Relationship of structure to properties of some anionic surfactants as collectors in the flotation process. 1. Effect of chain length

Article abstract of DOI:10.1021/je9801359

The surface and thermodynamic properties of some synthetic surfactants, as well as their efficiency as collectors in the flotation of petroleum coke, are studied. These surfactants are monoisomeric alkylbenzenesulfonate of different alkyl chains (C12 to C14). The results show that the length of the hydrocarbon chain of these surfactants plays a major role in determining their surface and thermodynamic properties. The values of surface excess concentration (Γ_max) and Gibbs energy of micellization (ΔG°_mic) are found to increase with increasing number of carbon atoms in the chain while the values of critical micelle concentration (cmc) are decreased. The results indicate, also, that there is a good relationship between effectiveness of adsorption of a surfactant and its efficiency as a collector. A surfactant of higher Γ_max produces a concentrate of lower ash content and higher flotation yield. Thus, the surfactant with longer alkyl chain (C14) and highest Γ_max value is more selective, as a collector, than others of shorter carbon chain.

Full text of DOI:10.1021/je9801359

J . Chem. Eng. Data 1999, 44, 133-137
133
Rela tion sh ip of Str u ctu r e to P r op er ties of Som e An ion ic Su r fa cta n ts
a s Collector s in th e F lota tion P r ocess. 1. Effect of Ch a in Len gth
N. A. Abd el-Kh a lek *
Central Metallurgical Research and Development Institute, P.O. Box 87 Helwan, Cairo, Egypt
A. M. A. Om a r a n d Y. Ba r a k a t
Egyptian Petroleum Research Institute, Cairo, Egypt
The surface and thermodynamic properties of some synthetic surfactants, as well as their efficiency as
collectors in the flotation of petroleum coke, are studied. These surfactants are monoisomeric alkylben-
zenesulfonate of different alkyl chains (C12 to C14). The results show that the length of the hydrocarbon
chain of these surfactants plays a major role in determining their surface and thermodynamic properties.
The values of surface excess concentration (Γmax) and Gibbs energy of micellization (∆G°mic) are found to
increase with increasing number of carbon atoms in the chain while the values of critical micelle
concentration (cmc) are decreased. The results indicate, also, that there is a good relationship between
effectiveness of adsorption of a surfactant and its efficiency as a collector. A surfactant of higher Γmax
produces a concentrate of lower ash content and higher flotation yield. Thus, the surfactant with longer
alkyl chain (C14) and highest Γmax value is more selective, as a collector, than others of shorter carbon
chain.
In tr od u ction
ture, (d) the position of the ionic group(s) in the structure,
(e) the number and nature of nonionic hydrophilic group-
(s) in the structure, and (f) the presence, position, and type
of cyclic group(s) in the structure (Omar and Abdel-Khalek,
1998; Smith, 1989).
The mineral industry requires the use of a wide variety
of reagents for its operation. These reagents are commonly
used as flotation surfactants, grinding aids, flocculants, and
dewatering aids. However, flotation surfactants predomi-
nate over any other mineral industry chemicals because
the flotation process has become the single most important
method for separation of minerals from ores.
As part of a study of the relationships between the
chemical structure of well-purified surfactants and their
surface and thermodynamic properties, a number of sul-
fonate surfactants with different hydrocarbon chains, and
a benzene ring attached at carbon atom number four, are
synthesized and their properties are investigated. These
surfactants are monoisomeric alkylbenzenesulfonates. They
have the following alkyl chains: 4-phenyldodecylsulfonate
(4φC12), 4-phenyl tridecylsulfonate (4φC13) and 4-phen-
yltetradecylsulfonate (4φC14). The properties of these
surfactants are correlated with their efficiency as collectors
in the flotation of petroleum coke to be suitable for electrode
manufacture.
In flotation practice, mineral selectivity can be achieved
through the addition of various reagents that can control
the wettability of particular minerals in an ore in the
flotation pulp. Flotation reagents are commonly classified
into collectors, activators, depressants, frothers, and modi-
fiers. Collectors are surface-active organic reagents that
adsorb at the surface of the desired mineral so that it
becomes hydrophobic and in turn it can attach to an air
bubble. Flotation collectors include reagents such as thiol
compounds, alkyl carboxylates, alkyl sulfates, alkylsul-
fonates, alkyl phosphates, amines, chelating agents, and
alkyl phosphonic acids (Fuerstenau and Urbina, 1988).
