WO1999035090A2

WO1999035090A2 - Improvements in flocculants

Info

Publication number: WO1999035090A2
Application number: PCT/GB1998/003788
Authority: WO
Inventors: Neil Clarke; John Newton; Kevin Parkes; Michael Whiting
Original assignee: Laporte Industries Limited
Priority date: 1998-01-09
Filing date: 1998-12-17
Publication date: 1999-07-15
Also published as: WO1999035090A3; AU1676299A; GB9800356D0

Abstract

A flocculant composition comprises a polyaluminium calcium magnesium chloride or chloride sulphate gives effective turbidity reduction and transmissivity increase in waters, especially in waters having a hardness no more than 120 mg/l CaCO3. The composition is produced by the reaction of aluminium chloride in an acidic aqueous medium containing chloride and/or sulphate ions and also containing one or more magnesium carbonate-containing minerals such as dolomite. The aluminium chloride may be aluminium chloride contaminated with organic impurities as a result of use as a catalyst for organic transformations such as the alkylation of aromatic or aliphatic compounds by means of the Friedel-Krafts reaction.

Description

Improvements in Flocculants

This invention relates to flocculants and to a method for the production of the same which may satisfactorily be operated using organics-contaminated aluminium-containing raw materials.

Flocculants are in widespread use in the clarification of potable or waste waters by encouraging the sedimentation of finely divided particulate matter in suspension in the water. A well known class of flocculants are based on cationic polymeric aluminium ions, such as polyaluminium chloride and modifications thereof such as sulphate derivatives. It would be of advantage to industry to provide alternatives to, or improvements on, known polyaluminium flocculants or to provide alternative, or improved, processes, or processes utilising impure or waste raw materials, for the production of the same.

Polyaluminium chloride or chloride sulphate flocculants may be produced by the reaction of aluminium compounds in an aqueous acidic medium containing chloride or chloride and sulphate ions.

The invention provides a method for the production of a polyaluminium chloride or chloride sulphate flocculant by the reaction of an aluminium compound in an acidic aqueous medium containing chloride and/or sulphate ions the method being characterised in that there are included in the acidic aqueous medium magnesium and calcium compounds the magnesium compounds comprising or consisting of one or more magnesium carbonate- containing minerals and in that the aluminium compound comprises or consists of aluminium chloride, the flocculant so produced being a polyaluminium calcium magnesium chloride or chloride sulphate.

The present invention also particularly provides a flocculant composition, which may be produced by the process of the invention comprising a polyaluminium calcium magnesium chloride or chloride sulphate having the molar ratios of aluminium, magnesium, calcium, hydroxide, chloride and sulphate defined by the general formula:

Al.Mg_x.Ca_y.OH_wCl/S0₄ _ wherein x+y has a value of 0.042 to 0.75 but preferably to 0.5, particularly preferably to 0.425 x has a value of 0.002 to 0.2, preferably to 0.15 y a value of 0.04 to 0.6, but preferably to 0.3 and particularly preferably to 0.275 for the low calcium product described hereafter z has a value of 0.75 to 3.5, preferably to 2.8 provided that w has a value of at least 0.1, preferably from 0.5 to 2.

The polyaluminium flocculant composition according to the invention may advantageously be used in combination with a cationic polymer such as, for example, a polyethyleneamine, polyamidoamine or a polyvinylamine or a polydiallyl ammonium compound. In some cases the presence of the polymer enhances the flocculation ability of the polyaluminium compound. The polymer preferably has a cationic charge density of from 4 to 24 m.eq./g and is water soluble. A suitable quantity of polymer is from 1% to 10% by weight of the flocculant solution. It has also been found, according to the present invention, that when in combination with a cationic polymer, to preserve the stability of the polyaluminium compound in solution, the content of calcium, calculated as the element, in the polyaluminium compound is suitably reduced and is preferably less than 3.5% and particularly preferably less than 2% and at least 0.25%, by weight. To enhance stability the polyaluminium flocculant of the invention, as a separate feature or in combination with the control of the calcium level described above, preferably has a sodium content of at least 0.5%, particularly preferably at least 0.75%, for example, very suitably, at least 1%, and preferably up to not more than 3% by weight calculated as the element.

