Chemical forms of metals

Table 2.3 Approximate size of the physico-chemical forms of metal species in natural waters3...

Pecheyran, C. (1997) Speciation of chemical forms of metals and metalloids in air challenges and perspectives. Analusis, 25, M41-M44. 

III. Physical and Chemical Forms of Metal Ions in Sea Water. 143... 

Understanding the distribution of chemical forms of metals within certain water types, and their uptake into biota, is based on the electronic configuration of elements and the empirical classification of electron acceptors (metals) and donors (ligands) to hard and soff categories (Morgan and Stumm 1991, Raspor 1991). The relationship between the chemical properties of elements, and their uptake and accumulation - which has implications on detoxification and food chain transfer - will be considered. Classification of trace metals as either essential (Fe, Cu, Mn, Zn, Co) or non-essential (Hg, Cd, Ag, Pb) should be performed with caution, bearing in mind that the former can exert beneficial effects at low concentrations and harmful ones at higher levels. 

There are two routes to developing the informational needs on the role of trace metals in health and disease. The first is to conduct fundamental studies on the physiological effects of metals and metal combinations. Such studies are extremely expensive and time-consuming and would require an almost infinite number of combinations of metals and chemical forms of metals if this approach were used. 

The term speciation refers to the determination of the chemical form of metals and metalloids and according to lUPAC it is the process yielding evidence of the atomic or molecular form and oxidation state of an analyte. Included in this definition are the organometallic compounds and those of N, P, S and Si. The determination of organic substances is not referred to. 

There are a number of general chemical forms of metals in soils and these differ in their mobility and bioavailability. A listing of some of the common chemical forms of metals ranging from most available to least available is as follows (Gambrell and Patrick, 1991 Shannon and White,... 

General Chemical Forms of Metals in Wetland Soils and Sediments... 

Consequently, the objective of this study is to establish the nature of the effect of roots on mineral weathering in the rhizosphere of forested soils based on differences in (1) the mineralogical composition and (2) the chemical forms of metals. 

In order to insure the sufficient efficiency of electrokinetic removal of multiple heavy metals from porous media, it is essential to understand the main parameters affecting the transport and electrokinetic phenomena. Such parameters can be summarized as (a) the theoretical ionic mobility related to the ionic valance and molecular diffusion coefficient of species, (b) the delaying or retardation effect caused by the affinity of heavy metals in solid matrix, and (c) the chemical forms of metal contaminants initially existing in soils. In addition, some unexpected effects especially brought about in the electrokinetic remediation of mixed metal contaminants should be considered. The electrokinetic remediation for mixed metal contaminants generally shows lower removal efficiency than that for individual metal contaminants. High concentrations of multiple metal contaminants can be related to other parameters, for example, transference number, zeta potential, electroosmotic flow, and so on, which are factors that should be taken into consideration with regard to the removal mechanisms. 

Load (=dose) factors there are various processes causing high lake loads of metals, e.g., direct metal deposition to the lake surface, input of metal from the drainage area (from natural weathering and outflow of anthropogenic metals), and internal fluxes from sediments. There are many ways to define load variables for metals in water, suspended matter and bottom sediments, and many different chemical forms of metals (metallic, ionic, etc.)... 

A further complication in the identification of target sites and chemical forms of metals is the kinetic lability of coordinate covalent bonds. Metal ligands exchange rapidly in and out of the coordination sphere, in particular for first-row transition metals. This kinetic lability varies between metals, and, as indicated above, is influenced by the nature of the ligand, whether mono- or multidentate, and by the pH and ionic strength of its immediate environment. Copper, for example, forms relatively low affinity complexes with albumin or amino acids, but is tightly bound to ceruloplasmin. Similarly, mercury and cadmium form kinetically labile complexes with amino acids, glutathione, or albumin, but more stable chelates with metallothionein. 

