Article Investigation on a Novel Galena Depressant in the Flotation Separation from Molybdenite
Yangjia Hu 1, Zhiqiang Zhao 1,2, Liang Lu 1,3,4 , Huanyu Zhu 5, Wei Xiong 1,3,4, Yangge Zhu 1,3,4, Sigang Luo 1, Xingrong Zhang 1,3,4,* and Bingqiao Yang 5,*
1 State Key Laboratory of Mineral Processing, BGRIMM Technology Group, Beijing 102600, China; [email protected] (Y.H.); [email protected] (Z.Z.); [email protected] (L.L.); [email protected] (W.X.); [email protected] (Y.Z.); [email protected] (S.L.) 2 Civil and Resource Engineering School, University of Science and Technology Beijing, Beijing 100083, China 3 China-South Africa Joint Research Center on the Development and Utilization of Mineral Resources, Beijing 102628, China 4 China-South Africa Belt and Road Joint Laboratory on Sustainable Exploration and Utilization of Mineral Resources, Beijing 102628, China 5 School of Resources and Safety Engineering, Wuhan Institute of Technology, Wuhan 430073, China; [email protected] * Correspondence: [email protected] (X.Z.); [email protected] (B.Y.)
Abstract: In this study, a novel organic depressant maleyl 5-amino-1,3,4-thiadiazole-2-thiol (MATT) was synthesized and utilized as a galena depressant in the flotation separation of molybdenite and galena. The results of the flotation test indicated that MATT exhibited an excellent depression ability on galena but barely influenced the flotation of molybdenite in the pH range of 6.0–11.0.
Zeta potential results suggested that MATT preferentially adsorbed on galena surface. UV-visible spectroscopy analysis indicated that the stoichiometric ratio of lead ion and reagent in the complex
Citation: Hu, Y.; Zhao, Z.; Lu, L.; compound. XPS analysis demonstrated that the S (-SH) atom and N (1,3,4-thiadiazole group) atom of Zhu, H.; Xiong, W.; Zhu, Y.; Luo, S.; MATT coordinated with the Pb atom on galena surface. Zhang, X.; Yang, B. Investigation on a Novel Galena Depressant in the Keywords: flotation; galena; molybdenite; depressant; MATT Flotation Separation from Molybdenite. Minerals 2021, 11, 410. https://doi.org/10.3390/min11040410 1. Introduction Academic Editor: Cyril O’Connor Molybdenum plays a vital role in steel, petroleum and chemical industries due to its excellent physical-chemical properties and mechanical performances [1]. Mo metal is Received: 4 March 2021 mainly extracted from molybdenite, which is generally associated commonly with other Accepted: 10 April 2021 Published: 13 April 2021 sulfide ores like chalcopyrite, pyrite and galena [2–4] etc. Since the floatability of these minerals is very similar, it is difficult to obtain molybdenite of a high grade and few
Publisher’s Note: MDPI stays neutral impurities. Especially, the presence of lead impurities in molybdenite concentrate not only with regard to jurisdictional claims in degrades the quality of Mo metals, but also causes serious environmental contamination published maps and institutional affil- during the processing of Mo ores [5,6]. Generally, the content of lead in molybdenite iations. concentrate is limited to be less than 0.05% [7]. Therefore, the removal of galena impurity from molybdenite is critical for the production of Mo metals of a high quality. Froth flotation, as a physicochemical separation technique, is an efficient and environm- entally-friendly approach to separate galena from molybdenite, based on the difference in surface properties [8,9]. In most cases, bulk flotation is adopted to recover molybdenite Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. and galena from Mo-Pb raw ores, then molybdenite and galena is separated by preferential This article is an open access article flotation [10]. It has been noted that both molybdenite and galena have a good floatability distributed under the terms and in the presence of a collector (non-polar oil or xanthate) or a frother (Z-200 or pine oil) [11]. conditions of the Creative Commons Therefore, it is hard to separate galena from molybdenite efficiently without any depres- Attribution (CC BY) license (https:// sant. At present, inorganic depressants have a wide application in industrial production, creativecommons.org/licenses/by/ such as potassium dichromate, sulfite and sodium hydrosulfide [12–16]. Although these 4.0/). depressants mentioned above could selectively separate galena from molybdenite, these
Minerals 2021, 11, 410. https://doi.org/10.3390/min11040410 https://www.mdpi.com/journal/minerals Minerals 2021, 11, x FOR PEER REVIEW 2 of 13
production, such as potassium dichromate, sulfite and sodium hydrosulfide [12–16]. Alt- hough these depressants mentioned above could selectively separate galena from molyb- Minerals 2021, 11, 410 2 of 12 denite, these inorganic ones suffer from many disadvantages, which are highly toxic and could cause damage to human health. In view of these disadvantages, many researchers have turned to research into some organicinorganic depressants. ones suffer It fromhas been many reported disadvantages, that L-cysteine which [17] are could highly selectively toxic and depress could cause the flotationdamage ofto human galena health.in Pb-Mo flotation. The results showed that the thiol and primary amineIn groups view ofof theseL-cysteine disadvantages, could coordinate many researcherslead sites on have galena turned surface to research. Similarly, into Zhang some etorganic al. [18] depressants. found that poly(acrylamide It has been reported-allylthiourea) that L-cysteine (PAM- [ATU)17] could could selectively separate depressgalena fromthe flotationartificially of mixed galena minerals in Pb-Mo successfully flotation. at The pH resultsaround showed10.5. Acetic that acid the-[(hydrazinyl- thiol and pri- thioxomethyl)thio]mary amine groups-sodium of L-cysteine (AHS) was could synthesized coordinate and lead applied sites in on the galena flotation surface. of galena Simi- andlarly, molybdenite Zhang et al. [7]. [18 It] was found found that that poly(acrylamide-allylthiourea) AHS chemisorbed on galena (PAM-ATU) surface to form could a five sep- numberarate galena ring with from lead artificially atoms on mixed a galena minerals surface. successfully at pH around 10.5. Acetic acid-[(hydrazinylthioxomethyl)thio]-sodiumAlthough a lot of efforts have been made (AHS)to exploit was eco synthesized-friendly and and high applied-selective in the depressantflotation of of galena galena, and it is molybdenite still a difficult [7 ].task It wasto explore found novel that AHS reagents chemisorbed to substitute on galenatradi- tionalsurface galena to form depressants. a five number In this ring work, with a novel lead atoms depressant on a galena named surface. MATT was synthesized and appliedAlthough in athe lot separation of efforts have of molybdenite been made to and exploit galena eco-friendly in various and conditions high-selective (dies de-el pressant of galena, it is still a difficult task to explore novel reagents to substitute traditional dosage, MATT dosage, and pH). Besides, its adsorption mechanism was studied through galena depressants. In this work, a novel depressant named MATT was synthesized and zeta potential, UV-Visible spectroscopy and X-ray photoelectron spectroscopy (XPS) anal- applied in the separation of molybdenite and galena in various conditions (diesel dosage, ysis. MATT dosage, and pH). Besides, its adsorption mechanism was studied through zeta potential, UV-Visible spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis. 2. Materials and Methods 2.1.2. MaterialsMinerals and and Reagents Methods 2.1.Pure Minerals galena and and Reagents molybdenite minerals were collected from Guangdong Province, China.Pure The galena ores were and firstmolybdenite selected minerals by hand werecarefully, collected and thenfrom crushed, Guangdong ground Province, and sievedChina. to The obtain ores various were first size selected fractions. by hand The fractions carefully, containing and then crushed, 38~74 μm ground particles and sievedwere collectedto obtain for various flotation size exper fractions.iments The and fractions the others containing less than 38~74 5 μmµm particlesfor analysis were tests. collected The XRDfor flotation spectra experiments of galena and and molybdenite the others less was than presented 5 µm for in analysis the Figure tests. 1. The The XRD results spectra of chemicalof galena analysis and molybdenite and XRD show was presented that the purities in the Figure of MoS1.2 The and results PbS are of more chemical than analysis95%. and XRD show that the purities of MoS2 and PbS are more than 95%.
