IL34700A - A method of flocculating solid particles in an aqueous medium and a flocculating composition for use in said method - Google Patents

Description

t na* a ©lasfr nwa rawm noma o»psio a>p*j?Vn mn's new A METHOD OF FLOCCULATING SOLID PARTICLES IN AN AQUEOUS MEDIUM AND A FLOCCULATING COMPOSITION FOR USE IN SAID METHOD The present invention relates to acrylic floccu at-thg agents* The use of acrylic polymers to facilitate the separation of solid materials, by coagulation or flocculation, from aqueous media, in which the solid materials are present in suspension, such as is the case in waste waters, sewage and sludges from the extraction of minerals, is known. Thus homopolymers of aery1amide, of acrylic acid and/or acrylates of alkali metals, and binary copolymers of acrylamide with acrylic acid salts, and of acrylamide or acrylic acid with copolymerisable monomers such as styrene, vinyl acetate and vinylpyridine have been used commercially.

We have now found, according to the present invention, a new group of flocculating agents consisting of certain water- soluble acrylic terpolymers, the performance of which, in particular the degree of adsorption by the colloidal substances to be precipitated, is generally better than that of the known commercial products* According to the present invention, there is provided.a flocculating composition for use in aqueous media which comprises an oxide or salt of aluminium or iron which forms a hydrated oxide in water and, as flocculating agent, a water-soluble terpolymer having a molecular weight (determined by intrinsic viscosity) above 50GQ000, and derived from 35 to 97%, preferably 70 to 95% by weight of acrylamide, 2 to 55%, preferably 5 to 20%, by weight of partially neutralised acrylic acid and I to 20%, preferably 3 to t5%, by weight of acrylonitrile. Such polymers, or polymers similar thereto, have been disclosed in United states Patents Nos. 2,632,704, 2β93,977 and 3,050,486 but none of these suggest that the polymers may be useful as flocculating agents. Suitably, when aluminium oxide for aluminium sulphate and sodium aluminate) is the metal oxide, the proportion of terpolymer is In order to obtain the excellent results which are illustrated below the acrylic acid in the terpolymer must be partially neutralised, for example, with an alkali metal or alkaline earth metal salt, generally to a 500,000 as stated above. It is generally from 1 to 8 x 10**.

The preparation of the terpolymers for the flocculating agents of this invention can be effected using conventional techniques employed for the preparation of acrylic polymers0 A particularly suitable method consists in dispersing the various monomers, in aqueous solution, in an organophilic phase, with . stirring, and in the presence of a suitable surface-active agent. The organophilic phase can be, for example, an organic hydrocarbon such as toluene or xylene. The polymerisation, initiated by a conventional oxidation-reduction catalyst, makes, it possible to obtain a water-soluble copolymer of molecular weight at least 1 x 10 , in the form of a powder, in a very short time, (of the order of 10 to 20 minutes) and in a pratically quantitative yield. Alternatively, the comonomers can be polymerised in an aqueous-organic medium, such as water and acetone, at ordinary temperature in the presence of conventional catalysts.

The water-soluble acrylic polymers used in this invention display characteristics which are generally considerably better than those of the knowihomologues. In effect, they make it I possible to effect a faster rate of sedimentation of sludges.

Furthermore, their degree of adsorption on the colloidal ub tances to be reci itated a roaches 100%. These characteristics enable the terpolymers used in this invention to be used to advantage in the flocculation of industrial waste waters, of wash waters from mines, of sewage and of impure waters which are usually purified with the aid of metallic oxides such as Al^O^ or Fe203, optionally combined with a flocculating polyelectrolyte. Accordingly the present invention also provides a method 6<S flocculating solid particles in an aqueous medium which comprises adding a terpolyaier as described above or a flocculating composition of the present invention to the medium. Further details of the terpolymers, flocculating compositions and method can be ascertained from the JExampes which follow.

EXAMFLE 1 Preparation of the polymers t Several conventional processes were used to obtain the co- used in the other polymers »£· this invention, and k»ow«-homopolymers and copolymers used for the purposes of comparison in the flocculation experiments given below.

According to a first process, pure acrylamide was polymerised in demineralised water, previously freed of oxygen, under conventional conditions (ordinary temperature, redox catalyst).

According to another technique, partially neutralised acrylamide/acrylic acid copolymers, and several ternary acrylamide/ acrylic acid/acrylonitrile copolymers were prepared by polymerising the monomers or comonomers in a mixture of water and acetone, at a temperature of 10 to 30°C., in the presence of a redox catalyst, so as to obtain the polymers directly, in the form of small spheres. i Finally, terpolymers were also manufactured by the so-called, | "inverse emulsion" technique, by polymerising the comonomers in a water (disperse phase)-hydrocarbon (continuous phase) mixture in the presence o of an emulsifier and conventional initiator, at a temperature of 20 to 50 C, A potassium persulphate/sodium bisulphite mixture was used as redox catalyst and initiator. The emulsified was- sorbitan stearate. :Ί A list of the polymers tl us prepared, as well as their * U principal' characteristics, is given iir'Table 1, * d - h - ' e TABLE I EXAMPLE 2 Application of the polymers as flocculating agents t (a) Since waste waters are freqently purified by means of coagulants such as, especially, Al 0 , we first carried out a series of « 3 comparative experiments so as to measure the flocculating power of the various polymers mentioned in Example 1 on precipitates or "flocks" hydrated alumina at pH 7.1» at various concentrations. These precipitates were obtained by adding aluminium sulphate and Na aluminate to the waste water, the resulting hydrated alumina being expressed in mg/l of A1„0_· To do this, the optimum amount of flocculating agent for a given amount of Al 0 was determined by a series of preliminary experiments.

