RU2714309C1 - Method for purification of oil-contaminated soils from natural radionuclides - Google Patents

Abstract

FIELD: environmental protection.

SUBSTANCE: invention relates to environmental protection in terms of decontaminating and recycling oil-contaminated soils (OCS) with high content of natural radionuclides (NRN) and can be used in reclamation and rehabilitation of territories. Oil-contaminated soils are pre-extruded to size of 1–8 mm, the extrudates are annealed in oxidizing conditions at excess air in the temperature range of 600–700 °C for 0.5–1 hour to obtain the ash (S). At first step by percolation method leaching first of calcium, then barium and radium by aqueous solutions of sodium hydroxide – 8–15 g/dm³ and disodium salt of ethylenediaminetetraacetic acid – 20–50 g/dm³ (L). Process is carried out at pH 10–12, temperature 20–25 °C, by volume ratio of L:S=3:1, to obtain non-radioactive engineering soil and mother leaching solutions. Calcium is deposited from mother solution of first leaching stage in form of CaSO₄⋅2H₂O sulfuric acid at pH 3.5–4.0. Barium and radium are deposited from the mother solution of the second leaching stage in the form Ba(Ra)SO₄ with sulfuric acid at pH 6.0–7.0. Formed pulps are fed for separate filtration of precipitation in form of non-radioactive CaSO₄⋅2H₂O and radioactive Ba(Ra)SO₄. Regeneration of non-radioactive filtrates is carried out separately. Regenerated solution is returned to turn cycle 3–5 times at leaching stage.

EFFECT: invention increases efficiency of the method, which reduces level of average specific activity of oil-contaminated soils to values at which they can be used in reclamation of territories.

1 cl, 5 tbl

Description

The invention relates to the field of environmental protection in terms of decontamination and disposal of oil-contaminated soils (NZG) with a high content of natural radionuclides (ERN), and can be used in the reclamation and rehabilitation of territories.

A known method of disposing of waste containing oil and petroleum products, which consists in mixing waste with a neutralizing component. As a neutralizing component, calcium and magnesium oxide are used. Mixing is carried out in the following ratios of components, wt. %: calcium oxide - 10-40; magnesium oxide - 3-5; oil sludge - up to 100. RU 2187466 C1, publ. 08/20/2002.

This method cannot be used to remove radionuclides, since Ba (Ra) SO ₄ radio barite is a sparingly soluble compound.

A known method of processing the bottom-hole zone of the formation, including sequential injection of alkaline buffer fluid, the active reagent is a solution of the composition, wt. %: Trilon-B 0.35-28, alkali metal hydroxide 0.05-7, water the rest, exposing them to react with the rocks of the formation and colmatizing substances, conducting a selection of spent active reagent cyclically to restore the natural permeability of the bottomhole formation zone and regeneration. Moreover, the ratio of the volume of alkaline buffer fluid to the volume of the active reagent is taken from the conditions: k = 1.0-1.5. The reaction products from the reservoir are removed and the wells are put into operation. RU 2232879 C1, publ. 07/20/2004.

The disadvantages of this method include the use of hydrochloric acid as a neutralizing agent, as a result, in addition to the sulfate ion, chloride ion is accumulated in the solution, which must be isolated.

A known method of regeneration of ethylenediaminetetraacetic acid from the spent washing solution of steam generators of power plants. The precipitation of ethylenediaminetetroacetic acid (EDTA) is carried out with sulfuric acid at pH = 1.0-1.5, while the complex of EDTA with ferrous iron and monovalent copper is destroyed and it is precipitated in pure form. The solid precipitate is dried or dissolved in an alkaline solution for reuse. At pH greater than 2, the solubility of EDTA increases. In the presence of calcium ions at pH = 1.6, the solubility of EDTA is 2.1 g / dm ³ . The method allows to isolate EDTA in its pure form in one technological stage. RU 2213064 C1, publ. 09/27/2003.

The disadvantages of this method include the high consumption of sulfuric acid by lowering the pH to 1-1.5.

The closest way to the claimed combination of essential features is a method for cleaning radioactive oil sludge, which consists in leaching radium from oil sludges using hot water, acidic or alkaline solutions. At the same time, radioactive oil sludge is preliminarily subjected to reductive annealing with a lack of oxygen in the atmosphere of incomplete combustion of carbon and hydrocarbons, for the production of which oil products are used. The temperature of reductive annealing is maintained in the range of 700-900 ° C for 1 to 3 hours. The annealed oil sludge is treated with hot steam and re-treated with hot steam with hydrochloric acid at a concentration of hydrochloric acid from 5 to 10% with respect to the weight of the leaching solution. RU 2251167 C2, publ. 04/27/2005.

