Morpholine-Based Gemini Surfactant: Synthesis and Its Application for Reverse Froth Flotation of Carnallite Ore in Potassium Fertilizer Production

Article abstract of DOI:10.1021/acs.jafc.8b05560

Potassium fertilizer plays a critical role in increasing the food production. Carnallite is concentrated by reverse froth flotation and used as a raw material to produce potassium fertilizer (KCl) in agriculture. However, all the surfactants used in the carnallite reverse flotation process are conventional monomeric surfactants contain a single similar hydrophobic group in the molecule, which results in a low production efficiency. In this work, a new morpholine-based Gemini surfactant, 1,4-bis (morpholinododecylammonio) butane dibromide (BMBD), was prepared and originally recommended as a collector for reverse froth flotation separation of halite (NaCl) from carnallite ore. The flotation results indicated BMBD had higher flotation recovery and stronger affinity of halite against carnallite compared with conventional monomeric surfactant N-(n-Dodecyl) morpholine (DDM). Fourier transform infrared spectra suggested that BMBD molecules were adsorbed on halite surface rather than the carnallite surface. Additionally, BMBD molecules can strongly reduce the surface tension of NaCl saturated solution. Considering the BMBD's unique properties, such as double reactive centers to mineral surfaces, double hydrophobic groups, and stronger surface tension reducing ability, made it be a superior collector for reverse flotation desalination from carnallite ores than DDM.

Full text of DOI:10.1021/acs.jafc.8b05560

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Agricultural and Environmental Chemistry
Morpholine-based Gemini surfactant: synthesis and its application for
reverse froth flotation of carnallite ore in potassium fertilizer production
Zhiqiang Huang, Chen Cheng, Liqing Li, Zhizhong Guo, Guichun He,
Xinyang Yu, Rukuan Liu, Haijun Han, Lanqing Deng, and Weng Fu
J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.8b05560 • Publication Date (Web): 28 Nov 2018
Downloaded from http://pubs.acs.org on November 30, 2018
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Page 1 of 28
Journal of Agricultural and Food Chemistry
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Morpholine-based Gemini surfactant: synthesis and its application
for reverse froth flotation of carnallite ore in potassium fertilizer
production
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1
1
2, *
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1
1
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Zhiqiang Huang , Chen Cheng , Liqing Li , Zhizhong Guo , Guichun He , Xinyang Yu ,
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2
4
5, *
Rukuan Liu , Haijun Han , Lanqing Deng , Weng Fu
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1School of Resource and Environment Engineering, Jiangxi University of Science and
Technology, Ganzhou, Jiangxi,34100, China
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2School of Metallurgical and Chemical Engineering, Jiangxi University of Science and
Technology, Ganzhou, Jiangxi,34100, China
3Hunan Academy of Forestry, Changsha, Hunan, 410004, China
4School of Pharmacy, Hunan University of Chinese Medicine, Changsha, Hunan, 410083, China
5School of Chemical Engineering, The University of Queensland, St Lucia, 4072 QLD, Australia
 Corresponding authors: Tel & Fax number: +86-797-8312131; E-mail: liliqing790827@163.com
(L. Li); w.fu1@uq.edu.au (W. Fu)
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Abstract
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Potassium fertilizer plays a critical role in increasing the food production. Carnallite is
concentrated by reverse froth flotation and used as a raw material to produce potassium fertilizer
(KCl) in agriculture. However, all the surfactants used in the carnallite reverse flotation process
are conventional monomeric surfactants contain a single similar hydrophobic group in the
molecule, which results in a low production efficiency. In this work, a new morpholine-based
Gemini surfactant, 1,4-bis (morpholinododecylammonio) butane dibromide (BMBD) was
prepared, and originally recommended as a collector for reverse froth flotation separation of halite
(NaCl) from carnallite ore. The flotation results indicated BMBD had higher flotation recovery
and stronger affinity of halite against carnallite, compared with conventional monomeric
surfactant N-(n-Dodecyl) morpholine (DDM). FTIR spectra suggested that BMBD molecules
were adsorbed on halite surface rather than the carnallite surface. Additionally, BMBD molecules
can strongly reduce the surface tension of NaCl saturated solution. Considering the BMBD’s
unique properties, such as double reactive centers to mineral surfaces, double hydrophobic groups,
and stronger surface tension reducing ability, made it be a superior collector for reverse flotation
desalination from carnallite ores than DDM.
