GB2209744A - Pelletised products - Google Patents

Abstract

Materials for ground treatment, especially limestone for treatment of acid soils, are pelletised using a binder comprising a swelling clay (e.g. bentonite) and a starch material in an amount up to 2% of the mixture. The pellets disintegrate rapidly and are easy to scatter.

Description

"PEliErISED PRODUCTS" This invention concerns pelletised products, more especially it concerns pellets which have the property of rapid disintegration on contact with moisture.

The present invention was developed for pelletised limestone for liming soils, but it is believed to be applicable to other materials which may be pelletised, especially for ground treatment, such as acidity regulators, eg quicklime, fertilisers, herbicides and plant growth regulators in general, and pesticides. Hereinafter, however, the invention will be specifically described with reference to limestone.

The liming of soils is a common practice in agriculture, and has been suggested for the catcheent areas for lakes and rivers which exhibit high acidity, whether from "acid rain" or other reasons. It has been found that relatively large particles, eg of above about 2.0arm, tend to become coated with iron or manganese hydroxide and to be inactivated, although such particles are easy to spread mechanically. Fine limestone is particularly effective by reason of its rapid reaction, but has to be spread by hand if the ground is rough, and this is clearly labour intensive and hence expensive. Fine powder cannot easily be spead by aircraft, eg helicopters, because of drifting caused by air currents.We now propose a pelletised limestone of a few lO's of mm size, which may be readily spread from the air, but which disintegrates. upon contact with water in a few hours to a few weeks when exposed to ambient conditions and is an effective liming agent.

The e present invention provides a pelletised material for ground treatment, comprising a mixture of a finely-divided active ingredient and a binder comprising a swelling clay and less than 2% by weight of the mixture of a starch material.

Preferably, the active ingredient is limestone. Preferred particles sizes of limestone are below 60 microns, and, in general, the finer the particle size the better.

Suitable swelling clays are bentonite clays, which are commercially available in various forms. The clay may be used in an amount of up to 5% by weight of the mixture, preferably up to about 3% by weight.

Suitable starch materials are commercially available in various forms. It is preferred to use a pre-gelatinised starch.

Routine testing will establish whether a particular starch material and ooncentration offers desirable binding and disintegration properties. Experiments indicate that starch concentration greater than about 2% tend to give pellets which are undesirably resistant to breaking upon contacting moisture, but it will be realised that starch materials of different origins may exhibit different behaviours. It is preferred to use a starch binder in a concentration of up to about 1% by weight of the mixture.

The mixture may be prepared by mixing in conventional mechanical mixers. The starch is preferably introduced into the mixture in the form of a powder, but may be a previously prepared solution in water. It is preferred to pelletise with total moisture contents in the range 10 to 20% by weight, especially in the range 13 to 16% moisture by weight for ring die pelletising.

Depending upon the moisture content of the limestone, water may be added in increments to achieve a desired final moisture content before pelletising. Because of the heat generated during ring roll pelletising, moisture will be driven off, and in general the pellets are allowed to lose moisture to the atmosphere. Because of the rapid disintegration characteristics of the pellets, they should be maintained under cover or in water-resistant or - proof bags until use.

The mixture may be pelletised by any convenient method. It is preferred to use a ring roll press, and to form pellets of approximate cylindrical shape, eg of approximately 12mm diameter and 20mm length. Other pelletisng methods may be used, however, such as pan pelletisers, roll presses and pug extrusion.

The e invention will now be described by way of example only.

EXAMPLE Limestone ground to a particle size below 60 microns was mixed with "Brebent" Bentonite, available fran Fullers Earths (Laporte), Redhill, Surrey, and a soultion of "Amijel" Code No 12014 pre-gelatinised starch in water. The quantities were such as to give a bentonite content of 2%, and a starch content of 1%, by weight of the total solids. Water was added in increments to achieve a moisture content of 14-15% and the mixture fed to a commercial ring die pelletiser with die diameters of 12 mm. Pellets of average length of 20 mm were produced, which after being allowed to dry were hard, and were readily scattered on the ground yet rapidly disintegrated on contact with moisture.

Claims (7)

CLAIMS:

1. A pelletised material for ground, treatment, comprising a mixture of a finely-divided active ingredient and a binder comprising a swelling clay and less than 2% by weight of the mixture of a starch material.

2. A material according to claim 1, in the form of a pellet made by ring die pelletising.

3. A material according to claim 1 or 2, wherein the active ingredient is limestone.

4. A material according to claim 3, wherein the particle size of the limestone is below 60 microns.

5. A material according to any one of the preceding claims, wherein the swelling clay is bentonite.

6. A material according to any one of the preceding claims, wherein the amaunt of clay is up to 3% by weight of the mixture.

7. A material according to claim 1, substantially as hereinbefore described.