The effect of humic substances on metal migration at the border of sediment and water flow
2020
Bondareva, Lydia | Fedorova, Nataliia
The speciation of radionuclides in bottom sediments of the Yenisei River, sampled in the near-field region of the nuclear fuel cycle enterprise, was studied. It has been established that most of ¹⁵²Eu and ²⁴¹Am radionuclides isolated by sequential chemical fractionation are in a bound state with the organic matter of bottom sediments (up to 35% of the total amount). In this case, the content of ¹⁵²Eu and ²⁴¹Am in depth of the bottom sediment layers is directly dependent on the change in the organic matter content. Bottom sediments containing a high content of organic substances (humic acids – HA and fulvic acids – FA) were studied. By the HA: FA ratio, the studied bottom sediments are related to a fulvate-humate type. When fractionating the organic matter of bottom sediments, it was revealed that the distribution occurred as follows (% of the total content): in the form of fulvates ¹⁵²Eu – 53, ²⁴¹Am–16, ⁶⁰Co – 10, ¹³⁷Cs–3; ²⁴¹Am–28% associated with humin; in the form of organomineral compounds ~ 2–5%; in the form of organometallic complexes ~ 2–3%. Model experiments with addition of HA to the aqueous medium of the bottom sediments-water system. HA was previously isolated from bottom sediments and identified by IR Fourier spectroscopy. The introduction of HA significantly influenced the release of radionuclides and some metals from bottom sediments into the liquid medium. So, the content of ¹⁵²Eu and ²⁴¹Am radionuclides are intensively released into the water: from 0 to 198 ± 8 Bq·L⁻¹ and 167 ± 7 Bq·L⁻¹, respectively. The content of ⁴ K, ⁶⁰Co, ¹³⁷Cs was not considerable. The content of some analysed metals in the aqueous medium also increased significantly: 9 times for U⁶⁺ and 32 times for Cu²⁺.
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