lead concentrate

International Journal of Mining Science and Technology 23 (2013) 179–186

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International Journal of Mining Science and Technology journal homepage: www.elsevier.com/locate/ijmst

Utilization of polysaccharides as depressants for the flotation separation of copper/lead concentrate Qin Wenqing a,b,⇑, Wei Qian a, Jiao Fen a, Yang Congren a, Liu Ruizeng a, Wang Peipei a, Ke Lifang a a b

State Key Laboratory of Comprehensive Utilization of Low-Grade Ores, Shanghang 364200, China School of Mineral Processing and Bio-Engineering, Central South University, Changsha 410083, China

a r t i c l e

i n f o

Article history: Received 9 August 2012 Received in revised form 17 September 2012 Accepted 3 October 2012 Available online 13 May 2013 Keywords: Polysaccharides Chalcopyrite Galena Depressant Depressing mechanism

a b s t r a c t The interaction mechanism between dextrin and minerals has been investigated through micro-flotation, adsorption density measurements, Fourier transform infrared ray (FTIR) spectroscopic studies and dissolution tests. Dextrin shows a good depressing action towards galena but not chalcopyrite. FTIR spectroscopic studies indicate that dextrin chemically adsorbed on galena surface in alkaline pH range. Dissolution tests confirm leaching action of metal ions from chalcopyrite and galena surfaces, and dextrin-lead ion interaction. Adsorption measurements present that the higher adsorption density of O-isopropyl-N-ethyl thionocarbamate (IPETC) onto chalcopyrite than that onto galena, and IPETC adsorbed on galena decrease with increasing dextrin concentrations in the presence of dextrin, attesting the flotation results. Ó 2013 Published by Elsevier B.V. on behalf of China University of Mining & Technology.

1. Introduction In the flotation of complex sulfide ores, the two methods most widely used for the separation of economic amounts of copper and lead are presents as the following: (1) bulk copper/lead flotation followed by copper/lead separation; (2) sequential copper/lead flotation [1]. The sequential separation has some disadvantages, for example, large reagent dosage, complex flowsheet, etc. Therefore, mainly due to the extremely similar floatability of chalcopyrite and galena, the separation of bulk copper/lead concentrate is common used in commercial process and forms the backbone of this investigation. Inorganic depressants, duo to their irreplaceable properties, low price and excellent chemical properties, have been extensively used in the field of sulfides flotation separation. The list of depressants used to facilitate separation include sulfur-oxy depressants, added in the forms of sulfite, bisulphate, metabisulfite or sulfur dioxide sodium dichromate, cyanide, etc [2]. In order to obtain satisfactory separation results, cyanides are widely used in the selective flotation of copper/lead/zinc and copper/zinc ores as depressant for sphalerite, pyrite, and certain copper sulfides, and sodium dichromate (Na2Cr2O7) is used to depress galena in copper/lead separation [3]. Dichromate and cyanide are the commonly used depressants in copper/lead separation, but they are known to

⇑ Corresponding author. Tel.: +86 731 88830346. E-mail address: [email protected] (W. Qin).

be toxic and the use of them often is associated with environmental problems and large losses of precious metals from mineral concentrates. Consequently, attempts are being made to develop alternative selective depressants. Polymers have the advantages of being nontoxic, biodegradable and relatively inexpensive than the more widely used inorganic depressants, and interest in their use has been growing. They and their derivatives, both in the laboratory and in the commercial processes, have been used many years as depressants to depress talc, other magnesia-bearing and sulfide minerals [4]. And duo to their large molecular size, the polysaccharide family also was applied as flocculants. Extensive investigations have been carried out by Liu et al. on the adsorption of polysaccharide (CMC, CMS and dextrin) onto talc [5]. Bicak et al. reported the depressing action on pyrite by using guar gum and CMC, and the interaction mechanism was investigated through measurements of zeta potentials, adsorption density and micro-flotation [6]. Rath et al. showed that sphalerite can be separated from its synthetic mixture with using dextrin at pH 12.1 by using xanthate as collector [7]. Lopez et al. proposed dextrin can effectively depressed pyrite with xanthate as collector, it is proposed that dextrin depresses pyrite by enveloping the dixanthogen resulting from adsorption of xanthate ions [8]. Boulton et al. found that separation of copper-activated sphalerite from pyrite was achieved by using low molecular weight polyacrylamide polymer as depressant and isobutyl xanthate as collector [9]. The depression of pyrite in sulfide flotation with types of polysaccharides, namely CMC and guar and the depressing mechanism was investigated and presented by Bicak et al. [6].

