zhu et al., 2007), among others. With some of them, ments were carried out using galena, cerussite, anglesite, pyrite and
good recoveries and concentrate grades have been achieved at the la- quartz samples, all of them of high purity. The galena sample was
boratory scale. Unfortunately, some drawbacks complicate their use; provided by a Peñoles mine (Mexico); the cerussite sample is from
namely, (1) low solubility due to its high molecular weight and (2) Morocco, analytically pure anglesite was purchased from Sigma
relatively high consumption. Furthermore, some researchers have stu- Aldrich, the quartz is from Queretaro (Mexico) and finally, the pyrite is
died the effect of collector mixtures on mixed ores, for which the sul- from the mining district of Concepción del Oro, Zacatecas (Mexico).
phidization stage was not consistent or less effective in comparison with Hydrochloric acid (HCl) and sodium hydroxide (NaOH) that were
the use of collector mixture (Davidson and Kelebek, 2014; Tijsseling used as pH regulators were purchased from Sigma Aldrich.
et al., 2019). Benzohydroxamic acid, supplied by Sigma Aldrich, and octanohy-
In recent decades, hydroxamic acids and their salts have shown droxamic acid synthesized in the laboratory using the procedure de-
good results at the laboratory scale in the flotation of oxidized copper scribed by Hauser and Renfrow (1939) and Marion et al. (2017), were
ores and some rare earth, as evidenced by the large number of pub- used as collectors. The chemical structure of both collectors is illu-
lished studies (Bulatovic, 2010; Das and Pradip, 1987; Espiritu et al., strated in Fig. 2.
2018; Espiritu and Waters, 2018; Fuerstenau and Pradip, 1984; Lee
et al., 1998, 2009; Lenormand, 1974; Lenormand et al., 1979; Li et al.,
2019; Marion et al., 2017; Meng et al., 2015; Yao et al., 2018). These 2.2. Mineral characterization
collectors can form highly insoluble complexes with specific metal ca-
tions of the mineral surface, which gives them high selectivity The mineral composition was determined by elemental metal ana-
(Fuerstenau et al., 2000; Natarajan, 2013; Türkel, 2011). The presence lysis by atomic absorption spectroscopy (AA) and ICP, while the
of a hydroxyl group and an oxygen double bond (]O) coordination site quantification of carbon and sulfur was carried out by chemical analysis
in the acid molecule, makes this ligand capable of complexing with the by combustion (LECO). Table 1 shows the results of the elementary
metal ion through two sites, as illustrated in Fig. 1, the reason whereby chemical analysis, where it can be seen that the minerals are relatively
hydroxamic acid belongs to the category of bidentate ligand pure. Likewise, the samples were characterized by X-Ray diffraction
(Somasundaran and Nagaraj, 1984). (XRD). Fig. 3 shows the diffraction spectra obtained, in which only the
Lee et al. (2009) conducted a study focused on determining the characteristic peaks of anglesite, cerussite, galena, quartz and pyrite are
flotation response of a mixture of sulfide and copper oxide minerals, observed. No other mineral phase was identified.
composed of 70% by weight of sulfide and 30% by weight of oxide. The
authors demonstrated that with the use of octyl hydroxamate in con- 2.3. Microflotation experiments
junction with amyl xanthate, sulfides and copper oxides can be suc-
cessfully recovered simultaneously, without the need of a previous Microflotation tests were conducted in a Partridge-Smith cell
sulfidation stage. Similarly, Marion et al. (2017) studied the effect of (80 mL) using 1 g sample of mineral (galena, cerussite, anglesite, pyrite
five alkyl hydroxamates and two aromatic hydroxamates on the flota- or quartz) of the size fraction −106+75 µm, which was conditioned for
tion of a synthetic mixture of malachite and quartz. The best flotation 5 min in 100 mL of the collector solution (BHA or OHA), at the con-
results, around 95% copper recovery, was obtained at pH 8 with ben- centration and pH of interest. Next, the mineral and 80 mL of the so-
zohydroxamic and octanohydroxamic acids. The authors suggest that at lution were transferred to the cell and floated for 1 min with 23 mL/min
pH 8, the CuOH+ species on the surface of the mineral is the one that of high purity nitrogen. The remaining solution (20 mL) was progres-
interacts with the benzohydroxamate and octanohydroxamate anions. sively added to the cell as make-up water. At the end of the test, the
Recently, Yao et al. (2018) studied the behavior in the flotation of floated and sink solids were filtered, dried, and weighed, to calculate
synthetic anglesite using salicylhydroxamic acid (SHA) as collector. The the recovery. In some specific measurements, galena was subjected to a
results obtained by these authors showed high recoveries of anglesite, preconditioning stage, which consisted in treating the mineral in
around 90%, for a wide range of pH (from 4 to 10), using 50 mg/L of 100 mL NaNO3 solution (10−3 mol/L) open to the atmosphere for
15 min, and at the pH of interest, prior to the conditioning with the
collector. This stage allows the controlled oxidation of the mineral,
creating an increased concentration of active sites for collector ad-
sorption. The experiments were carried by triplicate and the average
recovery is reported together with the error bars of the 95% confidence
Fig. 1. Schematic representation of the metal-hydroxamate complex. interval of a Student’s t-distribution (Montgomery, 2001).

