WO1994020417A1

WO1994020417A1 - Flocculating agents

Info

Publication number: WO1994020417A1
Application number: PCT/GB1994/000402
Authority: WO
Inventors: John Harris Newton; Neil Clarke
Original assignee: Laporte Industries Limited
Priority date: 1993-03-09
Filing date: 1994-03-02
Publication date: 1994-09-15
Also published as: GB9304778D0; AU6145894A

Abstract

A basic poly(aluminium/iron) halide flocculating agent having a charge density of at least 600 microequivalents/g, a basicity of 30 % to 80 %, an aluminium content of 2 % - 12 %wt as Al2O3, an iron content of 0.5 % to 4.0 %wt as Fe2O3, a total aluminium and iron content of not more than 12.5 %wt on the same basis, a pH above 2 and, preferably, a majority of the iron content in the ferric form is useful for treating potable water sources, industrial effluents or sewage effluents. It can give relatively low aluminium residuals, at pH levels previously regarded as non-preferred, and/or relatively low residual iron, organic and turbidity levels in treated aqueous liquids.

Description

Flocculating agents.

This invention relates to flocculating agents, to a process for the manufacture of the same and to a process for the treatment of water or aqueous effluents, such as sewage effluents, using the same. It is known to treat water with flocculating agents. Finely divided particulate matter present in the water under the conditions of treatment are enveloped in floes and are caused to sediment enabling the relatively purified supernatent water to be withdrawn. Such a treatment method may be applied to the production of potable water, to the treatment of industrial effluents, for example to reduce the content of metallic contaminants in such effluents, to sewage effluents, for example to reduce the content of organic matter or to other aqueous liquids requiring purification.

The European Economic Community Standards for potable water specify stringent guide and mandatory levels for a wide range of^" inorganic contaminants. These levels for aluminium, which are of importance in relation to the possible long term biological affect of aluminium contamination, are a guide level of 0.05 mg/1 and a mandatory level of 0.2 mg/1 as Al. The corresponding levels for iron are 50 micrograms/1 and 200 micrograms/1 as Fe. It is usual practice for the water producers to require adherence to the guide levels in their treatment processes.

The European Community Directive relating to the quality of bathing water has stimulated research into means for increasing the quality of sewage outfall discharges. As a result, in the United Kingdom; the ultraviolet irradiation of sewage effluents has been approved as a means of decreasing the bacterial content of the effluent. This requires the installation of ultraviolet sources such as quartz lamps which are prone to masking by the deposition of organic matter from the effluent and, if a traditional iron salt has been used to decrease the organic content prior to irradiation, to the plating out of residual iron values onto the lamps. Hardness salts also give rise to considerable plating problems. There is therefore a requirement for a flocculant which will give low residual organic and iron contents in, treated sewage effluents. Examples of commonly used flocculating agents are the salts of aluminium or iron such as aluminium sulphate or ferric chloride or the polyaluminium halides. The last mentioned materials are basic compounds containing aluminium in polymeric form. Polyaluminium halide flocculating agents are most effective in the pH range of the treated water of 6.2 to 6.8. Outside this range there tends to be an increased level of residual aluminium or other metals which may make it difficult to comply with the guide or mandatory levels referred to above. It has therefore been regarded as desirable to control the pH of the treated water to avoid or minimise this. The iron salts are inherently acidic and tend to contribute to a lowering of the pH of generally alkaline potable water sources towards the required range although some further pH adjustment may be required. Polyaluminium flocculants, due to the hydrolysis of some of the acidic sites, are less acidic and usually require a substantial acid dosing procedure as part of the flocculation process.

United States Patent Specification No 4417996 discloses reacting an aqueous polyaluminium halide solution with ferrous and ferric halide. The coagulants so obtained are reported to be at least equivalent to a conventional polyaluminium chloride sulphate coagulant. The stability of the solutions decrease with increasing metal concentration, increasing iron to aluminium ratio and increasing basicity although solutions containing higher proportions of ferrous iron are more stable so long as the ferrous iron is not oxidised to the ferric form. Ferric iron tends to impair coagulation performance except at high basicity under which conditions the Fe/Al ratio which may be used is limited since an increased ratio tends to lead to physical instability. There is also disclosed in United States Specification No 4417996 a process comprising reacting an aqueous aluminium halide solution with metallic iron. In the resulting solution the iron is present largely as divalent iron. On storage, there is a tendency for the iron to oxidise to the ferric form so that, after almost 1 year of storage, about 38% of the ferrous iron had become oxidised. The compositions of the solutions produced by this method ranged from a Fe:Al atomic ratio of 0.2:1 to one of 1.16:1.