2095-2686/$ - see front matter Ó 2013 Published by Elsevier B.V. on behalf of China University of Mining & Technology. http://dx.doi.org/10.1016/j.ijmst.2013.04.022

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Reports on the use of polysaccharides as depressants for the differential separation of chalcopyrite and galena are scarce. Liu et al. have investigated the interaction mechanisms between dextrin and chalcopyrite and galena surfaces, and found that metal hydroxide appeared on mineral surface lead to the adsorption of dextrin onto sulfide minerals surfaces at different pH ranges [10]. Bhaskar et al. noted that the industrial application of starch in differential flotation of sulfide minerals especially in the separation of galena from chalcopyrite [11]. The flotation of chalcopyrite from galena using dextrin was studied by Liu et al. [12]. New depressant based on dichromate complexed with carboxymethyl cellulose (CMC) and sodium phosphate (Na2HPO4) for copper/lead separation was investigated by Bulatovic et al. [13]. Recent years, the application of polysaccharides has gained importance and they are worth investigating as alternative selective depressants. Although they have been reported as selective depressants in the field of differential flotation of sulfide minerals, a general lack of understanding of the interaction mechanism between the polysaccharides and sulfide minerals surfaces hampers their widely application in this area. Polysaccharide family was found to interact with mineral surfaces in several different ways: chemical interaction, hydrophobic interaction, electrostatic attraction, etc [11,14]. And studies on adsorption of polysaccharides which render metal surface hydrophilic highlighted the importance of metallic sites for enhanced adsorption [15,16]. Researchers conducted detail work both on metal salts and on mineral samples, they observed no interaction between dextrin and metal cations. It is also reported that dextrin was proposed to coprecipite with metal hydroxides but not with metal cations in aqueous solutions [17]. Liu et al. have revealed that dextrin adsorbs on the sulfides surface through interactions with the surface by bonding with metal hydroxide species, possible though an acid/base interaction [10]. However, the concrete reason why dextrin forms chemical complexes with metal hydroxides but not with metal cations is not clear. It is also noted that when mineral surface and dextrin are oppositely charged, the adsorption of dextrin onto minerals was drove by electrostatic interaction [11]. Dextrin was proposed to adsorb on those hydrophobic minerals like talc and molybdenite maybe duo to polymer/mineral structure matching, in other words, to interact with mineral through hydrophobic– hydrophobic interaction based on the free energy of adsorption, this physical interaction mechanism (hydrophobic bonding) was also proposed by Wei et al. through measurements of zeta potentials, adsorption density, contact angles and micro-flotation [18,19]. In this investigation, three natural polysaccharide derivatives and one inorganic depressant, namely, dextrin, soluble starch, carboxymethyl cellulose (CMC) and sodium silicate (Na2SiO3), having been compared with respect to flotation behaviors onto chalcopyrite and galena. Dextrin and soluble starch were chosen for the further investigation such as adsorption measurement, infrared spectroscopic analysis and dissolution tests, and finally possible mechanisms of adsorption were proposed.

