Regeneration of cobalt complexes by thermal decomposition and acid treatment for NO absorption

- The spent cobalt based absorbent was regenerated for NO scrubbing.
- The chemical components of the spent absorbent were studied.
- Thermal decomposition was effective for regeneration.
- Regenerated absorbent showed original performance for NO scrubbing.

Wet scrubbing of NOx was accomplished by hexamminecobalt(II) solution in a laboratory setting, and the spent absorbent was regenerated by thermal decomposition and acid treatment. The spent absorbent contained precipitates (cobalt nitrosyl) and soluble cobalt in the solution. Thermogravimetric analysis (TGA) showed that the spent sorbent could be decomposed to CoO at temperatures above 900 °C. Caution needed to be exercised to ensure that the samples were not exposed to oxygen when cooling down to ambient temperature in order to prevent oxidation of CoO to Co3O4. The regenerated cobalt(II) oxide was dissolved in HCl for preparation of hexamminecobalt(II) solutions, and such a regenerated cobalt-based sorbent for NO removal performed at the same level as the fresh one. This study suggests a practical method for the regeneration of a cobalt-based absorbent involved in NO absorption.

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