Cationic metal species

To understand chemical exposure and bioavailability the biotic ligand model (BLM) was developed for single (cationic) metal species, assuming that the amount of a... 

Reduced acceptor substrates such as n radical anions can form complexes with neutral or cationic metal species which may be quite persistent, especially if the acceptors contain good metal coordination sites such as carbonyl oxygen or imine nitrogen groups (3,8) [14,78]. 

For simplicity, in this equation, we have assumed that activities are equal to concentrations and brackets refer to activities. C is a units conversion constant = Vy m relating void volume Vy (mL) in the porous media and the mass m (g) of the aquifer material in contact with the volume Vy, is the formation constant for an aqueous uranyl complex, and the superscripts i, j, k describe the stoichiometry of the complex. The form that the sorption binding constant takes is different for the different sorption models shown in Figure 4 (e.g., see Equation (5)). Leckie (1994) derives similar expressions for more complex systems in which anionic and cationic metal species form poly dentate surface complexes. Equation (7) can be derived from the following relationships for this system ... 

Lopez-Gonzalez et al. [218] also failed to cite the study by Humenick and Schnoor [216], but they analyzed in some detail the effect of carbon-oxygen and carbon-sulfur surface complexes on the uptake of mercuric chloride, which is very weakly ionized in aqueous solution. (The effectiveness of sulphurized carbons in removing mercury from air or water streams had been demonstrated earlier by Sinha and Walker [219], Humenick and Schnoor [216], and more recently by G6mez-Serrano and coworkers [208].) Their key results are summarized in Fig. 9. There was a noticeable uptake decrease when the activated carbons were oxidized with H Oi (AO). This decrease was not due to a reduction in the surface area and is contrary to the behavior of cationic metallic species, whose uptake is typically enhanced as a consequence of a lower pHp/x of the oxidized carbon. Upon subsequent heat treatment in helium at 873 K (A-873), the adsorption ca-... 

Several approaches to immobilize transition metal catalysts on polymer supports have been reported in the literature. The most representative ones are (1) immobilization of ligands as well as ligand-metal complexes by covalent and/or coordination bonds (2) adsorption of catalysts on the supports (3) formation of ionic pairs between, for example, the surface of the support bearing anionic functional groups and cationic metal species and (4) entrapment of catalysts... 

Donnan dialysis In Donnan dialysis, a cation-exchange membrane separates the donor and receptor solutions. Cationic metal species are transported across the membrane driven by the negative electrostatic potential (the Donnan potential) across the membrane, until equilibrium is achieved. Matching of the ionic strengths of donor and acceptor solutions is necessary. Since cationic species exchange readily compared to neutral and anionic species, it is claimed that the measurement more closely relates to the free metal ion. 

Ion exchange is used in the metal plating industry to purify rinse water and spent plating bath solutions. Cation exchangers ranove cationic metal species, such as Cu, from such solutions. Anion exchangers remove anionic cyanide metal complexes, such as Ni(CN), and chromium(VI) species, such as CrOI. Radionuclides can be ranoved from radioactive and mixed radioactive/ hazardous chemical waste by ion exchange resins. 

Because there are three separate retention equations (eqns. 12, 17, 18) to account for the three cationic metal species in solution, one might expect to find three peaks in the final chromatogram. In reality, however, only one peak is usually evident. The number of peaks that appear is a function of the kinetics of the equilibrium processes occurring in solution. One peak is seen if the rate of all reversible and/or irreversible chemical equilibria associated with an eluite as it migrates through the column is fast relative to the elution time of the eluite. If interconversion between the metal-ligand species is slow, however, aqrmmetric or multiple peaks may result. 

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