Simultaneous sequestration of uranyl and arsenate at the goethite/water interface

Uranyl uptake into metal-organic frameworks: a detailed X-ray structural analysis

Metal-organic frameworks (MOF) are a subclass of porous framework materials that have been used for a wide variety of applications in sensing, catalysis, and remediation. Among these myriad applications is their remarkable ability to capture substances in a variety of environments ranging from benign to extreme. Among the most common and problematic substances found throughout the world's oceans and water supplies is [UO2]2+, a common mobile ion of uranium, which is found both naturally and as a result of anthropogenic activities, leading to problematic environmental contamination. While some MOFs possess high capability for the uptake of [UO2]2+, many more of the thousands of MOFs and their modifications that have been produced over the years have yet to be studied for their ability to uptake [UO2]2+. However, studying the thousands of MOFs and their modifications presents an incredibly difficult task. As such, a way to narrow down the numbers seems imperative. Herein, we evaluate the binding behaviors as well as identify the specific binding sites of [UO2]2+ incorporated into six different Zr MOFs to elucidate specific features that improve [UO2]2+ uptake. In doing so, we also present a method for the determination and verification of these binding sites by Anomalous wide-angle X-ray scattering, X-ray fluorescence, and X-ray absorption spectroscopy. This research not only presents a way for future research into the uptake of [UO2]2+ into MOFs to be conducted but also a means to evaluate MOFs more generally for the uptake of other compounds to be applied for environmental remediation and improvement of ecosystems globally.

Estimating Release of Trace Elements from an Area with Historical Open Pit Mining of Alum Shale Using Mass Transport and Element/Sulfate Ratios Calculations

Alum shale was mined for oil and uranium production in Kvarntorp, Sweden, 1942–1966. Remnants such as pit lakes, exposed shale and a 100-meter-high waste deposit with a hot interior affect the surrounding environment, with elevated concentrations of, e.g., Mo, Ni and U in the recipient. Today most pit lakes are circumneutral while one of the lakes is still acidic. All pit lakes show signs of sulfide weathering with elevated sulfate concentrations. Mass transport calculations show that for elements such as uranium and molybdenum the western lake system (lake Söderhavet in particular) contributes the largest part. For sulfate, the two western lakes contribute with a quarter each, the eastern lake Norrtorpssjön about a third and a serpentine pond system receiving water from the waste deposit contributes around 17%. Except for a few elements (e.g., nickel 35%), the Serpentine system (including the waste deposit area) is not a very pronounced point source for metal release compared to the pit lakes. Estimates about future water runoff when the deposit has cooled down suggest only a slight increase in downstream water flow. There could possibly be first flush effects when previous hot areas have been reached by water.

Uranium biosorption mechanism model of protonated Saccharomyces cerevisiae

Further understanding absorption uranium mechanism of the regenerational biosorbent is very interesting in application of the biosorbent. The regeneration adsorbent of Saccharomyces cerevisiae biomass was made by hydrochloric acid. Using it to absorb uranium at low constant pH(2.50), accompanied with proton releasing the ratio almost 1:2 which is to be analyzed in this paper. The type and amount of functional groups in the biomass such as carboxyl, amino, phosphoryl were determined by Potentiometric titrations and FTIR analysis. Chemical modification showed that the contribution of functional groups to uranium adsorption was carboxyl, phosphoryl and amino in turn. Analysis of SEM-EDX and staining microscopy showed that uranium on the surface of cells did not exist in the form of precipitation at lower pH 2.98, but at higher pH 4.52. The effects of phosphorus release and pH on uranium species was analyzed by MINTEQ software 3.0. Based on the above boundary conditions of the model construction, a multi-site of functional groups model equation of ion exchange absorption mechanism was built in which the final uranium ion concentration and pH as functions. It could well describe the exchange equilibrium of proton with uranium ion at pH2.50 to pH4.00.

Uranyl Arsenate Complexes in Aqueous Solution: Insights from First-Principles Molecular Dynamics Simulations

In this study, the structures and acidity constants (p K_a's) of uranyl arsenate complexes in solutions have been revealed by using the first principle molecular dynamics technique. The results show that uranyl and arsenate form stable complexes with the U/As ratios of 1:1 and 1:2, and the bidentate complexation between U and As is highly favored. Speciation-pH distributions are derived based on free energy and p K_a calculations, which indicate that for the 1:1 species, UO₂(H₂AsO₄)(H₂O)₃⁺ is the major species at pH < 7, while UO₂(HAsO₄)(H₂O)₃⁰ and UO₂(AsO₄)(H₂O)₃^- dominate in acid-to-alkaline and extreme alkaline pH ranges. For the 1:2 species, UO₂(H₂AsO₄)₂(H₂O)⁰ is dominant under acid-to-neutral pH conditions, while UO₂(HAsO₄)(H₂AsO₄)(H₂O)^-, UO₂(HAsO₄)(HAsO₄)(H₂O)^2-, and UO₂(AsO₄)(HAsO₄)(H₂O)^3- become the major forms in the pH range of 7.2-10.7, 10.7-12.1, and >12.1, respectively.