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Article

Selective Adsorption of 2-Hydroxy-3-Naphthalene Hydroxamic Acid on the Surface of Bastnaesite and Calcite

by
Wenliang Xiong
1,2,3,
Maoyuan Wang
1,2,3,*,
Junhui Xiao
4 and
Da Chen
1,2,3
1
Institute of Multipurpose Utilization of Mineral Resources, Chinese Academy of Geological Sciences, Chengdu 610041, China
2
Sichuan Rare Earth Technology Innovation Center, Chengdu 610041, China
3
Engineering and Technology Innovation Center for Comprehensive Utilization of Strategic Minerals, Ministry of Natural Resources, Chengdu 610041, China
4
School of Environment and Resource, Southwest University of Science and Technology, Mianyang 621010, China
*
Author to whom correspondence should be addressed.
Minerals 2022, 12(11), 1341; https://doi.org/10.3390/min12111341
Submission received: 3 October 2022 / Revised: 19 October 2022 / Accepted: 20 October 2022 / Published: 22 October 2022
(This article belongs to the Section Mineral Processing and Extractive Metallurgy)
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Abstract

:
In this study, 2-hydroxy-3-naphthalene hydroxamic acid (NHA) was used as a collector in microflotation experiments. By comparing the flotation performance of NHA with that of sodium oleate (NaOL) and salicylhydroxamic acid (SHA) commonly used in industry, the performance of NHA in the flotation separation of bastnaesite and calcite was studied. Potentiodynamic (zeta) measurements, Fourier transform infrared spectroscopy (FTIR) measurements and X-ray photoelectron spectroscopy (XPS) measurements were used to reveal the interaction mechanism of bastnaesite with NHA. The results of the pure mineral microflotation test showed that when the pH value was 9 and the dosage of NHA was 4.0 × 10−4 mol/L, the recovery of bastnaesite reached 93.5%. A concentrate with a bastnaesite grade of 87.08% was obtained from the flotation test of artificially mixed ore, and the recovery of bastnaesite was 90.83%. The zeta measurements and FTIR experiments showed that NHA adsorbed onto the surface of bastnaesite, which changed the surface state of bastnaesite. XPS testing showed that NHA chemically adsorbed onto the bastnaesite, and Ce3+ formed a chelated structure with − C ( OH ) = NO − . The hydrophobicity of the surface of bastnaesite was improved, which made it easier for bastnaesite to adhere to the slurry surface by bubbles. At present, most of the domestic methods for recovering fine-grained bastnaesite use flotation recovery. Calcite and other gangue minerals inevitably enter into the concentrate resulting in low-grade REE concentrate.

1. Introduction

Rare earth elements consist of 17 metal elements in the periodic table, such as lanthanides, scandium and yttrium, including light, medium and heavy REEs [1,2]. Light REEs are widely used in catalysis, superconductivity, the chemical industry and other fields because of their unique physical and chemical properties [3,4]. Along with the development of technology, the demand for light REEs has increased dramatically [5,6]. China is a major source of rare earth resources, with reserves accounting for approximately 35% of the global rare earth reserves and supplying more than 90% of the global market. Bastnaesite is the main mineral source from which rare earth elements are extracted at present [7,8]. Compared with gravity separation and magnetic separation, flotation is the most effective method for recovering fine bastnaesite. It can effectively separate valuable minerals and gangue minerals by using the difference in mineral surface hydrophobicity [9,10,11]. The flotation collector can be selectively adsorbed on the valuable mineral to increase its surface hydrophobicity, so that the surface hydrophobicity of the valuable mineral and gangue mineral is different [12,13].
Fatty acids and hydroxamic acids are the main collectors used in foam flotation of rare earth minerals [14,15,16]. The carboxyl group of fatty acid collectors can react with metal ions on the mineral surface to form metal ion carboxylates, and the lower solubilities of metal ion carboxylates means that fatty acids are more strongly adsorbed onto the mineral surface [17,18]. The carboxylate salt of the Ce3+ ion has similar solubility to Ca2+, and bastnaesite is often associated with calcium-bearing vein minerals, such as fluorite (CaF2) and calcite (CaCO3) [19,20]. Thus, fatty acid collectors showed unsatisfactory selectivity in bastnaesite flotation since calcite and other gangue minerals inevitably enter into the concentrate, resulting in low-grade REE concentrate [21]. Therefore, it is difficult to obtain satisfactory results by using only a single flotation agent, and it is necessary to use targeted agents and a reasonable reagent system to separate rare earth elements from complex ores. However, fatty acids with low selectivity can be used only in the initial nonselective flotation stage, and hydroxamic acid collectors can be used to selectively recover bastnaesite in the later cleaning stage [22]. Hydroxamic acid shows better selectivity than fatty acid collectors [23]. Hydroxamic acid collectors have the dual properties of “amide” and “oxime”, have strong coordination with metal ions on the surfaces of minerals through hydroxyl and N-bonded oxygen atoms and strongly form chelates with highly charged rare earth element cations but weakly form chelates with alkaline earth metal ions, such as Ca2+ and Mg2+ [24,25]. Therefore, they have been more studied and more widely used as selective collectors for rare earth minerals [26,27,28,29].
NaOL, NHA and SHA are three widely used collectors in bastnaesite flotation. In this paper, the collection properties of these three collectors were studied through microflotation experiments. In addition, the mechanism of NHA in collecting bastnaesite was systematically discussed by means of potentiodynamics, infrared spectroscopy and XPS. The conclusion will provide a reference for the future design and development of new flotation collectors for bastnaesite.