Key words: Potassium fertilizer; Morpholine-based Gemini surfactant; Reverse flotation; Halite;
Carnallite ore
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INTRODUCTION
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As food and agriculture are essential to the development of human civilization, modern
technology and innovation have been used to address the challenge of the increasing food
demand1. In modern agriculture, potassium fertilizer is one of the major nutrient to boost the
growth of agricultural plants2, 3. Carnallite is used as a raw material to produce potassium fertilizer
by cold decomposition, with formation of MgCl2 in solution and KCl as a solid phase4-6. Reverse
froth flotation is widely used in mining industry to produce upgraded carnallite concentrate with
low NaCl level7-9. Various surfactants are assessed as flotation collectors to float out halite from
carnallite ores by reverse froth flotation. In the early stages, fatty acids (R–COOH) have been used
for flotation desalination10. Later on, N-alkylamides (R–CONH2) have been proved to be the
effective collectors in the reverse flotation of carnallite ores11. Recently, N-alkylmorpholines
(R–N(CH2CH2)2O) were used as flotation collectors in industry and possessed significant
collecting power for halite and selectivity against carnallite12,13. Unfortunately, all the surfactants
used in the carnallite reverse flotation process are conventional monomeric surfactants contain a
single similar hydrophobic group in the molecule, which results in a low production efficiency.
Gemini molecules are a new type of surfactants that consist of two traditional monomeric
amphiphiles that are covalently connected by a spacer unit14,15. In contrast to conventional
monomeric surfactants, Gemini molecules possess superior properties, such as lower critical
micelle concentration, lower Krafft point, higher solubilization power, higher surface activity,
improved wetting and foaming properties16,17. Therefore, Gemini surfactants are widely applied in
different fields such as phase transfer catalysts, drug entrapment/release, body care products,
biomedical processes including gene transfection, preparation of high-porosity materials, synthesis
of nanomaterials, food industry, oil recovery, polymerizations, antibacterial and antifungal
preparations, etc18-20
.
As far as we know, however, Gemini surfactant has not been used as a collector reagent in
carnallite flotation desalination process. There is interest in determining whether the Gemini
would be more efficient and/or effective in the reverse froth flotation of carnallite ores than
conventional monomeric surfactant which contains a single similar hydrophobic group in the
molecule. Its unusual amphiphilic properties and the tailored structure, makes it attractive for
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beneficiation purposes.
In this paper,
a
novel
morpholine-based
Gemini
surfactant,
1,4-bis
1
(morpholinododecylammonio) butane dibromide (BMBD) was prepared and tested by FTIR, H
and 13C NMR spectra, and its flotation behaviors to carnallite ore were assessed via
micro-flotation and bench-scale flotation experiments. Afterwards, the adsorption mechanism of
Gemini collector BMBD to halite and carnallite, and air/NaCl saturated solution interface was
evaluated through FTIR and surface tension measurement.
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MATERIALS AND METHODS
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Materials
Pure halite and carnallite minerals were recieved from Taian and Geermu, respectively.
Chemical compositions of the two minerals were shown in Table 1. The crystallinity of these
minerals tested by powder XRD was shown in Figure 1. The grinded minerals within a size range
of 150–270 µm were chosen for micro-flotation tests. The fine minerals (< 5 µm) were used for
FTIR tests. Saturated halite or carnallite solutions for micro-flotation tests and surface tension
measurements were separately obtained by dissolving individual halite or carnallite mineral into
DI water. Then the obtained saturated solutions were passed through filters to remove mineral
residues.
