GB1560504A - Synthesis of clay-like materials - Google Patents

Description

(54) SYNTHESIS OF CLAY-LIKE MATERIALS (71) We, IMPERIAL COLLEGE OF SCIENCE & TECHNOLOGY, of London SW7 2BP, do hereby declare the invention for which we pray that a Patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to the synthesis of clay-like materials from naturally occurring igneous rocks.

The swelling clays are naturally occurring group of minerals which have a number of uses, for example, as binders for foundry sand and in pelletising, as dispersants, as a component in drilling muds, and as fillers in paints and plastics compositions.

It is an object of the present invention to provide synthetic materials which can be used as substitutes for these swelling clays.

According to the invention there is provided a process in which an igneous rock classified as intermediate to ultrabasic (as hereinafter defined) is subjected to a hydrothermal treatment by being agitated and heated in the presence of water to a temperature of from 350 to 450"C under a pressure of up to 350 atmospheres.

The material which results from this hydrothermal treatment is found to have properties which make it similar to the naturally occuring swelling clays. Thus, the product has saponite-like properties, e.g. its X-ray diffraction analysis is consistent with saponite although it does not necessarily have the same structural state. For convenience saponite can be represented by a planar unit cell of the structural formula:

In this formula mX~Y indicates the presence of compensator cations totalling x-y valencies per unit cell, with x-y roughly equal to unity, and other symbols have their usual significance (see Soil Components, Vol. 2, Chapter 4, by J. Mering, published by Springer-Verlag 1975).

In the materials resulting from the process of the invention iron species may substitute partly for the aluminium and magnesium in the unit cell shown above for saponite. Additionally considerable quantities of other minerals may be present.

Because the materials resulting from the process of the invention have similar properties to the swelling clays they have similar commercial applications, e.g. as foundary binders. Further the final product may be useful directly as a foundry sand by choosing as the initial igneous rock a material part of which becomes converted to the synthetic clay-like material and part of which remains as the sand.

The igneous rocks which can be subjected to the hydrothermal treatment according to the invention are those classified as intermediate to ultra basic (as defined in Igneous Rocks, Chapter 1, by Carmichael, Turner and Vehoogen, published by McGraw-Hill, 1974). The igneous rock which is preferably used is that classified as basic (as defined above). These rocks are mineral aggregates of widely varying composition but generally contain as major constituents feldspars, ferro-magnesium silicates, e.g. olivine and pyroxenes, and metallic oxides such as iron oxide.It appears that the olivine and other ferromagnesium minerals together with any glassy matrix, are the main components required to give the synthetic clays, and accordingly the igneous rock can be preconcentrated in such materials by taking out a proportion of the feldspar according to established mineral processing practice, (e.g. as described in Mineral Processing, Third Edition, 1965-E. J. Pryor).

As noted above we believe the olivine and/or other ferro-magnesium minerals, cryptocrystalline and glassy matrix (possibly as poorly defined feldspar) comprise the main reactive constituents of the igneous rock required in the process according to the invention. The hydrothermal treatment of the invention does not produce a single chemical reaction but rather a number of chemical and physical changes resulting in a mineral mixture with saponite-like properties. Idealized equations representing two possible reaction paths are:

in which x has a value of 0 to 1 depending upon the proportion of calcium present.

The cryptocrystalline and glassy matrix components are represented by, but not substituted for, the plagioclase molecule in the above reaction paths.

The final product of these reaction paths is a mineral which has a similar structure to saponite and so has comparable properties.

The igneous rocks used as starting materials occur very widely in nature.

Accordingly, the synthetic clays obtained from them by the process of the invention will be readily obtainable irrespective of the availability of naturally occuring swelling clays.

It can be desirable for the hydrothermal treatment according to the invention to be effected in the presence of one or more additives which promote the desired conversion. The proportion of any additive used is preferably up to about 6V by weight of the dry igneous rock.

