“Hydraulic granular” ammonium sulphate refers to granules produced on high-pressure hydraulic compaction presses rather than on conventional roll compactors. The higher and more sustained compaction pressure produces a denser granule with greater crushing strength and less tendency to generate fines in transfer. The term is a trade description rather than a standard-defined grade, so the useful test is the measured crushing strength and fines content, not the name.
Substance identity
Ammonium sulfate · (NH₄)₂SO₄ · CAS 7783-20-2 · PubChem CID 6097028 · 132.14 g/mol · dense angular granules, 2–4 mm; colour follows the crystal feed.
Specification
— typical commercial ranges
| Parameter | Typical range | Note |
|---|---|---|
| Total nitrogen (N) | 20.5 – 21.0 % min | |
| Sulfur (S) | 23 – 24 % | |
| Moisture (H₂O) | ≤ 0.5 % | dry feed is required for good compaction |
| Particle size, 2 – 4 mm | ≥ 90 % | |
| Crushing strength | ≥ 3 kgf reported for this form | the parameter to verify on the delivered lot |
| Bulk density | ≈ 1.0 – 1.1 t/m³ | at the upper end for granular ammonium sulphate |
| pH, 5 % solution | 5.0 – 6.0 |
Properties
Higher compaction pressure reduces intra-granule porosity. The measurable consequences are higher crushing strength, higher bulk density, and lower attrition — the granule survives more handling before breaking down into fines. A less obvious consequence is slightly slower disintegration in the soil wetting zone, because water must penetrate a denser particle; for field fertiliser use this is not a practical drawback and can moderate the initial salt concentration around the granule.
Chemistry is unchanged: same solubility, same critical relative humidity near 79–81 % at 30 °C, same decomposition behaviour, same acidifying reaction on nitrification. Feed-derived parameters — free acid, insolubles, iron, colour — pass through unchanged, exactly as in roll compaction.
Applications
The case for paying for a harder granule is handling-chain length. A product that will be bagged, containerised, shipped, discharged, road-hauled, blended and hopper-fed passes through many attrition points, and the fines that arrive at the field are both a spreading problem and a dust problem. Where the chain is short, standard roll-compacted product is usually adequate.
Beyond that, use is identical to any granular ammonium sulphate: bulk blending with size-matched granular DAP, MAP, MOP and granular urea, and mechanical broadcast application as a straight N+S source.
Handling and storage
As for compacted granular — dry, covered, away from strong alkalis, minimise drop heights even though the granule tolerates them better. Not classified as dangerous goods for transport.
Notes
Because “hydraulic granular” is not defined in any public standard, two suppliers can use the term for products of materially different strength. Specify crushing strength as a numerical contract parameter and, where the chain is long, agree a fines limit measured on arrival rather than on despatch. For hydraulic granular made from coke-oven feed, see the steel variant page.