Selection of a collector (surfactant) with the right struc-
ture can greatly enhance selective flotation in any number
of practical flotation separations (Smith, 1989). The surface-
active properties of a collector are therefore determined,
among other things, by its numerous structural charac-
teristics, which include the following (Smith, 1987): (a) the
length and number of hydrocarbon chains in the structure,
(b) the configuration of the chain or chains including
branching and the number and location of double bonds in
the chains, (c) the number, type (anionic or cationic), and
cross-sectional area of the polar ionic group in the struc-
Ma ter ia ls a n d Meth od s
P r epa r a tion a n d Ch a r a cter iza tion of Su r fa cta n ts.
Three anionic surfactants of sodium salt of monoisomeric
alkylbenzenesulfonate were prepared according to recom-
mended procedures as follows (El-Mergawy, 1988; Omar,
1994):
A tertiary carbinol (φRR′C-OH) of the required chain
length was prepared, using alkylphenyl ketone (φRCO) and
alkylmagnesium bromide (R′MgBr), where R was C3H7 and
R′ varied between C8H17 and C10H21. The product (tertiary
carbinol) was subjected to a hydrogenation process, using
Pd/C in glacial acetic acid, to form linear alkylbenzene
(φRR′CH). The latter product was subjected to a sulfonation
process, using fuming H2SO4, and a neutralization step,
with NaOH, to produce the sodium salt of alkylbenzene-
sulfonates.
* To whom correspondence should be sent. Current address: Depart-
ment of Materials Science and Engineering, Engineering Research
Center for Particle Science and Technology, University of Florida,
Gainesville, FL 32611. E-mail: nagui@ufl.edu.
10.1021/je9801359 CCC: $18.00 © 1999 American Chemical Society
Published on Web 12/04/1998

134 J ournal of Chemical and Engineering Data, Vol. 44, No. 1, 1999
F igu r e 3. IR spectrum of 4-phenyldodecane: X-axis, wavenum-
ber, cm-1
.
Ta ble 1. Ch em ica l An a lysis of th e P etr oleu m Cok e
Sa m p le
constituents
ash
volatile matter
nitrogen
%
constituents
%
1.38
14.50
2.0
fixed carbon
sulfur
87.20
4.2
F igu r e 1. Mass spectrum of 4-phenyldodecane: X-axis, mass/
charge; Y-axis, abundance.
metal content
ppm
metal content
ppm
V
Si
Ni
Na
Ca
Fe
500
410
380
130
110
83
Ti
Cu
Cr
Mo
Co
14
11
9
2
1
spectrum of 4-phenyldodecane is shown in Figure 3. The
intense band at 3000 cm-1 is found to be due to the carbon-
hydrogen stretching of aromatic protons. The bands be-
tween 3000 and 2800 cm-1 are found to be associated with
aliphatic carbon-hydrogen stretching. The low-intensity
bands in the region from 2000 to 1600 cm-1 are due to
overtones and combination frequencies of aromatic hydro-
gen vibrations. The band at 760 cm-1 is due to the out-of-
plane bending of five adjacent hydrogen atoms on the
aromatic ring.
F igu r e 2. NMR spectrum of 4-phenyldodecane: X-axis, ppm (δ).
Purification of the prepared surfactants was carried out
as follows:
(a) Desalting step to remove any traces of hydroxide or
organic sulfate. This was performed by shaking the sur-
factant-2-propanol solution in 250 mL of 30% NaCl
solution.
