Review clay flotation - Jeldres et al., 2019.pdf

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Applied Clay Science
journal homepage: www.elsevier.com/locate/clay
Review article
The effect of clay minerals on the process of flotation of copper ores - A
critical review
Ricardo I. Jeldresa,⁎
, Lina Uribeb
, Luis A. Cisternasa
, Leopoldo Gutierrezc
, Williams H. Leivaa,d
,
Julio Valenzuelae
a
Departamento de Ingeniería Química y Procesos de Minerales, Universidad de Antofagasta, PO Box 170, Antofagasta, Chile
b
Department of Mining Engineering, Universidad de Talca, Talca, Chile
c
Department of Metallurgical Engineering, Universidad de Concepción, Concepción, Chile
d
CSIRO Chile, International Center of Excellence, Las Condes, Santiago, Chile
e
Departamento de Ingeniería Química, Universidad Católica del Norte, Antofagasta, Chile
A R T I C L E I N F O
Keywords:
Clays
Copper
Flotation
Seawater
Rheology
Reagents
A B S T R A C T
The presence of clay leads to low recoveries in the process of flotation of copper ores which is also reflected in a
decrease of the concentrates grades. Due to this, the scientific interest in studying the effect and mechanisms of
action of clay minerals in the flotation process has increased, which has resulted in a better understanding of the
physicochemical foundations behind. This paper reports a comprehensive bibliographic review in which the
mechanisms through which clay minerals cause harmful effects in the flotation process are explained. The main
studies reported to date are systematised and classified in five topics in this paper: i) rheology of clayey pulps; ii)
specific reagents for dispersing clays; iii) interactions between clays and valuable minerals in saline media; iv)
mechanical entrainment and v) copper oxidation on clay coating. The strategies currently used to improve the
processing of clayey mineral pulps have been insufficient to achieve optimal operational results, so the following
work is intended to promote the development of new technologies that allow improving the performance of
these processes. In this review, research opportunities which consider the use of nanoparticles, based reagents
organic polymers, technologies using seawater inter exposed.
1. Introduction
The mining industry is continually facing operational challenges
that threaten the sustainability of the sector. It is common that the
grade of minerals has decreased, so their processing becomes more
complicated. In many cases, it is necessary to perform demanding
grinding to achieve an adequate liberation of valuable minerals, which
inevitably brings unfavourable consequences such as high energy con-
sumption, and generation of significant quantities of fine and ultra-fine
particles. The gangue also contains complex minerals like clays that are
part of numerous deposits, including copper, platinum, nickel, and
potash ores (Senior and Thomas, 2005). Clay minerals are phyllosili-
cates that have an anisotropic structure and usually encompass col-
loidal sizes. They are composed of tetrahedral silica (T) and octahedral
alumina (O) layers, which join with specific proportions 1: 1 (TO) and
2: 1 (TOT) (see Fig. 1), presenting two surfaces that are crystal-
lographically different: the faces, which tend to show anionic charge,
and the edges, that present anionic or cationic charge depending on the
pH (Lagaly, 1978). Clays can be classified in two types according to
their ability to absorb water, swelling and non-swelling clays. Kaolinite
is a non-swelling clay mineral, which adopts layers with a 1:1 structure
and has a general composition of Al2Si2O5(OH)4. It is characterised by
the predominance of Al+3
in its octahedral sites, where isomorphic
substitutions occur with Mg+2
, Fe+3
, Ti+4
, and V+3
(Rand and Melton,
1977). Another clay mineral like montmorillonite has a 2:1 structure
with a general composition described by the following composition
(My
+
x nH2O)(Al2−y
+3
Mgy
+2
)Si4
+4
O10(OH)2 (Lagaly, 1978).
Processing of high clay ores is usually related to negative effects in
particular in the flotation stages. A good description was made recently
in the work by Chen and Peng (2018), who developed a general review
about the mechanisms and behaviour of clays in mineral flotation. The
background they presented is general and useful for any situation in
which clays appear since most of the challenges are transversal for any
valuable mineral that is processed. In this sense, the issues are generally
related to the froth stability, overconsumption of reagents, mechanical
entrainment, or even the pulp rheological properties can change to
https://doi.org/10.1016/j.clay.2019.01.013
Received 5 July 2018; Received in revised form 15 January 2019; Accepted 20 January 2019
⁎
Corresponding author.
E-mail address: ricardo.jeldres@uantof.cl (R.I. Jeldres).
Applied Clay Science 170 (2019) 57–69
0169-1317/ © 2019 Elsevier B.V. All rights reserved.
T

prohibitive conditions for the operation (Bulatovic, 2007; Goh et al.,
2011; Ata, 2012; Ndlovu et al., 2013; Gutierrez and Melipichun, 2014).
In the particular situation of copper flotation, various minerals can be
found like chalcopyrite (CuFeS2), chalcocite (Cu2S), covellite (CuS),
bornite (Cu5FeS4), and enargite (Cu3AsS4). Farrokhpay and Ndlovu
(2013) found that the chalcopyrite recovery is affected by phyllosili-
cates in the following order talc > montmorilonite > muscovite >
kaolinite > illite, with talc and montmorillonite being the ones that
have the strongets negative effect, most probably because of the sig-
nificant differences in crystallinity, cation exchange capacity, and
swelling degree (Farrokhpay and Ndlovu, 2013) (Fig. 2). Uribe et al.
(2016) studied the depressing effect of clay minerals on the floatability
of chalcopyrite using PAX as collector through flotation tests, induction
time and settling-turbidity measurements. It was found that the de-
pressing effect of clay minerals was stronger at pH 10 which was cor-
related to a possible effect of Ca+2
from lime on the process of het-
erocoagulation between clay minerals and chalcopyrite. Coating of
bubbles with clays was also detected and proposed as a mechanism that
might explain the depressing effect of clays on the floatability of chal-
copyrite. Further research is needed to propose a mechanism that ex-
plains this phenomenon.
Some strategies to reduce the negative effect of clay minerals on the
process of flotation are the use of a variety of reagents such as rheology
modifiers and/or the use of reagents that adsorb on the surfaces of clay
particles thus preventing them to attach to valuable minerals. A dif-
ferent alternative is to lower the pulp solids concentration to obtain low
viscosities and yield stresses. However, this methodology may lead to
reduce metal production. Using physical methods to remove clays be-
fore the flotation stage is another possibility. Recent studies conducted
with coal showed that a high intensity agitation during conditioning
improve the performance when kaolinite is present (Yu et al., 2017a,
2017b). On the other hand, Oats et al. (2010) and Quast et al. (2008)
found that the desliming by hydrocyclones could be more effective than
the addition of dispersants. However, a huge amounts of valuable mi-
neral may be lost with the slimes, so the recommendation is that the
method can only be applied when the quantity of valuable minerals is
negligible. In the case of ultrasonic treatment, Celik et al. (1998) stu-
died showed that for boron flotation in the presence of high con-
centrations of clay minerals ultrasonic pretreatment showed promising
benefits in the lab trials, but they indicate that the application of this
technique at an industrial scale can be challenging when compared to
intense agitation and hydrocyclone desliming.
