Chlorine regeneration of a zeolite ion-exchange column for ammonia removal from an explosives-impacted mining wastewater.

Abstract

Zeolite ion-exchange column system has been suggested as a viable option for the removal of total ammonia nitrogen (TAN) from explosives-impacted mining wastewater (EIMWW) in cold regions. The objective of this bench-scale study was to compare the effectiveness of several NaOCl, NaOCl-NaCl and NaCl regeneration solutions on the performance of a zeolite column loaded with a synthetic EIMWW. The NaOCl experiments confirmed that effluent pH, total chlorine level, and free chlorine levels during the chlorine regeneration were positively related, thus indicating that ammonia is oxidized to nitrogen gas accompanied by production of hydrogen ions. This led to the regeneration of TAN-containing sites but it also regenerated sites containing K and Ca, this appears to be accomplished through the Na ions in the NaOCl solution and H⁺ ions generated in the breakpoint chlorination reaction. The three regeneration schemes worked effectively, they did not significantly impact TAN uptakes and TAN selectivity. The NaOCl-NaCl regeneration scenario was superior to the NaOCl regenerations as it was faster and resulted in shorter low-pH periods that may damage the zeolite. And unlike the NaCl regeneration, the NaOCl-NaCl used regenerant was essentially TAN free, so it permits regenerant reuse and avoids creating a secondary waste stream. Thus, zeolite column treatment coupled with NaOCl-NaCl regeneration is a practical approach for the treatment of TAN-laden EIMWW.