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Article

The Influence of Branched Chain Length on Different Causticized Starches for the Depression of Serpentine in the Flotation of Pentlandite

by
Chenxu Zhang
1,2,3,
Yiping Tan
1,2,3,
Fengxiang Yin
1,2,3,
Jiamei Wu
1,2,3,
Lichang Wang
4,* and
Jian Cao
1,2,3,5,6,*
1
School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China
2
Hunan International Joint Research Center for Efficient and Clean Utilization of Critical Metal Mineral Resources, Central South University, Changsha 410083, China
3
Key Laboratory of Hunan Province for Clean and Efficient Utilization of Strategic Calcium-Containing Mineral Resources, Central South University, Changsha 410083, China
4
School of Geosciences and Info-Physics, Central South University, Changsha 410083, China
5
State Key Laboratory of Mineral Processing, Beijing 100814, China
6
State Key Laboratory of Comprehensive Utilization of Nickel and Cobalt Resources, Jinchang 737100, China
*
Authors to whom correspondence should be addressed.
Minerals 2022, 12(9), 1081; https://doi.org/10.3390/min12091081
Submission received: 4 August 2022 / Revised: 24 August 2022 / Accepted: 25 August 2022 / Published: 26 August 2022
(This article belongs to the Section Mineral Processing and Extractive Metallurgy)
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Abstract

:
Although studies on starch have developed in polymer chemistry research, their structure-activity relationship remains indistinct in the flotation depressants field. In this work, the utilization of five types of causticized starches from different botanical sources as depressants in the flotation of pentlandite/serpentine pure mineral systems was studied. The branched chain length of the starches was quantitatively analyzed using a high-performance anion-exchange chromatography system, and the average branched chain lengths of the causticized starches were obtained. The flotation results demonstrated that the depression effect of all causticized starches on serpentine had a positive correlation with the average branched chain length. Zeta potential tests, FTIR experiments, and XPS analysis confirmed that the causticized starches with a longer branched chain were absorbed more strongly on the serpentine surface. In the present study, the influence of branched chain length on the depression effect of causticized starch was investigated, which deepened our understanding of the depression mechanism of traditional macromolecule depressants and will promote the development of new macromolecule depressants.

1. Introduction

Starch is a class of natural, renewable, and biodegradable polysaccharide polymer [1,2]. Most starches are a mixture of unbranched amylose (content < 30%) and branched amylopectin (content >70%) [3,4]. Amylose consists of linear chains linked by (1→4) bonds, while amylopectin consists of linear chains linked by (1→4) bonds and branched chains by (1→6) bonds (Figure 1) [5]. The applications of amylopectin are much broader than those of amylose because of its solubility (linear chains tend to form insoluble semi-crystalline aggregates) [6]. For amylopectin, the branched chains have a clear influence the properties of amylopectin. The main parameter that measures the properties of branched chains is branched chain length, which is defined by the degree of polymerization of the branched chains [7]. For instance, J. Jane revealed that branched chain length has a critical impact on the gelatinization and pasting properties of amylopectin [8]. C. Menzel declared that the branched chain length of amylopectin has significant implications for the thermal and mechanical stability of film materials [9].
Starch, starch derivatives, and similar polysaccharides have been frequently used as depressants in the flotation of sulfide and oxide minerals. For example, they can take effect in the depression of millerite [10], galena [11], pyrrhotite [12], pyrite [13], chlorite [14], hematite [15], serpentine [16,17,18,19,20], talc [21,22,23,24,25], forsterite [26], and so forth. At present, the chemical modification of these polymers to improve their depression effect is a research hotspot in mineral processing. D.A. Beattie replaced the hydroxyl groups at positions C2 and C6 of starch with hydroxypropyl groups, which improved the depression effect of the modified product for talc in the flotation of Ni-Cu sulfide ore [21]. F. Tian reported that carboxylated starch showed a superior depression effect towards forsterite in the flotation of ilmenite [26]. In addition, carboxymethyl starch, oxidized starch, and amphoteric starch were shown to facilitate the depression effect of molybdenite [27], graphite [28], and diaspore [29], respectively.
Although starch and modified starch have been frequently used as depressants in mineral processing, there is still a lack of understanding of the relationship between the molecular structure and depression effect. For instance, the influence of branched chain length on the depression effect of starch depressants is still unclear. In order to address this issue, this work investigated the utilization of causticized starches with different branched chain lengths as depressants for serpentine in a pentlandite/serpentine flotation system, which is a common problem in the flotation of Ni-Cu sulfide ore [17,30,31,32]. This work provided a new approach to study the depression mechanism of starch depressants.