An additional challenge is to understand the clays interaction in
saline environments, like seawater (Uribe et al., 2017; Hernández et al.,
2012, 2015; Ordóñez et al., 2013; Cisternas, 2014; Goñi et al., 2015;
Jeldres et al., 2016, 2017a, 2017b; Quezada et al., 2017; Cisternas and
Gálvez, 2018; Costine et al., 2018; Romero et al., 2018). A highly saline
environment modifies the inter-surface interactions that govern the
pulp stability, and the impact is mainly reflected by the changes in the
electrostatic and hydration forces. A strong compression of the ionic
cloud surrounding the active sites, either from the particle surface or
chemical reagents may act, but also, the water molecules undergo a
rearrangement that depends if the ions have a maker or breaker char-
acter (Hancer et al., 2001; Jeldres et al., 2014). Maker ions like Li+
,
Na+
, Mg+2
, and Ca+2
are small and have a strong electric field, causing
that the water molecules around these ions to become highly struc-
tured. Otherwise, breaker ions like Cs+
, K+
, Cl−
and I−
generally have
a larger size and weaker electric fields, which is considered insufficient
to provide any structure to the water molecules that surround them
(Moreira and Firoozabadi, 2010; Ozdemir et al., 2011).
There are some important differences between the flotation of
copper ores and other applications. First, several types of mineral spe-
cies that contain copper can be found (CuFeS2, Cu2S, CuS, Cu5FeS4, and
Cu3AsS4, among others) which respond differently to the oxidizing and
reducing conditions of the particulate system. As a result, some ions
such a copper, iron and arsenic can be released and induce hetero-
coagulation between clay minerals and valuable species. Secondly, the
presence of pyrite in copper ores requires the use of lime in such a way
as to avoid the flotation of this iron sulfide mineral. Previous studies
show that calcium generates an effect that boosts the negative effect of
clays in the flotation process of copper ores. This is an important dif-
ference compared to other applications. Finally, copper ores contain a
great variety of different types of clay minerals and phyllosilicates,
which implies a complex system which is different to other applica-
tions. In the present review, we analyse the principal researches de-
veloped to date, which deals with the impact of clay minerals on the
flotation of copper ores. Particular emphasis is placed in five issues: i)
rheology of clayey pulps, ii) use of clay-specific reagents, iii) clay in-
teraction in saline medium, iv) mechanical entrainment, and v) impact
of copper oxidation on clay coating. Finally, the main research oppor-
tunities offered by this subject are presented.
2. Impact of clays on copper ore flotation
2.1. Rheological behaviour of clay suspensions
The presence of clay minerals leads to rheological challenges, which
are generally a significant problem in flotation operations (Schubert,
2008; Ndlovu et al., 2011; Farrokhpay, 2012). When mineral pulps
Fig. 1. Schematic representation of clays with structures 1:1 and 2:1; O and T
refer to octahedral and tetrahedral layers, respectively.
Phyllosillicate addition, %
0 5 10 15 20 25 30 35
Cu
grade,
%
20
22
24
26
28
30
32
34
36
Illite
Kaolinite
Muscovite
Montmorillonite
Talc
Fig. 2. Effect of phyllosilicates on the copper grade in chalcopyrite flotation
(adapted from Farrokhpay and Ndlovu, 2013).
R.I. Jeldres et al. Applied Clay Science 170 (2019) 57–69
58

display a non-Newtonian behavior, properties like viscosity and yield
stress have a significant importance in the hydrodynamics of the pulps,
and consequently in all the physical sub-processes that take place
within the flotation cell, which ultimately control the process effi-
ciency. Bakker et al. (2009) and Shabalala et al. (2011) showed that
both bubble size and gas hold-up decreased significantly with the pulp
solid concentration. The authors explained this finding by indicating
that the high value of yield stress led to the formation of a kind of ‘pulp
cavern’ around the impeller. This logically generated a poor bubble
dispersion through the cell. Additionally, an interesting relationship
was found between the pulp rheology and the froth stability, wherein
Farrokhpay and Zanin (2011) found that froth stability increases at
lower pH values, which agrees with the increase in pulp viscosity.
The rheological behaviour of clayey pulps varies in terms of thixo-
tropy, viscoelasticity, and yield stress, and fundamentally depends on
the type of clay, nature of the interchangeable cation, and medium
conditions (Paineau et al., 2011; Jeldres et al., 2017c). For example,
some papers indicate thatpH and the presence of salts substantially alter
the rheological behaviour of different types of clayey slurries like,
montmorillonite and kaolinite among others (Brandenburg and Lagaly,
1988; Cruz et al., 2013; Tombácz and Szekeres, 2004; Basnayaka et al.,
2017; Jeldres et al., 2017c). Cruz et al. (2015) showed that the main
rheological differences between clay minerals are explained by ana-
lysing how the particles are associated. With the support of Cryo-SEM
images, the authors show remarkable structural differences depending
on whether they correspond to bentonite or kaolinite. While the ag-
gregates formed by bentonite are structures in the shape of ‘honeycomb’
or ‘houses of cards’ where the E-E and E-F bond dominate (Fig. 3a),
kaolinite aggregates mainly show structures of FeF and E-E types
(Fig. 3b). No honey-comb-like network structure was observed in the
pulp of ore-kaolinite mixtures.
Zhang and Peng (2015) performed rheograms for mixtures of copper
minerals (chalcopyrite) with three different types of clay minerals, in
this case, bentonite and two kinds of kaolinite. The first result, and as it
was expected, was that the highest increase in pulp viscosity generated
by bentonite which was explained by the 2:1 structure that produces a
higher viscosity than kaolinite (1:1 structure). Regarding the two kao-
linite types, the one whose structure was less crystalline generated in
turn higher rheology. The authors found a direct correlation between
the viscosity of the pulp (at 100 s−1
) and the copper recovery in flo-
tation tests, with bentonite causing the most damaging effect (see
Fig. 4). In any case, some issues in the rheological measurements sug-
gest that the reported values are debatable. For example, the timing to
perform the rheograms was very short (only 100 s), so thixotropy could
hide the real rheological values; no treatment is mentioned to avoid the
effects of coarse particles sedimentation, which could have an impact
during the test due to fine mineral drag or even disturbances for an
eventual sediment at the bottom of the cup; nor was the value of the
shear rate determined in which the Taylor vortices could appear. For
this reason, the results should be analysed with caution; however, at a
qualitative level, the information is useful.