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M.A. Elizondo-Álvarez, et al. Minerals Engineering 155 (2020) 106456

Fig. 2. The structural formula of (a) benzohydroxamic acid (BHA) and (b) octanohydroxamic acid (OHA).

2.4. Collector adsorption measurements (UV/Vis Spectroscopy)

Collector adsorption tests were conducted using a spectrometer UV/

Vis (Varian Cary 100) equipped with a continuous-flow quartz cell. The
experiments consisted of measuring the evolution of absorbance as a
function of time, of a solution of BHA or OHA (10−4 mol/L), at the
wavelength at which hydroxamate anion exhibits its characteristic ab-
sorption peak, 267 nm and 227 nm, respectively (Exner and Kakáč,
1963; Plapinger, 1959). Subsequently, the absorbance was converted
directly into concentration according to Beer-Lambert's law, and finally
to adsorption percentage. The evolution of this adsorption percentage is
presented as a function of time. More details of the technique are given
in previous works (Elizondo-Álvarez et al., 2019; Elizondo-Álvarez
et al., 2017). In all cases, 1 g of mineral (size fraction −106+75 µm)
and 50 mL of collector solution were used. In some specific measure-
ments, 1 g of galena was preconditioned for 15 min in 100 mL NaNO3
(10−3 mol/L) open to the atmosphere and at the pH of interest, prior to
the stage of collector adsorption. It is worth mentioning that NaNO3
(10−3 mol/L) was used to fix the ionic strength and avoid changes in
the ionic species activities by maintaining constant their activity coef-
ficient. The use of nitrate is preferred over chloride since this can form
metal complexes with some metal cations of interest in the flotation
operations. The measurements were made by duplicate. The average of
the two curves is reported with a confidence interval defined by the
standard deviation. Fig. 3. X-ray diffraction spectra: (a) Anglesite (PDF: 00-005-0575), (b)
Cerussite (PDF: 01-070-2052), (c) Galena (PDF: 01-078-1058), (d) Quartz (PDF:
00-033-1161) and (e) Pyrite (PDF: 03-065-1211).
2.5. Contact angle experiments

The contact angle measurements were carried out using high-purity contact between the three phases was recorded, and the image was fi-
galena, pyrite, quartz and cerussite samples, which were mounted on nally processed with the Image-Pro plus 5.1 image analyzer. The
metallographic resin. It is worth to note that no contact angle tests were measurements were carried out in triplicate, and the average value is
carried out with anglesite since only ground samples of the mineral reported. More details of the technique are given elsewhere (Dávila-
were available. Pulido and Uribe-Salas, 2014).
The specimen with the mineral sample was polished using silicon
carbide sandpaper and deionized and deoxygenated water (by bubbling 2.6. Thermodynamic modeling
N2), in order to minimize surface oxidation due to the presence of
dissolved oxygen. The specimen was conditioned in an aqueous solution The objective of the thermodynamic modeling was to determine the
with the desired chemical characteristics, for a pre-established time stable species formed on the mineral surface, in equilibrium with the
(5–20 min). Once the conditioning was completed, the specimen was aqueous species present in the solution. Such equilibrium was evaluated
transferred to an acrylic box where an air bubble of about 1 mm dia- based on the pH of the mineral water suspension. The modeling was
meter was contacted with the specimen; then, the photograph of the conducted at room temperature (25 °C), considering a concentration of

Table 1
Elemental analysis (in wt %) of the mineral samples.
Mineral Elements (in wt %)

Pb Fe S Cu Zn C Si Insoluble

Anglesite (PbSO4) 68.5 – 11.0 0.0005 – 0.14 – –

Cerussite (PbCO3) 73.77 0.02 0.067 0.02 0.0033 4.56 0.418 –
Galena (PbS) 85.74 0.015 13.25 0.010 0.013 – – 0.95
Quartz (SiO2) 0.078 0.02 0.048 0.02 0.0047 0.0047 99.83 –
Pyrite (Fes2) 0.025 42.95 50.2 0.003 0.003 – – 6.8

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M.A. Elizondo-Álvarez, et al. Minerals Engineering 155 (2020) 106456

Fig. 4. Effect of pH on the recovery of galena, pyrite and quartz using: (a) benzohydroxamic acid (10−4 mol/L) and (b) octanohydroxamic acid (10−4 mol/L). The
measurements were carried out at 25 °C. The galena and pyrite were floated for 1 min while the quartz was floated for 5 min.