2. Materials and Methods

2.1. Samples and Reagents

Pure mineral samples of serpentine and pentlandite for micro-flotation tests and other experiments were obtained from Jinchuan, Yingkou in China. The pentlandite sample were crushed, handpicked, and then dry-ground with a porcelain ball mill and dry-sieved to obtain different size fractions. The magnetic separation method was used to remove the pyrrhotite, and the final non-magnetic mineral was the desired product (pentlandite). The samples of pentlandite with particle sizes ranging from −74 to +38 μm were utilized for the micro-flotation tests. The −38 μm size fractions were used for the other tests. The serpentine sample was ground using an agate ball mill and the average particle size of serpentine minerals was about 4.3 μm, as measured by a laser particle size analyzer. The X-ray diffraction (XRD) analyses confirmed that the purity of serpentine (lizardite) and pentlandite was very high (Figure 2).
Potassium butyl xanthate (PBX) was used as the sulfide collector [33]. The causticized starches described in Section 2.2 were utilized as depressants for serpentine and methyl isobutyl carbinol (MIBC) acted as the frother [32,34]. Hydrochloric acid (HCl) and sodium hydroxide (NaOH) were used as the pH regulators in micro-flotation and the other tests. Milli-Q water with a resistivity of 18.2 mΩ cm was utilized in all the experiments. All the reagents described above were of analytical grade.

2.2. Causticization of Starch

Due to the poor water solubility of starch, it is generally causticized before use in flotation. Causticized starch was prepared as follows [35,36]: (1) 0.1 g starch and 0.025 g sodium hydroxide were added to 50 mL deionized water in a 100 mL round bottom flask; (2) the mixture was incubated and reacted at 85–90 °C in a sand bath for 40 min; (3) it was then cooled to room temperature to obtain a relatively transparent causticized starch solution.
The difference between original and causticized starch was assessed through scanning electronic microscope images (Figure 3). As can be seen from Figure 3A, the initial starch had a smooth granule surface. However, it can be seen from Figure 3B that the causticized starch had a completely different surface morphology from that of the untreated starch, i.e., the causticized starch had a rough and irregular granule surface.

2.3. Determination of Branched Chain Length of Amylopectin

A total of 5 mg oligosaccharide standard of DP4-DP7 (Oligosaccharides Kit, from sigma company) was dissolved in 5 mL of water in a boiling water bath for 60 min; 50 μL of sodium acetate (0.6 mol/L), 10 μL NaN3 (2% w/v), and 10 μL isoamylase (1400 U) were added and the mixture was incubated at 37 °C for 24 h [37,38]. Thereafter, 0.5% (w/v) sodium borohydride solution was added to the mixture and it was left to stand for 20 h. Then, 600 μL of the sample solution was transferred into a centrifuge tube and dried with nitrogen at room temperature. The samples were dissolved in 30 μL NaOH (1 mol/L) for 60 min, diluted with 570 μL water, and centrifuged at 12,000 r/min for 5 min, to complete the process. Starch samples were treated with the same method as above.
The sample extracts were analyzed by high-performance anion-exchange chromatography (HPAEC) on a CarboPac PA-100 anion-exchange column (4.0 mm × 250 mm; Dionex) using a pulsed amperometric detector (PAD; Dionex ICS 5000 system) [39,40]. The flow rate was 0.4 mL/min, the injection volume was 5 μL, the solvent system (flow phase) was 0.2 M NaOH or 0.2 M NaOH/0.2 M NaAc, and the gradient program was as follows: 90:10 V/V at 0 min, 90:10 V/V at 10 min, 40:60 V/V at 30 min, 40:60 V/V at 50 min, 90:10 V/V at 50.1 min, and 90:10 V/V at 60 min.
Data were acquired on ICS5000 (Thermo Scientific, Waltham, MA, USA), and processed using chromeleon 7.2 CDS (Thermo Scientific) [40]. Quantified data were output into excel format.

