Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
  • G21F9/28—Treating solids
  • G21F9/30—Processing
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
  • G21F9/04—Treating liquids
  • G21F9/06—Processing
  • G21F9/12—Processing by absorption; by adsorption; by ion-exchange

Definitions

• Completion of the dissolution may be aided by the detailed design of the dissolver vessel and equipment.
• certain other methods are well known in the art for increasing the effectiveness of dissolution reactions. Examples are counter-current contact, in which the solid passes through the dissolution vessel in the opposite sense to the solution - thus the emerging undissolved solid is contacting the cleanest solution. Contact of the solid and solution can also be enhanced by a "high-shear" mixer.
• any undissolved solid from the dissolution reaction vessel is separated from the dissolution solution by conventional means, such as settling and filtration.
• the solid is rinsed with clean water (if necessary) and sentenced, according to its radioactivity specific activity (in Becquerels per gram) , to radioactive or non- radioactive disposal.
• the undissolved solid is likely to be either a significant proportion of the original oil scale and non-radioactive, or a very small proportion of the original solid and radioactive.
• the scale solution is then subjected to an anion exchange resin so as to remove sulphate ion therefrom.
• said anion exchange resin is in the chloride form, the chloride ions replacing the sulphate ions in the solution.
• the optimum procedure is to absorb the combined radioactive (radium, etc.) and non-radioactive (Sr, Ba etc) constituents onto at least one cation exchange column. The separation of the constituents is then made by differential elution.
• the most preferred embodiment is to use an eluting solution that has a chemical composition equivalent to the dissolving solution, but at a slightly different pH.
• eluting solution that has a chemical composition equivalent to the dissolving solution, but at a slightly different pH.
• alternatives are possible, such as different chelating agents, e.g. the use of EDTA in the dissolving solution and DCyTA in the eluting solution.
• the output solution from the ion exchange column is diverted to collect radioactive and non-radioactive fractions separately. The correct collection of fractions may be facilitated by equipment which continuously analyses the radioactivity and chemical composition of the output solution.
• the partial separation can be used to good effect by "cascading" ion exchange columns, i.e. feeding radium-depleted barium and barium-depleted radium to further ion exchange separation columns. It is also possible that the ion exchange conditions can be designed to concentrate the radium into a series of bands or "pulses" of radioactivity going down the ion exchange column, interspersed with bands of non- radioactive material.
• the radioactive fraction and/or the non-radioactive fraction is (are) optionally converted into solid form(s) .
• this is accomplished by means of precipitation operation (s) , which can be performed in accordance with techniques known per se, e.g. by sulphate precipitation (s) with sulphate ions.
• the obtained radioactive and/or non- radioactive solids can then be used or disposed of in any suitable manner.
• radioactive and non-radioactive cationic constituents have been recovered, recovery of dissolving constituents (e.g. chelating agent) can be achieved, e.g. by the appropriate pH adjustment of the effluent solutions to cause precipitation.
• the filtered chelating agent can be recycled. Residual salt solutions can then be discarded as effluent, though if it is absolutely necessary to have a zero effluent operation, the salt solutions can be reconstituted into acid and alkali by appropriate electrical processes.
• a simple and efficient apparatus for performing a process as defined above comprises:
• the apparatus also preferably comprises a grinding unit, before said dissolver vessel, for reducing solid oil scale to a particulate material, preferably to a particle size of at most 50 ⁇ m.
• Fig. 4 shows dissolution of activity and weight in oil scale samples as described below in Example 1;
• Fig. 6 shows ion exchange separation with EDTA as described below in Example 3 ;
• Fig. 2 shows how an input solution is subjected to a first separation stage in a cationic exchange resin, the barium rich and radium rich fractions from said first separation then being passed to separate new, cationic exchange resins, respectively, etc. Barium sulphate and radium sulphate solids are separately recovered for disposal, while radium and barium rich fractions, as shown, are recycled to the first exchange resin.
• Example 1 Dissolution Duplicate oil scale samples from two sources (“A” and "B”) were heat treated to pyrolyse organics, and were separately ground to ⁇ 50 ⁇ m particle size and homogenised using a Retsch (S100) centrifugal ball mill with reversing mechanism. Two 5 g portions of each were accurately weighed and submitted for gamma-spectrometry counting to determine Ra-226 activity. The samples were counted in the same geometry as a 50 Bq standard prepared from 5 g of the natural mineral clinoptilolite spiked with an aqueous certified Ra-226 reference standard. Multiple contact dissolution tests were carried out on 5 g portions of the ground samples. In this technique, the oil scale was contacted with chemical dissolving solution, filtered and then contacted with a fresh batch of solution. The number of contacts was recorded and the cumulative dissolution of activity and weight measured.
• a 75 cm 3 cation exchange column in the sodium form was prepared from Amberlite IR-120 resin (capacity
• the overall capacity of the column provided approximately 75% excess.
• the column was converted into the chloride form from the hydroxide form by passing through of 5 bv (bed volumes) 2 M sodium chloride solution, followed by a 2 bv deionised water rinse.
• the pH 7 adjusted dissolution liquor spiked with additional Ra-226 (described above) was loaded onto a 75 cm 3 cation exchange column in the sodium form (pH 7) prepared in the manner described above .
• the column was rinsed with 2 bv deionised water followed by an additional 1 bv deionised water.
• 13 bv 0.05 M DCyTA at pH 8.5 was passed through the column to elute the barium taking column effluent fractions for counting and qualitative barium analysis after 5 bv, 10 bv and 13 bv.
• 5 bv 0.05 M EDTA at pH 8.5 was passed through the column to elute the radium followed by a 2 bv deionised water rinse.
• the first contact oil scale dissolution liquors from samples A (5) and B(5) were combined and subjected to sulphate removal by anion exchange as described above .
• the combined anion exchange effluent was adjusted to pH 7 with 2 M HCl.
• the entire solution (unspiked, combined Ra- 226 activity -500 Bq) was loaded onto a 75 cm 3 cation exchange column in the sodium form (pH 7) , prepared in the manner described above.
• a total of 12 bv i.e.
• Example 4 Ion Exchange Separation with EDTA using a loading and elution technique
• the solution was measured for radium and barium after passing through the column, and no radium or barium was detected (ie all the barium and radium had been retained on the column.
• the ion exchange column was then eluted with 10 bed volumes of 0.1 M EDTA adjusted to pH 7, followed by 3 bed volumes of 0.1 M EDTA adjusted to pH

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Fats And Perfumes (AREA)
• Processing Of Solid Wastes (AREA)
• Treatment Of Liquids With Adsorbents In General (AREA)

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Cited By (7)

Citations (3)

• 2000
  • 2000-08-10 SE SE0002869A patent/SE517130C2/sv unknown
• 2001
  • 2001-08-09 AU AU2001280375A patent/AU2001280375A1/en not_active Abandoned
  • 2001-08-09 WO PCT/SE2001/001723 patent/WO2002013202A1/en active Application Filing

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