2. Methodology

cover the desired size fraction. All the different size fractions were collected and stored separately in sealed glass bottles to prevent further surface oxidation. The 38 lm size fraction was further pulverized using carnelian mortar and pestle to 2 lm, which was prepared for infrared spectroscopic analysis, whereas (+74 to 38 lm) fraction was used for micro-flotation, adsorption measurements and dissolution tests. The chemical analysis of chalcopyrite revealed a composition (mass percent) of 38.30% Cu, 23.24% Fe, 31.99% S and 0.81% Pb, while the galena sample contained 84.61% Pb, 1.96% Fe and 10.12% S. And the average BET specific surface area for the ground chalcopyrite and galena samples was 0.26 and 0.13 m2/g. The collectors used were butyl xanthate (BX) and O-isopropylN-ethyl thionocarbamate (IPETC), which were all industrial grade reagents supplied by Zhuzhou Flotation Reagents factory in Hunan province. Sodium sulfide (Na2S), dextrin, soluble starch, carboxymethyl cellulose (CMC) and sodium silicate (Na2SiO3) were of analytical grade. The frother No. 2 oil was of an industrial grade. Preparation of dextrin solution has been done by adding it to warm water (70 °C) on a water bath and stirred for a few minutes; while the soluble starch solution was obtained by mixing it with sodium hydroxide at the ratio of 4:1 and then putting them on a water bath of around 70 °C and stirred for a few minutes. Fresh dextrin and soluble starch solution were prepared each day to minimize the effect of microbiological degradation, as there is evidence that the polymer solution degrades over time [20]. The dilute solutions of sodium hydroxide and sulfuric acid were used to adjust pH, potassium nitrate was used to maintain the ionic strength. And solutions of all the reagents were prepared using distilled water. 2.2. Micro-flotation tests As shown in Fig. 1, the single mineral flotation tests were carried out in micro-flotation cell with an effective volume of roughly 40 mL. A 2.0 g sample (+74 to 38 lm size fraction) was used in each experiment and was cleaned by ultrasonic treatment prior to the tests. The micro-flotation tests involved the following procedures: (1) after agitation for 1 min, the pH of the pulp was first adjusted to a desired value by adding concentrated sodium hydroxide or sulfuric acid, then the sample was treated with BX while conditioning for 2 min; (2) in the reagent removal step, the excess collector and frother absorbed onto sample were removed by adding Na2S for 4 min, then the solution was sunk for another 10 min to obtain the sedimentary product for further depressing

2.0 g sample Agitating 1 min Adjusting pH 2 min BX 1 min Frother 1 min Na2S 1 min Depressant 1 min

Flotation 2 min

IPETC 1 min

2.1. Materials and reagents X-ray powder diffraction data confirmed that the samples of chalcopyrite and galena were of high purity. The chemical analysis of the chalcopyrite revealed a composition (mass percent) of 38.30% Cu, 23.24% Fe, 31.99% S, and 0.81% Pb, while the galena sample contained 84.61% Pb, 1.96% Fe, and 10.12% S. The samples were first hand-picked and then prepared by grinding (a porcelain ball mill) and sieving through 74 and 38 lm series sieves to re-

Tailings 1

Frother 1 min Flotation 2 min Tailings 2

Concentrate

Tailings 3

Fig. 1. Flowsheet of bulk copper/lead flotation-reagent removal-separating flotation.

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2.3. FTIR studies The infrared spectra of chalcopyrite, galena, BX and the products of interaction between mineral and BX were obtained using NEXUS-470 spectrometer, and the infrared spectra of chalcopyrite, galena, dextrin, soluble starch and the products of interaction between mineral and the polymers were also obtained. Samples were ground to be less than 2 lm and prepared in the same way used in micro-flotation tests, a 1.0 g sample was settled in 20 mL BX solution at pH 7 and agitated for 30 min, filtrated and flushed 2–3 times using the corresponding pH buffer solution. Treated sample was dried in vacuum desiccator and prepared for analysis. 2.4. Adsorption tests The adsorption of BX onto chalcopyrite and galena in the absence and presence of Na2S at different concentrations at pH 8.5 were determined by measuring the adsorption density at its characteristic UV adsorption wavelength of 301 nm. For the depressant adsorption tests, the adsorption of IPETC onto chalcopyrite and galena in the absence and presence of dextrin or soluble were investigated by measuring the adsorption density at a wavelength of 241 nm. All the tests were carried out by using ultra-violet (UV1810) spectroscopy. The experiments were carried out by taking 1.0 g mineral simple into 50 mL solution, adjusting pH value and adding corresponding reagents. The conditioning time between reagent and minerals here was identical with the third stage of micro-flotation tests aforementioned. After conditioning, the pulp was centrifuged and the solutions were withdrawn from the supernatant for analysis of residual BX or IPETC concentrations. So the amount of reagents adsorbed onto minerals was calculated from the difference between initial and residual reagent concentration of the solution.

tation recovery of galena decreases rapidly in the pH value from 8.5 to 12, complementing the findings investigated by researchers [21,22]. It is well known that sulfides interacts readily with xanthate species, forming a hydrophobic surface layer, thiol collectors like xanthate are powerful collectors in sulfide mineral flotation but they suffer from practical disadvantages due to their instability and lake of selectivity [2,23]. As shown in Fig. 2, galena shows good floatability in acidic and neutral range, therefore, pH 8.5 was chosen for next regent removal and depressing tests.