2.4. Micro-Flotation Experiments

The micro-flotation tests were carried out in an XFG-1600 flotation machine with a 40 mL Plexiglass cell at a rotating speed of 1800 r/min [41]. The single mineral suspensions were prepared by adding 2.0 g of pentlandite or serpentine to 40 mL of water. The mixed mineral suspensions were prepared by adding 1.0 g of pentlandite and 1.0 g serpentine to a micro-flotation cell with 40 mL water. NaOH or HCl solutions acted as the pH regulator to adjust the pH to the desired value, and the depressant (causticized starch), collector (PBX), and frother (MIBC) were added to the suspension in sequence, with 2 min of agitation after each addition. Hereafter, the flotation was conducted for a period of 3 min. The floated and unfloated minerals were collected, filtered, and dried to calculate flotation recovery and determine the ore grade.

2.5. Zeta Potential Measurements

Zeta potential measurement was carried out using a Malvern Zetasizer nano ZS zeta potential meter (Bruker Instruments Ltd., Karlsruhe, Germany). The ionic strength of the sample solution was maintained with 1 × 10−3 mol/L potassium nitrate (KNO3). The mineral suspension was prepared by adding a 30 mg sample to 10 mL of KNO3 electrolyte solution in the absence and presence of depressants for each test. The desired pH value above the solution was adjusted by adding hydrochloric acid (HCl) or sodium hydroxide (NaOH) stock solutions. The supernatant was then measured using the zeta potential analyzer after stirring for 10 min and standing for 5 min. Each zeta potential was tested three times, and the average value was calculated and recorded.

2.6. FT-IR Experiments

The Fourier transform infrared spectra (FTIR) of mineral samples obtained from micro-flotation was recorded using a Nicolet iS20 (Thermo Fisher Scientific, Waltham, MA, USA). After obtaining the flotation concentrate samples in the presence or absence of depressants, the mineral samples were washed repeatedly with deionized water, then put into a vacuum oven, and dried at 35 °C for testing. The dried flotation concentrate samples were mixed with KBr in an identical proportion (1:100) to prepare the powder mixtures needed for the FT-IR spectrometer, and therefore the absorbance in their infrared spectra was proportional to the concentration of the species present in these samples.

2.7. XPS Analysis

X-ray photoelectron spectroscopy (XPS) measurements were performed using the Thermo Scientific K-Alpha (Thermo Scientific Co., Waltham, MA, USA) spectrometer. For each test, 1 g of serpentine was mixed with a 20 mg/L depressant solution. The solution was filtered and washed three times using milli-Q water. The filtered solids were dried in a vacuum drying oven at 35 ℃ and then analyzed using XPS. All binding energies were referenced to the neutral C1s peak at 284.80 eV to compensate for the surface charge effect.

3. Results

3.1. Branched Chain Length of Amylopectin

Branched chain plays a major role in the application of causticized starch, and as a result, the branched chain length of amylopectin has a decisive influence on the depression effect of causticized starch. Chromatograms analysis was used to determine the branched chain length distributions of amylopectin isolated from different causticized starches (Figure 4), and the computed results are summarized in Table 1.
In general, five kinds of causticized starches had a first peak at DP 12–13 at short chain lengths and a second peak at DP 41–46 at long chain lengths (Figure 4). Corn starch (Figure 4A) exhibited a gradual increase in chains of the polymerization degree (DP) 6–12, and formed two peaks at DP 12 and 43. Wheat starch (Figure 4B) also had a gradual increase in chains of the polymerization degree (DP) 6–12, and formed two peaks at DP 12 and 44. Moreover, it exhibited a low proportion of very long chains (DP ≥ 37) and this starch displayed a shoulder at DP 18–24. These results are in agreement with those reported by Jane et al. [8]. Cassava starch (Figure 4C) had a distribution similar to that of wheat starch, but the relative intensity of the shoulder was lower, which is in agreement with the report of Santacruz et al. [42]. A low proportion of very short chains (DP 6–12) and a high proportion of very long chains (DP ≥ 37) in branched chain length distributions were observed for the amylopectin isolated from cassava starch (Table 1). Rice starch (Figure 4D) did not show a shoulder on its distribution; in addition, it exhibited the lowest proportion of very short chains (DP 6–12) (Table 1). Potato starch (Figure 4E) displayed a trough at DP 6–10 and did not show a shoulder on its distribution. A similar distribution was found by Yoo et al. [43] in potato starch.
The distribution results of wheat starch suggested that DP 18–21 represented the full length of the crystalline region, and the ratio of the intensities of peak 1 and the shoulder indicated the proportion of short chains in the crystallites that result in defects [44], which could affect the flotation performance.
The large proportion of short chains and the small proportion of chains of DP 13–36 in rice starch may form a weak crystalline structure, which is unable to hold the clusters together or maintain the integrity of starch granules, as observed by Jane et al. in the case of sugary-2 maize starch [45]. This phenomenon may also influence the flotation performance.
In Table 1, the difference in the branched chain length distribution of the five starches is more obvious. It is not difficult to see that the average branched chain length of cassava and corn starch is the largest, followed by potato and wheat starch, with rice starch exhibiting the smallest length. At present, the starch depressants used in flotation are mostly from cassava and corn [46,47,48,49,50,51].