Farrokhpay et al. (2016) indicated that the main parameter to
evaluate the difference between clays is through their ‘swelling’ or ‘non-
swelling’ properties. The authors found that clays that have a higher
capacity to absorb water and increase their size are the ones that reduce
the efficiency in the flotation stages, while clays that do not have this
quality (such as kaolinite) generate a minor impact either in rheology,
froth stability, or recovery of valuable ore. However, these results are
not a general trend, since other authors have shown a considerable
impact caused by kaolinite. For example, Forbes et al. (2014) conducted
copper flotation studies using synthetic minerals composed of mixtures
of quartz, chalcopyrite, and kaolinite, considering the concentration of
the latter as the variable. An increase in the proportion of kaolinite
meant an evident reduction in the chalcopyrite recovery (Fig. 5), but
this also caused an intense increase in viscosity, moving away from a
Newtonian behaviour. The authors also observed that the detrimental
effect of kaolinite is exacerbated at pH < 6 (Fig. 6); however, only a
30/70 ratio of quartz/kaolinite was used, so it is possible that the ef-
fects are different with other gangue compositions. For that matter, it
would have been interesting to apply techniques to obtain a statistical
model like soft computing technique or even a factorial experimental
design. These techniques allow the analysis of each variable in different
Fig. 3. Comparison of the structural networks formed by a) bentonite-ore mixture and b) kaolinite-ore mixture, in flotation pulps (Cruz et al., 2015).
Clay mineral concentration (wt%)
0 5 10 15
Copper
recovery
(%)
0
20
40
60
80
100
Apparent
viscosity
(cP)
0
20
40
60
80
100
Fig. 4. Effect of clay minerals concentration on copper recovery (empty sym-
bols), and apparent viscosity (solid points) of flotation pulp: snobrite (circle),
kaolinite (triangle), bentonite (square) (adapted from Zhang and Peng, 2015).
59

zones to which the experimental assays were performed. For example.
How do the tests respond to the quartz/clay ratio, but at different pH
values (beyond pH 8).
The complexity of the rheological behaviour is increased when
considering the interaction that arises between clay particles with the
reagents used in flotation. This aspect has been little explored, although
the selectivity and recovery of minerals could be substantially improved
if suitable rheology modifiers are selected, as well as dispersants that
can control the clays detrimental effects (Section 2.2). Cruz et al. (2013)
showed that the use of different pH modifiers could alter the rheological
properties of clay suspensions very differently. The researchers used
lime, sodium carbonate, and sodium hydroxide to reach pH 10 in sus-
pensions of kaolinite and bentonite. While lime promoted the kaolinite
aggregation, sodium carbonate disperses them (Fig. 7a). On the con-
trary, sodium carbonate acts as a coagulating agent instead of a dis-
persant for bentonite suspensions, even generating a more significant
effect than lime. Sodium hydroxide also induces aggregation in bento-
nite suspensions but is having a minor impact on kaolinite (Fig. 7b).
While literature offers a wide range of reports that show the effects
of surfactants on clay rheology (Güngör, 2000; Abu-Jdayil and
Ghannam, 2014; Abu-Jdayil et al., 2016, Magzoub et al., 2017), un-
fortunately, no systematic studies integrate this behaviour with
flotation operations. However, the knowledge that has been generated
can be of great help to propose new guidelines regarding the handling
of reagents. For example, Goodwin and Hughes (2008) showed the ef-
fect of hexadecyltrimethylammonium bromide (HDTAB), which corre-
sponds to a cationic surfactant, on the rheology of two different sus-
pensions of kaolinite with a volumetric fraction of 0.02. In both cases,
the suspensions without surfactant showed a pseudoplastic behaviour,
with the appearance of yield stress, due to the particles networks gen-
erated by interactions between the edges and the faces of the clays.
However, the addition of HDTAB changed the aggregation mechanism
by increasing the face-face interactions and caused the suspensions to
behave under a Newtonian regime. Abu-Jdayil et al. (2016) found that
sodium dodecyl sulfate (SDS) was very effective in modifying the
bentonite rheology. The authors found that in the range of concentra-
tions close to the critical micelle concentration (cmc), the suspension
showed an increase in viscosity and even a certain degree of thixotropy.
However, the addition of cetyltrimethylammonium bromide (CTAB)
significantly reduced the viscosity and changed the behaviour from
shear thinning with yield stress to a pure Newtonian fluid. Desai et al.
(2010) studied the effect of the surfactant concentration (including
anionic, cationic, and non-ionic) on the viscosity of pyrophyllite sus-
pensions. The viscosity, measured at a fixed rate of 60 s−1
, depended
fundamentally on the surfactant charge. The authors said that when the
reagent was anionic (sodium dodecylbenzenesulfonate - SDBS) or non-
ionic (TX-100), there was an increase in viscosity with respect to their
concentration, although the change was much more significant with
TX- 100 (see Fig. 8), in fact with SDBS a plateau was reached. While
with the cationic surfactant (Cetilpiridinium Bromide - CPB) there was
an increase in viscosity, but after a specific value, this began to de-
crease. According to the authors, this was due to the formation of
Cumulative flotation time (min)
0 2 4 6 8
Cumulative
copper
recovery
(%)
0
20
40
60
80
100
0/100
30/70
70/30
100/0
Quartz/kaolinite ratio
Fig. 5. Cumulative copper recovery with time, as a function of different quartz/
kaolinite ratios in the gangue phase, at pH 8 (adapted from Forbes et al., 2014).
Cumulative flotation time (min)
0 2 4 6 8
Cumulative
copper
recovery
(%)
0
20
40
60
80
100
pH 4
pH 6
pH8
pH 10
Fig. 6. Cumulative copper recovery with time, as a function of pH, at a 30/70
quartz/kaolinite ration in the gangue phase (adapted from Forbes et al., 2014).
Shear rate (s-1
)
0 100 200 300
Shear
stress
(Pa)
0
1
2
3
4
5
6
7
8
Natural pH 7.6
NaOH pH 10
Lime pH 10
Na2CO3 pH 10
a)
Shear rate (s-1
)
0 100 200 300
Shear
stress
(Pa)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Natural pH 8.7
NaOH pH10
Lime pH10
Na2CO3 pH10
b)
Fig. 7. Rheograms of clay suspensions in the presence and absence of pH
modifiers: a) kaolinite 30%wt; b) bentonite 5% (adapted from Cruz et al.,
2013).
