Ammonia and Ammonium Reactions with Some Layer-Silicate Minerals
- J. L. Young and
- B. L. McNeal
Retention of NH3 and fixation of NH4+ by 16 specimen layer-silicate minerals was investigated using anhydrous and aqua NH3, NH4Cl, and different degassing and fixing conditions.
Despite a much greater partial pressure differential, vacuum degassing (to remove excess and physically sorbed NH3) greatly accentuated the retention and apparent NH3 fixation as compared with diffusion degassing.
The great bulk of NH3 initially sorbed by anhydrous NH3-treated layer-silicates was rapidly dissipated (few hours to < 3 days) when samples were exposed to the atmosphere. Redisplacement by competitive water vapor evidently was a principal driving force. The equivalent of tons of NH3 per acre-furrow-slice, however, was retained longer than 3 days by the expandable layer-silicates. The major portion (68 to 99+%) of retained NH3 was KCl leachable in all except the vermiculitic samples in which > 90% was fixed.
Wide variability in basal spacing changes resulted from ammoniation and wetting treatments. Physical changes as reflected by X-ray diffraction were in general accord with chemical data.
Vermiculitic minerals under wet or air-dry conditions fixed quantities of NH4+ greatly in excess of amounts fixed by other minerals. Metabentonite 38 and biotite 33 fixed moderate quantities under these conditions.
In a comparison of N sources under wet fixing conditions, less than 20% as much N was fixed by vermiculite from aqua NH3 as from NH4Cl. All other minerals fixed roughly equivalent amounts from both sources.
Montmorillonites fixed very small quantities of NH3 or NH4+ under wet or air-dry conditions but showed a roughly 20-fold increase in NH4+ fixation resulting from drying at 105°C.
Anomalous retention and mechanisms of NH3 retention and fixation are briefly discussed. Results re-emphasized need for continued restraint to minimize overextrapolation of data from a few type minerals to complex mixtures as generally encountered in soils.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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