NEW METHODOLOGY TO EVALUATE NALCO WATER ANTIFOAM PROGRAMS IN THE ALUMINA TRIHYDRATE PRECIPITATION CIRCUIT

Foams are composed of gas dispersed in liquid; in the case of alumina refineries, this is air in liquor. Pure liquids do not foam in the absence of impurities, which are generally soluble surfactants in the liquid phase. Antifoam additives have been used in alumina precipitation for several decades. These products must have a reactive surface to remove the impurities, lower surface tension and be rapidly dispersed in the alkaline liquor. Laboratory trials must be conducted using different formulations to evaluate the most suitable candidates for an industrial application, but it is difficult to quantify product effectiveness in terms of foam generation and foam persistence with currently used methods. This work introduces a new laboratory methodology for the Bayer process to control foam height and persistence under different antifoam chemicals in alumina trihydrate precipitation. The method uses a Foam Cell, which has a volumetric cylinder with a scale to measure the foam height and a recirculation pump connected to a frequency inverter that allows adjustment in foam generation. It is well suited to evaluate a wide range of liquor and antifoam products due its precision and sensitivity of adjustment. Results obtained using this method are presented and the effect of different antifoam dosages applied to liquor from an alumina refinery is discussed.