Combining Advanced Analytical Methods to Assess Interfacial Change during Bioweathering of Silicates and Sulfides

Jon Chorover 한국토양비료학회 2014 한국토양비료학회 학술발표회 초록집 Vol.2014 No.6

Soil Biogeochemical Processes in the Critical Zone

Jon Chorover 한국토양비료학회 2014 한국토양비료학회 학술발표회 초록집 Vol.2014 No.6

Colloid Formation and Transport along Hillslopes Modifies Erosion and Ridge - Valley Spacing in Post-orogenic Landscapes

Oliver Chadwick,Carleton Bern,Jon Chorover 한국토양비료학회 2014 한국토양비료학회 학술발표회 초록집 Vol.2014 No.6

Rates and mechanisms of uranyl oxyhydroxide mineral dissolution

Reinoso-Maset, Estela,Steefel, Carl I.,Um, Wooyong,Chorover, Jon,O'Day, Peggy A. Pergamon Press 2017 Geochimica et cosmochimica acta Vol.207 No.-

<P><B>Abstract</B></P> <P>Uranyl oxyhydroxide minerals are important weathering products in uranium-contaminated surface and subsurface environments that regulate dissolved uranium (U) concentrations. However, dissolution rates for this class of minerals and associated dissolution mechanisms have not been previously reported for circumneutral pH conditions, particularly for the case of flow through porous media. In this work, the dissolution rates of K- and Na-compreignacite (K<SUB>2</SUB>(UO<SUB>2</SUB>)<SUB>6</SUB>O<SUB>4</SUB>(OH)<SUB>6</SUB>·8H<SUB>2</SUB>O and Na<SUB>2</SUB>(UO<SUB>2</SUB>)<SUB>6</SUB>O<SUB>4</SUB>(OH)<SUB>6</SUB>·8H<SUB>2</SUB>O, respectively) were measured using flow-through columns reacted with two simulated background porewater (BPW) solutions of low and high dissolved carbonate concentration (ca. 0.2 and 2.8mmolL<SUP>−1</SUP>). Column materials were characterized before and after reaction with electron microscopy, bulk chemistry, and EXAFS to identify structural and chemical changes during dissolution and to obtain insight into molecular-scale processes. The reactive transport code CrunchFlow was used to calculate overall dissolution rates while accounting for fluid transport and changes in mineral volume and reactive surface area, and results were compared to steady-state dissolution rate calculations. In low carbonate BPW systems, interlayer K and Na were initially leached from both minerals, and in Na-compreignacite, K and minor divalent cations from the input solution were incorporated into the mineral structure. Results of characterization analyses suggested that after reaction both K- and Na-compreignacite resembled a disordered K-compreignacite with altered surfaces. A 10-fold increase in dissolved carbonate concentration and corresponding increase in pH (from 6.65 to 8.40) resulted in a net removal of 58–87% of total U mass from the columns, compared to <1% net loss in low carbonate BPW systems. Steady-state release of dissolved U was not observed with high carbonate solutions and post-reaction characterizations indicated a lack of development of leached or altered surfaces. Dissolution rates (normalized to specific surface area) were 2.5–3 orders-of-magnitude faster in high versus low carbonate BPW systems, with Na-compreignacite dissolving more rapidly than K-compreignacite under both BPW conditions, possibly due to greater ion exchange (1.57·10<SUP>−10</SUP> vs. 1.28·10<SUP>−13</SUP> molm<SUP>−2</SUP> s<SUP>−1</SUP> [log <I>R</I> =−9.81 and −12.89] and 5.79·10<SUP>−10</SUP> vs. 3.71·10<SUP>−13</SUP> molm<SUP>−2</SUP> s<SUP>−1</SUP> [log <I>R</I> =−9.24 and −12.43] for K- and Na-compreignacite, respectively). Experimental and spectroscopic results suggest that the dissolution rate is controlled by bond breaking of a uranyl group and detachment from polyhedral layers of the mineral structure. With higher dissolved carbonate concentrations, this rate-determining step is accelerated by the formation of Ca-uranyl carbonate complexes (dominant species under these conditions), which resulted in an increase of the dissolution rates. Optimization of both dissolution rate and mineral volume fraction in the reactive transport model to account for U mass removal during dissolution more accurately reproduced effluent data in high carbonate systems, and resulted in faster overall rates compared with a steady-state dissolution assumption. This study highlights the importance of coupling reaction and transport processes during the quantification of mineral dissolution rates to accurately predict the fate of contaminants such as U in porous geomedia.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Compreignacite dissolution rates vary with the interlayer cation (Na>K). </LI> <LI> Detachment of uranyl groups from polyhedral layers is the rate-determining step. </LI> <LI> I

