Stable U(IV) Complexes Form at High-Affinity Mineral Surface Sites

Uranium (U) poses a significant contamination hazard to soils, sediments, and groundwater due to its extensive use for energy production. Despite advances in modeling the risks of this toxic and radioactive element, lack of information about the mechanisms controlling U transport hinders further improvements, particularly in reducing environments where UIV predominates. Here we establish that mineral surfaces can stabilize the majority of U as adsorbed UIV species following reduction of UVI. Using X-ray absorption spectroscopy and electron imaging analysis, we find that at low surface loading, UIV forms inner-sphere complexes with two metal oxides, TiO2 (rutile) and Fe3O4 (magnetite) (at <1.3 U nm–2 and <0.037 U nm–2, respectively). The uraninite (UO2) form of UIV predominates only at higher surface loading. UIV–TiO2 complexes remain stable for at least 12 months, and UIV–Fe3O4 complexes remain stable for at least 4 months, under anoxic conditions. Adsorbed UIV results from UVI reduction by FeII or by the reduced electron shuttle AH2QDS, suggesting that both abiotic and biotic reduction pathways can produce stable UIV–mineral complexes in the subsurface. The observed control of high-affinity mineral surface sites on UIV speciation helps explain the presence of nonuraninite UIV in sediments and has important implications for U transport modeling

Ironic and Overcompensating Processes Under Avoidance Instructions in Motor Tasks

Thought-suppression research showed, when asked to suppress a given thought (e.g., a white bear), people ironically report thinking more of the suppressed thought. Testing motor performance given avoidance goals (e.g., avoid putting the ball short of the target in golf) represents an interest to transfer thought-suppression findings to motor tasks. However, instead of revealing an ironic process, motor studies showed mixed results, suggesting a coexistence of ironic and overcompensating processes. The present study investigates the coexistence of ironic and overcompensating processes induced by avoidance goals in motor tasks. Adopting a dual-process framework, an Attention Imbalance Model (AIM) was proposed to conceptualize such a coexistence. Four golf-putting experiments were conducted to test the AIM by manipulating the degree of attentional imbalance. Results indicated the factor of attentional imbalance moderates the likelihood between ironic and overcompensating processes in golf putting, and such a moderating effect demands task-specific considerations. In addition, performance feedback confounded the putting performance by reducing the likelihood of overcompensating process. The implications of the AIM are discussed in an extended context of motor performance under avoidance goals and thought suppression