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DOI: 10.1016/j.jmrt.2018.05.015
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Depressant behavior of tragacanth gum and its role in the flotation separation of chalcopyrite from talc
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Guo Wei, Feng Bo
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315450646@qq.com

Corresponding author.
, Peng Jinxiu, Zhang Wenpu, Zhu Xianwen
Jiangxi Key Laboratory of Mining Engineering, Jiangxi University of Science and Technology, Ganzhou, China
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Table 1. The chemical composition results of chalcopyrite and talc.
Table 2. The binding energy of elements on talc surface with/without depressant.
Table 3. The separation of mixture of chalcopyrite and talc.
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Abstract

Guar gum is an effective depressant of talc, but it also has some depression effect on sulfide minerals. To find new selective depressants, the depression effects and mechanisms of tragacanth gum to talc were studied and its role in the flotation separation of chalcopyrite from talc was investigated by flotation test, adsorption and zeta potential tests as well as XPS analysis. The individual mineral flotation test results showed that the natural flotability of talc is good which make it easy to be reported into the concentrate. The guar gum and tragacanth gum can effectively depress the flotation of talc, and their depression effect is not affected by pH. The mixed minerals flotation tests indicated that the tragacanth gum can effectively separate chalcopyrite from talc, both the copper concentrate grade and recovery are high, besides, tragacanth gum exhibits less depression effects for chalcopyrite compared with guar gum. According to the Zeta potential and XPS measurements, it can be concluded that tragacanth gum adsorbed on talc surface mainly through physical interactions, and hydrophobic interaction was considered as the main driving force and hydrogen bond may also play a role.

Keywords:
Talc
Depression
Tragacanth Gum
Chalcopyrite
Full Text
1Introduction

Sulfide ores are the major sources of base metals such as copper, lead, zinc, nickel, etc. In most cases, copper–nickel sulfide ores are too dilute for directly smelting out the metal in a cost-efficient manner. The ore must be concentrated by froth flotation prior to smelting. However, the valuable sulfide minerals are typically intergrown with gangue minerals. When the gangue mineral is talc, the separation of sulfide minerals and talc by froth flotation is difficult as talc has good floatability and easily reports to flotation concentrates, thus reducing concentrate grade [1–4].

The depressants are usually added to selectively render talc hydrophilic, CMC, guar gum and sodium silicate were the commonly used depressants for talc. Shortridge et al. showed that the natural floatability of talc was diminished when guar gum was added [3]. The depression effect of guar gum increased with the increase of guar molecular weight but was not affected by changes in solution conditions such as pH and ionic strength [5]. Different from guar gum, CMC is an ineffective depressant for talc and its depression effect increased at either high ionic strength or low pH [6–9].

Separation of sulfides from talc will be easy when the depression effect of polymeric reagent only works on talc with no interference with the flotation of sulfides. However, both the guar gum and CMC are organic depressants and they will also adsorb on sulfide minerals to some extent and impair flotation performance. Mierczynska-Vasilev and Beattie [10] found that both talc and chalcopyrite are significantly depressed in the presence of CMC. Therefore, new efficient depressant in the selective flotation separation of chalcopyrite and talc is necessary. Zhao et al. [11] tested the effect of the depressant galactomannan (KGM) on the flotation of a nickel–copper sulfide ore and found that KGM had high depression selectivity for talc and little depression effect on sulfide minerals. Guo et al. [12] found that carboxymethyl chitosan had a selective depression effect on talc and the use of carboxymethyl chitosan as the depressant could achieve flotation separation of chalcopyrite from talc at pH 7. The reason that the depressants have selective depression effect on talc is that the binding mechanisms of the depressants on the talc and the sulfide minerals are different [1].

Tragacanth gum is a natural gum obtained from the dried sap of several species of Middle Eastern legumes of the genus Astragalus, including A. adscendens, A. gummifer, A. brachycalyx, and A. tragacantha. It is used in pharmaceuticals and foods as an emulsifier, thickener, stabilizer, and texturant additive. However, there are currently no studies on the application of tragacanth gum in froth flotation.

The aim of this study is to show the selective flotation of chalcopyrite from talc using tragacanth gum as depressant. Adsorption measurements, zeta potential measurements and XPS analysis were conducted to define the depression mechanism of tragacanth gum on talc.

