Description

Title: Composition for the treatment of surfaces in contact with water to preserve water quality

The present invention relates to the field of pipes or tanks intended to be in contact with water, in particular the field of pipe or tank elements internally coated with mineral binder-based coatings such as cement mortars for transporting or store drinking water or raw water intended for the production of drinking water (raw water being water that has not undergone any treatment and can supply a drinking water production station). In particular, the invention relates to a treatment of the internal surfaces of these containers intended to be in contact with water, and a container, such as a pipe or a tank, thus treated. By “drinking water”, we hereafter mainly mean drinking water strictly speaking, but also, where applicable, raw water when it is intended for the production of drinking water.

It is known to use coatings based on mineral binder such as Portland cement as interior coatings of containers for the transport and storage of drinking water, in particular because of the harmlessness of these materials in contact with this water. In the particular case of cast iron pipes or steel tubes, the cementitious coating, due to its alkaline nature, also makes it possible to passivate the metal and to protect it durably from corrosion.

However, in contact with particularly soft water (little calcium and carbonates) or aggressive (carbonic acid, acid pH) or solid particles, the durability of these coatings can be reduced, these waters can cause the dissolution less stable mineral phases, such as calcium hydroxide Ca(OH)2, with the consequences of a loss of the alkalinity of the binder and therefore of the protection of the metal, or even a loss of the harmlessness of the coating by rise in the pH of the water in contact with it and leaching of chemical species such as aluminium. In the case of particle-laden water, the resulting abrasion can also reduce the life of the coating.

To prevent this degradation without modifying the quality of the water, it is possible in certain cases to use a more stable and/or harder mineral binder, such as a slag cement or an aluminous cement, or to bring a polymer film, sometimes called “seal-coat”, on the surface of the coating to reduce interactions between water and the cementitious matrix. It is also possible to treat the coating with carbon dioxide under pressure in order to convert the less stable hydrated phases into calcite, as described for example in patent application DE 195 24 761.

The use of slag cement makes it possible to widen the field of use of the coating, but does not make it possible to cover all drinking and raw water. A binder from aluminous cement makes it possible to remedy this to a large extent and provides an improvement in abrasion resistance, but at the cost of a release of aluminum in quantities that can exceed the normative thresholds. The use of a chemically very stable mineral binder such as a geopolymer, having a very low soluble alkaline reserve, moreover compromises the protection of the metal in the case, for example, of pipes or tanks made of steel or comprising reinforced concrete reinforcements. . The use of a polymeric film has a limited effectiveness over time, which comes from the poor adhesion of such coatings on cementitious matrices, and requires costly surface preparation, these coatings also not being authorized. in a number of markets, by their organic nature. Finally, an accelerated carbonation treatment consumes mineral species present in the binder, which substantially reduces the alkaline reserve of the mortar, and therefore the life of the metal protection, and can be accompanied by a greater release of metals. heavy such as lead due to the resulting acidification of the matrix. In addition, this does not sufficiently block the porosities of the matrix, only delaying the effects of soft or aggressive water over time.

The present invention has therefore sought to improve the protection of containers intended to transport or contain water, in particular drinking water, against damage that may occur over time, in particular to further reduce the possible release of species not to exceed the normative thresholds, in particular to reduce the leaching of aluminum from coatings based on mineral binder, in particular cementitious, containers intended to receive (transport or contain) water.

The present invention thus proposes a treatment composition, in particular (a composition) for impregnating a coating, in particular of a coating based on a mineral binder, in particular (a coating) based on a cementitious binder, this coating being in particular the internal coating of a container intended to receive water, in particular drinking water , this composition being in the form of a solution comprising:

- at least one alkaline silicate and at least one lithium source, in particular at least one alkaline silicate and at least one separate lithium source, the total content of lithium source(s) in the solution being in particular less than 10% in weight,

Where

- at least one organic orthosilicate.

This treatment is intended to impregnate the coating based on mineral binder covering the internal surface of the containers intended to receive water, this treatment thus selected not remaining on the free surface of the said coating and not generating on the latter a layer reported, as is the case with other existing treatments, but impregnating said coating to a depth of impregnation typically of at least 50 μm, and preferably between 100 and 500 μm, thus allowing reinforced protection against leaching aluminum of said coatings based on mineral binder, in particular mineral binder based on cement (or cementitious binder). By free surface of the coating, we mean the inner surface of the coating, potentially in contact with water. By impregnation composition is therefore meant a composition that does not remain on the free surface of the coating on which it is deposited and does not generate an added layer on said free surface, but therefore impregnates said coating in depth without remaining on the surface (this impregnation being therefore an impregnation by absorption).

