Ammonium Nitrate Occlusion vs. Nitrate Ion Exchange in Natural Zeolites
- Man Park and
- Sridhar Komarneni
Several salts, such as NH4NO3 and KNO3, can be occluded in natural zeolites through molten salt treatments, which increase the capacity of zeolites to store nutrients in addition to exchangeable cations. Zeolites occluded with NH4NO3 are potential candidates as slow-release fertilizers. This study focuses on determining the rates of NH4NO3 uptake by natural zeolites from molten salt and on evaluating kinetics of ion release from NH4NO3-occluded zeolites. The kinetics of ion release from NH4NO3-occluded zeolites were compared with those of NH+4-saturated zeolites. NH4NO3-occluded zeolites were prepared by treatment in molten NH4NO3 at 185°C for different time periods, or at 250°C for 4 h. Uptake of molten NH4NO3 by erionite apparently reached equilibrium after 8 h of treatment at 185°C. The total N uptake by NH4NO3-occluded zeolites was not related to cation-exchange capacity but depended on the structural type of the zeolite. Approximately a twofold increase in total N loading capacities of zeolites was achieved through salt occlusion compared with NH+4 exchange from solution. For example, phillipsite exhibited a N loading capacity of 76 g N kg-1 when treated with molten NH4NO3, but showed a capacity of only 46 g N kg-1 through NH+4 exchange. A simulated soil solution was used to examine the kinetics of ion release from both NH4NO3-occluded and NH+4-saturated zeolites. Occluded NH+4 and NO-3 were released slowly and steadily as in the case of exchanged NH+4 alone from zeolites during 30-d treatment in a simulated soil solution. It is evident from this study that salt-occluded zeolites are potential candidates as slow-release fertilizers.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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