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Article

Investigation of the Flotation Separation of Scheelite from Fluorite with a Novel Chelating Agent: Pentasodium Diethylenetriaminepentaacetate

by
Chenhu Zhang
1,2,3,
Haijun Wu
1,3,
Wei Sun
2,
Yuehua Hu
2,*,
Chengyong Wang
1,3,
Shan Zhu
1,3 and
Peng Chen
1,3
1
School of Mining and Mechanical Engineering, Liupanshui Normal University, Liupanshui 553004, China
2
School of Mineral Processing and Bioengineering, Central South University, Changsha 410083, China
3
Guizhou Provincial Key Laboratory of Coal Clean Utilization, Liupanshui 553004, China
*
Author to whom correspondence should be addressed.
Minerals 2022, 12(5), 530; https://doi.org/10.3390/min12050530
Submission received: 29 March 2022 / Revised: 16 April 2022 / Accepted: 20 April 2022 / Published: 24 April 2022
(This article belongs to the Section Mineral Processing and Extractive Metallurgy)
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Abstract

:
The recovery of scheelite from calcium-bearing carbonate ores by foam flotation is challenging due to its low separation efficiency. This study investigated the effect of pentasodium diethylenetriaminepentaacetate (PD) on the surface properties of scheelite and fluorite. For this purpose, we performed micro-flotation tests and carried out zeta potential measurements, as well as Fourier transform infrared (FT-IR) and X-ray photoelectron (XPS) spectroscopic measurements, in order to analyze the surface properties of these minerals. The addition of PD as a novel depressor significantly improved the effect of fluorite and sodium oleate (NaOl) on the flotation-based scheelite recovery and separation from fluorite. PD was spontaneously adsorbed onto fluorite through electrostatic and chemical adsorption. By contrast, PD did not appear on the scheelite because of the reaction conditions, surface site, and steric hindrance. X-ray photoelectron spectroscopy measurements and a solution chemistry analysis were used for the determination of the PD-selective adsorption mechanism and key factors derived from multi-layer adsorption onto fluorite, which completely hindered that of NaOl.

1. Introduction

Tungsten is a strategic and scarce metal resource [1,2] which is widely used in several fields [3,4,5] because of its thermal expansion, low vapor pressure, good electrical and thermal conductivities, and high melting point and density. Tungsten predominantly originates from scheelite (CaWO4) and wolframite [6,7]. Scheelite turns into a principal raw material through an advanced exhaustion procedure of wolframite [8].
Scheelite, alongside other similar calcium-bearing minerals such as fluorite and calcite, is predominant in tungsten, and scheelite ores are commonly separated and utilized by the implementation of the froth flotation approach (an efficient physicochemical technique) [7,9,10]. The similarity of the Ca active sites in the cleavage planes of these minerals causes a demonstration of the same surface interactions with conventional collectors, including fatty acids and other related derivations during flotation [11,12]. In order to address this problem, anionic flotation procedures that are implemented by combining various depressors or anionic collectors have been widely explored [13,14,15]. Many studies have investigated the separation flotation of calcite and scheelite, but developing a procedure for the depression of fluorite and calcites remains difficult [16,17,18]. In order to address the difficulty of obtaining an effective flotation separation of scheelite from fluorite, novel depressants must be explored. Different depressants have varying mineral adsorption capabilities, and enhance the hydrophilicity of impure substances to varying degrees; thus, the choice of depressant is vital to the achievement of an effective flotation separation of scheelite from fluorite.
In the scheelite flotation strategy, the functional groups of the depressants perform crucial tasks, and are mostly organic or inorganic. Inorganic depressants comprise PO43−, SO42−, and SiO32−. The sodium silicate-based depressants can depress the gangue minerals by hindering oleate entities while demonstrating unavoidable effects on scheelite flotation [13]. Acidized sodium silicate (water-glass) is a desirable inorganic depressor in a weak acidic milieu [19,20,21]. Furthermore, phosphates—including sodium hexametaphosphate (NaPO3)6, sodium pyrophosphate (Na4P2O7), and sodium phosphate (Na3PO4)—are prevalent depressants for scheelite flotation [22,23]. However, their utilization can cause chemical contamination. Other organic depressants—such as –COOH, –OH, dextrin, quebracho, CMC, tannin, and starch—are extensively used as purifying depressants [24,25,26,27], which is likely because of their nontoxicity and biodegradability properties. The unfavorable selectivity of these organic depressants has not been unaddressed. Thus, novel depressants based on functional groups have been investigated by considering the potential of both depressant types.
Pentasodium diethylenetriaminepentaacetate (PD) (see Figure 1) is a chelator or complexing agent, and has been widely used for sewage treatment, papermaking, and spinning; it has also been used as a magnetic resonance imaging agent. PD is nontoxic and “green” [28,29,30], and as an ordinary polycarboxyl compound carbohydrate, its most desirable characteristics are its availability and cost-effectiveness [31,32]. Because five carboxyls are attached to three N bonds, PD chelates with numerous metal ions, such as Mg2+, Ca2+, Fe2+, Zn2+, and Cu2+ [33,34]. So far, no research has applied PD in the field of mineral manufacturing, or for the separation of fluorite and scheelite through flotation.
Herein, we investigated the floatation performance of PD and the performance of NaOl at the CaWO4 and CaF2 interfaces; we also investigated the effects of PD on flotation. The objectives of this study were to determine the effects of PD on scheelite and fluorite interactions. Therefore, the association between the flotation mechanisms and selective adsorption performances of PD were studied through various assessments, including micro-flotation, adsorption tests, zeta potential measurement, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS).

