Simultaneous Removal of NO and SO₂ by High-Temperature Fluidized Zero-Valent Iron Processes

Abstract

A new approach to simultaneously remove nitrogen mon-oxide (NO) and sulfur dioxide (SO₂) by zero valent iron (ZVI) was investigated. Three different parameters, temperature, flux, and ZVI dosage, were tested in fluidized ZVI column studies containing 500 ppmv of NO and SO₂, respectively. Under the ZVI dosage of 0.5 g at flux of 0.6 L/cm²·min for temperature 573 K, there is neither NO nor SO₂ reduction. For 623 K and 673 K, complete removal for NO and >90% removal for SO₂ were achieved. For temperatures of 723 K and 773 K, 100% removal was achieved for both NO and SO₂. The amounts of NO or SO₂ reduction (as milligrams of NO or SO₂ per gram ZVI) increased as temperature increased, and linearities were observed with both correlation coefficients >0.97. Compared with NO, SO₂ had earlier breakthrough because of a slower diffusion rate and less reactivity but higher mass reduction because of a higher molecular weight for SO₂ (64 g/mol for SO₂ and 30 g/mol for NO). At same temperature, both NO and SO₂ reductions (as milligrams of NO or SO₂ per gram of ZVI) were constant regardless of either flux or ZVI dosage variation, but breakthrough time was affected by both flux and ZVI dosage. A parameter weight of ZVI/flux (W/F) was developed to represent these two parameters at the same time to assess the breakthrough time of NO and SO₂. Higher breakthrough time was achieved for higher W/F value. Moreover, interestingly, longer breakthrough time and more NO and SO₂ mass reduction were achieved for combined NO and SO₂ than individual NO or SO₂ treated by ZVI, and both oxidation and reduction reactions occurred instead of a reduction reaction only. Chemical reactions among ZVI/NO, ZVI/ SO₂, and ZVI/NO/SO₂ were also proposed and verified by X-ray diffraction analyses.