Adsorption changes of starch on minerals in carbonate-containing iron ore flotation by introducing amino radicals

https://doi.org/10.1016/j.molliq.2021.117511Get rights and content

Highlights

  • Amino radical was introduced in starch to improve flocculation and depression properties.

  • Modified starch exhibited an excellent depression effect on hematite.

  • Modified starch is beneficial to the attachment of siderite to quartz.

  • Modified starch is a promising regulator for refractory iron ore separation.

Abstract

Starch was modified by introducing amino radicals to solve the problem of poor selectivity during flotation. Changes in the flocculation and depression properties of starch after introducing amino radicals were compared in carbonate-containing iron ore flotation. Differences in adsorption between corn starch and modified starch were determined through zeta potential measurements, X-ray photoelectron spectroscopy (XPS) analyses, and molecular simulations. The flocculating effects of corn starch and modified starch were explored by the particle dynamics analysis and an in situ scanning electron microscopy (SEM) method. Amino radical can enhance the adsorption of modified starch on quartz via enhanced electrostatic forces. Both corn starch and modified starch exhibit excellent flocculating effects on fine siderite. However, siderite flocs formed with modified starch tend to attach to the quartz. Modified starch is a promising regulator for improving the grade by scarifying recovery in the flotation of refractory carbonate-containing iron ore.

Graphical abstract

Introduction

With deeper exploration, ore grade declines, and the mineralogy becomes more complex. Thus, the requirements for depressants are increased. Both efficiency and selectivity are considered. Natural organic depressants are popular for their non-toxicity, biodegradability, availability and low cost [1]. Starch is a widely used depressant in mineral processing and preferable for inexpensive green flotation of oxidized ores, sulfide ores, and salt ores [2]. With abundant intramolecular hydrogen bonds, starch forms a hydration film on minerals [3]. And the number of hydroxyl groups enhances hydrophilicity. As a result, starch and its derivatives exhibit an excellent depression effect. Moreover, its macromolecular structure makes it an efficient flocculant for fine mineral flotation [4], [5].

Starch exhibits excellent adsorption performance on hematite at a slightly alkaline pH. The flotation of hematite is depressed with dodecylamine acting as a collector, however, the flotation of quartz is minimally influenced. Thus, starch is commonly used to depress the flotation of iron minerals in the reverse flotation of hematite [6], [7]. It can also be used to depress pyrite flotation [1]. With electrostatic forces, hydrophobic interactions, hydrogen bonds, and chemical bonds, the starch adsorbed on pyrite forms a hydrophilic layer and prevents adsorption of the collector. Flotation separation of chalcopyrite from pyrite can be achieved. Starch is also an effective depressant with high selectivity in the reverse flotation of diaspore from kaolinite. Starch is adsorbed on diaspore more stably than on kaolinite though formation of five-membered ring complexes. Furthermore, starch is a depressant in the reverse flotation of phosphate and the anionic flotation of fluorite from barite [8], [9].

However, starch has poor selectivity and low solubility in cold water during flotation [10]. The complex branching structure and chain length distributions result in unpredictable behavior [11], [12]. The amphiphilic characteristics produced by the hydrophilic –OH group, the hydrophobic –CH3 group, and α-glycosidic linkages are the main causes[13]. In recent decades, modification of starches, including changing the molecular size and inserting new chemical groups, has been performed to meet the requirements for high-efficiency ore separation [14]. After starch oxidation, carbonyl and carboxyl moieties appear during starch depolymerization occurs [15]. Thus, the oxidized starch improved the separation efficiency of chalcopyrite from graphite significantly. Grafting organic chains onto starch is a common modification method. With the separate introduction of acrylamide and acrylic acid, starch graft copolymers exhibit excellent flocculation and depression effects in the flotation of pentlandite [16]. Modification of starch has been demonstrated as an effective means of overcoming the structural limitations of native starch and improving depressive capacity [17]. However, the structural functionality of starch derivatives remains unclear. The binding mechanism and adsorption morphology requires further research.

This study focuses on changes in the flocculation and depression properties of starch after introduction of amino radicals. The flocculation and depression effects of starches, and the adsorption differences of starches on minerals were deeply investigated in carbonate-containing iron ore flotation.

Section snippets

Materials

The siderite, hematite, and quartz mineral samples originated from Liaoning Province, China. High-purity samples were hand-sorted, crushed, and ground. Particles smaller than 0.074 mm were collected. The detailed purification processes are described in our previous studies [5], [18]. Siderite samples were reground to obtain particles smaller than 0.010 mm. Some of the mineral samples were finely ground to obtain the particles smaller than 0.005 mm for further measurements.

Chemically pure sodium

Flotation of single minerals

Sodium oleate was used as the collector for the flotation of both single mineral and artificial mixtures. Based on the conditional experiment results shown in Fig. S1-S3, the optimal collector dosages for siderite, hematite, and quartz flotation were set as 200 mg‧L-1, 240 mg‧L-1, and 240 mg‧L-1, respectively. And the pH was set at 6.9, 10.5, and 11.0, respectively. In the optimal conditions, the recoveries of siderite, hematite, and quartz were 76.65%, 92.11%, and 14.00%, respectively.

The

Conclusions

In this study, amino radicals were introduced into starch to improve its flocculation and depression capacity. The performances of corn starch and modified starch in refractory carbonate-containing iron ore were compared. The flotation results showed that modified starch had a stronger depression effect on hematite and quartz. The introduction of amino radicals strengthened the electropositivity of starch and enhanced the electrostatic forces between the modified starch and the quartz. The

CRediT authorship contribution statement

Haiqing Hao: Investigation, Writing – original draft. Guixia Fan: Methodology, Conceptualization. Jie Yu: Investigation, Data curation. Yijun Cao: Supervision, Funding acquisition, Project administration. Jiongtian Liu: Conceptualization, Supervision. Subhabrata Das: 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.

Acknowledgements

This research was supported by the National Key Research and Development Program (No. 2018YFC1901601), the Henan Postdoctoral Foundation (No. 202001013), the National Natural Science Foundation of China (No. U1704252), and the Program for Innovative Research Team (in Science and Technology) at the University of Henan Province (No. 19IRTSTHN028). Technical support provided by the National Supercomputing Center in Zhengzhou is also acknowledged.

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