Flocculating properties of high molecular weight lignosulphonates

The flocculating properties of various molecular weight lignosulphonates have been examined. The low molecular weight polymers were found to act as dispersants at all concentrations even in the presence of alum. In contrast, lignosulphonates having an intrinsic viscosity greater than 0.11 dl/g acted as flocculants at low concentration and dispersants at high concentration. The flocculation rate increased with the molecular weight of the polymer, and was greatly enhanced by the presence of alum. Reducing the pH enhanced the dispersing properties of the low molecular weight lignosulphonates and the flocculating properties of the high molecular weight material.