Heavy metal cations, complexation

Alcohols react with boric acid with elimination of water to form borate esters, B(OR)3. A wide variety of borate salts and complexes have been prepared by the reaction of boric acid and inorganic bases, amines, and heavy-metal cations or oxyanions (44,45). Fusion with metal oxides yields... 

E. For any heavy-metal cation, when in the presence of two different anions, the anion with the highest potential to form surface complexes controls the metal s adsorption potential. For example, Ni2+ in the presence of Ca(N03)2 exhibits greater adsorption potential than Ni2+ in the presence of CaS04 owing to the sulfate s potential to react with the surface and produce sites with high specificity for Ca2+. 

The thermodynamic parameters and relative cation selectivity of some alkali and heavy metal cations with 1,5,14,18-tetraselena-8,11,21,24-tetracyclohexacosane 47 (selena-26-crown-8) were investigated for the first time by titration calorimetry in water-MeCN (l 24v/v) at 25°C to show the contrasting complexation behavior between Ag+ and alkali Tl+ and a very high Ag+ selectivity, originating from the exclusive contribution of the enthalpy term probably owing to the partially covalent interaction between Ag+ and Se-donor <1999JCM284>. 

Fig. 19 TSOSs used for complexing heavy metal cations...

Matejka, Z. Zitkova, Z. The sorption of heavy-metal cations from EDTA complexes on acrylamide resins having oligo(ethyleneamine) moieties. React. Funct. Polym. 1997, 35, 81-88. 

Sorption of heavy metal cations, chiefly the topics related to environmental protection, was reviewed by Charlet [45]. An entire recent book [46] is devoted to uptake of metals by metal oxides, clay minerals and more complex systems. 

Many publications report adsorption of heavy metal cations on activated carbon. Apparently, binding of metal cations is due to formation of surface complexes that are similar to chelate complexes in solution and some of them are very stable. The stability of these complexes is certainly dependent on the surface treatment. However, in some publications the sorption on activated carbons is treated as ion exchange. 

Heavy metal cations can be separated as chemical complexes with anion... 

Giannissis, D., G. Dorange, and M. Guy, (1985), Association (Complexation and Adsorption) Phenomena of Heavy Metal Cations with Humic Substances (Role of Calcium Ions), in T. D. Lekkas, Ed., 5th International Conference on Heavy Metals in the Environment, Vol. 2, pp. 469-471. 

Coordination number 2 collinear. Collmear complexes are common in the case of heavy metal cations of electron configuration. Examples of collinear complexes are [Au(CN)2], formed during the extraction of gold from its ore, and [Ag(NHj)2] formed when AgCl dissolves in ammonia solution. 

Thiols are sulfur analogs of alcohols. Thiols used to be called mercaptans because they form strong complexes with heavy metal cations such as mercury and arsenic (they capture mercury). 

Fourth, the presence of heavy metals cations, for example Cd(ll), Pb(ll) and Hg(ll) may lead to the inactivation of some enzymes (Vallee and Ulmer, 1972). The likelihood that an exchange of the bound metal between the labile complexes and the column increases... 

There appears to be little point in a detailed evaluation of the more ambiguous hypotheses of heavy metal fixation. However, it may be noted that a number of investigators have considered the possibility of either the sorption of complex ions on clay mineral surfaces or reaction of heavy metal cations with clay surfaces in some manner other than simple electrostatic sorption (31, 66, 67, 156, 157, 217), However, the solubility products of Cu(OH)2 and Zn(OH)2 in aqueous suspensions of montmorillonite (19) have been found to be quite similar to those previously found for solutions in contact with only the pure hydroxides. This would indicate that metal ion-clay mineral surface complex formation is not important otherwise the apparent solubility would have been greater in the presence of montmorillonite. 

As the NTA supply increases to 3 x 10 M, significant complexing of the above metals takes place for example Cu(II), 82 percent Pb(II), 80 percent Ni(II), 60 percent Fe(III), 34 percent and Zn(II), 20 percent. Again, since the NTA is not present in a quantity in excess of the combined concentration of all the heavy metals, there is incomplete complexing of each of them. Moreover, the completeness of complexation is in strict order of values of the stability constants of the heavy metal NTA complexes. At a total NTA level of 2 x lO"" all of the heavy metals are completely complexed by NTA. In addition, some of the major cations, Ca(II) and Mg(II), which form weaker NTA complexes than the heavy metals, are bound to NTA at levels of 17 and 2 percent, respectively. 

Heavy metal cations can be separated as chemical complexes with anion exchangers e.g. Fe + forms a stable complex with chloride ... 

Because of its cationic characta-, chitosan interacts with negatively charged biological surfaces, such as skin and hair [200]. Otha- relevant characteristics of chitosan for cosmetic applications are its high molecular weight, water retention and film formation capacity as well as its heavy metal ion complexing abOity. 

Polyvinylpyrrolidine has been shown to be very suitable as the sorbent for the separation of humic materials, tannins, lignins, as well as organic dye compounds, phenolic materials, aldehydes, and aromatic acids. Non-polar solid-phase extraction can be used for the preconcentration of heavy metals as complex compounds and their subsequent determination by cation-exchange chromatography. 

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