60

bilayers between the molecules of the adsorbed surfactant. They also
explained that the increase in viscosity produced by the anionic sur-
factant, SDBS, could have been caused by the formation of bridges
between two particles due to the possible presence of calcium ions,
which would be released by the clay. Unfortunately, the authors for-
mulated their explanations considering different concentration ranges
for each surfactant. For example, the non-ionic reagent TX-100 was
analysed regarding the range 0–2 mM approx, but what would have
happened if the concentration reached the same value that was reached
with the cationic reagent CPB (0–10 mM)? For this reason, we believe
that the explanations proposed by the researchers should be re-ana-
lysed.
Undoubtedly, a deeper understanding of this matter is necessary for
the application in flotation operations, where industrial waters usually
have significant levels of hardness, and the primary reagent to modify
the pH is lime (CaO).
In general terms, the effect caused by surfactants on rheology is
diverse and in some cases difficult to understand. These could cause the
system to acquire a Newtonian behaviour, while in other cases a sub-
stantial rheology increase appear. However, this not only depends on
the surfactant characteristics, but also of the nature of the clays and on
the medium conditions.
Section 2.2 delves in one of the leading strategies to face the clays,
which is using polymeric reagents that can coat their surfaces. Although
this technique has been useful, few studies have examined the results
caused by the polymer addition on the pulp rheology. Amarasinghe and
Abelev (2015) found that small doses of guar gum significantly in-
creases the viscosity of clay suspensions, although the effect was much
higher in suspensions of montmorillonite compared to that obtained
with kaolinite (see Fig. 9).
2.2. Specific reagents for clays
A strategy used to counteract the damaging effects of clays is
through the use of specific reagents, which exert a dispersing role be-
tween the clay and the valuable minerals. These reagents usually cor-
respond to polysaccharides (e.g., carboxymethylcellulose, guar gum,
etc.) that can adsorb onto the particle surface, creating electrostatic
and/or steric repulsions that stabilise the suspension (Pawlik et al.,
2003). One of the first studies reported dates back at the beginning of
the 80s, when Edwards et al. (1980) proposed the use carbox-
ymethylcellulose (CMC) to improve the recovery of pentlandite, after
reducing the effects caused by the serpentine sludge. Since then, the
application of lignosulfonates was popularised to the point that nowa-
days they are commonly used in the industry, highlighting in nickel,
potash and talcflotation. (Crozier, 1992; Wellham et al., 1992; Pawlik
et al., 2003; Song et al., 2006; Ma and Pawlik, 2007; Peng and Seaman,
2011). However, the application in the copper industry is recent and
the first systematic studies emerged from the work of Seaman et al.
(2012) who used three polymers (polyacrylate, modified carboxylic
acid, and lignosulfonate-based polymer F-100) to improve the recovery
of copper and gold ores in Minera Telfer operations, Australia. All the
dispersants showed positive results, being the biopolymer F-100 who
achieved better recoveries, in particular, the secondary copper sulfide
chalcocite. Unfortunately, the promising results obtained in the la-
boratory were not able to replicate in-plant trials, and the main reason
was attributed to the differences in the grinding media. Corrosion-re-
sistant stainless steel grinding media were used in the laboratory, while
carbon-forged steel media that corrodes quickly when exposed to air
and moisture was used in the plant. This is a critical consideration for
flotation efficiency, given that the conditions under which grinding is
carried out, including the type of mill, the gaseous atmosphere, and pH,
lead to electrochemical behaviours that can significantly modify the
hydrophobicity of the copper minerals (Bruckard et al., 2011). Based on
the previous observation, Wei et al. (2013) studied the impact of lig-
nosulfonates on a low clay ore and a high clay ore, obtained from un-
derground and open pits of Telfer operation, respectively. The analyses
to determine the nature of copper ores indicated that both ores contain
copper associated with oxides, secondary copper minerals, but mainly
primary copper minerals (over 65%). The different grinding media
demonstrated the enormous influence of comminution stage. For ex-
ample, Fig. 10a shows the results obtained by using a mild steel
medium, where there was no improvement in copper and gold recovery
after applying the dispersing reagents (F-100). The explanation was
that the steel medium produces large amounts of oxidised iron, which
depresses valuable minerals independent of the presence of dispersants.
On the contrary, when using a stainless steel medium, the products of
iron oxidation are minimised, facilitating the activity of the clay dis-
persant. The radical contrast in the performance of the biopolymer is
evidenced in Fig. 10b, where the floatability of copper, gold and mass is
shown as a function of the water recovery after grinding in a stainless
steel medium. After the application of 100 g/t of F-100, the copper
recovery increased by 7% while that of gold by 20%.
Important work was recently published by Wang et al. (2016). The
researchers considered an aspect that had not been reported in the
literature, where they quantified the surfactant properties of some
dispersants, especially when they interact with the frother. For this
study, three lignosulfonate-based polymers (DP1775, DP1777, and
DP1778) were analysed for the flotation of copper minerals with the
presence of kaolinite. The three polymers improved the copper recovery
and in turn decreased its grade, with a tendency that was strongly de-
pendent on its structural characteristics such as the content of func-
tional groups, molecular weight, and type of counterion. However, one
of the main conclusions was that the surface activity of the biopolymers
could play a preponderant role on their performance, mainly when they
interact with the frother since essential changes in the froth properties
can be generated, with consequences in the mechanical entrainment.
For example, in Fig. 11a, is observed that the froth height has little
sensitivity to the frother (DSF004) and the biopolymer DP-1777 dosage,
but in the case of the biopolymers DP-1775 and DP-1778, the behaviour
was different since there was a gradual growth of the froth height. On
the other hand, Wang et al. showed the synergistic effect that can arise
when mixing a biopolymer with a frother. For this, 10 ppm DSF004 was
applied, and the biopolymer dosages varied. The results, presented in
Fig. 11b, showed that the joint action of the reagents could cause more
intense changes than when they act separately. This synergy was very
easy to detect in the biopolymers DP-1775 and DP-1778.
An issue of great interest is to identify how these reagents behave
when operating at different types of waters, especially those with high
Concentration (mM)
0 2 4 6 8 10
Viscosity,
[Pas]
0.0
0.5
1.0
1.5
2.0
2.5
TX-100 (non-ionic)
CPB (cationic)
SDBS (anionic)
Fig. 8. Viscosity of 55 wt% pyrophyllite suspensions at a constant shear rate of
60 s−1
, in the presence of TX-100, CPB, and SDBS (Adapted from Desai et al.,
2010).
