FR2778652A1 - Cement material comprising hydrated calcium silicate with lithium used for e.g. the retention of cations, for nuclear waste storage containing e.g. cesium, for improving the mechanical strength of material in civil engineering - Google Patents

Abstract

A cement material comprises at least a hydrated calcium silicate substituted by lithium, the substituted silicate having a mol ratio Ca:Si of 0.3-1.7 and a mol ratio Li:Si of 0.01-1. Independent claims are also included for: (1) a process for making the above cement material; (2) a waste storage process comprising using the above cement material as a barrier for isolating the waste from the environment; (3) retention of water soluble cations by contacting this solution with the above cement material; and (4) process for improving the mechanical strength of a cementitious material.

Description

CEMENT MATERIAL CONTAINING LITHIUM PROPERTIES

  IMPROVED MECHANICS FOR USE IN THE RETENTION OF

  CATIONS, AND METHODS FOR THE PRODUCTION THEREOF.

DESCRIPTION

  Technical Field The invention relates to a new cementitious material which has, on the one hand, the property of being able to adsorb water-soluble cations, in particular cesium, and on the other hand, improved mechanical properties. This material can be used for the retention of cations, in particular for the

nuclear waste storage.

  It can also be used in other fields where a fixation of the cations and / or good mechanical properties is sought, in

particularly in civil engineering.

  State of the prior art Cementary materials are used in civil engineering for their "bonding" properties, making it possible to ensure the mechanical cohesion of the parts making up a civil engineering structure. The cement mainly used is Portland cement, which hydrated, consists mainly of hydrated calcium silicates which give hydrated cement its

  assembly and bonding properties.

  Cementitious materials are also used in the context of nuclear waste storage as a coating matrix for nuclear waste.

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  low activity and medium activity. They are also used as an engineered barrier in low-level waste storage sites and in medium and high-level waste storage sites, as well as in possible disposal sites.

deep storage.

  The cementitious material used mainly for these storage is also Portland cement, which hydrates, is made up

  mainly hydrated calcium silicates.

  In hydrated Portland cement, the molecular structure of hydrated calcium silicates presents certain analogies with a structure

smectite clayey.

  FIG. 1 schematically represents a sheet of the structure of a hydrated calcium silicate of this type which consists of a stack of

several sheets.

  In this figure, we see that the sheet includes two tetrahedral layers (Te) constituted by chains of SiO2 tetrahedra of variable lengths and not planes as in a smectite, between which is placed an octahedral layer

(Oc) formed by the CaO plane.

  Figure 2 illustrates the nuclear magnetic resonance spectrum of silicon at the magic angle of these hydrated calcium silicates. It allows the determination of the length of the chains which consist of tetrahedra Si [Q2], Si [Q2L] and Si [Q1]

referenced in Figure 1.

  The mechanical properties conferred by hydrated calcium silicates are linked to

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  interlayer charges of hydrated calcium silicates. Unlike clay, hydrated calcium silicates do not have a "structural" charge deficit linked to cationic substitutions in the CaO plane or in the layers of silicon tetrahedra (Te). This absence of cationic substitutions prevents the specific adsorption of soluble cations by hydrated calcium silicates, which does not allow good cation retention when these cements are used for the storage of radioactive waste. coating of waste such as glass and ceramics has also been used to confine radionuclides, but the use of such materials leads to very low costs

  disadvantageous compared to cement.

  Clay is known for its adsorption properties for soluble cations, but it can hardly replace cement for the creation of an engineered barrier. Furthermore, if the waste is itself cemented, this solution will present a risk of chemical incompatibility between the cemented waste and the clay barrier. In addition, it is very often desirable to use the concrete necessary for the construction of the storage site as a containment barrier. However, the concrete and cementitious materials currently used do not have the property of specifically adsorbing cations

soluble such as cesium.

  To increase the mechanical resistance of cementitious materials based on calcium silicates

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  hydrated, public works companies are currently gaining strength

  mechanical by reducing the porosity of these materials.

  This reduction is obtained by reducing the quantities of water in the water-cement mixture (making it possible to obtain hydrated calcium silicates), or even by adding silica smoke or aggregates. We can also improve the dispersion of the initial mixtures or play on the pressure and the temperature

hardening.

