Patent Number: 045444994
Section: description

The following examples are presented. Unless otherwise specified all solutions are aqueous solutions, the "aqueous ammonium hydroxide" or "NH.sub.4 OH" wherever used in the Examples contains about 28% NH.sub.3, ppm means parts per million parts of solution, ppb means parts per billion parts of solution, ppt mean parts per trillion parts of solution, all parts and percentages are on a weight bases, all temperatures are given in degrees Centigrade, and anion exchange tests were carried out at room temperature and at a pH of 6 unless otherwise indicated. EXAMPLE 1 This example illustrates the preparation of the porous glass that is used in the subsequent examples. In the subsequent examples, unless otherwise specified, the porous glass that is used is in the form of cylinders or rods 6 to 9 mm in diameter and one to several centimeters in length. The porous glass is formed by the method disclosed hereinabove; that is, a mixture of powders of silica, boric acid, sodium carbonate and potassium carbonate is prepared in such proportions that yield a glass nominally comprising 3.5 mol percent Na.sub.2 O, 3.5 mol percent K.sub.2 O, 33 mol percent B.sub.2 O.sub.3 and 60 mol percent SiO.sub.2. The mixture is heated in a Pt crucible up to 1400.degree. C. in an electric furnace and thus is melted into a molten glass which is pulled into rods about 8 mm in diameter and cut to about 2.5 cm long. After cooling, the glass is phase-separated by heat treating at 550.degree. C. for 2 hours and then is leached in a 3N HCl bath at 95.degree. C. for three days. Phase-separation results in two phases; one, a high silica phase and a low silica phase comprising the remaining silica, boron trioxide and alkali metal oxide. Leaching removes the boron-rich phase leaving behind a porous glass comprising about 95 mol percent SiO.sub.2 and about 5 mol percent B.sub.2 O.sub.3 and having interconnected pores and at least about 3 mol percent silicon-bonded hydroxyl groups. Subsequent rinsing in water yields a porous glass preform ready for use in the following examples. EXAMPLE 2 In this example, there is described the use of an organofunctionalsilane possessing a single-NH.sub.2 functional group, namely, the gamma-aminopropyltriethoxysilane to alter the surface characteristics of the porous glass so as to give it anion exchange capability when hydrated. Six 1" porous glass rods prepared as described in Example 1 were soaked in an aqueous solution containing 2% gamma-aminopropyltriethoxysilane by weight of the solution at 5.degree. C. for 5 hours. This aqueous solution was prepared by first forming a dilute aqueous ammonium hydroxide solution having a pH of about 9, cooling it to a temperature of about 5.degree. C. and then introducing the above-mentioned silane. The treated porous glass rods were then dried under vacuum at 5.degree. C. for 18 hours, allowed to warm to room temperature, and finally were heated from room temperature to 200.degree. C. in order to react the silicon-bonded ethoxy groups of the silane with the silicon-bonded hydroxy groups of the glass to form .tbd.SiOSi.tbd. bonds between the glass and the silane, thus bonding the silane to the glass surface. Two anion-containing test media were prepared comprising 100 ml of an aqueous solution containing 56.0 ppm CrO.sub.4.sup.-2 and a 100 ml of an aqueous solution containing 41.8 ppm MoO.sub.4.sup.-2. Three glass rods treated as described above were immersed in the chromate solution and three were immersed in the molybdate solution. The decreases of CrO.sub.4.sup.-2 and MoO.sub.4.sup.-2 anions in the respective solutions due to anion-exchange into the glass rods were measured against soaking time. The results are shown in Table 3 below. TABLE 3 ______________________________________ Soaking Time CrO.sub.4.sup.= MoO.sub.4.sup.