10 g/L (Pb2+, PbOH+, Pb(OH)2, PbO, PbO2, PbSO4, PbCO3, Pb(OH)2, hydrophilic in nature, and it will be addressed later.
Pb4(CO3)2(SO4)(OH)2, Pb3(CO3)2(OH)2, H2CO3, HCO3, CO32−, SO42−, BHA proved to be highly selective against pyrite while OHA was
S2−). A relatively small volume atmosphere (79% v/v N2, 21% O2, able to recover about 80% at pH between 5 and 8. The loss in OHA
0.03% CO2) was considered for initial thermodynamic evolution of the selectivity is due to the increase in the number of carbon atoms (from 6
system. The evolution of the concentration of chemical species in to 8) in the collector molecule and to steric factors (that is, interaction
equilibrium, both aqueous and solids, was plotted against pH. Only difficulties due to volume and atoms arrangement). Structural changes
those species in thermodynamic equilibrium (i.e. sulfate, but not sulfite, in the molecule of chelating reagents have different effects on the ef-
thiosulfate, etc.) were considered. The modeling was performed using ficiency of the collector (Somasundaran et al., 1993). Increasing the
the thermodynamic software HSC Chemistry 6.1. length of the collector's hydrocarbon chain increases the level of hy-
drophobicity imparted to the particle. However, the more reactive the
collector, in general, the less selective it becomes (Somasundaran and
3. Results and discussion
Moudgil, 1987). Furthermore, OHA has frothing properties, and having
collecting and frothing properties in the same reagent can make se-
3.1. Effect of pH in the flotation of galena, pyrite and quartz
lective flotation difficult (Wills and Finch, 2016).
Furthermore, at pH values above 8, the recovery of pyrite decreases
Fig. 4 shows the effect of pH on the recovery of galena, pyrite and
as the pH increases (Fig. 4b); at pH 11, pyrite does not float due to the
quartz, using BHA (Fig. 4a) and OHA (Fig. 4b) as collectors. The figure
vast abundance of hydroxide sites on the surface of the mineral, these
shows that the galena has a certain floatability without the use of a
sites are highly hydrophilic and nullify any hydrophobic effect caused
collector, this effect is attributable to elemental sulphur (Hu et al.,
by collector adsorption. This behavior suggests that selective flotation
2020; Kelebek and Yoruk, 2002). In general, it is observed that the use
of galena may be feasible at pH 11.
of hydroxamic acids and a pre-conditioning stage of the mineral for
Concerning quartz, this did not show significant recoveries with
15 min, significantly increase the recovery of the galena in all the pH
both collectors, which is because the benzohydroxamate and octano-
range studied, which is due to the chemical affinity that both collectors
hydroxamate anions are not chemically adsorbed on its surface, since
show toward the species produced during the pre-conditioning stage.
these collectors do not have chemical affinity for the surface of non-
For galena with BHA, the maximum recovery of about 70% was
metallic minerals. Besides, it is well known that quartz dispersed in
achieved at pH 8, while recoveries of up to 86% were obtained at pH 7
water has an extremely negative surface charge, in practically the
and 8 using OHA.
whole pH range (Marion et al., 2017), which prevents the physical
At pH 8, where the higher recovery occurs, probably a greater
adsorption of the anionic collector on its surface.
number of benzohydroxamate and octanohydroxamate anions chemi-
The results discussed above have implications with the future use of
cally react with the PbOH+ and PbCO3 sites on the galena surface,
OHA since at pH below 11, it is possible to recover the pyrite in the
establishing bidentate chelates as shown in Fig. 1.The increase in pH
concentrate. For a more selective separation, the use of a pyrite de-
from 8 to 10 and the decrease from 8 to 5, result in a reduction of the
pressant will be necessary.
galena recovery (see Fig. 4a). A similar trend, although less pro-
nounced, is observed with OHA (Fig. 4b). The decrease in recovery as
the pH decreases from 8 to 5 could be attributed to the dissociation of 3.2. Effect of pH and a pre-conditioning stage on the adsorption of BHA and
the acids, occurring at a pH of approximately 8.8 (pKa) for BHA (Xu OHA on galena
et al., 2017) and at a pH of approximately 9 (pKa) for OHA (Meng et al.,
2015). According to this, for pH values below 8, there is a higher Fig. 5 shows the adsorption curves of BHA and OHA on galena, in
concentration of the molecular form of the acids, which does not react the absence and presence of a preconditioning stage of the mineral at
with the fixed metal cation in the crystal lattice, and also a lower three pH values: 8, 9 and 10. In this figure three situations are observed:
concentration of benzohydroxamate and octanohydroxamate anions, The first is that the use of a preconditioning stage, which creates an
which are the most active collector species. The drop in recovery ob- increased concentration of active sites, favors the adsorption of both
served in the pH range of 8 to 10 could be attributed to the presence of collectors; the second is that the adsorption of BHA and OHA is

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M.A. Elizondo-Álvarez, et al. Minerals Engineering 155 (2020) 106456

Fig. 5. Effect of pH and the presence and absence of a pre-conditioning stage (15 min), on the adsorption of: (a) benzohydroxamate (10−4 mol/L) and (b) octa-
nohydroxamate (10−4 mol/L) on galena: 1 g (−106+75 µm)/50 mL. The measurements were carried out at 25 °C.

