Hydrophobic C18 Bound Organic Complexes of Chromium and Their Potential Impact on the Geochemistry of Cr in Natural Waters

1994 ◽  
Vol 28 (5) ◽  
pp. 799-804 ◽  
Author(s):  
Scott E. Kaczynski ◽  
Robert J. Kieber
Keyword(s):  
Natural Waters ◽  
Organic Complexes ◽  
Potential Impact

Organic complexes of iron and aluminium in natural waters

Nature ◽  
1976 ◽  
Vol 260 (5550) ◽  
pp. 418-420 ◽  
Author(s):  
EDWARD M. PERDUE ◽  
KEVIN C. BECK ◽  
J. HELMUT REUTER
Keyword(s):  
Natural Waters ◽  
Organic Complexes

scholarly journals The Solubility and Hydrolysis of Aqueous Aluminium Hydroxides in Dilute Fresh Waters at Different Temperatures

1990 ◽  
Vol 21 (3) ◽  
pp. 195-204 ◽  
Author(s):  
Espen Lydersen
Keyword(s):  
Natural Waters ◽  
Equilibrium Constants ◽  
Relative Concentration ◽  
Amorphous Solid ◽  
Effect Of Temperature ◽  
Natural Soil ◽  
Exchange Reactions ◽  
Organic Complexes ◽  
Inorganic Species ◽  
Different Temperatures

This study is mainly focusing on the effect of temperature and pH on the chemistry of Al(OH)3(s) using available thermodynamic data. The calculations show that a doubling of the [H+] or a decrease in temperature by 15°C, approximately yields the same solubility increase of the various Al(OH)3(s) presented. The relative concentration of aqueous aluminium hydrolysis complexes is also highly temperature dependent. At 25°C and pH 5, the calculated distribution of dissolved, inorganic aluminium hydroxides corresponds to about 36% of Al3+, 37 % of Al(OH)2+, 26 % of Al(OH)2+ and 1 % of Al(OH)30. At the same pH but at 0°C, about 84%, 13%, 2% and 0% are present as Al3+, Al(OH)2+, Al(OH)2+ and Al(OH)30, respectively. This temperature effect is of major importance as the hydroxide species are supposed to be the most toxic species to aquatic biota. Literature reports on the equilibrium constants Al(OH)3(s), log*Ks, vary from about 8 to 11, a variation in the product by a factor of 1000. In natural soil/water systems the solubility products of crystalline and amorphous solid aluminium sources are unknown and the solubility may also be coupled to combined weathering/ion exchange processes. In addition substantial amount of aluminium may be present as organic complexes where aluminium by cation exchange reactions may enter the solution as monomeric inorganic species. Thus, if a low value for the equilibrium constants of Al(OH)3(s) is used as reference when calculating the degree of aluminium saturation, an apparent oversaturation will often be demonstrated. To estimate the degree of aluminium saturation in natural waters whould therefore only be of theoretical interest.

Chemical Speciation of Environmentally Significant Metals: An IUPAC contribution to reliable and rigorous computer modelling

2015 ◽  
Vol 37 (1) ◽  
Author(s):  
Kipton J. Powell ◽  
Paul L. Brown ◽  
Robert H. Byrne ◽  
Tamas Gajda ◽  
Glenn Hefter ◽  
...  
Keyword(s):  
Metal Ions ◽  
Natural Waters ◽  
Chemical Speciation ◽  
Computer Modelling ◽  
Adsorbed Species ◽  
Mineral Phases ◽  
Organic Complexes ◽  
Anionic Ligands ◽  
Ligand Species ◽  
Metal Ligand

The mobility and bioavailability of metal ions in natural waters depend on their chemical speciation, which involves a distribution of the metal ions between different complex (metal-ligand) species, colloid-adsorbed species and insoluble phases, each of which may be kinetically labile or inert. For example, in fresh water the metal ions are distributed among organic complexes (e.g., humates), colloids (e.g., as surface-adsorbed species on colloidal phases such as FeOOH), solid phases (e.g., hydroxide, oxide, carbonate mineral phases), and labile complexes with the simple inorganic anionic ligands commonly present in natural waters (e.g., for Zn

