An Environmentally Friendly Chelator for Improving the Flotation Separation of Magnesite and Dolomite: Flotation Behavior and Adsorption Mechanism

Abstract

During the grinding process, magnesite (MgCO₃) and calcareous gangue minerals, such as dolomite (MgCa(CO₃)₂), are prone to surface dissolution. The dissolved metal ions adsorb onto the mineral surfaces, causing the surface properties of both minerals to converge, which complicates flotation separation. This study investigates the use of ethylene glycol tetra-acetic acid (EGTA) to optimize the grinding–flotation system for the recovery of magnesite. The mechanisms underlying EGTA’s effects on the minerals were examined through various characterization techniques, including contact angle measurements, zeta potential analysis, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectrometry (ICP-OES). Single-mineral flotation tests revealed that EGTA addition during grinding enhanced the separation between magnesite and dolomite in flotation. An artificial mixed-ore flotation yielded a concentrate with 46.47% MgO grade and 92.21% MgO recovery. Mechanistic studies indicated that EGTA selectively adsorbed onto Ca sites on the surface of dolomite, increasing its hydrophilicity. Additionally, EGTA effectively chelated Ca²⁺ in the slurry, improving the chemical environment. Therefore, EGTA demonstrated significant potential for improving the flotation of magnesite.

1. Introduction

Magnesite is the main raw material of the magnesium industry, commonly used in refractories, building materials, and the production and processing of magnesium metal [1,2]. With the development and utilization of resources, high-grade magnesite ore resources are depleting [3]. Due to the high content of calcium gangue minerals and the difficulty in separation, a large amount of low-grade dolomite ore is abandoned and stored [4,5]. Ore stacking not only wastes resources and occupies a large amount of land but also causes serious pollution to the surrounding soil system [6]. Therefore, there is an urgent need to research and develop efficient separation technology for low-grade magnesite ore.

The main gangue minerals in low-grade magnesite are dolomite and quartz [7]. At present, flotation is the most effective and widely used method to separate magnesite and gangue [8]. The surface properties of quartz and magnesite differ greatly and can generally be removed by single-cation reverse flotation [9,10]. However, dolomite (CaMg(CO₃)₂) and magnesite (MgCO₃) are calcite alkaline–Earth metal carbonate minerals whose crystal structure and surface properties are similar, which makes flotation separation difficult [1,11]. At the same time, the existing magnesite flotation process has the problems of low separation efficiency and high calcium content in the concentrate product [12,13]. This is mainly due to the dissolution of carbonate minerals in the separation process, resulting in a poor flotation separation effect [14]. Fine-grained carbonate minerals are more likely to dissolve metal ions, which adsorb onto the surface of minerals, resulting in the convergence of surface properties between different minerals [15,16]. Therefore, the selective regulation of mineral dissolution can be an effective way to strengthen the flotation separation of magnesite and dolomite.

Grinding is a necessary process before separation, has high energy consumption and low efficiency, and can also have an important impact on the subsequent flotation indexes [17,18,19]. It has been found that the addition of reagents containing some specific groups at the grinding stage can selectively chelate Ca²⁺ and Mg²⁺ ions produced by mineral dissolution in the ore pulp [20,21]. This can alleviate the phenomenon of surface property convergence caused by dissolved ions. In this process, the selection of suitable reagents is key to optimizing the grinding process [22,23].

Ethylene glycol tetra-acetic acid (EGTA) is an environmentally friendly chelating reagent with an excellent chelating effect on Ca²⁺ and Mg²⁺ [24,25]. EGTA has been used in environmental remediation to remove metal ions from the soil [26]. In this study, EGTA was added to the grinding stage for the enhanced flotation separation of magnesite and dolomite. The effect of EGTA on the separation of magnesite and dolomite was investigated by flotation tests. In addition, the influence of EGTA on the flotation separation of the two minerals was investigated by contact angle test, zeta potential inspection, FTIR, XPS, and ICP-OES analyses. The results of this study can provide guidance for improving the separation of low-grade magnesite ore.

2. Materials and Methods

2.1. Materials

2.1.1. Minerals

The test mineral samples of magnesite and dolomite were obtained from the Haicheng ore dressing plant, Liaoning, China. After being crushed, screened, and classified, raw ore samples were obtained with particle sizes meeting the test requirements. Representative samples were ground to −38 μm and analyzed by X-ray diffraction (shown in Figure 1) and chemical testing. The analytical results showed that the purity of magnesite was 97.0% and that of dolomite was 98.2%. The purity of the raw ore was high and met the requirements of the test.

