The Desulfurization of Magnetite Ore by Flotation

minerals Article

The Desulfurization of Magnetite Ore by Flotation with a Mixture of Xanthate and Dixanthogen Jun Yu, Yingyong Ge * and Xinwei Cai School of Resources and Environment Engineering, Wuhan University of Technology, Wuhan 430070, China; [email protected] (J.Y.); [email protected] (X.C.) * Correspondence: [email protected]; Tel.: +86-27-8747-1645 Academic Editor: Kota Hanumantha Rao Received: 27 May 2016; Accepted: 4 July 2016; Published: 8 July 2016

Abstract: The contamination of sulfur emanating from pyrrhotite in magnetite concentrates has been a problem in iron ore processing. This study utilized froth flotation to float pyrrhotite away from magnetite using collectors of xanthate and dixanthogen. It was found that xanthate or dixanthogen alone could not achieve selective separation between pyrrhotite and magnetite in flotation. A high loss of magnetite was obtained with xanthate, while a low desulfurization degree was obtained with dixanthogen. It was interesting that a high desulfurization ratio was achieved with little loss of magnetite when xanthate was mixed with dixanthogen as the collector. The synergistic effect of the mixed collector on pyrrhotite was studied by electrokinectic studies and FTIR measurements. It was found that xanthate was the anchor on pyrrhotite and determined its selectivity against magnetite, while dixanthogen associated with xanthate, enhancing its hydrophobicity. This study provides new insights into the separation of iron minerals. Keywords: pyrrhotite; mixed collectors; flotation; synergetic effect

1. Introduction In recent decades, there has been an ever-increasing demand for iron ore because of its great demand in metallurgy industries [1]. Due to the depletion of high quality iron ores, complex ultrafine iron ores with a high content of impurities, such as sulfur, have been processed [2]. Pyrrhotite (Fe1´x S) is a kind of common sulfide which exists in magnetite ore as an associated mineral with little industrial value. The contamination of sulfur emanating from pyrrhotite in magnetite concentrates has been a problem in iron ore smelting process. However, the magnetic separation of pyrrhotite from magnetite is problematic, due to their similar magnetic property and magnetic flocculation between pyrrhotite and magnetite [3]. Flotation has been commercially used as a method for removing pyrrhotite from magnetite for high sulfurous iron ores [4]. In this process, pyrrhotite as a primary impurity is separated from iron ore using typically potassium butyl xanthate as the primary collector. The flotation process normally adds copper sulfate as an activator which could accelerate the flotation rate of pyrrhotite. The flotation is conducted at the natural pH of the milled ore which may vary between 7.5 and 9 but it is typically closer to the higher value [5]. However, in the practice of iron ore flotation, the loss of valuable mineral in tailings is the major problem confronting the iron ore industry. Thus, the reagent suit is formulated to create the appropriate chemical environment for effective separation. The collector suit is often tuned to use mixed collectors to enhance both grade and recovery of the concentrate, and to lower cost [6]. The use of dissimilar surfactant mixtures can have a synergistic advantage over the use of individual surfactants [7–11]. The influence of nonionic reagents on anionic collector flotation of calcium minerals was investigated [12]. The addition of nonionic reagents to anionic collectors Minerals 2016, 6, 70; doi:10.3390/min6030070

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enhanced the flotation separation efficiency of calcium minerals due to hydrophobic chain interactions and reduction of electrostatic repulsion between ionic head groups that are shielded from each other by the nonionic surfactant molecules. A process involving the use of mixed anionic and cationic collectors for muscovite mica was studied [13]. The flotation recovery could be enhanced using a mixture of dodecylamine acetate with sodium oleate. The adsorption of both the cationic and anionic collectors was enhanced due to co-adsorption. A combined cationic (amine) and anionic collector (sodium xanthate) was also reported to be effective for the flotation of zinc oxide at pH 11 [14]. In this study, attempts were made to enhance the selective separation of pyrrhotite from magnetite. Flotation experiments were conducted with different collector suits (xanthate, dixanthogen, and their mixture). The synergetic effects of mixing dixanthogen with xanthate were also studied by zeta potential and infrared spectroscopic measurements. 2. Materials and Methods 2.1. Materials A magnetic concentrate was obtained from Baogang plant (Neimeng, China). The principal research sample was the magnetic product of the primary iron ore containing 65.10% Fe. The results of chemical analyses of this sample are given in Table 1 and the chemical compositions of which are given in Table 2. From Tables 1 and 2, it is observed that the magnetite, pyrrhotite, quartz, and calcite are the main compositions in this sample. Table 1. Chemical analysis results of magnetic concentrate (mass fraction, %). Composition

TFe *

Fe2 O3

SiO2

Al2 O3

K2 O

CaO

MgO

P

S

TiO2

wt %

65.10

92.35

3.54

0.35

0.026

1.68

0.25

0.049

1.64

0.10

* TFe: Total iron.

Table 2. Analysis of iron chemical phase in the magnetic concentrate (mass fraction, %). Composition wt %

Magnetite Pyrrhotite 86.88

4.32

Pyrite

Quartz

Calcite

Dolomite

Phyllite

Barite

0.23

3.56

2.56

1.22

0.47

0.75

The pure pyrrhotite mineral and magnetite used in this study was provided by Baogang Mine, Neimeng Province, China. The mineral compositions of pure pyrrhotite and magnetite were analyzed by Mineralogical Liberation Analysis (MLA). The analysis results in Tables 3 and 4 show that it was of high purity with minor impurities in pyrrhotite and magnetite. The lumps of pyrrhotite and magnetite were crushed and ground to a particle size less than 74 µm in a ceramic ball mill. The powder of ´74 µm was further ground to ´2 µm for zeta potential and FTIR experimental studies. The mineral sample was stored in a glass drying dish for further investigations. Table 3. Minerals compositions of pure pyrrhotite. Minerals