The carnallite ore for bench-scale flotation tests were acquired from Qinghai Salt Lake
Industry Group Company in China. The samples were mainly composed of 77.95% carnallite,
21.01% halite, 0.91% gypsum and 0.13% sylvite by the results of mineralogy analysis. The bench
tests were conducted in saturated carnallite solutions at a temperature of 20 °C. Chemical
composition of carnallite ore and saturated carnallite solutions were shown in Table 2.
Morpholine-based Gemini surfactant 1,4-bis(morpholinododecylammonio) butane dibromide
(BMBD), as a collector, was synthesized by our team. Both the solvent and reagents applied in
synthesis process were of analytical grade. They were used as received without further
purification. To verify the chemical structure of BMBD, carbon-13 and hydrogen-1 NMR spectra
were collected by Bruker Avance 400 spectrometer (Switzerland) in CDCl3 solvent with
tetramethylsilane. Fourier-transform infrared spectroscopy (FTIR, Nicolet iS50) was also used to
disclose BMBD structure.
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Micro-flotation experiments
Micro-flotation experiments were conducted by a 50 mL of flotation equipment (XFG2) at
1500 rpm impeller speed. For each flotation experiment, 3 g of pure mineral particles was put into
30 mL saturated solution in flotation equipment. The slurry was mixed for 4 min in presence of
the desired collector. After 7 min of flotation, both the froth products and tailings were separated,
filtrated, dried under vacuum condition and finally measured by mass. In each test, the flotation
recovery was measured, according to the mass ratio of different solid fractions.
Bench–scale froth flotation
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Bench-scale tests were conducted in a 1.5 dm3 of XFDC cell at l500 rpm impeller speed.
500g carnallite ores were added into 1 L saturated carnallite solutions in the cell. Then, the
prepared slurry was mixed with a certain amount of BMBD collector for 6 min. After that, a
quantitative amount of air was pumped into the centre of the cell and mixed thoroughly with the
pulp for 8 min, leading to the exposure of slurry to froth. Finally, halite-laden bubbles floated out
to the top of cell and separated from carnallite mineral. After collecting dry carnallite concentrates
and tails separately, the mass of them were measured by the assay for KCl and NaCl, from which
the metal recoveries were acquired. Replication were tested three times under each conditions,
mean values of which were measured. The flotation flowsheet was shown in Figure 2.
FTIR spectra measurement
Fine mineral (<5 µm, 2g) solid was soaked in 30 mL of saturated halite or carnallite solutions
with or without 3×10-6 mol/L BMBD at natural pH and 20 °C for 6 h. Then, the residue from the
mixed solution was filtrated and dried under vacuum condition. 1mg of dried sample and 150 mg
of KBr powder were mixed and pressed into a tablet for FTIR test (700-4000 cm-1) using Nicolet
iS50 equipment.
Surface tension measurement
The surface tensions of saturated halite solutions in presence of BMBD or DDM were tested
by the Du Noüy ring equipment at 20 °C. Before each test, the platinum Du Noüy ring was treated
through a standard cleaning procedure to remove the impurities. In every test, 30 ml of saturated
solution was mixed by a certain amount of BMBD or DDM.
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RESULTS AND DISCUSSION
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Synthesis of morpholine-based Gemini surfactant BMBD
The synthesis of morpholine-based Gemini surfactant BMBD was described in Figure 3.