2. Materials and Methods

Scheelite and fluorite were collected from Hunan (China), and were analyzed by X-ray powder diffraction (XRD) to confirm their compositions and purities, which were ≥98.41% and ≥95.79%, respectively (see Figure 2). The 37~74 μm fractions of scheelite and fluorite, selected for the flotation tests, were adjusted to −5 μm in agate mortars, and were subsequently analyzed through zeta potential assessments, FTIR spectroscopy, and XPS measurements.
The other chemicals—PD (C14H18N3Na5O10, molecular weight: 503.26), NaOH, and sodium oleate (NaOl, C18H33O2Na, molecular weight: 304.44)—were chemically pure, and were purchased from Aladdin Biological Technology and Baisaiqin Chemical Technology Co. (Shanghai, China). The pH values were modified using HCl or NaOH stock solutions. Distilled water (with a resistivity above 18 mΩ·cm) was also used for the measurements.

2.1. Micro-Flotation Tests

We performed flotation tests using an XFG setup equipped with a 40-mL plexiglass cell at a 1650-rpm impeller speed. Approximately 2.0 g of the pure compounds was placed into the cell and filled with approximately 35 mL water. The pH was modified by increasing the NaOH or HCl concentration when necessary. Subsequently, the solution was allowed to equilibrate for 2 min, after which the depressants were added. The suspension was further allowed to equilibrate for 3 min, after which NaOl, acting as a collector, was added; the suspension was then stirred vigorously for 3 min. The floating and sunk species were accumulated separately, filtered, and dried. The micro-flotation measurements were performed three times using fresh samples, and the means of the measurements were obtained as the final assessment values.