2Materials and methods2.1Minerals and reagents

The pure talc was obtained from Haicheng, Liaoning, China and the chalcopyrite was obtained from Saishitang, Qinghai Province, China. The samples were crushed, handpicked and then dry-ground with a porcelain ball mill and dry-sieved to obtain different size fractions. XRD was performed on a DX-2700 X-ray diffractometer (Dandong fangyuan instrument co. LTD) with Cu-Kα radiation, in the range of 10–80° 2α and at a step size of 0.02°. According to XRD (Fig. 1) and elemental analysis (Table 1), the purity of chalcopyrite and talc were 96.18% and 93.44%, respectively. The surface areas of chalcopyrite and talc were analyzed using a specific surface area analyzer (Micromeritics ASAP 2020, Micromeritics Instrument co. Ltd, USA) and their specific surface area was 0.28 and 8.65m2/g, respectively.

Fig. 1.
(0.12MB).

X-ray diffraction analysis of chalcopyrite and talc.

Table 1.

The chemical composition results of chalcopyrite and talc.

Elements  Cu  Fe  MgO  SiO2 
Chalcopyrite  33.24  27.18  35.94  –  – 
Talc  –  0.56  –  30.39  63.05 

Guar gum and tragacanth gum used in the current study were obtained from Shanghai Civi Chemical Technology Co., Ltd. Methyl xanthate (PBX), and methyl isobutyl methanol (MIBC) were used as collector and frother, respectively. Deionized water was used for all tests.

The FTIR spectrum of the tragacanth gum was studied and the result is shown in Fig. 2. It can be seen that the spectrum of tragacanth gum shows peaks at 2936.66cm−1 (due to the CH stretching vibration of the CH2 groups), 1642.33cm−1 (due to the ring stretching vibration of glucopyranose that belong to galactose and mannose) and 1096.92cm−1 (due to the stretching vibration of the CO).

Fig. 2.
(0.09MB).

Infrared spectrum analysis of tragacanth gum.

2.2Flotation tests

All the Micro-flotation tests were carried out in a XFGC flotation machine with a 50mL cell, and the stirring speed was controlled at 1896rpm, at the temperature between 24°C and 26°C. For each flotation test, 2g of sample was added to the flotation cell with 50mL distilled water. The slurry was conditioned for 2min after adding NaOH or HCl stock solutions (10wt %) to adjust the pH to a desired value. The collector PBX and frother MIBC were added sequentially, with 3minutes of stirring after adding each reagent. After 3min of flotation, flotation products were collected, filtered, dried with a vacuum drying oven, and weighed. For individual mineral flotation, the flotation recovery was calculated based on the solid weight distributions between the products. In mixed minerals flotation, both the froth product and tailings were assayed for Cu content. This was done by using a Varian SpectrAA-220FS (Varian, USA) atomic absorption spectrometer.

2.3Adsorption tests

The amount of depressant adsorbed onto the talc surface was measured by using a total organic carbon analyzer Elementar vario TOC (German, Elementar Co.). 1g talc was weighted into a beaker and 100mL of distilled water were added to stir evenly, then the pH of the pulp was adjusted to a desired value, after which an appropriate amount of depressant solutions was added. After stirring the slurry, the upper layer liquid was collected and centrifuged in a high-speed centrifuge, then filtrated with a filter membrane (aperture is 0.45μm). The total organic carbon in the supernatant was measured based on the calibration curve, the amount of adsorption was determined based on the difference in depressant concentration before and after adsorption [13], samples for adsorption tests were ground to −38μm.

2.4FTIR study

For the infrared studies, 1g of the −2μm mineral sample was conditioned in flotation reagent solutions for 20min at pH 7 and 25°C with a magnetic stirrer. After conditioning, the suspensions were centrifuged. The precipitation was washed three times with distilled water and then vacuum dried at 45°C. Samples for spectroscopy measurement were prepared through diluting 1mg of the dry precipitation to 150mg potassium bromide (KBr) pellet. Fourier-transformed infrared (FTIR) spectra were measured in a KBr pellet in the 4000–400cm−1 region at 4cm−1 by using a Spectrum GX spectrometer (Nicolet is5, Thermo Nicolet Corporation, Waltham, MA, USA).