The present invention also relates to a container, such as a pipe or water reservoir element, in particular drinking water (or "for drinking water" or "to receive drinking water"), this container having an internal coating based on mineral binder, in particular cementitious, said internal coating being impregnated to a depth of at least 50 μm, preferably between 100 and 500 μm, and in particular between 100 and 300 μm, by at least a silicate, in particular by a solution comprising:

- at least one alkaline silicate and at least one lithium source, in particular at least one alkaline silicate and at least one separate lithium source, the total content of lithium source(s) in the solution being in particular less than 10% in weight,

Where

- at least one organic orthosilicate.

Throughout this text, the mineral binder is advantageously a cementitious binder.

The alkaline silicate is preferably (at least) a sodium silicate, a potassium silicate or a lithium silicate, and in a particularly advantageous way is a (or at least one) sodium silicate or a (or at least one) silicate potassium.

Very advantageously, the alkaline silicate is a potassium silicate, which contributes to less precipitation of Na2C03 on the surface.

The alkaline silicate, in particular potassium, preferably has an S1O2/R2O molar ratio ranging from 1 (inclusive) to less than 5 (5 being excluded), in particular ranging from 1 to 4 (1 and 4 being inclusive) or comprised between 1 and 4, in particular ranging from 2 to 3 (2 and 3 being included) or between 2 and 3, where R denotes the alkali metal. Silicates with too low a ratio are too reactive, while silicates with too high a ratio are not very soluble and lend themselves less easily to impregnation. A S1O2/R2O molar ratio of 2.45 or even

4 is particularly preferred.

The concentration by mass (or by weight or by mass) of alkali silicate in the solution is preferably at least 2%, in particular is between

5 and 40% and more particularly between 10 and 30%.

The or each lithium source may in particular be a lithium salt. It is preferably chosen from lithium carbonate, lithium sulphate or other organic salts of lithium (for example lithium acetate), or else from lithium hydroxide, lithium silicate, and their derivatives. . The most preferred salts are lithium sulfate, lithium carbonate and lithium hydroxide. A mixture of two or more of these salts is also suitable.

It will be noted that in the composition according to the invention, the lithium silicate can act both as an alkali silicate and as a source of lithium. However, the case in which the only alkali silicate present and the source of lithium are one and the same compound is preferentially excluded in the present invention, the lithium silicate having not only a high cost that is incompatible with such an embodiment but such a mode also involving too large a quantity (for reasons in particular of health compliance) of lithium after deposition with regard to the quantities of compounds are applied (to obtain the desired effects) according to the present invention (preferably between 50 and 500 g/m2 as indicated later). In the case nevertheless where the composition comprises at least one lithium silicate, this silicate being in this case both a source of lithium and all or part of the alkali metal silicate(s) within the meaning of the present invention, or even in the case where the lithium source is a (or at least one) compound other than a lithium silicate, the total content of lithium source(s) (therefore including the lithium silicate(s) possible) is preferably strictly less than 10% by weight, thus in particular limiting the risk of salting out into the water too high amounts of lithium with regard to the amounts of composition applied according to the present invention.

Thus, preferably according to the invention, the solution therefore comprises, in its first variant (the second variant being the use of at least one organic orthosilicate), at least one alkali silicate and one separate source of lithium, in the sense where, either it does not comprise any lithium silicate, or when it comprises one, the solution then also comprises a source of lithium other than a lithium silicate and/or at least one other alkali silicate (for example sodium or potassium), and/or, preferably also according to the invention, the total content of lithium source(s) in the solution is less than 10% by weight. According to a particularly preferred embodiment, the alkali metal silicate(s) according to the invention consist(s) wholly or mainly of silicates other than a lithium silicate.

The source of lithium combined with alkaline silicate delays the reaction with calcium ions without disturbing the formation of the majority hydrates such as hydrated calcium silicates and hydrated calcium silico-aluminates (C-S-H and C-A-S-H in cementitious notation), and thus makes it possible to ensure deep penetration of the treatment composition. Without this combination, the silicate would react immediately on the surface with the calcium ions resulting from the binder, resulting in the formation of a dense layer on the surface that does not allow the composition to penetrate in depth.

The total content of lithium source(s) in the solution or in the treatment composition according to the invention is in particular (strictly) less than 10% by weight, in particular between 0.05% and 10%, and preferably is less than or equal to 2%, in particular between 0.05 and 2%, especially between 0.05 and 1%, preferably between 0.10 and 1.0% by weight, or even between 0.15 and 0.50 % in weight. The total content corresponds to the sum of the contents of each source of lithium when the solution contains several of them.

