Chlorine vs. Sodium Chloride Regeneration of Zeolite Column for Ammonium Removal from an Explosives Impacted Mining Wastewater

Abstract

There has only been limited research on ammonium removal by zeolites followed by chlorine regeneration; these studies used batch tests and, in many cases, only dealt with single solute solutions as opposed to multi-component ones. To better simulate full-scale applications, this study used a continuous-flow ion exchange (IE) column system to assess the feasibility of chlorine regeneration of a zeolite IE column used for the removal of ammonium from synthetic explosives impacted mining wastewater (EIMWW). Multi-cycle column loading-regeneration tests were used to evaluate and compare the performance of a NaOCl (1000 ppm as free Cl2) solution with that of a standard salt regeneration solution (5% NaCl). In addition, the impact of two loading cycle durations was evaluated. After three operational cycles with 6 h loading phases, the TAN (total ammonia nitrogen) uptake after NaOCl regeneration was almost the same as that obtained with salt regeneration (0.21 meq/g vs. 0.21 meq/g). The zeolite with NaOCl regeneration showed a higher preference for TAN than with NaCl regeneration (Ca:TAN:K = 2.8:2.3:1 vs. 2.5:1.9:1 for the 6 h loading phase); however, the NaOCl regeneration took longer to complete. It was also found that effluent pH, total chlorine level, and free chlorine level during the chlorine regeneration were positively related, seemingly confirming that the ammonium is oxidized to nitrogen gas and producing hydrogen ions. Regardless of the regeneration solution, if one uses a two-column system, with one column online and the other offline, the shorter loading cycles (6 h) yield a substantially higher daily TAN removal rate.