Causes of transient flocculation of fines with polyethylene oxide and a cofactor: Implications for mill performance

Abstract

Neutral polyethylene oxide (PEO) is conventionally used with a cofactor (CF) as a retention aid system. Challenges to their performance, mainly poorly reproducible flocculation efficiencies, are the subject of many studies. In this work, we have found a number of results. Fines flocculation with PEO alone, and in combination with CF, was found to be transient at low and high shear rates, as deflocculation occurred after equilibrium. Amplitude and initial rate of flocculation showed with CF addition significant increase, which agrees with literature work, and is attributed to CF role in strengthening bridging bonds and stiffening entangled PEO coils. Adding more, CF with PEO showed a contradiction as it enhanced both flocculation and deflocculation. Transient regime can be attributed to PEO, since increasing PEO concentrations in experiments with PEO alone enhanced deflocculation. On the other hand, CF addition with PEO enhanced deflocculation rates several magnitudes compared to PEO alone. In mills using CF–PEO, unit designs and operating systems differ from mill to mill, resulting in different flocculation and residence times. Knowledge of flocculation time, after CF and PEO additions is essential to operators and designers to select a residence time which minimizes deflocculation to get optimum operation.