3.1.2. Infrared spectra analysis between minerals and BX Many investigations have noted the adsorption of BX on chalcopyrite and galena surfaces [24–26]. As shown in Fig. 3, with regard to the adsorption products on chalcopyrite surface, there are two viewpoints: only dixanthogen is observed on chalcopyrite surface, on the other hand, both dixanthogen and xanthate exist by chemiadsorption on the surface. For galena, it is generally proposed that the adsorption product is lead xanthate. The Fourier transform infrared ray (FTIR) reflection spectra of chalcopyrite, galena and the two minerals interacted with BX at pH 7 are presented in Fig. 4. In this study, the infrared spectral tests are carried out to identify whether the chemical adsorption of BX is occurred onto chalcopyrite and galena. From Fig. 4a, after comparison with the FTIR reflection spectrum of chalcopyrite without any disposal, the sample of treated chalcopyrite shows the characteristic peaks (1029, 1093, and 1186 cm1 of reagent appear, which are precisely the characteristic peaks of xanthate copper complexes, providing that the chemical adsorption occurs after treated with BX [22,27]. Fig. 4b shows the infrared spectra of galena treated with or treated without BX. It is demonstrated that the infrared spectrum of galena presents new formed peaks at 970.1, 1119, and 1191.8 cm1, which are proposed in literatures as the characteristic peaks of xan-

Recovery (%)

process; (3) in the next stage, pH regulator was added to obtain the desired pH value and the conditioning procedure was performed in the following order: depressant, collector and frother, and the conditioning time was 2, 4, and 1 min, respectively, the flotation time was set to 2 min. The products and tailing were weighted separately after filtration and drying, and then analyzed for copper and lead.

2.5. Dissolution tests

3. Results and discussion 3.1. Bulk copper/lead flotation 3.1.1. Flotation of chalcopyrite and galena with BX as collector Fig. 2 shows that chalcopyrite and galena are readily floatable with BX as collector within the whole pH range, however, the flo-

Chalcopyrite

Galena

0

2

4

6 pH

8

10

12

Fig. 2. Effects of pH value on the mineral flotation using BX as collector: C(BX) = 10  105 mol/L, C(No. 2 Oil) = 10 mg/L.

110 100

Transmittrance (%)

The concentration of copper and lead leaching from chalcopyrite and galena was measured using inductively coupled plasma atomic emission spectrometry (ICP-AES). The dissolution tests were carried out as a function of time, both in the absence and presence of the polymers (dextrin or soluble starch). A 1.0 g mineral was used in each test and was cleaned by ultrasonic treatment to avoid oxidation, and then was transferred into 40 mL aqueous solutions. After agitating for various time intervals at a given pH value, the solution phase was separated from slurry by centrifugation at 4500 r/min for 15 min using a high speed refrigerates centrifuge. And then the suspensions were filtered, acidified and analyzed for ion concentration.

100 90 80 70 60 50 40 30 20 10

1

90 3751

2068

80 2874.4

70

822.4

1376 1606.2 1462.3 964.9

60

618.9

2961.2

50

1183.2

40 3401.9

30

1113

1060.2

4000 3500 3000 2500 2000 1500 1000 500 Wavenumber (cm-1) Fig. 3. FTIR spectra of BX.

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1000

1645.4

900

900 800 700

Chalcopyrite

800

1093 1029

Reflectance

1186

Reflectance

Galena interacted with BX

1000

Chalcopyrite interacted with BX

1870 1540 1160 696

600

2874.2 2960.3

1498 1191.8 1119 970.1

Galena

700 1430

600 500

1150

400

500

4000 3500 3000 2500 2000 1500 1000 -1 Wavenumber (cm )

500

(a) Chalcopyrite and chalcopyrite interacted with BX

300 3000

2500

2000 1500 1000 Wavenumber (cm-1 )

500

(b) Galena and galena interacted with BX

100 90 80 70 60 50 40 30 20 10 0

40

Chalcopyrite

Galena

40

80

120

160

200

Adsorption density of BX (10-7 mol/m2)

Recovery (%)

Fig. 4. FTIR spectra of chalcopyrite, galena and the two minerals interacted with BX.

35

25 20 15 10

Galena

5 0

240

CNa 2S (mg/L)

Chalcopyrite

30

0

40

80

120 160 CNa 2S (mg/L)

200

240

Fig. 5. Flotation recovery of chalcopyrite and galena after removing BX on their surfaces: C(BX) = 104 mol/L, C(No. 2 Oil) = 10 mg/L, pH = 8.5.

