Absorption of dilute SO2 gas stream with conversion to polymeric ferric sulfate for use in water treatment

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 degreesC, 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. (C) 2004 Elsevier B.V. All rights reserved.