= (hrs) Concentration (ppm) Concentration (ppm) ______________________________________ 0 56 41.8 1 54.5 35 2 53 28 3 52 21 11 44.5 11 24 44 6 ______________________________________ These results illustrate the effectiveness of the treated porous glass rods in removing anions from highly dilute aqueous solutions and illustrates the special effectiveness with respect to the molybdate solution. The anion exchange capacity of the treated porous glass rods for the chromate anion would be capable of removing radioactive chromate anions from very large volumes of radioactive coolants (typically containing 4.times.10.sup.-9 ppm of Cr as CrO.sub.4). For example, it would be capable of removing chromate anions from 7.times.10.sup.8 cc of coolant per cc of treated porous glass on a calculated basis. EXAMPLE 3 The procedure of Example 2 was repeated except that: (i) the organofunctionalsilane had one --NH.sub.2 group and one .dbd.NH group; specifically, N-beta-aminoethyl-gamma-aminopropyltrimethoxysilane was used here to change the surface characteristics of the porous glass; (ii) the silane concentration in the glass rod treatment step was 4% instead of 2%; and (iii) the anion concentrations of the anion-containing media were initially 52.4 ppm CrO.sub.4.sup.-2 and 45.4 ppm MoO.sub.4.sup.-2, respectively. The results of the anion exchange test are given in Table 4 below. TABLE 4 ______________________________________ Soaking Time CrO.sub.4.sup.= MoO.sub.4.sup.= (hrs) Concentration (ppm) Concentration (ppm) ______________________________________ 0 52.4 45.4 1 43 19 2 41 10 4 34.5 4 24 36 4.5 ______________________________________ These results illustrate the effectiveness of the treated porous glass rods in removing anions from highly dilute aqueous solutions and illustrate the special effectiveness of the treated porous glass rods in respect to the molybdate solution. EXAMPLE 4 This example illustrates the treatment of porous glass which is provided with anion exchange capability by hydrous zirconium bonded through oxy groups to silicon of the glass. Two 3" porous glass rods prepared as described in Example 1 were immersed in an 11.7% Zr(NO.sub.3).sub.4.5H.sub.2 O aqueous solution at room temperature for 17 hours thus allowing the Zr(NO.sub.3).sub.4 to diffuse inside the pores of the glass. The stuffed rods were then transfered to an oven at 100.degree. C. for 11/2 hours to evoke precipitation of the Zr salt by evaporation of the water. Finally the rods were heated to 200.degree. C. under vacuum to decompose the nitrate within the glass pores into zirconium oxide which hydrates in the presence of water to impart anionic exchange capability. It is believed that the hydrated zirconium atoms bonded to each other in the form of crystals and that some of the zirconium atoms are bonded to silicon of the glass rod through divalent oxygen linkages. Two anion-containing test media were prepared comprising 100 ml of an aqueous solution of 56.0 ppm CrO.sub.4.sup.-2 and 100 ml of an aqueous solution of 41.8 ppm MoO.sub.4.sup.-2. One treated rod was immersed in the chromate solution to remove CrO.sub.4.sup.-2 therefrom and the other rod was immersed in the molybdate solution to remove MoO.sub.4.sup.-2 ions therefrom. The results are given in Table 5 below. TABLE 5 ______________________________________ Soaking Time CrO.sub.4.sup.= MoO.sub.4.sup.= (hrs) Concentration (ppm) Concentration (ppm) ______________________________________ 0 56 41.8 1 48.5 40 2 42.5 33.5 4 26 27 11 15 16 24 8 10 ______________________________________ These results show that the hydrated zirconium oxide treated porous glass rods are highly efficient in removing chromate and molybdate anions from very dilute solutions containing same. These rods were heated to 850.degree. C. to collapse the pores thus permanently fixating the exchanged anions (CrO.sub.4.sup.= and MoO.sub.4.sup.=) into the glass structure. EXAMPLE 5 The procedure of Example 4 was repeated except that: Hydrous oxides of lead instead of zirconium were impregnated into the porous glass by molecular stuffing with Pb(NO.sub.3).sub.2, then precipitating the salt at 100.degree. C., and finally decomposing the nitrate at 500.degree. C. and then hydrating. The concentration of the aqueous stuffing solution was 45% Pb(NO.sub.3).sub.2 at 95.degree. C. The results of removal by anion exchange of the anions from the anion-containing test media are given in Table 6 below. TABLE 6 ______________________________________ Soaking Time CrO.sub.4.sup.