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1-Bromododecane (1; 49.85 g, 0.2 mol) was placed in a 250 mL three neck flask with NaOH (12
g, 0.3 mol) and heated to 130 °C. Over 20 minutes, morpholine (2; 20.91 g, 0.24 mol) in 25 mL of
H2O was added in dropwise. The mixture was heated for 6 hours further, then cooled to room
temperature over 30 minutes, causing 2 layers to form. The top layer of reaction mixture was
collected, dried by anhydrous CaCl2, and filtrated to generate the colorless oil of N-(n-Dodecyl)
morpholine (3; 48.53 g, 0.19 mol), the yield of which was 95%. The resulting compound
N-(n-Dodecyl) morpholine (3; 30.65 g, 0.12 mol) and 1,4-dibromobutane (4; 10.8 g, 0.05 mol)
were placed in a 250 mL round bottom flask containing ethanol (50 mL), and the mixture was
agitated for three days at the reflux temperature of 90 °C. After removing the ethanol by rotary
evaporation, the crude product acquired was subsequently washed three times with 150 mL of
ethyl acetate, and then purified by recrystallization from ethyl acetate/ethanol (10/1 v/v ) at least
three times. The precipitates after removal of ethanol and ethyl acetate through vacuum filtration
were dried in vacuum drying oven for 24 h, which gave pure corresponding morpholine-based
Gemini surfactant 1,4-bis (morpholinododecylammonio) butane dibromide (5, 27.66 g, 0.038
mol).
1,4-Bis (morpholinododecylammonio) butane dibromide (5, BMBD), a white powder, yield
76.19%. 400 MHz 1H NMR (CDCl3, TMS): δ 0.87 (t, 6H), 1.16~1.45 (m, 40H), 1.93 (m, 8H), 2.98
(m, 4H), 3.47 (m, 4H), 3.97 (m, 8H), 4.37 (m, 4H). 100 MHz 13C NMR (CDCl3): δ 13.98, 22.50,
23.13, 26.56, 28.90, 29.41, 31.71, 51.61, 57.65, 63.34. IR (KBr): 2923, 2853, 1468, 1112, 1066
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cm−1.
Micro-flotation of pure minerals
As shown in Fig. 4(a), the relationship between halite recovery and the concentration of
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BMBD or DDM collectors suggested that halite recoveries grew fast with the increase of collector
concentrations, reaching the high recoveries (>99%) at 1×10-5 mol/L of BMBD and 1×10-4 mol/L
of DDM, respectively. The result clearly illustrated that BMBD was more potent collector for
halite than DDM, since the BMBD concentration required for high halite recovery was one order
of magnitude less than that of DDM concentration at neutral pH.
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Fig. 4(b) presented the effect of collector concentration on the carnallite recovery, indicating
that both BMBD and DDM had extremely low affinity for carnallite mineral surface due to the
low carnallite recoveries (<6%) in the whole range concentration of collectors. In particular, the
optimum concentration of BMBD collector was 1×10-5 mol/L owing to the high halite recovery
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(98%) and low carnallite recovery (<4%).
Bench froth test of carnallite ore
The flotation flowsheet of bench tests was shown in Figure 2. The test conditions and results
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in Table 3 indicated that the carnallite concentrates containing 22.44 % KCl and 2.45 % NaCl
was produced via adding 40 g/t BMBD collector at pH of 6.83, and the KCl recovery was
98.17%. This indicated Gemini surfactant had powerfully collecting power for halite and
excellent selectivity against carnallite at natural pH. While for 120 g/t DDM, the grade of its
carnallite concentrates were 22.07 % KCl and 4.04 % NaCl, and the flotation recovery of KCl
was 93.93 %. Therefore, achieving the comparative flotation performance (KCl recovery >90%),
the dosage of Gemini type BMBD collector (40 g/t) is three times less than that of monomeric
DDM collector (120 g/t). The results also suggest the tailing produced by 40 g/t BMBD contains
slightly higher amount of KCl and lower NaCl content than the tailing generated by 120 g/t
DDM. Therefore, compared with DDM, Gemini BMBD has been demonstrated as a better
collector of carnallite ore for potassium fertilizer production.
FTIR spectra
Figure 5 presented the FTIR spectra of BMBD, halite and carnallite particles with or without
BMBD treatment. As shown in Fig. 5(a), the IR spectra of BMBD indicated that the absorption
bands at 2923, 2853 and 1468 cm-1 were attributed to stretching of C–H21-25. The C–N vibrations
occurred on 1112 cm-1 26-29. The band at 1066 cm-1 was attributed to C–O stretching vibration30-32
.
