research article activation of sphalerite by ammoniacal...

Research ArticleActivation of Sphalerite by Ammoniacal CopperSolution in Froth Flotation

Xian Xie,1,2 Kai Hou,3 Bo Yang,1,2 and Xiong Tong1,2

1Faculty of Land and Resource Engineering, Kunming University of Science and Technology, Kunming, Yunnan 650093, China2State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Kunming 650093, China3School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China

Correspondence should be addressed to Xiong Tong; [email protected]

Received 13 October 2015; Accepted 15 February 2016

Academic Editor: Davide Vione

Copyright © 2016 Xian Xie et al.This is an open access article distributed under the Creative Commons Attribution License, whichpermits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The activation of sphalerite particles by ammoniacal copper solution (ACS) was investigated in this study.Thismicroflotation studywas conducted on a single sphalerite mineral with the particles size of 38𝜇m to 75 𝜇m. Results showed that ACS has somewhatbetter activation effect than copper sulphate (a traditional activator) with sodium isobutyl xanthate as the collector. Agglomerationobservation, contact anglemeasurement, andX-ray photoelectron spectroscopymeasurement results of sphalerite particles verifiedthe superiority of this new activator.Therefore, the substitution of copper sulphatewithACSwould increase the separation efficiencynot only in marmatite flotation but also in sphalerite flotation.

1. Introduction

Naturally occurring zinc minerals, such as sphalerite, areabundant inChina.According to theUnited StatesGeologicalSurvey, geologists have confirmed total reserves of 430million tons of zinc resources (the second largest in theworld) in China. China is the largest zinc producer, and5 million tons was produced in 2013. However, given theunique geological structure of China, sphalerite is commonlyassociated with metallic sulphide ores, such as chalcopyrite,galena, marmatite, pyrite, and pyrrhotite, which makes itdifficult to differentiate sphalerite efficiently [1, 2].

Usually, copper sulphate is used in zinc flotation asan appropriate activator. The activation mechanisms ofsphalerite with Cu2+ or Cu(OH)

2have been investigated

using different analysis and experimental methods, such asmicroflotation, electrochemistry, atomic force microscopy,X-ray photoelectron spectroscopy (XPS), scanning elec-tron microscopy with energy dispersive X-ray spectroscopy,and density functional theory computation [3–8]. Manyresearchers believed that chemisorption and substitutionreactions occur among Zn, S, and Cu atoms or Cu(OH)

2

molecule during activation flotation. However, the copper-ammonia complex has not been extensively investigated.

Recently, ammoniacal copper solution (ACS) wasobserved to have a better effect on the activation of marma-tite in a weak alkaline situation compared with coppersulphate, ammonium chloride, and lead nitrate [9, 10]. ACShas been commercially used in Dulong Mine of YunnanProvince in the southern part of China [11]. Because of thesimilarity between marmatite and sphalerite, we assumedthat ACS might also be appropriate for the selective flotationof sphalerite. In this study, we determined whether ACS canbe an effective activator for sphalerite.

2. Experimental

2.1. Materials. Sphalerite was obtained from Dulong Mine,Yunnan Province, China. The sample was crushed, hand-sorted, dry-ground in a mechanical agate mortar and pestle,and dry-screened to obtain sphalerite particles of 38 𝜇m to75 𝜇m. The X-ray diffraction (XRD) patterns of the sampleshowed that sphalerite was of high purity, with no impuritypeaks detected (Figure 1). The sphalerite sample assayed64.96% Zn, 33.83% S, 0.89% Fe, 0.26% Pb, and 0.03% Cu.TheXRDpattern of sample was conducted by using aD/max-2200 X-ray diffractometer (Rigaku, Japan).

Hindawi Publishing CorporationJournal of ChemistryVolume 2016, Article ID 7614890, 6 pageshttp://dx.doi.org/10.1155/2016/7614890

2 Journal of Chemistry

Sphalerite

20 30 40 50 60 70 80102𝜃 (∘)

0

1000

2000

3000

4000

5000

Inte

nsity

(cou

nts)

Figure 1: XRD pattern of the sphalerite sample.