61

salinities. Unfortunately no studies were found to evaluate copper mi-
nerals; however, it is worth mentioning the work of Liu and Peng
(2015), who assessed the flotation of coal minerals with high clay
content, both in freshwater and in saline water (processed water). The
dispersing agent (lignosulfonate) showed results that much depending
on its dosage and the medium conditions, moreover, the only case
where the biopolymer showed good results was when it was applied in
small doses (< 100 g/ton) in deionised water. For example, the addi-
tion of 50 g/ton of lignosulfonate increased carbon recovery from 45%
to 63%; but when 200 g/ton was applied, the recovery fell to 26%.
However, when using industrial water, the beneficial effect of lig-
nosulfonate was not observed, in fact, the coal recovery decreased to all
the dosages used. The researchers correlated the behaviour with in-
terfacial studies that allowed to establish the mechanisms by which
these reagents act. Then, measurements of adsorption isotherms
showed that the affinity of lignosulfonate with the surfaces of kaolinite
and carbon depends fundamentally on the type of water employed
(Fig. 12). The proposed explanation was that in the deionised water
there is minimal adsorption of the dispersant onto the clay mineral, but
it can adhere onto the carbon surface generating a better electrostatic
repulsion between the minerals. This reduces the heterocoagulation,
improving the coal recovery. A subsequent increase in the lig-
nosulfonate dosage is counterproductive since it continues to adhere to
the valuable mineral surface, giving it a higher hydrophilic character
that reduces its floatability. In saline water, the situation was different
where the lignosulfonate adsorption on the surfaces of both minerals
increased markedly (Fig. 12), but as stated above, the carbon recovery
decreased for all range of dosages. The authors indicated that low
polymer dosages would not be enough to generate a steric repulsion.
Meanwhile, increasing the doses would expect steric repulsion among
the minerals, but the carbon surface begins to lose hydrophobicity
which directly affects its floatability.
Recently, Ramirez et al. (2018) published results on the interactions
between chalcopyrite and kaolinites of different crystallinity, over the
pH range from 7 to 12, in both fresh and seawater. The effect of the
dispersants, sodium hexametaphosphate (SHMP) and sodium silicate
(SS), was evaluated in this work. It is shown that both tested dispersants
are able to restore the chalcopyrite flotation in the presence of kaolinite
in seawater over the pH range from7 to 11. These authors also report a
better effect when a poorly-crystallized kaolinite was used, which was
the one that caused the stronger depressing effect.
Another type of reagents are the so-called ‘clay binders’, developed
by Giorgia Pacific (Tao et al., 2007). The goal is that the reagent can
adhere to the clay surfaces and promote their agglomeration to act as
depressants. Tao et al. (2010) showed the performance after using them
in phosphate flotation, whose pulp had high contents of insoluble clays.
The results were very interesting, where the use of the reagent im-
proved the recovery between 5 and 7%, under a fixed grade of con-
centrate. At first glance, it is appreciated that the clay binder made the
flotation faster, in fact, Tao et al. determined that the reagent increase
the flotation rate by 17.1% (this when fitting a first-order flotation
model).
Total guar gum content [g/L]
0.0 0.1 0.2 0.3
Apparent
Bingham
viscosity
[mPas]
1.0
1.2
1.4
1.6
1.8
2.0
2.2
1 g/L
3 g/L
5 g/L
a)
Total guar gum content [g/L]
0.0 0.1 0.2 0.3
Apparent
Bingham
viscosity
[mPas]
1.0
1.2
1.4
1.6
1.8
2.0
2.2
1 g/L
3 g/L
5 g/L
b)
Fig. 9. Bingham apparent viscosity as a function of the guar gum and clay mineral content: a) montmorillonite, b) kaolinite (adapted from Amarasinghe and Abelev,
2015).
Water recovery (%)
5 10 15 20
Cumulative
recovery
(%)
0
20
40
60
80
100
Mass recovery with F-100
Copper recovery with F-100
Gold recovery with F-100
Mass recovery without F-100
Copper recovery without F-100
Gold recovery withou F-100
a)
Water recovery (%)
2 4 6 8 10 12 14 16 18
Cumulative
recovery
(%)
0
20
40
60
80
100
Mass recovery with F-100
Copper recovery with F-100
Gold recovery with F-100
Mass recovery without F-100
Copper recovery without F-100
Gold recovery withou F-100
b)
Fig. 10. Cumulative gold, copper, and mass recovery, as a function water recovery in the flotation of a high clay ore with F-100 dispersant and without dispersant
after grinding with a) mild steel and b) stainless steel (adapted from Wei et al., 2013). (For interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
62

The clay binders correspond to low molecular weight polymers that
arise from the condensation of urea and formaldehyde. An advantage
mentioned by the researchers is that the polymer properties can be
adapted depending on the desired application, that is, they might pre-
pare reagents that work for copper ores, in fact, the clay binders have
also been used for coal and potash flotation (Tao et al., 2007, 2010).
This is interesting since the efficiency is fundamentally determined by
the physicochemical properties of the polymer, such as the molar ratio
between formaldehyde-urea, the addition of functional groups, the
degree of functionalization, the molecular weight, and the cross-linking
density. The mechanism with which these polymers act is very well
exemplified in Fig. 13. The first phenomenon that happens is the
polymer adhesion onto the clay surface, which occurs mainly by dipole-
dipole interactions and strong hydrogen bonds. After its addition, two
significant consequences arise: first, there are fewer available spaces on
the clay surface for the collectors to deposit, which are used to cover the
valuable mineral. Moreover, these hydrophilic polymers have a floc-
culating effect, which promotes the clay aggregation and depression,
decreasing the number of them that adheres to the valuable mineral
and/or bubbles.
2.3. Clays behaviour in flotation with saline water
Clays are active from the physicochemical point of view. The che-
mical reactivity is related to the internal and stoichiometric structure
and is a consequence of the small particle size and its predominantly
laminar morphology, which give a high surface area. Likewise, the
external and internal surface charges attract ions and water molecules,
giving rise to significant desorption characteristics and cation exchange
capacity.
