Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng XPS study on the mechanism of starch-hematite surface chemical complexation Gabriela F. Moreira a , Elaynne R. Peçanha b , Marisa B.M. Monte a,b , Laurindo S. Leal Filho a , Fernando Stavale c, ⁎ a Instituto Tecnológico Vale - ITV, Avenida Juscelino Kubitschek, 31, Ouro Preto, MG 35.400-000, Brazil b Laboratory for Surface Chemistry, Coordination of Mineral Processing – CETEM, Avenida Pedro Calmon, 900 Ilha da Cidade Universitária, Rio de Janeiro, RJ 21941- 972, Brazil c Centro Brasileiro de Pesquisas Físicas – CBPF/MCTI, Rua Xavier Sigaud 150, Rio de Janeiro, RJ 22290-180, Brazil ARTICLE INFO Keywords: Iron ore Starch Flotation XPS FTIR ABSTRACT Polysaccharides are some of the most widely employed flotation reagents in the mineral processing industry. Among several, starch is of particular importance for reverse flotation of iron ores. It is known to behave as an efficient depressant for hematite and, therefore, its interaction is of great relevance. In this paper, we investigate the surface chemistry of starch adsorbed onto hematite by means of X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Our results indicate that starch undergoes an important oxidation process under industrial gelatinization conditions, which favors the binding of starch molecules. Meanwhile, the oxide surface is subjected to full hydroxylation, leading to strong polysaccharide-metal hydroxide interaction. Previously proposed starch interaction mechanisms are discussed, and the importance of acid-base interactions is underscored. 1. Introduction Adsorption of specific molecules on metal oxide and hydroxide surfaces is of significant importance in a variety of fields, ranging from catalysis to corrosion science and semiconductor manufacture (Shrimali et al., 2016). Applications involving separation of minerals by flotation are particularly relevant for this paper (Araujo et al., 2005). In this field, a metal oxide surface immersed in aqueous solution undergoes several reactions at acid-base sites, including the formation of surface hydroxyl groups and eventual adsorption of organic molecules, result- ing in hydrophobicity or hydrophilicity. The adsorbed species can interact upon the oxide surface in different ways, such as through electrostatic or hydrophobic interactions and chemical complexation, depending on the choice of appropriate aqueous solution conditions. Therefore, a significant step toward understanding their chemical interaction can be made by investigating surface composition and associated changes (Laskowski et al., 2007; Liu et al., 2000; Filippov et al., 2013). In this study, we focus on the interaction between iron oxide (hematite) and cornstarch, one of the mostly widely used organic depressants. Adsorption of starch on iron oxides has been widely investigated and debated in the literature as it represents a relatively inexpensive and environmentally-friendly separation agent, besides acting as a very effective depressant (Laskowski et al., 2007; Liu et al., 2000; Weissenborn et al., 1995; Kar et al., 2013; Tang and Liu, 2012; Pavlovic and Brandao, 2003; Martins et al., 2012). Moreover, the starch adsorption mechanism is of major importance not only for the separation of iron ores, but also because it is largely employed for a number of other minerals, including sulfide and phosphate ores (Laskowski et al., 2007; Liu et al., 2000; Filippov et al., 2013; Raju et al., 1997; Leal Filho et al., 2000). In short, the separation process is based on the adsorption of starch molecules onto iron oxide, which renders the surface hydrophilic, preventing, at the same time, the adsorption of hydrophobic amine molecules present in the aqueous solution. In earlier studies, non- selective hydrogen bonding and electrostatic forces were proposed as the primary adsorption mechanism for carbohydrate molecules, mainly because of the large number of hydroxyl groups on both starch and oxide surfaces (Balajee and Iwasaki, 1969). Later investigations sug- gested, however, that polysaccharide molecules might preferably adsorb through acid-base interactions, as discussed by Laskowski et al. in a recent review article (Laskowski et al., 2007). Current research on starch adsorption addresses the important role of metal- hydroxylated oxide surface, supported by a number of studies using http://dx.doi.org/10.1016/j.mineng.2017.04.014 Received 26 October 2016; Received in revised form 6 April 2017; Accepted 21 April 2017 ⁎ Corresponding author. E-mail address: stavale@cbpf.br (F. Stavale). Minerals Engineering 110 (2017) 96–103 0892-6875/ © 2017 Elsevier Ltd. All rights reserved. MARK