Fig. 6. Effect of Na2S on the adsorption density of BX on chalcopyrite and galena surfaces: C(BX) = 104 mol/L, pH = 8.5.

thate lead complexes, thus chemical interaction between galena and BX is occurred [22,27]. And peaks at 2960.3, 2874.2, 1645.4, and 1498 cm1 present the characteristic peaks of methylene, the characteristic peaks of dixanthogen were not found in this analysis. In this study, after treaded with BX, copper xanthate and lead xanthate was observed on chalcopyrite and galena surfaces, respectively, which is marginally different from that mentioned in literatures.

tion of Na2S and BX chemically adsorbed at chalcopyrite and galena surfaces were mutually exclusive, which is correlated well with the results of flotation test. And the mechanism of reagent removal by using Na2S may be explained as following two ways:

3.2. Reagent removal process 3.2.1. Flotation of chalcopyrite and galena as a function of Na2S concentration From Fig. 5, it is apparent that the flotation recovery of both chalcopyrite and galena declined sharply using BX as collector in the presence of Na2S, but the decreasing action of galena recovery is much more obvious than that of chalcopyrite. For these findings, the concentration of 250 mg/L Na2S is the preferred candidate for further trials. 3.2.2. Adsorption density of BX on two mineral samples in the presence of Na2S The effect of Na2S on the adsorption density of BX onto chalcopyrite and galena was investigated with varying Na2S concentrations at pH 8.5, the adsorption density of BX onto the two minerals in the absence and presence of Na2S are measured and demonstrated in Fig. 6. Compared with the conditions without Na2S, the adsorption density of BX on chalcopyrite surface decreased dramatically with increasing BX concentrations, from around 3.76  104 to 9.23  105 mol/m2. With regard to galena, that figure dropped from 3.75  104 to 4.85  105 mol/m2. It is observed that addi-

(1) As shown in Fig. 7, HS is the main hydrolyzed component of Na2S within the pH range from 8.5 to 10, these species would compete with butyl xanthate ion (BX) and inhibit the further xanthate adsorption onto chalcopyrite and galena. This is compatible well with the results of micro-flotation and adsorption measurements, and is also reported in other literatures [28–30]. The competitive adsorption onto minerals surfaces between HS and BX also can be explained by Langmuir mixed adsorption formula [31]:

Ci Ci ¼K Cj Cj

ð1Þ

where Ci =Cj is the ratio of adsorption density of the two solute; C i =C j the ratio of concentration of the two solute; and K the constant concerning adsorption heat. As shown in Eq. (1), the competitive adsorption relationship can be described as following: the addition of HS can lead the declining adsorption density of BX onto minerals surfaces, and the adsorption density of BX decreasing proportionally with increasing HS concentration added in pulp, which well corresponds with the results of adsorption measurements.

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100

H2S

HS

Recovery ( )

80 60 40

S2-

20

0

2

4

6

8

10

12

14

2þ

PbS ¼ Pb

þ 2BX

þ S2

HS ¼ S2 þ Hþ

½Hþ ½BX 2 ½HS 

ð2Þ

K 2 ¼ ½Pb ½BX 2 ¼ 1018:0

ð3Þ

K1 ¼

2þ

2þ

K 3 ¼ ½Pb ½S2  ¼ 1027:5

K 1 ¼ ðK 2  K 4 Þ=K 3 ¼

ð4Þ

½S2 ½Hþ  ¼ 7:1  1015 ½HS 

ð5Þ

½Hþ ½BX 2 ¼ 7:1  105:5 ½HS 

ð6Þ

K4 ¼

30 20 10 2

4

6

8

10

12

Fig. 8. Effects of pH value on the mineral flotation using IEPTC as collector: C(IEPTC) = 104 mol/L, C(No. 2 Oil) = 10 mg/L.

(2) HS can desorb copper butyl xanthate (Cu(BX)2) and lead butyl xanthate (Pb(BX)2) on mineral surfaces, the interaction between HS and Pb(BX)2 can be cited as example, and the reactions are as the following [32]:

2þ

Galena

50 40

pH

Fig. 7. Distribution diagram of Na2S solution as a function of pH.