2. Materials and Methods

2.1. Materials

The bastnaesite and calcite utilized in the tests are from Sichuan and Hubei, China, respectively. The purities of the bastnaesite and calcite based on X-ray diffraction (Figure 1) and chemical analysis (Table 1 and Table 2), which proved their high purities, satisfied the test requirements. Large samples of both minerals were first dry milled using ceramic balls, and the resulting product was dry sieved. The size of − 75 + 45 μm was used for the microflotation experiment, and a finer fraction with a size less than 5 μm was used for zeta potential measurements, FTIR spectroscopy, and XPS tests.
The test regulators (NaOH and HCl), and collectors (2-hydroxy-3-naphthalene hydroxamic acid, salicylhydroxamic acid and sodium oleate) were all analytically pure. All tests were performed using deionized water.

2.2. Flotation Experiments

Microflotation tests were carried out using an XFG II flotation machine with an impeller speed set at 1780 rpm and a 50 mL flotation tank, as shown in Figure 2. The flotation test procedure is shown in Figure 3. Bastnaesite or calcite particles (2.0 g) were mixed with 35 mL of deionized water and stirred in a flotation cell for 2 min to prepare the flotation pulp. Afterwards, a pH regulator (NaOH or HCl), collector (NaOL, SHA or NHA) and foaming agent (terpineol) were added to the flotation cell every 3 min in sequence, and the bubble flotation time lasted for 4 min. Recovery was calculated by weighing the dried concentrate of each sample three times, and the average was calculated. The main influencing factors, such as pH value and the amount of collector, were studied, and the optimum separation conditions of bastnaesite and calcite were determined.

2.3. Zeta potential Measurements

The zeta potential of bastnaesite and calcite samples before and after flotation reagent was measured using a Malvern Zetasizer nano ZS instrument. The flotation reagent sample preparation method was as follows: 30 mg of a single mineral (after fine grinding to −5 μm) was placed in a conical flask, 35 mL of deionized water was added to the flask and the pulp was adjusted according to the single mineral flotation process. The pulp was oscillated in a constant temperature shaker for 30 min. The pH value of the pulp was measured, and the supernatant was centrifuged to measure the zeta potential of the sample. The results of three measurements were averaged to give the final result.

2.4. FTIR Measurements

A measure of 35 mL of deionized water was poured into a beaker containing a fine mineral sample with a particle size less than 5 μm, 40 mg/L SS was added and stirred for 1 h, and then 4 × 10−4 mol/L SHA was added and agitated for 1 h. After agitation, the suspension was cooled, and the mineral particles treated with flotation reagents were washed three times with deionized water. Finally, the ore samples were filtered and dried in a vacuum oven at 40 °C. The potassium bromide (KBr) disk method was used to prepare samples from dried mineral particles, and the FTIR spectra were obtained using an IRffinity-1 Fourier transform infrared spectrometer (Shimadzu, Japan). The spectral data area was 400–4000 cm−1.

2.5. XPS Measurements

XPS images were measured using a Thermo ScientificESCALab 250Xi XPS tester. XPS spectra of bastnaesite (or calcite) before and after flotation reagent treatment were analyzed to clarify their concrete form. The sample preparation process was the same as that for FTIR.