Fig. 5(a) also showed that the C–H stretching peaks at 2923, 2853 and 1468 cm-1 appeared at
halite surface in presence of BMBD, and the stretching vibrations of C–N bonds originated from
BMBD appeared at 1112 cm-1 on halite, indicating the adsorption of BMBD on halite surfaces.
But for carnallite treated with BMBD shown in Fig 5(b), the absence of FTIR bands of BMBD
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molecules suggested the negligible interaction between BMBD and carnallite 33-36
.
Surface tension results
The surface tension (γ) measurements of BMBD and DDM in a NaCl-saturated solution at
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natural pH were shown in Fig. 6. The CMC values (critical micellization concentration) and the
γCMC values were shown in Table 4.
Surface tension in Fig. 6 declined fastly with the rise of surfactant concentration, then
reached a platform at CMC concentration. The results also suggested that Gemini surfactant
BMBD was a stronger collector than the conventional monomeric surfactant DDM at decreasing
the air–NaCl surface tension. At 3×10-6 mol/L, BMBD reduced the solution surface tension to 28.6
mN/m, whilist the surface tension in presence of DDM was 60.7 mN/m. Table 4 showed that the
CMC values of BMBD and DDM were 3×10-6 mol/L and 2.5×10-5 mol/L respectively, wherein
CMC value of BMBD was nearly one order of magnitude less than that of DDM, which was
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consistent with prior studies37-39
.
Discussion
The micro-flotation and bench-scale flotation results suggested that Gemini surfactant BMBD
had better flotation ability of carnallite ore than the conventional monomeric surfactant DDM, as
well as excellent collecting power for halite and significant selectivity against carnallite. FTIR
spectra results showed that the characteristic absorption peaks of C–H and C–N stretching
vibrations in BMBD moleucles appeared on halite surfaces, indicating the adsorption of BMBD
on halite. No adsorption band of BMBD was found on the surface of carnallite, suggesting that the
BMBD had a negligible effect on the carnallite surface. Therefore, BMBD presented excellent
collecting power for halite and significant selectivity against carnallite in accrodance with the
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micro-flotation and bench-scale flotation findings, which was consistent in prior studies 40,41
.
Surface tension measurements results suggested BMBD molecule was much stronger than the
conventional monomeric surfactant DDM in reducing the air-NaCl saturated solution interfacial
tension. BMBD was able to decrease the air-NaCl saturated solution interfacial tension to 28.6
mN/m, compared with the corresponding value (60.7 mN/m) for DDM at the same concentration
3×10-6 mol/L (Fig.6). A low surface tension could be beneficial to the formation of stable and
small bubbles in the flotation process42,43. Besides, in consequence of the addition of collector
BMBD or DDM, the air bubbles generated below the surface of NaCl-saturated solution were
partly lined with a monomolecular sheath of BMBD or DDM molecules that decreased the
air-NaCl saturated solution interfacial tension44. This enabled each bubble with its lining to
approach other bubbles without coalescing. Since BMBD was much stronger than DDM in
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reducing the air-NaCl saturated solution interfacial tension, the obstruction of bubble coalescence
and the stability of froth generated by BMBD were greater than that by DDM, which was
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consistent in prior studies 45,46
.
As BMBD or DDM was put to the pulp, they might adsorb on the mineral particles with their
non-polar ends orientated towards the bulk solution, thus transforming the surfaces of minerals
from a hydrophilic condition to a hydrophobic condition, which created the required condition for
attachment to air bubbles47. BMBD had two hydrophobic chains per molecule, and this might raise
the collision probability between the hydrophobic minerals and bubbles. Whilst, the hydrophobic
minerals attached to bubbles via collector’s non-polar groups orientated towards the air48, and the
interfacial tension of BMBD at air-NaCl saturated solution interface was lower than that of DDM,
hence the attachment between minerals and froth might be more stable by using BMBD as a
collector. Therefore, BMBD presented better flotation ability of carnallite ore than DDM for
potassium fertilizer production. The potential flotation mechanism of BMBD or DDM for
carnallite ore was illustrated in Fig. 7.