2.1.2. Reagents

The molecular formula of glycol diethyl ether diamine tetra-acetic acid (EGTA) was C₁₄H₂₄N₂O₁₀ (the molecular structure is shown in Figure 2). The molecular formula of the collector sodium oleate (NaOL) was C₁₈H₃₃O₂Na. The pH adjusters were NaOH and HCl. All the reagents were purchased from Shanghai McLean Biochemical Science and Technology Company Limited (Shanghai, China).

2.2. Methods

2.2.1. Flotation Test

A small laboratory ceramic ball mill was used to grind magnesite and dolomite single minerals and artificial mixed ores. EGTA was added to the grinding, and the grinding time was set to 6 min [27]. After grinding, the slurry was transferred to the XFG flotation machine, and the flotation test’s flowchart is shown in Figure 3. NaOL was used as a collector, and NaOH or HCL was used as the pH adjuster. At the beginning of the flotation test, the slurry was stirred for 2 min, and then the reagents were added sequentially at 2 min intervals. After the reagents were fully adsorbed on the mineral surface, the foam was scraped manually for 3 min. Each set of flotation tests was repeated three times, and the average value was taken as the final result. After the flotation test, the concentrate and tailings were weighed and assayed. In this way, the effect of EGTA on the flotation behavior of the minerals was investigated. With reference to the grade of the minerals in the actual ore, magnesite and dolomite were mixed at a mass ratio of 9:1 for the flotation test. The flotation process of the mixed ore was consistent with that of the single minerals. The separation efficiency was calculated according to Equation (1) [28,29]:

$$\mathrm{E}={\displaystyle \frac{\epsilon -\gamma }{1-\alpha /{ \beta }_{\mathrm{x}}}}\%$$

(1)

where ε is the recovery, %; γ is the concentrate yield, %; α is the grade of the original ore, %; and β_x is the grade of the useful component of the destination mineral, %.

2.2.2. Contact Angle Detection

The effect of EGTA on the wettability of mineral surfaces in a flotation environment was investigated. The contact angle of the mineral surfaces was measured using an XG-CMAB contact angle meter. The procedure involved placing the prepared mineral samples on the sample stage, rotating the injector to drop droplets from the needle tip onto the surface and then performing the contact angle measurement using a five-point fitting method on the acquired image. Each test was repeated three times, and the average value was recorded [30].

2.2.3. Fourier Transform Infrared Spectroscopy (FTIR) Detection

The FTIR spectrometer effectively provided detailed insights into the structure and properties of unknown substances, as well as the chemical groups present. Prior to measurement, 1 mg of mineral sample was mixed with 100 mg of KBr. Then, the sample was placed in an agate mortar and finely ground. Finally, the sample was compacted in a specific press model. The scanning range was 400–4000 cm⁻¹, and the number of scans was 30 [31,32].

2.2.4. Zeta Potential Detection

The zeta potential measurements were conducted using a Zeta Potential Tester from Malvern Panaco Ltd., (London, UK), which is capable of accurately determining the zeta potential of solid substances, highly concentrated suspensions, and other materials. Before testing, the raw minerals were finely ground to a particle size of less than 2 μm. A 0.3 mg sample of the minerals was weighed, and 40 mL of deionized water along with the appropriate reagents was added. The pH of the solution was then adjusted using HCl or NaOH, and the mixture was continuously stirred using a magnetic stirrer. Each sample was tested in triplicate, and the average value was calculated and used as the final result [33].

2.2.5. X-Ray Photoelectron Spectroscopy (XPS) Testing

XPS analysis was conducted using an X-ray photoelectron spectrometer from Thermo Fisher (Waltham, MA, USA). Initially, the samples were scanned in full spectrum using an Al-Kα monochromatic X-ray source. Subsequently, detailed scans were performed on the elemental regions of calcium, magnesium, and oxygen. For each test, 1 g of single mineral was mixed with 30 mL of distilled water, and the pH of the slurry was adjusted to 10 using NaOH. EGTA was then added according to the experimental requirements, followed by magnetic stirring for 10 min to allow adsorption of the agent. The slurry was filtered and dried under vacuum at 30 °C. The resulting spectra were analyzed using Thermo Avantage 2020 software, with binding energies calibrated using the C 1s peak (284.8 eV) as the reference [34,35].