3. Results

3.1. Microflotation Results

3.1.1. Pure Mineral Flotation Tests

The pH of the slurry is one of the important influencing factors affecting flotation recovery [30]. Flotation experiments were conducted using 1.0 × 10−4 mol/L NHA (SHA or NaOL) and 20 mg/L terpineol, and the results are shown in Figure 4a. With NHA and SHA, the recovery rate of bastnaesite increased as the pH of the pulp increased from 2 to 10, reaching a maximum of approximately 92% at a pH of 9–10, and when using NaOL the recovery rate of bastnaesite was maximized between pH 6–8. When using NaOL as a collector, the recovery of calcite increased sharply to approximately 92% as the pH increased from 2 to 10, and the recovery remained stable as the pH continued to increase. When SHA was used as a collector, the recovery of calcite increased from 2 to approximately 40% as the pH increased from 10, and as the pH continued to increase, the recovery of calcite began to decrease. When NHA was used as a collector, the calcite recovery was less than 20% as the pH increased from 12. The order of the recovery capacity of calcite is NaOL > SHA > NHA. At pH 8–10, calcite recoveries using SHA harvesters are much higher than calcite recoveries using NHA harvesters. The results show that NHA has a good ability to collect bastnaesite. When the pH value is 9, NHA has a strong selectivity for bastnaesite.
The amount of collector used can significantly affect the flotation test. The flotation tests were conducted using a slurry at pH 9 and 20 mg/L terpineol, and the results are shown in Figure 4b. At a pH of 9, the recovery of bastnaesite or calcite increased as the amount of collector increased. When NHA was used as a collector, using this method, the maximum recovery of bastnaesite reached 93.51% at a dosage of 4.0 × 10−4 mol/L. The recovery of bastnaesite was 93.29% (NaOL) or 90.34% (SHA) at the same dosage. The recovery of calcite in the flotation test was 20.1% (NHA), 96.72% (NaOL) or 43.7% (SHA) at a dosage of 4.0 × 10−4 mol/L. Thus, when NHA is used as a collector, the recovery of bastnaesite and calcite differs by more than 65% compared to NaOL or BHA as a collector at different doses. It can be concluded that NHA has a good harvesting capacity and, in addition, under the same conditions, NHA is also highly selective for bastnaesite.
Figure 4c shows the relationship between the recoveries of bastnaesite and calcite and the dosage of terpineol at pH 9 and 4.0 × 10−4 mol/L NaOL and SHA or NHA. In the range of terpineol studied, when NaOL was used, the recoveries of bastnaesite and calcite were similar. The recovery rate of bastnaesite using SHA or NHA gradually increased. At 0 mg/L terpineol, the recovery of bastnaesite with SHA was slightly higher than that with NHA, and SHA may have had a better foaming ability than NHA, reaching a saturation value at 20 mg/L, and both recovery rates reached approximately 90%. The recovery of calcite increased slightly with the amount of terpineol when SHA was used and reached saturation when the amount of terpineol was 15 mg/L. When NHA was used as a collector, the increase in terpineol dosage had little effect on the recovery of calcite, which indicates that NHA rarely adsorbs onto the surface of calcite at pH 9, which makes it difficult for the calcite to float.

3.1.2. Flotation Separation Tests of Mixed Ore

To evaluate the selection performance of collectors NaOL, SHA and NHA, the flotation of 2.0 g artificially mixed minerals consisting of bastnaesite and calcite at a mass ratio of 1:1 was studied at pH 9.0 and 20 mg/L terpineol with three collectors in the range of 4 × 10−4 mol/L, and the best results are shown in Table 3.
Table 3 shows that the NHA collector obtained bastnaesite with a grade of 87.08% and a recovery of 90.83%. SHA had a low collecting ability. When SHA was used as the collector, the grade of bastnaesite was 66.98%, and the recovery was 80.68%. NaOL had a strong collection ability but low selectivity. Therefore, the NaOL collector obtained bastnaesite with a grade of 47.98% and a recovery of 86.86%. These results further confirm that NHA performs better than SHA or NaOL in the flotation separation of bastnaesite and calcite.
In order to compare the usability of the three collectors in industrial production, the cost of flotation agent consumption in the beneficiation process was simply estimated (technical grade), as shown in Table 4. It was found that SHA has the highest cost as a flotation agent and NHA and NaOL have similar costs, however, NHA is much better than NaOL in terms of selectivity. Therefore, NHA can be used as a better collector of bastnaesite.