2.2. Reagents. Copper sulphate pentahydrate (CuSO4⋅5H2O;

Kunming Chemical Reagent Co., Ltd., China), ammoniachloride (NH

4Cl; Kunming Chemical Reagent Co., Ltd.,

China), sodium isobutyl xanthate (SIBX; C5H9OS2Na; Yun-

nan Hualian Zinc & Indium Stock Co., Ltd., China), andsodium hydroxide (NaOH; Chengdu Chemical Reagents Co.,Ltd., China) were used as received. Distilled water was usedthroughout the tests. SIBX was purified by recrystallising100 g of xanthate into 1,000mL of warm acetone at 40∘C ina water bath, stirred for a few minutes, and precipitated byether following an established method. ACS was prepared inthe laboratory. A detailed description of the preparation ofACS was provided by Tong et al. [9].

2.3. Experimental Methods

2.3.1. Contact Angle Measurements. Contact angle tests wereconducted at 22∘C to 25∘C room temperature and 67% rela-tive humidity. Pure sphalerite discs were polished mechan-ically and manually burnished with fine grit sandpaper toproduce a smooth surface. Then, a microsyringe was usedto drop 5 𝜇L distilled water onto the sphalerite surface withor without reagents. Finally, contact angle measurementwas conducted with a JY-82-type contact angle analysermanufactured by Chengde Test Factory, China. The reagentconcentration and action duration were the same as the mostoptimal conditions in flotation operation. Each surface wasmeasured thrice on average.

2.3.2. XPSMeasurements. TheQuantera IImicroprobe (ScottInternet Technology Co., Ltd.) was used in the XPS measure-ments conducted at the Analysis and Test Center of KunmingUniversity of Science and Technology. Copper sulphate orACS at a concentration of 1.0 × 10−4mol/L was added to soakthe test sample for 5min. Then, SIBX was added for 1min.Finally, the sample was dried and tested.

2.3.3. Small-Scale Flotation Test. The flotation tests wereconducted in a modified Hallimond tube, as described in

0

20

40

60

80

100

Cum

ulat

ive r

ecov

ery

(%)

4 6 8 102Flotation time (min)

pH = 6.8

3 × 10−5 mol/L copper sulphate

3 × 10−5 mol/L butyl xanthate

Figure 2: Effect of flotation duration.

detail by Cao and Liu [12]. In this tube, a sintered glass fritwith a pore size of 1.6𝜇m was fitted at the base, on which astirring bar was used to agitate the flotation pulp. Gas flowsthrough the frit base to generate small bubbles that float upto a narrow throat, which connects the flotation tube to acollection bulb. The narrow throat allows only one bubble topass at a time. Thus, mechanical entrainment is minimised.In a typical test, 1.1 g of sphalerite with the particles size of38 𝜇m to 75𝜇m was firstly mixed with distilled water in a50mL beaker; then, the pH of pulp was adjusted by usinghydrochloric acid or sodium hydroxide. After that, a certainamount of either 0.1mol/L CuSO

4⋅5H2O or ACS was added

and stirred for 5min. After the addition of SIBX, the pulpwas quickly transferred to the Hallimond tube and floatedfor 10min with a N

2flow rate of 0.01 dm3/min. During the

conditioning process, the stirring speed was maintained at1,300 rad/min. Finally, the mixed pulp was transferred to theHallimond tube, with an agitation speed of 1,000 rad/min.The floated and nonfloated products were filtered, dried,and weighed. Then, the recovery of each flotation test wascalculated by using the following equation: Recovery =weightof the floated sample/weight of the nonfloated and floatedsample.

3. Results and Discussion

3.1. Effect of Flotation Duration. Figure 2 shows the effect offlotation duration on sphalerite cumulative recovery in thepresence of the activator and collector. The result shows that6min is the appropriate duration to float sphalerite becausea longer duration would lead to 100% recovery, which wouldresult in loss of comparability.

3.2. Effect of Activator Types and Their Dosages. The effect ofdifferent activator types and their dosages on the recovery ofsphalerite is shown in Figure 3. Two types of activators, thatis, copper sulphate and ACS, at different dosages were tested.The results showed that recovery increased with increasingactivator dosage and reached its peak at a dosage of 4.0 ×10−5mol/L for copper sulphate and 5.0 × 10−5mol/L for ACS.