adversely affected by the increase in pH from 8 to 10, and the last is that microflotation results.
in all cases galena adsorbs more OHA than BHA.
The behaviors described above can be explained suggesting that the
generation of active sites for the adsorption of collectors, is favored by 3.4. Effect of pH and particle size on cerussite flotation
the controlled oxidation of the mineral surface with the dissolved
oxygen absorbed from the atmosphere, which results in the formation In the grinding stage, it is common to produce fines of cerussite
of surface species such as PbOH+, PbCO3, PbSO4 or Pb(OH)2. As a since it is a relatively soft mineral. In order to study the impact of
consequence, some of these species are replaced spontaneously by particle size on cerussite floatability, microflotation tests were carried
benzohydroxamate and octanohydroxamate anions, through surface out using two different size fractions, one finer (−38+25 µm) than the
reactions (Pradip and Fuerstenau, 1983). It should be noted that the other (−106+75 µm). Fig. 7 shows the effect of pH and particle size on
nature of the predominant species (i.e., anion or molecule) depends on the recovery of cerussite using BHA (Fig. 7a) and OHA (Fig. 7b). The
the pH used and the oxidation of the mineral, as shown in the species figure shows that cerussite cannot be floated without collector, which is
distribution diagram of the PbS-H2O-CO2-O2 system presented in a due to the high wettability of its surface. The use of hydroxamic acids
previous work (Elizondo-Álvarez et al., 2019). significantly increases cerussite recovery at all pH values studied.
At pH 8, where maximum adsorption and higher recovery occurs, In case of the medium size fraction of cerussite (−106+75 µm),
probably the PbOH+ and PbCO3 sites on the galena surface chemically maximum recoveries of approximately 45% were obtained at pH 8 and
react with benzohydroxamate and octanohydroxamate anions, estab- 9 when 10−4 mol/L of BHA is used, while recoveries of up to 90% were
lishing bidentate chelates. In turn, at pH 10 where the drop in galena obtained using the same concentration of OHA at pH 7, 8, and 9. The
recovery is observed (see Fig. 4), the Pb(OH)2 sites reduce the ad- drop in recovery as the pH decreases from 7 to 5 is due to the increased
sorption of the collector due to two possible reasons: Pb(OH)2 is ne- concentration of the molecular form of both collectors since for slightly
gatively charged and this makes it difficult the approaching of the anion acid pH values there is a lower concentration of benzohydroxamate and
to the surface, or due to a steric impossibility, that is, because the OH− octanohydroxamate anions, which are the most active collector species.
groups bind to the metal cation Pb2+ and, consequently, do not allow By increasing the BHA concentration three times (3 × 10−4 mol/L),
the anion of collector to approach the Pb2+ site. Furthermore, Pb(OH)2 recovery is favored in all cases, achieving maximum recoveries of ap-
is highly hydrophilic and nullifies any hydrophobic effect caused by proximately 80% in the pH range of 7–9.
collector adsorption. As for the finer fraction of cerussite (−38+25 µm), recovery de-
creases in all cases when using 3 × 10−4 and 10−4 mol/L of BHA and
OHA, respectively. These behaviors can be explained from the point of
3.3. Contact angle measurements of galena and pyrite view that finer particles have a larger specific surface area (334 cm2/g),
approximately twice as large as the medium size fraction (153 cm2/g),
Fig. 6 illustrates the contact angle developed by galena and pyrite in and therefore, they require larger quantities of collector. However, the
the presence of hydroxamic acids. In the case of galena, higher contact figure shows that by increasing the concentration to 5 × 10−4 mol/L of
angles were obtained with OHA, compared to those obtained with BHA. BHA and 3 × 10−4 mol/L of OHA, the recovery is very similar to that
As a result, high hydrophobicity translates into greater PbS recoveries, obtained with 3 × 10−4 mol/L BHA and 10−4 mol/L OHA. This be-
as shown by the microflotation results presented above. The largest havior suggests that the phenomenon that may be governing flotation is
contact angle was obtained at pH 8, 49° and 53°, with BHA and OHA, the low probability of bubble-particle collision (Trahar, 1981), attrib-
respectively. uted to the fine particle size. According to the above, floatability of fine
In the case of pyrite conditioned with OHA, the contact angles ob- cerussite and consequently, its recovery, are significantly affected, even
tained were 54°, 56° and 31° for pH 5, 8 and 10, respectively. The de- though the concentration of collector was significantly increased.
crease in hydrophobicity at pH 10 is due to the massive presence of iron Comparing the recoveries of fine cerussite (−38+25 µm) with BHA
hydroxides on its surface. Iron hydroxide gives hydrophilic character to and OHA, higher recoveries are clearly observed when OHA was used.
pyrite and, consequently, inhibits its flotation (Senior and Trahar, This behavior suggests OHA can reduce the surface tension of the
1991). It should be noted that the pyrite showed a practically null aqueous solution more than BHA and, consequently, generates smaller
contact angle when using BHA, due to the weak interaction that oc- and a larger number of bubbles, which favors the flotation rate constant
curred between the bubble and the pyrite sample. This low hydro- of fines.
phobicity translates into a low recovery, as evidenced by the

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M.A. Elizondo-Álvarez, et al. Minerals Engineering 155 (2020) 106456

Fig. 6. Contact angle generated at the gas/

solid/liquid contact. PbS pre-conditioned
with NaNO3 (10−3 mol/L) and conditioned
with BHA (10−4 M): (a) pH 5, (b) pH 8 and
(c) pH 10; PbS pre-conditioned with NaNO3
(10−3 mol/L) and conditioned with OHA
(10−4 M): (d) pH 5, (e) pH 8 and (f) pH 10;
FeS2 conditioned in OHA (10−4 M): (g) pH
5, (h) pH 8 and (i) pH 10. The measurements
were carried out at 25 °C.