Advantageous treatment compositions according to the invention are, for example, aqueous solutions comprising a potassium silicate, in particular with an S1O2/K2O molar ratio of between 1 and 5, in particular between 1 and 4 or ranging from 1 to 4, or even between 2 and 3 or ranging from 2 to 3, said silicate preferably being in a mass concentration of between 5 and 40%, more particularly between 10 and 30%, said solutions further comprising a source of lithium chosen from lithium sulphate (L12SO4 ), lithium hydroxide (LiOH), lithium silicate and lithium carbonate. The content of lithium source(s) in the treatment composition/in the solution according to the invention is in particular between 0.05 and 10%, and preferably is less than or equal to 2%, in particular between 0, 05 and 2%, especially between 0.05 and 1%, preferably between 0.10 and 1%, or even between 0.15 and 0.50% by weight for said compositions.

By organic orthosilicate is meant an organic salt of the orthosilicate. The organic orthosilicate is preferably chosen from tetramethyl orthosilicate (TMOS) and tetraethyl orthosilicate (TEOS). The organic orthosilicate is preferably tetraethyl orthosilicate (TEOS). In the case of the use of an orthosilicate as silicate in the treatment composition according to the invention, the combination with a source of lithium is not necessary, said composition penetrating in depth without initial formation of a dense layer on the surface. .

The treatment compositions based on silicates selected according to the invention are in the form of a liquid composition (or solution) in which the silicates, dissolved in metastable form, are capable of precipitating inside the coating near the surface, under the effect of contact with the mineral binder of the coating present inside the container.

In the case of an alkali silicate, the solution is preferably an aqueous solution. In the case of an organic orthosilicate, the solution can be pure orthosilicate or orthosilicate in an organic solvent, the solvent being t preferably an alcohol. The alcohol is typically ethanol or isopropanol. In the case where the organic orthosilicate is dissolved in a solvent, the mass concentration of organic orthosilicate in the solution is preferably at least 2%, in particular between 10 and 30%.

Advantageously, in addition to the aforementioned components, namely silicates and sources of lithium or orthosilicates, and water or organic solvents, the composition according to the invention comprises less than 0.5% by weight of other components. In other words, the content of components other than alkali silicate(s), lithium source(s), organic orthosilicate(s) and aqueous or organic solvent(s) is less than 0.5% by weight. As other components, the composition generally advantageously comprises at least one surfactant, so as to facilitate impregnation, this surfactant preferably being nonionic. Mention may in particular be made of alkylpolyglucosides and ethoxylated fatty alcohols. The total content of surfactant in the solution is preferably at least 0.01%, in particular at least 0.05%, or even between 0.1 and 0.5% by weight.

On the other hand, the composition is advantageously devoid of components considered as pollutants with regard to the quality of the water (including for example heavy metals, etc.), just as, apart from the surfactants, it is devoid of any other organic component of non-reactive type with hydrated compounds or (of non-hydrolyzable type) which would be likely to remain after application of the composition. It is also devoid of any hardener, their presence can lead to the formation of a surface layer contrary to the desired impregnation.

The treatment according to the invention makes it possible to better preserve the quality of the water transported or stored in contact with a coating based on mineral binder, in particular cementitious (coating in particular of the "cement mortar" type), in particular by reducing the aluminum leaching. Indeed, without the treatment according to the invention, a large quantity of Ettringite is detected on the surface of cement mortar coatings, Ettringite being a mineral phase rich in aluminum and likely to dissolve in contact with drinking water. or raw. After impregnation with the treatment composition, it surprisingly appears that the aluminum-rich hydrates have been converted into amorphous phases. Aluminum is thus mainly incorporated in an environment typical of C-S-H phases, thus forming very stable C-A-S-H phases in which aluminum is trapped, the reduction in the leaching of aluminum thus resulting from this trapping in very stable phases by reaction of the alkaline silicate with the Ettringite-type phases initially present in the binder of the cementitious coating (or cement mortar coating). The treatment thus makes it possible to form under the surface of the coating a barrier layer limiting the release of aluminum ions, preserving both the composition of the water in contact with the coating and the structural integrity of the latter.

The treatment according to the invention thus makes it possible to functionalize the surface of a coating based on mineral binder, in particular cementitious, without changing the formulation of said coating before treatment. The treatment with the composition according to the invention acting from the surface and inside the coating, this makes it possible to overcome any adhesion problem; moreover, no surface preparation is necessary beforehand. The treatment can be applied during the manufacture of the container in the factory, on a stockyard or also on an installation site. It can also be applied in rehabilitation.