Polymerised iron chloride has also been proposed as a flocculating agent and is the subject of a review paper in Journal AW A, Oct 1984, pages 93-97. The polymerisation of ferric chloride is by the addition of alkali to a ferric chloride solution under controlled conditions or the heating of the solution to about 100°C with vigorous stirring. The iron species present in the treated solutions were identified by the methods of Hsu described in J.Soil Sci.,23:409(1972) and Clay and Clay Minerals,21:2δ7(1973). Polymerised iron chloride produced by the heating process was found to be potentially unstable and it was therefore found necessary to use this material almost immediately and to design equipment capable of achieving this in a water treatment process. Material made by both methods gave a somewhat better performance than ferric chloride in reducing turbidity. Only the material produced by the heating process was capable of giving a performance equivalent to that of ferric chloride in reducing organics levels. The present invention provides a flocculant which is relatively physically stable for a iron-containing flocculant and may be used at a pH outside the range referred to above, for example at the ambient water source pH. The flocculant may be used to give a low residual iron, aluminium or organic level or a low residual level of turbidity. The invention also provides, without limitation to these applications, processes for the purification of water to a low residual iron or aluminium level and for the purification of sewage effluent to low residual iron or organic levels making use of the new knowledge provided by the invention in these respects. It is also a particular advantage of the use of the invention that it is accompanied by the conversion of alkaline earth bicarbonates and/or hydroxides to insoluble carbonates thereby reducing the adverse effect of alkaline earth salts on the irradiation process. The flocculant of the invention has a high charge density which offers high performance characteristics in potable and waste water treatment and gives a relatively dense floe blanket. The present invention provides a new or improved aluminium and iron containing flocculating agent suitable for use in the treatment of water, aqueous industrial or sewage effluents or other aqueous liquids, the flocculating aging being a basic poly(aluminium/iron) halide. The use of the term "aqueous" does not exclude the presence of a minor proportion, for example up to 10% by volume, of a water-miscible or soluble organic substance.

It is a characteristic of the flocculant of the invention that,as well as the aluminium content, at least a proportion of the iron content, for example at least 50% and preferably at least 60% is in a polymeric form. It is believed that the iron and aluminium components of the flocculant are present as a single polymeric species although the invention also encompasses the alternative of the basic polyaluminium and the basic polyiron halides being separate species. The terminology "poly(aluminium/iron)" is intended to encompass both of these alternatives.

According to a further and separate aspect of the invention the basic poly(aluminium/iron) halide flocculant has a charge density of at least 600 microequivants per gram and a basicity of from 30% to 80% and the solution of the flocculant has a content of aluminium (calculated as AI2O3 of from 2% to 12% by weight, a content of iron

(calculated as Fβ2θ3) of from 0.5% to 4% by weight and a total content of aluminium and iron (calculated on the same basis) of not more than 12.5% by weight. The presence of undue free acidity in the product of the invention or during its manufacture can prevent or reduce polymerisation. The pH is therefore preferably maintained at above 2.0 particularly above 2.1 and, eg., up to 4.2 or even 4.5 and/or the acid derived content of Cl^~ or of SO-j^- is below 12.5% particularly preferably below 4% in the case of the latter. The observance of the above guidelines as to acidity is usually indicated by the production of a solution having a dark brown colour. The flocculant solution of the invention is further preferably characterised by a pH of from 2.1 to 4.2. The density of the flocculant solution is preferably no more than 1.25 g/ml. Preferably the iron content, or at least 40%, preferably at least 60% thereof, is in the trivalent form for effective flocculation performance and the invention also comprises a process feature, described hereafter, designed to attain this.

The charge density of the flocculant species and/or the molecular charge level is an indication of polymerisation. Preferably the charge density is up to 1100, for example at least 700 microequivalents/gram.

