Speciation of naturally occurring radionuclides in Mediterranean soils: bioavailabilty assessment

Fractionation of some natural radionuclides in Albic Retisol

In the present work, the fractionation of heavy natural radionuclides was investigated in Albic Retisol in the Moscow region of Russia. Fractionation was performed using the Pavlotskaya method. ²³⁸U and ²³²Тh were measured via inductively coupled plasma mass spectrometry and ²²⁶Ra was measured using an alpha-radiometer that considered the decay of Ra isotopes and accumulation of the resulting decay-related products. Results showed that the potential mobility of radionuclides during migration to adjacent environments and biological availability to plants follows the order ²²⁶Ra > ²³⁸U > ²³²Тh. The depletion of ²²⁶Ra in the humus horizon A was manifested as a decrease in the ²²⁶Ra/²³⁸U activity ratio to below 1 in fraction F4.1 (associated with organic matter) and fraction F4.2 (acid-soluble compounds). The profile distribution of ²²⁶Ra and ²³⁸U in the residual fraction revealed the genetic relationship between these radionuclides. Mobile compounds of ²³⁸U and ²³²Th leached into the lower part of the profile where they became fixed, mainly as the components of fractions associated with organic matter and crystallized iron oxides. A similar profile distribution was found for ²³⁸U, ²³²Тh, and Fe in the acid-soluble fraction associated with crystallized iron oxides. The results obtained herein can form the basis for regulating the mobility and bioavailability of radionuclides to ameliorate their adverse effects on plants and soil ecosystems.

Phosphorus-modified biochar cross-linked Mg-Al layered double-hydroxide composite for immobilizing uranium in mining contaminated soil

The decommissioning of uranium mill tailings (UMTs) is usually accompanied by uranium (U) contamination in soil, which poses a serious threat to human health and ecological safety. In this study, a novel phosphorus-modified bamboo biochar (PBC) cross-linked Mg-Al layered double-hydroxide (LDH) composite ("PBC@LDH") was successfully prepared by phosphate pre-impregnation and a hydrothermal method with Mg-Al LDH. Physicochemical analysis revealed that phosphorus-containing functional groups and Mg-Al LDH were grafted onto the pristine biochar (BC) matrix. Laboratory-scale incubation and column leaching experiments were performed on the prepared BC, PBC, and PBC@LDH. The results showed that, at a dosage of 10%, the PBC@LDH composite had a commendable ability to immobilize U in soil. After 40 days of incubation with the stabilizer, the more mobile U was converted into immobilized species. Furthermore, during a column leaching experiment with simulated acid rain, the cumulative loss and leaching efficiency of U were remarkably reduced by PBC@LDH treatment compared with the control, reaching 53% and 54%, respectively. Surface complexation, co-precipitation, and reduction described the adsorption and immobilization mechanisms. In conclusion, this research demonstrates that the PBC@LDH composite offers a potentially effective amendment for the remediation of U contaminated soil.

Basic Characteristics of Coal Gangue in a Small-Scale Mining Site and Risk Assessment of Radioactive Elements for the Surrounding Soils

The accumulation/improper treatment of coal gangue will not only lead to waste of land, but also cause environmental pollution. Especially the impact of radioactive elements on the surrounding ecological environment is widely concerned by many scholars. In this study, the concentration of radioactive elements (uranium (U) and thorium (Th)) of small-scale coal gangue mining site and surrounding soil in the northern region of Xieqiao coal mine were tested, the material composition of coal gangue was analyzed via XRF and XRD, the modes of occurrence of U and Th elements were investigated, and their potential ecological risks and ecological effectiveness were evaluated. The results show that the clay minerals with high content in coal gangue are the key minerals for the adsorption of uranium and thorium in coal gangue. The specific activity of two radioactive elements (U and Th) in soil is much lower than that of coal gangue. With the increase of the distance from the soil collection point to the gangue piles and the depth of the soil profile, the specific activities of the two radioactive elements decrease gradually. On the basis of the concentration curve, the range of the radioactive contamination halo of gangue piles is limited (≤30 m), speculating qualitatively that the gangue dump has no significant influence on the radioactivity of the surrounding water. The modes of occurrence of U and Th in coal gangue and soil are altered. According to the index of geo-accumulation, Th is easier to accumulate in soil environment, but Th and U pollution in soil is not obvious. In contrast to U element, the active state of Th element in soil is generally affected by exogenous (coal gangue) export, which may have a potential environmental effects. This study provides a research idea for the investigation of radioactive element pollution to the surrounding soil in small-scale coal gangue plies.

Modification of natural radionuclide uptake by wheat using a NORM by-product as soil amendment

Drinking Water Treatment Plants (DWTPs) can be optimised for removal of natural radionuclides, thus meeting EU legislation. Removed radionuclides (^234,238U, ²²⁶Ra and ²¹⁰Po) go into sludges. What would happen if these sludges were used in agriculture? Wheat plantlets were cultivated in original and sludge-amended soils under laboratory controlled conditions. Soil-to plant transfer was significantly increased in factors ranging 1.2-3.7, 2.0-5.6, and 1.6-2.4 for ^234,238U, ²²⁶Ra and ²¹⁰Po, respectively. The additional input was preferentially accumulated in roots.