Simultaneous adsorption of 3H-dodecylamine and 14C-starch onto hematite was investigated by two-channel liquid scintillation counting. Floatability of the resultant hematite was determined using a new type of laboratory test cell. Amine adsorption followed a Freundlich type isotherm, T = KC^n , n varying with pH and starch concentration. Adsorption increased with pH, especially at pH 8 - 10, and was enhanced by starch at low pH. Starch decreased amine adsorption at high pH. Starch adsorption increased with concentration and rose with amine concentration to 10^-4 molar. Higher amine concentrations lowered starch adsorption. Floatability increased with amine concentration up to 10^-3 molar and fell at 10^-2 molar amine. Maximum flotation was achieved in slightly alkaline solution. Starch was most effective as a depressant at high and low pH but the maximum floatability value was little affected. Starch produced a shift of the maximum floatability peak to higher pH levels. An explanation, based on amine-starch complexing, is proposed.
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