Binder and the use thereof for conditioning waste containing aluminium metal

Abstract

The present invention relates to a binder composition comprising (i) a phospho-magnesium cement; (ii) a boron source; (iii) a lithium salt; and (iv) water and to its preparation method. The present invention also relates to the use of such a binder for confining wastes and notably nuclear wastes containing aluminum metal.

Claims

1. A binder composition comprising: (i) a phospho-magnesium cement; (ii) a boron source; (iii) a lithium salt; and (iv) water.

2. The composition according to claim 1, wherein said phospho-magnesium cement consists of a magnesium source in the oxidized state and of a phosphate source.

3. The composition according to claim 2, wherein said magnesium source in the oxidized state is selected from the group consisting of magnesium oxide (MgO), magnesium hydroxide (Mg(OH).sub.2), magnesium carbonate (MgCO.sub.3), magnesium hydroxycarbonate (4MgCO.sub.3.Mg(OH).sub.2.5H.sub.2O) and one of their mixtures.

4. The composition according to claim 2, wherein said phosphate source is selected from the group consisting of phosphoric acid, aluminium phosphate, sodium phosphate, potassium phosphate, aluminium monohydrogenphosphate, sodium monohydrogenphosphate, potassium monohydrogenphosphate, aluminium dihydrogenphosphate, sodium dihydrogenphosphate, potassium dihydrogenphosphate and one of their mixtures.

5. The composition according to claim 1, wherein said boron source is selected from the group consisting of boric acid, metaboric acid, borax, a borate salt, a monohydrogenborate salt, a dihydrogenborate salt, a metaborate salt, a polyborate salt and one of their mixtures.

6. The composition according claim 1, wherein said lithium salt is selected from the group consisting of lithium nitrate, lithium carbonate, lithium sulfate, lithium phosphate, lithium triazole, lithium borate, lithium monohydrogenborate, lithium dihydrogenborate, lithium metaborate, lithium polyborate and one of their mixtures.

7. The composition according to claim 1, wherein in said composition: the molar ratio between the elements Mg and P is between 0.5 and 1.5; the molar ratio between the elements B and Mg is between 0.03 and 0.3; the molar ratio between the elements Li and Mg is between 0.02 and 0.12; and the molar ratio between water and the element Mg is between 4 and 7.

8. The composition according to claim 1, wherein said composition comprises a filler.

9. The composition according to claim 8, wherein said filler a siliceous filler.

10. The composition according to claim 1, wherein said composition further comprises sand and optionally granulates.

11. The composition according to claim 7, wherein the molar ratio between the elements Mg and P is between 0.8 and 1.

12. The composition according to claim 7, wherein the molar ratio between the elements B and Mg is between 0.05 and 0.15.

13. The composition according to claim 7, wherein the molar ratio between the elements Li and Mg is between 0.05 and 0.10.

14. The composition according to claim 7, wherein the molar ratio between water and the element Mg is between 5 and 6.

15. The composition according to claim 9, wherein said siliceous filler is an alumino-siliceous filler.

16. The composition according to claim 15, wherein said alumino-siliceous filler is a filler, either natural or not, stemming from pozzolan, illite, opaline, cherts, volcanic ashes, pumice stone, schistous clays, calcined diatomaceous earths, baked clay, silica fume or fly ash.

17. A binder composition, comprising: (i) a phospho-magnesium cement; (ii) a boron source; (iii) a lithium salt; and (iv) water, wherein said binder composition is selected from among a grout composition formed with (i) a phospho-magnesium cement formed with magnesium oxide calcined between 1,000 and 1,500 C., with a specific surface area of less than 1 m.sup.2/g and with potassium dihydrogenphosphate; (ii) boric acid; (iii) lithium nitrate; (iv) a filler consisting of alumino-siliceous fly ash; and (v) water; a mortar composition formed with (i) a phospho-magnesium cement formed with magnesium oxide calcined between 1,000 and 1,500 C., with a specific surface area of less than 1 m.sup.2/g and with potassium dihydrogenphosphate; (ii) boric acid; (iii) lithium nitrate; (iv) a filler consisting of alumino-siliceous fly ash; (v) water; and (vi) siliceous sand with a grain size of less than 2 mm; and a concrete composition formed with: (i) a phospho-magnesium cement formed with magnesium oxide calcined between 1,000 and 1,500 C., with a specific surface area of less than 1 m.sup.2/g and with potassium dihydrogenphosphate; (ii) boric acid; (iii) lithium nitrate; (iv) a filler consisting of alumino-siliceous fly ash; (v) water; (vi) siliceous sand with a grain size of less than 2 mm; and (vii) a siliceous granulate.

