PROCEDURE FOR MANUFACTURING TITANATES

Abstract: The raw material in the manufacturing of titanates is the intermediate in the titanium dioxide pigment industry, titanium dioxide hydrate, which is suspended in water and alcohol; and after heating, a base is added to the boiling mixture. It is possible by varying the reacting base to vary the selectivity of the product to different metals. The titanates have high capacities for waste nuclides; they are suitable to be converted into ceramics; and they have a very good radiation tolerance.

Description: Procedure for manufacturing titanates The invention concerns a procedure for manufacturing titanates. In nuclear energy production, and also in the production and use of radionuclides, radioactive waste solutions are produced in ample quantity. The aim is, by treatment of these wastes, both to reduce their volume and to solidify them for easier subsequent handling and storing. The use of ion exchangers is one of the most important ways to bind radionuclides from waste solutions. Organic ion exchangers, which are employed in cleaning the primary circuits of nuclear reactors, are however not suited for use in solidifying high-active waste because they cannot tolerate high radiation doses. Instead, organic ion exchangers are used in solidifying power plant waste, the ion exchangers loaded with waste being immobilized, most commonly, in cement or bitumen. Inorganic ion exchangers, which group also includes titanates, are better appropriate for solidifying especially high-active waste. They tolerate radiation well as a rule. They may be used, for instance - as ion exchangers for cleaning the primary circuit of the reactors - for solidifying the waste nuclides eluted from organic ion exchange resins removed from the reactor's primary circuit - for solidifying evaporator concentrates • - for solidifying waste solutions accruing at decommissioning or repairs of a nuclear power plant - for solidifying high-active reprosessing waste. The ultimate object of nuclear waste treatment is to achieve a low-soluble, both mechanically durable and radiation and heat resistant final waste product. Inorganic ion exchangers are OMPI converted into final waste product either as they are at high pressure and temperature, or by admixing to them vitrifying or ceramizing substances before they are heated. The state of the titanate manufacturing technology is illustrated by the British Patent No. 1.493.698 (Sandia Laboratories, U.S.A.) and by U.S. Patent No. 4.161.513 (PRAV Project, Sweden). However, the manufacturing procedures disclosed in these patents present the drawback of costliness and complexity of the titanate syntheses. In the syntheses expensive chemicals are required and they are in multiple steps. Moreover, the procedure of the first- mentioned patent is encumbered by the drawback that the synthetized sodium titanate loses half of its ion exchange capacity under a 10 Gy gamma radiation dose. Titanates are inorganic ion exchangers. They have the structure of hydrous oxides. In the procedure of GB Patent No. 1.493.698, sodium titanate is synthesized as follows: (CH 3 ) 4 N0H + C 3 H ? 0) 4 i j, (CH 3 ) 4 N(Ti 2 0 5 ) + C^OH and further CH 3 4 (Ti 2 0 5 H + NaNO > (CH ) 4 NN0 3 + aCTi^H) (s) or alternatively as follows 9 i (-_ NaOH + (C 3 H ? 0) 4 i 2 ^ Na(Ti 2 0 H) + C H OH In the procedure of U.S. Patent No. 4.161.513, sodium titanate is synthesized from titanium tetrachloride and sodium hydroxide. The object of the invention is to achieve an improvement in proce¬ dures for the manufacturing of titanates known at present. The more detailed object of the invention is to provide a procedure OMPI which is substantially simpler and less expensive than any proce¬ dures of prior art. The other aims of the invention and the ad¬ vantages gainable with its aid will become apparent from the disclosure of the invention. The aims of the invention are achieved by a procedure which is mainly characterized in that the procedure comprises the following steps: (a) titanium dioxide hydrate is dissolved in a solvent; (b) the mixture is heated; and (c) a base giving off exchangeable cation to the titanium dioxide hydrate is added. The remaining characteristic features of the procedure of the invention are stated in claims 2-9. Numerous remarkable advantages are gained by the invention. First of all, the procedure of the invention offers a single-step titanate synthesis based on an inexpensive and readily available raw material, titanium dioxide hydrate, which is obtained e.g. as