3.2. Zeta Potential Analysis

In the flotation process, zeta potential analysis is an important reference method used for interpreting mineral surface properties. Flotation agents exist in different forms at different pH conditions, and they are adsorbed on the surface of minerals thus affecting the zeta potential of minerals [31,32,33]. Figure 5 shows the variation in zeta potential of bastnaesite and calcite samples with/without 4 × 10−4 mol/L collector (NHA, SHA, NaOL) by pH value. The isoelectric points (IEP) of pure bastnaesite and calcite are about 7.2 and 9.3, respectively, which are consistent with previous studies [19,32]. In the presence of collectors (SHA, NaOL), the zeta potentials of the bastnaesite and calcite samples are more negative than those of the pure bastnaesite and calcite samples. The change in IEP can be explained by the collector being adsorbed onto the surface of bastnaesite or calcite, thereby reducing the IEP. The three kinds of collectors are anionic collectors so when the pulp pH value is greater than the IEP, and if there is only electrostatic force, the collector should not be adsorbed onto the surface of bastnaesite or calcite. However, when the surface is negatively charged, the zeta potential of bastnaesite or calcite still decreases. The results show that there is a new effect between NaOL or SHA and bastnaesite or calcite, which is much stronger than the electrostatic effect. In addition, compared with calcite, SHA can significantly reduce the zeta potential of bastnaesite, which could explain why SHA is more easily adsorbed onto the surface of bastnaesite. When pH > 7, there were 20 potential point differences between NHA-treated bastnaesite and pure bastnaesite, indicating that NHA adsorption onto the surface of bastnaesite involved not only physical adsorption but also chemical adsorption. When pH > 10, the calcite site of NHA was almost unchanged, which may indicate that there is no chemical adsorption between NHA and calcite. NHA is an anionic collector. When calcite has a positive potential, its adsorption behavior involves electrostatic adsorption or van der Waals forces and other physical adsorption, resulting in a change in calcite potential.

3.3. Fourier Transform Infrared (FTIR) Spectroscopic Test Results

Figure 6 shows the FTIR spectra before and after the interaction of minerals and reagents. Table 5 shows the main bands corresponding to the relevant chemical bonds. In the FTIR spectra of NHA, 3752 cm−1 and 3625 cm−1 are the stretching vibrations of -OH with CH3 on the aromatic ring; the characteristic peak near 1535 cm−1 in the spectrum corresponds to the stretching vibration of naphthalene rings C=H and C=C. The spectra at 1101 cm−1 and 875 cm−1 are the symmetric and asymmetric stretching vibrations of =N-O and -C-N, respectively, which are the main functional groups of NHA [28,33]. Figure 6a shows the FTIR spectra of bastnaesite samples with and without NHA treatment. The characteristic peaks of CO 3 2 − group in pure bastnaesite spectrum are 729 cm−1, 868 cm−1, 1087 cm−1 and 1448.56 cm−1 [34]. The new characteristic peaks at 3732 cm−1, 3672 cm−1 and 3648 cm−1 of bastnaesite treated with NHA are caused by the tensile vibration of N-H and C-O [35,36], and the characteristic peaks at 665 cm−1 are caused by the bending of naphthyl ring C-H out of plane [28,36,37].
Figure 6b shows the infrared spectra of calcite treated with/without NHA. For pure calcite, the characteristic peaks at 872 cm−1 and 710 cm−1 are attributed to the deformation vibration of C-O, and the tensile vibration of C-O corresponds to the characteristic peak at 1421 cm−1 [38,39]. After the calcite was treated with NHA, there was no new band in NHA, indicating that NHA had little or no chemical adsorption on the calcite surface.
The FTIR test showed that NHA formed a new characteristic peak after interaction with bastnaesite, while calcite had no significant change after NHA treatment, indicating that NHA did not undergo chemical adsorption on the surface of calcite, which further confirmed the selective adsorption of NHA on the surface of bastnaesite.

