Evaluation of a novel morpholine-typed Gemini surfactant as the collector for the reverse flotation separation of halite from carnallite ore

Article abstract of DOI:10.1016/j.molliq.2020.113506

In froth flotation separation process, the collector molecular design has a crucial effect on potash processing to ensure sustainable production of potassium fertilizer (KCl) that is important to secure food supply in human society. Carnallite is an important source of KCl fertilizer production in industry. Reverse flotation has been used to separate halite (NaCl) impurities from carnallite (KCl·MgCl₂·6H₂O) for carnallite resources. However, progress in the carnallite resource reverse froth flotation has been constrained by the inherent limitation of traditional collector molecules with a single hydrophilic head and single hydrophobic chain per molecule. Herein, a novel morpholine-based Gemini molecule with double hydrophilic heads and hydrophobic chains, butanediyl-α, ω-bis (morpholino tetradecylammonium bromide) (BMTB) was synthesized and applied as the flotation collector in the reverse flotation separation for carnallite mineral. The better flotation performance of Gemini BMTB was achieved, compared to the traditional monomeric surfactant N-(n-Tetradecyl) morpholine (TDM). The bench-scale froth flotation separation results revealed that BMTB exhibited outstanding affinity and selectivity for NaCl crystals from carnallite at natural pH, resulting in less collector dosages – only 1/3 of TDM molecules. In contrast with traditional monomeric surfactant TDM (120 g/t), less amount of Gemini BMTB (40 g/t) – only one third of TDM molecules, was needed to obtain higher KCl recovery (KCl recovery raised by 4.69%). Meanwhile, the grade of NaCl with 40 g/t BMTB collector (2.19%) was lower than that with 120 g/t TDM collector (3.91%), and the grade of KCl with BMTB collector (22.59%) was higher than that with TDM collector (22.12%). Therefore, this work demonstrated the next-generation of flotation collector for the reverse froth flotation separation of the carnallite resources.

Full text of DOI:10.1016/j.molliq.2020.113506

Journal Pre-proof
Evaluation of a novel morpholine-typed Gemini surfactant as the
collector for the reverse flotation separation of halite from
carnallite ore
Zhiqiang Huang, Shiyong Zhang, Feng Zhang, Hongling Wang,
Jianrong Zhou, Xinyang Yu, Rukuan Liu, Chen Cheng, Zuwen
Liu, Zhiqun Guo, Guichun He, Guanghua Ai, Weng Fu
PII:
S0167-7322(20)32187-5
DOI:
https://doi.org/10.1016/j.molliq.2020.113506
MOLLIQ 113506
Reference:
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
9 April 2020
28 May 2020
1 June 2020
Please cite this article as: Z. Huang, S. Zhang, F. Zhang, et al., Evaluation of a novel
morpholine-typed Gemini surfactant as the collector for the reverse flotation separation of
halite from carnallite ore, Journal of Molecular Liquids (2020), https://doi.org/10.1016/
j.molliq.2020.113506
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Evaluation of a novel morpholine-typed Gemini surfactant as
the collector for the reverse flotation separation of halite from
carnallite ore
1
1
1
2
3
Zhiqiang Huang , Shiyong Zhang , Feng Zhang , Hongling Wang , Jianrong Zhou , Xinyang
1,
4
1
1,
1
1
1
Yu , Rukuan Liu , Chen Cheng , Zuwen Liu , Zhiqun Guo , Guichun He , Guanghua Ai ,
5
Weng Fu
1. School of Resource and Environment Engineering, Jiangxi University of Science
and Technology, Ganzhou, Jiangxi,34100, China
2. Guangdong Institute of Resources Comprehensive Utilization, Guangzhou, 510650,
China
3. Jiangxi Yaosheng Tungsten Co., Ltd, Ganzhou, Jiangxi, 341321, China
4. Hunan Academy of Forestry, Changsha, Hunan, 410004, China
5. School of Chemical Engineering, The University of Queensland, St Lucia, 4072
QLD, Australia
Abstract
In froth flotation separation process, the collector molecular design has a
crucial effect on potash processing to ensure sustainable production of potassium
fertilizer (KCl) that is important to secure food supply in human society.