an intermediate in the titanium dioxide pigment industry, and on a simple process technology. The product obtained by the procedure of the invention, titanate, has high capacities for radionuclides; it tolerates radiation exceedingly well; and it can be ceramized to final waste product. The use of the invention is illustrated in detail in the attached drawing, but to the used depicted in which the invention is not meant to be exclusively confined. The drawing shows the procedure of the invention in the form of a synthesis scheme. In the procedure of the invention, the raw material of the titanate synthesis is titanium dioxide hydrate mass. The titanium dioxide hydrate mass is an intermediate from the manufacturing of titanium dioxide pigment, from the so-called sulphate process. Herein, ilmenite mineral (mineral formula FeTiO,) is allowed to react with hot concentrated sulphuric acid. The "extraction cake" OMPI obtained in this reaction is dissolved in water or in a weak acid, whereby a mixture of titanium sulphate and iron sulphates is pro¬ duced. The ferrisulphate is reduced to ferrosulphate and removed by filtering. The solution is then concentrated and the concentrated titanium sulphate solution is converted by hydrolysis to titanium dioxide hydrate, which is the initial substance for the titanate synthesis. Its dry matter content is about 40 J.. As a result of the process, it is exceedingly acidic. The titanium dioxide hydrate mass is suspended in water or in an organic solvent, e.g. ethanol, propanol or butanol, at weight pro¬ portions 1/10-1/5. The mixture is heated to the boiling point (water 100 C, water/ethanol 78 C, water/propanol 88 C, water/- 1-butanol 93 C) . A 20-40 % aqueous solution of an alkali or earth alkali metal hydroxide, such as NaOH, KOH or Ca(0H) 2 , NH„ or of an organic amine, such as hydrazine, mono, di or trimeth lamine, is slowly added at weight proportion 1/3-1/1 referred to the wet weight of the titanium hydrate. It is possible by varying the bases, or when several different bases are used in one synthesis by varying their proportions, to influence the sorption properties of the product, in particular its ion selectivity. After adding the base, the mixture is allowed to react at the boiling point of the azeotrope, with powerful agitation, 2-4 hours. The mixture is left to stand over night and filtered and washed with water for 1-2 days. Drying at 105-110 C for 24 hours. The product is cake-like and can be ground and sieved to separate the desired grain sizes. In the following is presented an example of sodium titanate syn¬ thesis in 1-butanol. 2.025 kg of titanium hydrate mass were suspended in 5 litres of 1-butanol. Heating to 93 C. Addition during 15 min. of 4.313 kg of 30 % aqueous NaOH solution. Allowed to react at the boiling point of the azeotrope with powerful agitation, 3 hours. Allowed to stand over night, filtrated and washed with water in a Soxhlet extraction apparatus for two days. Drying for one day at 110 C. The cake was ground and the different grain sizes were separated by sieving. The filtered, wet product had the weight 3890 g The product dried at 110°C had the weight 920 g Of grain fraction 0.315-0.850 mm was obtained 480 g In the following are presented some properties of the sodium titanate typically obtained by this procedure. One sodium titanate product has the chemical composition: Ti ' 37 % by weight Na 16 % by weight H 2 0 12 % by weight C °3= 5 % by weight SO. 1 % by weight 4 The rest hydrogen and oxygen. 2 This sodium titanate had specific surface area 12 m /g. The product in completed form is cake-like. It can be ground and the different grain sizes can be separated by sieving. The greater part of the grains obtained are suitable for column use, and the grains are mechanically durable enough. The finest granular material may be used for batch equilibrations. The strontium sorption half-time is dependent on the grain size of the sodium titanate, the half-time with grain size 0.071-0.140 mm being < 20 s, and with 0.350-0.850 mm grain size 95 s. With the first- mentioned grain size the distribution coefficient is also higher 4 than in the latter case by a factor over 4, i.e., 5.6 x 10 . The sorption capacities of sodium titanate are high. The capacities determined by column experiments are: for strontium 1.4 mmol/g, cesium 1.5 mmol/g and cobolt 1.8 mmol/g. The distribution coefficients increase powerfully with increasing pH, being at pH higher than 6: several ten thousand for strontium, several thousand for cobolt, but for cesium only