The invention relates to the treatment of dispersions, typically aqueous dispersions, and particularly to the separation of the solid phases or liquid and solid phases of highly stable aqueous dispersions (including emulsions and colloidal suspensions). Examples of dispersions which can be treated by the invention include emulsions comprising water and used working fluids. Some specific examples include used metal working fluids and dyestuff dispersions. Some specific examples include used metal working emulsions consisting of an aqueous dispersion phase and a dispersed phase consisting substantially of mineral and synthetic oils stabilised by surfactants, emulsifiers etc. and aqueous dispersions containing dyestuffs, pigments, resins, hydrocarbons, etc.

It is one object of the invention to provide a method and chemical additive which can readily separate non-miscible phases and/or solid phases from a liquid, typically an aqueous, phase in a wide range of aqueous dispersions. It is another object of the invention to provide such a method and additive which can be used to separate the phases of the dispersion on a continuous basis with a high level of efficiency. It is yet another object to provide apparatus for the purpose specified. It is still a

further object to provide means for separating the phases efficiently.

In accordance with one aspect of the invention there is provided a method of separating the phases of a dispersion, comprising adding an additive in the form of a suspension of a separating agent in a carrier therefor to the dispersion, intimately mixing the suspension and the dispersion, and separating the phases.

Preferably the suspension is a homogeneous suspension of two or more separating agents. In a much preferred feature of the invention at least one agent is in the form of particles of sub micron size. Preferably one agent is a clay such as bentonite and the other is a salt. The salt may be selected from a wide range of salts which will tend to separate the phases of the dispersion. Such salts may be trivalent as in the case of aluminium sulphate or ferric chloride or ferrous sulphate or bivalent as in the case of magnesium chloride and calcium chloride. It is preferred that the salt is bound up in the clay and the carrier comprise water containing a dissolved salt (which may be the same as or di ferent from that in the clay) . Most preferably a stabilising agent is present to stabilise the suspension in the form of fine clay / salt composite particles. The stabilising agent is preferably selected from a wide range of surfactants; it is much preferred that the agent be an amphoteric surfactant and be in isoelectronic state in the

suspension and one which does not foam when the suspension is mixed with the dispersion. Specific preferred classes of suitable emphoteric surfactants include N-aminopropionateέ and N- iminodipropionateε; such surfactants can be prepared by the condensation of fatty primary amines and acrylic amines. The surfactant may be presented as a salt. The choice of stabilising agent will depend on the nature of the agents in the suspension, especially the salt. The stabilising agent will typically make up a low proportion, say 0.1% by weight, of the additive.

The clay is preferably a polar clay having a three layer structure. Preferred are natural and synthetic bentonites including montmorillonite . Preferably a sodium type montmorillonite is used. The clay will be in about the same weight concentration as the salt, or may be slightly less.

In a much preferred aspect the invention provides a method as defined, wherein the additive comprises a suspension comprising an aqueous phase containing dissolved salt, e.g. aluminium sulphate and a solid phase comprising particles of bentonite of about 0.1 micron in diameter and having a layered structure, aluminium sulphate being present as interlayers within the layers of the bentonite, an amphoteric surfactant being present to stabilise the particles in the suspension. Preferably the suspension has a pH of about 3.

A

Typically the dispersion to be treated is an aqueous dispersion, such as a dispersion of waste metal working oils and water.- An advantage of the invention is that the method can be performed continuously.

In a much preferred feature, the method is carried out by supplying the dispersion under pressure to a first mixing chamber, adding the additive to the dispersion adjacent its point of entry into the first mixing chamber, causing the mixture of dispersion and additive to be mixed by turbulent passage through the first mixing chamber, passing the mixture into a second mixing chamber and optionally adding gas thereto, causing the gasified mixture to be mixed by turbulent passage through the second mixing chamber, adding a flocculant to the mixture as it emerges from the second mixing chamber and then isolating the separate phases one from the other.

Preferably the materials are passed through each mixing chamber along a cyclonic path. Preferably the passage along the cyclonic path is caused solely by the pressure applied to the mixture. Most preferably the suspension is added in the form of a fine spray to a pressurised supply of the dispersion entering the first elongate mixing chamber adjacent one end thereof and the two are thoroughly mixed as they travel towards an outlet adjacent the other end thereof. The mixing takes place solely by the flow, and the interior of the vessel is free of baffles and

like structures so that eddy currents can pass in different directions. Preferably the centrifugal acceleration is between about 250g and about 350g. The mixing in the second mixing chamber may be arranged to take place in similar fashion.

The suspension is preferably supplied as a spray or atomised by being sprayed through a full cone nozzle by which a fine spray of uniform cone pattern is produced. Preferably the nozzle has paths which cause the suspension to undergo both axial flow and tangential flow.

As a result of the mixing as outlined, the particles of the organic phase of the dispersion can be isolated very efficiently at the later stage and the COD value of the separated aqueous phase is very low.