The presence of magnesium in the form of magnesium oxide or a hydrated magnesium oxide is often desirable as one such additive. This is particularly the case when the treated rock liberates inadequate or insufficient free magnesium ions, because they are unavailable from suitable ferromagnesium components, to react with the cryptocrystalline and glassy matrix; or when the major proportion of ferromagnesium minerals present, by their nature, provide insufficient free magnesium ions for complete reaction, e.g. in the case of the pyroxene in the first of the above two reaction paths. The presence of magnesium is not however usually an advantage when the treated rock contains a major proportion of olivine which under the hydrothermal conditions provides suitable free magnesium.Therefore according to one embodiment of the invention one can subject pure olivine sand to the hydrothermal treatment according to the invention, although to produce the most complete reaction, it is desirable to add silica as illustrated by the second of the above two reaction paths.

Another additive which may additionally or alternatively be present is a lithium or sodium compound such as sodium sulphate.

It is believed that the resulting sodium or lithium ions replace at least part of the calcium ions present as the interlayer cation in the product.

It appears to be desirable for the hydrothermal process of the invention to be conducted at a pH around neutral, e.g. a pH of from 6 to 8. Therefore this should be borne in mind when selecting appropriate additions.

For use in the process of the invention, the igneous rock is crushed and ground to a fine particle size. The initial size depends upon whether the particles are ground during the hydrothermal treatment. If they are, then the initial particle size should, for example, be below 1.7 mm, although it can be less, e.g. a size below 0.15 mm and more desirably in the region of 0.06 mm or below.

It is preferred that the particles be subjected to attrition by grinding during the hydrothermal treatment so that fresh surface is continually provided for reaction, the final particle size being, for example, 0.06 mm or less. If the particles are not intentionally ground during thy hydrothermal treatment, the initial particle size should, for example, be below 0.15 mm and more desirably in the region of 0.06 mm or below.

During the treatment according to the invention the rock needs to be agitated and this agitation can be achieved by grinding the rock by tumbling it in the presence of grinding rods or rolls or merely by tumbling the mixture.

As noted above the hydrothermal treatment is effected at a temperature of from 350 to 4500C since below that range the reaction required does not proceed at a sufficient rate whilst above that range the product appears to be unstable. The preferred temperature is about 400"C.

The pressure to which the igneous rock is subjected during the hydrothermal treatment is not above 350 atmospheres.

Higher pressures are difficult to produce economically and it does not appear that the required reaction proceeds significantly faster at pressures above 350 atmospheres.

Below pressures of 200 atmospheres there may be a reduction in reaction rate and so preferred pressures are in the range of from 250 to 350 atmospheres, with a figure of about 300 atmospheres most preferred.

These pressures can be obtained 6y subiecting the igneous rock to treatment in a pressure bomb and then the pressures are provided primarily by the presence of the appropriate quantity of water in the mixture.

Examples of hydrothermal treatments according to the invent;on to give a synthetic clay from an igneous rock will now be given by way of illustration.

Example 1 A sample of quartz hypersthene dolerite, taken from the large formation of basic rocks known as the Whin Sill in Northern England, was reduced to less than 0.15 mm.

For this purpose a laboratory jaw crusher and Krupp mill were used.

6g of the resulting powder together with 0.5g magnesium oxide and 0.5g sodium sulphate were pulped with 6g of water and heated in a rotary autoclave for 8 hours at 450"C. The autoclave consisted essentially of a nickel steel bomb of 30 cm3 capacity, a tubular furnace, an electrically driven spindle at the base of the furnace on which the bomb was located and conventional control equipment.

The product from the reaction, which had a plastic consistency was dried at 1 100C, disaggregated to a powder and subjected to various standard analysis tests. X-ray analysis showed the finished product to have a diffraction pattern consistent with saponite. Differntial thermal analysis showed dehydration and dehyroxylation effects to be compatible with saponite. A methylene blue test on the elutriated clay fraction gave a smectite content of 44 ".

When this fraction was subjected to standard foundry binding tests it gave results which were comparable with those given by pure montmorillonite under similar conditions.

Example 2 A further sample of quartz hypersthene dolerite from the Whin Sill formation was reduced to less than 1.68 mm using a laboratory jaw crusher and Krupp mill.

