Elsevier

Minerals Engineering

Volume 155, 15 August 2020, 106473
Minerals Engineering

New insights into lead ions activation for microfine particle ilmenite flotation in sulfuric acid system: Visual MINTEQ models, XPS, and ToF–SIMS studies

https://doi.org/10.1016/j.mineng.2020.106473Get rights and content

Highlights

  • Pb(NO3)2 improved micro-fine ilmenite flotation recovery by~12% with NaOL at pH 5.5.

  • ToF–SIMS technique was innovatively used to determine ilmenite surface properties.

  • H2SO4 promoted valence transitions of iron on ilmenite surfaces from Fe(II) to Fe(III).

  • Pb2+ ions enhanced adsorptions of molecule/colloid forms of oleate and PbOL complex.

Abstract

Recovering microfine particle ilmenite using froth flotation is extremely challenging. In this study, the flotation behaviors of microfine particle (−38 μm) ilmenite untreated or treated with lead ions using sodium oleate as a collector were studied. Micro-flotation experiments revealed that the ilmenite presented superior floatability at pH 5.5. Pb(NO3)2 increased the flotation recovery by~12%. Solution component analysis indicated that the presence of lead ions depressed the dissolution of Fe and Ti metal ions on the ilmenite surface. The dominant Pb(II) species and RCOOH(I) were responsible for ilmenite flotation. Zeta potential measurements suggested that the RCOOH (I) and RCOO ions mainly reacted with Fe and Pb on the ilmenite surfaces through electrostatic effects in addition to chemical adsorption. Fourier-transform infrared spectroscopy analysis showed that the new PbOL complex was formed on the ilmenite surfaces. X-ray photoelectron spectroscopy confirmed that the treatment of sulfuric acid promoted the valence transitions of iron ions. The proportion of the surface covered by Fe3+eventually increased from 32.51% to 63.22%. Time-of-flight secondary ion mass spectrometry (ToF–SIMS) provided strong evidence for the increased adsorption of oleate species on the ilmenite surfaces. Accordingly, the intensity of C4H7+ increased from 16,447 to 21089. New insights into lead ions activation for microfine particle ilmenite flotation in sulfuric acid system were mainly attributed to the oxidization of SO42− ions and the reinforced absorption of molecule/colloid oleate and PbOL complex compounds.

Introduction

Titanium has extensive applications in many fields, including aerospace, marine vessels, medical devices, catalytic materials, and military products due to its high strength to weight ratio and inertness in many corrosive environments (Niinomi, 2004, Wang et al., 2010, Tian et al., 2017). Ilmenite (FeTiO3) and rutile (TiO2) are suitable raw materials for the mass production of titanium white, sponge, and metal in contemporary industrial system (Bulatovic and Wyslouzil, 1999). Rutile is more preferred for Ti metal production because it has higher dioxide content (approximately 96%) than ilmenite (usually 50%) (Samal et al., 2009). At present, natural rutile resources are shrinking remarkably due to excessive exploitation and consumption (Bulatovic and Wyslouzil, 1999, Chachula and Liu, 2003). Therefore, ilmenite beneficiation has become increasingly important and sparked soaring interests. Gravity separation, high-intensity magnetic separation, electrostatic separation, or combinations of these techniques are conventionally used for the beneficiation of ilmenite ore (Cui et al., 2002, Chen et al., 2013b, Liu et al., 2015, Meng et al., 2018b). Ores containing microfine ilmenite are universally accepted as refractory resources for TiO2 concentration, and the above-mentioned separation methods fail to produce proper titanium concentration because of low grade ores, low liberation degree, and the similarities of some physical properties of ilmenite and gangue minerals (Bulatovic and Wyslouzil, 1999, Zhao and Zhou, 2007, Chen et al., 2013a, Zhou et al., 2013). Multitude amounts of fine-grained valuable ilmenite are discarded annually in the tailings of physical separations, thus leading to the striking loss of metal titanium (Zhai et al., 2019).

Pre-enrichment of low-grade ilmenite ores and subsequent employment of hydrometallurgical methods are necessary. As a physicochemical separation process, froth flotation is often cited as positive pre-enrichment technique for the selective separation of ilmenite mineral from these kinds of ores (Fan and Rowson, 2002, Li et al., 2016b, Chen et al., 2017b). However, recovering microfine particle ilmenite using froth flotation is extremely challenging. On the one hand, ilmenite displays inferior floatability to magnetite and rutile even at large dosages of collectors. This characteristic can be attributed to the interaction of the half of metallic cations (Fe2+ and Ti4+) as the surface-active sites with the collector anions in each pH range (Fan et al., 2009, Parapari et al., 2017). On the other hand, the problems posed by microfine ilmenite, such as small mass, large specific area, high surface energy, and high consumption of flotation reagents, contribute to the difficulties in ilmenite recovery (Bai et al., 2018). To overcome the limitations, researchers have made numerous efforts regarding the modification of surface properties of ilmenite, as well as reagents to facilitate the process of ilmenite flotation (Xu et al., 2015, Mehdilo and Irannajad, 2016, Wang et al., 2019).