Several components are required in the practical appHcation of nuclear reactors (1 5). The first and most vital component of a nuclear reactor is the fuel, which is usually uranium slightly enriched in uranium-235 [15117-96-1] to approximately 3%, in contrast to natural uranium which has 0.72% Less commonly, reactors are fueled with plutonium produced by neutron absorption in uranium-238 [24678-82-8]. Even more rare are reactors fueled with uranium-233 [13968-55-3] produced by neutron absorption in thorium-232 (see Nuclear reactors, nuclear fuel reserves). The chemical form of the reactor fuel typically is uranium dioxide, UO2, but uranium metal and other compounds have been used, including sulfates, siUcides, nitrates, carbides, and molten salts. 

The bioavailability, and hence the toxicity, of metal depends on the physical and chemical form of the metal, which in turn depends on the chemical characteristics of the surrounding water. The dissolved form of the metal is generally viewed as more bioavailable and therefore more toxic than the particulate form. Particiilate matter and dissolved organic matter can bind the metal, making it less bioavailable. What is not well known or documented is the various chemical transformations that occur both within the effluent stream and when the effluent reaches and mixes with the receiving water. Metal that is not bioavailable in the effluent may become bioavailable under ambient chemical conditions. 

The valence electron configuration of the atoms of the Group 2 elements is ns1. The second ionization energy is low enough to be recovered from the lattice enthalpy (Fig. 14.18). Flence, the Group 2 elements occur with an oxidation number of +2, as the cation M2+, in all their compounds. Apart from a tendency toward nonmetallic character in beryllium, the elements have all the chemical characteristics of metals, such as forming basic oxides and hydroxides. 

In this final section, the global cycles of two metals, mercury and copper, are reviewed. These metals were chosen because their geochemical cycles have been studied extensively, and their chemical reactions exemplify the full gamut of reactions described earlier. In addition, the chemical forms of the two metals are sufficiently different from one another that they behave differently with respect to dominant... 

As a result, it was found that the release of trace metals was affected by temperature, and atmosphere. The volatility of chemical form of trace metals in raw coal and the chemical change of trace metals during high temperature heat processing were very important for the... 

Important results and a detailed insight into aqueous chemical deposition processes have been reported and discussed elsewhere for CdSe [248, 249] and ZnS [250, 251] target products. We should note also the work of Davies et al. [252] who described an alternative method for the chemical growth of metal sulfides and selenides on the basis of polysulfide or polyselenide solutions (containing hexa- and tetra-chalcogen anions) formed by the dissolution of sulfur or selenium in hydrazine monohydrate. ... 

Sarret G, L Avoscan, M Carriere, R Collins, N Geoffroy, F Carrot, 1 Coves, B Gouget (2005) Chemical forms of selenium in the metal-resistant bacterium Ralstonia metallireducens CH34 exposed to selenite and selenate. AppZ Environ Microbiol 71 231-2337. 

In 1994, thiols were firstly used as stabilizers of gold nanoparticles [6a]. Thiols form monolayer on gold surface [18] and highly stable nanoparticles could be obtained. Purification of nanoparticles can be carried out, which makes chemical method of metal nanoparticles a real process for nanomaterial preparation. Various thiol derivatives have been used to functionalize metal nanoparticles [6b, 19]. Cationic and anionic thiol compounds were used to obtain hydrosols of metal nanoparticles. Quaternary ammonium-thiol compounds make the nanoparticle surface highly positively charged [20]. In such cases, cationic nanoparticles were densely adsorbed onto oppositely charged surfaces. DNA or other biomolecule-attached gold nanoparticles have been proposed for biosensors [21]. 

Humic substances can form complexes with metals, including cationic micronutrients (36), thanks to the presence of electron-donor functional groups in these molecules. It therefore appears evident that due to these properties, humic substances can contribute to the regulation of the chemical balances of metals, thus influencing their solubility (5). With regard to plant availability, the molecular dimension and solubility of humic substances are very important. 

The Fine Structure Before and After Each Edge. ELNES is the term use to describe the energy-loss near edge structure, and this can be quite different for an element in different compounds. For example the shape of the aluminium L edges are quite different in EELS spectra from metallic aluminium and aluminium oxide, so that the chemical form of a given element may be indentified from these small variations in intensity after the edge. 

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