  The present invention specifically relates to a new cementitious material which, thanks to its composition, has improved mechanical strength and the advantageous property of adsorbing cations. Therefore, the material can be used for the storage of waste, in particular radioactive waste containing

  cesium, and for the retention of soluble cations.

  It can also be used in the construction of civil engineering works to increase the

mechanical resistance of concrete.

  Disclosure of the invention According to the invention, the cementitious material comprises at least one hydrated calcium silicate substituted with lithium, said substituted silicate having a Ca: Si molar ratio of 0.3 to 1.7 and a

  Li: Si molar ratio of 0.01 to 1.

  In this material, the substitution of the Ca2 ′ ions of the hydrated calcium silicate by Li + ions makes it possible to create a deficit in structural charge, analogous to that observed in a smectite-type clay. This deficit is compensated by lithium ions

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  who can trade very easily with others

  cations, and in particular cesium.

  Thus, this new material has a modified surface charge due to the partial substitution of Ca by Li modifying the nature of the forces brought into play between each particle of hydrated calcium silicate. This modification is at the origin of the increase in the mechanical resistance of the material

cement containing lithium.

  Preferably, in this material, the Ca: Si molar ratio of said hydrated calcium silicate is 0.6 to 1.7, and the Li: Si molar ratio of said

  hydrated calcium silicate is 0.01 to 0.75.

  Such a substitution rate of calcium with lithium makes it possible to obtain the advantageous cation exchange properties described above,

  as well as an improvement in mechanical strength.

  The use of alkali metals, in particular sodium, in cements has already been envisaged to activate their hydration, as described in "Avances in Cement Research, 1995, 7, n 27, pages 93-102 [1]. However, the amounts added in this case are very small and do not make it possible to obtain hydrated calcium silicates

substituted as in the invention.

  According to the invention, the cementitious material can also comprise other constituents such as those which are usually present in hardened cements. These constituents can be chosen by

  example among calcium aluminates, ferro-

  calcium aluminates, silica, carboaluminates, calcite, all hydrates which can precipitate in

a cement, and their mixtures.

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  The cementitious material of the invention can be obtained from a cementitious material comprising at least one hydrated calcium silicate, by subjecting it to a complementary treatment of substitution of part of the calcium atoms by

lithium atoms.

  Also, according to a first embodiment, the method for preparing the cementitious material of the invention consists in bringing a cementitious material based on hydrated calcium silicate into contact with an aqueous solution of hydroxide or of lithium salt to replace a part of the calcium atoms of the calcium silicate hydrated by lithium atoms, the concentration of lithium in the aqueous solution being such that it corresponds to a ratio

molar Li: If at least 0.01.

  This embodiment is easy to implement since it suffices to carry out a treatment

  complementary on an existing cementitious material.

  Generally, the aqueous hydroxide or salt solution

  of lithium has a lithium concentration of 0.5 mol / l.

  In this embodiment, it is possible to use any hydrated cementitious material prepared from any cement capable of forming

  calcium silicates hydrated during hardening.

  For example, it can be Portland cement, blast furnace slag, silica smoke, pozzolanic material, fly ash and mixtures thereof. Preferably, any material is used

  hydrated cement based on Portland cement.

  The lithium salt which can be used for this treatment is a lithium salt

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  soluble in water, in particular a mineral acid salt such as a halide (fluoride, chloride, bromide and iodide), a nitrate, a sulfate, a carbonate or even a silicate. It can also be an organic salt. Preferably, lithium chloride is used. The starting cementitious material can be obtained from a composition comprising, in addition to the cement, one or more additives such as silica smoke (amorphous SiO2), fly ash, inert fillers such as sand, limestone aggregates or siliceous, or additives to adapt the properties of the cementitious material obtained, as well as thinning agents and agents

setting retarders.

  In this case, the starting cementitious material can be obtained by adding the composition to an aqueous solution, and hardening of the material.

cement in this solution.

  In this first embodiment, it is also possible to prepare the starting cementitious material based on hydrated calcium silicate, by mixing calcium and silicon compounds in water in amounts such as the Ca: Si molar ratio

greater than or equal to 0.3.

  Various calcium compounds can be used for this preparation, for example calcium oxide CaO, calcium hydroxide, calcium silicates, any calcium-based compound which can

to hydrate, and their mixtures.

