| 摘要 |
A cyclic process for removing lower valence nitrogen oxides from gaseous mixtures includes treating the mixtures with an aqueous media including alkali metal carbonate and alkali metal bicarbonate and an oxidant to form higher valence nitrogen oxides and to capture these oxides as alkali metal salts, especially nitrites and nitrates, in a carbonate/ bicarbonate-containing product aqueous media. 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 axe converted to nitrates by oxidation after lowering the product aqueous media pH to below about 9. A cyclic process for removing sulfur dioxide from gas mixtures includes treating these mixtures with aqueous media including alkali metal carbonate and alkali metal bicarbonate where the ratio of alkali metal to sulfur dioxide is not less than about 2. The sulfur values may be recovered from the resulting carbonate/bicarbonate/sulfite-containing product aqueous media as alkali metal sulfate or sulfite salts which are removed by crystallization from the carbonate-containing product aqueous media. As with the nitrates, the carbonate/ bicarbonate system strongly increases yield of sulfate or sulfite during crystallization. Where the gas mixtures include both sulfur dioxide and lower valence nitrogen oxides, the processes for removing and recovering lower valence nitrogen oxides and sulfur dioxide may be combined into a single removal/recovery system, or may be advantageously effected in sequence. |