PbðBXÞ2 ¼ Pb

70 60

0

pH

PbðBXÞ2 þ HS ¼ PbS þ Hþ þ 2BX

Chalcopyrite

100 90 80

-

where K is the ionization equilibrium constant. The micro-flotation was carried out at the pH value of 8.5, so the concentration of H+ is 108.5 mol/L, the concentration of BX is 104 mol/L. From Eq. (5), the minimum concentration of Na2S needed to interact with Pb(BX)2 is 0.14  1011 mol/L. In the case of the interaction between HS and Cu(BX)2, the needed concentration of Na2S can be calculated in the same way and the result is 0.04  1011 mol/L. As can be seen from adsorption tests, when the concentration of Na2S is 250 mg/L or 1.04  103 mol/L through conversion, the adsorption density of BX on the two minerals surfaces almost is nearly around zero, therefore, it can be indirectly concluded that the desorption reaction between HS and Cu(BX)2 and Pb(BX)2 was occurred. 3.3. Copper-lead separating flotation 3.3.1. Flotation of chalcopyrite and galena using IPETC as collector In the case of IEPTC, as presented in Fig. 8, chalcopyrite can be well floated, while the flotation recovery of galena was around 65% and did not drop through the whole pH region. The specificity of IEPTC towards chalcopyrite has been investigated by researches. Gao et al. observed that chemical adsorption was occurred at chalcopyrite surface after treated with IEPTC by adsorption/desorption tests, zeta potential measurements and infrared spectra analysis, and there exists new formed peaks of C@S and –NH presented in the FTIR spectra of treated chalcopyrite, a chemical compound made up of a ring of sulfur atom and nitrogen atom or sulfur atom oxygen atom was formed [33]. It is also reported that the strong electron-donating power of IEPTC renders it to react strongly with cations on the surface of copper and iron sulfide minerals through the formation of normal covalent bonds [34].

3.3.2. Effects of different depressants on the selective separation of copper-lead concentrate In this study, Na2SiO3, dextrin, soluble starch, CMC were selected as depressants for the selective separation of copper/lead concentrate. As shown in Fig. 9, it is clear that all these four depressants could depress galena while the floatability of chalcopyrite was slightly influenced within the depressant concentration range from 200 to 1200 mg/L, however, the effective of depressing action varies among different depressants. For comparison, addition of all depressants led to a significant decrease in galena flotation recovery, the effective order being: soluble starch > dextrin > CMC > Na2SiO3. And above results offer the conclusion that both dextrin and soluble starch are suitable for the separating flotation, based on their extremely similar structure, and for the sake of analysis, dextrin was chosen for the following mechanism analysis.

3.3.3. Infrared spectra analysis between minerals and dextrin In order to clarify whether or not, the chemical interactions have occurred between the polymers and the two minerals, the infrared spectra analysis were carried out, and the results are depicted in Figs. 10 and 11. Fig. 11a makes it apparent that the spectrums of chalcopyrite sample are identical before and after treated with dextrin, maybe the polymer adsorbed on chalcopyrite surface through hydrogen bonding. As seen in Fig. 11b, the bands at 3380 and 2924 cm1 of free dextrin due to O–H stretching vibration and C–H stretching of the –CH2 group, respectively, and appears at 3384 and 2924 cm1, in the case of dextrin-adsorbed galena sample. The bands at 1650 cm1 for free dextrin due to ring stretching of glucopyranose, appear at slightly lower wave numbers, namely 1501 cm1. The corresponding weak bands within the range of 1350 cm1 duo to the symmetrical deformations of CH2 group and numerous C–OH deformation appears at almost the same wavenumber after dextrin adsorption, although with reduced intensity. The bans from 1078 to 1155 cm1 mainly because of C–OH twisting vibrations and alcoholic –CH2OH stretching mode, respectively, for dextrin appear marginally altered after adsorption at 1087 and 1150 cm1. Meng et al. proposed that the polar group of the polymers are hydroxyl group and carboxyl group in alkaline solution, the hydroxyl group interacts with HPbO2 in solution and the carboxyl group, oxygen atom in glucopyranose ring interact with Pb(OH)2 through hydrogen bonding, thus inducing positive or negative migration of these bands [35]. It is reported that the bands at 930 and 760 cm1 of free dextrin primarily due to ring stretching and ring deformation modes of the a-D-(1-4) and a-D-(1-6) linkages, while the bands are at 980 and 767 cm1 of free dextrin in this study [16]. And it is noteworthy that the band at 980 cm1 of free dextrin was strongly reduced,