In particular, it has been proposed that the phenomena of hetero-
coagulation are the primary responsible for affecting the flotation
performance. This refers to the generation of a hydrophilic coating
formed by a layer of fine particles that adhere to the surface of the
valuable mineral, preventing the interaction with the bubbles and/or
with the collector. Due to the anisotropic characteristics, clay coatings
can occur in positively or negatively charged minerals (Peng and Zhao,
2011), and different researchers argue that the formation of this coating
is due to electrostatic attractions. For example, in the case of minerals
like chalcopyrite and chalcocite has been reported that their interaction
with kaolinite is due to an attraction between the negative charges of
the clay and the positive charges of the sulfide mineral (Gan and Liu,
2008; Peng and Zhao, 2011; Farrokhpay and Zanin, 2012). However,
the occurrence of chemical interactions between the species is not ruled
out, and the pH and the presence of soluble ions influence this coating
to a greater or lesser extent (Liu et al., 2002; Holuszko et al., 2008;
Gupta and Miller, 2010; Peng and Zhao, 2011; Zhao and Peng, 2012).
On the other hand, the adsorption of metal ions depends strongly on the
hydrolysis capacity of the cations. Studies carried out by Gan and Liu
(2008) showed that the presence of multivalent ions (Ca2+
, Mg2+
,
Fe3+
) generated a high heterocoagulation between kaolinite and bi-
tumen, due to a decrease in the magnitude of the zeta potential and an
increase in cation adsorption metallic on both minerals. Mpofu et al.
Fig. 11. Froth height in steady state, as a function of the frother or biopolymer concentration: (a) pure reagent; (b) biopolymer mixed with 10 ppm of frother (Wang
et al., 2016).
Lignosulfonate concentration (mg/L)
0 100 200 300 400 500
Polymer
adsorbed/Substrate
(mg/g)
0
1
2
3
4
LS on kaolinite in deionized water
LS on kaolinite in saline water
LS on pure coal in deionized water
LS on pure coal in saline water
Fig. 12. Adsorption isotherms of lignosulfonate in kaolinite and pure carbon in
deionised water and saline water at pH 8.5 (adapted from Liu and Peng, 2015).
Fig. 13. A mechanism in which binders interact with clay particles (Tao et al.,
2010).
63

(2003) evaluated the effect of chemical adsorption of the hydrolysable
cations of Mn2+
and Ca2+
on the kaolinite surface at pH 7.5 and 10.5.
They found that the ion adsorption behaviour led to significant con-
sequences on the zeta potential, shear yield stress, flocculant adsorp-
tion, and dewatering behaviour. Liu et al. (2002) described an inter-
esting methodology to analyse the phenomena of heterocoagulation
from measurements of zeta potential. When a system is composed of a
mixture of two minerals, it is common for the zeta potential to present
one or two picks, depending on the chemical condition of the suspen-
sion and the type of clay present. With this, the difference between
kaolinite and montmorillonite could be established in terms of its in-
teraction with bitumen. When adding a small amount of calcium ions
(1 mM), a single pick was generated in the zeta potential, which was
considered as an indicator of heterocoagulation, with negative con-
sequences for the bitumen floatability. For kaolinite, the addition of
calcium ions did not lead to significant changes in the bimodal form of
the zeta potential, considered as no heterocoagulation.
The heterocoagulation affects the subsequent interaction of the
mineral with bubbles (Laskowski et al., 1989; Johnson et al., 1998;
McFarlane et al., 2005; Elmahdy et al., 2008; Gan and Liu, 2008;
Farrokhpay and Zanin, 2012). For copper flotation, the electrostatic
attractions between fine clay particles with chalcopyrite and chalcocite
minerals affect the interaction with the collector and bubbles (see
Fig. 14) (Peng and Zhao, 2011). Likewise, evidence of an analogous
phenomenon was found, in which clays can form coatings on gas
bubbles, decreasing or preventing the adhesion capacity between the
bubbles with the minerals (Gutierrez and Melipichun, 2014).
Uribe et al. (2017) studied solutions with high ionic content, in-
cluding seawater, on the chalcopyrite floatability in the presence of
kaolinite. Interestingly, the significant copper depression at pH higher
than pH 9 (Fig. 15) was related, in no small extent, with the presence of
calcium and magnesium ions since they have the ability to hydrolyse
and hydrate, forming Ca(OH)+
, Mg(OH)+
and Mg(OH)2(s) species. The
authors suggested that these complexes adsorb onto the surfaces of
chalcopyrite and kaolinite particles, favouring their heterocoagulation
(Gan and Liu, 2008; Ozkan et al., 2009; Uribe et al., 2017). We must
emphasise that although sedimentation tests reinforced the authors'
argument, there was no evidence or demonstration through micro-
scopy. With the technologies currently available for the minerals
characterisation, the development of this type of experiments is pos-
sible.
2.4. Mechanical entrainment
One of the enormous challenges in the flotation of fine and ultrafine
particles is the high gangue entrainment (Liu and Peng, 2014). The
hydrophilic gangue is easily dragged in the interstitial fluid film be-
tween the air bubbles that form the froth layer (Warren, 1985), which
intensifies when the particle size is < 30 μm (Trahar, 1981; Smith and
Warren, 1989). In copper and lead flotation it has been found that the
recovery of non-metallic gangue is increased between 5% when having
a particle size of 40 μm to 20–30% in particles of 10 μm (Liu et al.,
2006; Wang and Peng, 2013).
Wang and Peng (2013) analysed the carbon flotation and found that
a saline medium increased the gangue entrainment for any particle size,
however, the effect was more evident for particles smaller than 38 um.
In general, the tendency is that the clay entrainment is more significant
in saline water, which could be closely related to the higher stability of
the bubbles and froth layer (Craig et al., 1993; Henry and Craig, 2008;
Wang et al., 2013; Wang and Peng, 2014). On the other hand, studies
carried out by Cao and Liu (2006) and Liu et al. (2006) showed the
feasibility to reduce the flotation entrainment, either by using inorganic
depressants or high molecular weight polymers, which allow coagu-
lating the fine gangue particles, forming more massive structures that
sediment by gravitational effects. In this sense, Gong et al. (2010) de-
monstrated that by applying PEO in the flotation of copper‑gold ores,
less quartz entrainment was achieved, and it also improved the re-
covery of the valuable minerals (Fig. 16). The phenomenon was asso-
ciated with the selective adsorption of PEO on the quartz surface, al-
lowing the vast floc generation enough to overcome the resistance to
the fluid. The size measurement was obtained by using a photometric
dispersion analyser (PDA) which is a technique capable of monitoring
the state of aggregation of suspended particles. According to Mpofu and
colleagues (Mpofu et al., 2003), PEO produces better inter-particle
bridges, a higher sedimentation rate, and a higher compaction beha-
viour of flocs than traditional reagents like PAM.
