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Poly ferric sulfate (PFS) was synthesized by absorbing a dilute sulfur dioxide gas stream into a bench-scale reactor containing a stirred solution of ferrous sulfate, with sodium chlorate added as an oxidant. The reaction product was a solution containing approximately 50 wt.% PFS, a highly effective coagulant used in water treatment. The reaction took place near atmospheric pressure and at temperatures of 30–80 °C. SO2 removal efficiencies greater than 90% were achieved with ferrous iron concentrations of less than 0.1% in the product. The product solution was evaluated by wet chemistry methods to verify that the process was capable of consistently producing high quality PFS. Quality parameters examined were total iron concentration, ferrous iron concentration, basicity (mass ratio of OH/Fe(III)), density, and pH. The PFS product was used in pilot-scale tests at a municipal water treatment facility, and gave good results in the removal of turbidity and superior results in the removal of organic materials when compared with equal doses of ferric chloride.

Use of sulfur dioxide (SO2) in the production of polymeric ferric sulfate (PFS) was investigated. PFS is a highly effective coagulant useful in treatment of drinking water and wastewater, and could serve as a value-added sink for sulfur removed during coal gas cleanup. SO2 was absorbed from a dilute gas stream by sparging it into a bench-scale reactor containing a stirred solution of ferrous sulfate with sodium chlorate added as an oxidant. The reaction took place near atmospheric pressure and at temperatures of 30–80 °C, and produced a solution containing approximately 50 wt.% PFS. SO2 removal efficiencies greater than 90% were achieved with ferrous iron concentrations in the product less than 0.1%. Other PFS quality parameters were also monitored, including total iron content, basicity, and pH. A factorial analysis of the effect of temperature, oxidant dosage, SO2 concentration, and gas flow rate on SO2 removal efficiency is presented. In general, higher synthesis temperatures increased iron conversion rates while decreasing SO2 removal efficiency, and increased oxidant dosages had a positive correlation with removal efficiency. In addition, X-ray diffraction analyses showed that all dried PFS samples were found to be highly amorphous regardless of drying conditions.