3.2. Flotation Experiments Results

Single mineral micro-flotation experiments were carried out to evaluate the depression effect of five kinds of causticized starches on serpentine and pentlandite in different flotation conditions (depressant dosage and pH value).
First, the single mineral flotation of serpentine (Figure 5A) and pentlandite (Figure 5B) was studied with different depressant dosages. The results indicated that causticized starches could effectively depress the floatation of serpentine particles, and the depression effects of five kinds of causticized starches were obviously different, especially in the depressant dosage range between 10–18 mg/L. It is worth noting that the depression effects of five causticized starches were positively correlated with the average branched chain length of these starches, i.e., the depression effects were as follows: cassava starch > corn starch > potato starch > wheat starch > rice starch. The recovery of pentlandite could maintain high values in the depressant dosage range tested (72–95%), especially in the depressant dosage range between 0–10 mg/L (>88%). In addition, the recovery of pentlandite using five causticized starches was almost indistinguishable, which was most likely due to the difference in the interaction of causticized starch with serpentine and pentlandite. According to the results of the dosage experiments, the optimal reagent dosage of causticized starches used as a depressant was 10 mg/L for the subsequent tests.
Next, under the optimal depressant dosage, the single mineral flotation of serpentine (Figure 5C) and pentlandite (Figure 5D) was studied at different pH values. The results of flotation tests indicated that, in the range of pH 6–10, the recovery of serpentine decreased gradually with the increase in pH value; in the range of pH 10–12, the recovery of serpentine increased with the increase in pH value. On the contrary, the recovery of pentlandite increased with increasing pH value in the pH range of 2–8, but in the range of pH 8–12, the recovery of pentlandite decreased with increasing pH value. This could be for two reasons: when the pulp pH value was more than 8, the xanthate may gradually decompose into thiocarbonatesm, which have no collecting ability [52], resulting in a lower collection efficiency; in the range of pH 8–12, some changes occurred on the surface of pentlandite (e.g., the formation of Ni hydroxide or Fe hydroxide [53]), resulting in reduced floatability of sulfide mineral. Dihydrocarbyl thiophosphates can be used as a sulfide collector in future research as their properties are more stable than those of butyl xanthate. As can be seen in the trend in Figure 5C,D, pH 9 was employed in follow-up flotation experiments.
After establishing the optimal flotation conditions (the dosage of depressant and the pH value of the pulp), the depression effect of different causticized starches on serpentine in the flotation of artificial mixed ore (pentlandite/serpentine system) was further investigated, and the results are shown in Figure 6 and Table 2. It was apparent that the depression effect of cassava starch and corn starch on serpentine was similar and the most effective, followed by potato starch and wheat starch, while rice starch exhibited the worst performance, i.e., close to the flotation effect without a depressant. Obviously, both single-mineral flotation experiments and mixed-mineral flotation experiments reached the same conclusion, i.e., the depression effect of causticized starches on serpentine exhibited a positive correlation with the average branched chain length. This may be due to the fact that starch with a longer branched chain could adsorb more serpentine particles.