Pyrrhotite

Chalcopyrite

Limonite

Dolomite

Quartz

Mica

wt %

98.51

0.32

0.10

0.35

0.08

0.40

Table 4. Minerals compositions of pure magnetite. Minerals

Magnetite

Quartz

Calcite

Ankerite

Phyllite

Siderite

wt %

97.12

0.84

0.45

0.33

0.41

0.22


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The collector used in the tests was sodium butyl xanthate (NaBX, CH3 CH2 CH2 CH2 OCS2 Na) supplied from Zhuzhou Flotation Reagents Plant (Zhuzhou, China). Dibutyl dixanthogen ((BX)2 ) was used as a collector which was synthesized with xanthate and hydrogen peroxide. The Dibutyl dixanthogen was purified by extraction. Sodium fluosilicate (Na2 SiF6 ) was used as an activator. Mineralscarbonate, 2016, 6, 70 sulfuric acid, hydrochloric acid, and sodium hydroxide of analytical grade 3 offrom 13 Sodium Kemiou Chemical Reagent Co. Ltd. (Tianjin, China) were used to regulate the pH of the system. Kemiou Chemical Reagent Co. Ltd. (Tianjin, China) were used to regulate the pH of the system. Pine Pine oil has been used as the frother. Distilled water was used in all the experiments. oil has been used as the frother. Distilled water was used in all the experiments. 2.2. Methods 2.2. Methods 2.2.1. Grinding and Flotation Experiments 2.2.1. Grinding and Flotation Experiments The grinding was carried out at room temperature using tap water. 400 g magnetic concentrate The grinding was carried out at room temperature using tap water. 400 g magnetic concentrate sample at 66.7% solid density was ground in a ball mill to gain an 85 wt % passing size of 74 µm. sample at 66.7% solid density was ground in a ball mill to gain an 85 wt % passing size of 74 µm. The The mill discharge was transferred to a 1.0 dm3 XFD-type laboratory flotation cell. The air flow mill discharge3 was transferred to a 1.0 dm3 XFD-type laboratory flotation cell. The air flow rate was rate was 345 dm /h and the agitation speed was 1800 rpm. The flotation experiments were carried 45 dm /h and the agitation speed was 1800 rpm. The flotation experiments were carried out in out in accordance with the flow sheet shown in Figure 1. The activator (Na2 SiF6 ) was added to the accordance with the flow sheet shown in Figure 1. The activator (Na2SiF6) was added to the slurry slurry conditioned 15 min. The pH regulator or 3Na pine added oil were 2 SO 2 CO3 ), collector, and and conditioned for 15for min. The pH regulator (H2SO(H 4 or Na42CO ), collector, and pineand oil were added successively to the slurry and conditioned for 3 min, 3 min, and 1 min, respectively before successively to the slurry and conditioned for 3 min, 3 min, and 1 min, respectively before flotation. flotation. The flotation tailing (froth product) was collected for 3 min. In the study, the effect of different The flotation tailing (froth product) was collected for 3 min. In the study, the effect of different collectors, flotation pH values, investigated. collectors, flotation pH values,and andmixed mixedcollector collector rates rates were were investigated.

Figure 1. Flow sheet of flotation tests. Figure 1. Flow sheet of flotation tests.

The concentrates and tailings from flotation after the filtering and drying were weighed and The concentrates from flotation after the filtering were values weighed and assayed, respectively.and Thetailings experiments were repeated three times, and and drying the average were assayed, respectively. The experiments were repeated three times, and the average values were reported. The experimental error was found to be 3%–5%. The magnetite recovery of flotation reported. Thewas experimental error was found to be 3%–5%. The magnetite recovery of flotation concentrate calculated by the following equation: concentrate was calculated by the following equation: γ ∙ (β − 1.59β ) (1) ε = β −´1.59β γ¨ pβ 1.59β2 q 1 εm “ (1) β0 ´β1.59β where Ɛm is the magnetite recovery in concentrate, 1 is the 3 Fe grade of concentrate, β2 is the S grade of concentrate, β0 is the Fe grade of raw ore, β3 is the S grade of raw ore, γ is yield of concentrate, and where εm isofthe magnetite recovery in concentrate, the Fe grade of concentrate, β2ofismagnetite. the S grade 1 is the rate Fe to S is 1.59 in pyrrhotite. The equationβis a criterion for evaluating the loss of concentrate, β0 is the Fe ratio gradeofofflotation raw ore,process β3 is the S grade of raw γ is yieldequation: of concentrate, and The desulfurization was calculated by ore, the following the rate of Fe to S is 1.59 in pyrrhotite. The equation is a criterion for evaluating the loss of magnetite. γ∙β The desulfurization ratio of flotation process D = 1was − calculated by the following equation: (2) β

γ¨ β where D is desulfurization ratio of flotation process, D“ 1 ´ γ1is yield of concentrate, β1 is the S grade of(2) β0 concentrate, and β0 is the S grade of raw ore.


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where D is desulfurization ratio of flotation process, γ is yield of concentrate, β1 is the S grade of Minerals 2016, 6,and 70 β0 is the S grade of raw ore. 4 of 13 concentrate, 2.2.2. Industrial Tests The industrial tests were performed in the Mineral Mineral Processing Processing Plant Plant at at the the Baotou Baotou iron iron Mine. Mine. experimental system S1 mixed used collector mixed collector ( pm : m = 3: 2) as collector. The The experimental system S1 used (mNaBX : m “ 3 : 2q as collector. The comparative ( ) BXq2 system S2 wassystem the original plant setup of plant the Baotou NaBX as collector in the flotation. comparative S2 was the original setupPlant, of the which Baotouused Plant, which used NaBX as collector Figure 2 shows Figure the flotation circuit of industrial in experiment Baotou ironinmine. The rougher in the flotation. 2 shows the flotation circuitexperiment of industrial Baotou iron mine. and The 3 cleaner thecleaner industrial experiment are composed of 6composed and 4 units 40 m4 units flotation cells, rougherofand of the industrialsystem experiment system are of of 6 and of 40 m3 3 3 respectively. scavengerThe consists of 4 units of 4 of m 4 flotation The flotation of flotation cells,The respectively. scavenger consists units of 4cells. m flotation cells. conditions The flotation industrial are also described in Figure 2. Theinprocessing capacities of S1 and S2 were conditionstests of industrial tests are also described Figure 2. The processing capacities of 169.73 S1 andand S2 186.37 t/h, respectively. were 169.73 and 186.37 t/h, respectively.

Figure 2. The flow sheet of industrial flotation in the Baotou iron Mine.

