Patent Number: 047972327
Section: description

The examples which follow will illustrate the invention. Example 1: 1st case The solutions On the laboratory scale, a solution of FP was simulated using a typical composition of a real solution of FP in the following manner: ______________________________________ Corresponding Quantity quantity of oxide Product used (g) (g) ______________________________________ 1- Al(NO.sub.3).sub.3.9H.sub.2 O 117.6 15.9 Fe(NO.sub.3).sub.3.9H.sub.2 O 146.7 29 Ni(NO.sub.3).sub.2.6H.sub.2 O 19.4 5 Cr(NO.sub.3).sub.2.9H.sub.2 O 26.3 5 Na.sub.4 P.sub.2 O.sub.7.10H.sub.2 O 9.4 5.6 NaNO.sub.3 103.6 37.7 2- Sr(NO.sub.3).sub.2 6.7 3.2 CsNO.sub.3 15.2 10.9 Ba(NO.sub.3).sub.2 9.7 5.6 ZrO(NO.sub.3).sub.2.2H.sub.2 O 34.7 15.9 Na.sub.2 MoO.sub.4.2H.sub.2 O 26.4 22.5 Co(NO.sub.3).sub.2.6H.sub.2 O 5.8 1.4 Mn(NO.sub.3).sub.2.4H.sub.2 O 27.7 9.5 Ni(NO.sub.3).sub.2.6H.sub.2 O 18.3 4.6 Y(NO.sub.3).sub.3.4H.sub.2 O 5.5 1.7 La(NO.sub.3).sub.3.6H.sub.2 O 23.7 8.8 Ce(NO.sub.3).sub.3.6H.sub.2 O 24.9 9.3 Pr(NO.sub.3).sub.3.4H.sub.2 O 10.6 4.3 Nd(NO.sub.3).sub.3.6H.sub.2 O 39.6 15.1 ZrO.sub. 2 4.6 4.6 Mo 3.5 5.3 U.sub.3 O.sub.8 8.8 8.5 ______________________________________ Group 1 represents the inactive components of the solution of FP and group 2 simulates the active components of this same solution and the insoluble materials. ZrO.sub.2 and Mo remain solid; they simulate the insoluble materials suspended in the solution. The total quantity of water added is 2972 g. The simulated solution of FP has a pH of 1.3. The composition of the final glass to be obtained is: ______________________________________ Composition of the glass introduced via ______________________________________ SiO.sub.2 45.5% Ludox B.sub.2 O.sub.3 14% Solution of ATB Al.sub.2 O.sub.3 4.9% Solution of adjuvant and simulated solution of FP Na.sub.2 O 9.8% Solution of adjuvant and simulated solution of FP ZnO 2.5% Solution of adjuvant and simulated solution of FP CaO 4.1% Solution of adjuvant and simulated solution of FP Li.sub.2 O 2% Solution of adjuvant and simulated solution of FP Active oxides 13.2% Simulated solution of FP Fe.sub.2 O.sub.3 2.9% " NiO 0.4% " Cr.sub.2 O.sub.3 0.5% " P.sub.2 O.sub.5 0.3% " ______________________________________ In the percentage composition shown, it is necessary to allow for the presence of Na and Ni in the active oxides (group 2 of the solution of FP defined above). Thus, the solution of the vitrification adjuvant is prepared according to the composition of the glass to be obtained and the composition of the solution of waste to be treated. For this example, the solution of vitrification adjuvant is prepared as follows: ______________________________________ Corresponding Quantity quantity of oxide Product used (g) (g) ______________________________________ Al(NO.sub.3).sub.3.9H.sub.2 O 243.6 33.1 NaNO.sub.3 148.4 54.1 Zn(NO.sub.3).sub.2.6H.sub.2 O 91.4 25 Ca(NO.sub.3).sub.2.4H.sub.2 O 170.1 40.4 LiNO.sub.3 91.4 19.8 ______________________________________ Each of the compounds is dissolved in the minimum quantity of water, i.e. a total of 640 g of water at 65.degree. C.; pH: 0.6. The precursor is Ludox AS40: 40% SiO.sub.2 /60% H.sub.2 O; .phi. of the particles: 21 nm; d.sub.25.degree. C. : 1.30; pH: 9.3; used at ambient temperature. The ATB solution is 265.2 g of (NH.sub.4).sub.2 0.2B.sub.2 O.sub.3.4H.sub.2 O dissolved in 663 g of water at 65.degree. C.; pH: 9.2. The device The device used is a conventional turbine having a mixing zone of small volume, in which a propeller with several blades rotates so as to effect mixing at a high rate of shear. It rotates at 2000 rpm in this example. The turbine used for the tests is manufactured by the Company STERMA, the mixing zone has a volume of 1 cm.sup.3 and the thickness of the stirred layer is of the order of mm. The procedure The solutions arrive at the turbine separately and simultaneously: ______________________________________ Flow rate Composition of pH T.degree. at T.degree. the solution ______________________________________ Ludox 9.3 20.degree. C. 12 kg/h 40% of SiO.sub.2 Ammonium tetra- 9.2 65.degree. C. 9.9 kg/h 21% of anhydrous borate.4H.sub.2 O (ATB) salt, i.e. 15% of B.sub.2 O.sub.3 Solution of 0.6 65.degree. C. 14.7 kg/h 40% of anhydrous vitrification salt, i.e. 12% adjuvant of oxides ______________________________________ 36.5 kg/h of borosilicate matrix are thus prepared. 