The limitations expressed above as to the iron and aluminium contents of the solution relate to the utility of the flocculant. For example, a total aluminium and iron content above about 12.5% by weight will result in physical instability in storage whereas a content below about 2.5% will undesirably dilute the active species. At least the minimum quanity of iron is required to attain suitable sedimentation whereas an unduly high quantity of iron may cause physical instability in storage.

The present invention also provides a new or improved process for the production of the flocculant of the invention. According to this aspect of the invention there is provided a process for the production of a basic poly(aluminium/iron) halide solution suitable for use as a flocculant comprising mixing metallic aluminium and metallic iron with an aqueous solution of aluminium halide, allowing at least some of the aluminium and of the iron to dissolve in the aluminium halide solution and contacting the solution so formed, containing iron in the ferrous state, with an oxidising agent thereby to convert at least a proportion of the ferrous iron to the ferric state. By appropriate control of the quantities and concentrations of the reactants in the above process a flocculant solution suitable for direct use and having a suitable charge density, basicity and aluminium and iron concentration and/or containing both aluminium and iron in a basic polymeric form may be produced. The process will now be described in more detail by reference, without limitation, to the chloride form of the product.

The aluminium chloride aqueous solution and other reactants used in the present process is preferably of at least technical grade purity to assist in the production of a flocculant solution which will be suitable for use for the production of potable waters which satisfy the Standards referred to above. It is possible, of course, that the flocculant might be used in situations where less stringent requirements apply in which event the reactants used in the production of the flocculant may be of lower purity. The aluminium chloride solution may very suitably be prepared by the dissolution of alumina, for example alumina hydrate, in hydrochloric acid. Alternatively a crude aluminium chloride solution may be reacted with hydrochloric acid to suitably increase the concentration of aluminium chloride in the solution. Alternatively, other known process for the production of the aluminium chloride solution may be used. To achieve a'flocculant product having the preferred concentration the concentration of the aluminium chloride solution is preferably from about 22% to 32% by weight as AICI3. If required, this may be assisted by dilution. The resulting solution may be subjected to suitable purification techniques such as ion exchange or filtration to raise the purity to technical grade. It is understood that the aluminium chloride solution used as a starting material in the present invention is not itself a part of the invention but is a standard item of commence which is to be selected or adjusted to have a suitable purity and concentration for use in the practice of the invention. The aluminium and iron used in the present process may be in the form of powder, pellets, swarf or the like provided, again, that they are of sufficient purity to enable a suitable flocculant product to be obtained. Very suitably the aluminium may be in the form of shot and the iron in the form of powder. The iron and aluminium are preferably present simultaneously for dissolution in the aluminium chloride solution and this is preferably assisted by elevated temperature, for example at least 50°C. The use of pressure and the higher temperatures normally associated with this is not necessary and a temperature slightly below reflux temperature, eg up to 20°C below reflux temperature, and/or of at least 85°C will suffice. The use of reflux temperature is not excluded but it may be preferred to avoid it for practical operational reasons. It is found that the dissolution of the aluminium metal proceeds relatively rapidly in the presence of the metallic iron and the entire dissolution reaction may be less than 10 hours duration or even below 5 to 6 hours duration. The quantities of iron and aluminium are preferably controlled to achieve the individual and total quantities preferred in the flocculant of the invention. The dissolution of the iron and/or aluminium may be conducted concurrently with the production of the aluminium chloride solution if desired. The polymerisation reactions may occur as the dissolution is proceeding.

The solution resulting from the dissolution of the iron and aluminium normally contains a substantial proportion, or all, of its iron content in the ferrous form. According to the present invention this solution is preferably treated to achieve the oxidation of the iron at least partly to the ferric form. This is preferably achieved by the addition of a quantity of a non-contaminating oxidant., such as hydrogen peroxide, or by bubbling oxygen gas through the solution.

In the case of hydrogen peroxide it is preferred to use a quantity of from above 1 to 2 times the, quantity theoretically required to convert the ferrous iron content of the solution, or the desired proportion of it into the ferric form. Ambient temperture or an only slightly elevated temperature of, for example, up to 50° is preferred to reduce decomposition. It may be found adequate from the point of view of flocculant properties to oxidise less than all, for example from 40% to less than

100% of the ferrous iron and in this case the quantity of the hydrogen peroxide may be adjusted accordingly.