2.2.3. Zeta Potential Measurements The zeta potentials of the minerals were measured using a ZetasizerNano ZS90 (Malvern, (Malvern, UK). A A suspension suspension containing containing 0.01 wt % % mineral mineral particles particles ground ground to to ´2 −2 µm in an Worcestershire, UK). agate mortar was prepared prepared in in the the KCl KCl solution solution(10 (10´−33 M). M). The The measurements measurements were were conducted at room ˝ toto a desired value using HCl or temperature (25 (25 °C). C). The ThepH pHvalue valueofofthe thesuspension suspensionwas wasadjusted adjusted a desired value using HCl NaOH solution. Besides, measurements were also carried or NaOH solution. Besides, measurements were also carriedout outwith withthe theaddition additionof of collector collector at at a constant concentration in the presence presence of of sodium sodium fluosilicate fluosilicate (10 (10´−44 M). M). The average zeta potential values ofofatatleast least three independent measurements were recorded with a measurement values three independent measurements were recorded with a measurement error of ˘2error mV. of ±2 mV. 2.2.4. FTIR Measurements

2.2.4.Fourier FTIR Measurements Transform Infrared (FTIR) spectra ranging from 4000 to 400 cm´1 were used to characterize −1 were the collectors and their adsorption on the spectra mineral ranging surface at room temperature. pure used mineral Fourier Transform Infrared (FTIR) from 4000 to 400 cmThe to ´3 M). The mineral samples were ground to less than 2 µm before conditioned with the collectors (10 characterize the collectors and their adsorption on the mineral surface at room temperature. The pure ´4 M). The pellets sample reacted with collector in the of sodium fluosilicate mineral was samples were ground to less thanpresence 2 µm before conditioned with (10 the collectors (10−3 M).were The −4 prepared by mixing KBr and sample at the mass ratio of 200/1. The spectra of the samples were mineral sample was reacted with collector in the presence of sodium fluosilicate (10 M). The pellets obtained with KBr pellets KBr by a and Fourier transform infrared WI, USA). were prepared by mixing sample at the mass ratiospectrometer of 200/1. The(Nicolet, spectra of the samples were obtained with KBr pellets by a Fourier transform infrared spectrometer (Nicolet, WI, USA).


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2.2.5. Contact Angle Measurements Minerals 2016, 6, 70

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The contact angle were measured using Kruss K100 instrument (KRüSS, Hamburg, Germany). 2.2.5.mineral Contactsamples Angle Measurements The pure (37–44 µm) were conditioned with collectors by laboratory flotation machine ˝ C) was pressed to round tablets (1800 rpm)The forcontact 5 min. angle The froth from flotation afterinstrument drying (60(KRüSS, wereproduct measured using Kruss K100 Hamburg, Germany). (d = 1The cm).pure Finally, the contact measurements were performed. The measurements repeated mineral samplesangle (37–44 µm) were conditioned with collectors by laboratorywere flotation (1800 for 5values min. The froth productdeviations from flotation after drying (60 °C) was pressed to three machine times and therpm) average and standard were reported. round tablets (d = 1 cm). Finally, the contact angle measurements were performed. The measurements

3. Results and Discussion were repeated three times and the average values and standard deviations were reported. 3.1. Flotation 3. Results and Discussion Flotation 3.1.1. 3.1. Effect of Collector

The tests ¯ were conducted with individual collector NaBX, (BX)2 and mixed collector 3.1.1flotation Effect of Collector mNaBX : mpBXq2 “ 3 : 2 . The recovery-collector concentration curves of magnetite at pH 6 are The flotation tests were conducted with individual collector NaBX, (BX)2 and mixed collector presented Figure=3.3: 2) It shows that the recoveryconcentration of magnetitecurves with (BX) 2 is independent (m in: m . The recovery-collector of magnetite at pH 6 of are(BX)2 ( ) concentration and the magnetite recovery changed in the range of 97.93%–98.24% in the studied presented in Figure 3. It shows that the recovery of magnetite with (BX)2 is independent of (BX)2 concentration range. using NaBX as collector, is theinlowest compared concentration andWhen the magnetite recovery changedthe in recovery the rangeof ofmagnetite 97.93%–98.24% the studied with concentration the other two groups and decreased sharply with the increase of theis collector range. When using NaBX as collector, the recovery of magnetite the lowest concentration. compared groups decreased with recovery the increase the collector In of In thewith casethe of other (BX)2two /NaBX, it isand clear that thesharply magnetite of of concentrate is concentration. higher than those the case of (BX) 2 /NaBX, it is clear that the magnetite recovery of concentrate is higher than those of single collectors, meanwhile the magnetite recovery has little decrease with an increase of collector single collectors, meanwhile the magnetite recovery has little decrease with an increase of collector concentration. Figure 4 shows the desulfurization ratio of flotation performance as a function of concentration. Figure 4 shows the desulfurization ratio of flotation performance as a function of collector concentration. For mixed collector system, the desulfurization ratio curve is similar to that of collector concentration. For mixed collector system, the desulfurization ratio curve is similar to that NaBX, which is much higher than that of (BX)2 . It can be concluded that a high desulfurization ratio of NaBX, which is much higher than that of (BX)2. It can be concluded that a high desulfurization was achieved littlewith loss little of magnetite when xanthate was mixed with dixanthogen as theascollector, ratio waswith achieved loss of magnetite when xanthate was mixed with dixanthogen the indicating thatindicating the mixed collector shows better selectivity than single collector, that the mixed collector shows better selectivity thancollectors. single collectors. ´

Figure 3. Flotation recoveries of magnetite with individual collector NaBX, (BX)2 and mixed collector

Figure 3. Flotation recoveries of magnetite with individual collector NaBX, (BX)2 and mixed collector ´ : m( ) = 3:¯2) as a function of collector concentration (NaSiF6 500 g/t, pine oil 46 g/t, pH = 6). (m mNaBX : mpBXq2 “ 3 : 2 as a function of collector concentration (NaSiF6 500 g/t, pine oil 46 g/t, pH = 6).

The order of collector strength for the reagents used in this study has been reported to be NaBX > (BX)of 2 based on the chemical nature of the collector’s group [15]. Results in this study match The order collector strength for the reagents used in this study has been reported to be this order, as NaBX was found to have much better desulfurization performance when compared to NaBX > (BX)2 based on the chemical nature of the collector’s group [15]. Results in this study match (BX)2. A possible explanation for this phenomenon is that NaBX is a stronger collector than (BX)2. It this order, as NaBX was found to have much better desulfurization performance when compared to has already been noted that the most significant decrease of magnetite recovery in flotation (BX)2 .concentrate A possibleisexplanation this phenomenon is that NaBX is a stronger collector than (BX)2 . It has when usingfor NaBX compared to that of (BX) 2. A possible reason could be that the already been noted the most significant decrease ofnoted magnetite recovery in flotation concentrate is selectivity (BX)2that is superior to NaBX. It should be also that the mixed collector resulted in an whenoverall using NaBX compared to that of (BX)2recovery . A possible could beperformance that the selectivity (BX)2 is enhancement in both magnetite and reason desulfurization since each individual collector playsbe a different rolethat on the In the mixed system, both the adsorption superior to NaBX. It should also noted the flotation. mixed collector resulted in an overall enhancement

in both magnetite recovery and desulfurization performance since each individual collector plays a

