Manganese(II)-Catalyzed and Clay-Minerals-Mediated Reduction of Chromium(VI) by Citrate

2013 ◽  
Vol 47 (23) ◽  
pp. 13629-13636 ◽  
Author(s):  
Binoy Sarkar ◽  
Ravi Naidu ◽  
Gummuluru SR Krishnamurti ◽  
Mallavarapu Megharaj
Keyword(s):  
Clay Minerals ◽  
Chromium Vi ◽  
Mediated Reduction

scholarly journals Chromium isotope fractionation during reduction of Chromium(VI) by Iron(II/III)-bearing clay minerals

2021 ◽  
Vol 292 ◽  
pp. 235-253
Author(s):  
Claresta Joe-Wong ◽  
Karrie L. Weaver ◽  
Shaun T. Brown ◽  
Kate Maher
Keyword(s):  
Clay Minerals ◽  
Isotope Fractionation ◽  
Chromium Vi

Impact of various inorganic oxyanions on the removal rates of hexavalent chromium mediated by zero-valent iron

2010 ◽  
Vol 7 (3) ◽  
pp. 250 ◽  
Author(s):  
Mario Rivero-Huguet ◽  
William D. Marshall
Keyword(s):  
Soil Solution ◽  
Active Sites ◽  
Reaction Rate ◽  
Soil Extract ◽  
Zero Valent Iron ◽  
Model Decomposition ◽  
Chromium Vi ◽  
Rate Of Reaction ◽  
Mediated Reduction ◽  
Model Reactions

Environmental context.Oxyanions in soil extract can interfere with the zero valent iron induced reduction of chromium(VI) to chromium(III). At pH 6, the reaction rate was decreased (2 to 6-fold) by an equivalent of arsenate, phosphate or silicate but was increased by sulfate and remained unchanged by borate or nitrate. At pH 2, not only was the rate of reaction dramatically increased (∼900-fold) but interferences from the major components of soil solution (nitrate, silicate and sulfate) were minimised. Abstract.The rate of zero-valent iron (ZVI) mediated reduction of CrVI was dependent on the condition of the ZVI surface, the pH of the medium and on the presence of inorganic oxyanions that can interfere with the process by competing for active sites on the ZVI surface. Whereas at pH 2, a single exponential decay provided an acceptable fit to the data, for pH 6 an appreciably better fit to the data was obtained with the sum of two exponential decays. The surface area normalised rate constant (kSA1) corresponding to the first decay was considered to model reactions at exposed active sites and kSA2, corresponding to the second decay, was considered to model decomposition kinetics through an intervening oxyhydroxide layer above the ZVI surface. The rate of CrVI reduction was decreased ∼900-fold when the pH was increased from 2 to 6 in the absence of competing ions. At pH 2, interferences from the major components of soil solution (nitrate, silicate and sulfate) were minimised.

scholarly journals Kinetics and Products of Chromium(VI) Reduction by Iron(II/III)-Bearing Clay Minerals

2017 ◽  
Vol 51 (17) ◽  
pp. 9817-9825 ◽  
Author(s):  
Claresta Joe-Wong ◽  
Gordon E. Brown ◽  
Kate Maher
Keyword(s):  
Clay Minerals ◽  
Chromium Vi

scholarly journals Kinetics and Products of Chromium(VI) Reduction by Iron(II/III)-Bearing Clay Minerals

2020 ◽  
Author(s):  
Claresta Joe-Wong ◽  
Kate Maher ◽  
Gordon Brown
Keyword(s):  
Clay Minerals ◽  
Chromium Vi

Hydrated form of some clay minerals observed using a film sealed environmental cell

1978 ◽  
Vol 36 (1) ◽  
pp. 72-73
Author(s):  
N. Kohyama ◽  
K. Fukushima ◽  
A. Fukami
Keyword(s):  
Clay Minerals ◽  
Morphological Changes ◽  
Carbon Film ◽  
Electron Microscopic Observation ◽  
Adsorbed Water ◽  
Electron Microscopic ◽  
Hydrated Form ◽  
Thin Carbon ◽  
Environmental Cell ◽  
Thin Carbon Film

Since the interlayer or adsorbed water of some clay minerals are quite easily dehydrated in dried air, in vacuum, or at moderate temperatures even in the atmosphere, the hydrated forms have not been observed by a conventional electron microscope(TEM). Recently, specific specimen chambers, “environmental cells(E.C.),” have been developed and confirmed to be effective for electron microscopic observation of wet specimen without dehydration. we observed hydrated forms of some clay minerals and their morphological changes by dehydration using a TEM equipped with an E.C..The E.C., equipped with a single hole copper-microgrid sealed by thin carbon-film, attaches to a TEM(JEM 7A) with an accelerating voltage 100KV and both gas pressure (from 760 Torr to vacuum) and relative humidity can be controlled. The samples collected from various localities in Japan were; tubular halloysite (l0Å) from Gumma Prefecture, sperical halloysite (l0Å) from Tochigi Pref., and intermediate halloysite containing both tubular and spherical types from Fukushima Pref..

Colloidal systems in soils

1994 ◽  
Vol 52 ◽  
pp. 64-65
Author(s):  
J. Thieme ◽  
J. Niemeyer ◽  
P. Guttman
Keyword(s):  
Clay Minerals ◽  
Polymeric Materials ◽  
Spatial Arrangement ◽  
High Specific Surface Area ◽  
Turnover Rates ◽  
Colloidal Systems ◽  
Chemical Conditions ◽  
Aggregation Phenomena ◽  
Iron And Manganese ◽  
Soil Colloids

In soil science the fraction of colloids in soils is understood as particles with diameters smaller than 2μm. Clay minerals, aquoxides of iron and manganese, humic substances, and other polymeric materials are found in this fraction. The spatial arrangement (microstructure) is controlled by the substantial structure of the colloids, by the chemical composition of the soil solution, and by thesoil biota. This microstructure determines among other things the diffusive mass flow within the soils and as a result the availability of substances for chemical and microbiological reactions. The turnover of nutrients, the adsorption of toxicants and the weathering of soil clay minerals are examples of these surface mediated reactions. Due to their high specific surface area, the soil colloids are the most reactive species in this respect. Under the chemical conditions in soils, these minerals are associated in larger aggregates. The accessibility of reactive sites for these reactions on the surface of the colloids is reduced by this aggregation. To determine the turnover rates of chemicals within these aggregates it is highly desirable to visualize directly these aggregation phenomena.

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