3.5. Effect of pH on the adsorption of BHA and OHA on cerussite recoveries (around 90%) at these two pH values. This behavior is
probably due to the fact that with 75% adsorption, the particles are
Fig. 8 shows the adsorption curves of BHA and OHA onto cerussite. hydrophobic enough to be floated and recovered.
In general, it is observed that this mineral is capable of adsorbing a Interestingly, the recovery of cerussite with OHA decreases to 64%
higher amount of OHA (Fig. 8b) than BHA (Fig. 8a). The figure shows (see Fig. 7b) at pH 10, while adsorption remains relatively high, around
that the adsorption of benzohydroxamate is adversely affected by the 65% (see Fig. 8b). The reason of this behavior will be discussed later.
increase in pH. These results corroborate the behavior of cerussite re-
covery curve (−106+75 µm, 10−4 mol/L BHA), obtained in the mi- 3.6. Contact angle measurements of cerussite
croflotation measurements (see Fig. 7a).
As for the case of OHA, the highest adsorption percentage is ob- In order to corroborate the measurements of cerussite microflota-
tained at pH 9 (about 85%), followed by pH 8 (75%), and finally pH 10 tion and adsorption of collectors BHA and OHA, presented and dis-
(65%). It should be noted that the difference between pH 8 and 9 is cussed above, a series of contact angle experiments were designed. The
about 10% adsorption. Nevertheless, in the microflotation measure- results obtained are presented in Fig. 9. In general, higher contact an-
ments (see Fig. 7b), no significant difference was observed in cerussite gles were obtained with OHA (10−4 mol/L) compared to BHA

Fig. 7. Effect of pH and particle size on the recovery of cerussite (−106+75 and −38+25 µm) using: (a) BHA (10−4, 3 × 10−4 and 5 × 10−4 mol/L) and (b) OHA
(10−4 and 3 × 10−4 mol/L). The measurements were carried out at 25 °C. The cerussite was floated for 1 min.

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M.A. Elizondo-Álvarez, et al. Minerals Engineering 155 (2020) 106456

Fig. 8. Effect of pH on the adsorption of: (a) benzohydroxamate (10−4 mol/L) and (b) octanohydroxamate (10−4 mol/L) onto cerussite: 1 g (−106+75 µm)/50 mL.
The measurements were carried out at 25 °C.

(3 × 10−4 mol/L). In both cases, the largest contact angle was obtained
at pH 8, 58° and 69° with BHA and OHA, respectively. These contact
angles decrease at pH 5 and pH 10. The low hydrophobicity observed at
pH 5 and 10 results in lower recovery, as evidenced by the micro-
flotation results presented above.
As mentioned earlier, cerussite is capable of adsorbing 65% of OHA,
although its recovery is limited. Fig. 9 shows that the contact angle with
10−4 mol/L OHA decreases from 69° to 41° when the pH increases from
8 to 10. According to the thermodynamic modeling of the PbCO3-H2O-
CO2-O2 system (see Fig. 10), this decrease in hydrophobicity is probably
due to the presence of hydrocerussite (Pb3(CO3)2(OH)2) (Keim et al.,
2017), hydrophilic in nature, on its surface. According to the literature
(López-Valdivieso et al., 1986), this species has a large surface area and
is capable of adsorbing abundant amounts of collector.

3.7. Effect of pH in the flotation of anglesite

Fig. 10. Species distribution diagram of the PbCO3-H2O-CO2-O2 system (10 g
Microflotation of anglesite was conducted using increasing dosages PbCO3/L) at 25 °C open to the atmosphere (79.02% N2, 20.94% O2, 0.03%
of collectors, as presented in Fig. 11. The figure shows that an increase CO2).
in the OHA collector dosage leads to an increase in recovery at slightly
acid conditions. However, this behavior is not observed when anglesite that in the pH range from 7 to 5, Pb2+ dissolves from the crystal net-
is floated using benzohydroxamic acid. This behavior is probably due to work of anglesite and reacts with the benzohydroxamate and octano-
less strong bonds between the benzohydroxamate with the lead sites of hydroxamate anions to form Pb-benzohydroxamate and Pb-octanohy-
the mineral, compared to those formed by the octanohydroxamate. droxamate precipitates, respectively, which are physically readsorbed
In accordance with the experimental results obtained, it is suggested in the vicinity of the anglesite surface, resulting in a hydrophobic

Fig. 9. Contact angle generated at the gas/solid/liquid contact. PbCO3 conditioned with BHA (3 × 10−4 mol/L): (a) pH 5, (b) pH 8 and (c) pH 10; PbCO3 conditioned
with OHA (10−4 mol/L): (d) pH 5, (e) pH 8 and (f) pH 10. The measurements were carried out at 25 °C.

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M.A. Elizondo-Álvarez, et al. Minerals Engineering 155 (2020) 106456

Fig. 11. Effect of pH and presence of sulfate (1000 mg/L) on the recovery of anglesite (−106+75 µm) using: (a) BHA (5 × 10−4 and 10−3 mol/L) and (b) OHA
(10−4, 3 × 10−4, and 5 × 10−4 mol/L). The measurements were carried out at 25 °C. The anglesite was floated for 1 min.