In
conclusion,
a
novel
morpholine-based
Gemini
collector
1,4-bis
(morpholinododecylammonio) butane dibromide (BMBD) was synthesized and characterized in
this paper. The flotation performance of BMBD was compared with conventional monomeric
collector N-(n-Dodecyl) morpholine (DDM) in reverse froth flotation of carnallite ore. The
micro-flotation and bench-scale flotation results indicated that Gemini surfactant exhibited higher
collector capacity and selectivity for halite than the conventional monomeric surfactants.
Compared with conventional monomeric collector DDM (120g/t), less amount of BMBD (40 g/t)
is needed to achieve better KCl recovery and lower NaCl content in the final tailing. FTIR spectra
recommended that BMBD could preferentially bind to the surface of halite mineral rather than the
carnallite surface. Surface tension measurements demonstrated that BMBD was more efficient
than DDM at decreasing the air-NaCl saturated solution interfacial tension. Therefore,
Gemini-type BMBD surfactant with both strong hydrophobic and hydrophilic groups is an
excellent collector candidate to separate halite from carnallite ore in potassium fertilizer industry.
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AUTHOR INFORMATION
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Corresponding Authors
*E-mail: liliqing790827@163.com (L. Li)
*E-mail: w.fu1@uq.edu.au (W. Fu)
ORCID
Zhiqiang Huang: 0000-0002-5562-8407
Weng Fu: 0000-0003-0664-2787
Funding
The authors express their appreciation for the support of the National Natural Science Foundation
of China (Grant No. U1607108 and 51774152), Natural Science Foundation of Jiangxi, China
(Grant No. 20181BAB216018, 20171BCB23065 and 20171BCB18002), China Postdoctoral
Science
Foundation
(Grant
No.
2016M592118),
Educational Commission of Jiangxi Province of China (Grant No. GJJ170504), and Hunan
Provincial Natural Science Foundation of China (Grant No. 2016JJ4086).
Notes
The authors declare no conflict of interest.
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Tables
373
374
375
376
377
378
Table 1. Chemical composition of the pure minerals (wt%)
Table 2. Chemical composition of carnallite ore and saturated carnallite solutions (wt%)
Table 3. Reverse flotation results of carnallite ore with 40 g/t BMBD or 120 g/t DDM as a
collector at natural pH 6.83
Table 4. Values of the CMC and γCMC for BMBD and DDM
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380
Table 1. Chemical composition of the pure minerals (wt%)
Sample
Halite
KCl
—
NaCl
99.50
0.66
MgCl2
—
CaSO4
—
H2O
0.50
Carnallite
26.33
33.62
1.05
38.34
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382
383
Table 2. Chemical composition of carnallite ore and saturated carnallite solutions (wt%)
Sample
KCl
18.13
0.88
NaCl
19.95
0.17
MgCl2
27.78
32.34
CaSO4
1.29
H2O
32.85
66.52
Carnallite ore
Saturated carnallite solutions
0.09
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385
386
387
388
Table 3. Reverse flotation results of carnallite ore with 40 g/t BMBD or 120 g/t DDM as a
collector at natural pH 6.83
Collector
Entry
1
Product
Weight/%
Grade/%
Recovery/%
KCl NaCl
KCl
NaCl
2.25
Tailings
Concentrates
Feed
80.19
19.81
100.00
80.51
19.49
100.00
81.08
18.92
100.00
22.46
1.92
97.93
2.07
8.92
91.08
100.00
9.91
92.98
20.22
2.48
18.39
22.33
1.71
100.00
98.18
1.82
2
3
Tailings
Concentrates
Feed
BMBD 40 g/t
93.15
20.15
2.61
90.09
100.00
10.85
89.15
100.00
9.89
18.31
22.52
1.58
100.00
98.39
1.61
Tailings
Concentrates
Feed
91.87
19.50
2.45
18.56
22.44
0.43
100.00
