Selective adsorption of a new depressant Na2ATP on dolomite: Implications for effective separation of magnesite from dolomite via froth flotation

https://doi.org/10.1016/j.seppur.2020.117278Get rights and content

Highlights

  • Flotation separation of magnesite from dolomite is very difficult using NaOl alone.

  • Na2ATP is chemically adsorbed onto dolomite due to its strong affinity to Ca sites.

  • Magnesite adsorbs larger amounts of NaOl than dolomite in the existence of Na2ATP.

  • Na2ATP can achieve the flotation separation of magnesite from dolomite.

Abstract

Up to now, there is still a great challenge to efficiently separate magnesite from calcium-bearing carbonate minerals, especially dolomite, via froth flotation owing to their similar physicochemical properties. In this investigation, a novel depressant adenosine 5′-triphosphate disodium salt (Na2ATP) was introduced into the flotation process using the collector sodium oleate (NaOl), which was proved to be effective for the separation of dolomite and magnesite. The flotation results demonstrate that Na2ATP exhibits a more intense depression on the flotation of dolomite than that of magnesite and can separate effectively magnesite from dolomite, which depends on much less NaOl adsorption onto dolomite in the presence of Na2ATP. Zeta-potential detection and adsorption amount tests illustrate that the pre-addition of Na2ATP strongly interferes with the interaction between NaOl and dolomite so that a more significant reduction in adsorption of NaOl on the surface of dolomite in comparison with magnesite. Moreover, infrared spectral (IR) and X-ray photoelectron spectroscopy (XPS) measurements further confirm that the depressant Na2ATP is adsorbed more strongly onto dolomite than magnesite. And the selective adsorption of Na2ATP onto dolomite rather than magnesite was mainly due to the strong bonding of its phosphate groups and the calcium sites only exposed to the dolomite surface, resulting in selectively depressing the flotation of dolomite.

Introduction

As a light metal, magnesium owns widespread applications in the industry. It has been reported that magnesium is widely used as the basis for constructional alloys and automobile manufacturers tend to use magnesium-based alloys instead of denser materials such as cast irons, steels, copper-based alloys and aluminum-based alloys due to the property of lightweight [1]. As we know, magnesite ore, a non-renewable and non-recyclable valuable resource, is a major raw material for the extraction of magnesium and the production of refractory materials [2], [3]. With the advantage of rich magnesite ore resources, China is always the largest producer and exporter of magnesia refractories in the world [4]. Magnesite, as the primary magnesium-rich carbonate mineral-, usually coexists with gangue minerals such as quartz and calcium-bearing carbonate minerals [3], [5]. In recent years, as the market demand for magnesite mineral is increasing, the amount of high-grade magnesite has been declining drastically with the over-exploitation of magnesite ore resources [6]. Thus, the development and utilization of low-grade magnesite ores with many impurities have attracted more and more concern [3], [7]. At present, froth flotation is still the most recognized technology to obtain the magnesite concentrate product [8], [9]. However, large amounts of carbonate minerals especially dolomite appearing in low-grade magnesite ore complicate- the selective separation of magnesite and dolomite, thereby causing great difficulties in obtaining high-quality magnesite concentrate containing low calcium. Generally, due to its similar surface properties to magnesite, for magnesite flotation, dolomite is easy to be transported into concentrate products through particle-to-bubble adhesion, slime coatings [10] and mechanical entrainment [11], [12]. Therefore, it is imperative to come up with an effective method for the flotation separation of dolomite and magnesite to meet this challenge.

As salt-type minerals, dolomite and magnesite have similar crystal, surface property (wettability and ions dissolution) and solution chemical properties that tend to reduce the difference in their flotation performance [13], [14], [15]. In flotation, collectors are often applied to enhance the hydrophobicity of the collected minerals after their adsorption on the mineral surfaces [16], [17], [18], [19]. Generally, dodecylamine and sodium oleate as the most common collectors are widely used in flotation separation of dolomite and magnesite [14]. Zhang et al. [20], [21] revealed that dodecylamine was physically adsorbed on the surfaces of dolomite and magnesite while sodium oleate was chemically adsorbed on the surfaces of dolomite and magnesite. However, the efficient separation of magnesite from dolomite cannot be realized by relying on these traditional collectors (i.e., sodium oleate) without any depressants [13]. Thus, the key to realizing the separation of magnesite from dolomite is to find an effective depressant that selectively depresses the dolomite flotation.