surface. The recovery results suggest that there is preferential adsorp-

tion of OHA over BHA, probably due to the less strong bonds formed by
the latter or due to stearic factors. It is important to emphasize that
being below the pKa of the OHA, where there is a lower concentration
of octanohydroxamate anions, higher concentration of collector is re-
quired to obtain good recoveries.
On the other hand, anglesite recovery is adversely affected when the
pH was increased from 7 to 10, even though the dosage of OHA was
increased from 10−4 to 5 × 10−4 mol/L. According to the thermo-
dynamic modelling of the PbSO4-H2O-CO2-O2 system (see Fig. 12), this
decrease in recovery is probably due to the presence of leadhillite
(Pb4(CO3)2(SO4)(OH)2) and hydrocerussite (Pb3(CO3)2(OH)2) on its
surface, which have hydrophilic properties and predominate in this pH
region.
It is observed in Fig. 11 that the use of sodium sulfate increases
recoveries under slightly acid conditions. The use of sulfate as a
common ion added to the solution, decreases the solubility of anglesite,
as observed in Fig. 13. Therefore, by avoiding dissolution, there are
more Pb2+ sites available on the anglesite surface to bond with octa- Fig. 13. Effect of the presence of sulfate on anglesite dissolution: 1 g
nohydroxamate anions and provide enough degree of hydrophobicity, (−106+75 μm)/200 mL of NaNO3 (10−3 mol/L) or Na2SO4 (1000 mg/L) so-
without requiring large amounts of collector. lution (pH 5); room temperature.

4. Conclusions

The OHA collector showed a better performance in the flotation of

galena, cerussite and anglesite, compared to that observed with BHA.
This behavior is probably due to the less strong bonds with the lead
sites developed by the benzohydroxamate, compared to those devel-
oped by the octanohydroxamate.
OHA showed a significant loss of selectivity against the pyrite, al-
though not against the quartz. Therefore, its use will depend on the
nature of the gangue present in the ore to be treated.
In order to find out a more selective window when using OHA as
collector, it will be necessary to study the performance of some pyrite
depressants.
The recoveries of anglesite and cerussite were affected under alka-
line conditions. Thermodynamic modeling suggests that the observed
behavior is due to the presence of hydrophilic species on their surfaces,
the hydrocerussite (Pb3(CO3)2(OH)2) and the leadhillite
(Pb4(CO3)2(SO4)(OH)2).
Fig. 12. Species distribution diagram of the PbSO4-H2O-CO2-O2 system (10 g Due to its high selectivity against pyrite and quartz, BHA may be
PbSO4/L) at 25 °C open to the atmosphere (79.02% N2, 20.94% O2, 0.03% considered a potential candidate to replace xanthate in the flotation of
CO2).

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M.A. Elizondo-Álvarez, et al. Minerals Engineering 155 (2020) 106456