The stability of flocculant solutions according to the invention, or of other flocculant solutions, may be judged by reference to the turbidity of the solution, measured in NTU, with time. Generally, there may be an initial slow increase in turbidity followed by a rapid increase to unacceptable levels together with an increase in viscosity and often, ultimately, solidification.

The composition of the invention preferably has a relative bacisity of from 20%, particularly preferably from 25% to 45%, and suitably up to 50% or more, a charge density of at least 500, preferably at least 600 and suitably up to 1200, or even 1500 milliequivalents/gram as measured by the streaming current method. Higher charge densities indicate increasing polymeric sizes.

As a further and separate feature there is also provided an acidic aqueous polyaluminium flocculant solution, by which term it is intended to include polyaluminium flocculants containing other metals, such as the polyaluminium flocculants of US-A-4566986 referred to above and also polyaluminium chloride or polyaluminium sulphate flocculants, containing less than 3.5%, preferably less than 2%, suitably less than 1%, and, for example at least 0.25% by weight of the flocculant solution of calcium, calculated as the element, and at least 0.5% preferably at least 0.75%, for example, very suitably, at least 1%, and preferably up to not more than 3%, particularly preferably not more than 2.5% by weight calculated as the element of sodium, also calculated as the element. The more specific teachings herein as to the composition of the flocculants of the present invention also apply to this further and separate feature. The process of the invention is particularly suitable for the conversion of aluminium chloride contaminated with organic impurities into a flocculant. Aluminium chloride is used on a large scale as a catalyst for organic transformations. For example, it is used as a catalyst in the alkylation of aromatic or aliphatic compounds by means of the Friedel-Krafts reaction. After use for this purpose the aluminium chloride may be comtaminated with compounds such as, for example, benzene, chloropropanol, alkyl substituted dioxolanes, dioxanes or methylene chloride, up to individual concentrations which may vary from as little as 4 micrograms/litre to as much as 200 micrograms/litre aluminium chloride solution or even up to a level as high as 1% by weight, in the case of methylene chloride. Commonly, the total organic carbon content of used catalytic aluminium chloride solutions may be over 100, often over 200 milligrams/litre. Such contaminated aluminium chloride solutions are usually deep yellow in colour. It may be undesirable to use a flocculating agent containing organic or aromatic impurities for the clarification of potable water, depending on the nature of the impurities, and for this reason organics-contaminated aluminium chloride may be considered to be unsuitable for use as a raw material for the production of flocculants. Alternatively, the acidic aqueous medium containing chloride and/or sulphate ions may be derived directly from synthetic raw materials such as, for example from anhydrous aluminium chloride or from a mixture of alumina trihydrate and hydrochloric acid.

According to the method of the present invention, if the reaction with the magnesium or magnesium and calcium compounds is conducted at a relatively low temperature over an extended period of time a proportion of the organic impurities may be stripped from the solution. The stripping agent is apparently carbon dioxide generated by the reaction of carbonate with chloride and emitted from the solution. This stripping agent is generated 'in situ' on a molecular level of contact with the other constituents of the solution in contrast to externally sourced gaseous stripping agents. The method of the present invention is preferably conducted by maintaining contact between the aluminium chloride and the carbonate compound or compounds at a temperature less than 60°C for a duration of more than 4 hours so as to maximise the effect by encouraging a slow rate of carbonate decomposition. The temperature may very suitably be at least 10°C and/or less than 50°C. The duration of the contact may very suitably be more than 8 hours and/or up to 36 hours although the effect anticipated may be attained in a lesser time than that, for example in no more that 24 hours. Where the aluminium chloride is sufficiently pure for use to produce a specific flocculant, a temperature of up to the boiling temperature at the prevailing pressure, and a correspondingly shorter time of contact, may suitably be used.

