GB1563996A

GB1563996A - Method of promoting the sedimentation of clay particles or other negatively charged particles in aqueous suspension

Info

Publication number: GB1563996A
Application number: GB2137875A
Authority: GB
Original assignee: CITY UNIVERSITY OF ST JOHN STR
Current assignee: CITY UNIVERSITY OF ST JOHN STR
Priority date: 1976-08-20
Filing date: 1976-08-20
Publication date: 1980-04-02

Description

(54) A METHOD OF PROMOTING THE SEDIMENTATION OF CLAY PARTICLES OR OTHER NEGATIVELY CHARGED PARTICLES IN AQUEOUS SUSPENSION (71) We, THE CITY UNIVERSITY of St. John Street, London, a British University granted a Royal Charter of Incorporation by Order of Her Majesty Queen Elizabeth 1t, and RICHARD HENRY FOSTER, a British subject, of 5, Oaks, Forstal Sandhurst, Hawkhurst, Kent, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to the sedimentation of fine particles and, more particularly, is concerned with a method of promoting the sedimentation of clay particles or of other negatively-charged particles in aqueous suspension.

According to the present invention there is provided a method of promoting the sedimentation of fine, negatively-charged particles in aqueous suspension which method comprises admixing with the suspension an aqueous solution of a hydrous polymeric hydroxy aluminium salt.

The solution of the hydrous polymeric hydroxy aluminium salt may be prepared by irrtermixing polymeric solutions or suspensions of (a) an aluminium salt and (b) a base of an alkali metal or an alkaline earth metal. Preferably the amounts of said aluminium salt and said base employed are such that the ratio of hydroxyl groups to aluminium atoms in the hydrous polymeric hydroxy aluminium cation is in the range of from 0.5 to 2.5.

Only a minor amount of the hydrous polymeric hydroxy aluminium salt needs to be added to the suspension of fine particles in order to achieve the desired result.

Generally there will be admixed with the suspension an amount of the hydrous polymeric hydroxy aluminium salt such that the concentration of aluminium does not exceed 1% by weight of the particles to be sedimented.

Usually, the cation of the hydrous polymeric hydroxy aluminium salt will have a molecular weight in the range 582 to 4,552.

The invention will be further described by reference to the following Examples.

Example 1.

There were prepared aqueous solutions of a hydroxy aluminium salt by intermixing a 0.2M aqueous solution of aluminium chloride and a 0.1M aqueous solution of sodium hydroxide. Two solutions of polymeric hydroxy aluminium salt were prepared, each having an aluminium concentration of 0.9 grms/litre but one having a ratio of hydroxyl ions to aluminium atoms of 1.5 and the other having a ratio of hydroxyl ions to aluminium atoms of 2.5. Six litres of the aqueous solution having a ratio of hydroxyl ions to aluminium atoms of 1.5 was used to treat 5.9 litres of an aqueous suspension in which 2Kg of kaolin had been suspended; the kaolin treated in this manner is referred to hereinafter as SCK material.

In a similar manner six litres of the aqueous solution having a ratio of hydroxyl ions to aluminium atoms of 2.5 was used to treat 5.9 litres of an aqueous suspension in which 2Kg of kaolin had been suspended; the kaolin treated in this manner is referred to hereinafter as LCK material. Each of the SCK and LCK materials was thus suspended in 11.9 litres of water at a concentration of 16.85% by weight and in both cases the concentration by weight of aluminium to clay mineral was 0.27%. A similar suspension of untreated kaolin was also prepared. Each of the three suspensions was allowed to sediment within a 150 mm dia. cylinder while.

under a consolidation pressure of 380 kN/m2. The times for consolidation were as follows: for the untreated material 28 days; the for SCK material 14 days; and for the LCK material 13 days. Immediately follow ing consolidation the untreated material and the LCK material treated were continuously stirred for I week in distilled water at pH6; and the particle size distributions measured.

Both suspensions were subsequently treated with sodium hexametaphosphate to bring their pH values to 7 and again analysed for particle size distribution. The resulting observations are given in the following table: Particle Sizes

Material D*,, D*,, D*,,, Untreated pH6 0.54 1.20 1.75 pH7 0.13 0.40 0.94 LCK pH6 1.50 2.30 3.20 pH7 0.24 0.55 0.95 * see "An Introduction to Soil Mechanics and Fdundations" by C.R. Scott, published by Applied Science Publishers Ltd., 2nd Edition, 1974, p. 12.

It is seen that even after dispersion at pH7 the effective particle sizes of the treated material were higher than those of the untreated material, notably at the lower end of the size range, this providing evidence of flocculation especially of the smaller particle sizes.

Example 2.

There were prepared aqueous solutions of a hydroxy aluminium salt by intermixing a 0.2M aqueous solution of aluminium chloride and an aqueous suspension of calcium hydroxide in its own saturated solution such that the total concentration of calcium hydroxide was 0.1M. The solutions of hydroxy aluminium salt prepared in this manner had an aluminium concentration of 1.54 g/l and a ratio of OH/A I of either 1.5 or 2.5 . 70 ml. of each solution was mixed with 930 ml of an aqueous suspension in which 3.98 gm. of kaolin (having a particle size such that 90% of the particles were smaller than 0.5 ,um) were suspended, thus giving a concentration by weight of aluminium to clay mineral of 0.27%. A similar aqueous suspension of untreated kaolin was also prepared and after mechanical stirring for 1/2 hour each suspension was allowed to sediment in a graduated cylinder. After 3 days, sedimentation of both treated materials was virtually completed, the sedimented material occupying 100 ml. in the case of the material treated with a hydroxy aluminium salt having a OH/A1 ratio of 1.5, and 110 ml. in the case of the material treated with a hydroxy aluminium salt having a OH/AI ratio of 2.5. After 3 days the untreated material still occupied 960 m and at 7 days this had reduced to 800 ml, including 30 ml. of sediment at the bottom. After 7 days each sample was resuspended by high-speed mechanical stirring for 1/2 hour and within 1 day the materials, treated with the hydroxy aluminium salts having OH/AI ratios of 1.5 and 2.5 had respectively settled to 90 ml.