2.2.6. Inductively Coupled Plasma Emission Spectrometer (ICP-OES) Detection

The ICAP 7400 DUO spectrometer produced by Thermo Fisher was used to determine the concentration of calcium and magnesium ions in the slurry. The wavelength range of the equipment was 166–847 nm; the optical resolution was ≤ 0.007 nm. During detection, the ore slurry after grinding was firstly left to stand, and the supernatant was extracted. After centrifugation and filtration, the sample was prepared for detection Then, the instrument was calibrated with a linear gradient standard solution of calcium and magnesium ions to ensure the accuracy and precision of subsequent measurements. Finally, the sample was diluted to a concentration suitable for measurement and entered the detection system via a peristaltic slurry [20,35].

3. Results and Discussion

3.1. Flotation Test

The effects of the collector NaOL and the pH of the slurry on the flotation behavior of magnesite and dolomite were first examined. The results of the flotation tests for single minerals are shown in Figure 4.

As shown in Figure 4a, the recoveries of both magnesite and dolomite increased with the increase in NaOL dosage at a natural pH (natural pH of magnesite slurry = 8.30; natural pH of dolomite slurry = 9.32). When the NaOL dosage was 80 mg/L, the magnesite recovery reached 88.00%, while the dolomite recovery was 69.00%. However, the flotation recovery difference between the two minerals was small, indicating that effective separation of magnesite and dolomite could not be achieved using NaOL as the sole collector. As shown in Figure 4b, the recovery of both magnesite and dolomite decreased with the increase in slurry pH at 80 mg/L NaOL dosage. At pH = 9.5, the difference between the flotation recovery of the two minerals was 26%.

Subsequently, EGTA was added to the grinding. The effect of the dosage of EGTA on the flotation behavior of magnesite and dolomite was investigated under the natural slurry at the dosage of the collector NaOL of 80 mg/L. The results of flotation tests for single minerals are shown in Figure 5.

As shown in Figure 5a, the dolomite recovery decreased significantly, while the magnesite recovery increased after adding EGTA to the mill. The largest recovery difference between the two minerals occurred at an EGTA dosage of 40 mg/L, with magnesite recovery reaching 91.5% and dolomite recovery at 12.0%. In Figure 5b, when the NaOL dosage was 80 mg/L and the EGTA dosage was 40 mg/L, magnesite recovery increased significantly as the slurry pH rose. The greatest difference in flotation recovery between the two minerals was observed at a slurry pH of 10.3. This demonstrated that EGTA effectively facilitated the selective separation of magnesite and dolomite.

A binary mixed-ore flotation separation test was carried out under the conditions of EGTA dosage of 40 mg/L, NaOL dosage of 80 mg/L, and pH = 10.3, and the results are shown in

Table 1. Indicators of flotation tests for artificially mixed ores.

Reagents	Products	Yield/%	Grade/%		Recovery/%		Separation Efficiency/%
			MgO	CaO	MgO	CaO
Without EGTA	Concentrate	79.12	45.75	2.77	81.12	66.82	80.97
	Tailing	20.88	40.35	5.21	18.88	33.18
	Feed	100.00	44.62	3.28	100	100
Added EGTA during grinding	Concentrate	88.54	46.47	1.64	92.21	44.42	83.60
	Tailing	11.46	30.33	15.91	7.79	55.58
	Feed	100.00	44.62	3.28	100.00	100.00

.

At the magnesite and dolomite mass of 9:1, the grade of MgO in the artificial mixed ore was 44.62%, and the CaO grade was 3.28%. When NaOL was added alone, the MgO grade in the concentrate increased to 45.75%, while the CaO grade remained relatively high at 2.77%. This indicated that NaOL alone could not achieve the effective separation of magnesite and dolomite. However, with a grinding time of 6 min and the addition of EGTA (40 mg/L) during grinding, improved flotation results were obtained. Under these conditions, the MgO grade in the concentrate increased to 46.67%, while the CaO grade decreased significantly to 1.64%. These results demonstrated that the addition of EGTA during grinding enhanced the flotation separation of magnesite and dolomite.

3.2. Contact Angle Detection

The effect of the reagent on the hydrophobicity of the mineral surface was investigated by contact angle measurements on the mineral surface, and the results are shown in Figure 6.

As shown in Figure 6, the natural contact angles of the magnesite and dolomite surfaces were 27° and 30°, respectively. This indicated that magnesite and dolomite had strong hydrophilicity and poor floatability. The contact angles of magnesite and dolomite were significantly increased after NaOL treatment, and the carbon chains in NaOL molecules could significantly enhance the hydrophobicity of the two minerals’ surfaces. However, the contact angle of magnesite (86°) was larger than that of dolomite (78°). After the addition of EGTA to the NaOL system, the contact angle of magnesite decreased slightly, while the contact angle of dolomite decreased significantly. This indicated that, in the NaOL system, EGTA could reduce the hydrophobicity of the dolomite surface, making the floatability of dolomite worse. This conclusion was consistent with the flotation test results.