Journal of Chemistry 3

Copper sulphateACS

pH = 6.83 × 10−5 mol/L butyl xanthate40

50

60

70

80

Reco

very

(%)

2 3 4 5 61Activator concentration (10−5 mol/L)

Figure 3: Effects of activator types and their concentration onsphalerite recovery.

With continued increase in activator dosage, the recoveriesof sphalerite with the two activators decreased. Popov andVucinic determined that, with a high Cu2+ concentration,excess Cu2+ would react with xanthate, thereby decreasingthe concentration of xanthate, which reacted with sphalerite.Thus, the recovery of sphalerite was reduced. Figure 3 showsthat, at the same activator dosage, ACS exhibits a certainadvantage on the recovery of sphalerite with 3.0 × 10−5mol/LSIBX at pH 6.8. The peak recovery is 77.1% with 4.0 ×10−5mol/L copper sulphate. By contrast, the peak recovery is80.99% with 5.0 × 10−5mol/L ACS.

3.3. Effect of SIBX Dosage. Different dosages of SIBX wereused during the flotation experiments. The optimal activa-tor dosages (4.0 × 10−5mol/L copper sulphate and 5.0 ×10−5mol/L ACS) were used to activate sphalerite. The effectof SIBX dosage on Zn recovery during flotation is shownin Figure 4. The recoveries increased with increasing SIBXdosage and reached the maximum value at the SIBX dosageof 4.0 × 10−5mol/L. At this SIBX dosage, the recovery ofsphalerite reached 87.5% when copper sulphate was used asactivator and 91.8% when ACS was used as activator at pH6.8. This finding suggests that ACS exhibited better activatoreffect than copper sulphate under the same conditions.

3.4. Effect of pH. Using the aforementioned optimised acti-vators and SIBX dosages, the effect of pH on the recoveryof sphalerite was also investigated. An “M-” type curve isshown in Figure 5. Two peaks appear at pH values of 6and 10. Under strong acidic conditions (pH < 4.0), SIBXwas decomposed rapidly, which resulted in low recovery. Bycontrast, under strong alkaline conditions (pH> 12.0), lowZnrecovery was probably caused by the excess copper hydroxidefilm, which led to hydrophilicity of the sphalerite surface [8].Under a weakly acidic condition, both activators showed highrecovery. Moreover, ACS was better than copper sulphatein activating sphalerite. Tong et al. calculated the species

pH = 6.8

4 × 10−5 mol/L copper sulphate5 × 10−5 mol/L ACS

50

60

70

80

90

100

Reco

very

(%)

2 3 4 5 61Butyl xanthate dosage (mol/L)

Figure 4: Effects of SIBX dosage on sphalerite recovery.

4 × 10−5 mol/L butyl xanthate

4 × 10−5 mol/L copper sulphate5 × 10−5 mol/L ACS

4 6 8 10 12 142pH

0

20

40

60

80

100Re

cove

ry (%

)

Figure 5: Effects of pH on sphalerite recovery (sulphuric acid andsodium hydroxide solution as pH regulator).

distribution of copper-ammonia complexes as a function ofpH at [Cu(II)]Total = 0.1mmol/L and [NH

3]Total = 0.4mmol/L

based on the equations and equilibrium constants [9]. Thisactivation might have originated from the adsorption ofthe copper-ammonia complexes, CuNH

3

2+ and Cu(NH3)2

2+,onto the surfaces of marmatite and sphalerite minerals at pH< 10. When pH was in the range of 10 to 14, Cu2+ was likelythe main activator of sphalerite.

3.5. Agglomeration Observation. Agglomerations of less than38 𝜇m sphalerite particles before and after the addition ofACS (or CuSO

4) and SIBX were observed and photographed

using the BH200microscope. Figure 6 shows sphalerite with-out reagents. Figure 7 shows the hydrophobic aggregationof sphalerite with ACS and SIBX treatment. In the flotation


50𝜇m

Figure 6: Sphalerite with no reagent treated.

50𝜇m

Figure 7: Hydrophobic aggregation photo of sphalerite (treatedwith ACS and SIBX).