and 100 ml., whereas the untreated material repeated its earlier behaviour. On repeating the whole cycle at 34 days after initial treatment the treated materials had settled to 85 ml. and 110 ml. respectively within 4 hours whereas the untreated material repeated its earlier behaviour. It can be seen that not only did the treatment produce flocculation but also the introduction of strong bonds which were not destroyed by high speed stirring and which increased in number and strength in time.

WHAT WE CLAIM IS: 1. A method of promoting the sedimentation of fine negatively-charged particles in aqueous suspension which method comprises admixing with the suspension an aqueous solution of a hydrous polymeric hydroxy aluminium salt.

2. A method according to claim 1 wherein the fine particles are clay particles suspended in water.

3. A method according to claim 2 wherein the suspension of fine clay particles in water exists in a mining process, a quarrying process, a clay refining process, or a water purification process.

4. A method according to claim 3 wherein the suspension is an effluent or tailing.

5. A method according to claim 1, 2, 3 or 4 wherein the hydrous polymeric hydroxy aluminium salt is formed by the progressive and continuous intermixing of aqueous solutions or suspensions of (a) an aluminium salt and (b) a base of an alkali metal alkaline earth metal.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. stirred for I week in distilled water at pH6; and the particle size distributions measured. Both suspensions were subsequently treated with sodium hexametaphosphate to bring their pH values to 7 and again analysed for particle size distribution. The resulting observations are given in the following table: Particle Sizes Material D*,, D*,, D*,,, Untreated pH6 0.54 1.20 1.75 pH7 0.13 0.40 0.94 LCK pH6 1.50 2.30 3.20 pH7 0.24 0.55 0.95 * see "An Introduction to Soil Mechanics and Fdundations" by C.R. Scott, published by Applied Science Publishers Ltd., 2nd Edition, 1974, p. 12. It is seen that even after dispersion at pH7 the effective particle sizes of the treated material were higher than those of the untreated material, notably at the lower end of the size range, this providing evidence of flocculation especially of the smaller particle sizes. Example 2. There were prepared aqueous solutions of a hydroxy aluminium salt by intermixing a 0.2M aqueous solution of aluminium chloride and an aqueous suspension of calcium hydroxide in its own saturated solution such that the total concentration of calcium hydroxide was 0.1M. The solutions of hydroxy aluminium salt prepared in this manner had an aluminium concentration of 1.54 g/l and a ratio of OH/A I of either 1.5 or 2.5 . 70 ml. of each solution was mixed with 930 ml of an aqueous suspension in which 3.98 gm. of kaolin (having a particle size such that 90% of the particles were smaller than 0.5 ,um) were suspended, thus giving a concentration by weight of aluminium to clay mineral of 0.27%. A similar aqueous suspension of untreated kaolin was also prepared and after mechanical stirring for 1/2 hour each suspension was allowed to sediment in a graduated cylinder. After 3 days, sedimentation of both treated materials was virtually completed, the sedimented material occupying 100 ml. in the case of the material treated with a hydroxy aluminium salt having a OH/A1 ratio of 1.5, and 110 ml. in the case of the material treated with a hydroxy aluminium salt having a OH/AI ratio of 2.5. After 3 days the untreated material still occupied 960 m and at 7 days this had reduced to 800 ml, including 30 ml. of sediment at the bottom. After 7 days each sample was resuspended by high-speed mechanical stirring for 1/2 hour and within 1 day the materials, treated with the hydroxy aluminium salts having OH/AI ratios of 1.5 and 2.5 had respectively settled to 90 ml. and 100 ml., whereas the untreated material repeated its earlier behaviour. On repeating the whole cycle at 34 days after initial treatment the treated materials had settled to 85 ml. and 110 ml. respectively within 4 hours whereas the untreated material repeated its earlier behaviour. It can be seen that not only did the treatment produce flocculation but also the introduction of strong bonds which were not destroyed by high speed stirring and which increased in number and strength in time. WHAT WE CLAIM IS:

1. A method of promoting the sedimentation of fine negatively-charged particles in aqueous suspension which method comprises admixing with the suspension an aqueous solution of a hydrous polymeric hydroxy aluminium salt.

6. A method according to claim 1, 2, 3 or

4 wherein the ratio of hydroxyl groups to aluminium atoms in the cation of the hydrous polymeric hydroxy aluminium salt is in the range of from 0.5 to 2.5.

7. A method according to claim 5 or 6 wherein the aluminium salt is aluminium chloride and the base is sodium hydroxide.

8. A method according to claim 5 or 6, wherein the aluminium salt is aluminium chloride and the base is calcium hydroxide.

9. A process according to any one of claims I to 8, wherein the cation of the hydrous polymeric hydroxy aluminium salt has a molecular weight in the range 582 to 4,552.

10. A method according to claim 1, substantially as described in the foregoing Examples.