There are many granules available on the market for cleaning up liquid spillages. Most such granules are of naturally occurring minerals, for example sepiolite, attapulgite, bentonite or olivine, which are obtained by mining or quarrying at sites throughout the world.

It is an object of the present invention to provide an alternative form of absorbent granules, which is environmentally friendly in that it uses waste materials rather than such specially mined minerals. The invention further includes a process for the manufacture of these absorbent granules, by means of which such granules may be more economically produced than by prior such processes for the production of absorbent granules. Other advantageous features of the novel process and product will be apparent from the following description.

The absorbent granules according to the present invention comprise:- (a) at least 50 per cent by weight of an absorbent industrial waste product comprising calcium carbonate or calcium sulphate; (b) up to 50 per cent by weight of a lightweight aggregate comprising expanded perlite or exfoliated vermiculite; (c) from 1 to 3 per cent by weight of potassium sulphate or of a cementitious binder; and (d) from 1 to 3 per cent by weight of water.

The process according to the present invention comprises mixing together in solid form said absorbent industrial waste product, said lightweight aggregate and said potassium sulphate or cementitious binder and subsequently spraying water on to the resulting mix, in such relative proportions as to yield absorbent granules of the foregoing composition.

In the foregoing absorbent granules and in the process for producing them, the weight of the absorbent industrial waste product comprising calcium carbonate or calcium sulphate preferably amounts to from 70 per cent to 80 per cent of the weight of the granules. The weight of the lightweight aggregate preferably amounts to from 30 per cent to 20 per cent, and the weight of the potassium sulphate or cementitious binder preferably amounts to from 1.5 to 2.5 per cent, of the weight of the granules.

In carrying out the process according to the present invention, the quantity of water sprayed on to the solid mix preferably lies within the range from 3 to 10 per cent of the weight of the solid mix, more preferably from 3 to 7 per cent of that weight. A proportion of the water evaporates from the resulting wet mix but, as a result of absorption of water into the mix, the retained percentage of water lies within the specified range of 1 to 3 per cent of the weight of the product.

Further mixing together of the solid components in the presence of the added water allows the materials to agglomerate and thereby together to form dry absorbent granules. Preferably the size of the resulting granules lies within the range from 1 to 10mm, more preferably from 2 to 6mm. Preferably the granules also contain some fines of a particle size below lmm.

The quantity of such fines preferably amounts to up to 1 per cent, preferably up to 5 per cent, by weight of the product.

The absorbent industrial waste product which is the primary component of the liquid-absorbent granules according to the present invention may for example be of calcium carbonate obtained as a by-product in the crushing and milling of limestone, or of calcium sulphate in the form of a by-product arising in the manufacture of hydrofluoric and in the most recent processes for producing ozone-friendly gases. Large quantities of these by-products are usually disposed of in landfill sites, in particular when the by-product in question is a very fine material having a size of less than 150 microns.

Such very fine materials are of particular value as a component of the absorbent granules according to the present invention.

The lightweight aggregate which is the second component of the absorbent granules of the present invention is an expanded perlite or an exfoliated vermiculite. Perlite and vermiculite are minerals which occur naturally throughout the world and which are subsequently subjected to a heating process to yield the expanded or exfoliated product, which typically has a density from 30 to 180kg/m3.

The lightweight aggregate acts as a seed about which the industrial waste product agglomerates. This agglomeration and the bonding of the waste product to the aggregate is greatly assisted by the potassium sulphate, which acts as an accelerator, or by the cementitious binder.

The choice between using potassium sulphate on the one hand and a cementitious binder on the other should take account of the chemical nature of the industrial waste product which is the main component of the granules. When the waste product is exclusively calcium sulphate or comprises that compound as a major part of the waste product, for example in the form of equal amounts of calcium sulphate and calcium carbonate, then it is preferred to use potassium sulphate. However, when the waste product is exclusively or mainly calcium carbonate, then the use of a cementitious binder is preferred. The binder may, for example, be a sulphate-resistant cement or starch.

The granules produced according to the present invention are an effective absorbent for spillages of oils, chemicals and other liquids. The granules have the particular benefit that a major part of the raw materials for their manufacture are by- products of other industrial operations and therefore do not require to be mined or quarried. The granules are comparatively lightweight and may weigh only half the weight of other available absorbent granules, enabling them to be readily carried by any man or woman to the site of the spillage.

The process according to the invention has the important advantage that the components of the granules do not require to be heated in order to bond them together. The inclusion of potassium sulphate accelerator or of a cementitious binder makes the use of heat unnecessary, thereby saving a valuable resource which must otherwise be expended.

In use, the liquid-absorbent granules according to the invention are placed upon the spilled material and allowed to absorb that material until they become saturated. Absorption begins immediately and then, after saturation, the granules may be left for a period to allow them to dry, whereafter they may be lifted for disposal as landfill. The fines present in the product assist in the complete removal of the spillage and ensure that no person or vehicle can slip on the cleaned area.

The larger particles may then absorb the bulk of the spilled liquid while the fines remove the residue.

The invention will now be further described and illustrated by means of the following Example, which describes, by way of example only, one preferred form of the process and product according to the present invention and wherein percentages are by weight.

Example A dry powder was formed comprising the following ingredients:- Absorbent industrial waste calcium sulphate: 74 per cent Expanded perlite: 25 per cent Potassium sulphate: 1 per cent These ingredients were blended in a low-shear drum rotating at 3 rpm for 15 minutes and then a fine spray of water amounting to about 5 per cent of the weight of the dry mix was added to the mix during continued blending over a period of a further 45 minutes. Dry absorbent granules of an average particle size of approximately 5mm were formed.

The density of the initial waste calcium sulphate was approximately 1000kg/m3 and that of the perlite was approximately 100kg/m3. In this Example, the density of the product granules was approximately 350 to 450kg/m3. By varying the densities of the chosen starting materials and by varying their relative proportions in the mix, finished granules having densities within the range 250 to 750kg/m3, preferably of the order of 350 to 500kg/m3, may be made. A 20-litre bag of such a preferred product will weigh about 10kg, which weight is within or below the requirements of United Kingdom Health and Safety Executive regulations for manually- carried or manually-lifted bags.

In use, the granules are spread upon the spilled liquid material and the material is absorbed until the saturation point is reached. The granules may then be left to dry out until their outer surface is dry. In this form, if necessary mixed with other materials, they may safely be disposed of by land-fill.