GB2052459A - Dispersions - Google Patents

Abstract

Aqueous dispersions containing a source of cation and having dispersed therein a synthetic material having a structure characteristic of a smectite clay mineral show advantageous properties if the synthetic material contains iron ions bound in the structure thereof. The synthetic material may have a hectorite structure, contain up to 1.5 atoms of Fe per unit cell, and be manufactured by known processes suitably modified by the inclusion of a soluble iron salt. The dispersions may have a pH below 4 or may have a high content of metal or ammonium cations. The dispersions may be of use in gelled acidic or electrolyte containing systems.

Description

SPECIFICATION Dispersions Certain naturally occurring clay minerals are dispersible in aqueous systems and show advantageous rheological properties in such systems. Examples of such clay minerals are to be found amongst the smectite family of clay minerals. The smectite group of clay minerals may be considered to consist of a notional series of minerals having structures intermediate to the minerals talc, which has the general formula Si8Mg6 O20(OH)4, and pyrophyllite, which has the general formula Si8A14O20(OH)4 the minerals talc and pyrophyllite themselves not being members of the series. Some at least of the Mg or Al ions may be replaced by ions of lower valency resulting in a negatively charged structure with associated exchangeable cation which may, commonly, be sodium or lithium cation.Smectite clay minerals have a characteristic X-ray diffraction pattern.

Further detail concerning the identification of clay minerals may be found in the "X-ray identification and crystal structure of clay minerals" Mineralogical Society (G. Brown) 1961. For the avoidance of doubt a material showing an X-ray diffraction pattern having a variable basal spacing having a minimum value of 10 Angstrom units which increases when water or glycerol are absorbed, and some or all of the following spacings 4.5, 2.6, 1.7, 1.5 and 1.3 Angstrom units which are not affected by absorbtion, is taken to have a structure characteristic of a smectite clay mineral". Within the smectite group of clay minerals certain members of the montmorillonite group and the hectorite group may show advantageous rheological properties.

It is of considerable commercial interest to synthesise materials having structures, examined by X-ray diffraction techniques, characteristic of naturally occurring clay minerals and having different or improved rheological properties whether in aqueous systems or in organic systems. The synthesis of materials having a structure characteristic of naturally occurring hectorite has been the subject of a considerable amount of research. Processes for the synthesis of material having a structure characteristic of hectorite are described in United Kingdom Patent Specification No.1054111 and 1213122 which processes enable the production of products having better rheological properties than natural hectorite.

There remain problems with regard to the behaviour of the synthetic materials referred to above in aqueous systems containing a substantial concentration of cation. One such problem, which is disclosed in United Kingdom Patent Specification No. 1427745, is that the ability of smectite, generally, to swell in water is sharply reduced by the presence of electrolyte dissolved therein. This phenomenon has been shown by both natural and synthetic smectites. United Kingdom Patent Specification No.

1427745 has as an object the provision of a product having a novel smectite composition akin to saponite containing intimately admixed and occluded hydrous magnesium oxide and having an extraordinary swelling behaviour in aqueous electrolyte solutions.

This product has wide utility and may be used as a gellant for fluids as varied as fresh water, sea water, saturated sodium chloride and sodium hydroxide 1 N concentration. The product of United Kingdom Patent Specification No. 1427745 also shows utility in organic media for which use it may be adapted by conversion to the organophilic state by the process disclosed in United States Patent No. 2531427.

Further problems with regard to the behaviour of synthetic materials having a structure characteristic of clay minerals in the presence of a substantial concentration of cation relates to the behaviour of a dispersion of the material in the presence of a substantial concentration of hydrogen ion. If a product synthesised according to the teaching of United Kingdom Patent Specification No. 1054111 or 1213122 is dispersed in water a slightly alkaline gel may be formed. If the hydrogen ion concentration of the dispersion is increased the gel is caused to flocculate. This phenomenon is noted by Neumann in Rheologica Acta, Band 4, Heft4 pages 250-255 (1965) at page 253 where it is disclosed that flocculation is observed at a pH below about 4.It is now further found that, if a product of a similar type is dispersed in an aqueous medium having a hydrogen ion concentration corresponding to a pH, of, for example, about 2, the pH of the dispersion will tend to increase gradually possibly due to attack, or ion exchange, on the structure of the product. This tendency shows itself after only about 1 hour and after about 1 day the dispersion may approach neutrality.