The product of the present invention may be sulphated either by including a water soluble sulphate or a solution containing sulphate values either with the aluminium chloride solution, or with the reactants at a stage in the manufacture of the aluminium chloride solution, or with the reactants during the dissolution of the metallic iron and aluminium, or with the polymeric product of the invention. It may be anticipated that the resulting sulphated basic poly(aluminium/iron) halide product, may give improved residual aluminium levels in comparison with sulphated basic polyaluminium chloride. It has been found by the

Applicants that the quantity of sulphate should be controlled for optimum performance at not more than 4.0% by weight calculated as SO4. A preferred range is from 0.5% to 3.5%. Above about 4% there is a marked instability. The products of the invention are homogeneous solutions, mainly dark brown in colour, which give a yellowish iodine-like tint to glass wetted with a thin film of the solution. These solutions are stable, in general, for at least 1 year in storage.

The invention will now be more particularly described by reference to the following Examples and Tests. It is understood that these Examples and Tests are illustrative of particular embodiments of the invention and are not limiting on the scope of the invention. Example 1 and Tests 1, 7 to 15, 31 to 40 and 51 to 59 are according to the invention. The remaining Tests are present for comparative purposes.

Example 1. Preparation of flocculant solution.

Using reactants satisfying the purity requirements indicated above the following reaction mixture was prepared:-

494.0 kg AICI3 27.77% solution

16.7 kg Al shot 14.4 kg Fe powder

474.9 kg water

The reaction mixture was heated at 95°C with stirring for 4 hours at the end of which time the metallic solids had completely dissolved.

To the resulting solution was added a quantity of hydrogen peroxide 35%wt. corresponding to 1.25 times the theoretical quantity to convert the iron present to the ferric state. The oxidation proceeded rapidly with slight exothermicity.

The resulting solution was dark brown in colour, giving a slight iodine-like tint to a glass container and contained 8%wt of aluminium (calculated as AI2O3), 2%wt of iron (calculated as Fβ2θ3), 9.32%wt of chloride (calculated as Cl~) and 4.81%wt of hydroxide (calculated as OH-). The product, when examined by the streaming current technique using a commercially available particle charge detector, showed a charge density of 890 microequivalents/g. The product also had a basicity of 51.8.

Tests 1 to 71. Purification of water.

,. In the following Tests raw river waters were treated with the product of Example 1 or with comparative competitive flocculants under varying conditions. The supernatant so obtained was tested for floe quality after 10 and 20 minutes treatment time and for colour, turbidity,

10 and organics content and was analysed for residual Al and Fe values. _The turbidity test is a standard test for the content of colloidal particles using a light scattering technique and is expressed in NTU units. The organics content is measured by the transmission test which is 5 conducted using a 1cm quartz cell by determining the transmission of light having a wavelength of 254nm through the sample and is expressed as a percentage. Floe quality was observed visually and allocated a grading of from A (unsatisfactory) to G (excellent). Colour was measured in 0 Hazen Units.

The following raw waters were used in the Tests:

River Sevt 2rn(S) Oiιse(O) Dee(D

PH 7.8 7.7 7.6

Colour (H) 41.0 24.6 32.1 5 Turbidity^' (NTU) 5.3 2.5 2.3

Trans % 66.7 75.1 66.1

Al (mg/dm-3) 0.01 0.00 0,00

Fe (" /" ) 0.05 0.28 0.06

The following comparative flocculating agents were used 0 in the Examples:

Poly(iron/aluminium)chloride (PFAC)-Tests 1,7-15,31- 35,51-59

Sulphated PFAC (PFACS)-Tests 36-40, Polyaluminium chloride (PAC) Sulphated polyaluminium chloride (PACS)

PAC/ferric sulphate mixture-8% Al₂0₃/2% Fe2θ₃ (PAC/F)

Aluminium sulphate (AS)

AS/H S0 mixture-5% sulphate/10% acid (AS/10) -3.75% sulphate/20% acid (AS/20)

Ferric chloride (FC)

In view of the significance of pH to the performance of the flocculant of the present invention the Test Results are set out in Tables corresponding to the three pH ranges 1(a) to I(j) (pH >6.8), II (pH 6.8 - 6.2) and IΙI(a) to

III(c) (pH <6.2) with the exception of Test 6 which belongs to category (b) but is included in Table 1(a).