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different role on6,the Minerals 70 flotation. In the mixed system, both the adsorption of (BX)2 and NaBX 6collectors of 13 of (BX)2016, 2 and NaBX collectors are enhanced due to co-adsorption. Adsorption of NaBX may be are enhanced due to co-adsorption. Adsorption of NaBX may be enhanced by the presence of (BX)2 enhanced by the presence of (BX)2 due to hydrophobic chain interactions and the reduction of ofhydrophobic (BX)2 and NaBX collectors are enhanced due to co-adsorption. Adsorption ofbetween NaBX may behead due to chain interactions and the reduction of electrostatic repulsion ionic electrostatic repulsion between ionic head groups of NaBX that are shield from each other by enhanced by the presence of (BX) 2 due to hydrophobic chain interactions and the reduction of groups of2 molecules. NaBX that are shield from each other by (BX)2 molecules. (BX) electrostatic repulsion between ionic head groups of NaBX that are shield from each other by (BX)2 molecules.

Figure 4. Desulfurization ratio of flotation performance with individual collector NaBX, (BX)2 and

Figure 4. Desulfurization ratio of flotation performance with individual collector NaBX, (BX) and ´ (m mixed collector : m( ) = 3: 2)¯ as a function of collector concentration (NaSiF6 500 g/t, pine2 Figure 4. Desulfurization ratio of flotation with individual collector(NaSiF NaBX, 6(BX) and pine mixedoil collector m : m “ 3 : 2 as aperformance function of collector concentration 5002 g/t, NaBX pBXq2 46 g/t, pH = 6). collector : m( ) = 3: 2) as a function of collector concentration (NaSiF6 500 g/t, pine oil 46mixed g/t, pH = 6). (m 46 g/t, pH = 6). 3.1.2.oil Effect of Mixed Collector Ratio

3.1.2. 3.1.2. Effect offlotation Mixed Collector Ratio The capacities ofRatio the NaBX, (BX)2, and their mixture were investigated with batch Effect of Mixed Collector flotation tests.capacities It is important to take into account that the were weight ratio of mixed collector The flotation of theofNaBX, (BX) , and their mixture investigated with batch flotation 2(BX) The flotation capacities the NaBX, 2, and their mixture were investigated with batch ((BX)2/[NaBX + (BX)2]) in pyrrhotite flotation tests. Figure 5 shows the flotation performances of tests. flotation It is important to take into account that the weight ratio of mixed collector ((BX) /[NaBX + (BX) tests. It is important to take into account that the weight ratio of 2mixed collector2 ]) in mixed collectors with various α( ) at pH = 6.0. The results show that the magnetite recovery pyrrhotite flotation 5 shows the flotation performances collectors with various ((BX)2/[NaBX + tests. (BX)2])Figure in pyrrhotite flotation tests. Figure 5 shows of themixed flotation performances of sharply increased with increasing α( ) , reaching a maximum value (98.11%) at α( ) = 40% with various α( that pHmagnetite = 6.0. The recovery results show that the magnetite recovery αpBXq2mixed at pHcollectors = 6.0. The results show sharply increased with increasing ) atthe (the weight ratio of (BX)2:NaBX = 2:3). At α( ) > 40%, the magnetite recovery becomes slowly value (98.11%) α( ):NaBX = 40%= 2:3). increased with increasing α( ) , reaching αpBXqsharply , reaching a maximum value (98.11%) at α BXq2 a=maximum 40% (the weight ratio ofat(BX) 2 decrease. It also can be seen from Figure 5 that pthe desulfurization ratio of concentrate 2decreased 2:NaBX = 2:3). At α( > 40%, the magnetite recovery becomes slowly (the weight ratio of (BX) ) At αpslowly 40%, the magnetite recovery becomes slowly decrease. It also can be seen from Figure 5 BXq2 > when 2 increased from 0 to 40 wt % and thereafter the desulfurization ratio the fraction of (BX) decrease. It also can be seen from Figure 5 decreased that the desulfurization ratio concentrate decreased that the desulfurization ratio of concentrate slowly when theof fraction (BX) 2 increased decreased significantly. There is a marked positive synergistic effect between NaBXofand (BX) 2 on slowly when the fraction of (BX)2 increased from 0 to 40 wt % and thereafter the desulfurization ratio from flotation 0 to 40 wt and thereafter the collector desulfurization ratiois decreased significantly. is a marked of % pyrrhotite. The mixed (BX)2/NaBX beneficial for the flotationThere of pyrrhotite, decreased significantly. There is a marked positive synergistic effect between NaBX and (BX)2 on and synergistic the optimumeffect weightbetween ratio of (BX) 2 to NaBX is 2:3. the of mixed (BX)2/NaBX a weight positive NaBX and (BX) on flotation pyrrhotite. Thewith mixed collector 2 Therefore, flotation of pyrrhotite. The mixed collector (BX)2/NaBX is beneficial for the flotation of pyrrhotite, of 2:3 is selected for the following study. (BX)2ratio /NaBX is beneficial for the flotation of pyrrhotite, and the optimum weight ratio of (BX) 2 to NaBX and the optimum weight ratio of (BX)2 to NaBX is 2:3. Therefore, the mixed (BX)2/NaBX with a weight is 2:3.ratio Therefore, mixed with a weight ratio of 2:3 is selected for the following study. 2 /NaBX study. of 2:3 is the selected for(BX) the following

Figure 5. The magnetite recovery and desulfurization ratio in flotation concentrate with mixed collector at different combinations (mixed collector 125 g/t, NaSiF6 500 g/t, pine oil 46 g/t, pH = 6). Figure 5. The magnetite recovery and desulfurization ratio in flotation concentrate with mixed Figure 5. The magnetite recovery and desulfurization ratio in flotation concentrate with mixed collector collector at different combinations (mixed collector 125 g/t, NaSiF6 500 g/t, pine oil 46 g/t, pH = 6).

at different combinations (mixed collector 125 g/t, NaSiF6 500 g/t, pine oil 46 g/t, pH = 6).