18. A method for preparing a binder composition, comprising the steps of: a) preparing a mixture comprising water, a boron source, a lithium salt, phosphorus-magnesium cement, and a filler; and b) kneading the obtained mixture subsequently to said step (a).

19. The method according to claim 18, wherein sand and optionally granulates are added during said step (a), subsequent to said step (a) or subsequent to said step (b).

20. The method of claim 18, further comprising confining nuclear wastes containing aluminium metal.

21. Packages of wastes confined in a binder with a composition comprising water, a boron source, a lithium salt, and phosphorus-magnesium cement, and conditioned in barrels or caissons.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the comparisons of the productions of hydrogen by corrosion of an aluminium bar coated with different cement materials.

(2) FIG. 2 shows the heating and reaction heat of a mortar elaborated according to the present invention (reaction enthalpy relatively to the mass of MgO+KH.sub.2PO.sub.4).

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

1. Hydrogen Evolvement During the Coating of an Aluminium Bar with Different Cement Materials

(3) A cylindrical aluminium bar (purity of 99.99%) with a diameter of 1 cm and a height of 3 cm is coated with different types of cement materials, the characteristics of which are summarized in Table 1 hereafter.

(4) First, the aluminium bar is immersed for 30 s in 20% sulfuric acid and then abundantly rinsed with demineralized water and dried. This operation aimed at removing any possible passivating layer at the surface of the metal.

(5) The aluminium bar is then immersed in 50 ml of fresh material cast into a polyethylene pot, and then placed in a metal reactor, the lid of which is equipped with a tapping which allows it to be connected to a vacuum pump, to a nitrogen supply network or to a gas chromatograph. The pot is hermetically closed. A depression is produced by means of a vacuum pump until a pressure of 150 mbar is reached. Nitrogen is then introduced up to a pressure of 750 mbar.

(6) The reactor is kept at room temperature (222 C.) and gas samples are regularly taken for hydrogen analysis by gas chromatography. FIG. 1 allows a comparison of the productions of hydrogen by the different materials.