3.3. Zeta Potential Measurements Results

One of the key factors that effects causticized starches’ ability to depress the floatation of serpentine is its electro-kinetic behavior [32]. Therefore, in order to further explore the reasons for and mechanism of the difference in flotation effect of causticized starches, zeta potential measurements were performed. The test results are shown in Figure 7.
As shown in Figure 7A, the addition of causticized starches caused the zeta potential of serpentine to exhibit negative shifts. This change in zeta potential may be attributed to the interaction between the oxygenated hydrocarbon chains on the polymer (starch) and the hydroxylated metal ions on the serpentine surface, a mechanism that has also been studied before [54]. Moreover, the five kinds of causticized starches decreased the zeta potential of serpentine to different degrees. The decreasing degree was in the following order: cassava starch > corn starch > potato starch > wheat starch > rice starch. However, the addition of causticized starches did not seem to have a significant effect on the zeta potential of pentlandite, which indicated that the adsorption of causticized starch on the surface of pentlandite was very weak.
In addition, the zeta potential measurement further elaborated the reasons for the difference in the depression effect of the five causticized starches on serpentine in the flotation of the pentlandite/serpentine system. When no depressant was added (with a natural pH value of 9), the zeta potentials of serpentine and pentlandite were positive and negative, respectively, which led to the phenomenon of electrostatic attraction between the two minerals and deteriorated their flotation separation ability [17]. When adding five kinds of causticized starches, the zeta potential of serpentine exhibited different degrees of reduction, which also reduced the effect that electrostatic attraction had on flotation to varying degrees. Therefore, the zeta potential measurement illustrated that the difference in the depression effect of five causticized starches on serpentine was caused by their different abilities to decrease serpentine’s potential.

3.4. FT-IR Experiments Results

To further investigate the depression effect of different causticized starches on serpentine, flotation concentrates with different depressants were collected for FTIR analysis. The results are shown in Figure 8. In Figure 8, the sharp peak at 3677 cm−1 was due to the stretching vibration of -OH, which is a characteristic and unique peak of serpentine [55]. The FTIR test results verified the adsorption of the serpentine “slime coating” on the surface of the pentlandite (serpentine is a hydrophilic mineral and therefore it should not reach the concentrate except by entrainment or if it is attached to pentlandite [17,56]). Due to the test sample preparation, the absorbance in their infrared spectra was proportional to the concentration of the species present in these test samples. Therefore, the FTIR test results could further prove that the depression effect of different causticized starches on serpentine was different, which was consistent with the results of the flotation experiment and zeta potential measurements. In conjunction with Section 3.1, it can be seen that causticized starches with longer branched chains could better disperse the serpentine particles from pentlandite and thus allow reduce the amount of serpentine adhering to the pentlandite.

3.5. XPS Analysis Results

Even though some indication of the interaction between depressant molecules and mineral surfaces were provided in the IR spectroscopy, some significant chemical bonds on the mineral surface and the imperceptible changes of certain atoms on the mineral surface could not be characterized in this manner. XPS analysis can be used precisely determine the chemical state and elemental composition of a mineral surface and is utilized to study the interaction between depressants and serpentine [54,57,58,59]. Therefore, in order to further explore the interaction of the five causticized starches on the serpentine surface and what changes occurred to the serpentine surface, XPS analysis was performed. The results are shown in Figure 9 and Table 3.
In the Mg1s spectrum shown in Figure 9A, the Mg1s peak of bare serpentine appears at approximately 1304.16 eV in Mg-OH, as in previous studies [58,59]. In Figure 9B, it can be seen that no new peaks appeared on the surface of the serpentine treated with rice starch, which indicated that there was almost no chemical adsorption between rice starch and the serpentine surface. Figure 9C–F showed the Mg1s spectrum obtained after adding other causticized starches, where the new Mg1s peaks at 1302.80 eV, 1302.87 eV, 1302.88 eV and 1302.74 eV are assigned to Mg-OR (R refers to hydrocarbon chain) on the serpentine surface [60,61], evidencing chemisorption between the causticized starches and the Mg sites of the serpentine surface. It can be seen that the interaction between the causticized starch and serpentine was mainly through the oxygen atoms of the branched chains combining with the Mg atoms on the serpentine surface.
Moreover, the element atomic content analysis in Table 3 showed the proportion of Mg atoms in different states. The results in Table 3 proved that the proportion of Mg atoms adsorbed by the five kinds of causticized starches was different, and the proportions were arranged in the following order: cassava starch > corn starch > potato starch > wheat starch > rice starch.
By combining the results of the branched chain length distribution with those of the XPS analysis, it can be concluded that the causticized starches with longer branched chains were adsorbed more strongly on serpentine surface, and thus had a better depression effect. Based on this idea, Figure 10 shows the influence mechanism of the branched chain length on the depression effect on serpentine. It can be seen from Figure 10 that the branched chain length is a crucial factor in the depression effect of causticized starch on serpentine in the flotation of the pentlandite/serpentine system.