Carnallite is an important source of KCl fertilizer production in industry. Reverse
flotation has been used to separate halite (NaCl) impurities from carnallite
(KCl·MgCl2·6H2O) for carnallite resources. However, progress in the carnallite
resource reverse froth flotation has been constrained by the inherent limitation of
traditional collector molecules with a single hydrophilic head and single
hydrophobic chain per molecule. Herein, a novel morpholine-based Gemini
molecule with double hydrophilic heads and hydrophobic chains, butanediyl-α,
 Corresponding author: Tel & Fax number: +86-797-8312131;
E-mail: 172004588@qq.com (X. Yu); liuzw@jxust.edu.cn (Z. Liu)
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ω-bis (morpholino tetradecylammonium bromide) (BMTB) was synthesized and
applied as the flotation collector in the reverse flotation separation for carnallite
mineral. The better flotation performance of Gemini BMTB was achieved,
compared to the traditional monomeric surfactant N-(n-Tetradecyl) morpholine
(TDM). The bench-scale froth flotation separation results revealed that BMTB
exhibited outstanding affinity and selectivity for NaCl crystals from carnallite at
natural pH, resulting in less collector dosages – only one third of TDM
molecules. In contrast with traditional monomeric surfactant TDM (120 g/t), less
amount of Gemini BMTB (40 g/t) – only one third of TDM molecules, was
needed to obtain higher KCl recovery (KCl recovery raised by 4.69%).
Meanwhile, the grade of NaCl with 40 g/t BMTB collector (2.19 %) was lower
than that with 120 g/t TDM collector (3.91 %), and the grade of KCl with BMTB
collector (22.59 %) was higher than that with TDM collector (22.12 %).
Therefore, this work demonstrated the next-generation of flotation collector for
the reverse froth flotation separation of the carnallite resources.
Key words:
Flotation; Morpholine-typed Gemini surfactant; Synthesis; NaCl; Carnallite
1. Introduction
Potassium (K) fertilizer, as one of the most essential fertilizer for the growth of
crops in agricultural production [1-4], is critical to secure global food supply [5, 6]. In
recent years, world consumption of potassium fertilizer has been continuously
increasing due to world population growth and the concurrent need for increased
production of food and biofuels. In industry, carnallite ores obtained by evaporation
of salt lake solution are the main source for producing potassium fertilizer [7, 8].
Reverse froth flotation is an important method to remove NaCl crystals from
carnallite ores to have upgraded carnallite concentrate with NaCl content less than 5%
[9-12]. Multifarious surfactants are recommended to be collectors of NaCl flotation.
At the inchoate period, aliphatic acid (R–COOH) has been applied in the reverse froth
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flotation process [13]. Afterwards, fatty acid primary amide (R–CONH2) has been
verified to be a efficient flotation collector during the reverse froth flotation for
carnallite resources [14]. Currently, alkyl morpholine (R–N(CH2CH2)2O) was applied
as the reverse froth flotation collector for the carnallite ores in production and showed
notable collecting ability to NaCl and selectivity against carnallite [15-17]. However,
current surfactant applied on the carnallite reverse froth flotation separation procedure
is traditional monomeric surfactant with a single hydrophilic head and single
hydrophobic chain per molecule, leading to a low production efficiency.
Gemini surfactant, comprising of two hydrophobic and two hydrophilic groups,
has received attention as a new-style surfactant category [18-20]. It is deserving to be
studied in synthesis, physical chemistry and apply because of its unique and special
properties [21-23]. By comparison to its constituent monomer, Gemini surfactant
exhibits superior surfactivity for instance higher water solubility, lower Krafft point,
improved wetting and foaming properties, lower CMC (critical micelle
concentration), and higher efficiency in decreasing the interfacial tension [24].
