Depression behavior and mechanism of pyrogallol on bismuthinite flotation

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Highlights

  • The floatability of bismuthinite decreases with increasing pH.

  • Pyrogallol exhibits excellent depression effect on bismuthinite flotation.

  • Bi sites in bismuthinite surface account for pyrogallic acid adsorption.

  • Pyrogallol chemisorbs on bismuthinite surface via the formation of Bi–O–C bonds.

Abstract

Pyrogallol, an eco-friendly derivative of tannic, was a potential substitute of toxic depressant used in bismuth-molybdenum (Bi–Mo) sulfide ore flotation. However, unclear depression mechanisms of pyrogallol on bismuth sulfides hindered its further application in the industry. In this work, the effect of pyrogallol on the flotation performance of bismuthinite was evaluated using flotation tests, and associated interaction mechanisms were investigated by using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. Micro-flotation tests showed that pyrogallol exhibited excellent depressing performance to bismuthinite in the whole pH range tested (2–12). In the presence of 300 g/t pyrogallol, over 95% of bismuthinite was effectively depressed in the real flotation process at pH around 9. FTIR and XPS results demonstrated that pyrogallol was chemisorbed on bismuthinite through the interactions among Bi atoms exposed on the bismuthinite surface and O−H groups in pyrogallol. The adsorption mechanism was further ascertained by DFT calculations, which revealed that the Bi–O–C single bond and the five-membered ring complex models were involved in the chemisorption of pyrogallol on bismuthinite surface. The work presented here not only provides new insights into the inhibition mechanisms of pyrogallol on bismuthinite but also provides theoretical support for the industrial application of pyrogallol.

Introduction

Bismuth, an important eco-friendly metal (Mohan, 2010), has been widely employed in many technological fields (Liu et al., 2016). Its harmless nature made it a viable alternative for metals that are considered less environmentally preferred (Zhan et al., 2015). As a primary source of bismuth, bismuthinite is the only commercially viable mineral where bismuth is extracted (Zhan et al., 2015). However, in China, naturally occurring bismuthinite is frequently found to be associated with molybdenite (Cao et al., 2015), which makes effectively extracting bismuth difficult because both minerals are naturally hydrophobic and exhibit virtuous flotation response (Lin et al., 2018).

Conventional flotation processes for bismuth-molybdenum (Bi–Mo) sulfide ores involve bulk sulfide flotation in the first stage and the separation of molybdenite from Bi–Mo bulk concentrates in the second stage (Lin et al., 2020b). This processing technique is diffusely employed at the industrial level (Lin et al., 2019). However, residual collectors in bulk concentrates result in unsatisfactory separation results (Zhao et al., 2018). In order to remove the residual collectors and increase the floatability difference between bismuthinite and molybdenite for favorable separation results, bismuth sulfide depressants are imperative introduced to depress bismuthinite (Lin et al., 2020a). Sodium sulfide (Na2S), sodium hydrosulfide (NaHS), and Nokes reagents (P2S5+NaOH) have been the most commonly utilized depressants for removing adsorbed collectors and forming a hydrophilic layer on bismuthinite surface (Qin et al., 2017). However, these inorganic reagents are generally toxic and not eco-friendly (Suyantara et al., 2018b). Moreover, large dosages are usually required during their application (Zhang et al., 2020), which would increase the production cost (Huang et al., 2014), lead to poor selectivity (Yang et al., 2020), and finally affect recovering valuable minerals (Tang et al., 2019).

Another method for achieving selective flotation is employing different oxidation treatments (Hirajima et al., 2014). Oxidation reagents, such as sodium hypochlorite and hydrogen peroxide, could be used to promote the separation selectivity of molybdenite as well as other sulfide metals (Suyantara et al., 2018b). Lin et al. (2018) proposed that the floatability of bismuthinite dropped with increasing surface oxidation utilizing hydrogen peroxide. In recent years, plasma pretreatment (Hirajima et al., 2014), thermal pretreatment (Tang et al., 2019), and Fenton-like oxidation treatment (Suyantara et al., 2018a) were developed for the selective surface oxidation of sulfide minerals. These studies provide a novel idea to depress bismuthinite using an innocuous technology. However, some ineluctable disadvantages, for instance, complicated operation, uneconomic production, and low separation efficiency, block its further application in the industry (Castro et al., 2016). Hence, the exploitation of new depressants with high-efficiency, high-effectiveness and low- or non-toxicity remains an urgent task in the area of Bi–Mo sulfide flotation.

