The chemical species distribution and transformation of polyaluminum silicate chloride coagulant

The chemical species distributions of polyaluminum silicate chloride (PASC) and polyaluminum chloride (PACl) determined by Al-Ferron complexation timed spectrophotometric and Al-27-NMR methods, respectively, have been compared and analyzed. The experimental results show that the species distribution and transformation of PASC are different from those of PACl, due to the interaction of polysilicic acid and hydrolyzed aluminum species. At the same basicity (B), the contents of, Al-b, Al-13 and the monomer species Al-mono (also determined by Al-27-NMR) in PASC are lower than those in PACl, while the contents of Al-c and the Al-other determined by Al-27-NMR in PASC are higher than those in PACl. The differences between PASC and PACl with respect to these species enlarge as the molar ratio of Al/Si in PASC decreases. Further, in PACl the ratio of Al-13 to Al-b Closes to 1.0, indicating that the amount of the two fractions are similar. In PASC, however, such an agreement does not exist at the lower B values and Al/Si molar ratios. When the B value and Al/Si molar ratios increase, however, the amount of Al-13 and Al-b species tends to close. The study findings indicate that polysilicic acid can react with hydrolyzed aluminum species to form an aluminum silicate polymer composite and result in the change in species distribution of PASC. (C) 2002 Elsevier Science Ltd. All rights reserved.