galena and cerussite. Also, its use would mitigate the impact on health Herrera-Urbina, R., Sotillo, F.J., Fuerstenau, D.W., 1999. Effect of sodium sulfide addi-
and the environment that results from the use of xanthates. tions on the pulp potential and amyl xanthate flotation of cerussite and galena. Int. J.
Miner. Process. 55 (3), 157–170.
Hu, Y., Wu, M., Liu, R., Sun, W., 2020. A review on the electrochemistry of galena flo-
CRediT authorship contribution statement tation. Miner. Eng. 150, 106272.
Jones, M.H., Woodcock, J.T., 1979. Control of laboratory sulphidization with a sulphide
ion-selective electrode before flotation of oxidized lead-zinc-silver dump material.
Martha Araceli Elizondo-Álvarez: Visualization, Investigation, Int. J. Miner. Process. 6 (1), 17–30.
Writing - original draft. Alejandro Uribe-Salas: Supervision, Keim, M.F., Gassmann, B., Markl, G., 2017. Formation of basic lead phases during fire-
Resources, Writing - review & editing. Fabiola Nava-Alonso: setting and other natural and man-made processes. Am. Mineral. 102 (7), 1482–1500.
Kelebek, S., Yoruk, S., 2002. Bubble contact angle variation of sulphide minerals in re-
Resources, Writing - review & editing. lation to their self-induced flotation. Colloids Surf., A 196 (2), 111–119.
Lee, J.S., Nagaraj, D.R., Coe, J.E., 1998. Practical aspects of oxide copper recovery with
Declaration of Competing Interest alkyl hydroxamates. Miner. Eng. 11 (10), 929–939.
Lee, K., Archibald, D., McLean, J., Reuter, M.A., 2009. Flotation of mixed copper oxide
and sulphide minerals with xanthate and hydroxamate collectors. Miner. Eng. 22 (4),
The authors declare that they have no known competing financial 395–401.
interests or personal relationships that could have appeared to influ- Lenormand, J., 1974. The adsorption of potassium octyl hydroxamate on malachite, PhD
Thesis, McGill University, Montreal, Canadá.
ence the work reported in this paper. Lenormand, J., Salman, T., Yoon, R.H., 1979. Hydroxamate flotation of malachite. Can.
Metall. Q. 18 (2), 125–129.
Acknowledgments Li, Z., Rao, F., Song, S., Uribe-Salas, A., López-Valdivieso, A., 2019. Reexamining the
adsorption of octyl hydroxamate on malachite surface: Forms of molecules and an-
ions. Miner. Process. Extr. Metall. Rev. 1–9.
The authors thank the support received by the personnel of Liu, J., Hu, Z., Liu, G., Huang, Y., Zhang, Z., 2019. Selective flotation of copper oxide
Cinvestav-IPN Unidad Saltillo as well as the scholarship awarded by minerals with a novel amino-triazole-thione surfactant: a comparison to hydroxamic
acid collector. Miner. Process. Extr. Metall. Rev. 1–11.
CONACYT (México). López-Valdivieso, A., Herrera-Urbina, R., Olivas, S.A., Fuerstenau, D.W., 1986. Química
superficial y flotación de cerusita y anglesita (in Spanish). Geomimet 13 (140),
Appendix A. Supplementary data 38–62.
Marabini, A., Cozza, C., 1988. A new technique for determining mineral-reagent chemical
interaction products by transmission IR spectroscopy: Cerussite-xanthate system.
Supplementary data to this article can be found online at https:// Colloids Surf. 33 (C), 35–41.
doi.org/10.1016/j.mineng.2020.106456. Marabini, A.M., Barbaro, M., Passariello, B., 1989. Flotation of cerussite with a synthetic
chelating collector. Int. J. Miner. Process. 25 (1–2), 29–40.
Marion, C., Jordens, A., Li, R., Rudolph, M., Waters, K.E., 2017. An evaluation of hy-
References droxamate collectors for malachite flotation. Sep. Purif. Technol. 183, 258–269.
Meng, Q., Feng, Q., Shi, Q., Ou, L., 2015. Studies on interaction mechanism of fine
Bulatovic, S.M., 2010. Flotation of oxide copper and copper cobalt ores. In: Handbook of wolframite with octyl hydroxamic acid. Miner. Eng. 79, 133–138.
Flotation Reagents: Chem. Theor. Pract., ed. Elsevier, Amsterdam, pp. 47–65. Montgomery, D.C., 2001. Experiments with a single factor: The analysis of variance. In:
Castro, S., Goldfarb, J., Laskowski, J., 1974. Sulphidizing reactions in the flotation of Design and Analysis of Experiments, ed. Montgomery, D.C., New York, pp. 60–119.
oxidized copper minerals, I. Chemical factors in the sulphidization of copper oxide. Nagaraj, D.R., Farinato, R.S., 2016. Evolution of flotation chemistry and chemicals: a
Int. J. Mineral Process. 1 (2), 141–149. century of innovations and the lingering challenges. Miner. Eng. 96–97, 2–14.
Corin, K.C., Kalichini, M., Connor, C.T., Simukanga, S., 2017. The recovery of oxide Natarajan, R., 2013. Hydroxamic acids as chelating mineral collectors. In: Gupta, S.P.
copper minerals from a complex copper ore by sulphidisation. Miner. Eng. 102, (Ed.), Hydroxamic Acids: A Unique Family of Chemicals with Multiple Biological
15–17. Activities. Springer, Berlin Heidelberg, Berlin, Heidelberg, pp. 281–307.
Das, K.K., Pradip, 1987. Flotation of oxidised chalcopyrite with hydroxamate collectors. Önal, G., Bulut, G., Gül, A., Kangal, O., Perek, K.T., Arslan, F., 2005. Flotation of Aladaǧ
In: Proceedings of the Int. Congr. Phenomena in Biotechnology and Materials, Boston, oxide lead-zinc ores. Miner. Eng. 18(2 SPEC. ISS.) 279–282.
pp. 305–316. Park, K., Park, S., Choi, J., Kim, G., Tong, M., Kim, H., 2016. Influence of excess sulfide
Davidson, M., Kelebek, S., 2014. Effect of a mixed-collector system on flotation of a mixed ions on the malachite-bubble interaction in the presence of thiol-collector. Sep. Purif.
copper ore through statistical analysis. In: Proceedings of the XXVII International Technol. 168, 1–7.
Mineral Processing Congress, Santiago. Parker, G.K., Buckley, A.N., Woods, R., Hope, G.A., 2012. The interaction of the flotation
Dávila-Pulido, G.I., Uribe-Salas, A., 2014. Effect of calcium, sulphate and gypsum on reagent, n-octanohydroxamate, with sulfide minerals. Miner. Eng. 36–38, 81–90.
copper-activated and non-activated sphalerite surface properties. Miner. Eng. 55, Plapinger, R.E., 1959. Ultraviolet absorption spectra of some hydroxamic acids and hy-
147–153. droxamic acid derivatives. J. Org. Chem. 24 (6), 802–804.
Elizondo-Álvarez, M.A., Dávila-Pulido, G.I., Bello-Teodoro, S., Uribe-Salas, A., 2019. Role Pradip, Fuerstenau, D.W., 1983. The adsorption of hydroxamate on semi-soluble mi-
of pH on the adsorption of xanthate and dithiophosphinate onto galena. Can. Metall. nerals. Part I: Adsorption on barite, calcite and bastnaesite. Colloids Surf. 8 (2),
Q. 58 (1), 107–115. 103–119.
Elizondo-Álvarez, M.A., Flores-Álvarez, J.M., Dávila-Pulido, G.I., Uribe-Salas, A., 2017. Rey, M., 1958. Differential flotation of lead-zinc ores. In: Proceedings of the International
Interaction mechanism between galena and calcium and sulfate ions. Miner. Eng. Mineral Dressing Congress, Stockholm, pp. 525–537.
111, 116–123. Rey, M., Chataignon, P., Formanek, V., 1950. The influence of certain inorganic salts on
Espiritu, E.R.L., Naseri, S., Waters, K.E., 2018. Surface chemistry and flotation behavior of the flotation of lead carbonate. AIME Trans. 187, 1126.
dolomite, monazite and bastnäsite in the presence of benzohydroxamate, sodium Rey, M., Chataignon, P., Formanek, V., 1954. Flotation of oxidised ores of lead, copper
oleate and phosphoric acid ester collectors. Colloids Surf., A 546, 254–265. and zinc. Inst. Mining Metall. Trans. 63, 541–548.
Espiritu, E.R.L., Waters, K.E., 2018. Flotation studies of monazite and dolomite. Miner. Rey, M., Formanek, V., 1960. Some factors affecting selectivity in the differential flotation
Eng. 116, 101–106. of lead-zinc ores, particularly in the presence of oxidised lead minerals. In:
Exner, O., Kakáč, B., 1963. Acyl derivatives of hydroxylamine. VIII. A spectroscopic study Proceedings of the International Mineral Processing Congress, the Institution of
of tautomerism of hydroxamic acids. Collect. Czech. Chem. Commun. 28 (7), Mining and Metallurgy, London, pp. 343–353.
1656–1663. Rinelli, G., Marabini, A.M., 1973. Flotation of zinc and lead oxide - Sulphide ores with
Fleming, M., 1952. Effects of alkalinity on the flotation of lead minerals. AIME Trans. 193, chelating agents. In: Jones, M.J. (Ed.), 10th International Mineral Processing
1231–1236. Congress, London, pp. 493–521.
Fleming, M., 1953. Effects of soluble sulphide in the flotation of secondary lead minerals. Senior, G.D., Trahar, W.J., 1991. The influence of metal hydroxides and collector on the
Trans. IMM 521–548. flotation of chalcopyrite. Int. J. Miner. Process. 33 (1), 321–341.
Fuerstenau, D.W., Herrera-Urbina, R., McGlashan, D.W., 2000. Studies on the applic- Somasundaran, P., Moudgil, B.M., 1987. Collectors for sulfide mineral flotation. In:
ability of chelating agents as universal collectors for copper minerals. Int. J. Miner. Somasundaran, P., Moudgil, B.M. (Eds.), Reagents in Mineral Technology, New York,
Process. 58 (1), 15–33. NY, USA, pp. 335–370.
Fuerstenau, D.W., Pradip, 1984. Mineral Flotation with hydroxamate collectors. In: Jones, Somasundaran, P., Nagaraj, D.R., 1984. Chemistry and applications of chelating agents in
M.J., Oblatt, R. (Eds.), Reagents in Mineral Industry. The Institution of Mining and flotation and flocculation. In: Jones, M., Oblatt, R. (Eds.), Reagents in Mineral
Metallurgy, London, pp. 161–172. Industry. Institution of Mining and Metallurgy, London, pp. 209–219.
Hauser, C.R., Renfrow, W.B., 1939. Benzohydroxamic acid. Org. Synth. 19 (15), 15–17. Somasundaran, P., Nagaraj, D.R., Kuzugudenli, O.E., 1993. Chelating agent for selective
Herrera-Urbina, R., 1980. Flotation characteristics of oxide lead minerals with amine as flotation of minerals. In: Proceedings of the XVIII lnternational Mineral Processing
collector. MSc Thesis. South Dakota School of Mines and Technology. Congress, Sydney, pp. 577–585.
Herrera-Urbina, R., 2003. Recent developments and advances in formulations and ap- Tijsseling, L.T., Dehaine, Q., Rollinson, G.K., Glass, H.J., 2019. Flotation of mixed oxide
plications of chemical reagents used in froth flotation. Miner. Process. Extr. Metall. sulphide copper-cobalt minerals using xanthate, dithiophosphate, thiocarbamate and
Rev. 24 (2), 139–182. blended collectors. Miner. Eng. 138, 246–256.
Trahar, W.J., 1981. A rational interpretation of the role of particle size in flotation. Int. J.