Pyrogallol, a decomposition product of tannins, is extensively distributed in nature (Pommerenk and Schafran, 2005). Owing to its low harmful effects to the environment and biology, pyrogallol is widely used in photography, food, and medicine (Chen et al., 2016). It is an aromatic compound whose molecular structure is majorly characterized via the existence of hydroxy and benzene groups (Thakuria et al., 2012) and tends to strongly interact with mineral surfaces. Chen et al. (2017) showed that pyrogallol chemically adsorbed on the calcite surface and exhibited negative effects on the recovery of calcite. Lin et al. (2019) demonstrated that naturally hydrophobic bismuth sulfide could be depressed by pyrogallol during the flotation separation of Bi–Mo sulfide ores. The approach of applying pyrogallol to depress bismuthinite seems to be a promising strategy for improving separation selectivity during Bi–Mo sulfide flotation and preventing toxic depressants usage. However, this method raises some technical issues when applied on the industrial production because the influences of pyrogallol on the floatability of bismuthinite is unclear and the detailed depression mechanisms involved remain unexplored. On this basis, the recent study was conducted to assess the influences of pyrogallol on the flotation performance of bismuthinite. The adsorption properties and interaction mechanisms of pyrogallol on bismuthinite surfaces were investigated through micro-flotation tests, bench-scale flotation tests, Fourier transform infrared spectroscopy (FTIR), X–ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. This work sheds light on the depression mechanisms of pyrogallol on bismuthinite and provides a theoretical guidance for the application of pyrogallol at the industrial level.

Section snippets

Materials

Chemosynthetic bismuthinite (Bi2S3, 10 μm) and molybdenite (MoS2, 10 μm) were provided by HAOXI Research Nanomaterials, Inc. The purity of bismuthinite and molybdenite was 99.99%, which was confirmed by X-ray diffraction (shown in Fig. 1). Typical bismuth-molybdenum (Bi–Mo) bulk concentrates was provided by Hunan Shizhuyuan Nonferrous Metals Co., Ltd. The contents of bismuth and molybdenum in the Bi–Mo bulk concentrates were 6.52% and 3.49%, respectively.

Analytical-grade pyrogallol was

Micro-flotation results

To investigate the inhibition effect of pyrogallol on the bismuthinite, the influence of pyrogallol on the flotation performance of bismuthinite and molybdenite was studied. The results are presented in Fig. 4, Fig. 5.

As evident from Fig. 4, the presence of pyrogallol considerably affected the flotation recovery of bismuthinite. In the absence of pyrogallol, the flotation recovery of bismuthinite was more than 83%. At an increasing pyrogallol dosage, the flotation recovery of bismuthinite

Conclusions

In this work, the effect of pyrogallol on the flotation performance of bismuthinite were investigated, and the underlying mechanisms were studied through micro-flotation tests, bench-scale flotation tests, FTIR, XPS, and DFT calculations. The main findings are summarized as follows:

  • Pyrogallol adversely affected the flotation response of bismuthinite over the entire pH range tested (2–14), especially in alkaline environments, but did not affect the molybdenite flotation. The flotation recovery

CRediT authorship contribution statement

Shangyong Lin: Conceptualization, Methodology, Writing - original draft. Jianyong He: Software, Investigation. Runqing Liu: Data curation, Validation, Writing - review & editing. Yuehua Hu: Data curation, Writing - review & editing. Wei Sun: Data curation, Writing - review & editing.

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

This work was supported by the Natural Science Foundation of China (No.51634009), National Key Scientific Research Project (No. 2018YFC1901601, 2018YFC1901602, and 2018YFC1901605), the Collaborative Innovation Center for Clean and Efficient Utilization of Strategic Metal Mineral Resources, the Natural Science and Technology Support Project of China (No. 2015BAB14B02), and the National 111 Project (No. B14034).

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