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3.1.3 Effect 3.1.3. Effectof ofthe thepH pHValue Value pHpH plays an important role in flotation systemsystem by controlling both mineral As we weall allknow, know,thethe plays an important role in flotation by controlling both solubilitysolubility and acid-base property of mineralof pulp. Figure 6 shows the6flotation response of magnetite mineral and acid-base property mineral pulp. Figure shows the flotation response recovery and desulfurization ratio as ratio a function of pH with NaBX/(BX)22 of magnetite recovery and desulfurization as a function of pH withmixed mixedcollectors collectors NaBX/(BX) (αp( BX)q2 =“40%). 40%).The Theresults resultsclearly clearlyindicate indicatethat, that,with withmixed mixedcollector, collector, the the recovery recovery of magnetite value increased from 5.05.0 to 8.0. It also can can be seen that increased from from 96.66% 96.66%to to99.33% 99.33%when whenthe thepH pH value increased from to 8.0. It also be seen the desulfurization ratioratio of flotation concentrate had little decrease that the desulfurization of flotation concentrate had little decreasewith withthe theincrease increaseof of pH pH until around pH 6.0 and thereafter the desulfurization ratio decreased dramatically, which indicated that pyrrhotite flotation is sensitive to pH value. Therefore, the maximum flotation response of pyrrhotite mixed collector collector at at pH pH around around 6. 6. away from magnetite was attained with the mixed

The magnetite magnetiterecovery recoveryand anddesulfurization desulfurizationratio ratio flotation concentrate a function of Figure 6. The in in flotation concentrate as aasfunction of pH pH with mixed collector (NaBX 75 g/t, 2 50 g/t, NaSiF 6 500 g/t, pine oil 46 g/t). with mixed collector (NaBX 75 g/t, (BX)(BX) 50 g/t, NaSiF 500 g/t, pine oil 46 g/t). 2 6

It is is aa reactive mineral and and easy easy to to be It is well well known known that that pyrrhotite pyrrhotite is reactive sulphide sulphide mineral be oxidized oxidized in in alkaline alkaline solutions [16]. The general oxidation mechanisms may be described by the following reactions [17,18]. solutions [16]. The general oxidation mechanisms may be described by the following reactions [17,18]. The formation of Fe(OH)3 precipitation on the surface of pyrrhotite decreases surface hydrophobicity The formation of Fe(OH)3 precipitation on the surface of pyrrhotite decreases surface hydrophobicity of pyrrhotite and this is why the desulfurization ratio decreased as the pH increased. In addition, of pyrrhotite and this is why the desulfurization ratio decreased as the pH increased. In addition, another possible reason could be that the synergetic effect was poor since part of dixanthogen may another possible reason could be that the synergetic effect was poor since part of dixanthogen may transform into xanthate in an alkaline environment. transform into xanthate in an alkaline environment. 1˙ ˆ (3) O + H O → (1 − )Fe + SO + 2 H Fe S + 2 −1 Fe1´x Ss ` 2 ´ 2x O2 ` xH2 O Ñ p1 ´ xq Fe2` ` SO24´ ` 2xH` (3) 2 1 1 (4) Fe 2` +14 O + H` → Fe 3` + 21H O Fe ` O2 ` H Ñ Fe ` H2 O (4) 4 2 3` + 3H O → Fe(OH) + 3H ` (5) FeFe ` 3H2 O Ñ Fe pOHq ` 3H (5) 3

3.2. Industrial Tests 3.2. Industrial Tests Because of the good effect of mixed NaBX/(BX)2 for pyrrhotite flotation, the mixed collector Because of the good effect of mixed NaBX/(BX)2 for pyrrhotite flotation, the mixed collector (mNaBX : mpBXq2 “ 3 : 2) was selected in the industrial tests performed in the Mineral Processing (m : m( ) = 3: 2) was selected in the industrial tests performed in the Mineral Processing Plant Plant of the Baotou iron Mine. The flotation flowsheet and flotation conditions are listed in Figure 2, of the Baotou iron Mine. The flotation flowsheet and flotation conditions are listed in Figure 2, and and the flotation results are shown in Table 5. It can be seen from the results that the grade and the flotation results are shown in Table 5. It can be seen from the results that the grade and recovery recovery of iron increased significantly when the industrial tests were performed in the S1 system, of iron increased significantly when the industrial tests were performed in the S1 system, which which indicates that mixed collector had a good selectivity on the flotation of pyrrhotite while having indicates that mixed collector had a good selectivity on the flotation of pyrrhotite while having a similar desulfurization capacity in comparison with the system S2. Since the industrial tests, mixed collector has been commercially used in the Baotou iron Mine.


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a similar desulfurization capacity in comparison with the system S2. Since the industrial tests, mixed collector has6,been Minerals 2016, 70 commercially used in the Baotou iron Mine. 8 of 13 Table Table5.5.The Theresults resultsofofindustrial industrialflotation flotationtests testson onSeptember. September.

Grades Grades (%) (%) Products Yield Yield (wt %) (wt %) Fe S Fe S Concentrates 91.23 69.25 0.43 Concentrates 91.23 69.25 0.43 S1 Mixed collectorTailings Tailings 8.77 8.77 58.42 58.4218.75 18.75 S1 Mixed collector Feed 100.00 68.30 2.05 Feed 100.00 68.30 2.05 Concentrates88.92 88.92 69.13 69.13 0.440.44 Concentrates S2 NaBX Tailings 11.08 11.08 60.01 60.0114.75 14.75 Tailings S2 NaBX Feed Feed 100.00 100.00 68.12 68.12 2.03 2.03 System System

Products

Recoveries Recoveries(%) (%) Fe S Fe S 92.50 19.62 92.50 19.62 7.50 80.38 7.50 80.38 100.00 100.00 100.00 100.00 90.24 19.32 90.24 19.32 9.76 80.68 9.76 80.68 100.00 100.00 100.00 100.00

