A systematic study for the characterization of a novel coagulant (polyaluminium silicate chloride)

The current research in coagulation-flocculation field has focused mainly in understanding the behavior and chemistry of pre-polymerized coagulants, such as polyaluminium chloride (PACl), and the improvement of their properties. A possible way to increase the efficiency of PACl is claimed to be the incorporation of silica in its structure, in the form of polysilicates. The new product is called polyaluminium silicate chloride (PASiC) and is supposed to be more effective than PACl, when applied in the coagulation-flocculation process. The purpose of this study was the synthesis and characterization of many possible derivatives of polyaluminium silicate chloride, based on different basicity (OH/Al molar ratio), silica content (Al/Si molar ratio) and preparation method (co-polymerization or composite polymerization) to get an overall picture of their major physico-chemical properties. Overall 32 silica based coagulants were prepared with different OH/Al (1-2.5) and Al/Si (5-20) ratios. Their properties were mainly evaluated by means of polymerization degree and aluminium species distribution employing either the ferron technique or the 27Al NMR method, in order to evaluate the impact of silica addition in the new coagulants. Moreover, the formation of new species was investigated with the use of X-ray diffraction, FTIR, and SEM methods. Finally, their stability was investigated over a time period of several months.