3.3. FTIR Detection

FTIR spectral analysis could be used to further investigate the adsorption status of EGTA and NaOL on the mineral surface. As can be seen in Figure 7, in the FTIR spectra of NaOL, the C-H-stretching vibration absorption peaks at 2932.64 cm⁻¹ and 2851.72 cm⁻¹ indicated the C-H stretching vibration absorption peaks of -CH₂ and -CH₃ groups [36,37]. The peaks at 1567.83 cm⁻¹ and 1446.93 cm⁻¹ corresponded to the asymmetric stretching vibration absorption peaks and symmetric stretching vibration absorption peaks of -COO⁻ [38]. The peaks at 3059.99 cm⁻¹ and 2923.07 cm⁻¹ in the FTIR spectrum of EGTA corresponded to C-H stretching vibrations. The peak at 2545.57 cm⁻¹ represented the stretching vibration of the ether bond, while the peak at 1433.81 cm⁻¹ was attributed to the stretching vibration of the carboxyl group. The peaks at 881.30 cm⁻¹ and 749.68 cm⁻¹ corresponded to the stretching vibration peak of the amine group [39]. Figure 8 shows the infrared spectra of magnesite and dolomite before and after treatment with EGTA and NaOL. As can be seen from Figure 8a, the peaks appearing at 1831.56 cm⁻¹, 859.77 cm⁻¹, and 734.26 cm⁻¹ were characteristic of magnesite. Among them, the peak at 1831.56 was the asymmetric stretching vibration peak, and the peaks at 859.77 cm⁻¹ and 734.26 cm⁻¹ were the out-of-plane bending vibration peak and in-plane bending vibration peak of ${\mathrm{CO}}_3^{2-}$ [40,41]. After the addition of EGTA, the infrared spectrum of magnesite was essentially the same as that of the original ore. This indicated that the adsorption of EGTA on the surface of magnesite was weak or the adsorption amount was small and difficult to detect [29,42]. In addition, in the reagent environment of EGTA + NaOL, C-H symmetric vibrational absorption peaks in NaOL appeared on the surface of magnesite at 2924.03 cm⁻¹ and 2 856.24 cm⁻¹. The -COO⁻ stretching vibration absorption peaks in NaOL appeared at 1563.53 cm⁻¹ and 1424.39 cm⁻¹. This suggested that EGTA did not interfere with the adsorption of NaOL on the surface of magnesite.

As can be seen from Figure 8b, the peaks appearing at 1823.26 cm⁻¹, 897.21 cm⁻¹, and 734.34 cm⁻¹ were characteristic peaks of dolomite [43], corresponding to the asymmetric stretching vibrational, the out-of-plane bending vibrational peak, and the in-plane bending vibrational peak of ${\mathrm{CO}}_3^{2-}$, respectively [44]. After the addition of EGTA, the characteristic peak of ether bonding appeared at 1431.07 cm⁻¹ for dolomite. The C-H stretching vibration peaks were all present at 2538.24 cm⁻¹. In addition, the characteristic peak at 897.21 cm⁻¹ was shifted to 887.09 cm⁻¹, and the characteristic peak at 734.34 cm⁻¹ was shifted to 730.40 cm⁻¹. This demonstrated that EGTA produced strong chemisorption on the surface of dolomite [44]. Further, in the reagents system of EGTA + NaOL, the characteristic peaks of C-H and -COO⁻ of NaOL disappeared [45]. This indicated that EGTA hindered the adsorption of NaOL on the dolomite surface.

3.4. Zeta Potential Detection

The adsorption of reagents on the mineral surface leads to changes in the zeta potential, which in turn affects the floatability of the minerals [46]. To examine the difference in adsorption of NaOL and EGTA on the mineral surface, zeta potential measurements were conducted, and the results are shown in Figure 9.