  The silicon compound can be chosen from silica, silica fume,

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  calcium, any silicon compound that can hydrate,

and their mixtures.

  For this preparation, it is important that the amounts of compounds added to the aqueous solution are such that the Ca: Si molar ratio is at least 0.3, preferably at least

  0.66 to ensure the formation of calcium silicate.

  The amount of water is variable and can be

  adjusted so as to obtain a suspension or a paste.

  It is preferable to obtain a suspension and, in this case, the water weight ratio: (compounds of Ca and Si) is greater than 1, preferably greater than 20, by

example of 50.

  According to the invention, the cementitious material based on hydrated calcium silicate substituted by lithium can also be obtained directly by coprecipitation from a mixture of compounds of

calcium, silicon and lithium.

  Also, according to a second embodiment, the process for preparing the cementitious material comprises the following steps: - mixing in an aqueous solution of calcium, silicon and lithium compounds in proportions such as the molar ratio Ca: Si in the solution is greater than or equal to 0.3 and that the molar ratio Li: If in the solution is greater than or equal to 0.01, and - harden the cementitious material in this

aqueous solution thus obtained.

  For this preparation, the calcium and silicon compounds mentioned above can be used in the case of the preparation of a

cementitious material without lithium.

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  The lithium compound used can be lithium hydroxide or a lithium salt such as those mentioned above. Lithium chloride is preferred. As before, it is important that the amounts of calcium and silicon compounds are such that the Ca: Si molar ratio is at least 0.3, preferably at least 0.66, to ensure

  the formation of calcium silicate.

  Likewise, the amount of lithium compound must be such that the Li: Si ratio is at least 0.01. The amount of water is variable and can be

  adjusted so as to obtain a suspension or a paste.

  In the case of a suspension, the water weight ratio: (compounds of Ca, Si and Li) is preferably greater than 20, for example 50. In the case of a paste, the water weight ratio: (compounds of Ca , Si and Li)

is less than 1.

  The invention also relates to a waste storage method comprising the use of a barrier made of cementitious material described above for

  isolate environmental waste.

  The waste is preferably waste containing water-soluble cations which are likely to migrate into the environment

by water infiltration.

  As an example of such waste, one can

  cite radioactive waste containing cesium.

  It also relates to a process for retaining water-soluble cations such as cesium, by bringing an aqueous solution into contact

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  said cations with a cementitious material according to the invention. Finally, it relates to a process for improving the mechanical strength of a cementitious material comprising at least one hydrated calcium silicate, which consists in bringing the cementitious material into contact with an aqueous solution of lithium salt or hydroxide to replace part of the calcium atoms of calcium silicate by atoms

lithium.

  In this process, the starting cementitious material can be a material obtained from Portland cement, slag, blast furnace, material

  pozzolanic and / or fly ash.

  Other characteristics and advantages of the invention will appear better on reading the

  description which follows, of course given as

  illustrative and not limiting, with reference to the accompanying drawings.

Brief description of the drawings

  FIG. 1 already described illustrates the structure of a hydrated calcium silicate in accordance with

prior art.

  Figure 2 illustrates the nuclear magnetic resonance spectrum of silicon at the angle

  magic, hydrated calcium silicate of figure 1.

  Figure 3 illustrates the X-ray diffractogram of non hydrated calcium silicates

  substituted in accordance with the prior art.

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  FIG. 4 illustrates the X-ray diffractogram of hydrated calcium silicates substituted for

  lithium of Examples 1 to 4, in accordance with the invention.

  Figures 5 and 6 illustrate the nuclear magnetic resonance spectra of silicon at the magic angle of unsubstituted hydrated calcium silicates (Figure 5) and substituted with lithium (Figure

6) examples 1 to 4.

  FIG. 7 illustrates the static nuclear magnetic resonance spectra of lithium of hydrated calcium silicates substituted by lithium

examples 1 to 4.

Figure 8 illustrates the two lines

  identified in each of these spectra.

  FIG. 9 illustrates the structure of hydrated calcium silicates substituted with

lithium, in accordance with the invention.

  FIG. 10 illustrates the nuclear magnetic resonance spectra of silicon, at the magic angle, of hydrated calcium silicates unsubstituted by Li of examples 13 and 14 and substituted

by Li of Example 15.

