Humic substances extraction, characterization and interaction with U(VI) at Ruprechtov site (CZ)

Abstract

Humic substances / Complexation / Cation exchange / Charge neutralization model / Ruprechtov site / Czech Republic / U(VI)Summary. The extent of complexation between natural humic acid (HA) and uranium(VI) has been investigated at the Ruprechtov natural analogue site, Czech Republic. Natural HA was extracted from the clay sediments enriched by organic matter and then characterized for their elemental composition, UV/Vis and infrared spectroscopic properties, exchange capacity and protonation constants. Moreover, the reference sample HA-leonardite was selected and studied for comparison. Complexation between natural HA and U(VI) was studied using the cation exchange technique at pH 5-6. The experimental work was focused on study dependence of U(VI) complexation with HA: i) on the concentration of HA 1-40 mg/l, and ii) on the concentration of U(VI) 1 × 10 −5 -1 × 10 −7 M. The charge neutralization model (CNM) was used for evaluation of the experimental data, modified in a way, that the total charge was divided among the individual U(VI) species in solution under given conditions. The stability constant value was determined to be log β = 4.32 ± 0.50, LC = 50-60%, being independent on the HA concentration at U(VI) concentrations of 1 × 10 −4 M. On the other hand, a dependence on the stability constant for the different U(VI) concentrations was observed. At close to real conditions of the site (U(VI) = 1 × 10 −7 M and mHA = 5 mg/l) the stability constant log β = 6.16, LC = 50.3-52.7%.

Chemometric approach for prediction of uranium pathways in the soil

“…Humic acids are the most important part of soil organic matter, which improves cation exchange of nutritive elements, increases the accessibility of phosphorus, has a buffer capacity and forms stable complexes with heavy metals, thereby reduces their potential risk [16,[33][34][35]. Results of Crancon and van der Lee [36] showed that complexation of uranium(VI) by humic substances tend to immobilise uranium in soils at pH below 5, when the reactive surface of quartz grains and aggregates are entirely coated by humic matter.…”