Agglomerate breakage in polymer-flocculated suspensions

Abstract

Studies of floc breakage have been carried out on a system of kaolin particles flocculated with a nonionic polyacrylamide. Experimental measurements of floc size distributions in agitated suspensions have been obtained using a sedimentation method. A mass-size balance model, used extensively in the analysis of grinding processes, has been adapted to the evaluation of floc breakage. A back-calculation procedure has been used to estimate breakage rates and primary breakage distributions from the observed floc size distributions. It has been shown that specific rates of breakage can be expressed as simple power functions of floc size and that they decrease significantly with increased polymer dosage. Based on earlier theories, the effects of agitation are less than expected. Primary breakage distributions seem to be generally insensitive to flocculation conditions except at a very low polymer dosage where breakage appears to be more thorough, leading to broad fragment size distributions. No evidence was found for significant reagglomeration during the floc breakage process. For the system studied here, it appears that floc growth occurs only while fresh polymer is being added to the suspension.