A new inorganic–organic composite coagulant, consisting of Polyferric Sulphate (PFS) and Polyacrylamide (PAA)

Currently, research is focused on the synthesis of new composite coagulants, which are constituted of both inorganic and organic materials. In this paper, the development of relevant reagents was investigated, by combining the inorganic pre-polymerised iron-based coagulant Polyferric Sulphate (PFS) with an organic, non-ionic polymer (Polyacrylamide, PAA) under different PAA/Fe (mg/l) and OH/Fe molar ratios. Moreover, the new reagents were characterised in terms of typical properties, stability and morphological analysis (XRD, FTIR, SEM). Their coagulation performance, when treating low or high turbid kaolin–humic acid suspensions, was also investigated, whereas the applied coagulation mechanisms were discussed by using the Photometric Dispersion Analysis (PDA) analysis. The results show that the new coagulation reagents present improved properties, including increased effective polymer species concentration, and they exhibit very good stability. The respective tests using PDA confirmed that the predominant coagulation mechanism of PFS–PAA is the bridge formation mechanism. Coagulation experiments in low or high turbid kaolin–humic acid suspensions reveal that the novel composite reagent PFS–PAA exhibits better coagulation performance, when compared with simple PFS, in terms of zeta-potential reduction, turbidity and organic matter removal and residual iron concentration.