Increased demand for sulphur-containing fertilizers steins from the discovery that low crop yields in certain cases may be related to deficiencies in sulphur in the soil. A shortage of sulphur can cause serious reductions in crop yield and quality.

Manufacturing processes for sulphur-containing fertilizers of the phosphate type often involve the use or incorporation of sulphates. A disadvantage of sulphates is that they are very mobile in the soil and easily leach out of the root zone, effectively making the sulphate nutrient unavailable to the plants. Elemental sulphur is not leached out of the soil as readily as sulphates. Instead, micron-sized elemental sulphur particles (e.g. with size from 1 to 200 μm) are oxidized to sulphate sulphur, which is the form utilised by the plants, by soil bacteria during the cropping season. Elemental sulphur can therefore be considered a slow (timed) release form of plant nutrient sulphur that is less prone to leaching out of the crops root zone.

A process for preparing an elemental sulphur-containing fertilizer was a challenge. Advancement in technology uses a dispersion mill, wherein a rotor turns within a slotted stator, to wet mill elemental sulphur in a liquid (preferably an aqueous liquid), thereby providing a dispersion of milled elemental sulphur in the liquid. The dispersion is combined with further components to provide a mixture of elemental sulphur and further components, and the mixture is granulated in a granulator unit to provide granulated elemental sulphur-containing fertilizer.

Hindu Engineers have sought to provide a process for manufacturing elemental sulphur- containing fertilizer, wherein the particle size of the elemental sulphur particles can be easily controlled.

Accordingly, the present process provides a course for preparing an elemental sulphur-containing fertilizer, comprising steps of:

(a) using a dispersion mill, wherein a rotor turns within a slotted stator, to wet mill elemental sulphur in a liquid, thereby providing a dispersion of milled elemental sulphur in the liquid;

(b) combining the dispersion of milled elemental sulphur with further components to provide a mixture of elemental sulphur and further components; and

(c) granulating the mixture in a granulator unit to provide granulated elemental sulphur-containing fertilizer.

It has surprisingly been found that the process according to the present invention effectively incorporates elemental sulphur into fertilizer in a surprising simple way. Low amounts of sulphur dust are created within the granulation process, thereby improving the safety aspects of the process.

In the first step of the process, elemental sulphur in a liquid (preferably an aqueous liquid) is wet milled in a dispersion mill, wherein a rotor turns within a slotted stator, thereby providing a dispersion of milled elemental sulphur in the liquid. The liquid and elemental sulphur are drawn by the rotation of the rotor into the rotor/stator assembly, and are accelerated and expelled radially through the openings in the slotted stator. With each pass through the rotor/stator assembly, the elemental sulphur is subjected to a combination of mechanical and hydraulic shear such that the particles of elemental sulphur are reduced in size.

The rotor turns at very high speeds, preferably such that the tip speed is from 1500 to 3500 metres per minute, more preferably from 2000 to 3000 metres per minute. Higher tip speeds result in a higher energy input in the dispersion mill and result in a smaller average sulphur particle size.