Strontium and Cesium Release Mechanisms during Unsaturated Flow through Waste-Weathered Hanford Sediments

Chang, Hyun-shik,Um, Wooyong,Rod, Kenton,Serne, R. Jeff,Thompson, Aaron,Perdrial, Nicolas,Steefel, Carl I.,Chorover, Jon American Chemical Society 2011 Environmental science & technology Vol.45 No.19

<P>Leaching behavior of Sr and Cs in the vadose zone of Hanford site (Washington) was studied with laboratory-weathered sediments mimicking realistic conditions beneath the leaking radioactive waste storage tanks. Unsaturated column leaching experiments were conducted using background Hanford pore water focused on first 200 pore volumes. The weathered sediments were prepared by 6 months reaction with a synthetic Hanford tank waste leachate containing Sr and Cs (10<SUP>–5</SUP> and 10<SUP>–3</SUP> molal representative of LO- and HI-sediment, respectively) as surrogates for <SUP>90</SUP>Sr and <SUP>137</SUP>Cs. The mineral composition of the weathered sediments showed that zeolite (chabazite-type) and feldspathoid (sodalite-type) were the major byproducts but different contents depending on the weathering conditions. Reactive transport modeling indicated that Cs leaching was controlled by ion-exchange, while Sr release was affected primarily by dissolution of the secondary minerals. The later release of K, Al, and Si from the HI-column indicated the additional dissolution of a more crystalline mineral (cancrinite-type). A two-site ion-exchange model successfully simulated the Cs release from the LO-column. However, a three-site ion-exchange model was needed for the HI-column. The study implied that the weathering conditions greatly impact the speciation of the secondary minerals and leaching behavior of sequestrated Sr and Cs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2011/esthag.2011.45.issue-19/es2010368/production/images/medium/es-2011-010368_0001.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/es2010368'>ACS Electronic Supporting Info</A></P>

Uranium Release from Acidic Weathered Hanford Sediments: Single-Pass Flow-Through and Column Experiments

Wang, Guohui,Um, Wooyong,Wang, Zheming,Reinoso-Maset, Estela,Washton, Nancy M.,Mueller, Karl T.,Perdrial, Nicolas,O’Day, Peggy A.,Chorover, Jon American Chemical Society 2017 Environmental science & technology Vol.51 No.19

<P>The reaction of acidic radioactive waste with sediments can induce mineral transformation reactions that, in turn, control contaminant fate. Here, sediment weathering by synthetic uranium containing acid solutions was investigated using bench-scale experiments to simulate waste disposal conditions at Hanford's cribs (Hanford, WA). During acid weathering, the presence of phosphate exerted a strong influence over uranium mineralogy and a rapidly precipitated, crystalline uranium phosphate phase (meta-ankoleite [K(UO2)(PO4).3H(2)O] was identified using spectroscopic and diffraction-based techniques. In phosphate-free system, uranium oxyhydroxide minerals such as K-compreignacite [K-2(UO2)(6)O-4(OH)(6).7H(2)O] were formed. Single-pass flow-through (SPFT) and column leaching experiments using synthetic Hanford pore water showed that uranium precipitated as meta-ankoleite during acid weathering was strongly retained in the sediments, with an average release rate of 2.67 X 10(-12) mol g(-1) s(-1). In the absence of phosphate, uranium release was controlled by dissolution of uranium oxyhydroxide (compreignacitetype) mineral with a release rate of 1.05-2.42 X 10(-1) mol g(-1) s(-1). The uranium mineralogy and release rates determined for both systems in this study support the development of accurate U-release models for the prediction of contaminant transport. These results suggest that phosphate minerals may be a good candidate for uranium remediation approaches at contaminated sites.</P>