Phosphorus adsorption on iron‐coated sand under reducing conditions

Mitigation measures are needed to prevent large loads of phosphate originating in agriculture from reaching surface waters. Iron-coated sand (ICS) is a residual product from drinking water production. It has a high phosphate adsorption capacity and can be placed around tile drains, taking no extra space, which increases the farmers’ acceptance. The main concern regarding the use of ICS filters below groundwater level is that limited oxygen supply and high organic matter concentrations may lead to the reduction and dissolution of iron (hydr)oxides present and the release of previously adsorbed phosphate. This study aimed to investigate phosphate adsorption on ICS at the onset of iron reduction. First, we investigated whether simultaneous metal reduction and phosphate adsorption were relevant at two field sites in the Netherlands that use ICS filters around tile drains. Second, the onset of microbially mediated reduction of ICS in drainage water was mimicked in complementary laboratory microcosm experiments by varying the intensity of reduction through controlling the oxygen availability and the concentration of degradable organic matter. After 3 yr, ICS filters in the field removed phosphorus under low redox conditions. Over 45 d, the microbial reduction of manganese and iron oxides did not lead to phosphate release, confirming field observations. Electron microscopy and X-ray absorption spectroscopy did not evince systematic structural or compositional changes; only under strongly reducing conditions did iron sulfides form in small percentages in the outer layer of the iron coating. Our results suggest that detrimental effects only become relevant after long periods of operation

Особенности разряда на границе раздела твердых слоистых диэлектриков

Установлена связь величины разрядного напряжения на границе раздела твердых слоистых диэлектриков от длины разрядного расстояния. Обнаружено явление заглубления канала разряда в диэлектрик, прилегающий к границе раздела, выход его на внешнюю поверхность с последующим развитием по воздуху

Direct Observation of Reductive Coupling Mechanism between Oxygen and Iron/Nickel in Cobalt-Free Li-Rich Cathode Material: An in Operando X-Ray Absorption Spectroscopy Study

Li-rich cathodes possess high capacity and are promising candidates in next-generation high-energy density Li-ion batteries. This high capacity is partly attributed to its poorly understood oxygen-redox activity. The present Li-rich cathodes contain expensive and environmentally-incompatible cobalt as a main transition metal. In this work, cobalt-free, iron-containing Li-rich cathode material (nominal composition Li$_{1.2}$Mn$_{0.56}$Ni$_{0.16}$Fe$_{0.08}$O$_{2}$) is synthesized, which exhibits excellent discharge capacity (≈250 mAh g$^{-1}$ and cycling stability. In operando, X-ray absorption spectroscopy at Mn, Fe, and Ni K edges reveals its electrochemical mechanism. X-ray absorption near edge structure (XANES) features of Fe and Ni K edges show unusual behavior: when an electrode is charged to 4.5 V, Fe and Ni K edges’ XANES features shift to higher energies, evidence for Fe$^{3+}$→Fe$^{4+}$ and Ni$^{2+}$→Ni$^{4+}$ oxidation. However, when charged above 4.5 V, XANES features of Fe and Ni K edges shift back to lower energies, indicating Fe$^{4+}$→Fe$^{3+}$ and Ni$^{4+}$→Ni$^{3+}$ reduction. This behavior can be linked to a reductive coupling mechanism between oxygen and Fe/Ni. Though this mechanism is observed in Fe-containing Li-rich materials, the only electrochemically active metal in such cases is Fe. Li$_{1.2}$Mn$_{0.56}$Ni$_{0.16}$Fe$_{0.08}$O$_{2}$ has multiple electrochemically active metal ions; Fe and Ni, which are investigated simultaneously and the obtained results will assist tailoring of cost-effective Li-rich materials

Thallium adsorption onto phyllosilicate minerals

The adsorption of thallium (Tl) onto phyllosilicate minerals plays a critical role in the retention of Tl in soils and sediments and the potential transfer of Tl into plants and groundwater. Especially micaceous minerals are thought to strongly bind monovalent Tl(i), in analogy to their strong binding of Cs. To advance the understanding of Tl(i) adsorption onto phyllosilicate minerals, we studied the adsorption of Tl(i) onto Na- and K-saturated illite and Na-saturated smectite, two muscovites, two vermiculites and a naturally Tl-enriched soil clay mineral fraction. Macroscopic adsorption isotherms were combined with the characterization of the adsorbed Tl by X-ray absorption spectroscopy (XAS). In combination, the results suggest that the adsorption of Tl(i) onto phyllosilicate minerals can be interpreted in terms of three major uptake paths: (i) highest-affinity inner-sphere adsorption of dehydrated Tl(+) on a very low number of adsorption sites at the wedge of frayed particle edges of illite and around collapsed zones in vermiculite interlayers through complexation between two siloxane cavities, (ii) intermediate-affinity inner-sphere adsorption of partially dehydrated Tl(+) on the planar surfaces of illite and muscovite through complexation onto siloxane cavities, (iii) low-affinity adsorption of hydrated Tl(+), especially in the hydrated interlayers of smectite and expanded vermiculite. At the frayed edges of illite particles and in the vermiculite interlayer, Tl uptake can lead to the formation of new wedge sites that enable further adsorption of dehydrated Tl(+). On the soil clay fraction, a shift in Tl(i) uptake from frayed edge sites (on illite) to planar sites (on illite and muscovite) was observed with increasing Tl(i) loading. The results from this study show that the adsorption of Tl(i) onto phyllosilicate minerals follows the same trends as reported for Cs and Rb and thus suggests that concepts to describe the retention of (radio)cesium by different types of phyllosilicate minerals in soils, sediments and rocks are also applicable to Tl(i)