Currently, Gemini surfactants have been diffusely used in many realms for instance
bactericidal and anti-fungal agents, dyeing detergents, gene delivery, phase transfer
catalysts, drug delivery, petroleum collection, fabric softeners, effective corrosion
inhibitors, microemulsion stabilization and so on [25-28].
To our knowledge, nevertheless, the method of using Gemini surfactant as a
collector during the reverse froth flotation separation of NaCl from carnallite ores has
not yet been introduced. It is interesting to determine whether Gemini surfactants
could be more efficient and/or effective during the reverse flotation separation of
NaCl from carnallite resources than traditional unimolecular surfactants which have
only a unitary similar hydrophobic group in molecules. Their unique amphipathy and
the well-designed molecular structure make them to become charming for flotation
separation aims. In this study, we systematically investigated the effect of Gemini
molecule as the flotation collector in the reverse flotation separation of the carnallite
minerals.
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2. Materials and methods
2.1. Materials
The carnallite mineral for flotation separation tests was obtained from Qarhan
Salt Lake (Qinghai Province, China). The ingredient of carnallite ores by mineralogy
analysis were largely 78.27% carnallite (KCl·MgCl2·6H2O), 19.94% halite (NaCl),
1.02% gypsum (CaSO4·2H2O) and 0.77% sylvite (KCl). The bench-scale flotation
separation tests were performed in saturated carnallite solutions at room temperature
(25 °C). The chemical composition of carnallite mineral and saturated carnallite
solutions are listed in Table 1.
Table 1 Chemical composition of carnallite minerals and saturated carnallite solutions
(wt%)
Specimen
KCl
17.14
0.49
NaCl
18.55
0.11
MgCl2
28.62
33.85
CaSO4
1.41
H2O
34.28
65.48
Carnallite minerals
Saturated carnallite solutions
0.07
Morpholine-typed Gemini surfactant butanediyl-α, ω-bis (morpholino
tetradecylammonium bromide) (BMTB), synthesized by ourselves, was introduced to
be a collector. The molecular structures of the morpholine-typed Gemini collector
BMTB and conventional unimolecular collector N-(n-Tetradecyl) morpholine TDM
are illustrated in Figure 1. All of the chemical reagents used in the experiment were
analytical grade and had not been further refinement. Carbon-13 and hydrogen-1
NMR spectrum were acquired by BRUKER AVANCE III HD 400 MHz spectrometer
(Switzerland) in CDCl3 solvent with tetramethylsilane to check on the molecular
structure of BMTB. Fourier-transform infrared spectroscopy (AVATAR 370 FT-IR,
Thermo Nicolet Corporation, USA) was also used to disclose the BMTB structure.
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-
2Br
O
N+
(CH2)4
N+
O
O
N
C14H29
C14H29
C14H29
(b)
(a)
Figure 1 Molecular structures of BMTB (a) and TDM (b)
2.2. Bench–scale flotation tests
Bench–scale flotation separation tests were implemented using XFD single-cell
flotation machine (self aeration, Jilin Prospecting Machinery, China) with 750 mL
cubage of cell. In the carnallite ore flotation separation tests, the pulp was prepared by
adding 225 g carnallite ore to 750 mL saturated carnallite solutions. Morpholine-typed
Gemini surfactant BMTB and traditional monomeric surfactant TDM were used as a
collector for these tests at 25 °C. The suspension was stirred for 2 min to
homogeneous, then add collector and stirred for 3 min, continue to float for 7 min.
These processing parameters were selected according to the previous flotation study
of carnallite ores [29, 30]. In the flotation process, halite (NaCl) - loaded foams rose
to the surface of the pulp and made NaCl to be separated from carnallite ore. The
carnallite concentrate was collected, filtered, dried, weighed and measured the
contents of NaCl and KCl in it. The diagrammatic sketch of flotation behavior with
using BMTB or TDM as the collector is depicted in Figure 2.