  Detailed description of the embodiments The examples which follow illustrate the preparation and the mechanical and retention properties of cations of conforming cement materials.

to the invention.

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  Example 1: Preparation of a Cement Based Material

  of calcium silicate substituted with lithium.

  In this example, the first embodiment of the process of the invention is used, that is to say the carrying out of a complementary substitution treatment with Li on a cementitious material already prepared. First a cementitious material is prepared from calcium oxide CaO and silica

  SiO2 by operating as follows.

  A total of 1.8 g of CaO and SiO2 are introduced in proportions such that the Ca: Si molar ratio is 0.66, in 90 ml of water, which corresponds to a water weight ratio: (CaO + SiO2) of 50, and the whole is left to stand for three weeks. A cementitious material based on

hydrated calcium silicate.

  Then added to this medium 1.89 g of lithium chloride and allowed to stand again for three weeks, at 25 ° C., in a nitrogen atmosphere

to avoid carbonation.

  This gives a cementitious material

substituted for lithium.

  In the appended Table 1, the starting Ca / Si molar ratio and the ratios are indicated.

  Ca: Si and Li: Si molars in the product obtained.

Examples 2 to 4.

  The same procedure is followed as in Example 1 to prepare other cementitious materials having different Ca: Si ratios, in

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  using in each case 1.8 g of mixture of CaO and SiO2 with different molar ratios, and the same

  amount of LiCl for substitution treatment.

  The Ca: Si starting and final molar ratios and the Li: Si molar ratio of cementitious materials obtained are also given in the

table 1.

  Comparative examples 1 to 4: preparation of cementitious materials based on unsubstituted calcium silicate. In these examples, the same procedure is followed as in Examples 1 to 4, but the substitution treatment is not carried out using

lithium chloride.

  Cement materials unsubstituted by lithium are thus obtained having Ca: Si molar ratios of 0.66; 0.83; 1.2 and 1.7 as

in examples 1 to 4.

  The cementitious materials obtained in Examples 1 to 4 and in Comparative Examples 1 to 4 are analyzed by X-ray diffraction and by nuclear magnetic resonance of silicon at the magic angle. Figure 3 illustrates the X-ray diffractogram of unsubstituted hydrated calcium silicates

  obtained in Comparative Examples 1 to 4.

  Figure 4 illustrates the X-ray diffractograms of substituted hydrated calcium silicates

  with lithium obtained in Examples 1 to 4.

  The comparison of Figures 3 and 4 shows that the addition of lithium did not cause the

  precipitation of new crystallized phases.

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  FIG. 5 illustrates the nuclear magnetic resonance spectra of silicon at the magic angle of hydrated calcium silicates not substituted with lithium obtained in comparative examples 1 to 4. FIG. 6 illustrates the spectra of similar products substituted with lithium obtained

in examples 1 to 4.

  If we compare Figures 5 and 6, we note that we find the same sites Q1, Q2L and Q2 and in the same proportions in the silicates substituted by Li and in the unsubstituted silicates. This indicates that the tetrahedral layers are identical in the lithium substituted products and in the

unsubstituted products.

  If we refer to Table 1, we note that when the Ca: Si molar ratio is 0.66 at the start, we obtain a final Ca: Si molar ratio of 0.579. Classically, this should correspond to the coexistence of a calcium silicate

  hydrated having a Ca: Si of 0.66 and silica gel.

  However, as shown in FIG. 6, no silica gel is detected by NMR of the silicon. In fact, part of the calcium in the octahedral sheet was replaced by lithium, explaining that the Ca: Si ratio is less than 0.66. chemical analyzes confirm the

  presence of lithium replacing calcium.

  The static nuclear magnetic resonance spectra of lithium of the lithium-substituted hydrated calcium silicates of Examples 1 to 4 are shown in FIG. 7, the peaks corresponding to the

  mobile lithium having been truncated.

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  In Figure 8, we have identified the two

  lines which appear on the spectra of figure 7.

  This figure makes it possible to identify two lines, one wide or site 1 (non-averaged quadrupole interaction) which corresponds to lithium ions that are not very mobile or not, and the other fine (site 2) corresponding to ions.

mobile lithium.