As a further and separate feature there is also provided a method for the purification of an acidic aqueous medium, for example a solution of aluminium chloride, containing organic impurities, for example at a level of total organic carbon of at least 50 milligrams/litre of the medium by contacting the medium with carbon dioxide characterised in that the purification is conducted by generating carbon dioxide in the interior of the medium by the reaction therein of an inorganic carbonate, for example magnesium carbonate or magnesium and calcium carbonates, at a temperature of less than 60°C and/or over a period of at least 4 hours. The more specific teachings herein as to the conditions of the reaction between the aluminium chloride and the magnesium carbonate in the preparation of the flocculants of the present invention also apply to this further and separate feature.

The one or more magnesium carbonate-containing minerals for use according to the present invention may preferably comprise or consist of calcium carbonate-containing minerals selected from dolomite, which is preferred, limestone and minerals of intermediate composition. By the term "limestone" we mean a rock which is mainly composed of calcium carbonate and which has at least a small content of magnesium carbonate, for example at least 0.1% for example at least 0.2%. By a "dolomite" we mean a double carbonate of magnesium and calcium usually containing at least about 30%, and possibly up to 70% by weight or more of magnesium carbonate. Examples of intermediate minerals are, for example, dolomitic limestone. Alternatively, minerals having a higher content of magnesium carbonate such as magnesite, which may contain up to over 90% by weight of magnesium carbonate, or carbonate minerals having a magnesium carbonate content between dolomite and magnesite may be used. Preferably, the content of mineral impurities in the magnesium carbonate mineral is less than 20%, particularly preferably less than 10% by weight. Preferably, the entire content of magnesium and calcium in the flocculant, or at least 80%, preferably at least 90% by weight thereof, is provided by minerals as above described. The quantity of the carbonate mineral is preferably at least sufficient, in theory, to react with the aluminium chloride. More suitably, the mineral is in at least 5% excess, preferably at least 20% excess, and possibly up to 100% excess or more as required at the reaction conditions used to achieve complete conversion of the aluminium chloride. Preferably a proportion of the calcium carbonate, if used, in replaced by sodium carbonate. This also helps to reduce sludge formation during the use of the flocculant, as a result of the precipitation of calcium compounds. If a content of sodium is required in the flocculant composition this may preferably be provided by an addition of soda ash or other sodium source or sodium carbonate material.

In a modification of the present invention one or more cationic materials other than magnesium and calcium ions may be associated with the aluminium although it is envisaged that this will be in less than 50% molar, preferably less than 25% molar, of the total cationic materials. Preferably, however, the composition of the reaction mixture is such as to give a flocculant as particularly provided by the present invention and defined by general formula above.

In the preparation of the flocculants of the invention the solution of the aluminium chloride preferably has a concentration of at least 5%, particularly preferably at least 8% and preferably up to 25% or more, particularly preferably up to 20%, calculated as A1C1₃. If the concentration of the aluminium chloride solution as supplied is towards the lower end of, or below, the range stated above its aluminium content may be augmented by the addition of further aluminium compounds or aluminium metal together with an addition of HC1 if required to ensure the conversion of the same to the chloride. The pH of the solution of aluminium chloride is preferably from 0.5 to 1.5. It is preferred to add the carbonate compounds to the acidic solution of the aluminium chloride, to maintain the resulting mixture with stirring or other means of agitation for the desired reaction period to allow the carbonate compounds to be sufficiently consumed having regard to any decrease in the reaction rate with decreasing concentration of reactants . If a carbonate other than magnesium carbonate is to be used it is found that this may materially reduce the reactivity of the magnesium carbonate, even to the extent that it is difficult to achieve the consumption of the last 5 of 10% by weight thereof, unless the magnesium carbonate is added to the aluminium chloride first and allowed to react, at least to a major extent, for example to more than 75%, preferably to more than 90% by weight, before the other carbonate is added. Preferably the magnesium carbonate is reacted with the aluminium chloride, at the reduced temperature preferred in the process of the present invention, for at least 8 hours. If a content of sulphate is required in the flocculant according to the invention a proportion of sulphuric acid and/or one or more sulphates may be added to the reaction mixture or to the floocculant product. On completion of the reaction to the desired extent the resulting solution may be filtered or otherwise separated from any residue and forms the product of the invention.

The present invention will now be described by reference to the following examples but without limitation to those examples.

Examples 1 to 6 are examples of the preparation of flocculant compositions according to the invention. Example 7 is not according to the invention but is comparative therewith.