The generally excellent performance of the PFAC flocculating agents of the invention is apparent from the data included in the Tables. It is also evident from a comparison of Examples 23 (ferric chloride), 27 (polyaluminium chloride/ferric sulphate) and 9 (polyaluminium/iron chloride) that the product of the invention gave a considerably better turbidity and residual organics performance than ferric chloride or the chloride/sulphate mixture in closely similar environments.

TABLE 1(a)

Test No 1 2 3 4 5 6

Flocculant PFAC PACS PAC AS5 AS3 PAC/F

Dosage mg/dm3 4 4 4 4 4 4 Water S S S S S S

Water pH 7.4 7.5 7.3 6.9 6.6 7.4

Floe. Qual. lOmins B E B B B A/B

Floe. Qual. 20mins D/E G D D E C/D

Colour H 6.9 7.5 6.3 4.5 3.9 7.2 Turbidity NTU 1 1.1 1.4 1.6 1.5 0.9

Trans. % 82.8 81.4 83.9 84.7.85.6 79

Al mg/dm3, <0.010.08 0.06 0.01 <0.010.02

Fe mg/dm3 <0.01<0.010.01 <0.010.01 <0.01

TABLE 1(b) Test No 7 8 9 10 11 12

Flocculant PFAC PFAC PFAC PFAC PFAC PFAC

Dosage mg/dm3 2 3 4 5 6 7

Water D D D D D D

Water pH 7.4 7.3 7.3 7.2 7.1 7 Floe. Qual. lOmins A A A/B B C D

Floe. Qual. 20mins A A D D/E E E

Colour H 14 6.9 4.2 3.9 3 3.3

Turbidity NTU 3.2 2.5 0.9 0.8 0.7 0.8

Trans. % 79 84.4 86.8 88.2 89.2 89.6 Al mg/dm3, 0.03 0.01 <0.01<0.01<0.01<0.01

Fe mg/dm3 0.01 0.01 <0.010.01 <0.01<0.01 TABLE 1(c)

Test No 13 14 15

Flocculant PFAC PFAC PFAC

Dosage mg/dm3 3 4 5

Water D D D

Water pH 7.5 7.6 7.5

Floe. Qual. lOmins A/B C D

Floe. Qual. 20mins C D E

Colour H 6.3 5.4 4.8

Turbidity NTU 1.4 0.8 0.6

Trans. % 85 86 86.5

Al mg/dπι3, 0.02 <0.01<0.01

Fe mg/dm3 <0.01<0.0K0.01

TABLE 1(d) Test No 16 17 18 19 20 21

Flocculant PAC PAC PAC PACS PACS PACS

Dosage mg/dm3 3 4 5 3 4 5

Water D D D D D D

Water pH 7.4 7.4 7.4 7.4 7.4 7.4 Floe. Qual. lOmins B C D B/C E F

Floe. Qual. 20mins C D E D G G

Colour H 7.5 6.3 4.5 7.2 6.3 5.7

Turbidity NTU 0.8 0.7 0.5 0.7 0.5 0.4

Trans. % 85.2 85.7 87 82.1 83.5 84.2 Al mg/dm3, 0.1 0.11 0.09 0.11 0.08 0.11

Fe mg/dm3 0.01 <0.010.02 <0.01<0.0K0.01 TABLE 1(e)

Test No 22 23 24

Flocculant FC FC FC

Dosage mg/dm3 3 4 5

Water D D D

Water pH 7.2 7.2 7.2

Floe. Qual. lOmins A A A

Floe. Qual. 20mins A A A

Colour H 16.5 15 9.9

Turbidity NTU 2.6 2.8 3.6

Trans. % 73.6 74.5 80.3

Al mg/dm3, <0.01<0.01<0.01

Fe mg/dm3 0.07 <0.010.06

TABLE 1(f) Test No 25 26 27 28 29 30

Flocculant PAC/FPAC/FPAC/FPAC/FPAC/FPAC/F

Dosage mg/dm3 2 3 4 5 6 7

Water D D D D D D

Water pH 7.3 7.2 7.2 7.1 7.1 7 Floe. Qual. lOmins A A A/B C D E

Floe. Qual. 20mins A A D E F F/G

Colour H 10.5 7.5 5.7 5.1 4.2 3.9

Turbidity NTU 3.1 3.3 1.1 0.7 0.8 0.7

Trans. % 80.5 83 85.3 87.5 88.1 89 Al mg/dm3, 0.05 0.07 0.04 <0.01<0.0K0.01

Fe mg/dm3 <0.010.01 <0.01<0.01<0.0K0.01 TABLE 1(g)