from a few tens to hundreds. OMPI The sorption mechanism is not fully understood. The exchangeable ion in sodium titanate is sodium. Since Sr, Cs and Co exchange the stoichiometric quantity of sodium, this suggests chemical ion exchange. Sorption takes place in two steps. The greater part of the sorption is very rapid. At the second step the sorption is lower by one order of magnitude. The first step is believed to be exchange onto the surface of the grains and to the fine dust that is present. The second step would seem to be exchange into the grains. Sodium titanate tolerates radiation very well. A 10 Gy gamma dose has no effect on the sorption capacity, on structure, nor on the specific surface area. The finest granular material may be used in batch operation. This material is added to the waste solution and mixed during a couple of hours at the most. The material is then either separated e.g. by filtering, or red clay or other brick clay is admixed to it for baking. In the first instance, the filtered titanate is usually dried at a few hundred degrees and ceramized after grinding. Titanates may be used in columns either completely separated or to the purpose of binding the waste nuclides remaining in the residual solution from batch running. After the use, the material is removed from the column and it is usually dried, ground and ceramized. The evaporator waste concentrates of nuclear power stations have greatly variable origins. They present a high salt concentration as a rule. Titanates may best be applied to solidify them by equi- librating the waste and titanate in a batch, by thereafter adding brick clay and by preparing a brick. 4-M sodiuπ concentration, which corresponds to the true situation in evaporator wastes, lowers the distribution coefficient of strontium in sodium titanate by one order of magnitude. A boric acid concentration of 1-M, also consistent with actual situations, lowers the distribution coef¬ ficient of strontium by one order of magnitude. The capacity is still high enough in spite of salt concentrations as mentioned "&J E4 OMPI above. The organic ion exchangers removed from, the primary circuits of reactors are, on the side of the evaporator concentrates mentioned, the most important source of medium activity waste. At present they are usually embedded in concrete or bitumen. However, an alterna¬ tive possibility is to elute the waste nuclides from the resins and to bind them e.g. to titanate in columns. In the elution may be used complex-forming agents such as oxalates, citrates and EDTA. One possible eluant, sodium citrate, causes ' no substantial weakening of the sorption of strontium in sodium titanate. In contrast, EDTA significally lowers the sorption at pH over 6. OMPI

Claims: Claims 1. Procedure for manufacturing titanates, characterized in that the procedure comprises the following steps: (a) titanium dioxide hydrate is suspended in a solvent, (b) the mixture is heated, and (c) a base giving off exchangeable cation to the titanium dioxide hydrate is added. 2. Procedure according to claim 1, characterized in that water is used for solvent. 3. Procedure according to claim 1, characterized in that an organic solvent is used for solvent. 4. Procedure according to claim 3, characterized in that as organic solvent is used ethanol, propanol or butanol or a mixture of these. 5. Procedure according to any one of claims 1-4, characterized in that for cation-releasing base is used an aqueous solution of an alkali or alkaling earth metal hydroxide, such as NaOH, KOH or Ca(0H) 2 . 6. Procedure according to any one of claims 1-4, characterized in that for cation-releasing base is used ammonia or an aqueous solution of an organic amine, such as hydrazine, mono, di or trimethylamine. 7. Procedure according to any one claims 1-6, characterized in that after adding base giving off exchangeable cation to the titanium dioxide hydrate the mixture is mixed and the mixture is allowed to react during a few hours. 8. Procedure according to claim 7, characterized in that after reacting the mixture is left to stand over night. 9. Procedure according to claim 8, characterized in that the mixture is filtered, washed and dried.

Inventors: HEINONEN OLLI J, LEHTO JUKKA KALEVI, MIETTINEN JORMA KALERVO, HEINONEN, OLLI, J., LEHTO, JUKKA, KALEVI, MIETTINEN, JORMA, KALERVO
Applicants: HEINONEN OLLI J, LEHTO JUKKA KALEVI, MIETTINEN JORMA KALERVO, HEINONEN, OLLI, J., LEHTO, JUKKA, KALEVI, MIETTINEN, JORMA, KALERVO
Application year: 1983
Main classification: C01G23
IPC codes: B01J39, C01G23