Monitoring the dynamics of concentrated suspensions by enhanced backward light scattering

The shear-induced flocculation of kaolin-polymer flocs in a stirred tank is investigated at medium to high solids concentrations (phi = 1 - 10% w/w). The evolution of the average floc size is monitored by the change in intens ity of laser light scattered in the 180 degrees direction. The measurements reflect the change in particle number concentration as flocculation procee ds. As flocculation begins, coagulation dominates and the flee size increas es (total particle number decreases) and then levels off at a steady state value as fragmentation becomes significant and balances coagulation. At ste ady state, the measurements indicate the extent of flocculation. Increasing the shear rate increases the coagulation and fragmentation rates, resultin g in smaller flee sizes at steady state. Increasing the flocculant concentr ation increases the steady state flee size by strengthening the bonds betwe en primary particles to resist fragmentation. At constant shear rate and fl occulant concentration, increasing the solids fraction decreases the steady state flee size indicating formation of weakly bonded flocs. Flocculant mi xing was the most important factor for flocculation efficiency at high soli ds concentrations.