50𝜇m

Figure 8: Microbubble with adhering sphalerite (treated with ACSand SIBX).

process, some microbubbles with adhering sphalerite werealso observed (see Figure 8). Without reagents, the sphaleriteparticles were in the dispersed state. However, agglomer-ates were observed after treatment with the activators ACSand SIBX. The aggregation of sphalerite was observed byMirnezami et al. [13], at a pH range of 7 to 9. However, withthe activator and collector, the agglomeration of sphaleritehas not been observed. The agglomeration of sphalerite maybenefit the flotation process. During flotation, we observedsome microbubbles with adhering sphalerite. These bubbles

Table 1: Contact angles of the sphalerite with different agentsdisposed/∘.

Treatment Experimentvalue

Added value (comparedwith the reagents untreated

surface)No 62.75 0Copper sulphate 67.72 4.97Copper sulphate +SIBX 74.28 11.53

No 70.50 0Copper sulphate 73.55 3.05Copper sulphate +SIBX 77.58 7.08

No 69.00 0ACS 76.45 7.45ACS + SIBX 81.80 12.80No 60.63 0ACS 70.38 9.75ACS + SIBX 79.17 18.54

were different from normal bubbles. The microbubbles weresmaller and more stable, and we were able to pick them outwith a glass rod and place them on a slide. The microbubblescannot easily be fractured. This finding suggests that spha-lerite particles tended to form hydrophobic agglomerates andstable microbubbles with ACS and SIBX, which can benefitthe flotation of sphalerite.

3.6. Contact Angle Measurements. Contact angle measure-ment is one of the analysis methods used to determine thehydrophobicity ofminerals. A solid–liquid–gas interfacewitha large contact angle had satisfactory water repellency andfloatability. The results of contact angle measurement areshown in Table 1. With the addition of reagents, the contactangle values increased to different degrees. Comparing thefour contact angles in Table 1, we determined that the lattertwo contact angles with larger value would allow for betterfloatability. This finding suggests that sphalerite with ACSand SIBX had a more hydrophobic surface, leading to betterfloatability.

3.7. XPS Measurements. The binding energy and relativeconcentration of elements before and after the reactions areshown in Table 2. The 2p spectra are shown in Figures 9, 10,and 11.

Table 2 shows that the relative concentration of coppersulphate is 0.2% higher than that of ACS on the sphaleritesurface; however, this finding could not explain the strongerforce between copper sulphate and sphalerite surface. Someof the copper ions may have entered the intracrystal spha-lerite, leading to bulk adsorption. Based on binding energy(Figure 9), a difference of 0.18 eV was obtained (932.49 eVfor copper sulphate + sphalerite and 932.67 eV for ACS +sphalerite), which was less than the test error. As such, we

Journal of Chemistry 5

Table 2: Binding energy and relative concentration of elementsbefore and after reactions.

Samples Atomicorbital

Bindingenergy/eV

Relativeconcentration/%

Copper sulphate +SIBX + sphalerite

Cu2p 932.49 9.3Zn2p 1021.56 18.6S2p 161.29 20.2

ACS + SIBX +sphalerite

Cu2p 932.67 9.1Zn2p 1021.64 17.0S2p 161.63 21.1

Copper sulphateACS

(Cou

nts/

s)

Cu

935 940 945 950 955 960930Energy

952.48

932.67

952.31

932.492p1/2

2p3/2

Figure 9: 2p spectra of Cu on sphalerite in the presence of differentactivator and collector butyl xanthate.

could infer that after the addition of different reagents to theactivators the same valence stage may be attained.

Table 2 and Figure 10 show that the relative Cu atom con-centration for copper sulphate activation is 1.6% higher thanthat ACS activation on the sphalerite surface. This findingsuggests that, for the Cu replacement ability substituting thesurface Zn atom of sphalerite, ACS was stronger than that ofcopper sulphate. ACS and copper sulphate also have the samevalence stage because of their similar binding energy.

Table 2 and Figure 11 show that the binding energy ofACS had a 0.34 eV positive deviation compared with thatof copper sulphate. This finding suggests that ACS hada stronger oxidation ability. As such, ACS could oxidisesurface sphalerite more effectively, thereby resulting in theproduction of more hydrophobic sulphur and leading to animprovement of the flotation process.

4. Conclusions

(1) The microflotation test conducted in this study hasshown that sphalerite flotation can be effectivelyactivated by ACS at pH 6 to 9, which is somewhatbetter than copper sulphate.

