Preparation of Polyferric Sulfate from By-Product Impure Ferrous Sulfate Monohydrate in Titanium Dioxide Industry

Polyferric sulfate (PFS), an important inorganic polymer coagulant, has various applications in water treatment. This study presents a cost-effective process for preparing PFS from impure ferrous sulfate monohydrate (FeSO4·H2O), a by-product of the titanium dioxide industry, with iron powder added to the system to neutralize the excess free sulfuric acid. Initially, commercial FeSO4·H2O served as the raw material to optimize the H2O2 direct oxidation process. The optimal process conditions were as follows: H2O2/commercial FeSO4·H2O molar ratio of 4.0, H2O2 addition rate of 0.4 mL/min, and reaction temperature of 55°C. Under these conditions, impure FeSO4·H2O and iron powder were used as raw materials to investigate the impact of different iron powder dosages. PFS performance was assessed based on variables including Fe(II) content, total iron content, basicity and turbidity removal rate. The products were characterized by XRD, FTIR, SEM, BET, and XPS. The results demonstrate that the incorporation of iron powder significantly enhanced the key properties of PFS. The PFS obtained in this study consisted of amorphous and basicity hydrated ferric sulfate with a large specific surface area. Moreover, the introduction of Ti4+ from impure FeSO4·H2O effectively reinforced the intermolecular complexation of PFS. This process realizes the utilization of industrial solid waste impure FeSO4·H2O without the addition of sulfuric acid. The economic assessment confirms its significant application advantages. The prepared PFS shows a high degree of polymerization and superior coagulation performance compared to previous studies.