  In FIG. 9, the structure of hydrated calcium silicates substituted with lithium is represented, as it emerges from the analyzes.

previously performed.

  In this figure, we find the tetrahedral layers (Te) consisting of chains of SiO2 tetrahedra in Figure 1 and the octahedral layer (Oc) of the CaO plane in which x calcium atoms are substituted by lithium atoms (xLiO). The substitution of Ca2 by Li 'creates a charge deficit compensated by lithium ions in interlayer

  (x / 2 Li ') on either side of the sheet.

  This structure is confirmed by the X-ray diffractograms of FIGS. 3 and 4 (no other crystallized phase) and by the spectra of FIGS. And 6 which give the same tetrahedral sites and by the spectra of FIG. 7 and the results of Table 2 which show that we have fixed lithium atoms

and mobile lithium atoms.

  The material of the invention is therefore very interesting because these lithium atoms mobile in interlayer can be exchanged very easily with other cations, for example with cesium as

will see it below.

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  EXAMPLE 5 Preparation of a Cement Based Material

  of calcium silicate substituted with lithium.

  For this preparation, the second embodiment of the process is used, namely the direct precipitation of the material from a mixture

  calcium, silicon and lithium compounds.

  As Ca, Si and Li compounds, calcium oxide CaO, silica SiO2 and chloride are used.

lithium LiCl.

  A quantity of lithium chloride is introduced into 90 ml of water such that the lithium concentration of the solution is 0.5 mol / l and 1.8 g are added to the total of CaO and SiO2, the proportions of CaO and SiO2 corresponding to a Ca: Si molar ratio of 0.66. The reaction medium is left to stand for three weeks at 25 ° C. in a nitrogen atmosphere to avoid carbonation, and the cementitious material based on calcium silicate is recovered from this medium.

hydrate substituted with lithium.

  In the annexed Table 2, the Ca: Si starting molar ratio and the ratios are indicated.

  Ca: Si and Li: Si molars in the product obtained.

Examples 6 to 8.

  The same procedure is followed as in Example 5 to prepare other cementitious materials having different Ca: Si ratios, using in each case 1.8 g of mixture of CaO and SiO2 with different molar ratios, and the same

amount of LiCl.

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  The Ca: Si starting and final molar ratios and the Li: Si molar ratio of materials

  cementitious obtained are given in table 2.

  The results of Table 2 show that the second embodiment of the method is less

  favorable for the substitution of Ca by Li.

  The X-ray diffraction analyzes of the materials obtained in Examples 5 to 8 give spectra identical to those of FIG. 4, and the same is true for the analysis by nuclear magnetic resonance spectrometry of silicon at the magic angle. , which gives spectra identical to those of the

figure 5.

  Thus, there is no lithium salt in the material, lithium therefore interacts with hydrated calcium silicates. It is incorporated into the structure and modifies the surface properties. As a result, the retention and interaction properties between two particles of hydrated calcium silicate are improved. This last property is at the origin of the increase in mechanical resistance observed

  later (examples 13 to 15).

  Examples 9 to 12 In these examples, the properties of the cementitious materials obtained in examples 5 to 8 are tested for fixing cesium. For this purpose, cesium salt (CsCl) is added to the mixtures of Examples 5 to 8. The concentration of cesium salt is adjusted to

0.5 mmol / l.

  The concentration of cesium remaining in solution is then determined by determination by

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  capillary electrophoresis after calibration

  prior, the detection limit being 0.1 mmol / l.

  The results obtained are given in the

table 3.

  It is thus noted that the cementitious materials of the invention which have a very low rate of substitution by lithium, make it possible to obtain

  cesium retention greater than 80%.

Comparative examples 5 to 8.

  In these examples, the same procedure is followed as in Examples 9 to 12, but a solution of cesium chloride at 0.5 mol / l and the cementitious materials of the comparative examples are used.

  1 to 4, not substituted by lithium.

  The results obtained are given in Table 4 as a percentage of fixed Cs. In this table 4, the percentage of fixed cesium was also given for a solution whose initial cesium concentration is 0.5 mmol / l, based on the fact that the quantity of fixed cesium is proportional to the quantity of initial cesium, as we have seen. Thus, with a solution of 0.5 mmol / l of cesium, cesium is practically not fixed by cementitious materials not substituted by lithium, the retention of cesium being at most 0.02%. The substitution by lithium of cementitious materials therefore makes it possible to obtain a retention rate of cesium

very high.