1.7 kg are spread over a plate with an average thickness of 2 cm and then placed in an oven at 100.degree.-105.degree. C. for 48 hours; 0.6 kg of dry matrix is obtained. 1.6 l of simulated solution of FP are placed in a 3 l container equipped with a rotating mechanical stirrer; the dried matrix is poured in uniformly, with stirring. The mixture obtained is stirred for about 30 min and then dried at 100.degree.-105.degree. C. in an oven on a plate, calcined for 2 h at 400.degree. C. and finally melted for 5 h at 1050.degree. C. The glass obtained (0.5 kg) satisfies the criteria of acceptability. In the tests, a glass of good quality was defined as being a homogeneous glass having no unmelted regions and no bubbles and also showing no traces of molybdate on the surface. The molybdate originating from the solutions of FP actually presents a major problem: part of the active Mo tends to separate out from the solution and deposit, so this phase is not completely dispersed in the mixture and hence is not totally included in the gelled solution. Furthermore, when it diffuses poorly, the molybdenum appears on the surface of the glass in the form of visible yellow traces of molybdate, which are considered to be an indication of inferior quality glass. Chemical analysis of the glass obtained further shows that the components are not volatilized in practice, so it can be considered that the composition of the mixtures (borosilicate matrix, then matrix+waste) virtually corresponds to that of the final glass. Example 2: 2nd case Test 1 3.7 kg of the borosilicate matrix coming from the turbine (preparation according to Example 1) are dried for 20 hours at 100.degree.-105.degree. C. on plates in an oven. The dried matrix is then placed in a furnace in which the temperature is gradually raised to 350.degree. C. over 2 hours, and calcination is carried out for 2 h at 350.degree. C. The product obtained is friable and is in the form of fragments of a few mm in diameter (on average 2-3 mm). The calcined matrix (1 kg) is ground (.perspectiveto.300-400 .mu.) and dispersed in the solution of FP (3 kg), simply with stirring (magnetic stirrer, 30-45 min). The mixture is calcined for 4 h at 400.degree. C. after being heated for 34 h at 120.degree. C., and is then melted at 1125.degree. C. 40 min in the introduction zone and 1 h in the refining zone lead to a glass of good quality. Test 2: This test relates to the treatment of the soda effluent used for washing, which is subsequently acidified. At present, in the vitrification (AVM) process based on the oxides, it is not easy to treat this effluent on its own. This AVM process actually uses the vitrification adjuvant in the form of a solid glass frit, a known composition being: ______________________________________ SiO.sub.2 55-60% by weight B.sub.2 O.sub.3 16-18 by weight Al.sub.2 O.sub.3 6-7 by weight Na.sub.2 O 6-7 by weight CaO 4.5-6 by weight ZnO 2.5-3.5 by weight Li.sub.2 O 2-3 by weight ______________________________________ If this composition were used to vitrify the soda effluent, the glass obtained would be very rich in sodium. One might consider reducing the level of sodium in the glass frit, even to zero, so that the final glass (frit+calcinate of soda effluent) has an acceptable sodium level (9 to 11% by weight). However, one is then faced with the difficulty of producing and melting a glass which is poor in sodium (and consequently richer in silica). The present invention makes it possible to produce, with the soda effluent, a borosilicate glass having a composition similar