Ion flotation of dichromate with a cationic surfactant



An experimental investigation is presented of the flotation of dichromate ion from aqueous solution with a cationic surfactant, ethylheaxadecyldimethylammonium (EHDA) bromide. Dichromate forms a colloidal complex with EHDA ion in a molar ratio of approximately 1 : 2. Excess surfactant causes the formation of a stable foam to which the complex is adsorbed, providing the separation of dichromate from aqueous solution. Batch flotation studies were conducted utilizing approximately 2-liter solutions containing from 10 to 200 mg. of dichromate ion (4.8 to 96.3 mg. of hevavalent chromium), with masses of EHDA-Br ranging from 400 to 800 mg. The effects of mass of surfactant added, dichromate concentration, pH, and possible interfering anions were determined. A comparison is made with pure surfactant solutions, and the mechanism of the process is discussed.

Most efficient operation is achieved with a molar feed ration of EHDA ion to dichromate ion from 2.1 to 3.0, and removal ratios ranging from 80 to 95% are obtained. Reduction of the residual dichromate below 10% of the feed concentration requires additional surfactant and produces excessive foam, which could be overcome by modifications in operating conditions.