  Therefore, the cement materials of the invention can be used for the storage of waste,

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  either as a storage matrix or as an engineered barrier arranged around coated waste. This makes it possible to isolate the waste from the environment and to ensure that the cesium is fixed in the barrier in case the cesium could be dissolved by water which has migrated into the waste. Likewise, the cementitious materials of the invention can be used for the retention of water-soluble cations such as cesium, by contacting an aqueous solution of

  these cations with the cementitious material of the invention.

  Examples 13 to 15 In these examples, the second embodiment of the process is used to prepare a cementitious material from fume of silica carbosil (SiO2) and calcium hydroxide Ca (OH) 2 with

  addition or not of lithium chloride.

  The compositions used for the preparation of the material are given in Table 5

following.

  In these examples, all of the constituents are kneaded for approximately 2 minutes, then each of the pastes is introduced into a mold of three test tubes (4 cm x 4 cm x 16 cm). The tightening of the pasta is obtained by introduction in two stages, in

  applying 60 shocks to the mold each time.

  The mold of Example 13 is stored in

water at 25 C for 28 days.

  The molds of Examples 14 and 15 are placed in an airtight plastic container filled with water

* at 85 C for 28 days.

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  The resistance to compression of the cementitious materials obtained is then determined in

each of the examples.

  The results obtained are given in Table 6 which follows. The values in the table are the average of three out of three measurements

  different test pieces (dispersion <10%).

  Thus, it is found that the mechanical strength of test pieces containing lithium (Ex 15) is significantly higher than that of test pieces without Li, whatever the hardening temperature. The use of a temperature of 85 C activates the kinetics of hydration because the smoke from

silica is not very reactive.

  FIG. 10 shows the nuclear magnetic resonance spectra of the silicon of the cementitious materials obtained in the examples.

13 to 15.

  In this figure, it can be seen that the residual silica smoke is high when the hydration takes place at 25 C. When the hardening temperature goes from 25 C to 85 C, the hydration of the silica smoke is accelerated. The system therefore contains more hydrated calcium silicate. The resulting hydrated calcium silicates have shorter chains than at 25 C. The proportion of Q1 tetrahedra is indeed lower at 85 C than at 25 C. We then observe a collapse in mechanical strength (Table 7) which is therefore not related to the amount of smoke from

hydrated silica.

  The addition of LiC1 slightly activates this hydration (known effect of salts). This addition changes

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  little or no structure of the chains of silicon tetrahedra for the same hardening temperature. Mechanical resistance is therefore not correlated in the present case to the length of tetrahedron chains in hydrated calcium silicates. The increase in mechanical strength can therefore be attributed to the addition of lithium, which is incorporated into the structure of hydrated calcium silicates by modifying their

interface properties.

  Indeed, it does not result from a greater hydration effect of the anhydrous materials due to the lithium salt because one would then have observed on the spectrum a significant reduction in the Q4 contribution corresponding to the silica smoke not hydrated with

adding LiCl.

  Reference cited [1]: Avances in Cement Research, 1995, 7, n 27,

pages 93-102.

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Table 1

  Ca / Si Ca / SiLi / Si Ex molar molar molar (start) (final) (final)

1 0 60.66 0.5790.534

2 0 0.830.71 4 0.74 0

3 1.2 1.008 0.720

4 1.7 1.359 0.688

Table 2

  Ex Ca / Si molar Ca / Si molar Li / Si molar (start) (final) (final)

0.66 6 0.67 0.07

6 0.83 0.77 0.08

7 1.2 1.01 0.09

8 1.7 1.47 0.07

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Table 3

  Ex Ca / Si% Cs fixed for initial [Cs] 0.5 mmol / l

9 0.66> 80%

  (ex. 5) (Cs in solution not detected)

0.83> 80%

  (ex. 6) (Cs in solution not detected)

11 1.20> 80%

  (ex. 7) (Cs in solution not detected)

12 1.70> 80%

  (ex. 8) (Cs in solution not detected)