The above-noted behaviour of dispersions of synthetic materials having a structure characteristic of clay minerals and, normally, having advantageous rheological properties makes such materials unsuitable for use in a strongly acidic system such as, for example, a gelled phosphoric acid-based rust remover since the gelling properties of the materials cannot be relied on in such a system which would, at any rate, be gradually neutralised in storage.

The present invention relates to dispersions of synthetic materials, which term includes party synthetic, materials, having a structure characteristic of a clay mineral said dispersion showing new or improved properties with regard to behaviour in the presence of a quantity of cation, whether metal or ammonium cation, present as a result ofthe inclusion of electrolyte in the dispersion, or hydrogen ion present as a result of the inclusion of a strong acid in the dispersion.

By electrolyte, herein, is meant a soluble compound which when dissolved in the dispersion results in a content of metal or ammonium cations therein. Normally the cations are monovalent or divalent although polyvalent metal cations are not excluded.

The present invention provides a composition of matter comprising a liquid medium having dispersed therein a synthetic material having a structure characteristic of the smectite group of clay minerals characterised by the dispersion containing a source of cation and the synthetic material containing iron ions bound in the structure thereof.

The liquid medium is suitably an aqueous medium which may, or may not, contain organic materials such as, for example, ethyl alcohol or ethylene glycol, which do not affect the function of the dispersion or of the synthetic material adversely.

The synthetic material, to be included in the dispersion according to the invention, may be manufactured by known techniques, such as, for example, those disclosed in United Kingdom Patent Specification No. 1054111, 1213122 or 1432770 suitably mod- ified to achieve the inclusion of iron ions bound in the structure thereof.

Suitably the iron ions are included in the synthetic material by including them, in the form of a soluble salt, at a suitable point in the synthesis of the said material, for example, by inclusion with the water soluble magnesium salt, e.g. magnesium sulphate, or the suspension of magnesium compound e.g.

magnesium carbonate or hydroxide, which is combined with silica or silicon delivering material in an aqueous alkaline solution of one or more sodium compounds to form a precipitate, for hydrothermal treatment by heating in an aqueous medium in the presence of excess dissolved sodium compound to obtain crystal formation, according to the techniques generally disclosed in any of United Kingdom Patent Specifications 1054111, 1213122 or 1432770.

The degree of hydrothermal treatment required may depend on the quantity of fluorine included and ranges from a boiling at atmospheric pressure for 10 hours or more to heating to at least 1700C at, at least 100 psi, e.g. pressures of up to 1000 psi in an autoclave, for up to one or more days.

Preferably the synthetic material having a structure characteristic of the smectite group of clay minerals has the formula: Si8(MgaLibFedHc) 020(0H)4-yFy2-zC+ where C is a cation, normally Na+ or Li+, z is the negative charge on the structure and a, b, c, d andy have the following values:- a =4.5 to 5.7 b = 0 two 1.2 c Oto less than 2 d = greater than 0 to 1.5 a + b + c + d = greaterthan 4.5to less than 8 y = 0 to less than 4 and the compositions and proportions of the reactants are controlled accordingly.

The iron ions may be included in the form either of divalent or trivalent iron containing salts, for example, the sulphate or chloride.

It is thought that the iron may enter the structure of the synthetic material in place of magnesium or, if appropriate in place of aluminium, but we do not bind ourselves to the operation of thins theory. The group of atoms indicated in the first round bracket in the formula describing the structure of the synthetic material are usually referred to as octahadrally coordinated atoms for reasons of their supposed position in the crystal structure and, theoretically, their number is 6 per unit cell. It has been found that synthetic materials having structures characteristic of smectite clay minerals can contain a number of octahadrally co-ordinated atoms varying from the theoretical 6 atoms per unit cell by up to 1.5 atoms even where no lithium or other replacement ions for the magnesium are present.In the present invention we preferto include from 0.2 to 1 atoms of iron per unit cell.

The product of the hydrothermal treatment is suitably washed and dried before further use. As explained above, the synthetic material so produced may be identified to have a structure characteristic of the smectite group of clay minerals by standard x-ray diffraction techniques and its overall composition may be determined by analysis. The bonding of iron ions in the structure of the product may be established by failure to leach out the ions with acid according to the test hereafter described.

The dispersion according to the invention may contain the iron containing synthetic material in a concentration dependent on the required application. Generally, for thickening purposes a concentration of from 0.5% to 10% by weight may be sufficient.