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Figure 2 The diagrammatic sketch of flotation separation behavior
3. Results and discussion
3.1. Synthesis of BMTB
The preparation of morpholine-typed Gemini surfactant BMTB is shown in
Figure 3. 1-Bromotetradecane (1; 27.73 g, 0.1 mol) was mixed in a reactor with
NaOH (4.8 g, 0.12 mol) at 130 °C for 30 mins. Then, an aqueous solution of
morpholine (2; 10.455 g, 0.12 mol) was injected slowly. The reaction time is 7 hours.
Then, cooling down the mixture to 20 °C leaded to two liquid phase separation. The
top phase contained the product, dried to remove water and produced the achromatous
oil which was N-(n- Tetradecyl) morpholine (3; 26.32 g, 0.093 mol, 93% yield). The
obtained N-(n-Tetradecyl) morpholine (3; 16.98 g, 0.06 mol) and 1,4-dibromobutane
(4; 5.40 g, 0.025 mol) were mixed and set into a reactor containing ethanol (50 mL),
and refluxed for 3 days. The obtained product butanediyl-α, ω-bis (morpholino
tetradecylammonium bromide) (5, 14.645 g, 0.0185 mol) was purified through solvent
evaporation, washing four times by 200 mL of ethyl acetate, recrystallization in mixed
solvent (9/1 v/v ethyl acetate/ ethanol) and vacuum drying.
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NaOH
O
N
C14H29
C14H29Br
O
NH
+
H2O
[2]
[1]
[3]
-
2Br
N+
(CH2)4
N+
O
O
N
C14H29
Br (CH2)4 Br
+
O
C14H29
C14H29
[4]
[3]
[5]
Figure 3 Synthesis equation of BMTB
Butanediyl-α, ω-bis (morpholino tetradecylammonium bromide) (5, BMTB), a
white powder, yield 74.93%. The result of nuclear magnetic resonance spectrum
analysis is showed in Figure 4. 400 MHz 1H NMR (CDCl3, TMS, ppm): δ 0.88 (t, 6H,
2 CH3), 1.15~1.48 (m, 48H, 24 CH2), 1.92 (m, 8H, 2 CH2N+CH2), 2.97 (m, 4H, 2
CH2), 3.51 (m, 4H, 2 CH2N+), 3.98 (m, 8H, 2 CH2OCH2), 4.38 (m, 4H, 2 CH2N+). 100
MHz 13C NMR (CDCl3, ppm): δ 14.04, 22.59, 23.15, 26.64, 28.97, 29.55, 31.82,
51.70, 57.77, 63.44.
a
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b
Figure 4 1H (a) and 13C (b) NMR spectrum of BMTB in CDCl3
The fourier-transform infrared spectroscopy of BMTB is shown in Figure 5. IR
(KBr, cm−1): υ 2921 (υCH3, υCH2), 2852 (υCH3, υCH2), 1467 (υCH3, υCH2), 1113 (υC—N),
1069 (υC—O).
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers /cm-1
Figure 5 Fourier-transform infrared spectroscopy of BMTB
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3.2. Bench-scale flotation tests of carnallite ore
To optimize the amount of collector BMTB or TDM in flotation, bench
experiments were carried out based on Figure 6. Under the flotation condition of
pulp natural pH 6.83, the influence of BMTB or TDM addition to the NaCl recovery
and grade in carnallite concentrate at natural pH 6.83 was illustrated in Figure 7. It
can be seen from Figure 7 that both NaCl grade and NaCl recovery in carnallite
concentrates reduced with a rise of flotation collector amount. Figure 8 shows the
KCl grade and recovery in carnallite concentrate by using TDM or Gemini BMTB at
pH 6.83. From Figure 8, we can see that KCl grade in carnallite concentrate raised
when adding more collectors, while the corresponding KCl recovery decreased. The
optimal collector amounts of BMTB and TDM are 40 g/t and 120 g/t, respectively.