3.4. XPS Measurement Results

XPS is an analytical method used to study the adsorption behavior of reagents on the surface of minerals. The adsorption behavior of NHA on two mineral surfaces was studied by XPS method. The concentration of NHA was 4 × 10−4 mol/L [40,41].
The relative atomic concentration changes before and after the interactions between NHA and the minerals are shown in Table 6. Before NHA treatment, the XPS spectra of pure bastnaesite and calcite did not contain the peak of impurity N1S, indicating the high purity of the tested bastnaesite and calcite samples. After NHA treatment, the N atom concentrations on the surface of ceria and calcite were 2.91% and 1.22%, respectively, and the C atom concentration was higher than that of pure ceria and calcite. The surface relative atomic concentration of bastnaesite was more obvious than that of calcite. In particular, the significant increase in N content indicates that a large amount of NHA was adsorbed on the surface of bastnaesite. In contrast, only a small amount of NHA was adsorbed on the calcite surface. To further investigate the adsorption of NHA on the surface of bastnaesite and calcite, the spectra of XPS with/without flotation reagents were investigated and are shown in Figure 7. After NHA treatment, the spectrum of calcite did not change significantly from that before NHA treatment, which indicates that the adsorption of NHA on the surface of calcite is very weak. However, a new N1S peak appeared on the surface of the bastnaesite after NHA treatment, indicating that a large amount of NHA covered the bastnaesite surface. Thus, the strong adsorption of NHA on bastnaesite contributes to the selective recovery of bastnaesite, which corresponds to the flotation results.
Figure 8 shows the high-resolution XPS spectra of Ce 3d5/2, C 1s, O 1s and N 1s treated with/without NHA. In the pure bastnaesite spectrum, the three-dimensional Ce spectrum is composed of spin-orbit splitting 3d5/2 and 3d3/2 nuclear pores, and the 3d5/2 and 3d3/2 spectra are closely linked. Usually, the binding energy of 3d3/2 is 18–19 eV higher than that of 3d5/2 and the strength ratio of 3d5/2 to 3d3/2 is 1.5 [16,19]. Figure 8a shows the high-resolution Ce 3d5/2 XPS spectra of pure and NHA-treated bastnaesite samples, and Table 7 shows the detailed analysis results of Ce 3d5/2 XPS spectra. The peaks near 885.66 eV and 882.84 eV are characteristic spectral characteristics of Ce(III) [19]. The peaks at 888.18 eV and 888.18 eV are more likely to be related to Ce(IV), which may be due to the complex electronic configuration of the Ce atom and the influence of the F atom on the crystal structure of bastnaesite [16,19]. The Ce 3d5/2 peak has been confirmed to decrease by 0.18 ± 0.02 eV after NHA treatment. The lower binding energy means that NHA adsorbs Ce onto the surface of bastnaesite through chemical adsorption.
Figure 8b shows the high-resolution C 1s XPS spectra of pure and NHA-treated bastnaesite samples, and Table 8 shows the detailed analysis results of C 1s XPS spectra. The results show that the C 1s of pure bastnaesite can be fitted to two component peaks at binding energies of 284.77 eV and 289.31 eV from C-C and CO 3 2 − , respectively. In the C 1s XPS spectra of NHA-treated bastnaesite, the peaks at 284.77 eV and 289.31 eV moved forward 0.22 ± 0.02. This may be due to the superposition of   CO 3 2 − on the surface of bastnaesite and the C=O in NHA [19,34,42].
Figure 8c shows the high-resolution O 1s XPS spectra of pure and NHA-treated bastnaesite samples, and Table 9 shows the detailed analysis results of O 1s XPS spectra. The results show that the O 1s spectrum of pure bastnaesite can be fitted to two component peaks at binding energies of 531.55 eV and 533.11 eV from CO 3 2 − and Ce-OH, respectively [19,42]. In the O 1s XPS spectra of NHA-treated bastnaesite, compared with pure bastnaesite, the O 1s XPS peak of CO 3 2 − shifts 0.23 eV in the positive direction because the naphthalene ring in NHA binds to the -OH group [34,43]. The positive shift of the O 1s XPS peak in Ce-OH at 0.21 eV is due to the C=O in NHA [21,43].
In addition, the detailed analysis results of N 1s XPS spectra from Figure 8d and Table 10 show that N 1s spectra were also detected for the NHA-treated bastnaesite surface, which is due to the N atom in -C(OH)=NO- and -C(=O)-NHO- It was further confirmed that NHA chelates with bastnaesite to form new bonds and chemical adsorption occurs [28,44].
Figure 9a shows the high-resolution Ca 2p XPS spectra of pure and NHA-treated calcite samples. In the XPS spectra of pure calcite samples, the peaks of Ca 2p3/2 and Ca 2p1/2 are located at binding energies of 347.78 eV and 351.30 eV, respectively [45]. The spectra of calcite samples treated with NHA show that the binding energies of the Ca 2p3/2 and Ca 2p1/2 peaks shift slightly compared with those of pure calcite samples, and the deviations are 0.10 eV and 0.02 eV (<0.20 eV), respectively, which are less than the instrument error.
Figure 9b shows the high-resolution O 1s XPS spectra of pure and NHA-treated calcite samples. In the XPS spectra of pure calcite samples, the O 1s peak is attributed to   CO 3 2 − [40,45]. In the XPS spectra of calcite samples treated with NHA, no characteristic peaks of the naphthalene ring and C=O of NHA appeared, and the binding energy deviation of the O 1s peak was also within the instrument error range.
Figure 9c shows that the N 1s spectra of calcite treated with NHA are chaotic, and no specific N 1s peaks are found. This result better indicates that NHA is not adsorbed onto the surface of calcite.
As discussed, the different active adsorption sites (Ce3+ or Ca2+ ions) exposed to bastnaesite and calcite surfaces led to the different adsorption behaviors of NHA. The XPS test results are consistent with the above experimental results; that is, the recovery of bastnaesite is higher than that of calcite, and the adsorption of NHA onto the bastnaesite surface is stronger than its adsorption onto the calcite surface.

