Analysis of synthesis structures and flocculation stability of a polyphosphate ferric sulfate solid

Abstract

A solid polyphosphate ferric sulfate flocculant was prepared by a one-step "solid-solid" method; it had a molar ratio of 0.12 phosphorus to iron, a molar ratio of 1.46 sulfur to iron, and a molar ratio of 0.24 [OH−]/[FeT]. The procedure was simple and economical. The synthesis of the "Fe-P-Fe" polynuclear PO43- complex in the polyphosphate ferric sulfate flocculant resulted in a compound that has stable performance and an effective flocculation effect. The three forms of iron in the new polyphosphate ferric sulfate product were 51.71% Fe(a), 38.15% Fe(b), and 10.14% Fe(c). The solid product was stable for at least half a year. FTIR, XRD, XPS and SEM were used to analyse the effect of PO43− on the structure and flocculation form of the solid polyphosphate ferric sulfate flocculant. The results show that the bridge between the phosphate and hydroxyl groups complicates the regular crystal structure formation of the product. The Turbiscan Stability Index (TSI) value of the flocculant in the wastewater system was 839.78; the flocculant can agglomerate and bond with smaller particles in wastewater to form larger particles that gradually precipitate. Moreover, the flocculant itself gradually transforms into iron hydroxide gel precipitates through hydrolysis and flocculation processes, reducing the surface charge of organic compounds or other pollutants and facilitating their removal. This new solid composite flocculant has a certain market potential.