Test No 31 32 33 34 35

Flocculant PFAC PFAC PFAC PFAC PFAC

Dosage mg/dm3 2 3 4 5 6

Water O O O O O

Water pH 7.2 7.3 7.3 72 7.2

Floe. Qual. lOmins A B C D E

Floe. Qual. 20mins B C/D D/E E E/F

Colour H 5.1 5.1 5.1 4.2 4.5

Turbidity NTU 1.3 1 0.7 0.6 0.6

Trans. % 83.6 83.6 85.3 85.8 85.6

Al mg/dm3, 0.04 0.05 <0.010.03 0.02

Fe mg/dm3 <0.01<0.01<0.0K0.0K0.01

TABLE 1(h) Test No 36 37 38 39 40

Flocculant PFACSPFACSPFACSPFACSPFACS

Dosage mg/dm3 2 3 4 5 6

Water O O O O O

Water pH 7.2 7.2 7.2 7.2 7.2 Floe. Qual. lOmins A A/B B C D

Floe. Qual. 20mins B C D E E/F

Colour H 5.1 4.8 4.5 4.2 3.9

Turbidity NTU 1 0.7 0.5 0.4 0.4

Trans. % 84.7 85.6 86.3 86.8 87.7 Al mg/dm3, <0.01<0.0K0.0K0.01<0.01

Fe mg/dm3 <0.01<0.010.01 0.01 0.01 TABLE I(i)

Test No 41 42 43 44 45

Flocculant PACS PACS PACS PACS PACS

Dosage mg/dm3 2 3 4 5 6

Water 0 0 0 0 0

Water pH 7.2 7.2 7.2 7.2 7.2

Floe. Qual. lOmins B D E F G

Floe. Qual. 20mins F G G G G

Colour H 6 5.7 5.4 4.8 3.6

Turbidity NTU 0.5 0.4 0.3 0.3 0.2

Trans. % 83.6 84.2 85 85.3 85.2

Al mg/dm3, 0.01 0.02 0.01 0.03 <0.01

Fe mg/dm3 0.01 0.01 <0.01<0.0K0.01

TABLE I ( )