Figures I and II are graphs of turbidity (NTU) against dose (mg/1) and Figures III and IV of % Transmission against dose of the Product of Example 1 and of known flocculants identified by reference to numerical indicators.

Examples 1- 7

The reactant materials used were:

Aluminium Chloride 10% Wt. As A1₂0₃ ex Friedel-Krafts catalyst

Deep yellow colour

Dolomite Particle size 300 microns max.

% MgO 20.9

% CaO 30.8

Limestone Particle size 300 microns max.

% CaO 55.5

% MgO 0.2

Light Ash Na,C0₃

MgS04.7H20

The flocculant compositions of these examples were produced by adding the remaining constituents to a 10% by weight A1C1₃ aqueous solution and maintaining the resulting mixture with stirring at 20°C for 8 hours. The mixture was then filtered to recover the product. In Example 5 the dolomite was added first and the light ash was added after the dolomite had dissolved and was maintained for a further 8 hours at the same temperature. The pH, charge density, specific gravity (Sp.G.) and % transmissivity (% Trans.) of the products of Examples 1-7 were measured. The % transmissivity was measured by spectrophotometry at a wavelength of 254 nm. The charge density was measured as indicated above.

The compositions of the reaction mixtures for each of the Examples were as follows . Example No . 1 2 3 4 5 6 7

A1C1₃ 500 500 500 500 500 500 500

Dolomite - 25 25 25 25 25

Limestone 60 - 30 40 -

Light Ash - 30 30

MgS0₄.7H₂0 - 10

The compositions of the products of Examples 1 to 7, in weight % as the oxides, and the properties of those products, were as follows:

Example No. 1 2 3 4 5 6 7

%A1₂0₃ 10 10 10 10 10 10 10

%CaO 5.93 1.48 4.38 5.30 1.39

%MgO 0.02 1.00 0.94 0.92 0.94 0.30

%Na₂0 - - - - 3.10 3.00 -

%C1 17.5 17.5 17.5 17.5 17.5 17.5

%S0₄ - - - - - 0.74 -

pH 1.00 0.60 0.70 0.95 0.1

Charge Den. +1000 +700 950 +1125 +300

% Trans. 12.0 14.6 26.7 30.2 35.8 22.1 8.1

Sp.G. 1.30 1.29 1.31 1.33 1.25 The relative basicity of the product of Example 4 was 37%. It is noted that the Transmissivity measurements serve to indicate the degree of colouration on the products of the Examples and enables a deduction as to relative freedom from organic impurities .

The products of the Examples were tested in use as flocculants in the clarification of certain commercial waters and compared in that use with certain known products . The % turbidity and % transmissivity of the treated water were measured for a series of different dose levels from 30 to 100 mg/litre of water. The % Turbidity was measured after stirring in the flocculant at 15 rpm. for 20 minutes and after settling for 30 minutes.

The waters treated in the tests had the properties set out below and comprised hard, soft and medium hard waters respectively.

A. B. C.

PH 7.8 7.2 7. ,6

Colour (Hazen) 39.6 21.6 54

Turbidity (NTU) 3.7 2.7 6. .8

% Transmission (254nm) 61.8 73.9 57. .7

Iron (mg.l) 0.03 0.01 0. .05

Aluminium (mg/1) 0.04 0.01 0. .04

Manganese (mg/1) 0.004 0.001

Alkalinity (mg/1 as CaC03) 12 200 15 60

Hardness (mg/1 as CaC03) 85 40 80

The flocculating agents used in the tests are identified in Figure I (Testing of Water A) , Figure II (Testing of Water B) and Figures III and IV (Testing of Water C) by numerals relating to the particular flocculation agents as indicated below:

(1) Product of Example 1 herein

(2) Product according to WO 95/11199 (3) Ferric sulphate

(4) Polyaluminium chloride

(5) Aluminium chloride

( 6 ) Alum

(7) Product of Example 4 herein

(8) Aluminium chloride

It can be seen from the Figures that the products of the invention give a particularly good performance in treating soft or medium hardness waters, for example having a hardness of no more than 120, preferably no more than 100 ml/1, as CaC03 and at relatively low dose rates.