2.2. Adsorption Tests

Two grams of scheelite or fluorite was placed in a 200-mL conical flask containing 100 mL water or a 1.6 × 10−3-mol/L PD solution with a pH of 9.0. The suspension was mixed for 2 h by an incubator shaker at 140 r·min−1 and 25 °C, after which specific NaOl amounts were added under constant shaking. After another 2 h, the supernatant was aliquoted for further total organic carbon (TOC) and nitrogen analyses in the remaining reagents (NaOl and NaOl + PD solutions). We used a TOC instrument to measure the organic carbon and total nitrogen amounts. The amount of organic carbon in the PD in the aliquot containing a mixture of NaOl + PD was recalculated using the total nitrogen amount. Subsequently, this value was subtracted from the organic carbon value obtained for the NaOl + PD mixture in order to obtain the organic carbon content for NaOl alone.
The reagent adsorption onto the minerals was evaluated using Equation (1):
Q e = ( C e − C 0 ) V m
where Qe is the amount of reagent adsorbed at the interface (mg/g); Ce and C0 are the primary and supernatant concentrations (mg/L), respectively; m is the mass of the mineral specimen (g); and V is the volume of the reagent solution (L).

2.3. Zeta Potential Measurement

We used a Zetasizer Pro (Malvern, UK) instrument for the zeta potential tests performed at 25 °C. A 0.02-g suspension of 40 mL 0.01M KCl (used as a background electrolyte), prepared at a specific pH and various PD values (NaOl and PD + NaOl concentrations), was allowed to settle for 5 min before the zeta potential measurements.

2.4. FTIR Spectral Analysis

The FTIR data were collected at the ambient temperature (25 ± 1 °C) using a Bruker Alpha instrument (Thermo Fisher IS50, Thermo Fisher Scientific, Waltham, MA, USA). The materials were prepared as follows: 200 mg of a specimen was blended with 30 mL water with a pH of 9.0 at 25 °C with or without the presence of a 2 × 10−4-mol/L depressor solution. After blending for 30 min, the solid material was filtered, vacuum-dried, and ground with KBr until a transparent pellet was obtained. Samples prepared under the same conditions but possessing untreated surfaces served as references.

2.5. XPS Analysis

The spectra of XPS for fluorite and scheelite pre- and post-PD were investigated using a K-Alpha 1063 XPS spectrometer (Thermo Scientific K-Alpha+, Thermo Fisher Scientific, Waltham, MA, USA) with Al Ka as the sputtering source at 6 mA and 12 kV. Furthermore, in the analytical chamber, the pressure was set to 1.0 × 10−12 Pa. A value of approximately 284.7 eV was used as the standard C (1 s) to calibrate the binding energy. The specimens were analyzed as follows: 0.2 g of the mineral specimen was added to a 30-mL aqueous solution with or without 2 × 10−4-mol/L PD at a pH of 9; the solution was stirred for 30 min at 25 °C, filtered, washed with deionized water, and vacuum-dried in a vacuum at the ambient temperature for one day. The XPS tests were performed in order to assess the compositions of the mineral surfaces.