3.2.Zeta-Potential Zeta-PotentialMeasurements Measurements 3.3. Zetapotentials potentials of of pyrrhotite pyrrhotite in in the the absence and presence of NaBX, Zeta NaBX, (BX) (BX)22 and andtheir theirmixture mixtureas asa function of pH are illustrated in Figure 7. The results show that the zeta potential of pyrrhotite in a function of pH are illustrated in Figure 7. The results show that the zeta potential of pyrrhotite distilled water decreased with thethe increase of the pH,pH, andand the isoelectric pointpoint of pyrrhotite was about in distilled water decreased with increase of the the isoelectric of pyrrhotite was 8.6 in8.6 distilled water,water, which is in agreement with with the results obtained by other researchers [19].[19]. The about in distilled which is in agreement the results obtained by other researchers zetazeta potential with dixanthogen when used range between between The potential with dixanthogen when usedalone aloneappeared appearedtotobe besimilar similar at at the pH range and12. 12.ItItindicated indicatedthat thatdixanthogen dixanthogenhad hadaalittle littleeffect effecton onthe the zeta zeta potential potential at at all all studied studied pH pH values. values. 22and Thiscould couldbe beattributed attributedto tolow lowionizability ionizabilityof ofdixanthogen dixanthogenor orlow lowadsorption adsorptionof ofthe thedesired desiredcollector collector This onthe thepyrrhotite pyrrhotitesurface. surface.In Inthe thepresence presenceof ofNaBX, NaBX,the thezeta zetapotential potentialdecreased decreasedsignificantly significantlyand andthe the on isoelectricpoint pointchanged changedfrom from8.6 8.6to toabout about4.5. 4.5.ItItindicated indicatedthat thatthe theanionic anioniccollector collectoradsorbed adsorbedonto onto isoelectric thepyrrhotite pyrrhotitesurface surfaceby bychemical chemicalbonding. bonding.InInthe thepresence presenceofofmixed mixedNaBX/(BX) NaBX/(BX)2 2,,the thezeta zetapotentials potentials the weremore morepositive positivethan thanthat thatininthe thepresence presenceofofNaBX NaBXalone, alone,but butmore morenegative negativewhen whencompared comparedto to were (BX)2 2alone. alone.This Thismight mightbe beexplained explainedby bythe the fact fact that that dixanthogen, dixanthogen,aa neutral neutraland andstrongly stronglyhydrophobic hydrophobic (BX) collector,adsorbed adsorbedon onthe thepyrrhotite pyrrhotitesurface surfaceasasa aco-collector co-collector[14]. [14]. collector,

Figure7.7.The The zeta potential of pyrrhotite the absence and presence of (BX) NaBX, (BX)2, and their Figure zeta potential of pyrrhotite in theinabsence and presence of NaBX, 2 , and their mixture mixture as a of function of pH value, respectively. as a function pH value, respectively.

It can be seen in Figure 8 that the zeta potential of magnetite in distilled water decreased with It can be seen in Figure 8 that the zeta potential of magnetite in distilled water decreased the increase of the pH, and the isoelectric point of magnetite was about 6.5 in distilled water. When with the increase of the pH, and the isoelectric point of magnetite was about 6.5 in distilled water. magnetite interacts with NaBX, (BX)2, and their mixture respectively, zeta-potential values are very close to that in water. Thereby, it may be concluded that no significant NaBX, (BX)2, and their mixture are adsorbed on magnetite.


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When magnetite interacts with NaBX, (BX)2 , and their mixture respectively, zeta-potential values are very close to that in water. Thereby, it may be concluded that no significant NaBX, (BX)2 , and their mixture on magnetite. Mineralsare 2016,adsorbed 6, 70 9 of 13 Minerals 2016, 6, 70

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Figure Thezeta zeta potentialof of magnetite in in the absence and NaBX, 2, and their mixture Figure 8. 8. The andpresence presenceof NaBX,(BX) (BX) , and their mixture Figure 8. The zetapotential potential ofmagnetite magnetite in the absence and presence ofofNaBX, (BX) 2, 2 and their mixture as a function of pH value, respectively. as as a function ofof pH a function pHvalue, value,respectively. respectively.

3.3 FTIR Analysis FTIRAnalysis Analysis 3.4.3.3FTIR In order to investigate the adsorption mechanism of NaBX, (BX)2, and their mixture on the order to investigate adsorption mechanism of NaBX, 2, and their mixture on the In In order to investigate the the adsorption mechanism of NaBX, (BX)2(BX) , and theirwith mixture on the mineral mineral surfaces, the collectors, minerals, and minerals after reacting collectors were mineral surfaces, the collectors, minerals, and minerals after reacting with collectors were surfaces, the collectors, minerals, and minerals after with characterized by infrared spectrometry at 298 K. Thereacting IR spectra of collectors NaBX andwere (BX)2characterized are shown in by characterized by infrared spectrometry at 298 K. The IR spectra of NaBX and (BX) 2 are shown in infrared at 298 K. The spectra NaBX showncm in −1Figures 2 are Figuresspectrometry 9 and 10, respectively. The IR spectra are of given forand the (BX) region 600–1600 where 9alland the 10, Figures 9 and 10, respectively. The spectra are given for the region 600–1600 cm−1 where all the ´ 1 respectively. The spectra are givenoffor region 600–1600 where all the absorption bands absorption bands are characteristic thethe NaBX and (BX) 2 polarcm groups. The characteristic IR spectral absorption bands are characteristic of the NaBX and (BX)2 polar groups. The characteristic IR spectral arepeaks characteristic of the NaBX and (BX) groups. IR spectral peaks 9, of the these 2 polar of these collectors are very similar to that gainedThe by characteristic other researcher [20]. In Figure peaks of these collectors are very similar to that gained by other researcher [20]. In Figure 9, the −1 collectors are very similar to that gained by other researcher [20]. In Figure 9, the characteristic peaks characteristic peaks at 1168.92 and 1191.95 cm −1 arise from asymmetric stretching vibration of characteristic peaks at ´ 1168.92 and 1191.95 cm arise from asymmetric stretching vibration of at C–O–C 1168.92in and 1191.95 arise fromatasymmetric of C–O–C in NaBX. The peak NaBX. Thecm peak1 frequency 1111.20 cm−1stretching originatesvibration from symmetric stretching vibration C–O–C in NaBX. The ´ peak frequency at 1111.20 cm−1 originates from symmetric stretching vibration 1 −1 is assigned of C–O–C in NaBX.cm The peak at 1062.06 cm to the stretching vibration of the C=S group frequency at 1111.20 originates from symmetric stretching vibration of C–O–C in NaBX. The peak of C–O–C in NaBX. The peak at 1062.06 cm−1 is assigned to the stretching vibration of the C=S group ´ 1 of NaBX. at 1062.06 of NaBX.cm is assigned to the stretching vibration of the C=S group of NaBX.

Figure 9. FTIR spectrum of sodium butyl xanthate. Figure 9. FTIR spectrum of sodium butyl xanthate. Figure 9. FTIR spectrum of sodium butyl xanthate.