98.17
0.23
Average Tailings
RSD
7.45
9.76
4
5
6
Tailings
Concentrates
Feed
78.21
21.79
100.00
79.07
20.93
100.00
78.60
21.40
100.00
22.08
5.66
3.89
83.13
21.16
4.17
93.33
6.67
14.38
85.62
100.00
15.57
84.43
100.00
15.29
84.71
100.00
15.08
4.13
18.50
22.01
4.94
100.00
94.39
5.61
Tailings
Concentrates
Feed
DDM 120 g/t
85.42
21.17
4.06
18.44
22.12
5.13
100.00
94.06
5.94
Tailings
Concentrates
Feed
82.64
20.88
4.04
18.48
22.07
0.25
100.00
93.93
0.58
Average
Tailings
RSD
3.49
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Table 4. Values of the CMC and γCMC for BMBD and DDM
390
Surfactant
BMBD
DDM
CMC (mol/L)
3×10-6
γCMC (mN/m)
28.4
2.5×10-5
31.1
391
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393
Figures
394
395
396
397
398
399
400
401
402
403
Figure. 1. XRD of halite and carnallite
Figure. 2. The flowsheet of reverse froth flotation experiments
Figure. 3. Synthetic route for morpholine-based Gemini surfactant BMBD
Figure. 4. Flotation recovery of halite (a) and carnallite (b) as a function of collector concentration
at natural pH
Figure. 5. FTIR spectra of BMBD, halite (a) and carnallite (b) before and after interaction with
BMBD
Figure. 6. The surface tension for BMBD and DDM in a NaCl-saturated solution
Figure. 7. BMBD or DDM as a collector for reverse froth flotation separation of halite from
carnallite ore for potassium fertilizer production
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C
H
C
C
Halite
H
Carnallite
C
C
C
C
C
C
H
C
C
C
C
C
C
C
H
H
C
H
C
H
C
C
H
14.98 24.98 34.98 44.98 54.98 64.98 74.98
14.98 24.98 34.98 44.98 54.98 64.98 74.98
Two-Theta/ deg
Two-Theta/ deg
404
405
Figure. 1. XRD of halite and carnallite
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Feed
Stirring time, 6min
Collector
Flotation time, 8min
Tailings (carnallite concentrates)
Concentrates (NaCl tailings)
406
407
Figure. 2. The flowsheet of reverse froth flotation experiments
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409
NaOH
O
N
C H
12 25
C H Br
12 25
O
NH
+
H2O
[2]
[1]
[3]
-
2Br
+
+
O
N
C H
12 25
Br (CH )
Br
+
O
N
(CH )
N
O
2 4
2 4
C
H
C
H
12 25
12 25
[4]
[3]
[5]
410
411
412
Figure. 3. Synthetic route for morpholine-based Gemini surfactant BMBD
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100
80
60
40
20
0
100
a
b
DMP
BMBD
DMP
BMBD
80
60
40
20
0
1E-7
1E-6
1E-5
1E-4
1E-7
1E-6
1E-5
1E-4
Concentration/ mol/L
Concentration/ mol/L
413
414
Figure. 4. Flotation recovery of halite (a) and carnallite (b) as a function of collector concentration
415
at natural pH
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417
a
BMBD
Halite with BMBD
Halite
4000
3500
3000
2500
2000
1500
1000
Wavenumbers /cm-1
418
b
Carnallite with BMBD
Carnallite
4000
3500
3000
2500
2000
1500
1000
Wavenumbers /cm-1
419
420
421
Figure. 5. FTIR spectra of BMBD, halite (a) and carnallite (b) before and after interaction with
BMBD
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65
60
55
50
45
40
35
30
25
DDM
BMBD
1E-7
1E-6
1E-5
1E-4
Surfactant concentration/ mol/L
422
423
Figure. 6. The surface tension for BMBD and DDM in a NaCl-saturated solution
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425
Figure. 7. BMBD or DDM as a collector for reverse froth flotation separation of halite from
carnallite ore for potassium fertilizer production
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Gemini surfactant as a collector for reverse froth flotation separation of halite from carnallite ore for
potassium fertilizer production
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