Where the gas is introduced, this is preferably in the form of small bubbles. Preferably the bubbles are of about 400 micron average diameter; the gas is air and the bubbles are produced by an aerator. Most preferably the aerator is arranged to produce bubbles at the rate of about 30 billion bubbles/cu.m.

The introduction of billions of tiny air bubbles to the mixture has two principal advantages, namely:

a) as the suspension and dispersion react, small and

independent micro-agglomerations form in the aqueous phase. Where air is present this becomes trapped within the agglomerations which facilitates the separation of the solid phase from the aqueous phase by floatation. This is particularly valuable where the densities of the two separate phases are similar.

b) As a result of the formation of large quantities of foam during the course of reaction the air bubbles are stabilised within the organic (or solid) phase, which will improve the efficiency and rate of separation.

Preferably the flocculant is added at the rate of about 0.5% by volume of the total volume of the treated dispersion.The flocculant can be cationic, anionic or amphoteric, according to the nature of the phases of the dispersion. Preferably the flocculant is cationic and has a molecular weight of about 4 to about 10 million. Preferably the mixture containing the flocculant is passed through an elongate reaction chamber before the phases are isolated. The elongate reaction chamber comprises a looped pipe system, and has inlets for the optional addition of other agents .

While we do not wish the scope of the invention to be limited by the following theories, our investigations suggest the following. When the submicron particles of e.g. sodium bentonite are added

to a solution of e.g. aluminium sulphate in water, the water is readily drawn by capillary action into the layers of the

, bentonite and the sodium ions are replaced by the aluminium. In addition the aluminium sulphate recryεtallises from solution into the bentonite layers to form composite aluminium sulphate- bentonite particles of needle like morphology as a solid phase in a liquid phase of water containing some dissolved aluminium sulphate. The surfactant stabilises the microsuspension and because the surfactant is in an isolectronic state foaming is largely avoided. When the microsuspension is added to the dispersion to be treated and the two are subjected to turbulent mixing the organic phase of the dispersion is destabilised and coalesces with the bentonite of the microsuspension to form separate droplets of organic material in the aqueous phase. When the flocculant is added the particles coalesce or agglomerate to form a layer of organic material which can be separated from the aqueous phase. Because the aluminium sulphate is already dissolved in the water of the microsuspension the destabilising reaction takes place quickly. The cyclonic circulating system of mixing set out above ensures that the maximum reaction potential is realised.

In another aspect the invention provides a method of making an additive for use in separating the phases of a dispersion, the method comprising dissolving a salt in water, adding a clay to _k the solution, the clay being in the form of submicron particles

and of layered form so as to cause the salt solution to penetrate the layers by capillary action. Preferably the proportion of ingredients is selected so that the salt solution forms an aqueous phase to a solid phase comprising the salt bound up in the clay. Preferably, the method includes the step of adding the defined stabilising agent to stabilise the suspension.

In another aspect the invention provides an additive for use in separating the phases of a dispersion, the additive comprising a suspension formed of an aqueous phase comprising a solution of a salt and a solid phase comprising a clay having a salt bound up therewith, the clay being in the form of sub-micron particles. Preferably the clay is in the form of particles of about 0.1 micron diameter.

Preferably the salt is as defined earlier. The suspension preferably contains a stabiliser, typically a surfactant, as defined.

In yet another aspect the invention provides apparatus for use in separating phases of a dispersion comprising a tank for holding the dispersion to be treated; means for transferring the dispersion to a first mixing chamber under pressure; means for adding a spray of separating additive to the pressurised dispersion adjacent its entry to the first

mixing chamber; means for turbulently passing the dispersion and additive through the first mixing chamber; means for adding gas to the mixed dispersion and additive, where required; means for transferring the mixed dispersion and additive and optional gas to a second mixing chamber; means for turbulently passing the dispersion and additive and optional gas through the second mixing chamber; means for adding flocculant to the optionally gasified mixture of dispersion and additive; optionally means for adding other agents to the flocculated mixture; and means for isolating the resultant separate phases one from the other.

In yet another aspect the invention provides a method of mixing two liquids, one being a dispersion and the other a separating agent therefor, the method comprising intimately mixing the two fluids together in a cyclonic fashion through a common vessel, solely under pressure. Preferably the separating agent is in the form of a suspension. Preferably the two fluids are mixed together from one end of an elongate cylinder towards the other end. Most preferably the separating agent is sprayed onto the dispersion and then the mixture is urged together through the

vessel .

In yet another aspect the invention provides a method of separating the organic and aqueous phases of a dispersion comprising adding a separating agent to the dispersion to form particles of organic material, adding bubbles of gas, and subjecting the gasified mixture to turbulent mixing to trap bubbles of the gas within agglomerations of the particles. Preferably the gas is air and the bubbles are about 400 micron average diameter.