Test No 46 47 48 49 50

Flocculant AS AS AS AS AS

Dosage mg/dm3 2 3 4 5 6

Water O O O O O

Water pH 7.2 7.1 7.2 7.2 7.1

Floe. Qual. lOmins A A/B B C D

Floe. Qual. 20mins A/B D D D/E E

Colour H 5.4 4.8 4.5 4.5 3.9

Turbidity NTU 1.3 0.7 0.7 0.7 0.5

Trans . % 84 84.2 85.2 85 85.3

Al mg/dm3 , 0.05 <0.01<0.010.03 0.02

Fe mg/dm3 <0.010.01 0.01 0.02 0.01 TABLE II*

Test No 51 52 53

Flocculant PFAC PFAC PFAC

Dosage mg/dm3 3 4 5

Water D D D

Water pH 6.5 6.5 6.4

Floe. Qual. lOmins A B/C D

Floe. Qual. 20mins B E E/F

Colour H 4.5 3.9 3

Turbidity NTU 2 1.3 1

Trans. % 86.7 89.2 90.3

Al mg/dm3, <0.01<0.0K0.01

Fe mg/dm3 <0.01<0.0K0.01

TABLE Ilia Test No 54 55 56 57 58 59

Flocculant PFAC PFAC PFAC PFAC PFAC PFAC

Dosage mg/dm3 3 4 5 3 4 5

Water D D D D D D

Water pH 5.8 5.9 6 5.5 5.5 5.5 Floe. Qual. lOmins A B/C D A B C

Floe. Qual. 20mins B/C E F C D F

Colour H 4.5 3 2.7 4.8 4.5 3.9

Turbidity NTU 1.8 1.6 1.2 1.5 1.2 1.1

Trans. % 88.1 89.6 89.7 86.6 87.7 89.1 Al mg/dm3, 0.1 <0.01<0.0K0.010.01 0.09

Fe mg/dm3 <0.0K0.0K0.01<0.01<0.01<0.01 TABLE 11lb

Test No 60 61 62 63 64 65

Flocculant PAC PAC PAC PACS PACS PACS

Dosage mg/dm3 3 4 5 3 4 5

Water D D D D D D

Water pH 5.6 5.6 5.6 5.5 5.5 5.5

Floe. Qual. lOmins A A/B B D E F

Floe. Qual. 20mins B/C C D F G G

Colour H 5.1 4.8 4.5 4.8 3.6 2.7

Turbidity NTU 2.2 1.6 1.6 0.6 0.4 0.5

Trans. % 86.6 87.7 89.4 86 87.6 89.2

Al mg/dm3, 0.35 >0.5 >0.5 0.09 0.08 0.09

Fe mg/dm3 <.00KO.0K0.OKO.OKO.0KO.01

TABLE IIIc

Test No 66 67 68 69 70 71

Flocculant AS AS AS PAC/FPAC/FPAC/F

Dosage mg/dm3 3 4 5 3 4 5

Water D D D D D D

Water pH 0.56 5.6 5.5 5.6 5.8 6

Floe. Qual. lOmins B C C/D A C/D E

Floe. Qual. 20mins D E F D F G

Colour H 3.6 2.4 2.1 4.2 3.7 4.8

Turbidity NTU 1.1 1.2 1.2 0.8 0.8 0.6

Trans. % 89 90.6 90.2 88 89.4 90.5

Al mg/dm3, <0.010.03 0.03 0.1 0.08 0.03

Fe mg/dm3 <0.0KO.0K0.0KO.OKO.OK0.01

Claims

Claims :

1. A basic aluminium and iron-containing flocculating agent for treating aqueous systems characterised in that it is a basic ρoly(iron/aluminium) halide.

2. A flocculating agent as claimed in claim 1 wherein the basic poly(aluminium/iron) halide has a charge density of from 600 to 1100 micro eq/g.

3. A flocculating agent as claimed in claim 1 or 2 wherein the basic poly(aluminium/iron) halide has a basicity of from 30% to 80%. 4. A flocculating agent as claimed in any preceding claim having a content of aluminium, calculated as AI2O3, of 2% to 12%wt, of iron, calculated as Fe2θ3, of 0.5% to

4%wt and a total content of aluminium and iron, calculated on the same basis, of not more than 12.5%wt.

5. A flocculating agent as claimed in any preceding claim in which at least 40% of the iron content is in the ferric state.

6. A flocculating agent as claimed in any preceding claim in the form of a solution having a pH of from 2.1 to 4.2.

7. A flocculating agent as claimed in any preceding claim having a content of SO^- ions of less than 10% by weight.

8. A process for the production of a flocculating agent as claimed in any preceding claim comprising forming a mixture of aqueous aluminium chloride and a metal selected from iron and aluminium and dissolving the metal in the aqueous aluminium chloride to form a solution the process being characterised in that the metal comprises both iron and aluminium.

9. A process as claimed in claim 8 wherein the aqueous aluminium chloride is held at elevated temperature during the dissolution of the metal.

10. A process as claimed in claim 8 or 9 wherein the solution is treated with an oxidising agent to convert at least 40% of the iron content into the ferric state.

11. A process as claimed in any one of claims 8 to 10 wherein the oxidising agent is hydrogen peroxide.

12. A process for purifying water or other aqueous liquid or suspension or effluent to a low residual aluminium or iron content or to a low turbidity or organics content the prosess comprising treating the water, liquid or suspension with a flocculating agent, allowing a floe blanket to form and removing the purified supernatant, characterised in that the flocculating agent comprises that claimed in any one of claims 1 to 7.

13. A process as claimed in claim 12 conducted at the ambient pH of the water, liquid or suspension.

14. A process as claimed in claim 12. or 13 wherein the supernatant layer is subjected to ultraviolet irradiation.