= MoO.sub.4.sup.= (hrs) Concentration (ppm) Concentration (ppm) ______________________________________ 0 56 42 1 48.5 39 2 47 36 4 46 36 11 43.5 33.5 24 41 31 ______________________________________ These results show that hydrated lead oxide treated porous glass rods are effective in removing chromate and molybdate anions from dilute solutions containing same. EXAMPLE 6 This example illustrates the anchoring of an insoluble salt moiety, namely --OZr(OH).sub.3 to silicon of porous glass and then making use of the zirconium-bonded OH groups to ion exchange with other anions. A 2" porous glass rod prepared as described in Example 1 was immersed in a solution containing 14 g NaNO.sub.3, 12 ml NH.sub.4 OH and 38 ml H.sub.2 O at room temperature for 17 hours to exchange the protons of the silicon-bond hydroxyl groups on the glass surface for Na ions in the ammonia base solution. The rod was washed afterwards to remove any excess Na.sup.+. The washed rod was then soaked in a 17% Zr(NO.sub.3).sub.4.5H.sub.2 O aqueous solution for 24 hours at room temperature to exchange Zr.sup.+4 for Na.sup.+. Finally, the Zr(NO.sub.3)-exchanged rod was immersed in a 24% NH.sub.4 OH solution at room temperature for 17 hours to replace the NO.sub.3 groups with the OH groups of the ammonia solution. Subsequently, the rod was washed free of excess ammonia and was immersed in a chromate anion exchange medium initially containing 13.1 ppm CrO.sub.4.sup.-2. The decrease of CrO.sub.4.sup.-2 ions in the solution due to ion-exchange vs. soaking time is shown in Table 7 below. TABLE 7 ______________________________________ Soaking Time CrO.sub.4.sup.= (hrs) Concentration (ppm) ______________________________________ 0 13.1 4 12 24 11 ______________________________________ These results show the anionic porous glass rods of this Example to be effective in removing anions from dilute solutions containing same and are capable of treating very large volumes of dilute radioactive coolants to remove radioactive anions therefrom. EXAMPLES 7-11 The procedures described for Examples 2 through 6 are respectively carried out in Examples 7 through 11 except that the chromate and molybdate anions used in the test media are radioactive; otherwise all steps, proportions, materials and conditions are the same. The concentrations of radioactive anions chemically bound in the final glass product are essentially the same as those concentrations correspondingly given in Tables 3-7. EXAMPLE 12 This example illustrates a method for treating primary coolant from a pressurized water nuclear reactor plant. A mixture of powders of silica, boric acid, sodium carbonate and potassium carbonate is prepared in such proportions that yield a glass comprising 3.5 mol percent Na.sub.2 O, 3.5 mol percent K.sub.2 O, 33 mol percent B.sub.2 O.sub.3 and 60 mol percent SiO.sub.2. The mixture is heated in a platinum crucible up to 1400.degree. C. in an electric furnace to produce a molten glass which is pulled into rods about 8 mm in diameter. The glass rods are cooled and the glass is phase-separated by heat treating at about 550.degree. C. for about 110 minutes. The rods are then crushed to form a powder which is sieved through a 32 mesh screen onto a 150 mesh screen. The glass particles collected on the 150 mesh screen are leached in 3NHCl at about 80.degree. C. for about 6 hours to remove the boron-rich phase and leave behind a porous glass comprising about 95 mol percent SiO.sub.2 and about 5 mol percent B.sub.2 O.sub.3. The porous glass has interconnected pores and contains at least about 5 mol percent silicon-bonded hydroxyl groups. The glass particles are then rinsed in deionized water until the rinse water reaches a pH of about 7. The porous glass powder is then immersed in an approximate 3.2 molar lithium nitrate-ammonium hydroxide aqueous solution (1 part ammonium hydroxide to 3 parts water) for three days and then is rinsed in water until the pH of the rinse water is reduced to about 8. The resulting powder is then placed into a Vycor glass* tube plugged with a filter at the bottom to prevent the powder from escaping, thus forming