a b Galena Molybdenite
Intensity
Intensity
10 20 30 40 50 60 70 80 10 20 30 40 50 60 70 80 2-Theta (°) 2-Theta (°)
Figure 1. a b XRD spectra of ( ) galena and ( ) molybdenite sample.
FigureSodium 1. XRD spectra hydroxide of (a) (NaOH),galena and hydrochloric (b) molybdenite acid sample. (HCl) and potassium nitrate (KNO3) purchased from Aladdin Chemical Reagent Co., Ltd. (Shanghai, China) were used in the experiments.Sodium hydroxide Diesel was (NaOH), obtained hydrochloric from Guangfu acid Chemical (HCl) Co.,and Ltd.potassium (Hengshui, nitrate China) (KNO and3) purchasedused as the from collector. Aladdin Diesel Chemical was added Reagent in the Co., form Ltd of. ( emulsification,Shanghai, China which) were was used prepared in the experiments.by a Cole Parmer Diesel ultrasonic was obtained processor from (750Guangfu W and Chemical 20 kHz) Co., at 60% Ltd. amplitude (Hengshui for, China 5 min.) andMethyl used isobutylas the collector. carbinol Diesel (MIBC) was purchased added in the from form Xilong of emulsification, Chemical Co., which Ltd. (Shantou,was pre- paredChina) by was a Cole used Parmer as the ultrasonic frother. Deionized processor water (750 (18.2W and M Ω20· cmkHz) resistivity) at 60% amplitude was used for in all5 experiments. The depressant MATT was synthesized in our lab according to the method provided in the reference [19].
2.2. Micro-Flotation Experiments
Micro-flotation tests were implemented using an XFG5-35 flotation machine (Jilin Prospecting Machinery Factory, Changchun, China) in a 40 mL cell. In each test, 2.0 g Minerals 2021, 11, 410 3 of 12
mineral sample and 30 mL deionized water was added into the cell, and pH was adjusted by using dilute hydrochloric acid and sodium hydroxide solution instead of commonly used pH regulator in industry in order to simplify the investigation. Subsequently, the depressant (MATT), the collector (kerosene) and the frother (MIBC) were introduced sequentially at each stage of 2 min conditioning before flotation. Finally, the flotation was performed for 3 min at an air flow rate of 0.2 L/min. The floated froth products and non-floated tailings were filtered, dried and weighted to a calculated floatability. Each test was performed three times and the average was reported. For micro-flotation tests of mixed minerals, 1.0 g galena and 1.0 g molybdenite was mixed and the flotation was performed as the same procedures mentioned above. The Pb and Mo grade of the concentrates was assayed using chemical assay method and the recovery of was calculated according the following equation: ε m R = c c × 100% (1) 50m0
where εc and mc represented the yield and grade of floated product, respectively. m0 represented the grade of pure mineral. Each test was repeated three times and the mean value was reported.
2.3. Zeta Potential Experiments Zeta potential tests were carried out on a Malvern Zeta Sizer Nano Series (Malvern Instruments Ltd., Malvern, UK) to study the adsorption behaviors of MATT on galena and molybdenite; 0.1 g samples with particle size of less than 5 µm were dispersed in 100 mL of 0.01 M KNO3 solution. Prior to the adjustment of pH, 30 mL of 0.02 M MATT solution was added into the slurry. After that, dilute hydrochloric acid and sodium hydroxide solutions were used to adjust the slurry pH to a desired value. Finally, 1 mL suspension was taken out and introduced into a standard cell to measure its zeta potential. Diesel was not used in Zeta potential measurement. The results presented here were an average value of ten independent measurements, with a typical variation corresponding to ±2 mV.
2.4. XPS Measurements The spectra of every samples were acquired by K-Alpha 1063 (Thermo Fisher Scientific Co., Waltham, MA, USA) using an Al Kα radiation (12 kV, 6 mA) in an analytical chamber with a pressure of 1.0 × 10–12 Pa. Galena samples were first treated in MATT solution (20 mg/L) at pH 9 for 20 min. Then the sample was filtered and dried in vacuum oven for 24 h. All binding energies were calibrated using the neutral C 1 s peak at 284.6 eV to eliminate the effect of surface charging. The XPS spectra was fitted and analyzed by Thermo Avantage software 5.5.
2.5. UV-Visible Spectroscopy of Complex The UV-Visible spectroscopy was employed to identify the stoichiometric ratio of lead ion and reagent using a Cary 60 UV-Vis spectrophotometer (Agilent, Santa Clara, CA, USA). The Pb2+ solution was mixed with MATT solutions at pH 6 with different concentration, and then the solution was stirred for 20 min to make sure the reaction was completed. The mixture was stood for 24 h. After that, the supernatant was transferred to quartz utensil and the absorbance was measured within the range of 200 to 800 nm.
3. Results and Discussion 3.1. Flotation Test 3.1.1. Effect of Diesel Dosage Figure2 shows the effect of diesel dosage on the floatability of galena and molybdenite at natural pH around 6.4. The experimental results showed that molybdenite exhibited excellent natural floatability with or without diesel. The floatability of galena was not as good as molybdenite, only above 25% galena floated under natural conditions without diesel. The floatability of galena increased gradually as increasing the diesel dosage and Minerals 2021, 11, x FOR PEER REVIEW 4 of 13
completed. The mixture was stood for 24 h. After that, the supernatant was transferred to quartz utensil and the absorbance was measured within the range of 200 to 800 nm.