As can be seen from Figure 9a, the zeta potential of magnesite kept moving negatively with increasing pH values. The isoelectric point of magnesite was about pH = 5.80, which was essentially consistent with that reported in the literature [37,47]. The change in the zeta potential of magnesite after the addition of EGTA was small. At pH = 10.2, the negative shift in magnesite’s zeta potential was significant (from −32.1 mV to −40.3 mV) under the condition of the EGTA + NaOL reagent. This indicated that NaOL could produce strong adsorption on the surface of magnesite. However, EGTA did not affect the adsorption behavior of NaOL on the surface of magnesite. As can be seen from Figure 9b, the zeta potential of dolomite kept moving negatively with increasing pH levels. The isoelectric point of dolomite was about pH = 5.5, in general agreement with reports in the literature [28,48]. The zeta potential of dolomite showed a significant negative shift after the addition of EGTA. At pH 10.2, the potential changed from −30.5 mV to −47.9 mV. When both EGTA and NaOL were used together, the negative shift in the zeta potential was smaller, changing from −47.9 mV to −49.5 mV at pH 10.2. This indicated that EGTA was more strongly adsorbed on the dolomite surface compared to magnesite.

3.5. XPS Analysis

To further investigate the adsorption mechanism between the reagents and the minerals, XPS analysis was conducted to examine the changes in the chemical states of the elements on the surfaces of magnesite and dolomite after EGTA treatment. The results are presented in Figure 10, Figure 11 and Figure 12.

As shown in Figure 10a, the XPS spectrum of magnesite exhibited characteristic peaks for Mg 1s, Mg 2s, Mg 2p, O 1s, O 2s, and C 1s. However, the characteristic peaks of EGTA were absent in the XPS spectrum after treatment with EGTA, indicating that the interaction between EGTA and magnesite was weak [49]. As shown in Figure 10b, the characteristic peaks of several elements—Mg 1s, Ca 2s, Ca 2p, O 1s, O 2s, and C 1s—appeared in the XPS measurement spectra of dolomite. After the addition of EGTA, the characteristic peaks of N 1s and N 2s appeared on the XPS measurement spectra of dolomite. This proved that EGTA led to adsorption on the surface of dolomite [36,37]. Figure 11 shows the XPS narrow-area scanning spectra of Mg 1s and O 1s on the surface of magnesite before and after the action of EGTA. As can be seen from Figure 12, the XPS spectrum of the magnesite surface contained the characteristic peaks of Mg 1s (1304.16 eV) and O 1s (531.75 eV). After the action of EGTA on the surface of magnesite, the characteristic peaks of Mg 1s (1304.21 eV) and O 1s (531.77 eV) showed a small displacement. However, no new peaks appeared in the XPS spectra of the magnesite surface. This reflected that EGTA had almost no effect on the chemical environment of Mg and O on the surface of magnesite, which was consistent with the results of FTIR analysis in the previous paper. Figure 12 presents the XPS narrow-region scanning spectra of Mg 1s, Ca 2p, and O 1s on the dolomite surface before and after EGTA treatment. As shown in Figure 12a, after EGTA treatment, the Mg 1s peak on the dolomite surface shifted slightly from a binding energy of 1303.86 eV to 1303.92 eV. This shift suggested that the interaction between the active Mg sites on the dolomite surface and EGTA was weak [40,50]. As can be seen from Figure 12b, the narrow-area scanning patterns of dolomite at binding energies of 347.12 eV and 350.48 eV corresponded to the characteristic peaks of Ca 2p3/2 and Ca 2p1/2 in dolomite, respectively. The EGTA-treated dolomite surface showed characteristic peaks of Ca 2p3/2 in RCOO-Ca and Ca 2p1/2 in RCOO-Ca at 347.04 eV and 350.57 eV, in addition to Ca 2p’s double peaks observed at 347.08 eV and 350.64 eV [28,51]. This was due to the formation of chelates between the EGTA and Ca sites exposed on the dolomite surface [1,12,14]. In addition, it can also be seen from Figure 12c that the dolomite surface after EGTA showed new O 1s characteristic peaks at 531.31 eV and 532.45 eV, in addition to the O 1s characteristic peaks at 531.12 eV which corresponded to the dolomite itself. This corresponded to the O 1s characteristic peaks in C-O and C=O in RCOO-Ca [4,6]. Based on the above analysis, it was evident that EGTA adsorbed strongly on the surface of dolomite, with the adsorption primarily occurring at the Ca sites rather than at the Mg sites.

3.6. ICP-OES Measurement

The dissolution characteristics of magnesite and dolomite under different grinding environments were explored. The results are shown in Figure 13.

