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Speciation and solubility of thallium in low temperature systems: Additional aqueous and solid thallium species potentially important in soil environments

Speciation Studies in Soil, Sediment and Environmental Samples

Xiong, Yongliang

Thallium has numerous applications in industry. It is also of great environmental concern because of its high toxicity. Therefore, stabilities of its aqueous and solid species under low temperature environments are fundamentally important to its impact on environments. In previous publications (Xiong 2007, 2009), a number of aqueous and solid thallium species and their stabilities were addressed. However, several thallium species that are potentially important to soil environments, especially saline soil environments, have not been covered.

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TYPE Presentation YEAR 2013
OSTIScopus

Experimental determination of solubility constant of hydromagnesite (5424) in NaCl solutions up to 4.4m at room temperature

Chemical Geology

Xiong, Yongliang

This study reports the solubility constants of both synthetic and natural hydromagnesite (5424) determined in NaCl solutions with a wide range of ionic strength regarding the following reaction:. Mg5(CO3)4(OH)2.4H2O (cr)+10H+⇆5Mg2++4CO2(g)+10H2O(l)Solubility experiments were conducted from undersaturation in deionized water and 0.10-4.4m NaCl solutions at PCO2 of 10-3.4atm and 22.5°C, and lasting up to 1870days. Based on the specific interaction theory, the weighted average solubility constant at infinite dilution calculated from the experimental results in 0.10-3.2m NaCl solutions using the natural hydromagnesite (5424) from Staten Island, New York, is 58.39±0.40 (2σ) in logarithmic units at 22.5°C with a corresponding value of 57.93±0.40 (2σ) at 25°C. Similarly, the weighted average solubility constant using the natural hydromagnesite (5424) from Gabbs, Nevada, is 59.54±0.72 (2σ) in logarithmic units at 22.5°C with a corresponding value of 59.07±0.72 (2σ) at 25°C. The weighted average solubility constant of synthetic hydromagnesite (5424) determined from experiments in 0.10-4.4m NaCl solutions is 61.53±0.59 (2σ) in logarithmic units at 22.5°C with a corresponding value of 61.04±0.59 (2σ) at 25°C. The natural hydromagnesite has lower solubilities because of its higher crystallinity related to their origins than synthetic hydromagnesite. The solubility constant of synthetic hydromagnesite is about one order of magnitude lower than the literature values. The Gibbs free energies of formation at the reference state (25°C, 1bar) are -5896±2kJmol-1, -5889±4kJmol-1, and -5,878±3kJmol-1 for the natural hydromagnesite from Staten Island, New York, from Gabbs, Nevada, and for the synthetic hydromagnesite, respectively. © 2011 Elsevier B.V.

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TYPE Presentation YEAR 2011
OSTIScopus

Establishment of uncertainty ranges and probability distributions of actinide solubilities for performance assessment in the Waste Isolation Pilot Plant (WIPP)

Xiong, Yongliang; Brush, Laurence H.; Long, Jennifer J.

The Fracture-Matrix Transport (FMT) code developed at Sandia National Laboratories solves chemical equilibrium problems using the Pitzer activity coefficient model with a database containing actinide species. The code is capable of predicting actinide solubilities at 25 C in various ionic-strength solutions from dilute groundwaters to high-ionic-strength brines. The code uses oxidation state analogies, i.e., Am(III) is used to predict solubilities of actinides in the +III oxidation state; Th(IV) is used to predict solubilities of actinides in the +IV state; Np(V) is utilized to predict solubilities of actinides in the +V state. This code has been qualified for predicting actinide solubilities for the Waste Isolation Pilot Plant (WIPP) Compliance Certification Application in 1996, and Compliance Re-Certification Applications in 2004 and 2009. We have established revised actinide-solubility uncertainty ranges and probability distributions for Performance Assessment (PA) by comparing actinide solubilities predicted by the FMT code with solubility data in various solutions from the open literature. The literature data used in this study include solubilities in simple solutions (NaCl, NaHCO{sub 3}, Na{sub 2}CO{sub 3}, NaClO{sub 4}, KCl, K{sub 2}CO{sub 3}, etc.), binary mixing solutions (NaCl+NaHCO{sub 3}, NaCl+Na{sub 2}CO{sub 3}, KCl+K{sub 2}CO{sub 3}, etc.), ternary mixing solutions (NaCl+Na{sub 2}CO{sub 3}+KCl, NaHCO{sub 3}+Na{sub 2}CO{sub 3}+NaClO{sub 4}, etc.), and multi-component synthetic brines relevant to the WIPP.

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TYPE Conference YEAR 2010
OSTI

Revised thermodynamic properties of brucite determined by solubility studies and its significance to nuclear waste isolation

Proposed for publication in Chemical Geology.

Xiong, Yongliang

MgO is the only engineered barrier certified by EPA for the Waste Isolation Pilot Plant (WIPP) in USA. The German Asse repository will also employ an Mg(OH){sub 2} (brucite)-based engineered barrier. The chemical function of the engineered barrier is to consume CO{sub 2} that may be generated by the microbial degradation of organic materials in waste packages. Experimental results at SNL indicate that MgO is first hydrated as brucite, and then brucite is carbonated as hydromagnesite (5424) (Mg{sub 5}(CO{sub 3}){sub 4}(OH){sub 2} {center_dot} 4H{sub 2}O). As MgO is in excess relative to CO{sub 2} that may be produced, the brucite-hydromagnesite (5424) assemblage would buffer f{sub CO2} in the repository. Consequently, the thermodynamic properties of this assemblage is of great significance to the performance assessment (PA) as actinide solubility is strongly affected by f{sub CO2}. In turn, PA is important to the demonstration of the long-term safety of nuclear waste repositories, as assessed by the use of probabilistic performance calculations. There is a substantial discrepancy for {Delta}{sub f}G{sub brucite}{sup 0} in recent publications, ranging from -830.4 (Harvie et al., 1984; Geochim. Cosmochim. Acta, 723-751), through -831.9 (Brown et al., 1996; J. Chem. Soc., Dalton Trans., 3071-3075), through -833.5 (Robie and Hemingway, 1995; USGS Bull., 2131), and to -835.9 kJ mol{sup -1} (Konigsberger et al., 1999; Geochim. Cosmochim. Acta, 3105-3119). Using the {Delta}{sub f}G{sub hydromagnesite (5424)}{sup 0} from Konigsberger et al., the predicted log f{sub CO2} for this assemblage would range from -5.96 ({Delta}{sub f}G{sub brucite}{sup 0} from Harvie et al.) to -4.84 ({Delta}{sub f}G{sub brucite}{sup 0} from Konigsberger et al.). Therefore, it is desirable to better constrain the {Delta}{sub f}G{sub brucite}{sup 0}. For this reason, a series of solubility experiments involving brucite in NaCl solutions ranging from 0.01 M to 4.0 M have being conducted at SNL. The derived {Delta}{sub f}G{sub brucite}{sup 0} from this study by extrapolation to infinite dilution via Pitzer formalism is -830.8 kJ mol{sup -1}, which is in excellent agreement with recommended values of Harvie et al. and Brown et al.

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TYPE Journal Article YEAR 2007
OSTI
Results 101–134 of 134
Results 101–134 of 134