FR2513619A1 - Waste water purificn. by flocculation with iron or aluminium salts - using aq. alkaline sodium silicate soln. as adjuvant - Google Patents

Abstract

In a process for purifying waste waters by coagulation -flocculation using iron or aluminium salts as coagulation agents, opt. in polymeric forms, the improvement comprises using an alkaline aq. Na silicate soln. as adjuvant. Amt. of coagulation agent used is 0.3-20 mg Fe2O3 or Al2O3 per l water to be treated. Amt. of Na silicate soln. used is such that the atomic ratio of Si/Fe or Si/Al is 0.1-1. The process combines the efficiency of "activated silica" or silico-aluminates with great simplicity of operation. The flocculation agent need not be previously prepd. and no particular appts. is required.

Description

 The present invention relates to a water treatment method by coagulation-flocculation, particularly suitable for the preparation of drinking water or water for industrial use from river water or water from the subsoil. This process consists in treating the water to be purified with an aqueous alkaline solution of sodium silicate combined with coagulation inorganic agents.

 In the treatment of waters laden with colloidal materials, it is well known to use procedures comprising a coagulation step of the colloidal materials and a flocculation step, which makes it possible to enlarge the precipitate to make it more easily separable. The separation of the precipitated materials can be done either by decomposition (clarification processes), by filtration (direct coagulation methods on filter), or by flotation.

 The most commonly used coagulant reagents are inorganic salts whose cation has a high valency. The best known and most economical are iron salts and aluminum salts, such as ferric chloride, ferrous sulphate, ferric sulphate, aluminum chloride and aluminum sulphate. The basic aluminum salts with a polymeric structure, especially the basic aluminum chlorosulfate polymer, prepared according to French Patent No. 2,036,685 and sold by the Applicant under the trademark WAC, or the basic aluminum chloride polymer, prepared according to French Patent No. 2,308,594, have a coagulant power greater than that of ordinary salts and at the same time have a good flocculating effect.

 In some cases, such as when the temperature of the water to be treated is particularly low, or when the linear velocity of passage in the settler is high, or when the coagulated sludge has a low coefficient of cohesion, it is necessary to adding to the coagulating reagent a flocculation adjuvant, which makes it possible to increase the size of the floc and / or its apparent density and / or its mechanical strength. This results in an increase in the settling rate, an improvement in the degree of uniformity of the flocs and an extension of the life of the filters.

 As flocculation additives, water-soluble organic polymers of natural origin such as alginates or of synthetic origin, such as homopolymers and copolymers of acrylamide, are sometimes used. However, it is often preferred, for reasons of lower cost, to use inorganic products, such as activated silica or sodium silicate complexes with an aluminum salt.

 By "activated silica" is meant the product obtained by reducing the pH of a sodium silicate solution by means of an acid, such as sulfuric acid, and maturing until the appearance of a colloidal suspension.

Although "activated silica" has the advantage of being a relatively inexpensive product and of being effective even on waters whose temperature is close to oac, it nevertheless presents serious drawbacks, well known to users:
- limited shelf life, involving the preparation of the product at the place and at the time of use,
variable flocculant properties as a function of the activation conditions, which requires a rigorous control of the reaction, which is not always easy to achieve at the point of use,
- risks of irreversible mass formation during the preparation.

It has been proposed, in particular in the patent
United States of America No. 2,310,009, British Patent No. 827,586, French Patent Nos. 2,143,474 and 2,453,107 and French Utility Certificate No. 2,376,688, reacting a solution of sodium silicate with aluminum sulphate or basic aluminum chloride to prepare complex salts, sometimes called silico-aluminates.

 In the case of the reaction of sodium silicate with aluminum sulphate, it is necessary to adjust the pH of the medium with precision and to avoid that the aluminum sulphate used is too contaminated with sulfuric acid. . The mixture of the aluminum salt with the sodium silicate solution must generally be carried out in very complex apparatus, bringing an intense mixing energy under shear, in order to ensure both the realization of the chemical reaction and the obtaining product in colloidal form.

 The reaction of sodium silicate with a basic aluminum chloride, according to French Patent No. 2,453,107, significantly simplifies the preparation and to avoid the risk of caking. At most a gel is formed if the pH of the preparation is not correct, and this gel can be broken down by the addition of hydrochloric acid or a new dose of basic aluminum salt. Nevertheless, preparation must always be done at the place and at the time of employment.