P r epa r a tion a n d Ch a r a cter iza tion of P etr oleu m
Coke Sa m ple. A technological sample of the Belayim
petroleum coke, Egypt, was kindly supplied by the Suez
Refining Co. The sample was obtained by thermal cracking
of heavy petroleum oil. It had a high percentage of
aromatics, other cyclic compounds, and asphaltene com-
ponents. The structure of this type of coke was character-
ized by a needle-shaped structure with wide unidirectional
voids. Yard sampling of thoroughly mixed ore was carried
out by coning and quartering methods. Ore pulverization
was carried out using a “Wedag” jaw crusher in closed
circuit with a 25 mm screen. This was followed by second-
ary crushing in a “Denver” roll crusher to 100% below 0.5
mm. The product was then dry screened on 0.063 mm sieve
the undersize of which was rejected. The fraction -0.5 +
0.063 mm (representing about 97.5 wt % of the sample)
was then subdivided, after thoroughly mixing, into 0.5 kg
batches and was stored in closed container as a flotation
feed. The chemical analysis of the flotation feed showed
that it contains about 87.2% fixed carbon and 14.5% volatile
matter. The ash content was 1.38%, while the total sulfur
was 4.2%. Ni, V, Si, Ca, and Na were the major (110-500
ppm) metallic inclusions of the coke, whereas Fe, Co, Mo,
and Cu were present in minor (1-83 ppm) concentrations
as shown in Table 1.
(b) Deoiling step by shaking with 150 mL of n-pentane
followed by the addition of 25-50 mL of water to facilitate
the separation of two layers. The upper layer consisted of
n-pentane contaminated with unsulfonated alkylbenzene,
while the lower layer contained surfactant-2-propanol-
water solution. The 2-propanol-water fraction was distilled
off at a reduced pressure to obtain the pure sodium
alkylbenzenesulfonate (Omar, 1994).
The prepared surfactants had different alkyl chains
(4φC12, 4φC13, and 4φC14, i.e., sodium salts of 4-phenyl-
dodecylsulfonate, 4-phenyltridecylsulfonate, and 4-phen-
yltetradecylsulfonate, respectively). Before sulfonation, the
structure of the prepared linear dodecyl-, tridecyl-, and
tetradecylbenzene was verified from IR, NMR, and mass
spectroscopic measurements (Omar, 1994). Mass, NMR,
and IR spectra of 4-phenyldodecane, as a representative
compound, are shown in Figures 1-3.
Mass spectra was recorded on CED-Du Pont 12-491 mass
spectrometer. Figure 1 shows the fragmentation pattern
of 4-phenyldodecane. The NMR spectra was measured
using a Varian associates model A-60 spectrometer. Figure
2 shows the NMR spectrum of 4-phenyldodecane. Two
major resonance bands are apparent. The first at the lower
field arises from the hydrogen atoms on the aromatic ring,
while the second band at higher field is produced by the
hydrogen of the alkyl chain. On the other hand, the IR
Flota tion Exper im en ts. The flotation tests were carried
out using a laboratory “Denver D12” flotation cell, with a
5 L container, at 10% solids and at room temperature (∼25
°C). The sample was conditioned at 1500 rpm with sodium
silicate, as an ash depressant, for 5 min. This was followed
by another 5 min for conditioning with the surfactant
before aeration. The pH was maintained constant at pH 7

J ournal of Chemical and Engineering Data, Vol. 44, No. 1, 1999 135
Ta ble 2. Effect of Ch a n gin g th e Ch a in Len gth on th e Su r fa ce P r op er ties of th e P r ep a r ed Su r fa cta n ts a t 25 ( 0.1 °C
CMC/
γcmc
Γmax × 106/
A° × 102/
Πcmc/
compd
10-2 × mol‚L-1
/mN‚m-1
mol‚m-2
nm2‚molecule-1
mN‚m-1
pC20
4φC12
4φC13
4φC14
122.8
76.3
31.6
27.84a
28.42a
28.07a
3.435
5.208
7.235
48.338
35.215
22.950
44.14
28.42
28.07
5.143
5.021
5.081
a
(0.1.
during flotation tests using H2SO4 or NaOH (BDH prod-
ucts). The flotation speed was kept constant at 1200 rpm.