3.5. Discussion

Calcite is a common calcium gangue mineral, often associated with bastnaesite. The work of other scholars has shown that the flotation separation of bastnaesite from calcite is very difficult and therefore requires the extensive use of inhibitors. The development of high-selectivity collectors is an important task for effective flotation separation of bastnaesite and calcite.
According to the experimental results and analyses, NHA can be chemisorbed onto the bastnaesite surface resulting in enhanced floatability, and NHA and calcite are mainly physically adsorbed. This is because Ce3+ ions can form new chemical bonds with NHA, while Ca2+ ions cannot react with NHA directly, resulting in great differences in the adsorption capacity of NHA between the two minerals. This is the reason for the significantly better floatability of bastnaesite compared to that of calcite. The adsorption model of flotation reagents on the mineral surfaces is shown in Figure 10.

4. Conclusions

The results of microflotation experiments show that 2-hydroxy-3-naphthyl hydroxamic acid (NHA) has excellent selectivity in the flotation separation of bastnaesite and calcite. The interaction mechanism between NHA and the surface of bastnaesite and calcite was investigated by zeta potential measurement, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS).
The results of microflotation experiments show that NHA has better flotation performance than traditional industrial collectors (NaOL, SHA). NHA not only has better selectivity than SHA, but also shows strong harvesting capacity, which is close to NaOL. Zeta potential results show that NHA is more easily absorbed by bastnaesite than calcite, and NHA has both electrostatic adsorption and other physical adsorption on the bastnaesite surface. FTIR measurement results further indicated that NHA significantly changed the surface state of bastnaesite and verified that NHA had chemical adsorption on the surface of bastnaesite in addition to physical adsorption and generated new chemical bonds. XPS measurements showed that NHA reacted with bastnaesite. The addition of NHA significantly increased the content of N on the surface of bastnaesite, and the binding energy of the Ce 3d peak changed obviously, indicating that NHA chelates with bastnaesite to form new bonds leading to chemical adsorption, and Ce3+ ions on the surface of bastnaesite formed the active site for NHA adsorption.

Author Contributions

W.X.: Data curation, Investigation, Visualization. M.W.: Data curation, Writing original draft, Writing—review & editing, Software, Validation. J.X.: Methodology, Investigation. D.C.: Funding acquisition, Supervision. All authors have read and agreed to the published version of the manuscript.