The present invention also relates to a process for treating (this process being in particular a process for impregnating or treating by impregnation) a container, in particular the internal coating of a container.

container, said container having to receive water (pipe or reservoir elements), in particular drinking water, said coating being based on a mineral binder, in particular cementitious, in particular being a cement mortar coating, process wherein the treatment composition according to the invention is applied inside said container, in particular to the surface of said internal coating.

The treatment (or impregnation) can be carried out by means of a brush, a brush, by spraying, by immersion or even by pouring (for example in the case of a rotating pipeline). If necessary, the coating may have been dried before treatment.

After impregnation treatment with the composition according to the invention, a heat treatment and in controlled humidity can be carried out in order to control the precipitation reactions. Such heat treatment can involve temperatures up to 80°C.

Preferably this, the treatment composition is deposited so as to apply between 50 and 500 g/m2, in particular between 100 and 300 g/m2 (the limits also being included), of the composition according to the invention to the surface of the internal coating. This ratio corresponds to the weight of solution relative to the surface of the coating treated.

The interior coating based on mineral binder, in particular cementitious, to be treated generally comprises at least one binder, in particular hydraulic, and in particular based on (or formed from) at least one cementitious binder. Among the cementitious binders, mention may in particular be made of Portland cements, aluminous cements, sulfoaluminous cements, belitic cements, blast furnace slag cements and pozzolanic mixture cements optionally comprising fly ash, silica fume, limestone, calcined shale and/or natural or calcined pozzolans. In particular, the binder is a blast furnace slag cement. The binder is generally formed predominantly (at least 75% by weight of the binder, and generally at least 90% by weight of the binder), or even solely of a cement-type hydraulic binder. The coating is also advantageously a cement mortar, its composition also advantageously containing aggregates, aggregates, sands, and / or fillers (finely ground mineral fillers) calcareous and / or siliceous, playing in particular on the rheology, the hardness or the appearance end of the product. The mortar composition may also comprise, initially or in the final mortar coating, other additives such as rheological or plasticizing agents, accelerators and/or retarders, and other agents making it possible to improve setting, hardening and /or the stability of the mortar after application or to adjust the workability, the implementation or the impermeability of the mortar.

The treatment composition according to the invention can be used advantageously to treat the interior coatings based on mineral binder, in particular cementitious, of containers intended to receive water, these containers possibly being in particular gray or ductile cast iron pipes coated cement mortar, steel pipes coated with cement mortar, cement concrete pipelines, metal tanks coated with cement mortar, cement concrete tanks, etc.

The present invention also relates to the use of the treatment composition described above for reducing the leaching of aluminum from coatings based on mineral binder, in particular cementitious, of containers intended to receive water, in particular drinking water. .

The examples below illustrate the invention without limiting its scope.

The treatment composition used was a solution composed of soluble potassium silicate with a S1O2/K2O molar ratio of 2.45 and in a mass concentration of approximately 20% and a mixture of lithium sulphate (L12SO4) in a mass concentration 0.15% and lithium hydroxide (LiOH), also in a mass concentration of 0.15%.

The treatment was applied to the surface of an internal lining of a ductile iron pipe, the lining being in CEMIII/B slag cement mortar, at a surface concentration of 150 g/m2. The treatment was applied in two different ways:

- two days after coating manufacture, cured in ambient conditions (natural curing);

- on a coating a year and a half after its manufacture.

The specimens (with a height and a diameter of 200 mm) were tested a few weeks after treatment according to the normative leaching protocol of standard EN 14944-3, and compared with the results of an untreated coating a few weeks after its manufacture, as well as those of an untreated coating aged one and a half years.

Surprisingly, the impregnation treatment according to the invention made it possible to reduce the leaching of aluminum by a factor of at least 20 compared to the untreated examples in the case of impregnation after natural curing. In the case of impregnation on a one and a half year old coating, this treatment surprisingly reduced aluminum leaching to a level below detection limits.

X-ray diffraction and nuclear magnetic resonance (NMR) experiments were performed to better understand the mechanisms behind this beneficial effect.

[Fig. 1] is an X-ray diffraction pattern performed on a hydrated paste of untreated CEM III/B slag cement. A certain amount of Ettringite was detected, this aluminum-rich mineral phase being likely to dissolve on contact with drinking or raw water.