(7) TABLE-US-00001 TABLE 1 Formulation of the tested materials for coating the aluminium bar. Type of Type of cement Composition material W/C * Comments Portland CEM I 52.5 PM ES CP2 Lafarge Le Cement 0.40 Portland Cement (CEM I) Teil slurry commonly used for inertization of wastes Ettringite 67% Molten aluminous cement Cement 0.48 Binder of the type (CAC + gypsum) (Kerneos) + 33% gypsum (VWR) slurry of that tested by Savannah River [15] Ettringite Sulfo-aluminous cement (75% Cement 0.55 Binder of the type (CSAC) clinker KTS100 of Belitex + 25% slurry of those studied gypsum VWR) by Hayes et al [2] Silico-magnesium 20% MgO (MagChem 10 CR from Cement 0.35 Binder of the type (MSH) M.A.F. Magnesite) + 5% slurry of that studied magnesium hydroxycarbonate by Zhang et al [17] 4MgCO.sub.3Mg(OH).sub.25H.sub.2O (VWR) + 25% silica fumes (Condensil S95 DM) + Boric acid (VWR) (2% based on the mass of MgO + magnesium hydroxycarbonate + SiO.sub.2) + Plasticizer (BASF Glnium 51 - 1% based on mass of MgO + magnesium hydroxycarbonate + SiO.sub.2) Phospho- MgO (MagChem 10 CR from Cement 0.51 ** Binder of the type magnesium + boric M.A.F. Magnesite) + KH.sub.2PO.sub.4 slurry of those developed acid (VWR) + alumino-siliceous flying by Wagh et al [8-14] (MKP + H.sub.3BO.sub.3) ashes + boric acid (VWR) Molar ratio Mg/P = 1 Molar ratio H.sub.2O/Mg = 5 Molar ratio B/Mg = 0.057 Phospho- MgO (MagChem 10 CR from Cement 0.51 ** Present magnesium + boric M.A.F. Magnesite) + KH.sub.2PO.sub.4 + slurry invention acid + lithium alumino-siliceous flying ashes nitrate (FA) + boric acid (VWR) + LiNO.sub.3 (MKP + H.sub.3BO.sub.3 + (VWR) LiNO.sub.3) Molar ratio Mg/P = 1 Molar ratio H.sub.2O/Mg = 5 Mass ratio FA/(MgO + KH.sub.2PO.sub.4) = 1 Molar ratio B/Mg = 0.057 Molar ratio Li/Mg = 0.051 Phospho- MgO (MagChem 10 CR from Mortar 0.55 ** Present magnesium + boric M.A.F. Magnesite) + KH.sub.2PO.sub.4 invention acid + lithium (VWR) + alumino-siliceous flying nitrate ashes (FA) + boric acid (VWR) + (MKP + H.sub.3BO.sub.3 + LiNO.sub.3 (VWR) + siliceous sand LiNO.sub.3) (Sifraco NE34) Molar ratio Mg/P = 1 Molar ratio H.sub.2O/Mg = 5.4 Molar ratio B/Mg = 0.057 Molar ratio Li/Mg = 0.051 Mass ratio FA/(MgO + KH.sub.2PO.sub.4) = 1 Mass ratio sand/(MgO + KH.sub.2PO.sub.4) = 1 * water/cement mass ratio ** water/(MgO + KH.sub.2PO.sub.4) mass ratio

(8) As expected, the hydrogen production from the reference coating prepared from Portland cement is massive. The test had to be interrupted after only one day because of the too high content of hydrogen in the reactor.

(9) With aluminous or sulfo-aluminous cements, evolvement of hydrogen is rapid for the first days following the mixing and then slows down. However, no stabilization is observed over the duration of the study. Resumption of the production of hydrogen even occurs after 60 d in the case of sulfo-aluminous cement. The latter is related to the depletion of gypsum in the cement slurry, which is accompanied by an increase in the pH of the interstitial solution by one unit (from about 11 to 12) and therefore by an increase in the corrosion rate of the aluminium.

(10) In the case of silico-magnesium cement, the hydrogen evolvement remains small for the first 24 hours, and then significantly increases. The limit of 4% of hydrogen in the headspace of the reactor is attained after 90 d.

(11) The best results are obtained with phospho-magnesium cement. With the existing formulations (curve <<MKP+H3BO3>> of FIG. 1), a slight production of hydrogen is nevertheless detected. Extrapolation over one year would lead to a production of 0.026 L/(m.sup.2.Math.yr). The present invention allows an improvement in this result. Aluminium bars were coated with the mortar according to the present invention or with a simplified formulation by suppressing sand (a slurry, the cement of which has the same composition as the mortar, the same additives, suppression of the sand, and reduction in the water content for preventing bleeding). In both cases, the hydrogen content in the gas headspace of the reactor remains lower than the detection limit of the analysis method used (0.01% of H.sub.2) over the whole duration of the study (curve <<MKP+H3BO3+LiNO3>> of FIG. 1). Extrapolation over one year would lead to a hydrogen production of less than 2.28.10.sup.4 L/(m.sup.2.Math.yr), i.e. reduced by a factor of more than 100 as compared with the state of the art.

2. pH of the Interstitial Solution of the Mortar According to the Present Invention

(12) A mortar was prepared according to the formulation described in the last line of Table 1. Its interstitial solution was extracted by pressing after 1 hour of preservation at 20 C. in a hermetically closed pot. The pH of the extracted solution was measured with a pH electrode calibrated beforehand between 4 and 7. A value of 5.0 was obtained. This result confirms that the present invention gives the possibility of obtaining a material, for which the pH of the interstitial solution at an early stage is located in the range of passivation of aluminium.