3. Results and Discussion

3.1. Micro-Flotation Results

Substantial amounts of experimental data regarding the flotation process of pure fluorite and scheelite have been obtained in several studies [35,36,37]. However, the origin change of these pure minerals causes different impurities to form in them, and the crushing process affects the results of the flotation experiment of these pure minerals. Figure 3 illustrates the flotation test results of pure scheelite and fluorite minerals, illustrating the comparability and consistency of the experimental data.
As demonstrated in Figure 3a, the recovery rate of scheelite increases rapidly when the pH ranges from 4 to 9. When the pH > 9, the recovery rate of scheelite fluctuates, and is slightly reduced. The best condition for fluorite recovery is a pH of approximately 7.8. Even with a pH between 7.8 and 9, the floatability index of scheelite is lower than that of fluorite at approximately 5–10%. The recovery dynamic is likely due to the conversion of positive to negative charges that occur on the fluorite surface in this pH range. The difference in recovery occurs mainly because the physical and chemical adsorptions of NaOl onto the fluorite surface are stronger than those of scheelite; this observation is consistent with that reported in previous studies.
Figure 3b shows that when the NaOl concentration is 0.5 × 10−4–1.0 × 10−4 mol/L, the floatability of scheelite and fluorite improve considerably at the optimum pH of 9. When the NaOl is 1.5 × 10−4 mol/L, the flotation recovery of the two minerals remains at the maximum, and only a slight change occurs subsequently. Figure 3a,b shows that NaOl has an advantageous adsorption influence on both minerals in an alkaline solution, resulting in the substantial recovery of fluorite and scheelite in the basic zone considered. The flotation conditions were as follows: the concentration of the collector NaOl was 1.5 × 10−4 mol/L, and the pH was 9.0. The flotation observations above indicate that separating the two minerals without a depressor is a persistent challenge.
Figure 4 illustrates the floatability of scheelite and fluorite conditioned with diverse PD concentrations at a fixed NaOl collector concentration and pH. Figure 4 clearly demonstrates that the floatability of scheelite and fluorite are significantly reduced when PD is added. However, the recovery rate of fluorite is reduced more significantly than that of scheelite. When the concentration of PD is raised to 16 × 10−4 mol/L, the fluorite recovery is only 15.28%. The scheelite flotation recovery is up to 73.41%. This shows that PD effectively separates scheelite from fluorite under the right conditions. However, PD adversely affects the recovery of scheelite. Hence, an increase in PD consumption affects the NaOl adsorption onto the minerals in the flotation environment. Meanwhile, the adsorption influence is much greater under a similar dosage. The addition of a considerable amount of polycarboxyl-PD may introduce a substantial amount of COO- into the solution, indicating that NaOl has different effects on both minerals during adsorption.

3.2. Adsorption Results

The flotation behavior of both minerals is correlated to the adsorption of different reagents, including collectors. Therefore, we studied the absorption behavior of the NaOl collector in order to understand the scheelite and fluorite flotation-based separation better (see Figure 5). Without PD, large amounts of NaOl are adsorbed onto the scheelite and fluorite surfaces (2.416 × 10−2 and 2.1102 × 10−2 mg/g, respectively). However, as the PD concentration gradually increases from 0.0 to 2.0 × 10−3 mol/L, the amount of adsorbed NaOl on the scheelite and fluorite surfaces continually drops to 1.387 × 10−2 and 0.5032 × 10−2 mg/g, respectively. Thus, adding PD (especially before NaOl) prevents NaOl adsorption onto the fluorite surface but has little effect on that of scheelite. This observation confirms the discussion above. When PD is present, scheelite has a higher floatability than that of fluorite because more NaOl adsorbs onto the scheelite surface under the same conditions.

3.3. Zeta Potential Results

Figure 6a,b illustrates the zeta potential of fluorite and scheelite, processed and unprocessed with PD, with and without NaOl, as a function of pH. Both graphs show that these potential surface differences are crucial to the flotation behavior of both minerals. In the flotation environment, scheelite is always negatively charged on the surface when the pH is in the range of 6~12; these results agree with those of previous studies. For the bare fluorite, the isoelectric point (IEP) is obtained at a pH of approximately 7.8, which is also consistent with the results of previous studies [38,39,40].
Figure 6a illustrates that in the pH range of 4~11, increasing the NaOl reduces the zeta potential of scheelite minerals by approximately 10 mV. This phenomenon demonstrates the adsorption of anionic molecules onto the scheelite surface via the hydrophobic correlation of hydrocarbon chains and the growth of calcium oleate, which has the propensity to precipitate [41,42]. By adding PD to both minerals, the zeta potential is reduced to approximately 40 mV, indicating sufficient adsorption. Increasing the NaOl and PD simultaneously reduces the zeta potential of scheelite by approximately 15 mV with a single PD, demonstrating that the NaOl interaction with scheelite is not influenced by PD, and can replace PD.
Figure 6b shows that when NaOl is added, the IEP value is reduced while the zeta potential becomes further negative, showing that the interaction between NaOl and fluorite occurs through the electrostatic and chemical adsorptions of the calcium–sodium oleate micelles mixture [43,44,45]. Furthermore, by increasing PD, considerably negative and reducing values of IEP are observed in the zeta potential, illustrating the coating progression. Subsequently, by increasing the amounts of NaOl and PD, the zeta potential for fluorite decreases along with that of PD-processed fluorite without NaOl. This finding shows that the adsorption of PD onto the surface of fluorite perfectly inhibits the adsorption of NaOl via potent chemical reactions. Based on these results, we confirmed the theoretical inferences using FTIR and XPS analyses.