[Fig. 2] is an X-ray diffraction diagram performed on a hydrated paste of CEM III/B slag cement treated with the composition of the example. It shows that ap After treatment by impregnation, the peaks corresponding to the existence of Ettringite disappeared. Surprisingly, this treatment with an alkali silicate solution therefore converted the aluminum-rich hydrates into amorphous phases (invisible by X-ray diffraction).

[Fig. 3] represents three NMR spectra. Analysis by NMR spectroscopy of aluminum was carried out on anhydrous CEM III/B slag cement (curve A), on this same hydrated cement (curve B), as well as on this hydrated cement then treated by impregnation with composition according to the invention (curve C). Before hydration, aluminum was mostly incorporated into the slag (bump at 60 ppm). After hydration, aluminum was predominantly incorporated in Ettringite-like phases (peaks at 15 ppm), consistent with X-ray diffraction analysis. After treatment, aluminum was predominantly incorporated in a typical C-S-H environment. (displacement at 70 ppm), thus forming C-A-S-H in which the aluminum was trapped, thus causing, as seen previously, a decrease in the leaching of aluminum.

Claims

1. Composition for treatment, in particular impregnation, of a coating, in particular of a coating based on mineral binder, in particular based on cementitious binder, this coating being in particular the internal coating of a container intended for receive water, in particular drinking water, this composition being in the form of a solution comprising:

- at least one alkaline silicate and at least one lithium source, in particular at least one alkaline silicate and at least one separate lithium source, the total content of lithium source(s) in the solution being in particular less than 10% in weight,

Where

- at least one organic orthosilicate.

2. Composition according to claim 1, in which the alkaline silicate is a potassium or sodium silicate or in which the organic orthosilicate is a tetraethyl or tetramethyl orthosilicate.

3. Composition according to one of the preceding claims, in which the mass concentration of alkaline silicate in the solution is at least 2%, in particular is between 10 and 30%, or in which the organic orthosilicate is dissolved in a solvent and the mass concentration of organic orthosilicate in the solution is at least 2%, in particular is between 10 and 30%.

4. Composition according to one of the preceding claims, in which the alkali metal silicate, in particular potassium silicate, has an S1O2/R2O molar ratio ranging from 1 to less than 5, in particular ranging from 1 to 4 or between 1 and 4, in particular between 2 and 3, R denoting the alkali metal.

5. Composition according to one of the preceding claims, in which the or each source of lithium is chosen from lithium carbonate, lithium sulphate or other organic lithium salts such as lithium acetate, or else from lithium hydroxide, lithium silicate, and their derivatives.

6. Composition according to one of the preceding claims, in which the total content of lithium source(s) in the solution is between 0.05 and 10% by weight, and preferably is less than or equal to 2%, by particular between 0.10 and 1.0% by weight.

7. Composition according to one of the preceding claims, in which the content of components other than alkali metal silicate(s), lithium source(s), organic orthosilicate(s), and solvent(s) aqueous or organic(s), is less than 0.5% by weight, the composition comprising in particular one or more surfactants as other components.

8. Composition according to one of the preceding claims, in which the said composition is devoid of hardeners, of pollutants with regard to the quality of the water and/or of organic components, other than surfactants, of the type which are non-reactive with compounds hydrated or non-hydrolyzable type which would be likely to remain present after application of said composition.

9. Use of the treatment composition according to one of the preceding claims to reduce the leaching of aluminum from coatings based on mineral binder, in particular cementitious, of containers intended to receive water, in particular drinking water.

10. Container, such as a pipe element or water tank, in particular for drinking water, said container having an internal coating based on mineral binder, in particular cementitious, said internal coating being impregnated to a depth of at least 50 μm, and preferably between 100 and 500 μm, by at least one silicate, in particular by a solution comprising:

- at least one alkaline silicate and at least one lithium source, in particular at least one alkaline silicate and at least one separate lithium source, the total content of lithium source(s) in the solution being in particular less than 10% in weight,

Where

- at least one organic orthosilicate.

11. Process for the treatment, in particular of impregnation, of a container, in particular of the internal coating of a container, said container having to receive water, in particular drinking water, said coating being based on mineral binder, in particular cementitious, in particular being a cement mortar coating, in which a treatment composition in the form of a

solution comprising:

- at least one alkaline silicate and at least one lithium source, in particular at least one alkaline silicate and at least one separate lithium source, the total content of lithium source(s) in the solution being in particular less than 10% in weight,

Where

- at least one organic orthosilicate,

is applied inside said container, in particular to the surface of said internal coating.

12. Process according to claim 11, in which the treatment composition is deposited so as to apply between 50 and 500 g/m2, and in particular between 100 and 300 g/m2, of said composition on the surface of said internal coating.