The presence of some divalent cations allows better flocculation
when using high molecular weight polymers (Mpofu et al., 2003), in
fact, Liu and Peng (2014) evaluated the PEO to reduce the entrainment
of Q38 kaolinite in flotation processes, using saline water and fresh
water (Figs. 17 and 18). The recovery of kaolinite increased linearly
with the water recovery, which is consistent with the observations of
Fig. 14. Chalcopyrite or chalcocite recovery as a function of flotation time in
the presence and absence of bentonite (Peng and Zhao, 2011).
Fig. 15. Effect of kaolinite in the recovery of chalcopyrite in chloride salts:
sodium (11,000 ppm), potassium (400 ppm), calcium (400 ppm), magnesium
(1300 ppm), using collector KAX (40 ppm) and MIBC (25 ppm) (Uribe et al.,
2017).
64

other researchers (Trahar, 1981). Under the PEO addition, lower kao-
linite entrainment was achieved in both media, while in a PEO-free
medium, a 30% of kaolinite was obtained in fresh water and 36% in
saline water. Consistent with what we have seen, the presence of
electrolytes again increased the kaolinite entrainment.
In Fig. 18 it can be seen that in saline water the lowest recovery of
kaolinite is obtained when using low PEO dosage. However, upon in-
creasing the polymer concentration, the effects were reversed, with the
same entrainment occurring in the absence of this reagent. The authors
recommended that when PEO is used, the aggregate growth is not the
only property that should be considered since the froth stability can
present changes that might decrease the performance.
2.5. Effect of copper sulphide oxidation on clay coating
Different studies have analysed the influence of the mill type and
grinding media on the sulphide ores flotation (Heyes and Trahar, 1977;
Gardner and Woods, 1979; Adam et al., 1984; Yelloji Rao and
Natarajan, 1990; Peng et al., 2003). Mild oxidation results in a surface
that is rich in polysulfides with some metal hydroxides, mainly due to
the dissolution of metal ions from the surface and near-surface layers, as
observed in air, acidic and alkaline conditions. Peng and Zhao (2011)
found that the oxidation of chalcopyrite and chalcocite had a different
effect on their interaction with bentonite. Under normal grinding and
flotation conditions, chalcopyrite displayed good floatability reaching
91% recovery at the completion of 8 min, meanwhile, the chalcocite
presented at lower recovery corresponding to 75% at the same flotation
time. When bentonite was added, both minerals reduced their re-
coveries; however, the decrease was much more significant with chal-
cocite (Fig. 14). The results were attributed to the strong surface oxi-
dation that takes place in the chalcocite surface, which is
electrostatically attractive to bentonite resulting in bentonite slime
coating. The results were complemented with zeta potential measure-
ments, where at pH 9.0 a slightly oxidised chalcopyrite is electro-
statically repulsed from bentonite, while oxidised chalcocite is strongly
attracted to bentonite (Fig. 19).The argument was then confirmed by
EDTA extraction and XPS analysis (Zhao and Peng, 2012). In the EDS
analysis, Si and Al signals from bentonite were detected on the ran-
domly chosen chalcocite particle. Meanwhile, in the case of chalco-
pyrite, the signals from bentonite were not detected, confirming that
bentonite particles coated the chalcocite but not the chalcopyrite sur-
face (Fig. 20). Recently, Zhao et al. (2017) showed through electro-
chemical impedance spectroscopy (EIS) the way in which electrolytes
reduce the kaolinite coating on chalcocite minerals. Interestingly, the
authors found that the ability of the ions to mitigate the coating effect is
related to the Hoffmeister series since larger ions reduce more the slime
coating than smaller ions.
Few studies have reported to date which consider the effect of
Fig. 16. Gold and copper recoveries, depending on the silica content in rougher
and cleaner flotation concentrates. Molecular weight of PEO 8 × 106
(Gong
et al., 2010). (For interpretation of the references to colour in this figure legend,
the reader is referred to the web version of this article.)
Fig. 17. Recovery of Q38 kaolinite as a function of water recovery, in the
presence and absence of PEO, using fresh water (Liu and Peng, 2014).
Fig. 18. Recovery of Q38 kaolinite as a function of water recovery, in the
presence and absence of PEO, using saline water (Liu and Peng, 2014).
Fig. 19. Zeta potentials of chalcopyrite and chalcocite after grinding, and zeta
potentials of bentonite (Peng and Zhao, 2011).
65

copper sulphide oxidation on flotation performance, and its interaction
with clays. However, they have been enough to prove the importance of
this phenomenon (Peng and Zhao, 2011; Zhao and Peng, 2012). We
suggest that this topic should be considered in future research, in order
to find alternatives that mitigate these detrimental effects. Peng and
Zhao (2011) showed that it is possible to overcome the slime coating
when the oxidation is reduced in the milling process but it is necessary
to evaluate if this alternative is feasible in plant conditions with real
ores.
3. Research opportunities
In the last years, significant advances have arisen on the clays
handling in flotation operations. Among them, the following stand out:
i) the use of physical methods to mitigate the adhesion of clays to va-
luable minerals, such as intense agitations prior to flotation, the use of
hydrocyclones, or ultrasound treatments; ii) use of specific reagents
that can cover the clay surface avoiding the slime coating effect and
reduce the excessive consumption of collectors; iii) use of rheological
modifiers, either inorganic or polymeric dispersants; and iv) decrease
the pulp solid concentration (Celik et al., 2002; Papo et al., 2002; Tao
et al., 2006; Oats et al., 2010; Cruz et al., 2013; Yu et al., 2017a).
However, the processes continue to be inefficient and in some cases
unsustainable. That is why the invitation to researchers is to address
this issue, introducing modern and non-conventional technologies that
can transcend beyond the limited improvements that can be obtained
by optimising traditional methods. In literature, there are many ex-
amples of researchers who have innovated flotation operations, ob-
taining promising results (see Calgaroto et al. (2014)).
Emerging techniques that could be explored to evaluate the feasi-
bility of their implementation are:
3.1. Nanoparticles
Nanoparticles present great capacities to modify the physicochem-
ical nature of clay surfaces. Studies like Bailey et al. (2014) have shown
that silica nanoparticles alter the stability of clay suspensions, with
important consequences in their rheological properties, which can in-
crease or decrease depending on the surface charge. Currently, no re-
ports show systematic studies on their use in mineral flotation with high
clay content, however, the possibility of manipulating the phenomena
of particle aggregation/dispersion at convenience, put this issue as an
interesting point to be addressed in future research.