3.4. FTIR Results

The spectra of FTIR for scheelite and fluorite pre- and post-interaction with PD are illustrated in Figure 7. According to Figure 7a, the distinctive peaks of absorption at 1659 cm−1 and 1762 cm−1 are attributable to the N–H bending vibration and C=O stretching vibrations of the COO- groups, respectively. The strong distinctive absorption at 1365 cm−1 is attributed to the C–O stretching vibration of the carboxyl groups, indicating the presence of a carboxyl group in the PD structures [46,47]. Following the PD processing, a single new peak emerges on the scheelite surface at 3442 cm−1, which can be assigned to the OH stretching vibrations. The first peak is caused by the stretching band of Ca–Ca–OH. In contrast, the distinctive peaks of bare scheelites do not shift, indicating that the adsorption of PD onto the scheelite surface is insignificant.
The obtained spectra for fluorite in the presence and absence of PD are presented in Figure 7b. After interacting with PD, the fluorite surface demonstrates new bands of adsorption at 1733 cm−1 and 1637cm−1, which are relevant to the distinctive bands C=O and –NH2 of PD, respectively. The C=O stretching vibrations at approximately 1762 cm−1 are reduced by 29 cm−1 to approximately 1733 cm−1, and the –NH2 stretching vibrations at approximately 1659 cm−1 are reduced by 22 cm−1 to approximately 1637 cm−1. This implies that PD can endure chemical adsorption on the fluorite surface. The stretching oscillation peaks in the 1000~1500 cm−1 band and the hydroxyl peaks in water in the 3000~3200 cm−1 band likely belong to the C–H, -OH, and other groups of PD, or the stretching vibration of O–H for the absorbed water. The electrostatic adsorption of PD occurs on the fluorite surface.
These findings show that PD electrostatically adsorbs and chemisorbs onto the surface of fluorite concurrently, whereas no clear interactions are detected between scheelite and PD.

