Thermodynamic properties and environmental chemistry of chromium

Schmidt, R.L.

doi:10.2172/6675931

Cited by 19 publications

(10 citation statements)

References 5 publications

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“…The DCBtreated kaolinite adsorbed the most CrO4 a-, whereas the kaolinite treated with acidified NaCIO4 adsorbed the least. Analyses of the equilibrium solutions from 14.56 Schmidt (1984) these experiments provided no explanation for this behavior. Silica, however, was present at approximately 10 -3.5 M concentration in all pretreatment solutions; this concentration decreased with pH, suggesting that Si was adsorbed on the kaolinite.…”

Section: Influence Of Kaolinite Pretreatmentmentioning

confidence: 90%

Chromate Adsorption by Kaolinite

Zachara

1988

Clays and clay miner.

136

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Abstract-Chromate (CrO4 2-) adsorption was investigated on kaolinite (0.2-2 ~m) saturated with NaC104 over a range of pH. Adsorption increased with decreasing pH because of protonation of chromate and/ or variable charge sites on kaolinite. Chemical pretreatment to remove noncrystalline and crystalline oxide contaminants affected the magnitude ofCrO42-adsorption, but not the pH range over which CrO42-adsorbed. Chromate adsorption at different sorbate and sorbent concentrations increased below the pHz~ for the kaolinite edge, suggesting the formation of weak surface complexes. If frO4 2-and SO42-were present at equal concentration (5.0 x 10 -7 M), the two solutes sorbed independently, suggesting binding to separate sites. The presence of excess SO42-(5.0 x 10 -4 M), however, unexplainably enhanced CrO42-adsorption. The adsorption of both chromate and sulfate can be described in terms of a site-binding model of the kaolinite edge, in which the edge is viewed as composite layers of AI and Si oxide. Surface complexation constants for CrO4 2-on kaolinite were similar to those for alumina, pointing to the importance of A1-OH edge sites in chromate adsorption.

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Section: Influence Of Kaolinite Pretreatmentmentioning

confidence: 90%

Chromate Adsorption by Kaolinite

Zachara

1988

Clays and clay miner.

136

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“…Clay minerals, which are abundant in mudstone, control cation exchange in the Central Oklahoma aquifer. Whole-rock X-ray diffraction (XRD) (Breit and (Wagman and others, 1968;Barton and Skinner, 1979); chromium (Schmidt, 1984;Rai, Sass, and Moore, 1987); iron (Wagman and others, 1968;Nordstrom and others, 1990); selenium (Wagman and others, 1968;Vaughn and Craig, 1978); uranium . others, 1990) determined that sandstones interbedded with mudstones in the clay-rich Chase, Council Grove, and Admire Groups, undivided, in the east, just below the confining layer, and at depth in the Garber Sandstone and Wellington Formation contain more clay than sandstones in the sand-rich part of the aquifer.…”

Section: Relation Of Mudstone Distribution To Water Chemistry and Arsmentioning

confidence: 99%

“…Uranium is oxidized to uranium (VI) at an Eh slightly higher than that required to oxidize arsenic (III) to arsenic (V). The oxycation adsorbs on Dissolved uranium activity = 10"7 M, carbon = 10"2-2 M, phosphorous = 10"6-3 M. Sources of thermodynamic data used to construct diagrams: arsenic (Wagman and others, 1968;Barton and Skinner, 1979); chromium (Schmidt, 1984;Rai, Sass, and Moore, 1987); iron (Wagman and others 1968;Nordstrom and others, 1990); selenium (Wagman and others, 1968;Vaughn and Craig, 1978); and uranium .…”

Section: Appendicesmentioning

confidence: 99%

Ground-water quality assessment of the central Oklahoma aquifer, Oklahoma: results of investigations

Christenson¹,

Havens²

1994

Open-File Report

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“…The secant iterative method was used to solve the equilibria problem [ 181. Recently MINTEQ, the geochemical model incorporated into MEXAMS (Metals Exposure Analysis Modeling System) [19], has been updated with a critically reviewed thermodynamic data base for chromium [20]. Preliminary com- parisons between our model and MINTEQ's predictions yielded no more than 10% variation in hexavalent chromium species distributions.…”

Section: Toxicity Data Analysis and Model Developmentmentioning

confidence: 99%

Comparative Toxicity and Speciation of Two Hexavalent Chromium Salts in Acute Toxicity Tests

Jop¹,

Parkerton²,

Rodgers³

et al. 1987

Environ Toxicol Chem

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The comparative acute toxicity of potassium chromate and dichromate salts to six aquatic species including both freshwater and marine forms was investigated. A thermodynamic equilibrium model was developed to aid in interpreting toxicity data with respect to hexavalent chromium speciation. Although parallel acute toxicity tests conducted with both salts yielded similar LCSO values, toxicity differences tended to become more pronounced as the sensitivity of the test species to the chemical decreased. Observed changes in pH and predicted changes in chromium speciation that occurred between the two salts in tests with less sensitive species were postulated to explain these findings. The implication of the aqueous chromium species to the relative toxicity of the hexavalent chromium are discussed. If hexavalent chromium is widely adopted as a standard reference toxicant for aquatic toxicity testing then the chromate salt should be used since it does not appreciably alter the initial pH of the dilution water and subsequent speciation to the extent that would be expected if the dichromate salt was employed. Standardization of the source of hexavalent chromium used in reference tests will facilitate intralaboratory comparison of toxicity data.

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Thermodynamic properties and environmental chemistry of chromium

Cited by 19 publications

References 5 publications

Chromate Adsorption by Kaolinite

Chromate Adsorption by Kaolinite

Ground-water quality assessment of the central Oklahoma aquifer, Oklahoma: results of investigations

Comparative Toxicity and Speciation of Two Hexavalent Chromium Salts in Acute Toxicity Tests

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