Recovery of ammonium from aqueous solutions using ZSM-5

The demand of reactive nitrogen (N), such as ammonium (NH₄⁺) and nitrate (NO₃^-), continues to increase for fertilizer applications as the population grows, but the Haber Bosch (HB) process currently employed for industrial N fixation is challenged by low efficiency and high energy consumption. Here we report on the investigation of ZSM-5 as a superior sorbent for the recovery of ammonium from aqueous solutions. Fast capture and release of ammonium (NH₄⁺) have been achieved with >90% overall efficiency of recovery using synthetic solutions of NH₄Cl and NaCl, respectively. The ZSM-5 sorbent has also been found to be recyclable and sustain high recovery efficiencies after multiple capture-release cycles. The capture of N has been further studied systematically in dependence of the dose of sorbent and reaction temperature, based on which the mechanism, thermodynamics and kinetics of ion exchange are discussed. Compared to other ion-exchange materials, the ZSM-5 sorbent exhibits superior selectivity for capturing ammonium in the presence of competing cations (NH₄⁺ » Ca²⁺ > Mg²⁺ > K⁺ > Na⁺) and demonstrates high efficiency of ammonium recovery from real wastewater streams.