Compacted granular ammonium sulphate is crystal ammonium sulphate that has been densified between counter-rotating rolls into a sheet, then crushed, screened and recycled until the target size band is met. No chemical change occurs — the granule is the same salt, mechanically consolidated. Compaction exists to solve the two field problems of crystal product: dust and poor spreading ballistics.
Substance identity
Ammonium sulfate · (NH₄)₂SO₄ · CAS 7783-20-2 · PubChem CID 6097028 · 132.14 g/mol · angular, irregular granules with fractured faces (not spheres); colour follows the feed crystal.
Specification
— typical commercial ranges
| Parameter | Typical range | Note |
|---|---|---|
| Total nitrogen (N) | 20.5 – 21.0 % min | slightly diluted if a binder or anticaking agent is used |
| Sulfur (S) | 23 – 24 % | |
| Moisture (H₂O) | ≤ 0.5 % | compaction requires a dry feed |
| Particle size, 2 – 4 mm | ≥ 90 % | screened; oversize crushed and undersize recycled |
| Crushing strength | 2 – 3 kgf typical | measure on the delivered lot, not on the specification |
| Bulk density | ≈ 1.0 – 1.1 t/m³ | higher than the crystal it was made from |
| pH, 5 % solution | 5.0 – 6.0 |
Properties
Because compaction is purely mechanical, solubility, hygroscopicity (critical relative humidity roughly 79–81 % at 30 °C), thermal decomposition above about 235 °C and soil acidification are unchanged. Dissolution is slower than for crystal of the same mass, since the granule must first disintegrate — normally an advantage in the field, since it moderates the initial salt concentration in the wetting zone.
The characteristic weakness of roll-compacted product is fines generation. Angular granules with fractured faces abrade against each other in every transfer, so a product that leaves the plant at 2 % fines can arrive at a field hopper with considerably more. Each transfer point — ship, silo, truck, blender, spreader hopper — contributes. Crushing strength on the certificate of analysis is the best available predictor, and it should be verified rather than assumed.
Applications
The principal use is bulk blending. Granular DAP, MAP, MOP and granular urea sit in the 2–4 mm band; a compacted ammonium sulphate in the same band blends without segregating, which crystal product cannot do. The second use is mechanical spreading: granular mass and shape give a usable spread width from a spinning disc, whereas fine crystal drifts and lands short.
Agronomically it is a straight 21-0-0 plus 24 S source, used wherever both nutrients are wanted — sulfur-responsive crops, alkaline soils where the acidifying reaction helps micronutrient availability, and surface applications where urea’s volatilisation risk is unwelcome.
Handling and storage
Minimise the number of transfers and drop heights; every fall generates fines. Dry, covered storage away from strong alkalis. Where the product carries an anticaking treatment, avoid re-wetting, which destroys it. Not classified as dangerous goods for transport.
Notes
Do not judge a compacted granule by its size alone. Two products both stated as “2–4 mm, 90 % min” can differ substantially in crushing strength and therefore in how much of the granular structure survives to the field. Where the granule is made from coke-oven feed, see the compacted granular steel page; where a harder granule is required, see hydraulic granular.