3. Results and Discussion 3.1. Flotation Test 3.1.1. Effect of Diesel Dosage Figure 2 shows the effect of diesel dosage on the floatability of galena and molybde- nite at natural pH around 6.4. The experimental results showed that molybdenite exhib- Minerals 2021, 11, 410 ited excellent natural floatability with or without diesel. The floatability of galena was not 4 of 12 as good as molybdenite, only above 25% galena floated under natural conditions without diesel. The floatability of galena increased gradually as increasing the diesel dosage and a maximum recovery of around 75.0% was obtained at diesel dosage of 30 mg/L. These resultsa illustrated maximum that recoverythe presence of ofaround diesel made 75.0% the effective was obtained flotation separation at diesel of dosage mo- of 30 mg/L. These lybdeniteresults and galena illustrated become thatdifficult the without presence any depressant. of diesel made the effective flotation separation of molybdenite and galena become difficult without any depressant.
100 90 80 70 60 50 40 Galena Molybdenite Floatability(%) 30 20 pH = 6.4 MIBC dosage: 20 mg/L 10 0 0 5 10 15 20 25 30 35 Diesel dosage(mg/L)
Figure 2. Floatability of galena and molybdenite as a function of diesel dosage. Figure 2. Floatability of galena and molybdenite as a function of diesel dosage. 3.1.2. Effect of the MATT Depressant Dosage 3.1.2. Effect of the MATT Depressant Dosage Figure 3Figure shows 3the shows effect of the depressant effect dosage of depressant on the floatability dosage of galena on the and floatability mo- of galena and lybdenite.molybdenite. Obviously, MATT Obviously, barely influenced MATT barelythe floatability influenced of molybdenite. the floatability Even at a of molybdenite. Even MATTat dosage a MATT of 35 mg/L, dosage the offloatability 35 mg/L, of molybdenite the floatability maintained of molybdenitearound 98%. How- maintained around 98%. ever, theHowever, presence of the MATT presence significantly of MATT influenced significantly the floatation influenced performance theof galena floatation performance of mineral particles. The floatability of galena reduced rapidly with the increase of the de- Minerals 2021, 11, x FOR PEER REVIEW galena mineral particles. The floatability of galena reduced rapidly with the increase5 of 13 of the pressant dosage until the dosage reached 30 mg/L, at which, only about 3% galena was floated,depressant indicating that dosage MATT until was an the effective dosage galena reached depressant 30 mg/L, in the flotation at which, separa- only about 3% galena was tion offloated, galena and indicating molybdenite. that MATT was an effective galena depressant in the flotation separation of galena and molybdenite.
100 90 80 70 Galena 60 Molybdenite 50 pH = 9.7 40 MIBC dosage:50 mg/L
Floatability(%) 30 Diesel dosage:30 mg/L 20 10 0 0 5 10 15 20 25 30 35 Depressant dosage(mg/L)
Figure 3. Floatability of galena and molybdenite as a function of depressant dosage. Figure 3. Floatability of galena and molybdenite as a function of depressant dosage. 3.1.3. Effect of the Pulp pH 3.1.3. EffectFigure of the 4Pulp shows pH the effect of the pulp pH on the floatability of galena and molybdenite Figurein the 4 absence shows the and effect presence of the of pulp MATT. pH on Molybdenite the floatability had of a goodgalena floatability and molybdenite with or without in the MATTabsence inand the presence whole of testing MATT. pH Molybdenite range of 6.0–11.0. had a good The floatability recovery with of molybdenite or with- was out MATTmaintained in the whole at 98% testing under pH varied range pH of conditions. 6.0–11.0. T However,he recovery the of pH molybdenite significantly was influenced maintained at 98% under varied pH conditions. However, the pH significantly influenced the floatability of galena. As shown in Figure 4, galena exhibited a very low floatability when the pH value was greater than 10.0 without MATT due to the formation of hydroxyl species, which made galena surface hydrophilic [20,21]. The addition of MATT led to a very strong depressing effect on galena, only less than 2% galena was floated, whereas the floatability of molybdenite barely changed in the presence of MATT. In addition, it could be observed that galena was strongly depressed within a board pH range, which sug- gested that MATT could realize the selective separation of molybdenite and galena and have a good application prospect.
100 90 80 70 Galena 60 Galena + 30 mg/L MATT 50 Molybdenie Molybdenite + 30 mg/L MATT 40
Floatability(%) 30 Diesel dosage: 30 mg/L MIBC dosage: 20 mg/L 20 10 0 6 7 8 9 10 11 12 pH
Figure 4. Floatability of galena and molybdenite as a function of the pulp pH.
Minerals 2021, 11, x FOR PEER REVIEW 5 of 13
100 90 80 70 Galena 60 Molybdenite 50 pH = 9.7 40 MIBC dosage:50 mg/L
Floatability(%) 30 Diesel dosage:30 mg/L 20 10 0 0 5 10 15 20 25 30 35 Depressant dosage(mg/L)
Figure 3. Floatability of galena and molybdenite as a function of depressant dosage.
3.1.3. Effect of the Pulp pH Figure 4 shows the effect of the pulp pH on the floatability of galena and molybdenite in the absence and presence of MATT. Molybdenite had a good floatability with or with- Minerals 2021, 11, 410 5 of 12 out MATT in the whole testing pH range of 6.0–11.0. The recovery of molybdenite was maintained at 98% under varied pH conditions. However, the pH significantly influenced the floatability of galena. As shown in Figure 4, galena exhibited a very low floatability whenthe the floatability pH value was of galena. greater Asthan shown 10.0 without in Figure MAT4,T galena due to exhibitedthe formation a very of hydroxyl low floatability specieswhen, which the pH made value galena was surface greater hydrophilic than 10.0 without [20,21]. MATT The addition due to theof MATT formation led to of a hydroxyl veryspecies, strong depressing which made effect galena on galena, surface only hydrophilic less than 2% [20 galena,21]. was The floated, addition whereas of MATT the led to a floatabilityvery strong of molybdenite depressing barely effect changed on galena, in the only presence less than of 2%MATT. galena In addition, was floated, it could whereas the be observedfloatability that of galena molybdenite was strongly barely depressed changed inwithin the presence a board ofpH MATT. range, In which addition, sug- it could gested that MATT could realize the selective separation of molybdenite and galena and be observed that galena was strongly depressed within a board pH range, which suggested have a good application prospect. that MATT could realize the selective separation of molybdenite and galena and have a good application prospect.