an ion exchange column. A radioactive primary coolant from a pressurized water nuclear reactor plant utilizing UO.sub.2 fuel clad in stainless steel (containing 4.9 weight percent .sup.235 U) is passed through the column. The primary coolant has the composition of 100 ppm boron, 1 ppm lithium, about 100 ppb silica and the radionucleides listed in Table 8 below which lists the radionuclide, the probable source, the probable form and the average concentration in microcuries per milliliter. FNT *Vycor brand silica glass No. 7913 made by Corning Glass Works and containing 96 wt. % silica and 4 wt. % B.sub. 2 O.sub.3. TABLE 8 ______________________________________ Average Average Radio- Probable Probable Concentra- Concentra- nuclide Source.sup.a Form.sup.b tion (uCi/ml) tion (ppb) ______________________________________ 3.sub.H (1),(2) Water, gas 2.4 0.249 14.sub.C 1.2 .times. 10.sup.-5 2.69 .times. 10.sup.-3 24.sub.Na (1) Cation 1.9 .times. 10.sup.-2 2.18 .times. 10.sup.-6 32.sub.p 3.3 .times. 10.sup.-5 1.16 .times. 10.sup.-8 35.sub.S 3 .times. 10.sup.-6 7.08 .times. 10.sup.-8 51.sub.Cr (1) Anion 3.7 .times. 10.sup.-4 4.02 .times. 10.sup.-6 54.sub.Mn (1) Cation, s 2.7 .times. 10.sup.-4 3.38 .times. 10.sup.-5 55.sub.Fe (1) Cation, s 1.9 .times. 10.sup.-4 7.6 .times. 10.sup.-5 59.sub.Fe (1) Cation, s 1.0 .times. 10.sup.-5 2.03 .times. 10.sup.-7 57.sub.Co (1) Cation, s 1.2 .times. 10.sup.-6 1.42 .times. 10.sup.-7 58.sub.Co (1) Cation, s 4.7 .times. 10.sup.-4 1.48 .times. 10.sup.-5 60.sub.Co (1) Cation, s 7.7 .times. 10.sup.-5 6.81 .times. 10.sup.-5 63.sub.Ni (1) Cation, s 8.0 .times. 10.sup.-6 1.30 .times. 10.sup.-4 64.sub.Cu (1) Cation, anion, s 5.4 .times. 10.sup.-4 1.41 .times. 10.sup.-7 89.sub.Sr (2) Cation 2.8 .times. 10.sup.-6 9.93 .times. 10.sup.-8 90.sub.Sr (2) Cation 4 .times. 10.sup.-7 2.84 .times. 10.sup.-6 91.sub.Sr (2) Cation 9.8 .times. 10.sup.-5 2.76 .times. 10.sup.-8 90.sub.Y (2) s 91.sub.Y (2) s 92.sub.Y (2) s 95.sub.Zr (1),(2) s 1.7 .times. 10.sup.-5 8.06 .times. 10.sup.-7 95.sub.Nb (1),(2) s 1.9 .times. 10.sup.-5 4.83 .times. 10.sup.-7 99.sub.Mo (1),(2) Anion 1.2 .times. 10.sup.-4 2.54 .times. 10.sup.-7 103.sub.Ru (2) s 0 106.sub.Ru (2) s 0 122.sub.Sb (1) s 1.0 .times. 10.sup.-4 2.62 .times. 10.sup.-7 124.sub.Sb (1) s 2.0 .times. 10.sup.-5 1.16 .times. 10.sup.-6 132.sub.Te (2) Anion, s 131.sub.I (2) Anion 4.6 .times. 10.sup.-5 3.71 .times. 10.sup.-6 132.sub.I (2) Anion 133.sub.I (2) Anion 6.2 .times. 10.sup.-4 5.5 .times. 10.sup.-7 135.sub.I (2) Anion 9 .times. 10.sup.-4 2.60 .times. 10.sup.-7 134.sub.Cs (2) Cation 4.7 .times. 10.sup.-7 3.62 .times. 10.sup.-7 136.sub.Cs (2) Cation 0 137.sub.Cs (2) Cation 1.1 .times. 10.sup.-6 1.26 .times. 10.sup.-5 140.sub.Ba (2) Cation 4.7 .times. 10.sup.-6 6.45 .times. 10.sup.-8 141.sub.Ce (2) Anion, s 0 143.sub.Ce (2) Anion, s 0 144.sub.Ce (2) Anion, s 0 143.sub.Pr (2) Anion, s 110m.sub.Ag (1) s 1.2 .times. 10.sup.-5 2.52 .times. 10.sup.-6 181.sub.Hf (1) s 6 .times. 10.sup.-6 3.70 .times. 10.sup.-7 182.sub.Ta (1) s 2.5 .times. 10.sup.-5 4.01 .times. 10.sup.-6 183.sub.Ta (1) s 6.2 .times. 10.sup.-5 4.34 .times. 10.sup.-7 185.sub.W (1) s 1.2 .times. 10.sup.-5 1.28 .times. 10.sup.-6 187.sub.W (1) s 3.7 .times. 10.sup.-4 5.30 .times. 10.sup.-7 85m.sub.Kr (2) Gas 85.sub.Kr (2) Gas 88.sub.Kr (2) Gas 133.sub.Xe (2) Gas 8.9 .times. 10.sup.-5 4.78 .times. 10.sup.-8 135.sub.Xe (2) Gas 9 .times. 10.sup.-5 3.54 .times. 10.sup.-8 ______________________________________ .sup.a (1) Neutron activation products of nuclides from fuel cladding, construction material, and water. (2) Leakage from fuel. Mostly fission products. .sup.b Gas: presumably as dissolved gas. s: insoluble solids. The radioactive cations listed in Table 8 cation-exchange with lithium cations bonded to silicon through oxy groups in the porous glass thereby binding the radionuclides to the porous glass through said silicon-bonded oxy groups and releasing lithium cations to the coolant solution. The insoluble radioactive solids in the coolant also filter out on the external surfaces of the porous glass particles. Additional porous glass particles can be added to increase the filtering capacity of the ion