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100 90

60 50

Recovery

80 70

Recovery

100 90 80

Chalcopyrite

Galena

40 30 20 10 0

200

400

600

800

70 60 50 40 30 20 10 0

1000 1200

Chalcopyrite

Galena

200

100 90 80 70

Chalcopyrite

Recovery

Recovery

70 60 50 40

Galena

10 0

200

400

600

800

800

1000

1200

(b) Dextrin: pH=11.2

100

30 20

600

Cdextrin (mg/L)

CNa 2SiO3 (mg/L) (a) Na2SiO3: pH=8.5

90 80

400

1000

1200

60 50 40

Galena

30 20 10 0

Csoluble starch (mg/L) (c) Soluble starch: pH=9

Chalcopyrite

200

400

600

800

1000

1200

CCMC (mg/L) (d) CMC: pH=8.5

Fig. 9. Flotation of chalcopyrite and galena in the presence of these four depressants as a function of depressant concentrations concentration: C(BX) = 104 mol/L, C(No.2 = 10 mg/L; C Na2 S = 250 mg/L, C(No. 2 Oil) = 5 mg/L; C(IEPTC) = 104 mol/L, C(No. 2 Oil) = 5 mg/L.

Oil)

2930.4 3411.1

1657.8 764.3 1458.7 576.4 1370.7 1160.5 1090.1 999.7

30 20 10 0 4000 3500 3000 2500 2000 1500 1000 -1 Wavenumber (cm )

500

Fig. 10. FTIR spectra of dextrin.

100 90 80 70 60 50

Chalcopyrite 1870 1540 1160

Chalcopyrite interacted with dextrin

700

1465.4 1027.2 608.4

40 30 20 10 0 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber (cm-1) (a) Chalcopyrite and chalcopyrite interacted with dextrin

Reflectance

60 50 40

and the band at 767 cm1 is almost absent after adsorption on galena, while the bands of 930 and 760 cm1 largely reduced after interaction with galena. It is reported by Rath et al. that the intensities of the bands at 928 cm1 are largely reduced, and they reasonably concluded that the reason why the characteristic peaks of dextrin disappeared was due to complexes formation between calcium hydroxide and dextrin [15]. A planar five membered ring complex, formed by hydroxyl group on C-2 and C-3 carbon atoms in a glucose unit and lead hydroxide, exerts strain on glucose ring and causes the glucose deformation, that was the reason of the elimination of infrared adsorption bands at around 930 cm1, reported by Laskowski et al. [36]. In the IR spectra of lead hydroxide treated with dextrin, the peak at 930 cm1 was reduced in intensity, and the peak at

2155.3

Reflectance

Reflectance

100 90 80 3738.9 70

110 Galena 100 1430 90 1150 80 Galena interacted 70 with dextrin 60 2936.2 1031.6 1412.7 1151.0 50 3404.4 40 30 20 10 0 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber (cm- 1) (b) Galena and galena interacted with dextrin

Fig. 11. FTIR spectra of chalcopyrite, galena and the two minerals interacted with dextrin.

185

767 cm1 was disappeared, on the other hand, in the case of soluble starch, the bands at 930 and 760 cm1 were both absence. These results demonstrated the dextrin or soluble starch interacts with galena through chemiadsorption, maybe by hydrogen bonding as well. 3.3.4. Effect of dextrin on IPETC adsorbed on minerals surfaces The effect of dextrin on the adsorption of IPETC onto minerals was clarified by investigating the adsorption density of IPETC onto the two minerals at pH 11.2. Various amounts of dextrin were added to the solutions and the results are depicted in Fig. 12. From Fig. 12, compared to those in absence of dextrin, the adsorption density of IPETC onto chalcopyrite decreased slightly by 7.03% from 3.644 to 3.39  106 mol/m2 over the dextrin concentration range investigated over the pH range from 10.5 to 11.5. Meanwhile a significant drop in the adsorption density of IPETC onto galena occurred, dropping from 1.92 to 1.19  106 mol/m2, a decrease of 37.90%. From what is discussed above, it makes clear that dextrin can apparently hinder IPETC adsorbed onto galena in alkaline pH range, but marginally on chalcopyrite surface, so a stronger depressing action on the galena flotation is observed compared to chalcopyrite.

