The adsorption of selected modifying agents (namely, starch, sodium, silicate, fluosilicic and oleic acids on collophane, calcite, and dolomite) was studied as a function of concentration and ph. Fluosilicate, silicate, and oleate anions chemisorb on collophane and dolomite, while high-molecular-weight starches hydrogen bond to these surfaces. Electrostatic adsorption of starch on calcite was also noted to occur. Selective flocculation of collophane from quartz and the carbonate minerals from three natural ores was achieved utilizing sodium silicate, sodium hexametaphosphate, and potato starch at ph 10.5. Additionally, small additions of polyelectrolyte were made to increase the settling velocity of the collophane floccules. With ores from Idaho and Florida, concentrates containing 32% to 33% p2o5 were satisfactorily recovered. However, several processing steps are required that result in large reagent consumption. Techniques are suggested to reduce the number of stages of concentrate cleaning.