100 90 80 70 Galena 60 Galena + 30 mg/L MATT 50 Molybdenie Molybdenite + 30 mg/L MATT 40
Floatability(%) 30 Diesel dosage: 30 mg/L MIBC dosage: 20 mg/L 20 10 0 6 7 8 9 10 11 12 pH Minerals 2021, 11, x FOR PEER REVIEW 6 of 13
Figure 4. Floatability of galena and molybdenite as a function of the pulp pH. Figure 4. Floatability of galena and molybdenite as a function of the pulp pH. 3.1.4. Artificially3.1.4. Artificially Mixed Minerals Mixed Flotation Minerals Flotation The flotationThe flotationtests of artificially tests of mixed artificially minerals mixedwere carried minerals out to werefurther carriedexamine out to further examine the effectthe of effect MATT of on MATTthe flotation on theseparation flotation of galena separation and molybdenite. of galena Figure and 5 molybdenite. shows Figure5 shows the flotation separation results of artificially mixed minerals at pH 9.0. The recovery of the flotation separation results of artificially mixed minerals at pH 9.0. The recovery of PbS decreased with the increase of MATT dosage, and the recovery of galena reduced to aroundPbS 8.6% decreased when MATT with dosage the reached increase to 30 of mg/L. MATT For dosage,the case of and molybdenite, the recovery the of galena reduced to recoveryaround of MoS2 8.6% still maintained when MATT at 88.9% dosage as the increase reached of MATT to 30 dosage, mg/L. which For thewas casein of molybdenite, the a good accordance with the results of single mineral flotation. The flotation separation recovery of MoS2 still maintained at 88.9% as the increase of MATT dosage, which was resultsin of aartificially good accordance mixed minerals with reconfirmed the results that of MATT single could mineral selectively flotation. separate The flotation separation galena from molybdenite. results of artificially mixed minerals reconfirmed that MATT could selectively separate galena from molybdenite.
100 MoS2 PbS
80
60
40
Recovery (%)
20
0 5 10 20 30 MATT dosage (mg/L)
Figure 5. The flotation separation results of artificially mixed minerals (diesel dosage 30 mg/L, MIBC Figure 5. The flotation separation results of artificially mixed minerals (diesel dosage 30 mg/L, MIBC 2200 m mg/L,g/L, pH = pH 9). = 9).
3.2. Zeta Potential Measurement The zeta potentials of galena, MATT-treated galena, molybdenite and MATT-treated molybdenite are presented in Figure 6. The decrease of PbS zeta potential at pH less than 5 was ascribed to the formation of sulphoxy species due to oxidation of PbS, whereas lead hydroxyl species were identified as the most likely candidates accounting for the behavior under alkaline conditions according to previous reports [20].
Minerals 2021, 11, 410 6 of 12
3.2. Zeta Potential Measurement The zeta potentials of galena, MATT-treated galena, molybdenite and MATT-treated molybdenite are presented in Figure6. The decrease of PbS zeta potential at pH less than 5 was ascribed to the formation of sulphoxy species due to oxidation of PbS, whereas lead hydroxyl species were identified as the most likely candidates accounting for the behavior Minerals 2021, 11, x FOR PEER REVIEW 7 of 13 under alkaline conditions according to previous reports [20].
Figure 6. The 6. zetaThe potentials zeta of potentialsgalena and molybdenite of galena as a function and of molybdenitepH. as a function of pH. After the treatment of MATT, zeta potential became more negative, which may be ascribed to the carboxyl acid (-COO-) and thiol (-SH) functional groups from the MATT molecule.After Thiol group the could treatment be adsorbed ofon the MATT, metal site zetaof galena potential surface, while became car- more negative, which may be boxylascribed acid group to (-COO the-)carboxyl formed negative acid molecular (–COO–) film, resulting and in the thiol more negative (–SH) functional groups from the MATT zeta potential than pure galena. The zeta potential of MATT-treated galena reached to a plateaumolecule. at pH of Thiolabout 9.0, group indicating could a maximum be ads adsorbedorption of MATT on theoccurred metal withinsite of galena surface, while carboxyl the pH range of 9.0–11.0. It should be noted that 1,3,4-thiadiazole group contributed to its adsorptionacid group onto the (–COO–) PbS surface. formed negative molecular film, resulting in the more negative zeta potentialHowever, it than also could pure be observed galena. from The Figure zeta 6 that potentialMATT barely influenced of MATT-treated the galena reached to a plateau zeta potentials of molybdenite, which indicated that MATT was weakly adsorbed on mo- lybdeniteat pH surface of about in the pH9.0, range indicatingof 5.0–12.0. These aresults maximum could explain well adsorption that the of MATT occurred within the pHfloatability range of molybdenite of 9.0–11.0. was almost It not should affected by bethe addition noted of thatMATT depressant 1,3,4-thiadiazole group contributed to its as shown in Figures 3 and 4. adsorption onto the PbS surface. 3.3. UV-Visible Spectroscopy Analysis FigureHowever, 7 shows the UV it spectra also of could Pb2+ in the be presence observed of various fromdosages of Figure MATT at6 that MATT barely influenced the azeta designed potentials desired concentration of molybdenite, ratio. There was a maximum which adsorption indicated peak in 304that nm, MATT was weakly adsorbed on which could be attributed to Pb-MATT complex. As the MATT concentration increased, themolybdenite absorbance at 304 surfacenm rose. Besides, in the it should pH be range noted that of these 5.0–12.0. lines overlap Theseped results could explain well that the whenfloatability the [Pb2+]/[MATT] of molybdenite ratio was 1:1, 1:2 and was 1:4, indicating almost that not the complexation affected r byeac- the addition of MATT depressant as tion was saturated when the ratio was close to 1:1. A conclusion can be drawn from this, thatshown the stoichiometric in Figures ratio of3 leadand ion4 .and reagent in this complex compound was 1:1, which was critical for estimating the adsorption mechanism of depressant MATT on the galena surface. 3.3. UV-Visible Spectroscopy Analysis Figure7 shows the UV spectra of Pb 2+ in the presence of various dosages of MATT at a designed desired concentration ratio. There was a maximum adsorption peak in 304 nm, which could be attributed to Pb-MATT complex. As the MATT concentration increased, the absorbance at 304 nm rose. Besides, it should be noted that these lines overlapped when the [Pb2+]/[MATT] ratio was 1:1, 1:2 and 1:4, indicating that the complexation reaction was saturated when the ratio was close to 1:1. A conclusion can be drawn from this, that the stoichiometric ratio of lead ion and reagent in this complex compound was 1:1, which was critical for estimating the adsorption mechanism of depressant MATT on the galena surface.
3.4. XPS Analysis The survey XPS spectra of galena treated at various conditions are shown in Figure8 . For galena treated by MATT, a new peak appeared at about 399.0 eV, which was the characteristic peak of N 1s. The surface atomic content of C, N, O, S and Pb atoms were presented in Table1. The concentration of N atoms on the surface of galena treated with MATT increased by 2.98%. It could be inferred from those results that MATT was effectively Minerals 2021, 11, x FOR PEER REVIEW 8 of 13
1.0 MS Minerals 2021 11 , , 410 C 2+:C = 1:0.5 7 of 12 0.8 Pb MATT 2+ CPb :CMATT = 1:1 Minerals 2021, 11, x FOR PEER REVIEW C 2+:C = 1:2 8 of 13 0.6 Pb MATT C 2+:C = 1:4 adsorbed on the galena surface,Pb MATT because MATT was the unique source of N element, which
Abs 0.4 was in agreement with the result of zeta potential.
