Easily reducible metal oxide-bound

Easily reducible metal oxide-bound Organic bound... 

Fraction 4. Easily reducible metal oxide-bound 0.1 M NHjOH HCl in 0.01 M HNO3 (soil/reagent = 1 20) shake for 30 min. 

The form of nickel in particles from different industries varies. The mineralogical composition, chemical content, and form of dusts from nine industries in Cracow, Poland, were examined (Rybicka 1989). The chemical form of a particle-associated heavy metal that was assessed by a five-step extraction scheme classified the metal as exchangeable, easily reducible (manganese oxides, partly amorphous iron oxyhydrates and carbonates), moderately reducible (amorphous and poorly crystallized iron oxyhydrates), organically bound or sulfidic, and residual. Dusts from power plants had a silicate characteristic with quartz and mullite predominant. Approximately 90% of the nickel from these... 

Easily reducible Specifically Organic metal oxide-bound adsorbed -bound... 

Zinc adsorption can occur via exchange of Zn2+ and Zn(OH)+ with surface-bound Ca2+ on calcite (Zachara et al., 1988). Zinc and Ni form surface complexes on calcite as hydrate until they are incorporated into the structure via recrystallization (Zachara et al., 1991). The selectivity of metal sorption on calcite is as follows Cd > Zn > Ni (Zachara et al., 1991). The easily reducible oxide bound metals are primarily from Mn oxides (Chao, 1972 Shuman, 1982 and 1985a). At pH > 6, Zn sorption on Mn oxide abruptly increases because of hydroxylation of the ions (Loganathan et al., 1977), and a high soil pH in arid soil may favor Zn sorption on Mn oxides due to a great... 

In a second group of metal oxides, which are not easily reduced, the oxygen is strongly bound and the catalyst is generally in a fully oxidized state. Thus O2- is not reactive, but an adsorbed form of oxygen, much more weakly bound, is active. This leads only to combustion. Quite a number of these metals are non-transition metal oxides. 

The metal phases which are presumed to be sequentially extracted are step 1, soluble, exchangeable and carbonate-bound metals step 2, metals occluded in easily reducible manganese and iron oxides step 3, organically bound metals and sulphides step 4 , metals in non-silicate minerals lattice structure. It is important to emphasise that these metal phases are nominal target only, operationally defined by the extraction used. Consequently, is highly desirable and recommended to refer to the sequentially extracted metal fractions as easily extractable , reducible , oxidi-sable and residual , respectively. 

The key points from these experiments are that the more easily replaceable monophosphine ligands are required for the reduction of N2, which is favored by the presence of oxo-anions. Thus, as the reaction proceeds and electron density passes from metal to N2, the 7r-acceptor phosphines are replaced successively by 7r-donor oxo species. This change in ligand encourages further release of metal electron density onto the bound, partially reduced N2, which results in its protonation. This resulting effective increase in the oxidation state of the metal then causes further substitution of the softer phosphines by the harder oxo-anions. These mutually enhancing effects result ultimately in complete loss of all phosphine ligands and the production of NH3. 

Charge transfer bands result whenever an easily oxidized ligand is bound to a trivalent lanthanide ion which can be reduced to the divalent state or when the ligand is bound to one of the tetravalent ions (J0rgensen, 1970). Such transitions are commonly observed in the spectra of complexes of samarium(III), euro-pium(III), thulium(III), ytterbium(III), and cerium(IV). The position of these bands in the spectrum is markedly dependent on the ligand and the metal ion. For example, in the ions RCU the charge transfer bands for europium(III),... 

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