Polyferric silicate sulphate (PFSiS): Preparation, characterisation and coagulation behaviour

The process of coagulation is a fundamental environmental protection technology, which is mainly used in the treatment of water and wastewater. The relevant research is currently focused on the development of new improved coagulation reagents. A characteristic example is polyferric silicate sulphate (PFSiS), a relatively new pre-polymerised inorganic coagulant. In this paper, PFSiS is prepared following two approaches: (a) hydroxylation of the mixture consisting of Fe2(SO4)3 and fresh polysilicic acid (PFSiSc); (b) hydroxylated polyferric sulphate (PFS) combined with fresh polysilicic acid (PFSiSm) under different Fe/Si and OH/Fe molar ratios. The prepared coagulants were characterised in terms of major typical properties, such as the degree of polymerisation, pH value, ζ -potential, conductivity, turbidity etc. Furthermore, the effect of different Fe/Si and OH/Fe molar ratios and of aging time on the values of pH and ζ -potential of products were also investigated. Finally, the coagulation behaviour of PFSiS was assessed by studying the reduction of the turbidity of kaolin (clay) model suspensions. The obtained results suggest that PFSiS exhibits a superior coagulation performance in comparison with other iron-based coagulants.