1.0 0.2 MS
2+ CPb :CMATT = 1:0.5 0.0 0.8 2+ CPb :CMATT = 1:1
2+ 200 300 400 500 600 700 CPb :C800MATT = 1:2 0.6 C 2+:C = 1:4 nm Pb MATT
Abs 0.4 Figure 7. UV spectra of MATT under various concentration ratios of Pb2+ ions and MATT.
3.4. XPS Analysis 0.2 The survey XPS spectra of galena treated at various conditions are shown in Figure 8. For galena treated0.0 by MATT, a new peak appeared at about 399.0 eV, which was the characteristic peak of N 1s. The surface atomic content of C, N, O, S and Pb atoms were presented in Table 2001. The concentration300 400 of 500N atom600s on the700 surface 800of galena treated with MATT increased by 2.98%. It could be inferrednm from those results that MATT was effec- tively adsorbed on the galena surface, because MATT was the unique source of N element, Figure 7. UV spectra of MATT under various concentration ratios of Pb2+ ions and MATT. which wasFigure in agreement 7. UV spectra with of MATTthe result under of zetavarious potential. concentration ratios of Pb2+ ions and MATT.
3.4. XPS Analysis
The survey XPS spectra of galena treated at variousPb 4f5 Oxides conditions are shown in Figure
Pb 4d3
Pb 4d5
Pb 4p3
8. For galena treated by MATT, a newO 1s peak appeared at about 399.0 eV, which was the
S 2p
S 2s characteristic peak of N 1s. The surface atomic 1s C content of C, N, O, S and Pb atoms were
Pb 5d5 presented inGalena Table 1. The concentration of N atoms on the surface of galena treated with MATT increased by 2.98%. It could be inferred from those results that MATT was effec-
Pb 4f5 Oxides
Pb 4d5 tively adsorbed on the galena surface, becausePb 4d3 MATT was the unique source of N element,
1s
Pb 4p3
O 1s which was in agreement with the result of zeta potential.S 2p
N
S 2s
C 1s C
Pb 5d5 Galena + MATT
Intensity
Pb 4d5
1s
Pb 4d3
O 1s
Pb 4f5 Oxides
Pb 4f5 Oxides
N
Pb 4d3
Pb 4d5
Pb 4p3
C 1s C
Pb 4p3
S 2p
O 1s
S 2s
S 2p
S 2s 2+ 1s C MATT + Pb Pb 5d5
Pb 5d5
Galena 1s
N
C 1s C
S 2p
S 2s
O 1s O
Pb 4f5 Oxides
Pb 4d5
Pb 4d3
1s
Pb 4p3
O 1s MATT S 2p
N
S 2s
C 1s C
1200 1000 800 600 400 200 0 Pb 5d5 Galena + MATT Intensity Binding energy(ev)
Pb 4d5
1s
Pb 4d3
O 1s
Pb 4f5 Oxides
N
Pb 4p3 Figure 8. The survey XPS spectra of galena, galena 1s C treated with MATT, MATT and MATT treated
Figure 8. The survey XPS spectra of galena, galena treated with MATT, MATTS 2p and MATT treated 2+ S 2s 2+ with Pb ions. with Pb ions. 2+ MATT + Pb Pb 5d5
1s
N
Table 1. Atomic concentrations of galena samplesbefore1s C and after treatment by MATT.
S 2p
S 2s 1s O Atomic Concentration of Elements (Atomic %) SamplesMATT C O S Pb N 1200 1000 800 600 400 200 0 MATT 26.98 2.55 39.99 30.48 GalenaBinding 22.70 energy(ev) 10.52 37.21 29.57 Galena + MATT 21.36 6.47 31.99 37.22 2.98 Figure 8. The survey∆a XPS spectra of galena,−1.34 galena treated−4.05 with MATT, MATT−5.22 and MATT 7.65 treated 2.98 2+ with Pb∆a isions. defined as the value of after MATT treatment minus than that of before treatment.
The C 1s spectra of galena and galena treated with MATT are shown in Figure9 . The peak located at 284.60 eV was represented as the referenced C 1s. For galena, the spectra Minerals 2021, 11, x FOR PEER REVIEW 9 of 13
Table 1. Atomic concentrations of galena samples before and after treatment by MATT.
Atomic Concentration of Elements (Atomic %) Samples C O S Pb N MATT 26.98 2.55 39.99 30.48 Galena 22.70 10.52 37.21 29.57 Galena + MATT 21.36 6.47 31.99 37.22 2.98 Δa −1.34 −4.05 −5.22 7.65 2.98 Δa is defined as the value of after MATT treatment minus than that of before treatment. Minerals 2021, 11, 410 8 of 12 The C 1s spectra of galena and galena treated with MATT are shown in Figure 9. The peak located at 284.60 eV was represented as the referenced C 1s. For galena, the spectra of 285.46 eV, 286.47 eV, and 287.76 eV would be attributed to C-C, C-O, and C=O respec- tively [18]. The peak at 289.16 eV was assigned to the lead carbonate (PbCO3) [22–24], due to the oxidationof 285.46 on galena eV, 286.47 surface. eV, As and for the 287.76 spectra eV of wouldgalena treated be attributed with MATT, to a C–C,new C–O, and C=O respec- peak increasedtively [at18 285.50]. The eV peak (-C-N at and 289.16 -C-S group) eV was [25,26] assigned appeared, to thewhic leadh reconfirmed carbonate (PbCO3) [22–24], due that MATTtothe could oxidation be adsorbed on on galena the surface surface. of galena. As for the spectra of galena treated with MATT, a new peak increased at 285.50 eV (–C–N and –C–S group) [25,26] appeared, which reconfirmed that MATT could be adsorbed on the surface of galena.
C 1s
Galena C-C 2- C=O CO3 C-O
Intensity Galena + MATT C-N C-C C-S 2- C=O C-O CO3
290 289 288 287 286 285 284 283 Binding energy(eV)
Figure 9.Figure C 1s spectra 9. C of 1s galena, spectra galena of treated galena, with galena MATT. treated with MATT.