to that which proves totally satisfactory in the AVM process. Moreover, the refining temperature can be considerably lowered or the refining times shortened. For tests, a soda solution was therefore simulated using 100 g of Na.sub.2 CO.sub.3 in one liter of water. The ATB solution contains 312 g/l of ATB.4H.sub.2 O. The boric acid solution contains 130 g/l (6.5% of B.sub.2 O.sub.3)-pH=2.7. To obtain a glass having a composition similar to that obtained by the AVM process, the following solution of vitrification adjuvant is prepared (amounts are per liter of aqueous solution): ______________________________________ Al(NO.sub.3).sub.3.9H.sub.2 O 209.0 g Ca(NO.sub.3).sub.2.3H.sub.2 O 98.5 g LiNO.sub.3 53.7 g Zn(NO.sub.3).sub.2.6H.sub.2 O 49.7 g Fe(NO.sub.3).sub.3.6H.sub.2 O 73.5 g Mn(NO.sub.3).sub.3.6H.sub.2 O 18.2 g Ba(NO.sub.3).sub.2 5.5 g Co(NO.sub.3).sub.2.6H.sub.2 O 11.3 g Sr(NO.sub.3).sub.2 4.1 g CsNO.sub.3 8.0 g Y(NO.sub.3).sub.3.4H.sub.2 O 71.0 g Na.sub.2 MoO.sub.4.2H.sub.2 O 16.6 g Monoammonium phosphate 2.8 g ______________________________________ The components Fe, Mn . . . phosphate were introduced into this solution so as to give a final glass with a composition similar to that given in the previous examples. On the other hand, Aerosil.RTM., marketed by the firm DEGUSSA, will be used instead of Ludox AS40 as the gel precursor. The gel precursor is formed by pouring the Aerosil gradually, with stirring, into water acidified with 3 N HNO.sub.3 (pH: 2.5), so as to give a solution containing 150 g of silica per liter. 3 diaphragm pumps are provided, which have been adjusted beforehand to give the desired flow rates. The following solutions are pumped simultaneously into a high-speed mixer (capacity: 1.5 liters) at the indicated flow rates and temperatures. The set flow rates are: ATB solution . . . 0.57 l/h at 65.degree. C., or alternatively PA0 H.sub.3 BO.sub.3 solution . . . 1.25 l/h at 65.degree. C. PA0 Adjuvant solution . . . 1.15 l/h at 65.degree. C. PA0 Aerosil solution . . . 2 l/h at 20.degree. C. PA0 ATB solution containing 15% of B.sub.2 O.sub.3 at 0.75 l/h, or alternating H.sub.3 BO.sub.3 solution containing 6.5% of B.sub.2 O.sub.3 at 1.7 l/h PA0 Aerosil solution containing 150 g of SiO.sub.2 /l at 1.3 l/h PA0 Adjuvant solution containing 12% of oxides at 0.75 l/h The borosilicate matrix, obtained in the form of a gelled solution, is dried for 24 h at 105.degree. C. and then calcined for 3 h at 350.degree. C.. The solid particles taken from the furnace have a large specific surface area which varies from test to test but is always close to 50 M.sup.2 /g. After cooling, these particles are poured into the effluent to be treated and the mixture is stirred for 2 h. A gelatinous mass is formed, which is dried at 105.degree., calcined at 400.degree. C. and finally melted at 1150.degree. C. Chemical analysis gives the following average composition: ______________________________________ SiO.sub.2 45.6% B.sub.2 O.sub.3 14% Na.sub.2 O 10% Al.sub.2 O.sub.3 4.9% CaO 4% Li.sub.2 O 2% Fe.sub.2 O.sub.3 2.9% MnO.sub.2 0.95% BaO 0.55% CaO 0.5% Cs.sub.2 O 1% SrO 0.35% Y.sub.2 O.sub.3 4% MoO.sub.3 2% P.sub.2 O.sub.5 0.3% ______________________________________ Example 3: 3rd case Test 1 The following are introduced simultaneously into a 2 l mixer in 1/2 h: 1.4 kg of mixture are obtained; this is dried at 100.degree.-105.degree. in an oven on a plate, then calcined for 3 h at 350.degree. and finally melted. 320 g of this inactive calcined matrix are added to 135 g of a calcinate of FP and the two are roughly mixed. A melting time of 2 h at 1100.degree. C. is required to give 300 g of a glass of the desired composition (that of Examples 1 and 2). This example shows that it is possible to prepare a calcined gel having the same composition as the glass frit used in the AVM process. Test 2 Here it is desired to vitrify a mixture of solution of FP+soda effluent. This is done by preparing a calcined matrix having a composition similar to the glass frit of the AVM process, except for the sodium: the sodium oxide level is reduced from 7% to 2.6%. The solution of vitrification adjuvant will have the following composition: ______________________________________ Corresponding Product used Quantity in grams weight of oxide ______________________________________ NaNO.sub.3 55.1 20.1 Al(NO.sub.3).sub.3.9H.sub.2 O 243.6 33.1 Zn(NO.sub.3).sub.2.6H.sub.2 O 91.4 25.0 Ca(NO.sub.3).sub.2.4H.sub.2 O 170.1 40.4 LiNO.sub.3 91.4 19.8 ZrO.