Observations of the comparative hydrolysis/precipitation behaviour of polyferric sulphate and ferric sulphate

The hydrolysis/precipitation behaviour of polyferric sulphate (PFS) and ferric sulphate (FS) under conditions typical for coagulation and flocculation in water treatment are investigated by studying the rate of floc size development, the zeta potential and chemical structure of precipitates and the iso-electric point of re-suspended precipitates. The results detailed in this study strongly suggest that, under the test conditions, the hydrolysis behaviour of PFS was significantly different from that of FS, with evidence of a relatively lower rate of floc size development and colloid charge reversal in the investigated Fe(III) dose range and a different chemical structure of the precipitates formed from PFS and FS.