 There is therefore an industrial need to have a water treatment process by coagulation flocculation, which combines the effectiveness of "activated silica" or silico-aluminates to a very great simplicity of implementation.

 The process according to the present invention makes it possible to satisfy this need, since it does not require either a prior preparation of the flocculation adjuvant or a particular apparatus. It consists simply of adding to the water to be treated a mineral coagulation agent and an aqueous alkaline solution of sodium silicate.

 The mineral coagulation agent is chosen from the mineral coagulants usually used in the treatment of water, that is to say the chlorides, sulphates and chlorosulphates of iron or aluminum, and the basic salts of aluminum with polymeric structure. . A dose corresponding to 0.3-20 mg of Fe 2 O 3 or Al 2 O 3 per liter of water to be treated is generally used.

The aqueous alkali solution of sodium silicate used is a concentrated commercial solution, having a very high pH, for example from 12 to 13, and containing from 24 to 30% by weight of SiO 2, which corresponds to a density of 1, 32 to 1.41 Kg / l or at a density of 35 to 42 degrees
Balm. The average SiO 2 / Na 2 weight ratio is preferably between 2.5 and 3.6. In the case where the flow rates of water to be treated are low, or if the available injection equipment makes it necessary, the concentrated commercial solution of sodium silicate can, without inconvenience, be diluted to water as much as necessary, before addition to the water to be treated.

 This addition to the water to be treated of the sodium silicate solution can be done before, during or after the addition of the mineral coagulation agent. In the case of already existing installations, the injection point provided for the flocculation adjuvant can therefore be used for the addition of sodium silicate.

 The level of sodium silicate introduced is chosen such that the atomic ratio of the silicon introduced into the iron or aluminum of the coagulant is between 0.1 and 1. A value close to 0.4 is particularly suitable.

 In practice, the coagulation inorganic agents available on the market are often presented also in the form of aqueous solutions. Experience has shown that satisfactory results are obtained when the weight ratio of the commercial solution of sodium silicate to the commercial solution of inorganic coagulant is between 1/20 and 1/2, and particularly when it is close to 1 / 5.

 The following examples illustrate in a non-limiting way the interest of the process according to the invention. They correspond to tests of coagulation-flocculation-decantation carried out according to the traditional method of "j ar-test", by means of a laboratory floculator.

 The reagents - mineral coagulation agent and sodium silicate - are added to the water to be treated with vigorous stirring. This strong agitation (160 rpm) is maintained for 90 seconds after the introduction of sodium silicate. The stirring speed is then reduced to 40 rpm, for 13 minutes 30 seconds, to allow the magnification of the floc. The stirring is then stopped and the settling takes place.

The measured parameters are as follows
the size of the floc, expressed by an arbitrary note ranging from 0 to 10, the score 0 corresponding to a microfloc and the note 10 to the largest floc that can be obtained,
the turbidity, expressed in JACKSON units (JTU), of the supernatant water after 3 minutes and after 20 minutes of settling,
- the pH of the decanted water,
permanganate oxidization in an acidic medium of the water decanted for 20 minutes, expressed in mg of oxygen consumed per liter of water,
- the complete alkalimetric titre, or TAC

the silica and aluminum content of the water decanted for 20 minutes, then filtered on a pore filter 0.45 μm in diameter,
for some tests, the liteau color decanted for 20 minutes, measured by comparison with a platinum / cobalt scale, according to the French standard T 90-034,
- for certain tests, the coefficient of cohesion of the sludge, measured after 20 minutes of settling, according to the method described in the book "Memento technique de l'eau", DEGREMONT, 1978, page 951. A high value of this coefficient is translated in practice by the possibility of having high rates of passage in the decanters and a low sensitivity to variations in the flow rate of the water to be treated.

EXAMPLE 1
A Seine water with the following characteristics is treated
Temperature: 140C
Turbidity: 24 JTU
pH: 8.20
Permanganate oxidation: 8.6 mg / l
Hydrotimetric Title: French 25.80
TAC: 22.40
SiO2: 7.1 mg / l
2
Ai: 0.014 mg / l on the one hand with polymeric aluminum basic chlorosulfate (WAC trademark) at the rate of 30 mg per liter of water, on the other hand, with 30 mg of WAC and 6 mg of commercial solution sodium silicate (25% SiO2) per liter of water.