Under this condition, the carnallite concentrate containing 22.59 % KCl and 2.19 %
NaCl was attained by adding 40 g/t BMTB at natural pH=6.83, and the KCl recovery
was 97.98 %. It means that the BMTB has outstanding collecting property to NaCl
and great selectivity for carnallite in actual production. When the dosage of TDM
was 120 g/t, the concentrate with TDM collector with 22.12 % KCl and 3.91 % NaCl
was produced, and the KCl recovery was 93.29 %. In contrast with traditional
monomeric surfactant TDM (120 g/t), less amount of Gemini BMTB (40 g/t) – only
one third of TDM molecules, was needed to obtain higher KCl recovery (KCl
recovery raised by 4.69%). Meanwhile, the grade of NaCl with 40 g/t BMTB
collector (2.19 %) was lower than that with 120 g/t TDM collector (3.91 %), and the
grade of KCl with BMTB collector (22.59 %) was higher than that with TDM
collector (22.12 %). So, we can know through this study that Gemini surfactant
BMTB is a sort of high-performance collector for reverse flotation of NaCl and has
surpassing selectivity for carnallite. It has the ability to become a more admirable
collector in carnallite ore flotation separation than traditional unimolecular collector.
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Feed
Stirring time, 6min
Collector
Flotation time, 8min
Carnallite concentrates
NaCl tailings
Figure 6 The flowsheet of condition flotation tests for reverse flotation of carnallite
minerals
35
TDM-Grade
BMTD-Grade
9
30
25
20
15
10
TDM-Recovery
BMTD-Recovery
8
7
6
5
4
3
2
20
40
60
80
100
120
140
160
Collector dosage/ (g/t)
Figure 7 Grade and recovery of NaCl in carnallite concentrate by using TDM or
BMTB at natural pH 6.83
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23
22
21
20
100
99
98
97
96
95
94
93
92
TDM-Grade
BMTD-Grade
TDM-Recovery
BMTD-Recovery
20
40
60
80
100
120
140
160
Collector dosage/ (g/t)
Figure 8 Grade and recovery of KCl in carnallite concentrate by using TDM or
BMTB at natural pH 6.83
4. Conclusions
A
new Gemini-typed molecule butanediyl-α, ω-bis (morpholino
tetradecylammonium bromide) (BMTB) was prepared and utilized as flotation
collector surfactant. Compared to traditional monomeric TDM collector (120 g/t),
only one third of BMTB dosage (40g/t) presented a better flotation performance for
better KCl recovery and higher NaCl rejection, producing high-quality carnallite
concentrate. Thus, the molecular-level designed Gemini collector meets the urgent
requirements for the next generation of reverse flotation reagents with improved
performance and less chemical usage in industrial application.
Acknowledgements
The authors express their appreciation for the support of the National Natural
Science Foundation of China (Grant No. U1607108, 51774152 and 51874150), The
Natural Science Foundation for Distinguished Young Scholars of Jiangxi province
(Grant No. 20192BCB23016 and 20192BCB23017), Jiangxi Double Thousand Plan,
The Youth Jinggang Scholars Program in Jiangxi Province, Natural Science
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Foundation
of
Jiangxi,
China
(Grant
No.
20171BCB18002),
Educational Commission of Jiangxi Province of China (Grant No. GJJ170504),
Program of Qingjiang Excellent Young Talents, Jiangxi University of Science and
Technology.
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Author Statement
Zhiqiang Huang: Methodology. Shiyong Zhang, Feng Zhang, Hongling Wang and
Jianrong Zhou: Investigation. Xinyang Yu: Funding acquisition. Rukuan Liu, Chen
Cheng and Zuwen Liu: Formal analysis. Zhiqun Guo and Guichun He: Data curation,
Formal analysis. Guanghua Ai: Investigation. Weng Fu: Writing - review & editing.
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Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be
considered as potential competing interests:
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Journal Pre-proof
Graphical abstract
Gemini surfactant as a collector for reverse froth flotation separation of halite from
carnallite ore for potassium fertilizer production
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Journal Pre-proof
Research highlights
► Halite was separated by reverse flotation using a Gemini surfactant BMTB.
► BMTB exhibited superior selectivity for halite against carnallite.
► BMTB displayed superior flotation performances than conventional surfactant
TDM.
► Gemini surfactant is hopeful to the reverse flotation separation of carnallite ore.
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