3.2. Rheological modifiers
Greater depth and systematic studies are required to extend the
knowledge on the rheological implications involved in the selection of
flotation reagents. Several studies have shown that pH modifiers,
frother, depressants, and eventually collectors, could have a significant
impact on the pulp rheology, although the effect is diverse and chal-
lenging to predict. For example, some surfactants could cause the
system to acquire a Newtonian behaviour, while in other cases a
rheological raising may appear showing even certain levels of thixo-
tropy. However, this not only depends on the surfactant characteristics
but also on the clay nature and the medium conditions (e.g., pH, sali-
nity, etc.). In general terms, it is proposed that when systems have
complex mineralogies, which generate rheological challenges, an ade-
quate reagent selection should include their implication in the flow
properties within the flotation cell.
3.3. Organic reagent
Organic reagents, such as polysaccharides, have shown promising
results for flotation operations since they can act as clay (Liu and Peng,
2015) and pyrite (Mu et al., 2016) depressants. However, the reports
published to date have considered few systems, focusing primarily on
phosphate, carbon, and potash minerals. As for copper mining studies
are scarce, it is attractive to deepen the research on this subject. Of
particular interest is the behaviour in seawater and its implication on
mechanical entrainment (Liu and Peng, 2014).
3.4. Seawater flotation
As previously stated, a high ionic content can increase the hetero-
coagulation between the valuable mineral and fine clay particles.
However, fundamental studies are required to evaluate the effect of
each type of clay and each primary ion in solution separately depending
on the different minerals of interest, to achieve a broad knowledge
about the interaction mechanism between the species. This fact is of
particular importance in operations that use seawater, where the con-
centrations of divalent ions are sufficient to generate heterocoagula-
tion. A strategy that has been proposed in the last years is to perform a
pretreatment to seawater, where only the calcium and magnesium ions
are removed, which has proved beneficial in copper‑molybdenum mi-
neral flotation operations. Considering that these divalent ions also
promote the clay heterocoagulation with valuable minerals (Uribe
et al., 2017), it was proposed that an attractive option is the use of
pretreated seawater in systems with high clay contents (Cruz et al.,
2019).
3.5. Industrial trials
Significant knowledge has been generated about strategies to im-
prove the treatment of mineral flotation in the presence of clays.
Fig. 20. The EDS analysis on the randomly chosen particle (bottom) of the
chalcocite (a) and chalcopyrite (b) samples ground in the presence of bentonite
particles (Zhao and Peng, 2012).
66

However, in the vast majority of cases, the studies have been conducted
only on a laboratory scale and have not faced the challenges involved in
the industry. A good example is a study conducted by Seaman et al.
(2012), who found that lignosulfonate reagents might significantly
improve the copper and gold recoveries in the presence of clays, but
when tests were conducted in Minera Telfer, Australia, the results did
not show the same efficacy than in the laboratory. The reason was that
a significant variable like the grinding type was not considered in the
study. Logically, this was not a positive result but generated a new
matter of study. In the same way, all the potential benefits of new
strategies like the use of nanoparticles, organic reagents, new rheolo-
gical modifiers, pretreated seawater, etc., should offer their industrial
validation.
4. Summary
When mineral deposits present high clay contents, significant
challenges for flotation operations appear. The pulps tend to behave
like non-Newtonian fluids and properties such as viscosity and yield
stress begin to have a preponderant role in the hydrodynamics of the
system and, consequently, overall the physical subprocesses that occur
within the cell. In general, high viscosity and yield stress are negative
and decrease the collision rates between bubbles and particles. Poor
bubbles dispersion can also be generated, and it has even been found
that there is a direct relationship between the pulp viscosity and the
froth stability. The most common strategies adopted today considers
the addition of rheology-modifying reagents, which logically involve an
extra cost to the process. In other circumstances, it is even necessary to
reduce the solid concentration in the feed. Although the pulp becomes
more manipulable, the processing capacity of the plant is sacrificed,
which inevitably leads to a decrease in production.
Clays are also capable of consuming many types of collectors and
covering the surfaces of valuable mineral, which is known as coating
effect. Some authors argue that the central mechanism is through
electrostatic attractions; however, the occurrence of chemical interac-
tions between species is not ruled out, and both the pH and the presence
of soluble ions influence this coating to a greater or lesser extent.
Additionally, it is known that the high ionic environment can induce
heterocoagulation phenomena between the particles, although this
depends on the hydrolysis capacity of the cations. Monovalent cations
like sodium and potassium have a minor effect, but divalent ions like
calcium or magnesium (present in seawater) have the ability to hy-
drolyse and hydrate, forming species such as Ca(OH)+
, Mg(OH)+
and
Mg(OH)2(s), which favour heterocoagulation, bringing consequences in
the subsequent interaction of particles with bubbles. In this sense, there
is evidence that fine clay particles can form coatings on gas bubbles,
decreasing the ability to form the bubbles-mineral adhesion. However,
less than a decade ago, the use of hydrophilic polymers with low mo-
lecular weight began to be included in copper flotation. These adhere to
the clay surface, reducing the area they have to join to the valuable
minerals, and also avoid the excessive consumption of collector. The
reagents, which are based on polysaccharides, have presented pro-
mising results for the copper industry; however, studies have only been
carried out in the experimental phase, and no successful cases have
been reported in the plant yet.
Another significant challenge is the high gangue entrainment, which
is often excessive and even increments in saline waters due to the ions
improve the froth stability. The most common way to reduce this
phenomenon is to use inorganic depressants or organic polymers of
high molecular weight, which allow coagulating the fine gangue par-
ticles. Also, the presence of some divalent cations enables better floc-
culation when using flocculants, as long as overdosing is prevented,
which usually leads to increase the froth stability, and might reverse the
positive effects.
In general, dealing with clays is a permanent challenge for the
copper ores flotation, wherein operators are obliged to adopt strategies
that in most cases involve extra costs for the process, or even sacrifice
part of the production or product quality. For this reason, the invitation
is for researchers to address this issue and include modern and un-
conventional techniques in their researches that can transcend beyond
the limited improvements that can be obtained by optimising tradi-
tional methods. Attractive alternatives for exploration include the use
of nanoparticles, and new organic reagents. Reagent selection meth-
odologies should also be expanded to understand the rheological im-
plications that this entails, and of course, the suggestion is that the new
findings obtained at the laboratory scale must be submitted to the
challenges involved in industrial scaling.
Acknowledgement
The authors are grateful for the financial support of CONICYT PIA
ACM 170005. RIJ thanks CONICYT Fondecyt n° 11171036. R.I.J. and
L.G. thank the support of Centro CRHIAM through Project Conicyt/
Fondap/15130015.
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