As we know, flotation depressants are often used to selectively decrease the floatability of non-target minerals but have slight impacts on the target mineral flotation [22], [23], [24]. Related investigations have shown that inorganic depressants used for flotation separation of magnesite include sodium hexametaphosphate (SHMP), sodium silicate, sodium pyrophosphate and sodium fluorosilicate [15], [25]. It has been reported that SHMP can strongly inhibit the flotation of dolomite in the magnesite flotation due to its strong depression of dolomite [25]. However, its selective depression performance in the separation of magnesite and dolomite is significantly affected by the concentrations of reagent and calcium ions in the pulp. An investigation by Luo et al. [6] confirmed that magnesite was also depressed by SHMP in the presence of calcium ions dissolved from dolomite for artificially mixed-mineral flotation, resulting in the low recovery of magnesite. Moreover, Chen and Tao [26] found that sodium silicate selectively depressed magnesite with dodecyl phosphate as the collector while it has no depression on the dolomite flotation under acidic conditions. However, in this case, a portion of magnesite was lost due to its dissolution in acidic medium. In addition, a large amount of magnesium and calcium (if present) ions dissolved from magnesite and dolomite in pulp reacted with the collector molecules, which led to an increase in collector consumption. Recently, polymer depressants have more and more widespread applications in mineral flotation [24]. As a macromolecular polymer inhibitor, carboxymethyl cellulose (CMC) displays a great depression influence on dolomite flotation in many previous studies [27]. However, CMC is not suitable for separating magnesite from dolomite as the depressant under alkaline conditions due to its poor selectivity [25]. Giving these significant disadvantages of traditional depressants, it is of necessity to develop novel high-performance depressants utilized in the selective flotation of magnesite and dolomite.

Adenosine 5′-triphosphate (ATP) and its disodium salt (Na2ATP) are recognized commonly as “energy currency” in most living beings where it plays a critical role in most enzyme reactivities apart from the fact that it acts as a crucial component of many biological cofactors [28], [29]. As one of the most important organic phosphate compounds, Na2ATP consists of three phosphate groups (see Fig. 1) and exhibits a great advantage of immobilizing metal ions [30]. In recent years, many investigations have illustrated that Na2ATP can form stable complexes with various divalent metal ions such as manganese, magnesium, zinc, calcium and copper ions [31], [32], [33]. Furthermore, Na2ATP has been also used as an excellent chelating ligand in the immobilized metal ion affinity chromatography (IMAC) materials because of superiorly intense and active metal phosphonate sites provided by its rich phosphate groups [34], [35]. In view of the above, based on the difference in active sites exposed on the surfaces of dolomite and magnesite, Na2ATP is believed to be able to selectively interact with dolomite rather than magnesite to affect the flotation behavior of dolomite. At present, however, few investigations into Na2ATP as a flotation depressant have been conducted using to separate magnesite from dolomite.

In this paper, Na2ATP was first applied as a depressant in the flotation separation of magnesite and dolomite with sodium oleate. The significant influence of Na2ATP on the flotation behavior of magnesite and dolomite was investigated via flotation tests. The selective adsorption behavior of Na2ATP on different mineral surfaces was studied through adsorption measurements, zeta-potential detection, XPS analysis and IR characterization. On the basis of the above analyses, a possible adsorption mechanism of Na2ATP on the water–solid interfaces of magnesite and dolomite was put forward.

Section snippets

Materials and reagents

Natural mineral samples of magnesite and dolomite were handpicked carefully from Liaoning Province, PR China. The mineral samples were dry-screened to produce different size fractions after being crushed by a hammer and then ground using a porcelain ball mill. The size fraction of −74 + 38 μm was employed for the subsequent flotation experiments and adsorption studies, whereas the other fraction of −38 μm were used for XPS measurements, IR analysis and zeta-potential measurements after being

Influences of NaOl concentrations on magnesite and dolomite flotation

The significant effects of NaOl concentrations on the flotation performance of magnesite and dolomite are shown in Fig. 4. It can be found from Fig. 4 that the magnesite and dolomite recoveries increased sharply with the increase in NaOl concentration at first, and then almost unchanged at higher concentrations. When the concentration of NaOl was 0.4 mM, magnesite and dolomite were stable at great flotation recoveries (more than or approximately 90%), which is in agreement with previous reports

Conclusions

In this work, the reagent Na2ATP, enriched with multiple electron-rich groups, was adopted as a novel inhibitor for the selective separation of magnesite from dolomite by froth flotation. A better reagent scheme (i.e., 0.4 mM NaOl and 0.9 mM Na2ATP) could achieve the effective separation of the two minerals under alkaline conditions. Moreover, the selective depression mechanism of Na2ATP on the dolomite surface was investigated via zeta potential measurements, IR analysis, adsorption amount

CRediT authorship contribution statement

Bin Yang: Methodology, Validation, Investigation, Writing - original draft. Haoran Sun: Resources. Donghui Wang: Methodology. Wanzhong Yin: Supervision, Conceptualization, Project administration. Shaohang Cao: Visualization. Yulian Wang: Resources. Zhanglei Zhu: Writing - review & editing. Kai Jiang: Visualization. Jin Yao: Supervision, Funding acquisition.

Declaration of Competing 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.

Acknowledgments

The authors appreciate the financial contributions to this study by the National Natural Science Foundation of China (Nos. 51874072 and 51974064) and the Fundamental Research Funds for the Central Universities (Nos. N180104017, N180106006 and N2001029), China. The authors also thank for the support from the Genetic Mineral Processing Research Center of Northeastern University, China, and the Liaoning Key Laboratory of Mineral Processing Science and Technology, China.

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