| 摘要 |
A cyclic process for removing lower valence nitrogen oxides from gaseous mixtures includes treating the mixtures in a first stage with an acidic aqueous media including a peroxygen oxidant to form nitric acid and higher valence nitrogen oides and to capture these oxides as alkali metal salts, especially nitrites and nitrates, in a carbonate/bicarbonate-containing product aqueous media in a second stage. Highly selective recovery of nitrates in high purity and yield may then follow, as by crystallization, with the carbonate and bicarbonate alkali metal salts strongly increasing the selectivity and yield of nitrates. The product nitrites are converted to nitrates by oxidation after lowering the product aqueous media pH to below about 9. Where the gas mixtures include both sulfur dioxide and lower valence nitrogen oxides, the processes for removing lower valence nitrogen oxides and sulfur dioxide may be combined into a single removal/recovery system, or may be effected in sequence.
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