1 keg of the resulting material together with 80g of magnesium oxide were pulped with 11 of water and heated and ground in a rotary autoclave for 8 hours at 4000C. The autoclave consisted essentially of a nickel steel bomb [Hastelloy (Registered Trade Mark) C276l of 51 capacity mounted on steel rollers, in a steel furnace heated by hot air from six industrial fan heaters. The rollers were electrically driven using a 1/2 h.p. motor connected via gears and a chain linkage. The temperature of the furnace was controlled by varying the hot air flow through the furnace. Grinding was achieved by means of nickel steel rods inside the autoclave.

The product of the reaction had a plastic consistency and was thixotropic. The material was dried at 110"C, disaggregated to a powder and analysed by X-ray diffraction analysis, which showed the material to be an aggregate of original rock powder and newly formed clay material.

The clay gave a diffraction pattern consistent with a saponite clay.

Example 3 A sample of olivine basalt taken from the "Lions Haunch" in Edinburgh. nas reduced. using a laboratory jaw crusher, Krupp mill and Tema mill to minus 0.06 mm.

Four 6g samples of the resulting powder were taken. Two 6g samples were pulped with 6g of water each. and two 6g samples.

each with 0.5g of magnesium oxide were similarly pulped with 6g of water each. The samples were placed in four nickel steel bombs of 30 cm3 capacity and heated in a rotary furnace for 8 hours at 400"C. The furnace consisted essentially of a steel back plate, upon which the bombs were symmetrically mounted, fitted to an electrically driven spindle. The bombs and back plate were covered by tubular furnace cover and heated by hot air, the whole being controlled by conventional equipment.

The material produced under both sets of experimental conditions had a plastic consistency and was dried at 110 C and disaggregated. X-ray analysis showed the finished products to be aggregates of original rock material and newly formed clay material possessing a diffraction pattern consistent with saponite. Semiquantitative analysis of the peak areas under the X-ray diffraction curved showed no difference in the amounts of clay produced by the two methods, and that in both cases there was a significant decrease in the amount of olivine present in the final product compared to that present in the initial rock powder.

Unlike rocks, such as the Whin Sill quartz hypersthene dolerite which require the addition of magnesium oxide to give a high yield of clay, rocks such as the basalt from "Lions Haunch" containing free olivine will yield a large proportion of clay by simple hydrothermal treatment with no addition of magnesium oxide, the olivine breaking down to provide the free magnesium required by the reaction.

WHAT WE CLAIM IS: 1. The process which comprises subjecting igneous rock classified as intermediate to ultrabasic (as herein defined) to a hydrothermal treatment by being agitated and heated in the presence of water to a temperature of from 350 to 4500C under a pressure of up to 350 atmospheres.

2. The process of Claim 1 in which the igneous rock is subjected to attrition by grinding during the hydrothermal treatment.