In order that the invention may be well understood it will now be described by way of example only with reference to the schematic flow diagram shown in the accompanying drawing. The basic apparatus comprises a reservoir 10 of the dispersion to be treated, a first mixing chamber 20 and a second mixing chamber 30, a reaction chamber 40, a separation tank 50, a hopper 60 of separation additive, an aerator 70 and a hopper 80 containing flocculant.

The tank 10 is connected to the first mixing chamber 20 by a pipe 11 which extends from the base of the tank to an inlet 21 adjacent the roof 22 of the first mixing chamber. A centrifugal pump 12 having wide spaced apart plates is present in the pipe 11 and a branch pipe 13 is connected to the pipe 11 via a three way valve 14 for recirculating dispersion so as to mix the dispersion

to be treated and to regulate pressure of dispersion in the pipe 11. A pressure gauge 15 is present in the pipe 11 adjacent the chamber 20. A pipe 23 leads from the reservoir 60 containing additive of the invention and opens into the roof 22 of the chamber 20 via a metal spray nozzle. The chamber 20 is an empty steel walled cylinder having an outlet 23 adjacent the floor. As will be explained, the pressured dispersion to be treated is forced into the chamber 20 and to the outlet 23 in a cyclonic fashion, additive being added in spray form as the dispersion enters the chamber 20. A pipe 24 leads from the outlet 23 to an inlet 31 adjacent the roof 32 of the scond mixing chamber 30.

An aerator 70 for generating air bubbles is mounted adjacent to the pipe 24 and is connected thereto by valves 71,72 for the introduction of small air bubbles into the additive - containing dispersion in the pipe 24. The aerator 70 is selected so that the bubbles are of 400 micron average diameter and produced at the rate of 30 billion bubbles/cu.m. The aerator 70 has an air inlet 73. The second mixing chamber 30 is of frustoconical form, as shown, and has an outlet pipe 33 in the roof 32, and is shaped so that the material introduced into the inlet will flow in a cyclonic manner and then emerge at the outlet 33. A valved pipe 81 leads from the hopper 80 to an inlet 34 in the outlet pipe 33. A pipe 41 leads from the pipe 33 to the reaction chamber system 40 which is of looped pipe form. As shown, an inlet 42 for the optional addition of additives is present in the pipe 41. A pipe

51 leads to the separation tank 50 which has an outlet tap 52 for removal of the aqueous phase. The organic phase is passed to other tanks, not shown, for collection.

The method of the invention is performed as follows.

The aqueous dispersion to be treated is pumped by pump 12 along the pipe 11 to the first mixing chamber 20 at a pressure of about 3.5 bar, regulated by the pressure gauge 15. The pressure level is ensured by means of the three way valve 14 which, as illustrated, provides a feedback system which also serves as a means of mixing the waste dispersion.

The hopper 60 contains a microsuspension comprising aluminium sulphate bound up in a bentonite clay in an aqueous phase containing dissolved aluminium sulphate. The suspension may however be selected from those specified earlier.

The microsuspension is introduced into the first mixing chamber 20 via the fixed metal full cone nozzle which is arranged to generate a fine spray of the microsuspension. As a result of the pressure the two components are encouraged to circulate in a cyclonic fashion down through the chamber to the outlet 24 at which point they are passed towards the second mixing chamber 30. The mixture remains in the first chamber 20 for a very short time period, which is considered to be insufficient for the pH to rise

above the value at which foaming of the liquid can occur. The inhibition of foaming is important as foam will reduce the degree of contact between the microsuspension and the dispersion and initiate premature floatation.

The aerator 70 is arranged to generate tiny air bubbles, about 400 micron average diameter, at the rate of about 30 billion/cu.metre. These are introduced into the microsuspension/dispersion in the pipe 24. The aerated mixture is then passed to the second mixing chamber 30.

The second reaction chamber 30 is constructed as the first but the outlet 33 is at the top of the reaction chamber as opposed to the base. The diagram illustrates the primary and secondary cyclonic circulation of the mixture, which is arranged to avoid the build up of solid material on the interior walls by control of the centrifugal forces generated.

The flocculant in the hopper 80 is added to the gasified mixture at a point just above the outlet of the second mixing chamber 30 as it is the region of maximum turbulence. The flocculant acts as a bridging agent and encourages the agglomeration and precipitation of all the micro-agglomerations (pin-point floe) formed as a result of the turbulent mixing of the microsuspension and the dispersion.

The flocculated aerated mixture is passed through the looped reaction chamber 40, to allow the organic agglomerates to form a separate organic phase layer. If additives are required, they can be introduced via the inlet 42. The two phases are passed to the tank 50, where the organic phases can be separated in known manner. The organic phase tends to form a sludge or precipitate when allowed to stand in a tank. The air introduced as bubbles escapes from the interstitial sites within the precipitate so increasing the density and leaving a honey-comb like structure within the solid mass.

The invention is not limited to the embodiments shown. The microsuspension may be prepared using a homogeniser; the salt may be ferric chloride or a bivalent salt or the like; the surfactant may be other than that named; the gas need not be air; the flocculant may be anionic.