Sorghum starch as depressant in mineral flotation: part 1 – extraction and characterization

The mineral industry is constantly searching for new and sustainable innovations, in order to improve its results and processes. In this context, sorghum (Sorghum bicolor (L.) Moench), a widely farmed crop, was characterized and tested as an alternative depressant in mineral flotation. Starch was extracted from sorghum flour produced with grains cultivated in Brazil, resulting in an extraction yield of approximately 26%. Under polarized light microscopy, starch showed Maltese crosses, indicating that the isolation method used produced intact starch granules. SEM images indicated that the starch granules were oval or semi-spherical, with the occasional presence of broken granules and surface pores. Granule size distribution ranged from 5.5 to 30μm with average size of 15.5μm. With 25.5% of amylose content and relative crystallinity around 26%, the sorghum starch was classified as medium size A-type starch. FTIR spectroscopy results confirmed the presence of polysaccharide characteristic peaks, as expected. Thermal properties were measured by DCS, with results similar to cornstarch. Rheological characterization indicated a pasting temperature of 67.1°C and viscosity peak of 2596cP. The characterization results indicate a high potential for sorghum as depressant in mineral flotation being a feasible option for cornstarch.