Table 4

  Ex Ca / Si% Cs fixed for% Cs fixed for Comparative initial [Cs] [Cs] initial 0.5M 0.5 mmol / l

0.66 10-20 0.01-0.02

(e.g. comp. 1)

6 0.83 10-20 0.01-0.02

(e.g. comp. 2)

7 1.20 <10 <0.01

(e.g. comp. 3)

8 1.70 <5 <0.005

(e.g. comp. 4)

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Table 5

  Ex Si02 (g) Ca (OH) 2 (g) LiCi (g) H20 (g) (Silica smoke (Prolabo, (Prolabo) Carbosil, 97% pure) 90% pure)

13,515,393 0,681

14,515,393 0,681

515 393 181.66 681

Table 6

  Ex Compressive strength (MPa)

13 2.5

14 0.5

9.5

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Claims (20)

  1. Cementary material comprising at least one hydrated calcium silicate substituted by lithium, said substituted silicate having a Ca: Si molar ratio of 0.3 to 1.7 and a molar ratio Li: If from 0.01 to 1.   2. A cementitious material according to claim 1, in which the molar ratio   Ca: If said silicate is from 0.6 to 1.7.   3. cementitious material according to claim 1 or 2, wherein the molar ratio   Li: If said silicate is from 0.01 to 0.75. 4. Cement material according to one   any of claims 1 to 3, comprising   in addition to the hardened cement constituents chosen from calcium aluminates, calcium ferroaluminates, silica, carboaluminates, calcite, all the hydrates which can precipitate in a cement, and their mixtures.   5. Method of preparing a material   cement according to any one of claims 1   to 4, which consists in bringing a cementitious material based on hydrated calcium silicate into contact with an aqueous solution of hydroxide or of lithium salt in order to substitute part of the calcium atoms of the hydrated calcium silicate by lithium atoms, the lithium concentration of the aqueous solution being such that it corresponds to a molar ratio Li: If at least 0.01.   6. The method of claim 5, wherein the aqueous solution of hydroxide or salt of   lithium has a lithium concentration of 0.5 mol / l. B 13119.3 MDT   7. The method of claim 5 or 6, wherein the cementitious material is any material   Portland cement based cement.   8. Method according to any one of   claims 5 to 7, wherein the lithium salt is lithium chloride.   9. Method according to any one of   claims 5 to 8, in which everything is prepared   first of all, the cementitious material based on hydrated calcium silicate, by mixing calcium and silicon compounds in water in amounts such as the Ca: Si molar ratio being greater than or equal to 0.3. 10. A process for the preparation of a cementitious material based on hydrated calcium silicate (s) substituted with lithium, comprising the following steps: - mixing in an aqueous solution of calcium and silicon compounds and lithium in proportions such that the Ca: Si molar ratio is greater than or equal to 0.3 to and that the Li: Si molar ratio is greater than or equal to 0.01, and - hardening of the cementitious material in this solution. 11. The method of claim 9, wherein the calcium compound is chosen from calcium oxide CaO, calcium hydroxide, calcium silicates, any calcium-based compound which can to hydrate, and their mixtures.   12. The method of claim 9 or 10, wherein the silicon compound is chosen from silica, silica fume, calcium silicates, any silicon compound that can hydrate, and mixtures thereof. 13. The method of claim 10, wherein the lithium compound is lithium chloride. 14. Waste storage method comprising the use of a material barrier   cement according to any one of the claims   1 to 4 to isolate waste from the environment.   15. The method of claim 14, wherein the waste is radioactive waste containing cesium.   16. Method for retaining water-soluble cations by bringing an aqueous solution of said cations into contact with a cementitious material   according to any one of claims 1 to 4.   17. The method of claim 16, in which said cation is cesium.   18. A method for improving the mechanical strength of a cementitious material comprising at least one hydrated calcium silicate, which consists in bringing the cementitious material into contact with an aqueous solution of lithium salt or hydroxide to replace part of the atoms of calcium calcium silicate by lithium atoms.   19. The method of claim 18, wherein the aqueous solution is a 0.5 M lithium chloride solution. 20. Method according to any one of   claims 18 and 19, wherein the material   cement is a material obtained from a cement chosen from Portland cements, blast furnace slag, pozzolanic materials,   fly ash and mixtures thereof.