 The results obtained are shown in Table 1.

TABLE 1

<tb><SEP> Oxydabi- <SEP>
<tb><SEP> Size <SEP> Turbidity <SEP> pH <SEP> unit <SEP> at <SEP> TAC <SEP> Si0 <SEP><SEP> Ai
<tb><SEP> of <SEP> 3 <SEP> mn <SEP> pH <SEP> 2
<tb><SEP> floc <SEP> (JTU) <SEP> KMn04 <SEP> (o) (mg / I) <SEP> (mg / i)
<tb><SEP> (mg / l)
<tb> Treatment
<tb> Treatment
<tb><SEP> WAC <SEP> and <SEP> 8 <SEP> 1.2 <SEP> a, o4 <SEP> 5.8 <SEP> 21.2 <SEP> 7.5 <SEP> 0, 16
<tb><SEP> silicate
<tb> of <SEP> sodium
<Tb>
This table shows that the use of sodium silicate with the WAC makes it possible to obtain appreciably larger flocs.

EXAMPLE 2
At another date, a Seine water is treated with the following characteristics:
Temperature: 190C
Turbidity: 12 JTU
pH: 8.03
Permanganate oxidation: 4.2 mg / l
TAC: 20.80
SiO2: 6.4 mg / l
Ai: 0.57 mg / l, on the one hand, with 30 mg of WAC per liter of water, on the other hand, with 30 mg of WAC and 6 mg of commercial sodium silicate solution (at 25% SiO 2) per liter of water.

 The results obtained are shown in Table 2.

TABLE 2

<tb><SEP> Size <SEP> Turbidity <SEP><SEP> Oxydabi- <SEP> TAC <SEP> SiO <SEP> Ai
<tb><SEP> (JTU) <SEP><SEP><SEP> unit to <SEP> 2 <SEP>
<tb><SEP> of <SEP> KMn04 <SEP> (o) <SEP> (mg / i) <SEP> (mg / i)
<tb><SEP> floc <SEP> 3 <SEP> min <SEP> 20 <SEP> min <SEP> P <SEP> (R9n / 1) <SEP> () <SEP> (mg / l)
<tb> Processing <SEP>
<tb><SEP> WAC <SEP> 5 <SEP> 2.4 <SEP> 0.717.85 <SEP> 2.4 <SEP> 18.9 <SEP> 6.0 <SEP> 0.19
<tb> Treatment
<tb><SEP> silicate <SEP> 8 <SEP> 1.8 <SEP> 0.7 <SEP> 7.88 <SEP> 2.4 <SEP> 19.4 <SEP> 6.8 <SEP> 0.11
<tb> of <SEP> sodium <SEP> ~
<Tb>
In this case, the addition of sodium silicate to
WAC not only increases the size of the floc, but also lowers the residual turbidity.

EXAMPLE 3
A water of the Braye is treated having the following characteristics:
Temperature: 170C
Turbidity: 7.8 JTU
pH: 7.95
Permanganate oxidation: 3.2 mg / l
TAC: 22.40
Hydrotimetric title: 25.6 French degrees
Color: 35 on the one hand with 25 mg of WAC per liter of water, on the other hand with 25 mg of WAC and 5 mg of commercial solution of sodium silicate (25% SiO 2) per liter of water.

 The results obtained are shown in Table 3.

TABLE 3

<tb><SEP> Turbidity <SEP> Oxydabi- <SEP>
<tb><SEP> Size <SEP> (JTU) <SEP> unit <SEP> at <SEP> TAC
<tb><SEP> of <SEP> ut <SEP> (JTU) <SEP> (o) <SEP> () <SEP> Color
<tb><SEP> floc <SEP> 3 <SEP> mn <SEP> 20 <SEP> mn <SEP> 4 <SEP> (o) <SEP>
<tb><SEP> (mg / i) <SEP>
<tb> Treatment
<tb><SEP> WAC <SEP> 5 <SEP> 1.5 <SEP> 0.78 <SEP> 2.0 <SEP> 21.4 <SEP> 5
<tb><SEP> Treatment
<tb><SEP> WAC <SEP> and <SEP> 7 <SEP> 1.1 <SEP> 0.66 <SEP> 2.1 <SEP> 21.6 <SEP> 5
<tb><SEP> silicate
<tb><SEP> of <SEP> sodium
<Tb>
On this type of water, the WAC and sodium silicate treatment also makes it possible to obtain larger flocs and a clearer water.