3. The process of Claim 1 or Claim 2 in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. according to the invent;on to give a synthetic clay from an igneous rock will now be given by way of illustration. Example 1 A sample of quartz hypersthene dolerite, taken from the large formation of basic rocks known as the Whin Sill in Northern England, was reduced to less than 0.15 mm. For this purpose a laboratory jaw crusher and Krupp mill were used. 6g of the resulting powder together with 0.5g magnesium oxide and 0.5g sodium sulphate were pulped with 6g of water and heated in a rotary autoclave for 8 hours at 450"C. The autoclave consisted essentially of a nickel steel bomb of 30 cm3 capacity, a tubular furnace, an electrically driven spindle at the base of the furnace on which the bomb was located and conventional control equipment. The product from the reaction, which had a plastic consistency was dried at 1 100C, disaggregated to a powder and subjected to various standard analysis tests. X-ray analysis showed the finished product to have a diffraction pattern consistent with saponite. Differntial thermal analysis showed dehydration and dehyroxylation effects to be compatible with saponite. A methylene blue test on the elutriated clay fraction gave a smectite content of 44 ". When this fraction was subjected to standard foundry binding tests it gave results which were comparable with those given by pure montmorillonite under similar conditions. Example 2 A further sample of quartz hypersthene dolerite from the Whin Sill formation was reduced to less than 1.68 mm using a laboratory jaw crusher and Krupp mill. 1 keg of the resulting material together with 80g of magnesium oxide were pulped with 11 of water and heated and ground in a rotary autoclave for 8 hours at 4000C. The autoclave consisted essentially of a nickel steel bomb [Hastelloy (Registered Trade Mark) C276l of 51 capacity mounted on steel rollers, in a steel furnace heated by hot air from six industrial fan heaters. The rollers were electrically driven using a 1/2 h.p. motor connected via gears and a chain linkage. The temperature of the furnace was controlled by varying the hot air flow through the furnace. Grinding was achieved by means of nickel steel rods inside the autoclave. The product of the reaction had a plastic consistency and was thixotropic. The material was dried at 110"C, disaggregated to a powder and analysed by X-ray diffraction analysis, which showed the material to be an aggregate of original rock powder and newly formed clay material. The clay gave a diffraction pattern consistent with a saponite clay. Example 3 A sample of olivine basalt taken from the "Lions Haunch" in Edinburgh. nas reduced. using a laboratory jaw crusher, Krupp mill and Tema mill to minus 0.06 mm. Four 6g samples of the resulting powder were taken. Two 6g samples were pulped with 6g of water each. and two 6g samples. each with 0.5g of magnesium oxide were similarly pulped with 6g of water each. The samples were placed in four nickel steel bombs of 30 cm3 capacity and heated in a rotary furnace for 8 hours at 400"C. The furnace consisted essentially of a steel back plate, upon which the bombs were symmetrically mounted, fitted to an electrically driven spindle. The bombs and back plate were covered by tubular furnace cover and heated by hot air, the whole being controlled by conventional equipment. The material produced under both sets of experimental conditions had a plastic consistency and was dried at 110 C and disaggregated. X-ray analysis showed the finished products to be aggregates of original rock material and newly formed clay material possessing a diffraction pattern consistent with saponite. Semiquantitative analysis of the peak areas under the X-ray diffraction curved showed no difference in the amounts of clay produced by the two methods, and that in both cases there was a significant decrease in the amount of olivine present in the final product compared to that present in the initial rock powder. Unlike rocks, such as the Whin Sill quartz hypersthene dolerite which require the addition of magnesium oxide to give a high yield of clay, rocks such as the basalt from "Lions Haunch" containing free olivine will yield a large proportion of clay by simple hydrothermal treatment with no addition of magnesium oxide, the olivine breaking down to provide the free magnesium required by the reaction. WHAT WE CLAIM IS:

1. The process which comprises subjecting igneous rock classified as intermediate to ultrabasic (as herein defined) to a hydrothermal treatment by being agitated and heated in the presence of water to a temperature of from 350 to 4500C under a pressure of up to 350 atmospheres.

2. The process of Claim 1 in which the igneous rock is subjected to attrition by grinding during the hydrothermal treatment.

3. The process of Claim 1 or Claim 2 in

which the igneous rock is classified as basic (as herein defined).

4. The process of any preceding claim in which the igneous rock is subjected to the hydrothermal treatment in the presence of magnesium oxide or a hydrated magnesium oxide.

5. The process of any of claims 1 to 3 in which the igneous rock is subjected to the hydrothermal treatment in the presence of magnesium oxide.

6. The process of any preceding claim in which the igneous rock is subjected to the hydrothermal treatment in the presence of a sodium or lithium compound.

7. The process of Claim 6 in which the igneous rock is subjected to the hydrothermal treatment in the presence of sodium sulphate.

8. The process of any preceding claim in which the hydrothermal treatment is effected at a pressure of from 250 to 350 atmospheres.

9. The process of any preceding claim which is effected at a temperature of about 400"C.

10. The process for preparing a synthetic clay-like material substantially as herein described with reference to Example 1.

11. The process for preparing a synthetic clay-like material substantially as herein described with reference to Example 2 or Example 3.

12. The product of the process of any preceding claim.