Adsorption density of IPETC -7 2 (10 mol/m )

3.3.5. Dissolution analysis tests In order to ascertain the dissolution of metal ions from minerals surfaces, dissolution studies were performed in the absence and presence of dextrin as a function of stirring time and the results are shown in Fig. 13. It is obvious from Fig. 13 that both chalcopyrite and galena exhibit considerable dissolution within the pH range from 5 to 6. And it is apparent that a much higher amount of lead ions are dissolved compared to copper and this could be attributed to higher oxidation of galena compared to chalcopyrite. In the presence of 900 mg/L dextrin, there is marginal decrease in the copper content for chalcopyrite compared to that in the absence of dextrin. However, the introduction of dextrin causes a significant decrease in lead ion in solution and prevents the continuing dissolution of galena. It is quite plausible that the lead ion leached from galena could chemically interact with dextrin. Maybe the interaction between metal ions and the polymers in bulk solution can be responded to the metal ions-ploymer at solidsolution interface. Investigators have clarified the ion hydroxy species-polymer interaction by interacting metal ions with the polymer, namely co-precipitation study [6,7]. The co-precipitation tests testify can be approximately described as follows: there is hardly any change of in the residual concentration of metal ions in the presence of dextrin, however, there is a dramatic decrease in the concentration of dextrin in the presence of metal ions, with minimum residual dextrin concentration at a certain pH range that is well correlated with the formated pH values of ion-hydroxy spe-

40

Chalcopyrite 35 30 25

pH=10.5-11.5

20

Galena

15 10

0

200

400

600

800

1000

1200

Cdextrin (mg/L) Fig. 12. Effect of dextrin on the adsorption of IPETC onto chalcopyrite and galena.

Dissolved copper ions or lead ions (mg/L)

W. Qin et al. / International Journal of Mining Science and Technology 23 (2013) 179–186

5

Galena

4 3

Chalcopyrite/dextrin (900 mg/L) Chalcopyrite

2

4 1

0

Galena /dextrin (900 mg/L)

20

40

60

80

100

120

Time (min) Fig. 13. Dissolution of metal ions from minerals surfaces as a function of stirring time, determined in oxygen in the pH range from 5 to 6 in the absence and presence of dextrin.

cies, attesting their interaction in the bulk solution. These findings are in good agreement with the results of the dissolution tests, giving expression to the interaction between metal ions and the polymers. Based on what have been discussed above, the possible mechanisms for the ploymers depressing galena but not chalcopyrite was proposed and could be described as follows: (1) Lead ions respectively leached from chalcopyrite and galena could form chemical complexes with dextrin as a function of pH. Within pH range from 9 to 11, the complexes could interact with dextrin in bulk solution or at the hydrolated galena surface mainly through chemical adsorption, and maybe by hydrogen boding as well, thus preventing IPETC from adsorbing onto galena and having depressing action towards galena. (2) At that pH range, because the polymers adsorb onto chalcopyrite only through hydrogen bonding, and the existence of IPETC and the polymers are not mutually exclusive, the flotation recovery of chalcopyrite is not influenced. 4. Conclusions (1) BX is able to float chalcopyrite and galena very well, the flotation recovery of the two minerals are around 90%, and infrared spectra analysis shows that chemical adsorption was occurred between BX and the two minerals. (2) In the process of reagent removal, the flotation recovery of chalcopyrite and galena were significantly decreased with increasing Na2S concentrations. From the results of solution chemistry studies and adsorption measurements, it is obvious that the presence of Na2S has an obvious effect on decreasing adsorption density of BX on the two mineral surfaces, indicating HS competed with BX and maybe desorbed copper butyl xanthate and lead butyl xanthate absorbed on mineral surfaces. (3) Both dextrin and soluble starch can strongly depress galena, where the flotation recovery of galena was around 20%, and that of chalcopyrite was about 90%. Infrared spectra analysis presents that the chemical interaction between the hydroxyl groups of the dextrin and hydroxylated lead. Adsorption measurements indicate that a higher amount of IPETC is adsorbed onto chalcopyrite than onto galena in the presence of dextrin. Dissolution tests demonstrate that the amount of lead ion leached from galena is decreasing with certain dextrin concentration with increasing stirring time, however, the copper ions leached from chalcopyrite remains almost constant with or without the addition of dextrin.

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