EXAMPLE 4
In order to determine the effectiveness of the process according to the invention on a water containing few suspended solids, a Dise water which has been pretreated by prolonged residence in a buffer tank is treated. The water before the coagulation-flocculation-settling tests has the following characteristics
Temperature: 150C
Turbidity: 2.8 JTU
pH: 7.80
Permanganate oxidation: 4.9 mg / l
TAC: 24.60
Si0: 10.4 mg / l
2 Al: <0.005 mg / i
This water is treated on the one hand with 15 mg of WAC per liter of water, on the other hand with 15 mg of WAC and 3 mg of commercial solution of sodium silicate (25% SiO) per
2 liters of water.

 The results obtained are shown in Table 4.

TABLE 4

<tb><SEP> Size <SEP> Turbidity <SEP> Oxydabi
<SEP><SEP> unit to <SEP> TAC <SEP> Si02 <SEP> Ai
<tb><SEP> of <SEP><SEP> 3 <SEP> mn <SEP> pH <SEP> KMnO <SEP>
<tb><SEP> floc <SEP> (JTU) <SEP><SEP> (mg /) <SEP> (o) <SEP> (mg / i) <SEP> (mg / i) <SEP>
<tb> Treatment
<tb><SEP> WAC <SEP> 3.5 <SEP> 1.4 <SEP> 7.88 <SEP> 3.2 <SEP> 23.5 <SEP> 9.9 <SEP> 0.13
<tb> Treatment
<tb><SEP> WAC <SEP> and <SEP> 5 <SEP> 0.8 <SEP> 7.84 <SEP> 3.4 <SEP> 24.5 <SEP> 9.3 <SEP> 0, 09
<tb><SEP> silicate
<tb> of <SEP> sodium
<Tb>
This table shows that, even on a water containing few suspended solids, the treatment according to the invention allows a magnification of the flocs and a lowering of the residual turbidity.

EXAMPLE 5
To show the influence of the process according to the invention on the coefficient of cohesion of the sludge, a water of the Braye having the following characteristics is treated:
Temperature: 170C
Turbidity: 8.2 JTU
pH: 8.00
Permanganate oxidation: 3.9 mg / l
TAC: 22.20
Color: 40
Hydrotimetric titre: 25.20 French on the one hand with 30 mg of WAC per liter of water, on the other hand with 30 mg of WAC and 6 mg of commercial solution of sodium silicate (25% SiO) per liter of water.

2
The results obtained are shown in Table 5.

TABLE 5

<tb><SEP> Turbidity <SEP> Turbidity <SEP> - <SEP><SEP> oxidabili <SEP>
<tb><SEP> 3 <SEP> mn <SEP> 10 <SEP> mn <SEP> pH <SEP> SE <SEP> at <SEP> KMnO <SEP> TAC <SEP> Color
<tb><SEP> (JTU) <SEP> (JTU) <SEP> (mg / l) <SEP><SEP> (o) <SEP>
<tb> Treatment
<tb><SEP> WAC <SEP> 1.5 <SEP> 0.74 <SEP> 7.78 <SEP> 2.1 <SEP> 21.5 <SEP> 7
<tb> Treatment
<tb><SEP> WAC <SEP> and <SEP> 1,2 <SEP> 0.60 <SEP> 7.77 <SEP> 2.3 <SEP> 21.6 <SEP> 5
<tb><SEP> silicate
<tb><SEP> of <SEP> sodium
<Tb>
The sludge cohesion coefficient measured after 20 minutes of settling is 0.26 in the case of WAC treatment alone and 0.40 in the case of co-treatment with
WAC and sodium silicate, which shows a clear improvement in sludge cohesion.

EXAMPLE 6
In order to show the influence of the order of the introduction of the reagents, a Seine water of turbidity equal to 11 JTU is treated with WAC (35 mg / l) and sodium silicate (6 mg of solution at 25% SiO / 1) while doing
2 the order of introduction of these 2 products.

