RU2200354C2 - Method for cleaning from liquid radioactive wastes - Google Patents

Abstract

FIELD: cleaning water from liquid radioactive pollutants. SUBSTANCE: method includes doping solution containing radioactive wastes with calcium, magnesium, and phosphate ions and its neutralizing with alkali to pH = 9.5-11. Magnesium ions are introduced in the amount of 300-600 mg/l. Solution may be doped in addition with cesium and/or rubidium ions in the amount of 0.5-5 mg/l and strontium ions in the amount of 1-300 mg/l. Apatite may be used as source of calcium, strontium, and phosphate ions and forsterite acid decomposition products, as source of magnesium ions. EFFECT: enhanced degree of cleaning due to removal of rubidium, cesium, and also additional removal of strontium. 3 cl, 4 ex

Description

 The invention relates to a technology for the purification of water from radioactive contaminants.

 Known methods of purifying water from radioactive contaminants using various sorbents (see. Basics of purifying water from radioactive contaminants. Yu. V. Kuznetsov, VN Shchebetkovsky, AG Trusov. M.: Atomizdat. - 1974 - S. 202 -250). Using sorbents, it is possible to conduct deep water purification from almost all impurities, however, natural sorbents are not very selective for many radionuclides, and synthetic ones are quite expensive, given that, after saturation, they are usually not subject to regeneration, but must be disposed of.

 There is also a method of purifying water from radioactive contamination by coagulation on phosphates (see ibid., Pp. 137-144). The method includes the introduction of calcium salts and phosphate ions and neutralizing the solution to a pH of 10-11.5. Deposition on phosphates is a simpler process and allows you to effectively purify water from strontium, rare earth and other 2-4 valence metals.

 The disadvantage of this method is that it does not purify from monovalent metals, mainly from rubidium and cesium, which are always present in the decomposition products and contribute the main share to the total activity. Under conditions of strontium deposition, the maximum deposition of cesium is not more than 15%.

 The present invention is directed to solving the problem of increasing the degree of purification due to purification from radioactive rubidium and cesium, as well as additional purification from strontium.

The problem is solved in that in the method of purifying the solution with phosphate coagulation, including introducing calcium and phosphate ions into the solution and neutralizing the solution to a pH of 10-11.5, magnesium ions are also introduced. The introduction of magnesium ions is due to the fact that monovalent rubidium and cesium are precipitated together with phosphates of two or more valence ions in the form of sparingly soluble salts of Cs (Rb) MgPO ₄ 6H ₂ O.

 The problem is also solved by the fact that for a more complete deposition of strontium and cesium, additional strontium ions are added in an amount of 1-300 mg and cesium or (and) rubidium in an amount of 0.5-5 mg per 1 liter of solution.

 The problem is also solved by the fact that to reduce the cost of the cleaning process, an acid extract of apatite is used as a source of calcium, strontium and phosphate ions, and an acid extract of forsterite (olivine) is used as a source of magnesium. An advantage of such sources is also that iron and silicon are present in olivine, which contribute to further purification.

 The amount of magnesium ion introduced depends on the composition of the solution: for a solution containing 45510 Bq / l, the introduction of 300 mg / l MgO in the form of chloride or sulfate gives an 80% purification. With an increase in the amount of magnesium introduced, the degree of purification increases, however, with the introduction of more than 600 mg / l, the effect of the increase is negligible. Before sanitary standards, purification is possible by the stepwise introduction of magnesium salts after separation of the precipitate.

The introduction of a solution of 0.5 mg / l Cs ₂ O or Rb ₂ O gives a noticeable effect, and more with their joint introduction. An increase in supplementation in excess of 5 mg / l, although not so large, is economically viable.

 The introduction of already 1 mg / l of strontium into the solution gives a noticeable increase in the degree of purification, with an increase in the amount of strontium introduced, the degree of purification increases. A complete replacement of calcium with strontium is possible, and this is determined by the availability of the reagent.

 Drugs based on apatite and olivine are administered in amounts close to reasonable.

 The essence of the proposed method can be illustrated by the following examples.

Example 1. In 100 ml of a solution (LRW) containing ⁹⁰ Sr - 15650 Bq / l, ¹³⁷ Cs - 45510 Bq / l (842 cpm / 100 s), 300 mg / l of calcium and magnesium chlorides were introduced (hereinafter, the concentration metals in terms of oxides) and up to 1.5 g / l PO ₄ ^{3 -} . The solution was neutralized with sodium alkali with stirring to pH 10 and the precipitate formed was filtered off. Solution activity: ⁹⁰ Sr - 630 Bq / l, ¹³⁷ Cs - 140 imp / 100 s. The degree of purification from strontium is 96%, from cesium - 83.4%.

Example 2. In 100 ml of a solution, as in example 1, 300 mg / L of calcium chloride, 600 mg / L of magnesium, 1.0 mg / L of strontium, 0.5 mg / L of cesium and up to 2 g / L of PO _{4 were} added. ³ . The solution was neutralized with sodium alkali with stirring to pH 10.5 and the precipitate formed was filtered off. Solution activity: ⁹⁰ Sr - 160 Bq / l, ¹³⁷ Cs - 89 imp / 100 s. The degree of purification from strontium is 99%, from cesium - 89.5%.

Example 3. In 100 ml of the solution, as in example 1, 100 mg / l of calcium chloride, 200 mg / l of strontium, 1 mg / l of cesium and rubidium, up to 2.5 g / l of PO ₄ ³ , 500 mg / were introduced l of magnesium and neutralized with sodium alkali to pH 10.5, the precipitate formed was filtered off. Solution activity: ⁹⁰ Sr - 160 Bq / L, ¹³⁷ Cs-66 cpm / 100 s. The degree of purification from strontium is 99.2%, from cesium after the first filtration - 92.2%. Up to 500 mg / L of magnesium was again added to the solution, and 1 mg / L of cesium and rubidium was added, and the precipitate was filtered off. The activity of the ¹³⁷ Cs solution is 26 imp / 100 sec or approximately 75 Bq / l, which corresponds to sanitary standards. If necessary, the solution can be subjected to further purification.

Example 4. Up to 5 mg / l of cesium, pulp from decomposition of 0.5 g of apatite (0.25 g of hydrochloric and 0.25 g of sulfuric acids) and pulp from decomposition of 0.15 were introduced into 100 ml of the solution, as in example 1, g olivine with hydrochloric acid, which approximately corresponded to the content of 1.1 g / l calcium, 600 mg / l magnesium, 3 mg / l strontium in the solution, up to 1.9 g / l PO4 ³ . The solution was neutralized with sodium alkali with stirring to pH 11.5 and the precipitate formed was filtered off. The activity of the solution: ⁹⁰ Sr - 120 Bq / l, ¹³⁷ Cs- 64 imp / 100 s. The degree of purification from strontium is 99.3%, from cesium - 92.4%. Thus, the inventive method allows the purification of strontium and cesium, and most of all can be effectively used for the treatment of highly active waste.

Claims (3)

 1. The method of purification of liquid radioactive waste by phosphate coagulation, comprising introducing calcium and phosphate ions into the solution to be neutralized with alkali to a pH of 10-11.5, characterized in that 300-600 mg / l of magnesium ions are additionally introduced into the solution .  2. The method according to p. 1, characterized in that the solution is additionally injected with strontium ions in an amount of 1-300 mg / l and cesium and / or rubidium ions in an amount of 0.5-5 mg / l.  3. The method according to p. 1 and / or 2, characterized in that the acid decomposition products of apatite are used as the source of calcium ions, phosphate ions and strontium ions, and the products of acid decomposition of forsterite are used as the source of magnesium ions.