Structural and functional insights into starches as depressant for hematite flotation

Starch is a cheap and eco-friendly polymer that has a broad range of industrial applications. In fine particle separation based on froth flotation, starch can be used to selectively depress the flotation of certain minerals such as iron oxides, sulphides and phosphates. Starch typically consists of two components: amylose (AM) and amylopectin (AP), which have distinct molecular structures. Despite its importance, there has been lack of quantitative, structural information on AM and AP adsorbed on solid particles. In the present work, hematite particles (80% passing 72 μm) were used as model particles, the adsorption densities of AM and AP of two different corn starches on hematite surface were measured at different pHs, and two important parameters of molecular structure of starch, the degree of branching and chain length distributions, were analyzed via size exclusion chromatography and 1H nuclear magnetic resonance spectroscopy, respectively. These results were compared to the corresponding outcomes of hematite flotation. It was found that the depressing ability of starch in hematite flotation had a positive correlation with the adsorption density of AP, and AP with longer branches would be more readily adsorbed onto hematite surface. In addition, adsorbed AP with more branches has stronger ability to depress hematite flotation. These insights will facilitate the development of novel starches for flotation processes and other industrial applications.