It may be that the function of the material is dictated by the charge on the structure thereof or by other quantifiable characteristics thereof in which case the concentration may be determined accordingly but would normally be between 0.1 and 20% by weight.

Depending on the nature of the added cation in the dispersion different features of the invention may come to the fore.

According to one preferred aspect of the invention the dispersion has a pH below 4, for example from 1 to 2. Suitably the source of hydrogen ion may be a strong acid, preferably a strong mineral acid such as hydrochloric acid or sulphuric acid. Such dispersions, advantageously, show at least some pH stability on storage.

According to a further and preferred aspect of the invention the dispersion has a content of metal or ammonium cations of at least 15 m. eq. suitably at least 40 m. eq. and up to 300 m. eq suitably up to 200 m. eq. per litre. The metal cations may, suitably, be alkali metal cations, alkaline earth metal cations, or ferrous or ferric cations or aluminium cations, or ammonium cations.

In cases where the source of cation is a base the overall pH of the dispersion may be above 7, for example from 7.5 to 9.5 or over. Such dispersions, advantageously show at least some gelling properties.

The present invention also provides the use of a synthetic material having a structure and composition characteristic of the smectite group of clay minerals and containing iron ions bound in the structure thereof, in the establishment of dispersions in a liquid medium containing a source of cation, and processes for the use of such dispersions whether by the inclusion of the dispersions in a storable commercial product or by the treatment of materials therewith.

One example of the preparation of a material suitable for inclusion in a dispersion according to the present invention is as follows:- A solution is prepared containing 375.59 MgSO4.7H2O, 41 .94g Fe2(SO4)3.9H2O, 5.449 Li2CO3 and 8509 H2O. There is introduced into this solution firstly, over a period of 1 hour, a solution containing 178.59 Na2CO3 and 6759 H2O, thereby forming a precipitate, and then, over a further period of 1 hour, a solution containing 493g of a sodium silicate containing 29wt% SiO2,8.8wt% Na2O and 5009 H,O.

Throughout the introductions, the solution of MgSO4 7H2O containing the iron and lithium compounds is stirred slowly. The composition of the solutions corresponds to an atomic ratio of Si:Mg:Li:Fe of8:5.12:0.49:0.5.

The precipitate is then boiled for 2 hours and then autoclaved for 5 hours at a temperature of 208"C.

The resulting material is filtered, washed, dried and comminuted and shows an x-ray diffraction pattern similar to that of natural hectorite. The material shows that it has iron bound within its structure when subjected to the following leaching test in combination with the fact that the x-ray diffraction pattern showed no evidence of separate iron compounds.

Approximately 29 (dry weight) of the synthetic material is dispersed in 40ml N/10 HCI. The dispersion is heated to reflux, refluxed for 30 minutes and examined for dissolved iron compounds by standard atomic absorbtion methods. Iron included in the synthetic material in the course of preparation and not found to be leached in the course of the test is taken to be bound within the structure of the synthetic material. In a sample test only 0.017% of the iron included in the synthesis was found to have been leached.

A material produced as specifically described above containing 0.5 atoms of Fe for every 8 atoms of Si was compared with a material prepared similarly, without any inclusion of iron compound but with an equivalent extra quantity of magnesium compound, with respect to their inclusion in acid solution.

2g of each material was dispersed by high speed mixing for 15 minutes in 88 ml distilled water. 10 ml HCI of Normal concentration was added and mixing was continued for a further 5 minutes. The pH of the two dispersions was measured as a function of time.

The results are plotted in Figure 1. the pH being indicated on the ordinate and the time in minutes on a logarithmic scale on the abscissa. The pH of the dispersion containing a material having no iron bound into its structure identified in Figure 1 as "Std" increased rapidly to near neutrality. The pH of the dispersion containing the material having iron bound into its structure identified in Figure 1 as "Fe" increased only slightly. Similar results were obtained where the concentration of the I-ICI in the dispersion was 0.2 Normal and 0.5 Normal.

A material produced by the general method described above had a hectorite structure and con tained 0.5 atoms of Fe for every 8 atoms of Si bound in the structure. Samples of the material were dis perused at a concentration of 3% by weight in water and different concentrations of sodium sulphate were added. The static gel strengths of the disper sions were compared on a Beam Baiance Disc Penet rometer which indicates the weight required to press a metal disc, in contact with the surface of the dis persion, a given distance downwards into a disper sion. A parallel series of tests was performed on samples of material prepared similarly but with the iron replaced by an equivalent further quantity of magnesium in the synthesis.The sodium sulphate concentration of the dispersions tested are indicated below as m. eq/g synthetic material, together with the equivalent quantity as m eq./l dispersion, for the iron-containing and standard (No-iron) containing synthetic materials.

