Exothermic adsorption of chromate by goethite

Dabizha, A. A.; Kersten, Michael

doi:10.1016/j.apgeochem.2020.104785

Cited by 16 publications

(12 citation statements)

References 43 publications

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“…− may act as oxidants of Cr(III) [6,56,57] because their higher standard potentials favor that reaction [58]. Experimental data have shown that chromate adsorption by goethite is thermodynamically favorable through both inner-and outer-sphere surface complexation reactions [2]. These authors indicated that chromate adsorption decreases with increasing pH towards the zero-point-of-surface-charge (pHPZC 9.1) of the adsorbent surface, and ionic strength and temperature both affected outer-sphere surface complex.…”

Section: Interaction Between Cr(iii) With Major Seawater Ions In Coasmentioning

confidence: 99%

“…Among heavy metals, chromium (Cr) has become widespread in the environment. It appears in several oxidation states, the trivalent Cr(III) and hexavalent forms [Cr(VI)] being the most thermodynamically stable Cr forms in nature [1,2]. Cr(III) is necessary for lipid and sugar metabolism, and it is an essential trace element for human and animal health, whereas Cr(VI) in the food chain (groundwater, soil and plants), has created an alarming situation for human life and ecosystems [3][4][5].…”

Section: Introductionmentioning

confidence: 99%

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The Cr(VI) Stability in Contaminated Coastal Groundwater: Salinity as a Driving Force

Eliopoulos

Economou-Eliopoulos

2021

Minerals

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Chromium concentrations in seawater are less than 0.5 μg/L, but the Cr(VI) in contaminated coastal groundwater affected by Cr-bearing rocks/ores and/or human activities, coupled with the intrusion of seawater may reach values of hundreds of μg/L. A potential explanation for the stability of the harmful Cr(VI) in contaminated coastal aquifers is still unexplored. The present study is an overview of new and literature data on the composition of coastal groundwater and seawater, aiming to provide potential relationships between Cr(VI) with major components in seawater and explain the elevated Cr(VI) concentrations. It is known that the oxidation of Cr(III) to Cr(VI) and the subsequent back-reduction of Cr(VI) processes, during the transport of the mobilized Cr(VI) in various aquifers, facilitate the natural attenuation process of Cr(VI). Moreover, the presented positive trend between B and Cr(VI) and negative trend between δ53Cr values and B concentration may suggest that seawater components significantly inhibit the Cr(VI) reduction into Cr(III), and provide insights on the role of the borate, [B(OH)4]− ions, a potential buffer, on the stability of Cr(VI) in coastal groundwater. Therefore, efforts are needed toward the prevention and/or minimization of the contamination by Cr(VI) of in coastal aquifers, which are influenced by the intrusion of seawater and are threatened by changes in sea level, due to climate change. The knowledge of the contamination sources, hotspots and monitoring of water salinization processes (geochemical mapping) for every coastal country may contribute to the optimization of agricultural management strategies.

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Section: Interaction Between Cr(iii) With Major Seawater Ions In Coasmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Cr(VI) Stability in Contaminated Coastal Groundwater: Salinity as a Driving Force

Eliopoulos

Economou-Eliopoulos

2021

Minerals

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“…The value of data integration and model recalibration has been recognized in the research community, and various efforts have been made to refine the models, which include formulating reactions consistent with molecular-scale information from spectroscopy, better constraining equilibrium constants with growing datasets, and accounting for the variations in temperature and solid properties in different studies. − Dzombak and Morel , developed a seminal method to estimate log K s of the surface complexation reactions under different experimental conditions. They used FITEQL to find best fits for each individual experimental adsorption edge and then estimated the equilibrium constants by taking the weighted average.…”

Section: Introductionmentioning

confidence: 99%

Intercomparison and Refinement of Surface Complexation Models for U(VI) Adsorption onto Goethite Based on a Metadata Analysis

Satpathy

Wang

Giammar

et al. 2021

Environ. Sci. Technol.

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Adsorption of uranium onto goethite is an important partitioning process that controls uranium mobility in subsurface environments, for which many different surface complexation models (SCMs) have been developed. While individual models can fit the data for which they are parameterized, many perform poorly when compared with experimental data covering a broader range of conditions. There is an imperative need to quantitatively evaluate the variations in the models and to develop a more robust model that can be used with more confidence across the wide range of conditions. We conducted an intercomparison and refinement of the SCMs based on a metadata analysis. By seeking the globally best fit to a composite dataset with wide ranges of pH, solid/sorbate ratios, and carbonate concentrations, we developed a series of models with different levels of complexity following a systematic roadmap. The goethite−uranyl−carbonate ternary surface complexes were required in every model. For the spectroscopically informed models, a triple-plane model was found to provide the best fit, but the performance of the double-layer model with bidentate goethite−uranyl and goethite−uranyl−carbonate complexes was also comparable. Nevertheless, the models that ignore the bidentate feature of uranyl surface complexation consistently performed poorly. The goodness of fitting for the models that ignore adsorption of carbonate and the charge distributions was not significantly compromised compared with that of their counterparts that considered those. This approach of model development for a large and varied dataset improved our understanding of U(VI)−goethite surface reactions and can lead to a path for generating a single set of reactions and equilibrium constants for including U(VI) adsorption onto goethite in reactive transport models.

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“…On the other hand, the literature indicates that oxyanion adsorption is generally exothermic. 7 Uranyl carbonate complexes are commonly negatively charged, which turns the uranyl oxycation into an U(VI) anion. Adsorption of U(VI) would then become exothermic, meaning that it would become weaker rather than stronger with increasing temperature under ambient CO 2 , which is not just what Estes and Powell claim on the basis of their limited experimental conditions.…”

mentioning

confidence: 99%

“…Estes and Powell correctly interpreted the literature yet available, indicating that cation (and hence also oxycation) adsorption is generally an endothermic process. On the other hand, the literature indicates that oxyanion adsorption is generally exothermic . Uranyl carbonate complexes are commonly negatively charged, which turns the uranyl oxycation into an U(VI) anion.…”

mentioning

confidence: 99%