Abstract:Using sodium oleat as collector and cassava starch, carboxymethyl starch with degree of substitution of 0.026 and 0.21, and phosphate ester starch with degree of substitution of 0.0065 and 0.055 as depressant, the floatability of hematite and quartz were investigated, and effect of degree of substitution of modified starches on capability of depression have been mainly studied. Results of flotation tests show that depressing to hematite of modified starches are similar with native starch, and the higher degree of substitution of modified starches, the stronger depression capability to hematite. For quartz activated by Ca2 , both native starch and modified starches have no obvious depression at lower Ca2 dosage, but with the increase of Ca2 dosage, modified starches show a certain depression which increase with the degree of substitution. The depression was related to the dosage of three reagents of sodium oleate, Ca2 , and modified starches. Ca2 was adsorbed on the surface of quartz in the form of Ca(OH) , then sodium oleate or modified starches reacted with Ca(OH) . If the dosage of sodium oleate is enough to react with all Ca(OH) , quartz would be collected. If the dosage of sodium oleate is relatively small, quartz would be depressed by modified starches which reacted with the other Ca(OH) . If sodium oleate and Ca2 are added in optimum dosage range, with the increase of the degree of substitution modified starches would have more effective depression in reverse flotation of removal quartz from hematite.