4. Conclusions

In this study, a method of examining the influence of different types of starches is presented through flotation experiments and mechanism studies. The following significant conclusions were drawn:
  • The results of the flotation experiments fully illustrated that the depression effect of causticized starches on serpentine were ranked as follows: cassava starch > corn starch > potato starch > wheat starch > rice starch.
  • The average branched chain length was arranged in the following order: cassava starch > corn starch > potato starch > wheat starch > rice starch, and the depression effect of causticized starches on serpentine exhibited a positive correlation with the average branched chain length.
  • Starch depressants depress the serpentine in the flotation system by combining the oxygen atoms on the oxygen-containing hydrocarbon chain with the Mg atoms on serpentine surface. Moreover, causticized starches with longer branched chains were adsorbed more strongly on serpentine surface, and thus had a better depression effect.

Author Contributions

Conceptualization, C.Z., F.Y. and Y.T.; methodology, C.Z. and F.Y.; formal analysis, C.Z. and J.W.; investigation, C.Z. and F.Y.; data curation, C.Z., F.Y. and Y.T.; writing—original draft preparation, C.Z.; writing—review and editing, J.C. and L.W.; supervision, J.C. and L.W.; funding acquisition, J.C. 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 (52004336), State Key Laboratory of Comprehensive Utilization of Nickel and Cobalt Resources (GZSYS-KY-2020-014), Open Foundation of State Key Laboratory of Mineral Processing (BGRIMM-KJSKL-2021-06), Science and technology innovation leading project of high-tech industry of Hunan Province, China (2020GK2067), Open Fund of Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring (Central South University) and Ministry of Education, China (2022YSJS15), National Key R&D Program of China (2019YFC1803503) and Graduate Research Innovation Project of Central South University (2022ZZTS0564).

Data Availability Statement

Data are available from the authors upon reasonable request.

Conflicts of Interest

The authors declare no conflict of interest.