3.5. XPS Results

Figure 8a illustrates the survey scan spectra for scheelite with and without PD processing over a range of binding energy of approximately 0–1000 eV. Following the processing of the scheelite surface with PD, the survey spectra of XPS for scheelite without PD processing are approximately similar. The O, W, and Ca elements are identified for scheelite, which agrees with the related molecular structure. Table 1 presents the surface atomic contents of N, O, W, Ca, and C. The content of N in CaWO4 is slightly enhanced following its processing with PD, which is most likely because of instrumental uncertainties (e.g., air or other contaminants). The greater C content illustrates that the scheelite surface is likely polluted by unknown carbon sources. Minor reductions in the concentrations of O, W, and Ca demonstrate the inadequate reaction of the PD molecule with scheelite, which corresponds with the FTIR and zeta potential assessments explained in previous sections.
The spectra of Ca2p for scheelite with and without PD are presented in Figure 8b. The peaks of Ca in CaWO4 + PD shift toward greater binding energies at 346.28 eV and 349.78 eV, with a binding-energy alteration of approximately 0.1 eV. Thus, PD has a negligible effect on the chemical state of Ca atoms in the scheelite structure. These findings agree with the W2p spectrum outcomes (see Figure 8c). Hence, the absorption of PD onto the scheelite surface is limited though surface sites, reaction circumstances, and steric hindrances; these interaction procedures are complicated. NaOl is simply adsorbed onto the scheelite surface, unlike PD; it creates layers of the NaOl molecules to provide hydrophobic surfaces.
Figure 9a shows the survey scan spectra for fluorite with and without PD processing. By processing the fluorite surface with PD, the spectral peak of N becomes more potent than that of scheelite. Furthermore, the strength of the spectral peak of C improves more significantly than that of bare fluorite. Table 2 presents the atomic proportions of O, F, Ca, and C, which are 2.41%, 43.62%, 24.96%, and 29.01%, respectively. Following PD processing, the N atom emerges on the mineral’s surface with a 6.07% concentration, and the atomic concentrations of F, Ca, and C change to 30.64%, 17.79%, and 45.50%, respectively. Unlike the bare fluorite specimen, the fractions of F and Ca are reduced, and those of N and C are enhanced. These phenomena illustrate the creation of PD entities on the fluorite surface. The mineral surfaces with PD require further assessment. In particular, the chemisorption site of fluorite with PD can be Ca2+ in the fluorite solution.
Figure 9b shows that the fluorite which is not processed with PD is carefully fitted with two spin-orbit split peaks, and the binding energies are 351.28 and 347.68 eV for Ca2p1/2 and Ca2p3/2, respectively. The fluorite peaks for CaF2 + PD move toward greater binding energies at 351.63 and 348.03 eV, which significantly alter the binding energy at about 0.35 eV. Thus, PD has a considerably strong effect on the chemical state of the Ca atoms of fluorite. The F1s peak required further assessment, considering the characteristics of the new Ca spectra (see Figure 9c). Following PD processing, one single spectral peak shifts to 684.5 and 685.7 eV, suggesting that when PD is adsorbed onto the fluorite surface, it is effectively bound to the surface with high behavioral possibilities via the polycarboxylate group. This observation implies that the surface chemistry reaction is slightly complex. Hence, the reactions of PD with fluorite occur spontaneously, and multiple layers of adsorption onto the fluorite surface strongly hinder that of NaOl.

3.6. Adsorption Mechanisms

On the basis of the flotation outcomes and surface assessments, we conclude that the adsorption of PD onto the fluorite surface occurs haphazardly, and its pre-adsorption considerably restricts the adsorption of NaOl onto the fluorite surface. Thus, the fluorite flotation is greatly reduced. Generally, the adsorption performances of diverse reagents, such as collectors and depressants, on various mineral surfaces are related to the interactions of the active groups in the molecules with the subjected chemical constituents on the mineral surfaces. Therefore, the chemical behaviors of PD and NaOl in solutions that adsorb onto fluorite and scheelite surfaces are important criteria, which influence the selective adsorption of reagents.
Based on the finding of [48], we aimed to sufficiently explain the dissolution depression of adsorption in the PD dissolution retardation in fluorite and scheelite, including in aqueous systems. The five carboxylic acid groups of PD and the long carbon chain of NaOl cause the hydrolysis products of PD and NaOl to become complex structures in the solution [49,50]. The procedure is well-ionized [51,52], as illustrated in Figure 10 and Figure 11.
Figure 10 shows that under weak alkaline and acidic circumstances, NaOl occurs mostly in the form of oleate molecules. By increasing the pH value, the oleate content ions and their dimer entities are enhanced, and the correlation complex of oleate molecules reaches its maximum at a high pH value before it is gradually reduced. Most species in the solutions are (RCOO−)22− and RCOO− when the pH is 9. In addition, PD is nearly always ionic, except in highly acidic environments. The fundamental species in the solutions are mostly H2L3− and HL4− (3- or 4-carboxyl states) when the pH is 9, as shown in Figure 11. Therefore, the volume and molecular weight of the ionized component of NaOl are larger than those of PD; however, the negative charge of the ionized component of PD is much larger than that of NaOl.
Scheelite has a negative surface charge because of the inconsistent hydration rates of ions. In addition, during scheelite hydration, Ca points coordinate with the oxygen atoms of two water molecules, increasing the negative surface polarity. Numerous anions are greatly repulsed by the scheelite surface after PD ionization, and the adsorption is not complete. The adsorption of NaOl is a single coordination [54,55,56]. NaOl has a high coverage of Ca particles on white mineral surfaces, and is unaffected by PD because of the spatial hindrance of large long-carbon chain groups between two adjacent particles and the electrostatic repulsion of surface ions. There is only one type of chemical bond, Ca–F, in the fluorite crystal, and the F ion is small, resulting in more Ca particles on the fluorite surface than on the scheelite surface. The Ca sites for NaOl adsorption decrease when PD bonds with the Ca sites, resulting in limited adsorption amounts of NaOl on the fluorite surface. Furthermore, PD (3- or 4-carboxyl state) chelate pre-adsorbed onto the fluorite surface significantly enhances the negative charge of fluorite and fills considerable surface space, which consequently hinders the adsorption of NaOl onto the fluorite surface through steric hindrance and electrostatic repulsion. Hence, when PD is present, the fluorite flotation reduces significantly and exhibits lower floatability. In such cases, we achieve efficient separation of scheelite from fluorite through direct flotation. To sum up, according to the analysis of adsorption, Figure 12 presents the adsorption mechanism of NaOl and PD on the scheelite and fluorite surfaces.