Copper sulphateACS

(Cou

nts/

s)

1020 1025 1030 1035 1040 1045 10501015Energy

Zn

1044.65

1021.64

1044.54

1021.56

2p1/2

2p3/2

Figure 10: 2p spectra of Zn on sphalerite in the presence of differentactivator and collector butyl xanthate.

Copper sulphateACS

S

158 160 162 164 166 168 170 172 174156Energy

(Cou

nts/

s) 162.90

161.63161.29

162.44

Figure 11: 2p spectra of S on sphalerite in the presence of differentactivator and collector butyl xanthate.

(2) The agglomeration with ACS and SIBX, contact anglemeasurement, and XPS measurement results verifiedthe superiority of this new activator. Therefore, thesubstitution of copper sulphate with ACS wouldincrease the separation efficiency in marmatite andsphalerite flotation.

Competing Interests

The authors declare that they have no competing interests.

Acknowledgments

The authors are grateful for the financial support from theApplied Basic Research Key Projects of Yunnan Province


(Grant no. 2014FA027) and the National Natural ScienceFoundation of China (Grant no. 51174103).

References

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[2] Y. Xu, W. Qin, and H. Liu, “Mineralogical characterizationof tin-polymetallic ore occurred in Mengzi, Yunnan Province,China,” Transactions of Nonferrous Metals Society of China, vol.3, pp. 725–730, 2012.

[3] S. R. Popov andD. R. Vucinic, “The ethylxanthate adsorption oncopper-activated sphalerite under flotation-related conditionsin alkaline media,” International Journal of Mineral Processing,vol. 30, no. 3-4, pp. 229–244, 1990.

[4] J. Liu, S. Wen, X. Chen, S. Bai, D. Liu, and Q. Cao, “DFTcomputation of Cu adsorption on the S atoms of sphalerite (11 0) surface,”Minerals Engineering, vol. 46-47, pp. 1–5, 2013.

[5] A. N. Buckley, R. Woods, and H. J. Wouterlood, “An XPS inves-tigation of the surface of natural sphalerites under flotation-related conditions,” International Journal of Mineral Processing,vol. 26, no. 1-2, pp. 29–49, 1989.

[6] A. R.Gerson, A.G. Lange, K. E. Prince, andR. St. C. Smart, “Themechanism of copper activation of sphalerite,” Applied SurfaceScience, vol. 137, no. 1–4, pp. 207–223, 1999.

[7] D. Fornasiero and J. Ralston, “Effect of surface oxide/hydroxideproducts on the collectorless flotation of copper-activatedsphalerite,” International Journal of Mineral Processing, vol. 78,no. 4, pp. 231–237, 2006.

[8] A. P. Chandra and A. R. Gerson, “A review of the fundamentalstudies of the copper activation mechanisms for selectiveflotation of the sulfideminerals, sphalerite and pyrite,”AdvancesinColloid and Interface Science, vol. 145, no. 1-2, pp. 97–110, 2009.

[9] X. Tong, S. Song, J. He, F. Rao, and A. Lopez-Valdivieso, “Acti-vation of high-iron marmatite in froth flotation by ammoniacalcopper(II) solution,” Minerals Engineering, vol. 20, no. 3, pp.259–263, 2007.

[10] X. Xie, X. Tong, Y. Cui, and D. Wu, “Study on activationperformance of several kinds of activators onmarmatite,”MetalMine, vol. 12, pp. 50–53, 2010 (Chinese).

[11] X. Tong, S. Song, J. He, and A. Lopez-Valdivieso, “Flotation ofindium-beard marmatite frommulti-metallic ore,” Rare Metals,vol. 27, no. 2, pp. 107–111, 2008.

[12] M. Cao and Q. Liu, “Reexamining the functions of zinc sulfateas a selective depressant in differential sulfide flotation-the roleof coagulation,” Journal of Colloid and Interface Science, vol. 301,no. 2, pp. 523–531, 2006.

[13] M. Mirnezami, L. Restrepo, and J. A. Finch, “Aggregation ofsphalerite: role of zinc ions,” Journal of Colloid and InterfaceScience, vol. 259, no. 1, pp. 36–42, 2003.

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