Investigation on the flotation separation of smithsonite from calcite using calcium lignosulphonate as depressant

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Abstract

The flotation separation of smithsonite and calcite is difficult due to their similar surface physicochemical characteristics. In this study, calcium lignosulphonate (CLS) was employed as a selective inhibitor for the flotation separation of smithsonite from calcite using sodium oleate (NaOl) as collector. Flotation experiments results indicate that the calcite flotation was strongly depressed by CLS, whereas the smithsonite flotation was barely interfered. The flotation separation of smithsonite from calcite could be achieved at pH 10. A concentrate with zinc grade and recovery of 45.16% and 85.60% respectively was obtained in the artificial mixed minerals flotation experiment in the presence of CLS. The interaction mechanism was investigated by zeta potential measurement, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) and results suggest that CLS chemically absorbed on the calcite surface in the form of Ca-SO3, which strongly hindered the successive NaOl adsorption on the calcite. However, it barely absorbed on the smithsonite surface, thus exhibiting little influence on the reaction between NaOl and smithsonite. Hence, CLS could be utilized as a selective depressant for calcite in the flotation of smithsonite.

Graphical Abstract

A conceivable adsorption model of CLS and NaOl on the smithsonite and calcite surfaces.

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Introduction

Zinc, the fourth most common metal in the world, plays a pivotal role in the modern society [1]. It is not only one of the essential trace elements for the human body, but also extensively utilized in the fields of battery, automobile, electricity and electronic engineering [2], [3]. In the past few decades, zinc sulfide (e.g., sphalerite) has been the most important mineral source of zinc extraction [4], [5]. However, with the rapid increase in the demand for zinc resources in the industrial area, the high-grade and easy-handling zinc sulfide resources become increasingly exhausted [6], [7]. Smithsonite, the most common zinc oxide minerals, has become a good alternative for zinc extraction. Flotation is the most widely used approach to separating smithsonite from gangue minerals, because of the its low cost, high selectivity and easy operation [8].

Calcite is one of the most common gangue minerals that coexists with smithsonite [9]. Since collectors usually reacted with metal ions on the mineral surface through hetero-coordination, the similar surface physicochemical properties of smithsonite and calcite make the high-efficient flotation separation of these two minerals rather difficult [10], [11]. In addition, both smithsonite and calcite are semi-soluble in nature, which means a large amount of Ca2+ and Zn2+ species would dissolve in the solutions in the grinding and flotation processes [7]. The dissolved species would not only react with flotation reagents but also hydrolyze and precipitate on the minerals surface and render them similar surface physicochemical properties. This severely deteriorates the flotation performance, making the flotation separation of these two minerals rather challenging. However, many attempts have been made to efficiently separate smithsonite from calcite. Specifically, flaxseed gum was found to be a potential inhibitor in the flotation separation of smithsonite and calcite, in which the chemical reaction between hydroxyl group and Ca sites on the calcite surface played a pivotal role [12]. Moreover, polyepoxysuccinic acid has been confirmed to achieve the flotation separation of smithsonite and calcite through its chemical adsorption on the calcite surface [13]. It is reported that amino trimethylene phosphonic acid was an effective depressant as it absorbed on the calcite surface in the form of Ca-PO3, which severely prohibited the subsequent NaOl adsorption on the calcite surface [14]. Additionally, glass water, fenugreek gum, sodium alginate and 2-phosphonobutane-1,2,4-tricarboxylic acid have also been utilized as efficient depressants in the flotation separation of smithsonite and calcite [6], [10], [15], [16]. Nevertheless, the high dosage of these depressants often has adverse influence on the subsequent sedimentation and filtration process. Besides, the macromolecule polymers utilized in the flotation process may also cause serious environmental problems. Hence, environmental friendly and high-efficient depressants for the flotation separation of smithsonite and calcite are still urgently needed.

Calcium lignosulphonate (CLS), a byproduct from the sulfite wood pulping industry, is also used as an ingredient in feed stock, dairy, poultry and fish industries [17]. It contains sulfonic group, alkel and phenelic hydroxyl groups, making it possess the ability to chelate with polyvalent metal sites on the mineral surfaces[18]. In recent decades, CLS has been applied in the minerals flotation separation. Chen et al. [19] has confirmed that CLS was an attractive selective inhibitor in the flotation of scheelite from calcite in natural environment. Wang et al. [20] found that Fe3+ activated quartz could be selectively depressed using CLS as depressant at alkaline pH in the flotation of hematite. Additionally, CLS has also been utilized as effective depressant for the pyrite flotation in a wide pH range using butyl xanthate as collector in the flotation of chalcopyrite [21]. However, to date, CLS has never been reported utilized as depressant in the flotation separation of smithsonite and calcite.

In this study, CLS was introduced as a potential depressant in the flotation separation of smithsonite from calcite using sodium oleate (NaOl) as collector. Flotation experiments and artificial mixed minerals flotation experiments were conducted to explore the inhibition performance of CLS in the flotation separation of smithsonite from calcite. Zeta potential measurement, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) were carried out to investigate the interaction mechanism of CLS on the mineral surfaces.

Section snippets

Samples and reagents

The smithsonite and calcite minerals were purchased from Guangdong province, China. The ore blocks were initially crushed by a hammer. Then they were crushed and ground separately in a ceramic ball mill. The products were sieved to different size fractions. The products of −74+38 µm size fraction were utilized for flotation experiment and XPS analysis. The particles less than 5 µm were collected for FTIR analysis and zeta potential test. The two mineral samples were characterized by X-ray

Flotation results

The effect of NaOl dosage on the flotation recoveries of smithsonite and calcite at pH 10 was presented in Fig. 4. As shown, when the NaOl concentration was 10 mg/L, the recoveries of smithsonite and calcite were 24.61% and 43.45%, respectively, indicating that both these two minerals could not be well collected at low NaOl dosage. However, the flotation recoveries of both smithsonite and calcite increased distinctly with the increment of NaOl dosage. When the NaOl dosage reached 100 mg/L, the

Conclusion

In this study, the flotation separation of smithsonite and calcite was achieved using CLS as selective depressant and NaOl as collector at pH 10. A concentrate with Zn grade of 45.16% and Zn recovery of 85.60% was obtained in the artificial mixed minerals flotation experiment in the presence of CLS. Zeta potential measurement and FTIR analysis indicate that CLS absorbed on the calcite surface, while it absorbed little on the smithsonite surface. XPS analysis implies that the sulfonic group of

CRediT authorship contribution statement

Huafeng Sun: Conceptualization, Investigation, Methodology, Writing – review & editing. Fusheng Niu: Methodology, Investigation, Validation, Funding acquisition. Jinxia Zhang: Supervision, Formal analysis, Software, 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.

Acknowledgements

The authors gratefully thank the National Natural Science Foundation of China (51904106, 51874135) for their financial support.

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