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Minerals 12 01081 g001 550
Figure 1. Two different molecular structures of starch: unbranched amylose and branched amylopectin.
Figure 1. Two different molecular structures of starch: unbranched amylose and branched amylopectin.
Minerals 12 01081 g001
Minerals 12 01081 g002 550
Figure 2. XRD spectra of serpentine (lizardite) and pentlandite samples.
Figure 2. XRD spectra of serpentine (lizardite) and pentlandite samples.
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Minerals 12 01081 g003 550
Figure 3. SEM photographs: initial starch (magnification 2000 (A) and 5000 (B)); causticized starch (magnification 2000 (C) and 10,000 (D)).
Figure 3. SEM photographs: initial starch (magnification 2000 (A) and 5000 (B)); causticized starch (magnification 2000 (C) and 10,000 (D)).
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Minerals 12 01081 g004 550
Figure 4. Amylopectin branched chain length distributions of different varieties of starch: (A) corn starch; (B) wheat starch (C) cassava starch; (D) rice starch; (E) potato starch.
Figure 4. Amylopectin branched chain length distributions of different varieties of starch: (A) corn starch; (B) wheat starch (C) cassava starch; (D) rice starch; (E) potato starch.
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Minerals 12 01081 g005 550
Figure 5. Recovery of serpentine (A,C) and pentlandite (B,D) as a function of the depressant dosage or the pH value ([PBX] = 1 × 10−4 mol/L; [MIBC] = 1 × 10−4 mol/L).
Figure 5. Recovery of serpentine (A,C) and pentlandite (B,D) as a function of the depressant dosage or the pH value ([PBX] = 1 × 10−4 mol/L; [MIBC] = 1 × 10−4 mol/L).
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Minerals 12 01081 g006 550
Figure 6. Recovery and grades of concentrate in the flotation of artificial mixed mineral with different causticized starches as depressants (pH = 9; [PBX] = 1 × 10−4 mol/L; [MIBC] = 1 × 10−4 mol/L).
Figure 6. Recovery and grades of concentrate in the flotation of artificial mixed mineral with different causticized starches as depressants (pH = 9; [PBX] = 1 × 10−4 mol/L; [MIBC] = 1 × 10−4 mol/L).
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Minerals 12 01081 g007 550
Figure 7. Zeta potentials of serpentine (A) and pentlandite (B) as a function of pH in the presence and absence of depressants (1 × 10−2 g/L).
Figure 7. Zeta potentials of serpentine (A) and pentlandite (B) as a function of pH in the presence and absence of depressants (1 × 10−2 g/L).
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Minerals 12 01081 g008 550
Figure 8. Infrared spectra of serpentine and flotation concentrate mineral samples of pentlandite mixed with serpentine in the absence and presence of 2 × 10−2 g/L of depressants (pH = 9; [pentlandite] = 25 g/L; [serpentine] = 25 g/L).
Figure 8. Infrared spectra of serpentine and flotation concentrate mineral samples of pentlandite mixed with serpentine in the absence and presence of 2 × 10−2 g/L of depressants (pH = 9; [pentlandite] = 25 g/L; [serpentine] = 25 g/L).
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Figure 9. Mg1s XPS spectra of clean serpentine surface (A) and the serpentine surfaces interacted with rice starch (B), potato starch (C), cassava starch (D), corn starch (E), and wheat starch (F).
Figure 9. Mg1s XPS spectra of clean serpentine surface (A) and the serpentine surfaces interacted with rice starch (B), potato starch (C), cassava starch (D), corn starch (E), and wheat starch (F).
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Minerals 12 01081 g010 550
Figure 10. The schematic diagram for the interactions between depressants and serpentine.
Figure 10. The schematic diagram for the interactions between depressants and serpentine.
Minerals 12 01081 g010
Table
Table 1. Branched chain length distributions of amylopectin.
Table 1. Branched chain length distributions of amylopectin.
SpeciesAverage
CL		% Distribution
DP 6–12DP 13–24DP 25–36DP ≥ 37
Corn starch21.2126.6946.6213.7112.98
Wheat starch19.9728.6247.8914.019.48
Cassava starch22.2719.2351.7614.9814.03
Rice starch19.4829.6249.1211.1510.11
Potato starch20.7523.4751.8313.7410.96
Table
Table 2. Flotation separation of mixed mineral with different causticized starch depressants.
Table 2. Flotation separation of mixed mineral with different causticized starch depressants.
DepressantMgO
Grade (%)		MgO
Recovery (%)		Ni
Grade (%)		Ni
Recovery (%)
No depressant11.6946.355.5396.92
Wheat starch11.6744.855.3493.68
Cassava starch10.6639.325.9493.86
Rice starch11.1345.185.5394.47
Corn starch10.2441.385.7594.52
Potato starch11.0842.035.6294.34
Table
Table 3. Quantification of Mg 1s species in serpentine and depressant-treated serpentine samples.
Table 3. Quantification of Mg 1s species in serpentine and depressant-treated serpentine samples.
SampleMg 1s
Binding Energy (eV)		Species
Distribution (%)
Serpentine—0.00
1304.16100.00
Serpentine + Rice starch—0.00
1304.22100.00
Serpentine + Potato starch1302.8025.71
1304.1374.29
Serpentine + Cassava starch1302.8731.76
1304.0868.24
Serpentine + Corn starch1302.8830.26
1304.1569.74
Serpentine + Wheat starch1302.7413.33
1304.2386.67
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Zhang, C.; Tan, Y.; Yin, F.; Wu, J.; Wang, L.; Cao, J. The Influence of Branched Chain Length on Different Causticized Starches for the Depression of Serpentine in the Flotation of Pentlandite. Minerals 2022, 12, 1081. https://doi.org/10.3390/min12091081

AMA Style

Zhang C, Tan Y, Yin F, Wu J, Wang L, Cao J. The Influence of Branched Chain Length on Different Causticized Starches for the Depression of Serpentine in the Flotation of Pentlandite. Minerals. 2022; 12(9):1081. https://doi.org/10.3390/min12091081

Chicago/Turabian Style

Zhang, Chenxu, Yiping Tan, Fengxiang Yin, Jiamei Wu, Lichang Wang, and Jian Cao. 2022. "The Influence of Branched Chain Length on Different Causticized Starches for the Depression of Serpentine in the Flotation of Pentlandite" Minerals 12, no. 9: 1081. https://doi.org/10.3390/min12091081

APA Style

Zhang, C., Tan, Y., Yin, F., Wu, J., Wang, L., & Cao, J. (2022). The Influence of Branched Chain Length on Different Causticized Starches for the Depression of Serpentine in the Flotation of Pentlandite. Minerals, 12(9), 1081. https://doi.org/10.3390/min12091081

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