The S 2p spectraThe S of 2p galena, spectra galena of treated galena, with galenaMATT and treated MATT are with shown MATT in Figure and MATT are shown in 10. Obviously,Figure the 10 peaks. Obviously, located at 160.71 the peaks and 161.92 located eV were at 160.71 the characteristic and 161.92 doublet eV were the characteristic peak of doubletgalena, which peak was of consistent galena, with which those was in previous consistent reports with [17]. those The S in 2p previousspectra reports [17]. The S 2p of the depressant could be deconvoluted into three peaks at 161.82 eV, 163.68 eV and 164.26 eV,spectra which represented of the depressant C=S (tautomer could form be of deconvoluted-N=C-SH), -SH and into C-S- threeC (from peaks 1,3,4- at 161.82 eV, 163.68 eV thiadiazoleand group) 164.26 respectively eV, which [27]. represented It should be C=Snoted (tautomer that the peaks form of the of –N=C–SH),thiol group –SH and C–S–C (from shifted to1,3,4-thiadiazole a higher binding energy group) significantly respectively after the [ 27adsorption]. It should of MATT, be while noted the thatre the peaks of the thiol was no obviousgroup displacement shifted to a that higher occurred binding to doublets energy of C=S significantly and C-S- C, thus after indicating the adsorption of MATT, while that the theresulfur atom was from no obvious the thiol group displacement might act as thatthe reaction occurred site when to doublets the depres- of C=S and C–S–C, thus Minerals 2021, 11, x FOR PEER REVIEWsant was adsorbed on the surface of galena. 10 of 13 indicating that the sulfur atom from the thiol group might act as the reaction site when the depressant was adsorbed on the surface of galena.
S 2p PbS
Galena
PbS Galena + MATT -SH C-S-C C=S
Intensity
C-S-C C=S
MATT -SH
170 168 166 164 162 160 Binding energy(eV)
Figure 10.Figure S 2p spectra 10. S 2p of spectragalena, galena of galena, treated galena with treatedMATT, and with MATT. MATT, and MATT.
Figure 11Figure shows 11 the shows N 1s spectra the N 1sof galena, spectra galena of galena, treated galena with MATT treated and with MATT MATT and MATT 2+ treated treatedwith Pb2+ with ions. Pb As shownions. Asin Figure shown 11, in the Figure spectra 11 of, the MATT spectra could of be MATT fitted couldwith be fitted with two components at 399.42 and 400.48 eV, which might be associated with C-N-C, C=N- N=C, or C=N-N-C, respectively [28,29]. From the survey spectra of galena, there was no characteristic peak on the surface of galena. After the addition of MATT depressant, three new peaks increased at 398.54 eV, 399.12 eV and 399.69 eV, which were very similar to the spectra of MATT treated with Pb2+ ions. The peaks at 398.54 eV and 399.69 eV could be assigned to C-N and C=N [30,31], whereas the peak centered at 399.12 might be ascribed to the Pb-N bond caused by the adsorption, proving that the nitrogen atom might also participate in the chemisorption.
C=N-N=C N 1s C-N-C MATT
Pb2+-N C=N C-N Galena + MATT
Intensity
Pb2+-N
C-N MATT + Pb2+ C=N
402 400 398 Binding energy (eV)
Figure 11. N 1s spectra of galena, galena treated with MATT and MATT treated with Pb2+ ions.
Minerals 2021, 11, x FOR PEER REVIEW 10 of 13
S 2p PbS
Galena
PbS Galena + MATT -SH C-S-C C=S
Intensity
C-S-C C=S
MATT -SH
170 168 166 164 162 160 Minerals 2021, 11, 410 Binding energy(eV) 9 of 12
Figure 10. S 2p spectra of galena, galena treated with MATT, and MATT.
Figure 11 shows the N 1s spectra of galena, galena treated with MATT and MATT treatedtwo with components Pb2+ ions. As shown at 399.42 in Figure and 11, 400.48 the spectra eV, which of MATT might could be be associated fitted with with C–N–C, C=N– two componentsN=C, or C=N–N–C,at 399.42 and respectively400.48 eV, which [28 might,29]. be From associated the survey with C spectra-N-C, C=N of- galena, there was no N=C, orcharacteristic C=N-N-C, respectively peak on [28,29]. the surface From the of survey galena. spectra After of the galena, addition there was of MATTno depressant, three characteristicnew peaks peak on increased the surface at of 398.54 galena. eV,After 399.12 the addition eV and of MATT 399.69 depressant, eV, which three were very similar to the new peaksspectra increased of MATT at 398.54 treated eV, 399.12 with eV Pband2+ 399.69ions. eV The, which peaks were atvery 398.54 similar eV to the and 399.69 eV could be spectra of MATT treated with Pb2+ ions. The peaks at 398.54 eV and 399.69 eV could be assignedassigned to C-N and to C–NC=N [30,31], and C=N whereas [30 ,the31], peak whereas centered the at peak399.12 centeredmight be ascribed at 399.12 might be ascribed to the toPb- theN bond Pb–N caused bond by causedthe adsorption, by the proving adsorption, that the provingnitrogen atom that might the nitrogen also atom might also participateparticipate in the chemisorption. in the chemisorption.
C=N-N=C N 1s C-N-C MATT
Pb2+-N C=N C-N Galena + MATT
Intensity
Pb2+-N
C-N MATT + Pb2+ C=N
402 400 398 Binding energy (eV) Minerals 2021, 11, x FOR PEER REVIEW 11 of 13
2+ Figure Figure11. N 1s spectra 11. N 1sof galena, spectra galena of galena, treated galenawith MATT treated and MATT with MATTtreated with and Pb MATT2+ ions. treated with Pb ions.
The highThe resolution high resolution spectra of spectra Pb 4f of of galena Pb 4f treated of galena and treated untreated and with untreated MATT is with MATT is displayed in Figure 12. For the original galena sample, the Pb 4f spectra located at 137.50 eV displayed in Figure 12. For the original galena sample, the Pb 4f spectra located at 137.50 eV andand 142.50 142.50 eV were eV were regarded regarded as the as characteristic the characteristic peaks peaksof galena of galenaand were and coherent were coherent with with thethe repor reportedted values values in previous in previous study study [32], while [32], whilethe binding the binding energy located energy at located 138.45 at 138.45 eV eV andand 143.45 143.45 eV were eV weredue to due oxidation to oxidation products products of lead ions of leadon galena ions surface. on galena After surface. the After the additionaddition of MATT of depressant, MATT depressant, the binding the energy binding of energyPbS was of shifted PbSwas to 137.29 shifted eV toand 137.29 eV and 142.18 142.18eV, lower eV, lowerthan that than of thatoriginal of original galena, galena,while the while spectra the of spectra Pb oxidizations of Pb oxidizations were were still still at at138.42 138.42 eV eVand and 143.42 143.42 eV. The eV. decrease The decrease of Pb of4f binding Pb 4f binding energy energydemonstrated demonstrated that that the the electronicelectronic density density of lead oflead atom atom was changed, was changed, which which might mightbe attributed be attributed to the combi- to the combination nation ofof PbPb sites and and MATT. MATT.
PbS Pb 4f PbS
PbO PbO Galena
PbS PbS
Intensity
Galena + MATT PbO PbO
147 144 141 138 Binding energy(eV)
Figure Figure12. Pb 4f 12. spectraPb 4f of spectra galena ofwith galena and without with and MATT without treatment. MATT treatment.