The results summarized in Table 6 are obtained:
TABLE 6

<tb><SEP> Turbidity <SEP> JTU <SEP> Oxidation <SEP> at
<tb><SEP> 3 <SEP> 3 <SEP> min <SEP> 10 <SEP> min <SEP> KMnO4 <SEP><SEP><SEP> (mg / l) <SEP>
<tb> Processing <SEP> with <SEP> WAC <SEP> and
<tb> silicate
<tb> 1) <SEP> WAC <SEP> and <SEP> silicate <SEP> intro
<tb><SEP> Dukes <SEP> in <SEP> same <SEP> time <SEP> 0.72 <SEP> 0.71 <SEP> 4.6
<tb> 2) <SEP> WAC <SEP> before <SEP> silicate <SEP> 0.76 <SEP> 0.70 <SEP> 4.5
<tb> 3) <SEP> silicate <SEP> before <SEP> WAC <SEP> 0.74 <SEP> 0, sorting <SEP><SEP> 4.9
<Tb>
This table shows that the order of introduction of the reagents is virtually without influence on the residual turbidity.

EXAMPLE 7
The water of Example 1 is treated on the one hand with 45 mg of solid aluminum sulphate at 18 H 2 O, on the other hand with 45 mg of the same aluminum sulphate and 9 mg of commercial silicate solution. sodium (25% Six2) per liter of water.

 The results obtained are shown in Table 7.

TABLE 7

<tb><SEP> Oxydabi- <SEP>
<tb><SEP> Size <SEP> Turbidity <SEP> unit <SEP> at <SEP> TAC <SEP> SiO2 <SEP> Ai
<tb><SEP> of <SEP> 3 <SEP> min <SEP> pH <SEP> KMnO4 <SEP> (o) <SEP> (mg / l) <SEP> (mg / l)
<tb><SEP> floc <SEP> (JTU) <SEP> (mg / i) <SEP>
<tb> treatment <SEP> 3 <SEP> 7r5 <SEP> 7.60 <SEP> 5.9 <SEP> 19.8 <SEP> 5.9 <SEP> 0.12 <SEP>
<tb> S. <SEP> Alumina <SEP> 3 <SEP> 7.5 <SEP> 7.60 <SEP> 5.9 <SEP> 19.8 <SEP> 5.9 <SEP> 0.12 <September>
<tb> Treatment
<tb> sulfate <SEP> of A <SEP>
<tb><SEP> lumen <SEP> and <SEP> 4 <SEP> 2.6 <SEP> 7.62 <SEP> 5.8 <SEP> 20.2 <SEP> 6.7 <SEP> 0, 12
<tb><SEP> silicate
<tb> of <SEP> sodium
<Tb>
In the presence of aluminum sulphate, the use of sodium silicate makes it possible to obtain larger flocs and a very significant lowering of the residual turbidity.

EXAMPLE 6
The water of Example 2 is treated on the one hand by 17.6 mg of solid aluminum sulphate at 18 H 2 O per liter of milk and on the other hand by 17.6 mg of this same sulphate of sulphate. aluminum and 6 mg commercial solution of sodium silicate (25% SiO2) per liter of water.

 The results obtained are shown in Table 8.

TABLE 8

<tb><SEP> Oxydabi ~ <SEP> ~
<tb><SEP> Size <SEP> Turbidity <SEP> Oxydabi- <SEP>
<tb><SEP> of <SEP> (JTU) <SEP><SEP> pH <SEP> to <SEP> TAC <SEP> Si02 <SEP> Ai
<tb><SEP> floc <SEP> 3 <SEP> min <SEP> 20 <SEP> min <SEP> KMn04 <SEP> (o) <SEP> (mg / l) <SEP> (mg / l)
<tb><SEP> fioc <SEP> (mg / i)
<tb> Treatment
<tb> sulf. <SEP><SEP> of AL <SEP> 3 <SEP> 5.0 <SEP> 1.7 <SEP> 7.76 <SEP> 2.4 <SEP> 18.4 <SEP> 5.9 <SEP> 0.17
<tb> Treatment
<tb><SEP> sulfate <SEP> 4 <SEP> 3.8 <SEP> 1.4 <SEP> 7.70 <SEP> 2.7 <SEP> 18.6 <SEP> 6.4 <SEP> 0.18
<tb><SEP> of Al. <SEP> and
<tb><SEP> silicate
<tb> of <SEP> sodium
<Tb>
Here again, the joint use of aluminum sulphate and sodium silicate makes it possible to enlarge the flocs and lower the turbidity.

EXAMPLE 9
The water of Example 3 is treated on the one hand with 50 mg of solid aluminum sulphate at 18 H 2 O, on the other hand with 50 mg of this same reagent and 10 mg of commercial sodium silicate solution (with 25% SiO2) per liter of water.