The froth (concentrate) and the tail fractions were collected,
dried, weighed, and analyzed.
ties. The length of the hydrophobic chain is changed from
C12 to C14, while a phenyl group is fixed at carbon number
4. It is clear that the value of critical micelle concentration
(cmc) for these surfactants decreases significantly, from
122.8 × 10-2 to 31.6 × 10-2 mol‚L-1, with increasing the
length of hydrophobic chain from C12 to C14. This behavior
is similar to that of all known ionic and nonionic surfac-
tants in aqueous media (Rosen, 1989). This decrease in the
cmc with increasing chain length is a result of the lower
solubility of the longer chain surfactants. The reduction
in solubility promotes the formation of micelles. When the
number of carbon atoms in the straight-chain hydrophobic
group exceeds 15, the water solubility of most surfactants
decreases and the cmc values remain substantially un-
changed (Rosen, 1989).
In the meantime, the surface excess concentration at
surface saturation (Γmax) is a useful measure of the ef-
fectiveness of adsorption of the surfactant at the liquid-
gas or liquid-liquid interface, since it is the maximum
value to which adsorption can attain. The effectiveness of
adsorption is an important factor in determining the
properties of surfactants such as foaming, wetting, and
emulsification, since tightly packed coherent interfacial
films have different interfacial properties than loosely
packed, noncoherent films (Rosen, 1989). The calculated
values of Γmax for the prepared surfactants are changed
from 3.435 × 106 to 7.235 × 106 mol‚m-2 with increasing
the carbon chain from 12 to 14 (Table 2). Some authors
have mentioned that a change in the length of the
hydrophobic group of straight chain ionic surfactants
beyond 10 carbon atoms appears to have almost no effect
on the effectiveness of adsorption at the aqueous solution-
heptane interface and little effect on the effectiveness at
the aqueous solution-air interface (Rosen, 1989).
Effectiveness of surface tension reduction, Πcmc, is usu-
ally considered to depend on the cohesiveness of the
collector molecules (low cohesiveness means high effective-
ness), since surface tension reduction requires the presence
of molecular dispersed collector molecules at the surface.
Comparison of the effectiveness of the prepared monoiso-
meric sulfonate collectors, given in Table 2, with those
reported in the literature (Rosen, 1989; Dahanayaka et al.,
1986) of similar carbon chains and hydrophilic head shows
that they have a fairly good effectiveness compared with
most surfactants of similar efficiency.
Effect of Tem per a tu r e on th e Su r fa ce P r oper ties of
th e P r epa r ed Su r fa cta n ts. It is well-known that the cmc
values of all known ionic surfactants increase with increas-
ing temperature (Rosen, 1989; Abdel-Khalek et al., 1997).
With this fact in mind and from the data in Table 3, it is
obvious that the cmc values of the investigated sulfonates
increase slightly with increasing temperature from 25 to
55 °C. For example, increasing the temperature for the
surfactant containing 14 carbon atoms from 25 to 55 °C
Su r fa ce Ten sion Mea su r em en ts. These measurements
were carried out using a “Dagnon Abribot” tensiometer, and
the points of intersection were determined using a linear
regression analysis technique (Drapper and Smith, 1968).
The uncertainties in the measurements of surface tension,
temperature, and concentration of surfactants were 0.10,
0.10, and 0.001% respectively. From the surface tension-
concentration isotherm, the other surface properties and
thermodynamic parameters of surfactants were calculated
(Rosen et al., 1982; Abdel-Khalek et al., 1997). Maximum
surface excess concentration (Γmax), in mol‚m-2, and area
per molecule (Amin), in nm2, at the aqueous-air interface
were calculated from the relationships
Γmax ) (1/2.303)RT (-dγ/d log C˙ )T
Amin ) 1014/NΓ
(1)
(2)
where (-dγ/d log C)T is the slope of the γ-log C plot at
constant temperature, T, R ) 8.314 J mol-1 K-1, and N is
Avogadro’s number.
The values of Γmax were taken as a measure for the
effectiveness of adsorption of the surfactants at liquid-
gas and liquid-solid interfaces (Rosen, 1989).
The surface pressure at the cmc (Πcmc) was calculated
from the relationship
Πcmc ) γ0 - γcmc
(3)
where γ0 is the surface tension of water at zero surfactant
concentration and γcmc the surface tension of the solution
at the cmc.
The values of Πcmc were taken as a measure for the
effectiveness of surface tension reduction (Rosen, 1989).