9
M.A. Elizondo-Álvarez, et al. Minerals Engineering 155 (2020) 106456

Miner. Process. 8 (4), 289–327. Sci. 425, 796–802.

Türkel, N., 2011. Stability of metal chelates of some hydroxamic acid ligands. J. Chem. Yao, W., Li, M., Cui, R., Jiang, X., Jiang, H., Deng, X., Li, Y., Zhou, S., 2018. Flotation
Eng. Data 56 (5), 2337–2342. behavior and mechanism of anglesite with salicyl hydroxamic acid as collector. JOM
Wills, B.A., Finch, J.A., 2016. Froth Flotation. In: Finch, J.A., Wills, B.A. (Eds.), Wills' 70 (12), 2813–2818.
Mineral Processing Technology (Eight Edition), Boston, pp. 265–380. Yao, W., Li, M., Zhang, M., Cui, R., Jiang, H., Li, Y., Zhou, S., 2019. Lead recovery from
Wu, D., Ma, W., Mao, Y., Deng, J., Wen, S., 2017. Enhanced sulfidation xanthate flotation zinc leaching residue by flotation. JOM 71 (12), 4588–4593.
of malachite using ammonium ions as activator. Sci. Rep. 7 (1), 2086. Zhu, Y., Sun, C., Wu, W., 2007. A new synthetic chelating collector for the flotation of
Xu, L., Tian, J., Wu, H., Lu, Z., Yang, Y., Sun, W., Hu, Y., 2017. Effect of Pb2+ ions on oxidized-lead mineral. J. Univ. Sci. Technol. Beijing: Mineral Metall. Mater. (Eng Ed)
ilmenite flotation and adsorption of benzohydroxamic acid as a collector. Appl. Surf. 14 (1), 9–13.

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