Iron-containing Synthetic material synthetic material containing no iron I m.eq.lg. m.eq/l 1.0 30 0 0 1 5 45 0.25 7.5 2.0 60 0.4 12 2.5 75 0.625 18.75 3.0 90 0.75 22.5 4.0 120 1.0 30 6.0 180 2.0 60 10.0 300 4.0 120 6.0 180 10.0 300 The results are plotted in Fig. 2 the plot for the iron-containing material being indicated as "Fe" and the plot for the material containing no iron being indicated as "Std". The comparative gel strengths are indicated on the ordinate on a scale ofO to 100 and the sodium sulphate concentration is indicated on the abscissa on a scale of 0 to 10 m.eq/g synthetic material. The Beam Balance Penetrometer equivalent reading given by water is indicated in Figure 2 by a broken line parallel to the abscissa.

Similar effects are obtained if the sodium sulphate is replaced by, for example, calcium chloride or aluminium sulphate although the optimum salt concentration is specific to each system.

Claims (21)

1. A con position comprising a liquid medium containing a source of cation, characterised in that the liquid medium has dispersed therein a synthetic material having a structure characteristic of the smectite group of clay minerals said synthetic material containing iron ions bound in the structure thereof.

2. A composition as claimed in claim 1 wherein the liquid medium comprises water.

3. A composition as claimed in claim 1 or claim 2 wherein the synthetic material has a structure characteristic of the smectite group of clay minerals and has the formula:- 5i8(MgaLibFedHc)o2o(oH)4-yFyz- zC- where C is a cation, z is the negative charge on the structure and a, b, c, d and y have the following val ues:- a =4.5to5.7 b Oto 1.2 c = Oto less than 2 d = greaterthan Oto 1.5 a + b + c + d = greaterthan 4.5 to less than 8 y = Oto less than 4

4. A composition as claimed in claim 3 wherein the value of "d" in the general formula is from 0.2 to 1.

5. Acomposition as claimed in any preceding claim containing between 0.1% and 20% by weight of the synthetic material.

6. A composition as claimed in claim 5 containing between 0.5% and 10% by weight of the synthetic material.

7. A composition as claimed in any preceding claim wherein the source of cation is a strong acid.

8. A composition as claimed in claim 7 wherein the strong acid is a mineral acid.

9. A composition as claimed in any preceding claim having a pH below 4.

10. A composition as claimed in claim 9 having pH of from 1 to 2.

11. A composition as claimed in any one of claims 1 to 6 containing at least 15m. eq., per litre, of metal orammonium cation.

12. A composition as claimed in claim 11 containing at least40m. eq., per litre, of metal or ammonium cation.

13. Acomposition as claimed in any one of claims 1 to 6,11 or 12 containing up to 300m. eq., per litre, of metal orammonium cation.

14. A composition as claimed in any one of claims 1 to 6 or 11 to 13 wherein the metal cations are selected from the group consisting of alkali metal, alkaline earth metal, ferrous, ferric or aluminium cations.

15. Acomposition as claimed in any one of claims 1 to 6 or 11 to 14 having a pH of at least 7.5.

16. A composition as claimed in claim 15 having a pH of from 7.5 to 9.5.

17. A method for preparing a dispersion comprising adding to a liquid medium a source of cation, and dispersing in the medium a synthetic material having a structure characteristic of the smectite group of clay minerals said synthetic material containing iron ions bound in the structure thereof.

18. A method as claimed in claim 17 wherein the liquid medium comprises water.

19. A method as claimed in claim 17 wherein the synthetic material has a structure characteristic of the smectite group of clay minerals and has the formula: Si8(MgaLibFedHc)020(oH)4-yFyz- zC+ where C is a cation, z is the negative charge on the structure and a, b, c, d andy have the following values: a =4.5to5.7 b = Oto 1.2 c = Oto less than 2 d = greaterthan Oto 1.5 a t b + c t d = greaterthan 4.5 to less than 8 y = Oto less than 4

20. The product of a method as claimed in any one of claims 17 to 19.

21. A composition as claimed in claim 1 and substantially as described herein.