This optimum corresponded to the highest rate of sedimentation measured in a 2 litre cylinder, 42 cm. high, (in which the precipitation was brought about ) · Thereafter, measurements were carried out, for each polymer and for various concentrations of Al 0 , of the solidity of the resulting "flocks" by subjecting the latter to strong mechanical stirring (speed of stirring 50 revolutions per minute), and also the quality of sediment tion observed by allotting scale ratings of between 1 (poor sediment tion) and 5 (excellent sedimentation)* The results obtained are given in Table II» TABLE II Various conclusions c n be drawn from these results, of which the most important can be summarised as follows: The mechanical rigidity of the sediments is considerably improved and the quality of sediment tion is considerably improved, as regards the use of the terpolymers of this invention (polymers D to G) compared to the use of known acrylic flocculating agents (polyacrylamide A and binary copolymer B).

The optimum amounts of terpolymers to be used for 50 to I50 mg/l of Λ1 0 are, firstly, similar for both these ^ 3 amounts of Al 0 and, secondly, half those of the known <2 3 acrylic polymers A and B» Comparison of the results of product C with those of products D to G demonstrates that it is necessary not to neutralise completely the acrylic acid comonomer used as the starting material* whilst the results recorded for products D, E, F and G are very good and are similar, it appears that for terpolymers of essentially similar molecular weight, the emulsion polymerisation technique yields products having optimum flocculation characteristics, (b) In order to investigate experimentally the effectiveness of several terpolymers of this invention in the flocculation of clay sludges - which represents a major problem in certain mining regions - various doses of the polyelectrolytes A to G were introduced into a clay water containing 50 g/l of a "montmorillonite" clay, and the rates of sedimentation were then measured as a function of the amounts of acrylic polymers introducede The results obtained are shown in Table III (it should be noted that the rate of sedimentation measured on an untreated comparison sample was 16 x 10 cnw/S).

TA3LE III It can be seen that , with equal amounts , the polymers F and G achieve a sedimentation of cl ay sludges which is 1 ,5 to 2.3 times more rapid than with an acryl amide homopolymer or an acryl amide/ acrylic acid copolymer (A and Β) · (c ) Finally , it appeared interesting to attempt to measure the degrees of adsorption of the polyelectrolytes of this invention on the colloidal substances to be precipit ated. In effect , the ideal degree of adsorption (100%) provides the possibility of recycling the crude waters to be treated without the danger that a part of the floccul ating agent , of low molecular weight , could stabilise the suspensions and thus make the subsequent floccul ation impossible.

For this purpose , me asurements of "COR" (chemical oxygen or demand requirement were carried out on montmorillonite filtrates , in the following manner : 200 g/l of montmorillonite (reference 205, from "Compagnie Commerci ale des Miner ais et Matieres premieres" ) were suspended in distilled water and the suspension was then floccul ated by introducing either 25, 50 or 75 ppm of the floccul ating agents A , B and F - of Table I, whilst stirring for 6 minutes. Thereafter the COR was determined in accordance with French Standard Specification AFNOR T. 90.101 (May 1968). The results summarised in Table IV were obtained.

TABLE IV As the COR measured on the reference clay (without the addition of flocculating agent) was 92.5 mg/l, the variation in COR can easily be deduced : TABLE V As can be seen, only the terpolymer F according to this invention gives negative results throughout. Thus not only does it not introduce an additional COR when used as a flocculating agent for clay- but it is even capable of holding back a part of the COR of the latter.

Similar results were obtained using hydrated alumina in place of clay and it was thus possible to show that the acrylic terpolymers were adsorbed to a degree of 100% on Al 0 . n H O flocks.

Claims (1)

1. WE β A flocculating composition for use in aqueous media which comprises an oxide or salt of iron or aluminium forms a hydrated oxide in water as flocculating a terpolymer having a molecular weight greater than and derived from 35 to by weight of 2 to by weight of partially acrylic acid and 1 to by weight of A according to Claim in the the acryli acid is 30 to composition according to Claim in the the acrylic acid is 55 to A composition according to any one of Claims 1 to in the the acrylic acid is neutralised with an or alkaline metal A composition according to any one of the preceding wherein the terpolymer has a molecular weight from 1 to 8 x A composition according to any one of the preceding wherein the terpolymer is derived rom to by weight of 5 to by weight of partially acrylic acid and 3 to by weight of A composition according to any one of the preceding wherein the terpolymer has been obtained by emulsion 3 A composition according to any one of the preceding wherein the metallic oxide is iron A composition according to any one of Claims to wherein the metallic oxide or salt is aluminium oxide or aluminium sulphate and sodium A composition according to Claim which contains 4 to by weight of terpolymer based on the weight of A according to Claim substantially as hereinbefore A method of flocculating solid particles in an aqueous medium which comprises adding a terpolymer defined in any one of Claims to to the A method according to Claim wherein the aqueous medium is a sewage or a sludge from the extraction of A method according to 12 or wherein the particles to be are of a hydrated metallic A method according to wherein the metallic oxide is method according to Claim 15 wherein the aqueous medium contains 50 to of A method according to Claim 15 or wherein 4 to by weight of terpolymer is based on the weight of A method according to Claim or wherein the solid particles are of a A method according to one of Claims to 18 wherein the terpolymer is added in the of a composition as claimed in any one of Claims 1 to A method according to Claim substantiall as hereinbefore A method according to Claim substantially as described in Example An aqueous medium which has been puri ied by a method of flocculation as claimed in any one of Claims 12 to Attorney for Applicants insufficientOCRQuality