Studies of metal–organic interactions in model systems pertaining to natural waters

1976 ◽  
Vol 54 (16) ◽  
pp. 2600-2611 ◽  
Author(s):  
Robert D. Guy ◽  
C. L. Chakrabarti
Keyword(s):  
Humic Acid ◽  
Organic Acids ◽  
Stability Constants ◽  
Tannic Acid ◽  
Natural Waters ◽  
Model Systems ◽  
Organic Complexes ◽  
Metal Organic ◽  
Acid Release ◽  
The Stability

The interactions of Cu(II), Pb(II), Cd(II), and Zn(II) with humic and tannic acids were studied to evaluate the possibility of metal speciation using a combination of dialysis/atomic absorption spectroscopy, and the pH characteristics of the metal–organic species. The stability constants of metal–organic complexes were found to decrease in the order Pb(II) > Cu(II) > Cd(II) > Zn(II) and EDTA > humic acid > tannic acid. Scatchard plots for the metal–humic acid systems indicated two types of binding sites with a difference in stability constants of about 10. Ultrafiltration of metal–humic acid solutions indicated that the metal ions were concentrated in the large molecular size fractions (> 3.1 nm). Separation by dialysis was used to investigate the release of metal from model sediment components by the organic acids (the metal–organic complexes were non-dialyzable). For release of copper from bentonite, it was found that the amount of copper released depended on both the concentration of ligand and the stability constant of metal complex, with the ratio of metal release to complexing sites decreasing in the order EDTA > humic acid > tannic acid. Release of metal from the solids decreased in the order: bentonite > MnO2 > humic acid. Release of metal from the hydrous oxides via a redox decomposition of the oxide by natural organics was investigated using pyrogallol, gallic, and tannic acids. At natural water pH levels (6–8), 20 μg/ml solutions of the organic acids released 20 μmol manganese per 100 ml solutions whereas at pH 2, 60 μmol manganese were released. The pH behaviour of the organic acids has been explained in terms of formation of oxalic acid at pH &([a-z]+); 5, which then reduces the hydrous oxide.

The Application of a Simple Chemical Model of Natural Waters to Metal Fixation in Particulate Matter

1975 ◽  
Vol 53 (5) ◽  
pp. 661-669 ◽  
Author(s):  
Robert D. Guy ◽  
C. L. Chakrabarti ◽  
Laurier L. Schramm
Keyword(s):  
Humic Acid ◽  
Natural Waters ◽  
Anodic Stripping Voltammetry ◽  
Copper Ion ◽  
Freundlich Isotherm ◽  
Stripping Voltammetry ◽  
Differential Pulse ◽  
Chemical Model ◽  
Organic Complexes ◽  
Simple Chemical

A simple chemical model was used to investigate the mechanisms controlling the distribution of metals between soluble and particulate fractions in natural waters. The model particulates used were potassium bentonite, hydrous MnO2, and solid humic acid. The soluble species in natural waters were modelled by soluble humic acid, tannic acid, and bicarbonate. The sorption curves for Cu(II), Cd(II), and Zn(II) onto humic acid and MnO2 obeyed Langmuir adsorption isotherms whereas the sorption of the above ions onto bentonite followed a Freundlich isotherm. Chemical analysis of the total model using atomic absorption spectroscopy and differential pulse anodic stripping voltammetry indicated that copper distribution depends on the pH of the suspension: above pH 6.0, 50 % of the copper is sorbed onto the particulates whereas the copper in solution is in a complexed form; between pH 6 and 3.8 the soluble copper is distributed between organic complexes and "free" copper ion; between pH 4.2 to 2.5 copper is being desorbed from the particulates; and below pH 2.5 all the copper is present in solution as "free" copper ion.