The efficiency (pC20) of the surfactant is calculated from
the relationship
pC20 ) log 1/CΠ)20
(4)
where CΠ)20 is the bulk molar concentration required to
reduce the surface tension by 20 mN/m.
Using the cmc values, the Gibbs energy change upon
micellization was calculated from the following equation
∆G°mic ) RT ln cmc
(5)
while the Gibbs energy of adsorption was calculated from
the following equation (Rosen et al., 1982; Abdel-Khalek
et al., 1997):
∆G°ad ) ∆G°mic - ΠcmcAcmc
Resu lts a n d Discu ssion
(6)
increases its cmc from 31.6 × 10-2 to 39.4 × 10-2 mol‚L-1
.
Consequently, no drastic changes are expected in the
behavior of these collectors, within this range of temper-
ature, i.e., during the flotation process. The insignificant
influence of temperature variation on γcmc values shown
Su r fa ce P r oper ties of th e P r epa r ed Su r fa cta n ts.
Table 2 shows the results of changing the length of the
hydrocarbon chain of surfactants on their surface proper-

136 J ournal of Chemical and Engineering Data, Vol. 44, No. 1, 1999
Ta ble 3. Effect of Tem p er a tu r e on th e Su r fa ce
P r op er ties of th e P r ep a r ed Su r fa cta n ts
ta/°C
4φC12
4φC13
4φC14
CMC × 10-2/mol‚L-1
25
35
45
55
25
35
45
55
25
35
45
55
25
35
45
55
25
35
45
55
25
35
45
55
122.8
124.3
129.6
132.2
27.84b
27.31b
26.65b
25.80b
3.435
2.863
2.787
2.610
48.338
57.986
63.614
69.969
44.14
39.69
38.36
37.21
5.143
5.146
5.188
5.143
76.3
79.6
83.3
87.5
28.42
27.93
26.89
26.77
5.208
3.682
3.208
2.789
76.3
31.6
31.6
36.0
39.4
28.07
27.60
27.08
26.60
7.235
4.018
3.383
2.977
31.6
γ
cmc/mN‚m-1
Γmax × 106/mol‚m-2
A° × 102/nm2‚molecule-1
F igu r e 4. Effect of changing the dosage of the surfactants of
different alkyl chain lengths on percent ash and yield of concen-
trates: X-axis, dose of surfactant, kg‚ton-1; Y1-axis, flotation yield
%; Y2-axis, ash content %. 0, yield % using C12; [, yield % using
C13; 2, yield % using C14; O, ash % using C12; *, ash % using
C13; × ash % using C14.
79.6
83.3
87.5
31.6
36.0
39.4
Π
cmc/mN‚m-1
28.42
27.93
26.89
26.77
5.021
5.138
5.162
5.179
28.07
27.60
27.08
26.60
5.081
5.318
5.313
5.281
pC20
Ta ble 4. Som e Th er m od yn a m ic P a r a m eter s of th e
P r ep a r ed Su r fa cta n ts
ta/°C
4φC12
4φC13
4φC14
∆Gmic/kJ ‚mol-1
∆Gad/kJ ‚mol-1
25
35
45
55
25
35
45
55
-32.28
-33.77
-35.17
-37.09
-45.13
-48.83
-51.70
-50.44
-33.51
-34.70
-35.92
-36.31
-43.25
-45.89
-47.96
-50.64
-35.64
-36.84
-37.69
-38.63
-41.07
-46.64
-48.90
-50.85
a
b
(0.1. (0.1.
in Table 3 indicates that both cmc and γcmc are solubility-
dependent properties.
For ionic surfactants, it is well-known that factors that
cause an increase in solubility with temperature (reflected
in most cases by an increase in cmc) also work to decrease
the effectiveness of adsorption, Γmax (Rosen, 1989; Daha-
nayaka et al., 1986). For the employed sulfonates, Γmax
decreases with increasing temperature but their cmc values
increase. For example, the 4φC12 sulfonate collector has
a
(0.1.
chain and the amount of water bound by the sulfonate
headgroup in the nonmicellar species decrease with in-
creasing temperature (Rosen, 1989). ∆Gmic values become
significantly more negative with increasing the length of
the alkyl chain from C12 to C14. This may indicate that
the amount of water, structured by the tail group, decreases
with increase of collector hydrophobicity.