Funding

The authors gratefully acknowledge the financial support of the Youth Talent Project of China’s Ministry of Natural Resources, grant number B1901, 12110600000018003914.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Minerals 12 01341 g001 550
Figure 1. XRD spectra of bastnaesite (a) and calcite (b) particles.
Figure 1. XRD spectra of bastnaesite (a) and calcite (b) particles.
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Minerals 12 01341 g002 550
Figure 2. XFG flotation machine used for the flotation tests.
Figure 2. XFG flotation machine used for the flotation tests.
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Minerals 12 01341 g003 550
Figure 3. Flotation experiment process.
Figure 3. Flotation experiment process.
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Minerals 12 01341 g004 550
Figure 4. Recoveries of bastnaesite and calcite as a function of pH (a), and dosages of NaOL,2-OH-3-NHA, SHA (b) and terpineol (c), respectively.
Figure 4. Recoveries of bastnaesite and calcite as a function of pH (a), and dosages of NaOL,2-OH-3-NHA, SHA (b) and terpineol (c), respectively.
Minerals 12 01341 g004
Minerals 12 01341 g005 550
Figure 5. Zeta potential measurement results of bastnaesite (a) and calcite (b).
Figure 5. Zeta potential measurement results of bastnaesite (a) and calcite (b).
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Minerals 12 01341 g006 550
Figure 6. FTIR spectra of pure, 2-OH-3-NHA-treated bastnaesite (a) and pure, 2-OH-3-NHA-treated calcite (b).
Figure 6. FTIR spectra of pure, 2-OH-3-NHA-treated bastnaesite (a) and pure, 2-OH-3-NHA-treated calcite (b).
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Minerals 12 01341 g007 550
Figure 7. FTIR spectra of pure, NHA-treated bastnaesite (a) and pure, 2-OH-3-NHA-treated calcite (b).
Figure 7. FTIR spectra of pure, NHA-treated bastnaesite (a) and pure, 2-OH-3-NHA-treated calcite (b).
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Minerals 12 01341 g008 550
Figure 8. High-resolution XPS spectra of Ce 3d5/2 (a), C 1 s (b), O 1 s (c) and N 1 s (d) of pure and NHA-treated bastnaesite particles, respectively.
Figure 8. High-resolution XPS spectra of Ce 3d5/2 (a), C 1 s (b), O 1 s (c) and N 1 s (d) of pure and NHA-treated bastnaesite particles, respectively.
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Minerals 12 01341 g009 550
Figure 9. High-resolution XPS spectra of Ca 2p (a), C 1 s (b) and N 1 s (c) of pure, NHA-treated calcite particles, respectively.
Figure 9. High-resolution XPS spectra of Ca 2p (a), C 1 s (b) and N 1 s (c) of pure, NHA-treated calcite particles, respectively.
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Minerals 12 01341 g010 550
Figure 10. Reaction of NHA with bastnaesite and fluorite surfaces.
Figure 10. Reaction of NHA with bastnaesite and fluorite surfaces.
Minerals 12 01341 g010
Table
Table 1. Chemical composition of bastnaesite powder samples (weight %).
Table 1. Chemical composition of bastnaesite powder samples (weight %).
ElementCeO2La2O3Nd2O3Pr2O3Gd2O3Sm2O3Fe2O3
Content35.28229.4767.0962.6240.5640.3001.248
ElementMoO3BaOPbOCaOSiO2ThO2Others
Content1.0551.0110.9140.6320.4160.3200.990
Table
Table 2. Chemical composition of calcite powder samples (weight %).
Table 2. Chemical composition of calcite powder samples (weight %).
ElementCaOSiO2MgOAl2O3SO3
Content55.7910.6590.3500.2950.023
ElementFe2O3ZnOSrOCuOOthers
Content0.1690.0230.0140.0050.012
Table
Table 3. The results of flotation separation of artificial mixed ore.
Table 3. The results of flotation separation of artificial mixed ore.
ProductYield(%)Bastnaesite Grade
(%)		Bastnaesite Recovery
(%)
NHAConcentrate53.0287.0890.83
Tailing46.989.929.17
Feed100.0050.83100.00
SHAConcentrate61.2366.9880.68
Tailing38.7725.3219.32
Feed100.0050.83100.00
NaOLConcentrate92.0247.9886.86
Tailing7.9883.6913.14
Feed100.0050.83100.00