2.5Zeta potential measurements

Talc was ground to a D90 value less than 2μm in an agate mortar and used for zeta potential measurements. The zeta potential measurements of talc were carried out using a ZetaProbe Zeta Potential Analyzer manufactured by Colloidal Dynamics, LLC, USA. The stock mineral suspension was prepared by adding 1g mineral to 50mL distilled water. The pH value was adjusted by adding NaOH or HCL solutions. Then gum solution was added to the suspension with a concentration of 100mg/L and magnetically stirred for 10min. After conditioning, the solution was transferred to a plastic sample cuvette for measurement. The final results were averaged over at least three repeated measurements [14].

2.6XPS measurements

X-ray photoelectron spectrometer (ThermoFisher K-Alpha, USA) was used to carry out the XPS analyses. The Source Type of instrument was monochromatic Al K Alpha. The vacuum pressure inside the analytical chamber was lower than 3×10−8Pa. For data acquisition, the high-resolution scans were obtained using analyzer pass energy of 50eV.

For the XPS tests, 1g talc was added into 50mL distilled water and then the gum solution was added to make the concentration of the agent 100mg/L. After pH adjustment, the suspension was conditioned for 10min. The slurries were then filtered, and dried in a vacuum drying oven, after which, the samples were ready for measurements.

3Results and discussion3.1The flotation behavior of talc with guar gum and tragacanth gum as depressant

Fig. 3 shows the depression effect of tragacanth gum on talc flotation at different pH. The flotation recovery of talc with guar gum as depressant is also shown as a baseline. It can be seen from the figure that the talc has good floatability over a wide pH range (3–11) and its recovery could reach more than 80% by adding frother MIBC only. Fig. 3 also indicates that tragacanth gum has strong depression effect on talc and the depression effect is not affected by pH. Compared with the commonly used talc depressant guar gum, the depression effect of tragacanth gum is stronger.

Fig. 3.
(0.08MB).

Effect of guar gum and tragacanth gum on the flotation of talc at different pH (c(MIBC)=1×10−4M; c(PBX)=1×10−4M; c(depressant)=100mg/L).

The effect of guar gum and tragacanth gum dosages on the talc and chalcopyrite flotation was studied at pH 7, As it can be seen from Fig. 4, the two of gum depressants exhibit a strong depression effect on talc at low dosage, and the depression effect of tragacanth gum on talc was stronger than that of guar gum in different dosage, but guar gum exhibit stronger depression effect for chalcopyrite, which are similar with the previous study of Rath [15].

Fig. 4.
(0.12MB).

Effect of depressants dosage on the flotation of talc and chalcopyrite (c(MIBC)=1×10−4M; c(PBX)=1×10−4M; pH=7).

3.2Adsorption behavior of gum depressants on talc surface

The guar gum and tragacanth gum are adsorbed on the surface of talc, it also shows the adsorption amount of guar gum and tragacanth gum on talc increase slowly in low dosage (<20mg/L), but increase quickly in high dosage (>50mg/L) (Fig. 5). The adsorption amount of tragacanth gum is greater than that of guar gum, which was consistent with the flotation tests.

Fig. 5.
(0.08MB).

The adsorption behavior of depressants on talc surface at pH 7.

3.3Interaction mechanisms of gum depressants with talc surface

Electrokinetic measurements can be utilized to study the adsorption behavior of reagents as small changes in adsorption amount will bring significant modifications in electrokinetic potentials. Fig. 6 shows the effect of pH on the zeta potential of talc in the absence and presence of gum depressants. The results show that talc was negatively charged in the pH range studied and the PZC (point of zero charge) lying somewhere between pH 2 and 3. In the presence of the gum depressants, the PZC of talc changed little, but the absolute value of the talc potential decreased, this is because the adsorption of gum depressants has shift the slip surface of electric double layer toward the outside.

Fig. 6.
(0.06MB).

The effect of depressants on talc surface potential.

X-ray photoelectron spectroscopic (XPS) technique was utilized to investigate the adsorption mechanism of tragacanth gum on talc. The XPS spectrum of C 1s, Si 1s, Mg 1s were collected on talc before and after it was treated by tragacanth gum. As can be seen from Fig. 7a that carbon was present on the talc surface, which were due to organic contamination during testing, while the spectrum was fitted by two peaks, the peaks at 284.8eV and 285.5eV were originated from CC and CC, respectively [16]. Fig. 7b shows the form of carbon has changed and CO bond appears, after treatment with tragacanth gum, which indicated the adsorption of tragacanth gum on talc.