The known method has the following disadvantages:

The leaching process produces large volumes of liquid radioactive solutions containing barium and radium chlorides, which must be processed according to a separate scheme.

When leaching with steam with hydrochloric acid, a significant amount of impurities passes into the solution, which is confirmed by a large reduction in the mass of the output of oil sludge, as a result of which it is impossible to recycle the solution in the technological scheme.

The process is carried out in periodic mode, which significantly increases the time of the entire technological cycle.

The technical problem solved by the claimed invention is the development of a method for cleaning oil-contaminated soils from natural radionuclides and the elimination of these disadvantages.

The technical result from the implementation of the invention is to increase the efficiency of the method, which reduces the average specific activity of oil-contaminated soils to the values at which they can be used in the reclamation of territories.

The technical result is achieved by the fact that in the method of purification of oil-contaminated soils from natural radionuclides, including roasting the soil and leaching of the radio barite, according to the invention, oil-contaminated soils are pre-extruded to a size of 1-8 mm, the extrudates are calcined under oxidizing conditions with an excess of air in the temperature range 600-700 ° C for 0.5-1 h to obtain a cinder (T), from which calcium is first leached out in a two-stage percolation method in the first stage, then bar minutes and radium aqueous sodium hydroxide solution - 8-15 g / dm ³ and the disodium salt of ethylenediaminetetraacetic acid (Trilon B) - 20-50 g / dm ³ (F), at pH 10-12, a temperature of 20-25 ° C, by volume ratio W: T = 3: 1, to obtain non-radioactive technical soil and mother leach solutions, then calcium is precipitated from the mother liquor of the first leaching stage in the form of CaSO ₄ ⋅ 2H ₂ O sulfuric acid at pH 3.5-4.0, and from the mother liquor of the second leach stage is precipitated barium and radium in the form of Ba (Ra) SO ₄ sulfuric acid at pH 6.0-7.0 formed pulp fed separate precipitation and filtration in the form of CaSO ₄ nonradioactive ⋅2H ₂ O and radioactive Ba (Ra) SO _4, nonradioactive regeneration filtrates performed separately, doukreplyaya them to the initial values of the concentration of sodium hydroxide solution and the disodium salt of ethylenediaminetetraacetic acid, after which the regenerated working solution returned to the cycle at the stage of leaching of calcium and barium.

At the same time, the regenerated solutions return from 3 to 5 cycles.

The inventive method consists of several technological operations:

1. Extrusion of oil-contaminated soils - the process of forming material in the form of extrudates-granules. Extrusion is carried out in order to reduce dust and sticking material to the walls of the apparatus during firing. The initial oil-contaminated soils are loaded into an extruder, formed extrudates granules 1-8 mm in size are unloaded from it.

2. The resulting extrudates are fired. Firing in a rotary kiln under oxidizing conditions at a temperature of 600-700 ° C for 0.5-1 hours is carried out to remove the organic phase and obtain a mineral residue in the form of an extruded cinder, not subject to colmatization and suitable for percolation leaching,

3. The cinder after firing is loaded into the percolation column and the leach solution (infiltration mode) is fed from top to bottom. Two-stage sequential percolation leaching of the extruded cinder is carried out with aqueous solutions of NaOH - 8-15 g / dm ³ and Trilon B - 20-50 g / dm ³ at pH = 10-12, temperature 20-25 ° C and W: T = 3: 1 first calcium, then barium and radium.

4. The precipitation of calcium in the form of CaSO ₄ ⋅ 2H ₂ O lead from the mother liquor of the first stage of leaching with sulfuric acid at pH = 3.5-4.0.

5. The precipitation of barium and radium in the form of Ba (Ra) SO _{4 is} carried out from the mother liquor of the second stage leaching with sulfuric acid at pH = 6.0-7.0.

6. The formed pulps enter separate precipitation filtration in the form of non-radioactive CaSO ₄ ⋅ 2H ₂ O and radioactive Ba (Ra) SO ₄ . Non-radioactive filtrates are regenerated separately, adding to the initial concentration of sodium hydroxide and disodium salt of ethylenediaminetetraacetic acid.

