Effect of charge type and molecular weight of polyacrylamide on the characteristics of kaolin floc

摘要

Although the synthetic organic polymers have been widely applied as flocculent aids to improve solid-liquid separation efficiency,it is not very clear how the charge type and molecular weight of the polymers influence the characteristics of floes.In this paper,floc characteristics.Such as floc size.Density,structure,strength and reversibility were investigated in details in terms of their response to the polyacrylamide(PAM)with difierent charge types and molecular weights.Small angle laser light scattenng,image analysis and settling technology were employed simultaneously.The results showed that floc size induced by anionic PAM with medium molecular weight(A130)and ultra high molecular weight (A115)was 418.5 μm and 437.8 μm respectively,whereas floc size induced by cationic PAM with medium molecular weight(C448)and very high molecular weight(C498)Was 731.1 μm and 796.4 μm respectively.And also.Floc fractal dimension was inversely propotional to polymer molecular weight(the values were between 1.91 and 2.40).Furthermore.Floc density was affected by molecular weight of anionic PAM more dramatically than that of cationic PAM.For a given floc size.The density increased with molecular weight.In addition,flocs formed by cationic PAM showed much greater shear-resistant ability and reversibility than anionic PAM.Nevertheless,the poor reversibility of the flocs formed by high molecular weight was also observed.An explanation for the distinguished characteristics of floes formed by various PAM types was offered in terms of flocculation mechanisms.