The data in Table 4 reveal also that ∆Gad values are
negative. These negative ∆Gad values indicate that adsorp-
tion of these collectors at the aqueous solution-air and the
aqueous solution-solid interfaces is spontaneous (Rosen,
1989). In the flotation process, properties that deal with
the adsorption of collector molecules at aqueous solution-
solid interfaces are highly considered.
Flota tion Efficien cy of th e P r epa r ed Alkylben zen e-
su lfon a tes. Optimization of different operating parameters
that affect floatability of Egyptian petroleum coke has been
conducted before, using the surfactant 4φC12 as a collector
(Abdel-Khalek et al., 1997). The optimum conditions are
as follows: pH 7, dosage of sodium silicate, as a depressant
for the gangue fraction, 1.0 kg‚ton-1, and pulp density 10
wt %. These conditions are applied to study the efficiency
of the prepared surfactants as collectors in the flotation
process. The dosage of surfactants is changed from 20 to
300 g‚ton-1. Figure 4 illustrates the effect of changing
dosage of surfactants on their efficiency to reduce percent
ash content. The results indicate that the ash content
decreases from 1.38% in the feed samples to 0.45%, 0.40%,
and 0.35% in the concentrates obtained by using just 50
g‚ton-1 of 4φC12, 4φC13, and 4φC14, respectively. It can
be seen that the selectivity of separation improves with
application of the surfactant of longer chain C14 as a
collector. Similar results have been mentioned by other
authors in flotation of alumina with some alkylbenzene-
Γmax values of 3.435, 2.863, 2.787, and 2.610 (mol‚m-2
×
106) at 25, 35, 45, and 55 °C, respectively. For collectors of
the same basic structure, the decrease in Γmax becomes
more pronounced by increasing the chain length of the
hydrophobic tail. It can be seen from the data in Table 3
that, within the same temperature range, the Γmax value
decreases from 5.208 to 2.789 and from 7.235 to 2.977
(mol‚m-2 × 106) for 4φC13 and 4φC14, respectively.
It is also seen from Table 3 that an increase in temper-
ature results in an increase in Amin presumably owing to
the increased thermal motion. The calculated efficiency and
effectiveness values for the employed sulfonate collectors
are also presented in Table 3. Insignificant changes have
been observed in these values by changing temperature
from 25 to 55 °C, since temperature has a rather minor
effect on these quantities. For instance, the 4φC12 sul-
fonate collector has effectiveness values of 44.14, 39.69,
38.36, and 37.21 at 25, 35, 45, and 55 °C, respectively. This
collector has efficiency values of 5.143, 5.146, 5.188, and
5.143 at the same temperatures, respectively. Many in-
vestigators (Rosen, 1989) have reached a general conclusion
that increasing effectiveness tends to decrease efficiency
and vice versa.
Som e Th er m od yn a m ic P a r a m eter s of th e P r epa r ed
Su r fa cta n ts. Table 4 depicts the results of calculation of
both the Gibbs energy of micelle formation (∆Gmic) and
Gibbs energy of adsorption (∆Gad) for surfactants at dif-
ferent temperatures. It is clear that ∆Gmic appears to
become more negative with increasing temperature from
25 to 55 °C regardless of the length of the hydrophobic alkyl
group in the surfactant. This may be attributed to the fact
that the amount of water structured by the hydrophobic

J ournal of Chemical and Engineering Data, Vol. 44, No. 1, 1999 137
sulfonates where their adsorption is found to increase with
For sodium alkylbenzenesulfonate collectors, ∆Gmic ap-
pears to become more negative with increasing tempera-
ture regardless of tail length. Meanwhile, the negative ∆Gad
values of these collectors indicate that the adsorption of
such collectors, at the interface, is spontaneous.
The required dosage of these surfactants for flotation of
an Egyptian petroleum coke sample is small (∼20 g‚ton-1).