The results obtained are shown in Table 9.

TABLE 9

<tb><SEP> Turbidity <SEP> (JTU) <SEP> Oxydabi
<tb><SEP> Size <SEP> turbidity <SEP> (JTU) <SEP> unit <SEP> at <SEP> TAC <SEP> Color
<tb><SEP> of <SEP> 3 <SEP> mn <SEP> 20 <SEP> mn <SEP> KMn <SEP> X <SEP>; / O) <SEP> TAC
<tb><SEP> 3 <SEP> mn <SEP> 20 <SEP> mn <SEP> Color
<tb><SEP> Treatment
<tb><SEP> sulfate <SEP> of Al. <SEP> 2 <SEP> 7e6 <SEP> 1.2 <SEP> 1.7 <SEP> 20, Z <SEP> 5
<tb><SEP> Treatment
<tb> sulfate <SEP> from Al. <SEP> 3 <SEP> 6.1 <SEP> 0.95 <SEP> 1.9 <SEP> 20.2 <SEP> 5
<tb><SEP> and <SEP> silicate <SEP> ~~
<Tb>
This type of water shows the same improvements as before.

EXAMPLE 10
The water of Example 2 is treated on the one hand with 45 mg of commercial solution of FeCl 3 (41% of FeCl 3) on the other hand with 45 mg of the same FeCl 3 solution and 6 mg of commercial silicate solution. sodium (25% SiO) per liter of water.

2
The results obtained are shown in Table 10.

TABLE 10

<tb><SEP> Size <SEP> Turbidity <SEP> (JTU) <SEP> Oxydabi
<SEP> unit <SEP> to <SEP> TAC <SEP> Si02
<tb><SEP> of <SEP> pH <SEP> KMn04 <SEP> (O) <SEP> (mg / i)
<tb><SEP> floc <SEP> 3 <SEP> mn <SEP> 20 <SEP> mn
<tb><SEP> (mg / i) <SEP>
<tb><SEP> Treatment <SEP> 5 <SEP> 2.9 <SEP> 1.4 <SEP> 7r47 <SEP> 1.7 <SEP> 18.6 <SEP> 5.6
<tb><SEP> FeC13
<tb> Treatment
<tb><SEP> FeCl3 <SEP> and <SEP> 6 <SEP> 3.0 <SEP> 1.3 <SEP> 7.52 <SEP> 1, Y <SEP> 18.6 <SEP> 6, 3
<tb><SEP> Treatment <SEP> 6.3
<tb> of <SEP> sodium
<Tb>
In the case of ferric chloride also, the addition of sodium silicate improves the floc size.

EXAMPLE II
The water of Example 2 is treated firstly with 49 mg of a solution of ferric chlorosulfate (CSF) at 13% Fe, and secondly with 49 mg of the same solution of ferric chlorosulfate and 6 mg of commercial solution of sodium bis (25% SiO) per liter of water.

2
The results obtained are shown in Table 11.

TABLE II

<tb><SEP>
<tb><SEP><SEP> Turbidity <SEP> (JTU) <SEP> Oxydai <SEP> TAC <SEP> Si02
<tb><SEP><SEP> unit at
<tb><SEP> of <SEP> 3 <SEP> mn <SEP> 20 <SEP> mn <SEP> pH <SEP> KWrn04 <SEP> (o) <SEP> (mg / i)
<tb><SEP> floc <SEP>
<tb><SEP> floc <SEP> (mg / l) <SEP>
<tb><SEP> Treatment
<tb><SEP> C <SEP> S, <SEP> F. <SEP> 4 <SEP> 5.2 <SEP> 1.6 <SEP> 7.37 <SE> 2.6 <SEP> 18 , 6 <SEP> 5.30
<tb><SEP> I
<tb> Treatment
<tb><SEP> C. <SEP> S. <SEP> F, <SEP> and <SEP> 5 <SEP> s, o <SEP> 1.4 <SEP> 7.41 <SEP> 2.6 <SEP> 19.0 <SEP> 6.75 <SEP> /
<tb> silicate <SEP> of
<tb><SEP> sodium
<Tb>
The use of sodium silicate together with ferric chlorosulfate improves floc size and clarity.