4. Conclusions

In this study, PD was comprehensively investigated as a highly efficient depressor in the separation of fluorite and scheelite. The flotation analyses, adsorption test, and zeta potential tests showed that the interactions of PD with the scheelite surface had lower effects on the chemisorption of NaOl. Owing to the chemical and electrostatic adsorption of PD on the fluorite surface, the adsorption of NaOl on the fluorite surface was substantially weakened in the target pH range. Furthermore, the results of XPS and FTIR spectroscopy demonstrated that the groups of carboxyl repeatedly formed from PD are a desirable configuration of adsorption on the fluorite surface. This study provides important prospects on the flotation separation of calcium-bearing minerals with organic small-molecule polycarboxyl group depressors and anionic collectors. Moreover, the study shows that exploring the inhibition impacts and the mechanisms of selective adsorption on the fluorite and scheelite surfaces is essential when separating fluorite and scheelite in the floatation.

Author Contributions

Formal analysis, C.Z.; investigation, H.W., C.W. and S.Z.; methodology, Y.H.; resources, W.S. and Y.H.; writing—original draft, C.Z.; writing—review and editing, P.C. and C.Z.; project administration, W.S. and Y.H. 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 Guizhou Province (qian ke he ji chu [2020]1Y218); the Young Talents Foundation of the Education Department of Guizhou Province (qian jiao he KY zi [2019]136) and the Scientific and Technological Innovation Platform of Liupanshui (52020-2019-05-06 and 52020-2019-05-08); the Academician Workstation of Liupanshui Normal University (qiankehepingtairencai-YSZ [2021]001 hao); and the Fund of Liupanshui Normal University (LPSSYKJTD201906).