3.5. The Suggested Adsorption Model These analysis results mentioned above approved that the sulfur atom (-SH), the ni- trogen atom from 1,3,4-thiadiazole group, and the lead atom from galena surface played as reaction sites. Therefore, a potential adsorption mechanism might be drawn from for- mer tests that four member rings could be formed on the galena surface through MATT and the lead atom. The potential adsorption model of MATT on the galena surface was proposed as shown in Figure 13, which was in agreement with the adsorption mechanism of CSC-1 (collector) [33] on the galena surface.
Figure 13. The potential adsorption mechanism mode of MATT on galena surface.
Minerals 2021, 11, x FOR PEER REVIEW 11 of 13
The high resolution spectra of Pb 4f of galena treated and untreated with MATT is displayed in Figure 12. For the original galena sample, the Pb 4f spectra located at 137.50 eV and 142.50 eV were regarded as the characteristic peaks of galena and were coherent with the reported values in previous study [32], while the binding energy located at 138.45 eV and 143.45 eV were due to oxidation products of lead ions on galena surface. After the addition of MATT depressant, the binding energy of PbS was shifted to 137.29 eV and 142.18 eV, lower than that of original galena, while the spectra of Pb oxidizations were still at 138.42 eV and 143.42 eV. The decrease of Pb 4f binding energy demonstrated that the electronic density of lead atom was changed, which might be attributed to the combi- nation of Pb sites and MATT.
PbS Pb 4f PbS
PbO PbO Galena
PbS PbS
Intensity
Galena + MATT PbO PbO
147 144 141 138 Binding energy(eV)
Minerals 2021, 11, 410 10 of 12 Figure 12. Pb 4f spectra of galena with and without MATT treatment.
3.5. The Suggested Adsorption Model 3.5.These The Suggested analysis Adsorption results mentioned Model above approved that the sulfur atom (-SH), the ni- trogen Theseatom analysisfrom 1,3,4 results-thiadiazole mentioned group above, and approved the lead that atom the from sulfur galena atom (-SH),surface the played as nitrogenreaction atom sites. from Therefore, 1,3,4-thiadiazole a potential group, adsorption and the lead mechanism atom from might galena be surface drawn played from for- as reaction sites. Therefore, a potential adsorption mechanism might be drawn from former mer tests that four member rings could be formed on the galena surface through MATT tests that four member rings could be formed on the galena surface through MATT and the andlead the atom. lead The atom. potential The potential adsorption adsorption model of MATT model on of the MATT galena on surface the galena was proposed surface was proposedas shown as in shown Figure in13 ,Figure which was13, which in agreement was in withagreement the adsorption with the mechanism adsorption of CSC-1mechanism of (collector)CSC-1 (collector) [33] on the [33] galena on the surface. galena surface.
Figure 13. The potential adsorption mechanism mode of MATT on galena surface. Figure 13. The potential adsorption mechanism mode of MATT on galena surface. 4. Conclusions In the present study, a novel galena depressant maleyl 5-amino-1,3,4-thiadiazole-2- thiol (MATT) was explored in the flotation separation of galena and molybdenite through flotation tests and various characterization techniques. The flotation experiments demon- strated that MATT could strongly depress the flotation of galena and realize the selective flotation separation of galena from molybdenite, which was more selective compared with traditional depressants. The proposed adsorption mechanism on the galena surface was investigated by zeta potential, UV-visible spectroscopy, and XPS methods. Zeta potential results revealed that the depression was due to the preferential adsorption of MATT on the galena surface other than molybdenite. UV-visible spectroscopy analysis further confirmed that the stoichiometric ratio of lead ions and MATT in this complex compound was 1:1. The XPS analysis indicated that MATT was complexed through the -SH and N atom from 1,3,4-thiadiazole group with Pb sites on galena surface (Figure 13). All these results shows that MATT might be a potential effective galena depressant in the flotation separation of Mo-Pb ores.
Author Contributions: Conceptualization, X.Z.; Data curation, Y.H. and W.X.; Formal analysis, Y.H., Z.Z., X.Z. and B.Y.; Funding acquisition, X.Z. and Y.Z.; Investigation, Y.H., L.L. and W.X.; Project administration, X.Z.; Supervision, X.Z.; Validation, Z.Z. and S.L.; Writing—original draft, Y.H. and H.Z.; Writing—review and editing, H.Z., X.Z. and B.Y. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the National Natural Science Foundation of China, grant number 51974030, the National Key R&D Program of China, grant number 2017YFE0133100 and the BGRIMM fund program, grant number 02-1903 and 02-1820. Data Availability Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest. Minerals 2021, 11, 410 11 of 12
References
1. Liu, Y.; Zuo, R.; Qi, S. Surfactant-free solvothermal synthesis and optical characterization of Bi2Fe4O9 in mixed H2O/EtOH solvent. Powder Technol. 2014, 254, 30–35. [CrossRef] 2. Kholmogorov, A.G.; Kononova, O.N. Processing mineral raw materials in Siberia: Ores of molybdenum, tungsten, lead and gold. Hydrometallurgy 2005, 76, 37–54. [CrossRef] 3. Zeng, L.; Cheng, C.Y. A literature review of the recovery of molybdenum and vanadium from spent hydrodesulphurisation catalysts. Hydrometallurgy 2009, 98, 1–9. [CrossRef] 4. Yan, H.; Yang, B.; Zeng, M.; Huang, P.; Teng, A. Selective flotation of Cu-Mo sulfides using xanthan gum as a novel depressant. Miner. Eng. 2020, 156.[CrossRef] 5. Fang, S.; Xu, L.; Wu, H.; Shu, K.; Xu, Y.; Zhang, Z.; Chi, R.; Sun, W. Comparative studies of flotation and adsorption of Pb(II)/benzohydroxamic acid collector complexes on ilmenite and titanaugite. Powder Technol. 