EXAMPLE 12
Seine water is treated with the following characteristics:
Temperature: 130C
Turbidity: 7.5 JTU
pH: 8.17
Permanganate oxidation: 3.84 mg / l
TAC: 21.30 SiO2: 5.2 mg / l
2
Al: 0.017 mg / l, on the one hand, by 31.5 mg of 29.2% AlCl 3 solution, on the other hand, by 31.5 mg of the same AlCl 3 solution and 6 mg of commercial silicate solution. sodium (25% 5iO2) per liter of water.

 The results obtained are shown in Table 12.

TABLE 12

<tb><SEP> Oxydabi- <SEP>
<tb><SEP> Size <SEP> Turbidity <SEP> S <SEP> lite <SEP> at <SEP> TAC <SEP> 5iO2 <SEP> A1 <SEP>
<tb><SEP> of <SEP> 3 <SEP> mn <SEP> pH <SEP> KMn04 <SEP> TAC <SEP> SiO <SEP> 2
<tb><SEP> floc <SEP> (J <SEP> (JTUn) <SEP>
<tb><SEP> floc <SEP> (JTU) <SEP> (mg / i) <SEP>
<tb> Treatment <SEP> 4 <SEP> 3.1 <SEP> 8.22 <SEP> 3.02 <SEP> 19.6 <SEP> 5.7 <SEP> 0.09 <SEP>
<tb> Treatment
<tb><SEP> AlCl3 <SEP> and <SEP> 6 <SEP> 2.1 <SEP> 8.21 <SEP> 3.12 <SEP> 20.0 <SEP> 6.1 <SEP> 0, 10
<tb><SEP> silicate
<Tb>
The use of sodium silicate together with aluminum chloride improves both floc size and residual turbidity.

EXAMPLE 13
The water of Example 2 is treated on the one hand with 27 mg of 29.2% AlCl 3 solution, on the other hand with 27 mg of the same solution of AlCl 3 and 6 mg of commercial silicate solution. sodium (25% SiO2) per liter of water.

 The results obtained are shown in Table 13.

TABLE 13

<tb><SEP> Size <SEP> Turbidity <SEP> Oxydabi
<tb><SEP><SEP> Size <SEP> (JTU) <SEP><SEP> pH <SEP><SEP> TAC <SEP><SEP> SiO2 <SEP> Ai <SEP>
<tb><SEP> floc <SEP> 3 <SEP> min <SEP> 20 <SEP> min <SEP> P <SEP> KMnO4 <SEP><SEP> (o) <SEP><SEP> (mg / l ) <SEP> (mg / l) <SEP>
<tb><SEP> (mg / i) <SEP>
<tb><SEP> Processing <SEP>
<tb><SEP> AlCl3 <SEP>
<tb><SEP> processing <SEP>
<tb><SEP> of <SEP> 3 <SEP> 3.3 <SEP> 1.77.88 <SEP> 3.3 <SEP> 19.66.2 <SE> 0.22 <SEP>
<tb><SEP> silicate
<tb><SEP> of <SEP> sodium
<Tb>
With the treatment according to the invention, the same improvements are observed as in the preceding example.

EXAMPLE 14
The treated water is that of Example 12, the coagulant used is a solution of basic aluminum chloride polymer (PCBA) prepared according to French Patent No. 2,308,594.

Water is treated on the one hand by a solution of
PCBA (treatment rate of 3.5 mg / l expressed as A1 203) and secondly by the same amount of PCBA and 6 mg of commercial sodium silicate solution (25% SiO 2) per liter of water .

 The results obtained are shown in Table 14.

TABLE 14

<tb><SEP> Size <SEP> Turbidity <SEP> Oxydabi- <SEP>
<tb><SEP><SEP> unit to <SEP> TAC <SEP> SiO <SEP> Ai
<tb><SEP> of <SEP> 3 <SEP> mn <SEP> (JTU <SEP> pH <SEP> KMnO4 <SEP> 2 <SEP>
<tb><SEP> floc <SEP> (mg / l) <SEP> (o) <SEP> (mg / l)
<tb> Treatment
<tb><SEP> PCBA <SEP> 5 <SEP> 1.1 <SEP> 8.08 <SEP><SEP> 3.2 <SEP> 20.4 <SEP> 5.5 <SEP> 0.06
<tb> Treatment
<tb><SEP> PCBA <SEP> and
<tb><SEP> silicate <SEP><SEP> 7 <SEP> 0.7 <SEP> 8.09 <SEP> 3.3 <SEP> 20.2 <SEP> 5.9 <SEP> 0.05 <September>
<tb> of <SEP> sodium
<Tb>
With this type of coagulant also, the addition of sodium silicate improves floc size and residual turbidity.