In Figure 10, the IR spectrum of (BX)2 contains intensive symmetric stretching vibration of In Figure 10, the IR spectrum of (BX)2 contains intensive symmetric stretching vibration of C–O–C with peak frequencies at 1157 and 1179 cm−1−1. The peak at 1265 cm−1−1 is assigned to the C–O–C with peak frequencies at 1157 and 1179 cm . The peak at 1265 cm is assigned to the asymmetric stretching vibration of C–O–C in (BX)2. The characteristics peak at 1027 cm−1−1 is attributed asymmetric stretching vibration of C–O–C in (BX)2. The characteristics peak at 1027 cm is attributed to stretching vibration of C=S in (BX)2. It can be seen that stretching vibration frequencies of C–O–C to stretching vibration of C=S in (BX)2. It can be seen that stretching vibration frequencies of C–O–C


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in (BX)2 shift toward higher frequencies when the vibration frequency of C=S shifts toward lower Minerals 2016, 6, 70 10 of 13 frequencies compared to that of NaBX. The same trend can be found in previous research [21,22].


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in (BX)2 shift toward higher frequencies when the vibration frequency of C=S shifts toward lower frequencies compared to that of NaBX. The same trend can be found in previous research [21,22].

Figure 10. FTIR spectrum of dibutyl dixanthogen.

The FTIR10, spectrum of pyrrhotite after reacting with NaBX is shown in Figure 11. The peak at In Figure the IR spectrum of (BX) 2 contains intensive symmetric stretching vibration of C–O–C −1 is assigned to C=S stretching vibration 1048 cm of Fe(BX) 3. The bond at 1117.39 cm−1 is ´ with peak frequencies at 1157 and 1179 cm 1 . The peak at 1265 cm´1weak is assigned to the asymmetric attributed to stretching vibration of C–O–C in Fe(BX)3. None of the characteristics peak to of stretching (BX)2 can ´1 is attributed stretching vibration of C–O–C in (BX) 2 . The characteristics peak at 1027 cm be seen in Figure 11. vibration of C=S in (BX) . It can be seen that stretching vibration frequencies of C–O–C in (BX) 2

2

shift toward higher frequencies when the vibration frequency of C=S shifts toward lower frequencies Figure 10. FTIR spectrum of dibutyl dixanthogen. compared to that of NaBX. The same trend can be found in previous research [21,22]. The FTIR FTIR spectrum spectrum of of pyrrhotite pyrrhotite after after reacting reacting with with NaBX NaBX is is shown shown in in Figure Figure 11. 11. The The peak peak at at The ´ 1 ´ 1 1048 cm assigned to to C=S C=S stretching stretching vibration vibration of The weak weak bond is 1048 cm−1 isis assigned of Fe(BX) Fe(BX)33.. The bond at at 1117.39 1117.39 cm cm−1 is attributed to stretching vibration of C–O–C in Fe(BX) . None of the characteristics peak of (BX) can be 3 2 attributed to stretching vibration of C–O–C in Fe(BX)3. None of the characteristics peak of (BX)2 can seen in Figure 11.11. be seen in Figure

Figure 11. FTIR spectra of pyrrhotite after reacting with NaBX at pH = 6.

The FTIR spectrum of pyrrhotite after reacting with mixed collector ( m : m( ) = 3: 2) is shown in Figure 12. After the interaction with the mixed collector, both the characteristic IR spectral peaks of Fe(BX)3 and (BX)2 can be observed on the mineral surface. The stronger characteristic peaks at 1029.01 and 1262.67 cm−1 could be identified as the stretching vibration of C=S in xanthate and the C–O–C stretching vibration of (BX)2, respectively [22,23]. The weaker peaks at 1102.15 and Figure FTIR spectra of after reacting with NaBX == 6. Figure 11. 11.to FTIR of pyrrhotite pyrrhotite after NaBX at at pH pH 6.be found that the 1131.90 cm−1 are assigned thespectra stretching vibration of reacting C–O–C with in xanthate. It can C=S stretching vibration of xanthate iron shifts toward to lower frequency compared to that of The FTIR spectrum of pyrrhotite after reacting with mixed collector ( m : m ) = 3: 2) is The FTIR spectrum of pyrrhotite after reacting with mixedmolecules collector (m : mp(directly : 2)the is NaBX. The results indicate that the xanthate and dixanthogen areNaBX bound BXq2 “ 3 to shown in Figure 12. After the interaction with the mixed collector, both the characteristic IR spectral shown in Figure 12. After the interaction with the mixed collector, both the characteristic IR spectral pyrrhotite surface. peaks of Fe(BX)3 and (BX)2 can be observed on the mineral surface. The stronger characteristic peaks of Fe(BX)3 and (BX)2 can−1be observed on the mineral surface. The stronger characteristic peaks at 1029.01 and 1262.67 cm´1could be identified as the stretching vibration of C=S in xanthate peaks at 1029.01 and 1262.67 cm could be identified as the stretching vibration of C=S in xanthate and the C–O–C stretching vibration of (BX)2, respectively [22,23]. The weaker peaks at 1102.15 and and the C–O–C stretching vibration of (BX)2 , respectively [22,23]. The weaker peaks at 1102.15 and 1131.90 cm−1 are assigned to the stretching vibration of C–O–C in xanthate. It can be found that the C=S stretching vibration of xanthate iron shifts toward to lower frequency compared to that of NaBX. The results indicate that the xanthate and dixanthogen molecules are bound directly to the pyrrhotite surface.


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1131.90 cm´1 are assigned to the stretching vibration of C–O–C in xanthate. It can be found that the C=S stretching vibration of xanthate iron shifts toward to lower frequency compared to that of NaBX. The results indicate that the xanthate and dixanthogen molecules are bound directly to the pyrrhotite Minerals 2016,surface. 6, 70 11 of 13 Minerals 2016, 6, 70

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Figure (NaBX ++(BX) Figure 12. FTIR spectra of pyrrhotite after reacting with mixed collector (BX) atpH pH==6. Figure12. 12.FTIR FTIRspectra spectraof ofpyrrhotite pyrrhotiteafter afterreacting reactingwith withmixed mixedcollector collector(NaBX (NaBX+ (BX)222))at 6.

