Sustainable green depression from natural starch modification: Improving flotation selectivity between ilmenite and forsterite

• SS exhibited a better selective depressing ability to forsterite than ilmenite. • SS performed chemisorption on the forsterite surface via Mg active sites. • At a SS dosage of 100 g/t, the TiO 2 grade in the concentrate increased by 5 percentage points to reach 40.55%, with a corresponding recovery of 61.75%. The efficient separation of ilmenite and forsterite using traditional collectors alone remains challenging. The main reason is that ilmenite and forsterite exhibit similar natural floatability. To address the issue, low-molecule sulfonated starch (SS) was successfully synthesized in this study by introducing highly polar sulfonate groups (−SO 3 − ) into the molecular chain of natural starch. The results indicate that the −SO 3 − groups endow SS with superior selectivity and dispersibility, which is attributed to the high selective binding capacity for metal ions and strong polarity. At an SS dosage of 100 g/t, the TiO 2 grade in the concentrate increased by 5 percentage points, reaching 40.55%, and the recovery was 61.75%. Mechanistic analysis demonstrated that SS underwent robust chemisorption on the surface of forsterite, whereas its interaction with Ti sites on ilmenite surface was feeble. Quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM) imaging provided definitive evidence for the adsorption behavior of SS on the surface of two minerals. On the surface of forsterite, the adsorption layer thickness (10.21 nm) and adsorption density (1040.19 ng/cm 2 ) of SS significantly exceeded those on the ilmenite (4.87 nm and 510.96 ng/cm 2 , respectively). These findings further demonstrate the depressive effect of SS on forsterite. It can thus be inferred that SS forms stable chemical bonds with Mg sites on the forsterite surface, whereas only weak physical adsorption occurs with Ti sites on the ilmenite surface.