Effects of Gender, Parental Role, and Time on Infant- and Adult-Directed Read and Spontaneous Speech

2019 ◽  
Vol 62 (11) ◽  
pp. 4001-4014
Author(s):  
Melanie Weirich ◽  
Adrian Simpson
Keyword(s):  
Parental Involvement ◽  
Gender Identity ◽  
Spontaneous Speech ◽  
First Year ◽  
Space Size ◽  
Vowel Space ◽  
Potential Impact ◽  
Phonetic Features ◽  
And Gender ◽  
Description Task

Purpose The study sets out to investigate inter- and intraspeaker variation in German infant-directed speech (IDS) and considers the potential impact that the factors gender, parental involvement, and speech material (read vs. spontaneous speech) may have. In addition, we analyze data from 3 time points prior to and after the birth of the child to examine potential changes in the features of IDS and, particularly also, of adult-directed speech (ADS). Here, the gender identity of a speaker is considered as an additional factor. Method IDS and ADS data from 34 participants (15 mothers, 19 fathers) is gathered by means of a reading and a picture description task. For IDS, 2 recordings were made when the baby was approximately 6 and 9 months old, respectively. For ADS, an additional recording was made before the baby was born. Phonetic analyses comprise mean fundamental frequency (f0), variation in f0, the 1st 2 formants measured in /i: ɛ a u:/, and the vowel space size. Moreover, social and behavioral data were gathered regarding parental involvement and gender identity. Results German IDS is characterized by an increase in mean f0, a larger variation in f0, vowel- and formant-specific differences, and a larger acoustic vowel space. No effect of gender or parental involvement was found. Also, the phonetic features of IDS were found in both spontaneous and read speech. Regarding ADS, changes in vowel space size in some of the fathers and in mean f0 in mothers were found. Conclusion Phonetic features of German IDS are robust with respect to the factors gender, parental involvement, speech material (read vs. spontaneous speech), and time. Some phonetic features of ADS changed within the child's first year depending on gender and parental involvement/gender identity. Thus, further research on IDS needs to address also potential changes in ADS.

Exploring the Potential Impact of Sentence-Level Comprehension and Sentence-Level Fluency on Deaf Students' Passage Comprehension

2020 ◽  
Vol 63 (7) ◽  
pp. 2281-2292
Author(s):  
Ying Zhao ◽  
Xinchun Wu ◽  
Hongjun Chen ◽  
Peng Sun ◽  
Ruibo Xie ◽  
...  
Keyword(s):  
Independent Predictor ◽  
Vocabulary Knowledge ◽  
Group Differences ◽  
Regression Analyses ◽  
Deaf Students ◽  
Mediating Role ◽  
Sentence Level ◽  
Mediating Mechanisms ◽  
Potential Impact ◽  
The Relationship

Purpose This exploratory study aimed to investigate the potential impact of sentence-level comprehension and sentence-level fluency on passage comprehension of deaf students in elementary school. Method A total of 159 deaf students, 65 students ( M age = 13.46 years) in Grades 3 and 4 and 94 students ( M age = 14.95 years) in Grades 5 and 6, were assessed for nonverbal intelligence, vocabulary knowledge, sentence-level comprehension, sentence-level fluency, and passage comprehension. Group differences were examined using t tests, whereas the predictive and mediating mechanisms were examined using regression modeling. Results The regression analyses showed that the effect of sentence-level comprehension on passage comprehension was not significant, whereas sentence-level fluency was an independent predictor in Grades 3–4. Sentence-level comprehension and fluency contributed significant variance to passage comprehension in Grades 5–6. Sentence-level fluency fully mediated the influence of sentence-level comprehension on passage comprehension in Grades 3–4, playing a partial mediating role in Grades 5–6. Conclusions The relative contributions of sentence-level comprehension and fluency to deaf students' passage comprehension varied, and sentence-level fluency mediated the relationship between sentence-level comprehension and passage comprehension.

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