7. The regenerated solutions are returned to the reverse cycle at the stage of leaching of calcium and barium. The number of revolutions of leaching solutions depends on the mineral composition of the extruded cinder and is regulated by the required residual specific activity of the target soil.

As a result, soil with a specific activity of ≤1.5 kBq / kg and liquid products A _eff <0.13 Bq / g, corresponding to the norms and rules of radiation safety of the Russian Federation, were obtained. The resulting soil can be used in the rehabilitation of territories.

The method of purification of radioactive oil contaminated soil is illustrated by specific examples given in tables 1-5.

As can be seen from Example 1, as a result of oxidative roasting and subsequent percolation leaching with solutions of NaOH and Trilon B, from a cinder of oil-contaminated soils containing natural radionuclides, technical soil with A _eff = 1385 Bq / kg and equivalent dose rate (DER) of 0.21 is obtained μSv / h, which, in accordance with radiation safety standards NRB-99/2009, is less than the permissible values of 0.3 μSv / h.

From example 2 it is seen that calcium is extracted in the first stage of percolation leaching, and barium in 2-3 stages.

From example 3 it is seen that the solutions after the deposition of calcium and barium sulfates contain calcium at the level of its solubility, and barium up to 30 mg / DM ³ . After strengthening, the solutions can be used in a reverse cycle at the leaching stage.

From example 4 it is seen that the regeneration of Trilon B in the first stage of percolation leaching takes place by about 60%, in the second - by about 80%, and in the subsequent ones it is completely regenerated.

From example 5 it is seen that the obtained precipitate of calcium sulfate is not radioactive and belongs to industrial waste of the 4th category. The precipitate of barium sulfate is RAO 3rd class.

The use of the proposed method in addition to cleaning contaminated territories will reduce the operating costs of enterprises for landfill maintenance, payments for environmental pollution, will provide a deactivated mineral leach residue with a specific activity of <1.5 kBq / kg, which can be used in the rehabilitation of territories and liquid products with activity <0.13 Bq / g, which meets the standards and rules of radiation safety of the Russian Federation and to remove radionuclides in the form of a radio barite. The barium sulfate radioactive deposit is cemented and transferred to the national operator.

Example 1. The distribution of Ca, Ba and activity on solid products of the technological scheme of purification of NG with a high content of EPH

Example 2 - Percolation reverse leaching of Ca and Ba from cinder

Example 3 - Conditions for the deposition of calcium and barium sulfuric acid from the mother liquor in the recirculation mode

Example 4 - Balance of flow and regeneration of Trilon B during reverse percolation leaching of extruded material

Example 5 - The quality of precipitates obtained by precipitation of calcium and barium by sulfuric acid from mother liquors of the 1st and 2nd stages of percolation leaching, respectively

Claims (2)

1. A method of purifying oil-contaminated soils from natural radionuclides, including roasting the soil and leaching barium from it, characterized in that the oil-contaminated soils are pre-extruded to a size of 1-8 mm, the extrudates are calcined under oxidizing conditions with an excess of air in the temperature range of 600-700 ° C for 0.5-1 h to obtain a cinder (T), from which, first, calcium, then barium and radium are leached out in an aqueous solution of sodium hydroxide in a percolation method in the first stage — 8-15 g / dm ³ and disodium ethylenediaminetetraacetic acid salt - 20-50 g / dm ³ (W) at pH 10-12, temperature 20-25 ° С, volume ratio W: T = 3: 1, to obtain non-radioactive technical soil and mother leach solutions, then from The mother liquor of the first leaching stage is precipitated with calcium in the form of CaSO ₄ ⋅ 2H ₂ O with sulfuric acid at pH 3.5–4.0, and barium and radium are precipitated from the mother liquor of the second leaching stage as Ba (Ra) SO _{4 with} sulfuric acid at pH 6.0-7.0 formed pulp fed to the separate filtration of precipitation in the form of CaSO ₄ nonradioactive ⋅2H ₂ O and radioactive th Ba (Ra) SO _4, nonradioactive regeneration filtrates performed separately, doukreplyaya them to the initial values of the concentration of sodium hydroxide and the disodium salt of ethylenediaminetetraacetic acid, after which the regenerated working solution returned to the cycle of the leaching step of calcium and barium. 2. The method according to p. 1, characterized in that the regenerated solutions are returned into circulation from 3 to 5 cycles.