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Minerals 12 00530 g001 550
Figure 1. Pentasodium diethylenetriaminepentaacetate (PD)’s structure.
Figure 1. Pentasodium diethylenetriaminepentaacetate (PD)’s structure.
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Figure 2. (a) XRD spectra of the scheelite and (b) fluorite test samples.
Figure 2. (a) XRD spectra of the scheelite and (b) fluorite test samples.
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Figure 3. Recovery of scheelite and fluorite as a function of the (a) pH and (b) NaOl concentration.
Figure 3. Recovery of scheelite and fluorite as a function of the (a) pH and (b) NaOl concentration.
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Figure 4. Recovery of scheelite and fluorite as a function of PD (NaOl: 1.5 × 10−4 mol/L; pH: 9.0).
Figure 4. Recovery of scheelite and fluorite as a function of PD (NaOl: 1.5 × 10−4 mol/L; pH: 9.0).
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Figure 5. NaOl adsorption by scheelite and fluorite as a function of the PD concentration when pH = 9.
Figure 5. NaOl adsorption by scheelite and fluorite as a function of the PD concentration when pH = 9.
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Figure 6. Effects of adding different reagents on the zeta potentials of (a) scheelite and (b) fluorite (NaOl = 1.5 × 10−5 mol/L; PD = 1.6 × 10−4 mol/L).
Figure 6. Effects of adding different reagents on the zeta potentials of (a) scheelite and (b) fluorite (NaOl = 1.5 × 10−5 mol/L; PD = 1.6 × 10−4 mol/L).
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Figure 7. FTIR spectra of (a) scheelite and (b) fluorite before and after interaction with PD.
Figure 7. FTIR spectra of (a) scheelite and (b) fluorite before and after interaction with PD.
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Figure 8. (a) Survey and high-resolution (b) Ca2p and (c) W2p XPS spectra recorded for scheelite pre- and post-PD processing.
Figure 8. (a) Survey and high-resolution (b) Ca2p and (c) W2p XPS spectra recorded for scheelite pre- and post-PD processing.
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Figure 9. (a) Survey and high-resolution (b) Ca2p and (c) F1s XPS spectra recorded for fluorite pre- and post-PD processing.
Figure 9. (a) Survey and high-resolution (b) Ca2p and (c) F1s XPS spectra recorded for fluorite pre- and post-PD processing.
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Figure 10. Hydrolysis species distribution of NaOl in aqueous solutions as a function of pH.
Figure 10. Hydrolysis species distribution of NaOl in aqueous solutions as a function of pH.
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Figure 11. Distribution coefficients for the complexes of PD in aqueous solutions as a function of pH (ionization constant [53]: pKa1 = 2.06; pKa2 = 2.73; pKa3 = 4.28; pKa4 = 8.65; and pKa5 = 10.59).
Figure 11. Distribution coefficients for the complexes of PD in aqueous solutions as a function of pH (ionization constant [53]: pKa1 = 2.06; pKa2 = 2.73; pKa3 = 4.28; pKa4 = 8.65; and pKa5 = 10.59).
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Figure 12. NaOl and PD adsorption mechanisms on scheelite and fluorite surfaces.
Figure 12. NaOl and PD adsorption mechanisms on scheelite and fluorite surfaces.
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Table
Table 1. Elemental composition of CaWO4 with and without PD on its surface.
Table 1. Elemental composition of CaWO4 with and without PD on its surface.
SimpleAtomic Concentration (%)
CCaWON
CaWO4 (untreated)28.6912.3511.0746.801.09
CaWO4 + PD31.4210.5910.5745.142.28
Table
Table 2. Elemental composition of CaF2 with and without PD on its surface.
Table 2. Elemental composition of CaF2 with and without PD on its surface.
SimpleAtomic Concentration (%)
CCaFN
CaF2 (untreated)29.0124.9643.622.41
CaF2 + PD45.5017.7930.646.07
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Zhang, C.; Wu, H.; Sun, W.; Hu, Y.; Wang, C.; Zhu, S.; Chen, P. Investigation of the Flotation Separation of Scheelite from Fluorite with a Novel Chelating Agent: Pentasodium Diethylenetriaminepentaacetate. Minerals 2022, 12, 530. https://doi.org/10.3390/min12050530

AMA Style

Zhang C, Wu H, Sun W, Hu Y, Wang C, Zhu S, Chen P. Investigation of the Flotation Separation of Scheelite from Fluorite with a Novel Chelating Agent: Pentasodium Diethylenetriaminepentaacetate. Minerals. 2022; 12(5):530. https://doi.org/10.3390/min12050530

Chicago/Turabian Style

Zhang, Chenhu, Haijun Wu, Wei Sun, Yuehua Hu, Chengyong Wang, Shan Zhu, and Peng Chen. 2022. "Investigation of the Flotation Separation of Scheelite from Fluorite with a Novel Chelating Agent: Pentasodium Diethylenetriaminepentaacetate" Minerals 12, no. 5: 530. https://doi.org/10.3390/min12050530

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