2019, 345, 35–42. [CrossRef] 6. Xu, L.; Tian, J.; Wu, H.; Lu, Z.; Yang, Y.; Sun, W.; Hu, Y. Effect of Pb2+ ions on ilmenite flotation and adsorption of benzohydroxamic acid as a collector. Appl. Surf. Sci. 2017, 425, 796–802. [CrossRef] 7. Yin, Z.; Sun, W.; Hu, Y.; Liu, R.; Jiang, W.; Zhang, C.; Guan, Q.; Zhang, C. Synthesis of acetic acid-[(hydrazinylthioxomethyl)thio]- sodium and its application on the flotation separation of molybdenite from galena. J. Ind. Eng. Chem. 2017, 52, 82–88. [CrossRef] 8. Choi, J.; Lee, E.; Choi, S.Q.; Lee, S.; Han, Y.; Kim, H. Arsenic removal from contaminated soils for recycling via oil agglomerate flotation. Chem. Eng. J. 2016, 285, 207–217. [CrossRef] 9. Yang, B.; Yan, H.; Zeng, M.; Huang, P.; Jia, F.; Teng, A. A novel copper depressant for selective flotation of chalcopyrite and molybdenite. Miner. Eng. 2020, 151.[CrossRef] 10. Cao, Z.; Yue, Y.; Zhong, H.; Qiu, P.; Chen, P.; Wen, X.; Wang, S.; Liu, G. A novel approach for flotation recovery of molybdenite, galena and pyrite from a complex molybdenum-lead ore. Metall. Res. Technol. 2017, 114.[CrossRef] 11. Qin, W.; Wu, J.; Jiao, F.; Zeng, J. Mechanism study on flotation separation of molybdenite from chalcocite using thioglycollic acid as depressant. Int. J. Min. Sci. Technol. 2017, 27, 1043–1049. [CrossRef] 12. Chen, W.; Chen, F.; Zhang, Z.; Tian, X.; Bu, X.; Feng, Q. Investigations on the depressant effect of sodium alginate on galena flotation in different sulfide ore collector systems. Miner. Eng. 2021, 160.[CrossRef] 13. Hu, Y.; Wu, M.; Liu, R.; Sun, W. A review on the electrochemistry of galena flotation. Miner. Eng. 2020, 150.[CrossRef] 14. Nikolaev, A.A.; Goryachev, B.E. Thermodynamic and flotation analysis of influence exerted by chromate ions on separation of galena and chaclopyrite in alkaline media. J. Min. Sci. 2007, 43, 670–679. [CrossRef] 15. Goryachev, B.E.; Nikolaev, A.A. Thermodynamics of the interaction between chromate ions and a mineral complex of polymetallic ores. Galena. Russ. J. Non Ferr. Met. 2011, 52, 337–343. [CrossRef] 16. Nikolaev, A.A.; Goryachev, B.E. Thermodynamics of the interaction of chromate ions with the mineral complex of polymetallic ores. Chalcopyrite. Russ. J. Non Ferr. Met. 2013, 54, 417–424. [CrossRef] 17. Yin, Z.; Xu, L.; He, J.; Wu, H.; Fang, S.; Khoso, S.A.; Hu, Y.; Sun, W. Evaluation of l-cysteine as an eco-friendly depressant for the selective separation of MoS2 from PbS by flotation. J. Mol. Liq. 2019, 282, 177–186. [CrossRef] 18. Zhang, X.; Lu, L.; Zeng, H.; Hu, Z.; Zhu, Y.; Han, L. A macromolecular depressant for galena and its flotation behavior in the separation from molybdenite. Miner. Eng. 2020, 157.[CrossRef] 19. Wang, T.; Zhang, Y.H.; Yu, S.; Ji, H.; Lai, Y.S.; Peng, S.X. Synthesis and biological evaluation of novel thalidomide analogues as potential anticancer drugs. Chin. Chem. Lett. 2008, 19, 928–930. [CrossRef] 20. Qin, W.; Wang, X.; Ma, L.; Jiao, F.; Liu, R.; Yang, C.; Gao, K. Electrochemical characteristics and collectorless flotation behavior of galena: With and without the presence of pyrite. Miner. Eng. 2015, 74, 99–104. [CrossRef] 21. Goryachev, B.E.; Nikolaev, A.A. Galena oxidation mechanism. J. Min. Sci. 2012, 48, 354–362. [CrossRef] 22. Jia, K.; Feng, Q.; Zhang, G.; Shi, Q.; Chang, Z. Understanding the roles of Na 2 S and Pb(II)in the flotation of hemimorphite. Miner. Eng. 2017, 111, 167–173. [CrossRef] 23. Pawel, N.; Kari, L.; Zhang, G. Oxidation og galena surface—An XPS study of the formation of sulfoxy species. Appl. Surf. Sci. 2000, 157, 101–111. [CrossRef] 24. Jia, K.; Feng, Q.; Zhang, G.; Ji, W.; Zhang, W.; Yang, B. The role of S(II) and Pb(II) in xanthate flotation of smithsonite: Surface properties and mechanism. Appl. Surf. Sci. 2018, 442, 92–100. [CrossRef] 25. Ikumapayi, F.; Makitalo, M.; Johansson, B.; Rao, K.H. Recycling of process water in sulphide flotation: Effect of calcium and sulphate ions on flotation of galena. Miner. Eng. 2012, 39, 77–88. [CrossRef] 26. Dodero, G.; Michiel, D.; Cavallri, O.; Rao, K.H. L-Cysteine chemisorption on gold: A XPS and STM study. Coll. Surf. A Physicochem. Eng. Asp. 2000, 175, 121–128. [CrossRef] 27. Huang, Y.; Liu, G.; Liu, J.; Yang, X.; Zhang, Z. Thiadiazole-thione surfactants: Preparation, flotation performance and adsorption mechanism to malachite. J. Ind. Eng. Chem. 2018, 67, 99–108. [CrossRef] 28. Liu, G.; Xiao, J.; Liu, J.; Qu, X.; Liu, Q.; Zeng, H.; Yang, X.; Xie, L.; Zhong, H.; Liu, Q.; et al. In situ probing the self-assembly of 3-hexyl-4-amino-1,2,4-triazole-5-thione on chalcopyrite surfaces. Coll. Surf. A Physicochem. Eng. Asp. 2016, 511, 285–293. [CrossRef] 29. Liu, S.; Liu, G.; Zhong, H.; Yang, X. The role of HABTC’s hydroxamate and dithiocarbamate groups in chalcopyrite flotation. J. Ind. Eng. Chem. 2017, 52, 359–368. [CrossRef] Minerals 2021, 11, 410 12 of 12
30. Liu, G.; Huang, Y.; Qu, X.; Xiao, J.; Yang, X.; Xu, Z. Understanding the hydrophobic mechanism of 3-hexyl-4-amino-1, 2,4-triazole- 5-thione to malachite by ToF-SIMS, XPS, FTIR, contact angle, zeta potential and micro-flotation. Coll. Surf. A Physicochem. Eng. Asp. 2016, 503, 34–42. [CrossRef] 31. Jia, Y.; Huang, X.; Huang, K.; Wang, S.; Cao, Z.; Zhong, H. Synthesis, flotation performance and adsorption mechanism of 3-(ethylamino)-N-phenyl-3-thioxopropanamide onto galena/sphalerite surfaces. J. Ind. Eng. Chem. 2019, 77, 416–425. [CrossRef] 32. Wang, X.; Qin, W.; Jiao, F.; Liu, R.; Wang, D. Inhibition of galena flotation by humic acid: Identification of the adsorption site for humic acid on moderately oxidized galena surface. Miner. Eng. 2019, 137, 102–107. [CrossRef] 33. Zhang, W.; Feng, Z.; Mulenga, H.; Sun, W.; Cao, J.; Gao, Z. Synthesis of a novel collector based on selective nitrogen coordination for improved separation of galena and sphalerite against pyrite. Chem. Eng. Sci. 2020, 226.[CrossRef]