Fig. 7.
(0.13MB).

The resolved narrow scan C1s spectrum for (a) talc and (b) talc treated with tragacanth gum.

The XPS spectrum of Si 2s and Mg 1s were also collected on talc after it was treated by tragacanth gum. By comparing the Si 2s and Mg 1s binding energies, a better understanding of the adsorption process can be obtained. According to the results in Fig. 8 and Table 2, the Si 2s and Mg 1s binding energies of the talc shift little after treatment by tragacanth gum, illustrating that the interaction mechanism of tragacanth gum with talc is a physical interaction.

Fig. 8.
(0.16MB).

The resolved narrow scan Si 2s and Mg 1s spectrum for (a, b) talc and (c, d) talc treated with tragacanth gum.

Table 2.

The binding energy of elements on talc surface with/without depressant.

Elements  Talc  Talc treated with tragacanth gum  variations 
Si 2s  154.64  154.46  −0.18 
Mg1s  1304.93  1304.74  −0.19 

The polysaccharides can adsorb on the mineral surfaces through the following physical interaction mechanism: hydrogen bonding, hydrophobic interaction, and electrostatic interactions [5,8,17,18]. The electrostatic interaction is caused by the charges on the polysaccharide and mineral surface. As tragacanth gum is a non-ionic polysaccharide, the electrostatic interaction was ruled out. So hydrogen bonding and hydrophobic interaction may play roles in the adsorption of tragacanth gum on talc surfaces. The impact of two hydrophobic species come together to avoid the water is known as hydrophobic interaction [19], Jenkins and Cubachiem indicated that the adsorption of guar at the talc could be stated as hydrophobic interactions [7,20].

There are also a number of studies were considered the hydroxyl groups of polysaccharide that can form hydrogen bonds with talc [21–23], but if the mechanism of interaction is hydrogen bonding, the formation of new hydroxyl groups are necessary, which requires the breaking of two existing hydrogen bonds that originate from talc and polysaccharide, but the energy issues were never be discussed, thus, it is short of evidence that the occurred of this adsorption are merely by hydrogen bonding, Based on the above discussion, we think hydrophobic interaction may play an important roles in the adsorption of tragacanth gum on talc surfaces.

3.4The flotation separation of mixed minerals

The flotation separation tests on mixed minerals (chalcopyrite and talc with 1:1 weight ratio, copper contains 15.21%) were carried out to verify the selectivity of the two depressants. The pH value of the slurry was fixed at 7 based on the results of individual mineral flotation tests. As can be seen from Table 3 that a concentrate with Cu grade of 24.35% and recovery of 78.27% was achieved when tragacanth gum was utilized as the depressant, which indicated that tragacanth gum show the selectivity in flotation separation of mixed minerals as a depressant. It can be seen from the result of flotation tests that tragacanth gum performed better than guar gum in terms of talc depression.

Table 3.

The separation of mixture of chalcopyrite and talc.

Reagents  Yield/%  Cu grade/%  Cu recovery/% 
Tragacanth gum 100mg/L  49.22  24.35  78.27 
Guar gum 100mg/L  40.04  28.33  74.58 
4Conclusions

As a useful depressant for talc flotation, the depression effect of tragacanth gum is independent of pH. Comparing with the commonly used depressant, guar gum, tragacanth gum shows less depression effects for chalcopyrite, and its separation capacity for chalcopyrite and talc are no worse than guar gum. The adsorption behavior of tragacanth gum on talc surface were similar with guar gum, their adsorption on the talc surface decreases the absolute value of the potential of talc. XPS analysis were performed to investigate the interactions of tragacanth gum and talc, the results indicated that the tragacanth gum adsorbed on talc surfaces through physical interactions, and hydrophobic interaction was considered as the main driving force and hydrogen bond may also play a role.

Conflicts of interest

The authors declare no conflicts of interest.

Acknowledgements

The authors acknowledge the support of the Natural Science Foundation of China (No. 51664020), Natural Science Foundation of Jiangxi Province (No. 20161BAB216125), the Science and technology project of Jiangxi Province Department of Education (No. GJJ160641), and Program of Qingjiang Excellent Young Talents, Jiangxi University of Science and Technology.

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Copyright © 2018. Brazilian Metallurgical, Materials and Mining Association
Journal of Materials Research and Technology

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