As shown in Figure 13a, the concentrations of dissolved Ca²⁺ and Mg²⁺ ions in the slurry increased with the grinding time. However, for the same grinding duration, the dissolved Ca²⁺ concentration in dolomite was higher than the dissolved Mg²⁺ concentration in magnesite. This suggested that the dissolution rate of dolomite was greater than that of magnesite. As shown in Figure 13a, the dissolved Ca²⁺ and Mg²⁺ ions in the slurry increased with the increase in grinding time. However, under the same grinding time, the dissolved Ca²⁺ of dolomite was larger than the dissolved Mg²⁺ of magnesite. This indicated that the dissolution rate of dolomite was greater than that of magnesite. There was a dissolution reaction between magnesite and dolomite, which is shown in

Table 2. Dissolution reactions of magnesite and dolomite.

Minerals	Equations for Dissolution Reactions	Equilibrium Constant
Magnesite	$\mathrm{MgC}{\mathrm{O}}_3\rightleftharpoons {\mathrm{Mg}}^{2+}+{\mathrm{CO}}_3^{2+}$	3.40
Dolomite	$\mathrm{CaMg}{(\mathrm{C}{\mathrm{O}}_3)}_2\rightleftharpoons {\mathrm{Mg}}^{2+}+{{\mathrm{Ca}}^{2+}+2\mathrm{CO}}_3^{2+}$	19.35

. The dissolution rate of dolomite was significantly higher than that of magnesite. After a grinding time of 8 min, the concentration of dissolved Ca²⁺ and Mg²⁺ in the dolomite slurry showed little change, indicating that dolomite reached dissolution equilibrium. In contrast, the concentration of dissolved Mg²⁺ in magnesite continued to increase significantly, suggesting that magnesite took longer to reach dissolution equilibrium compared to dolomite. As shown in Figure 13b, after the addition of EGTA to aid grinding during the grinding stage, both Ca²⁺ and Mg²⁺ in the slurry increased first and then decreased. Such a trend was linked to the equilibrium of mineral dissolution in the slurry (as shown in Table 2) [9,52]. EGTA had a chelating effect on the dissolved Ca²⁺ and Mg²⁺ of the minerals, resulting in a disruption of the dissolution equilibrium. As a result, the metal ions of the mineral slurry increased first and then decreased.

The solution chemistry calculations showed that the dissolved components of magnesite and dolomite in the slurry were very complex (as shown in Figure 14). When the pH was in the range of 0 to 14, the metal ions in magnesite were mainly in the form of Mg²⁺, MgCO_3(aq), MgOH⁺, and ${\mathrm{MgHCO}}_3^{+}$, while those in dolomite were mainly Ca²⁺, Mg²⁺, CaCO_3(aq), MgCO_3(aq), ${\mathrm{CaHCO}}_{3\left(\mathrm{aq}\right)}^{+}$, ${\mathrm{MgHCO}}_3^{+}$, CaOH⁺, and MgOH⁺. However, at the optimum flotation pH = 10.2, Mg²⁺ and MgOH⁺ were the dominant components of magnesite, while the dominant components of dolomite were Ca²⁺, Mg²⁺, and CaOH⁺. After its addition, EGTA chelated with metal ions, shifting the mineral dissolution equilibrium positively and accelerating the dissolution process. Once the chelation effect stabilized, the equilibrium was no longer disturbed, and the concentration of metal ions in the mineral slurry began to decrease.

4. Conclusions

To address the challenge of flotation separation between magnesite and dolomite, this study optimized the grinding–flotation system for magnesite using the chelating reagent EGTA. Single-mineral flotation tests demonstrated that EGTA increased the recovery difference between magnesite and dolomite. At a dosage of 40 mg/L EGTA, 80 mg/L NaOL, and pH 10.3, a flotation concentrate with 46.47% MgO grade, 1.64% CaO grade, and 92.21% MgO recovery was obtained, resulting in an increase in the separation efficiency from 80.97% to 83.60%. FTIR analysis revealed that EGTA’s impact on the surface of dolomite was more pronounced than on magnesite. The contact angle and zeta potential measurements showed that EGTA selectively adsorbed onto the surface of dolomite, inhibiting the adsorption of NaOL and making dolomite more hydrophilic and less floatable. The XPS analysis confirmed that EGTA selectively interacted with the Ca sites on the dolomite surface, forming a Ca-EGTA chelate. The ICP-OES analyses further indicated that EGTA chelated Ca²⁺ and Mg²⁺ in the slurry, promoting the dissolution of both dolomite and magnesite. However, EGTA’s chelation effect was stronger on Ca. Consequently, the addition of EGTA during the grinding process significantly enhanced the flotation separation of magnesite and dolomite.