Flotation of the coke sample using a small dosage of any
of these surfactants, and in the presence of 1 kg‚ton-1 of
sodium silicate at pH 7, gives the best selectivity where
concentrates of only 0.15-0.20% ash content, with percent
ash removal of 87.7-91.3%, are obtained from a feed
containing 1.38% ash content.
increasing chain length from 8 to 14 (Somasundaran et al.,
1984). On the other hand, higher recovery of concentrates,
at the expense of their quality, have been obtained by
increasing collector dosage. Flotation of the coke sample
using small dosage (20 g‚ton-1) of any of these surfactants
gives the best selectivity where concentrates of only 0.15-
0.20% ash content, with percent ash removal of 87.7-
91.3%, are obtained. From Figure 4 it may be concluded
that sodium 4φC14 sulfonate, among the investigated
anionic surfactants, is more selective as a collector since it
gives a concentrate of the highest recovery and lowest ash
content. It seems that the separation process, in terms of
grade and recovery, improves with application of the
surfactant of longer chain, C14, as a collector.
Ack n ow led gm en t
The results in Figure 4 indicate, also, that the three
surfactants behave, in general, similarly with a slight
increase in process recovery with increasing the chain
length of collector. For example, at a fixed dosage of 20
g‚ton-1, the 4φC14 sulfonate collector gives a concentrate
having an ash content of 0.18% with a yield of 83.12% as
compared with 0.19% ash content and 80.0% recovery in
case of 4φC12 collector. In fact, this is in agreement with
the results of surface properties of these collectors, which
show that the differences in the values of surface tension,
The authors thank Prof. Dr. T. R. Boulos, Central
Metallurgical Research and Development Institute, Cairo,
Egypt, for his help and concern.
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Dahanayaka, M.; Cohen, A. W.; Rosen, M. J . Relationship of Structure
to Properties of Surfactants. 13. Surface and Thermodynamic
Properties of Some Oxyethylenated Sulfates and Sulfonates. J . Phys.
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Drapper, N. R.; Smith, H. Applied Regression Analysis; J ohn Wiley &
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in Minerals Technology; Somasundaran, P., Moudgil, B. M., Eds.;
Marcel Dekker: New York, 1988; p 1-38.
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Egyptian Petroleum Coke. Ph.D. Thesis, Faculty of Science, Ain
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γcmc, and efficiency of surface tension reduction pC20 are
very small (Table 2).
However, the relatively higher effectiveness of adsorp-
tion, Γmax, of collector 4φC14 than 4φC12 (and the less
surface area occupied by a single molecule of the former)
may be in favor of such slightly better flotation results
obtained with this collector of longer chain length. In the
meantime, the more negativity of Gibbs energy of micel-
lization, ∆Gmic, of this surfactant as compared with others
should be taken into consideration. The general trend of
increasing floatability with increasing the negativity of
Gibbs energy of other surfactants has been reached before
(Abdel-Khalek et al., 1997; Omar, 1994).
Chemical analysis of the obtained concentrates indicates
that the carbon content is significantly improved to ∼96.1%
in comparison with 87.2% in the feed. This clearly confirms
the good selectivity obtained in the flotation process while
using such prepared surfactants. This, also, may encourage
their application as collectors in the flotation of other
minerals.
Rosen, M. J .; Cohen, A. W.; Dahanayake, M.; Hua, Xi-yuan. Relation-
ship of Structure of Properties in Surfactants. 10. Surface and
Thermodynamic Properties of 2-Dodecyl oxypoly(ethanoxyethanol)5,
C12H25(OC2H4)xOH, in Aqueous Solution. J . Phys. Chem. 1982, 86,
541-545.
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Mineral Technology; Somasundaran, P., Moudgil, B. M., Eds.;
Marcel Dekker: New York, 1987; pp 219-256.
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can Chemical Society: Washington, DC, 1984; pp 269-290.
Con clu sion s
For the employed anionic collectors, factors that cause
an increase in water solubility are indicated by an increase
in cmc and also work to decrease the effectiveness of
adsorption (Γmax) at the liquid-solid interface.
For the prepared surfactants, each having the same basic
structure, increasing the chain length of the hydrophobic
tail enhances their tendency for adsorption at the interface,
i.e., increases Γmax values.
Received for review J une 16, 1998. Accepted October 20, 1998.
J E9801359