exchange column as the insoluble solids build-up in the column. Under some conditions, mainly dependent on existing governmental regulations, the porous silicage glass containing bound cationic radionuclides may be disposed and/or buried or suitably containerized often times in steel and/or concrete or mixed with cement powder or urea-formaldehyde formulations and "set" therein and thereafter disposed and/or buried. The particulate porous glass can be heated to collapse the pores thereof as described herein. The anionic radionuclides are not substantially removed in the above-mentioned column and pass with the coolant through the column. The anionic radionuclides are subsequently removed by passing the coolant through a glass column packed with any one of the porous glass anion exchangers described in Examples 2-6. The glass column is prepared as follows: An open porous tube is prepared by pulling a glass tube of the same composition as described in Example 1 and phase-separated and leached as in Example 1, and having an outside diameter of 10 mm and a wall thickness of .about.1 mm. The porous tube is then soaked in a solution saturated with CsNO.sub.3 with enough NH.sub.4 OH to give a pH of 10 for 18 hrs, and washed in room temperature water until a pH of 7 is obtained. The Cs exchanged tube is subsequently dried under vacuum and is heated from room temperature to 600.degree. C. at 15.degree. C./hr and from 600.degree. C. to 870.degree. C. at 50.degree. C./hr to collapse the pores. When the porous anion exchange glass becomes loaded with anionic radionuclides, the entire column containing the loaded porous anion exchange glass is removed from the system and a fresh column is substituted. The loaded column is held in a safe location for three months to allow the I.sup.131 to completely decay, a precaution taken to avoid evaporation of I.sub.131 during subsequent heat treatments. Thereafter, the porous glass particles can be heated to collapse the pores thereof and, if desired, the column can be heated to collapse the glass tube around the particles thereby enveloping the filtered solids and the glass particles containing the cationic and anionic radio-nuclides within the glass column. While the glass column may crack because of differential thermal contraction, it still contains and further immobilizes the radioactive materials and forms a product that is many times more durable than cement or metal drums heretofore used. There is thus provided a durable package of concentrated radionuclides which is highly resistant to leaching by water or other fluids. As illustrated in Example 12, liquid radwaste that must be satisfactorily treated and disposed of can be highly dilute. The volume of dilute radwaste treated with a given amount of ion exchange porous glass or silica gel pursuant to this invention can be practically unlimited before all the available exchange sites (i.e. silicon-bonded alkali metal oxy, Group Ib, metal oxy, ammonium oxy, hydroxy ammonium organosiloxy, hydrous polyvalent metal oxy and carboxyorganosiloxy groups) in the porous silicate glass or silica gel are filled by radioactive cations. For Example, the weight of the dilute liquid radwaste described in Example 12 that could be expected to be treated before exhausting all exchange sites would be of the order of 10.sup.9 or more times the weight of the ion exchange porous glass or silica gel employed. Futhermore, it could be expected that other parts of the system would require overhaul, e.g., repair or replacement of pumps or piping or other equipment, before the ion exchange silicate glass or silica gel becomes exhausted. Consequently, it is quite possible, if not probable, that the radioactivity of the resulting porous glass or silica gel when disposed of may never reach 1 millicurie or even 1 microcurie per cc. of the glass or silica gel. In the absence of malfunction requiring overhaul of the other parts of the radwaste treatment system, 100 or less to 10.sup.9 or more, preferably 100 to 10.sup.6, weight parts of radwaste can be treated for each weight part of porous silicate glass or silica gel having silicon-bonded anion and/or cation