METHOD FOR PURIFICATION OF OIL-CONTAMINATED SOILS FROM NATURAL RADIONUCLIDES Russian patent published in 2020 - IPC G21F9/06 B09C1/08 G21F9/12 G21F9/30 C22B3/04 

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