(NO.sub.3).sub.2.2H.sub.2 O 11.7 5.4 ______________________________________ The matrix will be completed using: as the source of silicia: Ludox AS40 PA1 as the source of boron: a boric acid solution containing 130.5 g per 1000 g of water, kept at 60.degree. C. PA1 solution of vitrification adjuvant: 5 kg/h PA1 solution of Ludox: 9.5 kg/h PA1 solution of boric acid: 5.8 kg/h PA1 (1) Ludox AS40 at 65.degree. C., 1150 g PA1 (2) ATB.9H.sub.2 O at 65.degree. C. in solution at the saturation limit (about 40 g/100 g of water), 312 g PA1 (3) a solution of vitrification adjuvant practically saturated with lithium and sodium nitrates at 65.degree. C., containing 225 g of NaNO.sub.3 and 87.5 g of LiNO.sub.3 in 250 g of water. The following flow rates are delivered simultaneously to the turbine with three pumps: Practically 20 kg of a gel are recovered in one hour; this is dried on a plate in an oven at 100.degree.-105.degree. C. and then calcined at 400.degree. C. (with gradual increase in temperature and a plateau at 200.degree. C.). This gives a solid mass composed of irregular pieces of a few cm.sup.3. These are ground to a uniform size and sieved with a 2.5 mm mesh. Analysis of this calcined product gives: ______________________________________ SiO.sub.2 61.6 (% by weight) B.sub.2 O.sub.3 19 (% by weight) Na.sub.2 O 2.7 (% by weight) Al.sub.2 O.sub.3 4.5 (% by weight) ZnO 3.4 (% by weight) CaO 5.5 (% by weight) Li.sub.2 O 0.75 (% by weight) ______________________________________ This analysis can be seen to be very similar to the formulations of the typical frit used in the AVM process as regards all the constituents except sodium. The ratio of silica to boric oxide is equal to 3.244 in the theoretical formula and 3.242 in the calcined gel. The ratio of silicia to alumina is equal to 13.75 in the theoretical formulation and 13.69 in the calcined gel. By contrast, the ratio of silica to sodium is equal to 8.407 in the theoretical formulation and 22.82 in the calcined gel. The sodium level is 7% in the theoretical formula and 2.7% in the calcined gel. Thus, a mixture of solution of FP+soda effluent can be treated by vitrification while preserving a normal sodium level for the final glass, as shown in the remainder of the example. 2500 g of a solution of sodium nitrate containing 100 g/kg, simulating the soda effluent, are added to 10 liters of the solution simulating the FP (as described in Example 1). (Sodium nitrate is used because the solution simulating the FP contains no free nitric acid, which is unrealistic.) The mixture is dried at 105.degree. C. on a plate in an oven and then calcined at 400.degree. C. in a small furnace to give a powder consisting of grains of a few millimeters, which represent the calcinate of (FP+soda effluent) and which we will refer to as the calcinate. 375 g of the said calcinate are carefully mixed dry with 1000 g of the calcined gel. The mixture is introduced in several portions into a crucible placed in a furnace regulated at 1100.degree. C. Complete melting in 5 hours is followed by pouring. Very slight marbling is observed on the surface, which undoubtedly corresponds to traces of molybdate but is entirely acceptable. Analysis shows that the glass contains 10.2% of Na.sub.2 O for 46% of silica, i.e. a ratio of silica to sodium of 4.5, whereas this ratio is equal to 4.56 in the typical formulation of the final glass. This example demonstrates the possibility of producing, as required, a calcined gel having a composition