Table
Table 4. Cost estimation of flotation agent consumption in industrial production.
Table 4. Cost estimation of flotation agent consumption in industrial production.
Type (T.P.)Price (Yuan/t)Dosage (G/t)Cost (Yuan/ton of ore)
NHA20,500.00 21.30 436.65
SHA45,500.00 15.30 696.15
NaOL13,500.00 30.40 410.40
Table
Table 5. The bands corresponding to the relevant chemical bond in FTIR spectra of the minerals.
Table 5. The bands corresponding to the relevant chemical bond in FTIR spectra of the minerals.
FTIRBand (cm−1)Chemical Bond
NHA3752-OH stretching vibration
3625CH3 stretching vibrations
1638C=H stretching vibrations
1535C=C stretching vibrations
1101=N-O anti-symmetric stretching vibration
875-C-N symmetric stretching vibration
Bastnaesite3584-OH stretching vibration
1824C=O and cation coordination
1445CO3 anti-symmetric stretching vibration
1087symmetric stretching vibration
867plane bending vibration
723in-plane bending vibration
Bastnaesite + NHA3732N-H stretching vibrations
3672C-H stretching vibrations
3648C-H stretching vibrations
665C-H plane bending vibration
Table
Table 6. Atomic concentrations of various elements on the surfaces of bastnaesite and calcite untreated and treated with NHA.
Table 6. Atomic concentrations of various elements on the surfaces of bastnaesite and calcite untreated and treated with NHA.
SamplesAtomic Concentration/%
CNOCeLaCaF
Bastnaesite32.51-44.704.536.65-11.61
NHA-treated bastnaesite40.032.9136.883.435.21-11.54
calcite32.24-52.07--15.69-
NHA-treated calcite36.031.2249.21--13.54-
Table
Table 7. Analysis results of Ce 3d5/2 XPS spectra of bastnaesite samples untreated and treated with NHA.
Table 7. Analysis results of Ce 3d5/2 XPS spectra of bastnaesite samples untreated and treated with NHA.
SamplesBinding Energy/eVChemical Shift/eVAssignment
Bastnaesite881.89/CeO2
883.98/Ce
886.09/CeH3/CeO2
888.18/Ce2O3/CeOx
Bastnaesite + NHA881.77−0.12CeO2
883.82−0.16Ce
885.91−0.18CeH3/CeO2
888.02−0.16Ce2O3/CeOx
Table
Table 8. Analysis results of O 1 s XPS spectra of bastnaesite samples untreated and treated with NHA.
Table 8. Analysis results of O 1 s XPS spectra of bastnaesite samples untreated and treated with NHA.
SamplesBinding Energy/eVChemical Shift/eVAssignment
Bastnaesite531.55/CO3
533.11/Ce-OH
Bastnaesite + NHA531.770.22C10H7-OH/CO3
533.320.21C=O/Ce-OH
Table
Table 9. Analysis results of C 1 s XPS spectra of bastnaesite samples untreated and treated with NHA.
Table 9. Analysis results of C 1 s XPS spectra of bastnaesite samples untreated and treated with NHA.
SamplesBinding Energy/eVChemical Shift/eVAssignment
Bastnaesite284.77/C-C
289.31/CO3
Bastnaesite + NHA284.980.21C-C/naphthalene ring
289.730.42C=C/CO3
Table
Table 10. Analysis results of N 1 s XPS spectra of bastnaesite samples untreated and treated with NHA.
Table 10. Analysis results of N 1 s XPS spectra of bastnaesite samples untreated and treated with NHA.
SamplesBinding Energy/eVChemical Shift/eVAssignment
Bastnaesite + NHA399.48399.48-C(OH)=NO-
400.28400.28-C(=O)-NHO-
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Xiong, W.; Wang, M.; Xiao, J.; Chen, D. Selective Adsorption of 2-Hydroxy-3-Naphthalene Hydroxamic Acid on the Surface of Bastnaesite and Calcite. Minerals 2022, 12, 1341. https://doi.org/10.3390/min12111341

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Xiong W, Wang M, Xiao J, Chen D. Selective Adsorption of 2-Hydroxy-3-Naphthalene Hydroxamic Acid on the Surface of Bastnaesite and Calcite. Minerals. 2022; 12(11):1341. https://doi.org/10.3390/min12111341

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Xiong, Wenliang, Maoyuan Wang, Junhui Xiao, and Da Chen. 2022. "Selective Adsorption of 2-Hydroxy-3-Naphthalene Hydroxamic Acid on the Surface of Bastnaesite and Calcite" Minerals 12, no. 11: 1341. https://doi.org/10.3390/min12111341

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