Claims

Claims .

1. A method for the production of a polyaluminium chloride or chloride sulphate flocculant by the reaction of an aluminium compound in an acidic aqueous medium containing chloride and/or sulphate ions the method being characterised in that there are included in the acidic aqueous medium magnesium and calcium compounds the magnesium compounds comprising or consisting of one or more magnesium carbonate-containing minerals and in that the aluminium compound comprises or consists of aluminium chloride, the flocculant so produced being a polyaluminium calcium magnesium chloride or chloride sulphate.

2. A method as claimed in claim 1 wherein the magnesium carbonate-containing mineral is dolomite, limestone, magnesite or minerals of intermediate contents of magnesium and calcium carbonate.

3. A method as claimed in claim 1 or 2 wherein the reaction is conducted at a temperature of 10┬░C to less than 60┬░C for a duration of at least 4 hours.

4. A method as claimed in any preceding claim wherein the magnesium carbonate-containing mineral is reacted to an extent of at least 75% before any other reactant is introduced into the reaction mixture.

5. A method as claimed in claim 4 wherein the magnesium carbonate-containing mineral is reacted to an extent of at least 95% before the introduction of any other calcium carbonate- containing mineral or any sodium delivering substance.

6. A method as claimed in any preceding claim wherein the magnesium carbonate-containing mineral is dolomite.

7. A method as claimed in any preceding claim wherein the magnesium carbonate-containing mineral or minerals are present in a theoretical excess of at least 5% having regard to the quantity of aluminium chloride.

8. A method as claimed in any preceding claim wherein the aluminium chloride has an initial concentration of 8% to 20% by weight as A1C1₃.

9. A method as claimed in any preceding claim wherein the aluminium chloride has a content of organic impurities at least corresponding to 100 milligrams/litre of solution.

10. A method as claimed in claim 1 and substantially as described herein.

11. A method for the purification of an acidic aqueous medium containing organic impurities characterised in that carbon dioxide is generated in the interior of the medium by the reaction therein of an inorganic carbonate at a temperature of less than 60┬░C and/or over a period of at least 4 hours.

12. A method as claimed in claim 10 wherein the acidic aqueous medium comprises a solution of aluminium chloride and the inorganic carbonate comprises magnesium carbonate.

13. A method as claimed in claim 10 or 11 wherein the content of organic impurities is at least corresponding to 100 miligrams/litre of solution.

14. A flocculant composition which may be produced by the process of the invention comprising a polyaluminium calcium magnesium chloride or chloride sulphate having the molar ratios of aluminium, magnesium, calcium chloride and sulphate defined by the general formula:

Al .Mg_x . Ca_y. OH_wCl/S0₄ _ wherein x+y has a value of 0 . 042 to 0 . 75 x has a value of 0 . 002 to 0 .2 y has a value of 0 . 04 to 0 . 6 z has a value of 0 . 75 to 3 . 5 provided that w has a value of at least 0.1,

15. A composition as claimed in claim 14 wherein, in the general formula x+y has a value of 0.042 to 0.5 x has a value of 0.002 to 0.15 y has a value of 0.04 to 0.3 z has a value of 0.75 to 2.8 provided that w has a value of 0.1 to 2

16. A composition as claimed in claim 15 having a content of sodium of at least 0.5% calculated as the element.

17. A composition as claimed in claim 16 also containing a cationic polymer.

18. A composition as claimed in any one of claims 14 to 17 having a relative basicity of from 10% to 50%.

19.A composition as claimed in any one of claims 14 to 18 having a charge density of from 500 to 1500 eq./g.

20 A polyaluminium flocculant composition containing less than 3.5%, preferably less than 2%, suitably less than 1%, and, for example at least 0.25% by weight of the flocculant solution of calcium, calculated as the element, and at least 0.5% preferably at least 0.75%, for example, very suitably, at least 1%, and preferably up to not more than 3% by weight calculated as the element of sodium.

21 A composition as claimed in claim 20 also containing a cationic organic polymer in from 1% to 10% by weight of the composition.

22. A composition as claimed in claim 2o substantially as described in any one of Examples 1 to 6 herein.