MINTEQA2/PRODEFA2-A Geochemical Speciation Model and Interactive Preprocessor

2015 ◽  
pp. 241-252 ◽  
Author(s):  
Jerry D. Allison ◽  
David S. Brown
Keyword(s):  
Speciation Model ◽  
Geochemical Speciation

Development of a Geochemical Speciation Model for Use in Evaluating Leaching from a Cementitious Radioactive Waste Form

2021 ◽  
Author(s):  
Zhiliang Chen ◽  
Peng Zhang ◽  
Kevin G. Brown ◽  
Janelle L. Branch ◽  
Hans A. van der Sloot ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Waste Form ◽  
Speciation Model ◽  
Geochemical Speciation

scholarly journals GEOCHEMICAL SPECIATION AND BATCH MODE SIMULATION IN THE CARBONATE DEPOSITIONAL ENVIRONMENTS

2019 ◽  
Vol 16 (33) ◽  
pp. 736-748
Author(s):  
M. A. KLUNK ◽  
S. DASGUPTA ◽  
M. DAS ◽  
P. R. WANDER ◽  
A. DI CAPUA
Keyword(s):  
Geochemical Modeling ◽  
Chemical Species ◽  
Sedimentary Basins ◽  
Depositional Environments ◽  
Algebraic Equations ◽  
Batch Mode ◽  
Factors Affecting ◽  
Speciation Model ◽  
Depositional Settings ◽  
Geochemical Speciation

Geochemical modeling has been frequently used to understand and interpret water-rock interactions in sedimentary basins. Thermodynamic data, kinetic parameters, numerical methods, boundary history, and boundary conditions are factors affecting any geochemical modeling system. In the present study, we have attempted to establish a geochemical speciation model by comparing the interaction of formation water and carbonate rock in the carbonate depositional settings of Cambrian successions of Bachu and Tarim area. A comparative study of geochemical speciation has been performed using four different software: PHREEQCTM, GWBTM, TOUGHREACTTM, and GEODELING. GEODELING is a geochemical code simulator that we have developed, and the details are presented further in this work. All the software has been analyzed minutely, considering the distribution, mobility, and availability of chemical species in geological environments. Very similar results in speciation are observed while working with low-temperature systems. A discrepancy can be observed in the results while working with high temperatures. However, a thorough Newton-Raphson formulation, scaling of algebraic equations and master-species switching helps to reduce the possibility of failures of the numerical method used in PHREEQCTM.

Experimental Validation of a Speciation Model Applied to Organic-Rich Groundwaters

1994 ◽  
Vol 353 ◽  
Author(s):  
M. B. Crawford ◽  
J. J. W. Higgo ◽  
J. Davis
Keyword(s):  
Citric Acid ◽  
Experimental Validation ◽  
Hplc Method ◽  
Electrostatic Model ◽  
Speciation Model ◽  
Natural Organic Compounds ◽  
Anionic Ligands ◽  
Geochemical Speciation ◽  
Discrete Site ◽  
Inorganic Speciation

AbstractNatural organic compounds can play an important role in the transport of radionuclides through the geosphere, but the inclusion of polyelectrolytic fulvic and humic acids into geochemical speciation codes is not straightforward. Schubert ion-exchange experiments have been used to parameterise an equilibrium-based, discrete site-electrostatic model, Model V, which is concerned with predicting trace metal-humic interactions in solution. However, before such a model can be applied to natural groundwaters, its ability to deal with competition between trace cations and anionic ligands has to be tested.PHREEQEV, which incorporates Model V with the inorganic speciation code PHREEQE, has been used to guide experiments based on a modified Hummel-Dreyer method. To improve speed and precision, these experiments used a HPLC method rather than Sephadex gel, and measured the effect of Ca on Co and Ni binding to fulvic acid. The results were compared with the predictions made by PHREEQEV. Although the system was further complicated by the need to add citric acid to prevent binding of metals to the HPLC column, predictions at pH 5 were good for both metals. At pH 7, the Co binding results were not well predicted and the reasons for this are still unclear. Comparisons between the Schubert and Hummel-Dreyer-type experiments show that the two methods are compatible.

