Sorghum starch as depressant in mineral flotation: part 2 – flotation tests

In order to find a feasible replacement for cornstarch, the flour and starch of a graniferous variety of sorghum was tested as a depressant of hematite and quartz in a cationic microflotation in a modified Hallimond tube, using an ether amine as collector. Hematite and quartz samples from the Brazilian Iron Quadrangle were used in the flotation tests. The mineral samples were characterized by XRF, and SEM/EDS. Zeta potential measurements were performed in the pH range from 3.5 to 12.5. A commercial cornstarch was used as the depressant benchmark. Four depressants dosages and pH values were tested. A statistical test was used to verify the pH, dosage, and starch type influence on the minerals recoveries. At pH 10.5, the lowest average hematite recovery using sorghum starch was 7.27 ± 1.22% for a dosage of 40 mg/L, 13.24% lower than the value achieved for cornstarch. The results indicated that sorghum starch has a stronger depressant action on hematite than cornstarch. Quartz recovery was deeply influenced by the presence of cornstarch. Dosages below 40 mg/L of sorghum starch recovered more quartz than cornstarch in all tested pH values. At pH 9 and dosage of 5 mg/L, sorghum starch recovered 387% more quartz than cornstarch. The ANOVA test showed that pH, dosage, and starch type had significant impact on hematite and quartz recovery. The results suggest that sorghum has a great potential to replace corn as default depressant in iron ore flotation.