Cationic polymers prepared from partially neutralized ferric chloride solutions were investigated using photon correlation spectroscopy (PCS) techniques. To study the speciation and yield of the polymers, FeCl3 solutions were hydrolyzed by adding NaHCO3 solution for a range of hydrolysis ratios (B = [OH]/Fe-T) of 0 to 2.0 under different base addition rates. It was observed that the prepared solution has a higher degree of polymerization at a higher base addition rate. The "B rate" (R-B 1/time), i.e., the rate of change of B during preparation, was found to have a dramatic effect on the speciation of the partially neutralized ferric chloride solution. High-yield inorganic iron(Ill) polymer (similar to 80%) can be produced in a specific range of B rates. These iron(III) polymers, having a size ranging from 3 to 7 nm, were stable without precipitation of ferric hydroxide microcolloids after aging for 2 weeks. (c) 2004 Elsevier Inc. All rights reserved.