which is difficult to obtain in the form of a glass frit, and in particular the possibility of producing a low-sodium calcined gel which enables the solution of FP and the soda effluent to be vitrified at the same time. Example 4 This is an attempt to prepare 1 kg of glass immobilizing radioactive waste (solutions of FP), using an inactive matrix of the following composition: ______________________________________ SiO.sub.2 63.4% B.sub.2 O.sub.3 22.7% Na.sub.2 O 11.3% Li.sub.2 O 2.6% ______________________________________ This matrix is prepared by mixing the following solutions in a turbine: This gives a gelled solution which changes to a gel and is dried at 150.degree. C. for 24 h. The solution of FP to be treated in this example is simulated by dissolving the following compounds in 1400 g of water: ______________________________________ Sr(NO.sub.3).sub.2 6.7 g ZrO(NO.sub.3).sub.2.2H.sub.2 O 29.3 g Mn(NO.sub.3).sub.2.4H.sub.2 O 30.3 g Mo 11.3 g Te 1.4 g CsNO.sub.3 13.1 g Ba(NO.sub.3)2 8.7 g Y(NO.sub.3).sub.3.6H.sub.2 O 4.3 g La(NO.sub.3).sub.3.6H.sub.2 O 23.9 g Ce(NO.sub.3).sub.3.6H.sub.2 O 25.1 g Pr(NO.sub.3).sub.3.4H.sub.2 O 12.3 g Nd(NO.sub.3).sub.3.6H.sub.2 O 45.6 g Fe(NO.sub.3).sub.3.9H.sub.2 O 151.8 g Al(NO.sub.3).sub.3.9H.sub.2 O 448.5 g Mg(NO.sub.3).sub.2.6H.sub.2 O 356.1 g Cr(NO.sub.3).sub.3.9H.sub.2 O 21.1 g Ni(NO.sub.3).sub.2.6H.sub.2 O 17.1 g LiNO.sub.3 87.5 g ______________________________________ 240 g of commerical nitric acid (65% by weight) are added to this solution. The solution obtained is stirred for 1 hour, then dried for 24 hours at about 150.degree. C. and then calcined for 4 hours at about 400.degree. C. The resulting calcinate of FP and dried gel are then introduced simultaneously into a crucible. The mixture is melted at 1025.degree. C. for 5 hours. The glass obtained has the following composition: ______________________________________ SiO.sub.2 46% Cs.sub.2 O 0.95% B.sub.2 O.sub.3 16.5% BaO 0.51% Na.sub.2 O 8.2% Y.sub.2 O.sub.3 0.14% Li.sub.2 O 3.8% La.sub.2 O.sub.3 0.90% SrO 0.33% Ce.sub.2 O.sub.3 0.95% ZrO.sub.2 1.35% Pr.sub.6 O.sub.11 0.51% MnO.sub.2 1.05% Nd.sub.2 O.sub.3 1.75% MoO.sub.3 1.7% Fe.sub.2 O.sub.3 3% TeO.sub.2 0.17% Al.sub.2 O.sub.3 6.1% NiO 0.44% MgO 5.6% Cr.sub.2 O.sub.3 0.4% ______________________________________ This glass shows no precipitates or traces of molybdate on the surface. In the tests described, concentrated solutions were prepared (some even being close to saturation point) so as not to increase the drying times or the volumes of liquid to be handled. For reasons of pumping and flows in particular, it may be necessary to dilute these solutions more, but this has no adverse effect on the process. The process developed by the Applicant Company therefore differs from the processes described previously, especially the Westinghouse process. The Applicant Company considers that it has succeeded in preparing, in an aqueous medium, a borosilicate matrix which is ready to be employed for the treatment of nuclear waste, by virtue of the solutions and stirring method used. Stirring at a high rate of shear makes it possible to achieve thixotropic mixing and homogeneity. As soon as stirring stops, the viscosity increases and polymerization rapidly develops, thus "freezing" the ions before they can react (for example precipitation, sedimentation). The process forming the subject of the invention offers an important advantage when operated industrially in a nuclear environment: the matrix is prepared in an inactive environment, so the whole of this part of the process is not subject to the rigid and essential constraints to be observed in an active environment, and the technologies conventionally used in the chemical industry can be employed without modification. Furthermore, the second part of the process (heat treatment with introduction of the waste) can utilize, practically without modification, the existing production lines which are already installed and work with the oxides.