Surface modification can adjust wettability and surface chemical properties (Foster et al., 2006). Two methods have been developed to increase the number of surface-active sites and enhance ilmenite floatability. The first one is to change the valence state or structure of the surface elements, which can be achieved through surface oxidation, such as microwave irradiation (Irannajad et al., 2014), oxidation roasting (Mehdilo and Irannajad, 2016), and surface dissolution (Parapari et al., 2016, Parapari et al., 2017). This method usually produces many active surface sites and facilitates the adsorption of collectors. Nuri et al. (2014) showed that the irradiation of ilmenite surfaces converted Fe2+ to Fe3+ ions, and improved the ilmenite floatability because of the increased oleate adsorption on ilmenite surfaces and the formation of many insoluble ferric iron oleate particles. Parapariet al. (2016) found that Fe3+content increased from 48.5% to 59.8% after H2SO4 surface dissolution for 15 min. This conversion increased the oleate ion adsorption on the ilmenite surfaces. Zhu et al. (2011) showed that acid surface dissolution improved the selective froth flotation separation of ilmenite from titanaugite (XY(T2O6), where X represents Ca and Fe2+; Y represents Mg , Fe3+, Al, and Ti; and T represents Si and Al).

The second method is to introduce extra metal ions to be adsorbed on the ilmenite surfaces as potential determining ions. Literature review indicated that the sample with extra metal ions could attract more reagents to elevate the flotation behavior of ilmenite compared with that without metal ions (Chen et al., 2017a). Metal ions such as Cu(II), Bi(III), and Pb(II) are extensively used as surface modification agents in the flotation recovery of titanium minerals. Meng et al. (2018a) suggested that the lead species interacted with iron hydroxyl compounds to form lead-containing complexes on the ilmenite surface, and the adsorption of benzohydroxamic acid (BHA) increased. Xu et al. (2017) investigated the effect of lead ions on ilmenite flotation by using BHA as a collector and found that the formation of Pb–BHA complexes contributed to the improvement of ilmenite recovery by~43%. Chen et al. (2017b) suggested that the lead species interacted with iron–hydroxyl complex compounds and form Fe–O–Pb complexes. Li et al. (2016a) indicated that ilmenite surface properties were activated after modification by Cu(II), and the adsorption amount of a-hydroxyoctyl phosphinic acid increased by 0.2~0.6 × 10−5 mol/m2 from pH 3 to 11 ± 0.2. Xiao et al. (2018) reported that Bi(III) ions increased the activating sites and largely improved the rutile flotation recovery from 62% to 91%. The advantages of above-mentioned surface modifications primarily stem from the changes of the amount and state of active sites located on ilmenite surfaces. These alterations provide an easy access for ilmenite particles to be captured by air bubbles, resulting in the reinforcement of ilmenite floatability.

Lead ions facilitating ilmenite flotation have been applied in industrial production for decades (Fan and Rowson, 2000). Ilmenite separation can be achieved using fatty acid. Nevertheless, the mechanism underlying lead ions activation for microfine particle ilmenite flotation fails to receive further discussions. Furthermore, the interaction of lead ions on the ilmenite/water interface, especially in the H2SO4 system, is still unclear. Therefore, in this study, micro-flotation experiments, solubility tests, Visual MINTEQ model, Zeta-potential measurements, Fourier-transform infrared spectroscopy (FT–IR), X-ray photoelectron spectroscopy (XPS) analyses were conducted to investigate lead ions activation in the H2SO4 system and its response to ilmenite flotation in detail. Time-of-flight secondary ion mass spectrometry (ToF–SIMS) was also used to characterize ilmenite surfaces and provided new insights into the increase in lead species and the adsorption of sodium oleate (NaOL). Our results enriched the theoretical basis for ilmenite flotation.

Section snippets

Materials and reagents

The ilmenite samples used in this study were concentrates of gravity separation collected from Panzhihua region, Sichuan province of China. The − 38 μm size fraction with a > 95% purity of ilmenite particles were used in all the experiments after further grinding, physical purification, and analysis by wet sieving. The results for the particle size analysis of the samples are presented in Table 1. As seen from Table 1 that 50% of them (D[0.5]) had a size below 17.21 μm, hence, the sample was

Effect of pH

The micro-flotation experiments were conducted as a function of pH in the presence of NaOL dosage of 2.0 × 10−4 mol/L and the results are shown in Fig. 2. As seen from Fig. 2, pH played an essential role in the flotation of microfine particle ilmenite. Ilmenite exerted a relatively desirable floatability at the pH ranges of 4–6 and 9–11. The flotation recovery was only 32.8% at pH 2.65, and a further increase in pH in acidic environment was beneficial to ilmenite flotation. A maximum value of

Conclusion

Pb(NO3)2 addition enhanced the NaOL flotation of microfine particle ilmenite in H2SO4 system (pH = 5.5) and increased the flotation recovery by ~12%. Ilmenite solubility experiments and solution component analysis indicated that the presence of Pb2+ ions depressed the dissolution of Fe and Ti metal ions on ilmenite surface. Moreover, the dominant Pb(II) species and undissociated oleate species (RCOOH(I)) were responsible for the ilmenite flotation behavior. Zeta potential and FT–IR measurements

CRediT authorship contribution statement

Shaojun Bai: Conceptualization, Methodology, Writing - review & editing. : . Pan Yu: Writing - original draft, Data curation. Zhan Ding: Investigation, Data curation. Yunxiao Bi: Visualization, Investigation, Software. Chunlong Li: Visualization, Investigation, Software. Dandan Wu: Conceptualization. Shuming Wen: Supervision.

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 are grateful to the financial support of the Regions of the National Natural Science Foundation of China (Grant No. 51664027) and Natural Science Foundation of Yunnan Province (Grant No. 2019FB078). The authors are grateful to the Analysis and Testing Centre in Kunming University of Science and Technology for its technical support (2018M20172101100). We would like to thank shinewrite for providing linguistic assistance during the preparation of this manuscript.

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