3. Synergistic Effect of Boric Acid and of Lithium Nitrate for Retarding the Setting of the Phospho-Magnesium Cement

(13) In order to evaluate the influence of the additions (boric acid and lithium nitrate) on the reaction kinetics of the binder, tests were conducted on simplified formulations consisting of cement slurries. As compared with the material described in the present invention, only sand was suppressed.

(14) The setting time of the materials was evaluated by means of an automatic Vicat setting-time-meter. Table 2 shows the different tested configurations and the obtained results.

(15) TABLE-US-00002 TABLE 2 Study of the influence of lithium nitrate and boric acid on the setting time of phospho-magnesium cement slurries. Molar Molar Mass ratio Molar Molar Vicat setting time Constituents ratio ratio FA/(MgO + ratio ratio Initial Final and suppliers Mg/P H.sub.2O/Mg KH.sub.2PO.sub.4) B/Mg Li/Mg (min) (min) MgO Magchem 1 5 1 0 0 40 (5) 70 (5) 10CR (M.A.F 0 0.051 35 (5) 70 (5) Magnesite) 0 0.102 30 (5) 70 (5) KH.sub.2PO.sub.4 (VWR) 0.057 0 250 (15) 1080 (15) Flying ashes 0.057 0.051 420 (15) 1260 (15) AlSi 0.057 0.102 690 (15) 2400 (15) H.sub.3BO.sub.3 (VWR) LiNO.sub.3 (VWR)

(16) It appears that: used alone, lithium nitrate does not have any significant influence on the setting of the phospho-magnesium cement in the studied range of concentrations, used alone, boric acid has a retarding effect on the setting of the phospho-magnesium cement in the studied range of concentrations, the retarding action of boric acid is reinforced by adding lithium nitrate.

(17) This result underlines the original feature of the present invention, the synergistic action of nitric acid and of lithium borate cannot be simply inferred from the influence of both of these salts considered separately from each other.

4. Properties of a Mortar Elaborated According to the Present Invention

(18) A mortar was prepared according to the formulation described in the last line of Table 1 by means of a standardized laboratory kneader according to the EN196:1 standard. It was then subject to the following characterizations: measurement of the exuded water after 1 h, 3 h and 24 h per 100 ml of coating introduced into a graduated test tube and protected from drying, evaluation of the fluidity by measurement of the flow time of a liter of mortar through a Marsh cone provided with a fitting of 12.5 mm, measurement of the heating-up of 1,575 g of mortar placed in a Langavant semi-adiabatic calorimeter, measurement of the initial and final setting times by means of an automatic Vicat setting-time-meter, measurement of the compressive strength of specimens 4416 cm kept for 28 d at room temperature in water or in a bag.

(19) The obtained results are summarized in Table 3 and in FIG. 2.

(20) TABLE-US-00003 TABLE 3 Properties of a mortar prepared according to the present invention. Property Result Exuded water 1 h: 0% 3 h: 0% 24 h: 0% Flow time of one liter of mortar through the 80 s Marsh cone Vicat setting time Initial: 4 h Final: 12 h 30 min Maximum heating-up under the Langavant 35.7 C. semi-adiabatic conditions Reaction enthalpy (J/g de MgO + KH.sub.2PO.sub.4) 499 J/g Compressive strength at 28 d (MPa) Bag: 46 MPa Water: 36 MPa

(21) It appears that, in addition to its capability of strongly limiting corrosion of the aluminium, the mortar prepared according to the present invention has favorable features for an application to the immobilization of heterogeneous wastes: it does not exhibit any bleeding, its reactivity is under control (initial setting time of more than 3 h, final setting time of less than 24 h), its fluidity allows flow through the Marsh cone, its heating-up remains moderate (maximum temperature of less than 60 C. under the semi-adiabatic conditions of the Langavant test), its compressive strength considerably exceeds the required minimum limit of 20 MPa at the deadline of 28 d.

REFERENCES

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