Consideration on modeling of Nb sorption onto clay minerals

2020 ◽  
Vol 108 (11) ◽  
pp. 873-877
Author(s):  
Tetsuji Yamaguchi ◽  
Saki Ohira ◽  
Ko Hemmi ◽  
Logan Barr ◽  
Asako Shimada ◽  
...  
Keyword(s):  
Distribution Coefficient ◽  
Clay Minerals ◽  
Safety Assessment ◽  
Distribution Coefficients ◽  
Surface Species ◽  
Complex Species ◽  
Intermediate Depth ◽  
Speciation Model ◽  
Surface Phases ◽  
High Distribution Coefficient

AbstractSorption distribution coefficient (Kd) of niobium-94 on minerals are an important parameter in safety assessment of intermediate-depth disposal of waste from core internals etc. The Kd of Nb on clay minerals in Ca(ClO4)2 solutions were, however, not successfully modeled in a previous study. The high distribution coefficients of Nb on illite in Ca(ClO4)2 solutions were successfully reproduced by taking Ca–Nb–OH surface species into account. Solubility of Nb was studied in Ca(ClO4)2 solutions and the results were reproduced by taking an aqueous Ca–Nb–OH complex species, CaNb(OH)6+, into account in addition to previously reported Nb(OH)6− and Nb(OH)72−. Based on this aqueous speciation model, the Ca–Nb–OH surface species responsible for the sorption of Nb on illite in Ca(ClO4)2 solutions was presumed to be X_OCaNb(OH)6. Although uncertainties exist in the speciation of aqueous Ca–Nb–OH species, the result of this study proposed a possible mechanism for high distribution coefficient of Nb on illite in Ca(ClO4)2 solutions. The mechanism includes Ca–Nb–OH complex formation in aqueous, solid and surface phases.

Special Speciation

2015 ◽  
Vol 77 (2) ◽  
pp. 145-147
Author(s):  
Lyn L. Countryman ◽  
Jill D. Maroo
Keyword(s):  
High School ◽  
Elementary Education ◽  
Anecdotal Evidence ◽  
Education Students ◽  
Biology Students ◽  
Entry Level ◽  
Speciation Model ◽  
Hands On ◽  
Elementary Education Students

Considerable anecdotal evidence indicates that some of the most difficult concepts that both high school and undergraduate elementary-education students struggle with are those surrounding evolutionary principles, especially speciation. It’s no wonder that entry-level biology students are confused, when biologists have multiple definitions of “species.” We developed this speciation activity to provide clarity and allow students a hands-on experience with a speciation model.

Geochemical speciation and risk assessment of metals in the river sediments from Dan River Drainage, China

2016 ◽  
Vol 32 (3) ◽  
pp. 221-237 ◽  
Author(s):  
Qingpeng Meng ◽  
Jing Zhang ◽  
Jicheng Feng ◽  
Zhaoyu Zhang ◽  
Tairan Wu
Keyword(s):  
Risk Assessment ◽  
River Sediments ◽  
River Drainage ◽  
Geochemical Speciation

scholarly journals Assembly processes of gastropod community change with horizontal and vertical zonation in ancient Lake Ohrid: a metacommunity speciation perspective

2016 ◽  
Vol 13 (10) ◽  
pp. 2901-2911 ◽  
Author(s):  
Torsten Hauffe ◽  
Christian Albrecht ◽  
Thomas Wilke
Keyword(s):  
Community Composition ◽  
Community Assembly ◽  
Environmental Filtering ◽  
Dispersal Limitation ◽  
Species Interaction ◽  
Relative Importance ◽  
Lake Depth ◽  
Ancient Lake ◽  
Lake Ohrid ◽  
Speciation Model

Abstract. The Balkan Lake Ohrid is the oldest and most diverse freshwater lacustrine system in Europe. However, it remains unclear whether species community composition, as well as the diversification of its endemic taxa, is mainly driven by dispersal limitation, environmental filtering, or species interaction. This calls for a holistic perspective involving both evolutionary processes and ecological dynamics, as provided by the unifying framework of the “metacommunity speciation model”.The current study used the species-rich model taxon Gastropoda to assess how extant communities in Lake Ohrid are structured by performing process-based metacommunity analyses. Specifically, the study aimed (1) to identifying the relative importance of the three community assembly processes and (2) to test whether the importance of these individual processes changes gradually with lake depth or discontinuously with eco-zone shifts.Based on automated eco-zone detection and process-specific simulation steps, we demonstrated that dispersal limitation had the strongest influence on gastropod community composition. However, it was not the exclusive assembly process, but acted together with the other two processes – environmental filtering and species interaction. The relative importance of the community assembly processes varied both with lake depth and eco-zones, though the processes were better predicted by the latter.This suggests that environmental characteristics have a pronounced effect on shaping gastropod communities via assembly processes. Moreover, the study corroborated the high importance of dispersal limitation for both maintaining species richness in Lake Ohrid (through its impact on community composition) and generating endemic biodiversity (via its influence on diversification processes). However, according to the metacommunity speciation model, the inferred importance of environmental filtering and biotic interaction also suggests a small but significant influence of ecological speciation. These findings contribute to the main goal of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) deep drilling initiative – inferring the drivers of biotic evolution – and might provide an integrative perspective on biological and limnological dynamics in ancient Lake Ohrid.

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