EXAMPLE 15
A Seine water with the following characteristics is treated
Temperature: 140C
Turbidity: 8 JTU
pH: 8.10
Permanganate oxidation: 4.1 mg / l
TAC: 22.50
2: 6.2 mg / l
Ai: 0.013 mg / l
The coagulant used is a commercial solid aluminum basic chloride whose A 0 content is 31.5% and the Cl content is 34%.

 The water is treated on the one hand with 10 mg of this basic aluminum chloride per liter of water and on the other hand with 10 mg of this basic aluminum chloride and 6 mg of commercial silicate solution. sodium (25% SiO 2) per liter water.

 The results obtained are shown in Table 15.

TABLE 15

<tb><SEP> Oxydabi- <SEP>
<tb><SEP> gate <SEP> Turbidity <SEP> unit <SEP> to <SEP> TAC <SEP> SiO2 <SEP> Ai
<tb><SEP> of <SEP> pH <SEP> KMn04 <SEP><SEP> (o) <SEP><SEP> (mg / i)
<tb><SEP> floc <SEP> 3 <SEP> mn <SEP> (JTU) <SEP> pH <SEP> mg / l) <SEP> () <SEP> (mg / i) <SEP> (mg) / i)
<tb><SEP> floc <SEP> (mg / l)
<tb><SEP> Treatment
<tb><SEP> basic <SEP> of Al
<tb> Treatment
<tb> by <SEP> chloride
<tb> basic <SEP> of A <SEP><SEP> 6 <SEP> 1,2 <SEP> 7,95 <SEP> 3,2 <SEP> 21,2 <SE> 5,9 <SEP> 0.14
<tb> and <SEP> silicate
<tb><SEP> of <SEP> sodium
<Tb>
It is again noted that the treatment according to the invention improves both the floc size and the residual turbidity.

EXAMPLE 16
The same water is treated as in Example 2.

 The coagulant used is a solution of basic aluminum chloride, sold under the name of aluminum oxychloride, which has an Al 2 O 3 content of 22.3% and a Cl content of 8.3%.

 The water is treated on the one hand with 13.5 mg of this solution, on the other hand by 13.5 mg of this solution and 6 mg of commercial solution of sodium silicate (25% SiO 2) by liter of water.

 The results obtained are shown in Table 16.

TABLE 16

<tb><SEP> Size <SEP> Turbidity <SEP> (JTU) <SEP> Oxidation <SEP> TAC
<tb><SEP> of <SEP><SEP><SEP> 3 <SEP> mn <SEP> 20 <SEP> mn <SEP> pH <SEP> at <SEP> KMn0 <SEP>
<tb><SEP> floc <SEP> (mg / l)
<tb><SEP> floc <SEP> (mg / l) <SEP>. <SEP>.
<Tb>

<SEP> Treatment
<tb> per <SEP> chloride <SEP> 3 <SEP> 5.3 <SEP> 1.6 <SEP> 7.90 <SEP> 2.2 <SEP> 19.2
<tb><SEP> basic <SEP> of Al
<tb><SEP> Treatment
<tb><SEP> with <SEP> Chloride
<tb><SEP> and <SEP> 4 <SEP> 3.1 <SEP> 1.0 <SEP> 7.94 <SEP> 2.1 <SEP> silicate
<tb><SEP> and <SEP> silicate
<tb><SEP> of <SEP> sodium
<Tb>
The treatment according to the invention improves the floc size and the residual turbidity.

Claims (2)

1 - Process for the treatment of water purification by coagulation-flocculation # with the aid of mineral coagulation agents consisting of iron or aluminum salts, optionally in polymeric form, characterized in that the an aqueous alkaline-sodium silicate solution is used as flocculating adjuvant. 2 - Process according to claim 1, characterized in that the mineral coagulation agent is used in a proportion of 0.3 to 20 mg Fe203 or Al 0 0 per liter of water to be treated,  23 and that the alkaline solution of sodium silicate is used in a proportion such that the atomic ratio silicon / iron or silicon / aluminum is between 0.1 and 1.