exchange groups pursuant to this invention. For reasons of safety all simulated radwaste solutions used in the Examples were actually non-radioactive; however, radioactive solutions of the same kind can be substituted and concentrated and encapsulated in accordance with the foregoing Examples. EXAMPLE 13 In this example, there is described the use of particles of cation-exchange porous glass possessing a carboxyl functional group, namely ##STR14## groups, bonded to silicon of porous silicate glass on the internal surfaces of the pores thereof. Porous glass of this type is purchased from the Pierce Chemical Company, POB 117, Rockford, Ill. 61105. The glass particles containing the above-mentioned functional groups are immersed in an aqueous solution containing 10 ppm radioactive strontium cations (2.35 mg strontium per 100 ml H.sub.2 O) at about 25.degree. for about three days while occasionally stirring the solution. After this period of soaking the particles are removed and dried at room temperature. After the soaking period the solution is analyzed by atomic absorption for strontium and has a lower concentration of strontium illustrating the effectiveness of the carboxy organosiloxy group containing glass in removing radioactive cations from aqueous solutions containing same. EXAMPLE 14 This example illustrates the treatment of porous glass which is provided with anion exchange capability by hydrous titanium bonded through oxy groups to silicon of the glass as well as hydrous titanium oxides which are molecular stuffed in the pores of a glass matrix. Six 2" long porous glass rods prepared as described in Example 1 were immersed in a solution of 18 g TiO.sub.2 and 100 ml of 3N HNO.sub.3 at room temperature for about 65 hours thus allowing the TiO.sub.2 to become Ti(NO.sub.3).sub.4 and to diffuse inside the pores of the glass. Four of the resulting six stuffed rods were then transferred to an oven at 200.degree. C. for 2 hours under vacuum to dry the rods by evaporation of the water as well as to decompose the titanium nitrates residing in the pores of the glass. Two other rods were put into NH.sub.4 OH for 2 hours at room temperature and then evacuated for 2 hours at room temperature to dry them and subsequently were heated gradually from 200.degree. C. to 400.degree. C. to decompose the nitrates and precipitate Ti in the oxide form. All six rods were black indicating the presence of some reduced Ti.sup.+3 (e.g. Ti.sub. 2 O.sub.3). The titanium oxides within the pores hydrate upon contact with water (e.g., from the atmosphere or from the aqueous radwaste solution or otherwise) to impart anion exchange capability. It is believed that some of the hydrated titanium atoms are bonded to each other in the form of crystals and that some of the titanium atoms are bonded to silicon of the glass rods through oxy linkages. Two anion-containing test media were prepared comprising 35 ml of an aqueous solution of 5.5 ppm CrO.sub.4.sup.-2 and 35 ml of an aqueous solution of 31.7 ppm MoO.sub.4.sup.-2. Two treated rods from the first group were immersed in the chromate solution to remove CrO.sub.4.sup.-2 therefrom and the other two rods from the first group were immersed in the molybdate solution to remove MoO.sub.4.sup.-2 ions therefrom. The results are given in Table 9 below. TABLE 9 ______________________________________ Soaking Time CrO.sub.4.sup.= MoO.sub.4.sup.= (hrs.) Concentration (ppm) Concentration (ppm) ______________________________________ 0 5.5 31.7 1 4.6 14.8 2 3.7 7.2 6 2.2 2.7 19 0.8 1.4 ______________________________________ Similarly, one treated rod from the second group (of two rods) was immersed in an identical chromate solution to remove CrO.sub.4.sup.-2 therefrom and the other rod from the second group was immersed in an identical molybdate solution to remove MoO.sub.4.sup.-2 therefrom. The results are given in Table 10 below. TABLE 10 ______________________________________ Soaking Time CrO.sub.4.sup.= MoO.sub.4.sup.= (hrs.) Concentration (ppm) Concentration (ppm) ______________________________________ 0 5.5 31.7 1 5.3 29.9 2 4.6 27.3 6 3.7 21.4 19 1.7 11.2 ______________________________________