3.4. 3.4.Wetting Wetting Characteristic Collectors 3.5. Characteristic of of Pyrrhotite Pyrrhotite wih wih Mixed Mixed Collectors Collectors The wettability nature mixed (BX) 2/NaBX collectors on pyrrhotite and thereby synergistic wettabilitynature natureofof of mixed (BX) 2/NaBX collectors on pyrrhotite and thereby synergistic The wettability mixed (BX) collectors on pyrrhotite and thereby synergistic effect 2 /NaBX effect between (BX) 2 and NaBX on solid/liquid interface were investigated by contact angle effect between (BX) 2 and on solid/liquid interface were investigated by contact angle between (BX)2 and NaBX onNaBX solid/liquid interface were investigated by contact angle measurement. measurement. Figure presents the angle of ααseen ItItcan be seen ( ) .that measurement. Figure 13 presents theofcontact contact angle of pyrrhotite as function of . can be seen Figure 13 presents the13 contact angle pyrrhotite asof a pyrrhotite function ofas αpaaBXfunction . It can be there is an ( ) q2 2 is added to an NaBX in the low that an in angles of increase contact of pyrrhotite (BX)2 is when added to an NaBX intothe αpBX range, 2 is added anlow NaBX inq2the low thatthere thereinisisthe anincrease increaseangles inthe thecontact contact angleswhen ofpyrrhotite pyrrhotite when(BX) (BX) ˝ when αand range, and the reaches maximum value, up to when contact angle reachesangle the maximum value, improving upimproving to about 70 αpBX70° 45%. α(( ))the range, and the contact contact angle reaches the the maximum value, improving up to about about 70° q2 iswhen is 45%. In other words, combined use of the reagents strengthens the hydrophobicity of αIn ) words, combined use of the reagents strengthens the hydrophobicity of pyrrhotite surface is 45%. In other words, combined use of the reagents strengthens the hydrophobicity of α(( other ) pyrrhotite surface and produces greater contact angles. This phenomenon has been discovered and produces greater contact angles. This phenomenon has been discovered previously by Xu [24]. pyrrhotite surface and produces greater contact angles. This phenomenon has been discovered 2 is greater than NaBX, and previously Xu [24]. ItIt isis because the of It is becauseby that hydrophobicity of (BX) is greater than NaBX, NaBX could increase the 2 is the greater than NaBX, and the previously by Xuthe [24]. because that that the2hydrophobicity hydrophobicity of (BX) (BX)and NaBX could increase the solubility of (BX) 2 at the same time. However, as the α further increases, ( ) solubility of (BX) at the same time. However, as the α further increases, the contact angle of NaBX could increase the solubility of (BX)2 at the same time. as the α( ) further increases, 2 pBXqHowever, 2 2 . the contact angle of pyrrhoite decreases. The reason could be explained by low solubility of (BX) pyrrhoite The reason could be The explained low be solubility of (BX) 2 . solubility of (BX)2. the contactdecreases. angle of pyrrhoite decreases. reasonby could explained by low

Figure pyrrhotite with mixed collectors at pH 6.0. Figure13. 13.Contact Contactangle anglevs. vs.mass massfraction fractionof of(BX) (BX)22for for Figure 13. Contact angle vs. mass fraction of (BX) for pyrrhotite pyrrhotite with with mixed mixed collectors collectors at at pH pH 6.0. 6.0. 2

4. 4.Conclusions Conclusions The andNaBX NaBXwas wasinvestigated investigatedby byflotation flotation Thesynergetic synergeticeffect effectof ofmixed mixedcollector collectorsystems systemsof of(BX) (BX)22and tests. The separation effect between pyrrhotite and magnetite was dramatically enhanced tests. The separation effect between pyrrhotite and magnetite was dramatically enhancedin interms termsof of both magnetite recovery and desulfurization ratio. The ideal composition of the mixed collector was both magnetite recovery and desulfurization ratio. The ideal composition of the mixed collector was determined by batch flotation tests to be 40 wt % (BX)2 and 60 wt % NaBX for pyrrhotite flotation. A


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4. Conclusions The synergetic effect of mixed collector systems of (BX)2 and NaBX was investigated by flotation tests. The separation effect between pyrrhotite and magnetite was dramatically enhanced in terms of both magnetite recovery and desulfurization ratio. The ideal composition of the mixed collector was determined by batch flotation tests to be 40 wt % (BX)2 and 60 wt % NaBX for pyrrhotite flotation. A reasonable pH value for application of the collector mixture was determined to be around 6.0. The zeta potential experiments indicated that chemical adsorption occurred on the pyrrhotite surface. The FTIR analysis showed that the groups of NaBX and (BX)2 participated in the chemical reaction. The contact angle results indicated there was a synergistic effect of mixed (BX)2 and NaBX collectors at the solid-liquid interface. In the mixed systems, dixanthogen associated with xanthate, enhancing hydrophobicity of pyrrhotite due to co-adsorption. Acknowledgments: The authors acknowledge the support of the National Natural Science Foundation of China (Grant Nos. 51574188). Author Contributions: Yingyong Ge conceived and designed the experiments; the experiments, analysis of data and article writing are carried out by Jun Yu; Xinwei Cai performed a part of experiments. Conflicts of Interest: The authors declare no conflict of interest.

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Miller, J.D.; Li, J.; Davidtz, J.C.; Vos, F. A review of pyrrhotite flotation chemistry in the processing of PGM ores. Miner. Eng. 2005, 18, 855–865. [CrossRef] Bunkholt, I.; Kleiv, R.A. Pyrrhotite oxidation and its influence on alkaline amine flotation. Miner. Eng. 2015, 71, 65–72. [CrossRef] Chen, X.; Peng, Y. The effect of regrind mills on the separation of chalcopyrite from pyrite in cleaner flotation. Miner. Eng. 2015, 83, 33–43. [CrossRef] Hong, Q.Y.; Tang, Y.H.; Wang, Y.H. Investigation on properties and structure of pyrrhotite and the different of its floatability. Metal Mine 2011, 415, 64–67. Zhang, Y.; Cao, Z.; Cao, Y.; Sun, C. FTIR studies of xanthate adsorption on chalcopyrite, pentlandite and pyrite surfaces. J. Mol. Struct. 2013, 1048, 434–440. [CrossRef] Bulut, G.; Atak, S. Role of dixanthogen on pyrite flotation: Solubility, adsorption studies and Eh, FTIR measurements. Miner. Metall. Process. 2002, 19, 81–86. Zhang, Q.; Hu, Y.H.; Gu, G.H.; Xu, J. The study on the interaction between ethyl xanthate and pyrrhotitein electrochemical flotation by FTIR spectroscopy. Min. Metall. Eng. 2004, 24, 42–44. Mustafa, S.; Hamid, A.; Naeem, A. Xanthate adsorption studies on chalcopyrite ore. Int. J. Miner. Process. 2004, 74, 317–325. [CrossRef] Xu, L.; Hu, Y.; Tian, J.; Wu, H.; Wang, L.; Yang, Y.; Wang, Z. Synergistic effect of mixed cationic/anionic collectors on flotation and adsorption of muscovite. Colloids Surf. A Physicochem. Eng. Asp. 2016, 492, 181–189. [CrossRef] © 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).