Abstract
This paper is dealing with the obtaining of some coagulants from the polyferric sulfate (PFS) and Fe-based metal-polysilicate (PFSiS) classes and the preliminary assessment of the products performances. A series of partially hydrolyzed ferric solutions were obtained starting from copperas (FeSO4•7H2O), using exclusively hydrogen peroxide (H2O2) as oxidation – basification agent, in a molar ratio FeSO4/ H2O2 = 1:1 and FeSO4/H2SO4 molar ratios, from 20:1 to 2:1. The basification degree and stability of the basic Fe(III) salt solutions are mainly controlled by the FeSO4/H2SO4 ratio; FeSO4/H2SO4 ratios between 2.03:1 and 5:1 result in extremely stable solutions. The PFSiS coagulants were obtained through a modified copolymerization technique, involving the in situ generation of silicic acid (SA) at a Si/Fe molar ratio of 1:10, followed by oxidation-basification. Stable solutions were obtained over a narrow FeSO4/H2SO4 range, located around 2.5:1. All the solutions were characterized in terms of Fe(III) and residual Fe(II) concentration, free acidity, density, stability and time evolution of basicity. The coagulation tests indicate improved coagulation ability of the prehydrolized coagulants over the ferrous salt.