Metal ions in seawater

Complexation of fluoride by metal ions in seawater has previously been overcome by the addition of TISAB solution. The reagent is presumed to release the bound fluoride by preferential complexation of the metal ions with EDTA type ligands present in the TISAB. Examination of the metal ions present in seawater [66,67] suggests that magnesium is the major species forming fluoride complexes. Theoretical calculations demonstrate that even this species is unlikely to interfere. 

Figure 13 Speciation of metal ions in seawater and the main controlling mechanisms (Adapted from Ohman and Sjoberg, 1988. )...

Conclusions. Diphenyl mercury, a neutral organometallic compound, which does not contain any markedly acidic or basic functional groups was found to adsorb only onto humic acid. No sorptive behavior could be detected with respect to bentonite, MnO or Fe(OH)-. The rather low value of Kads indicates a simple molecular attraction. However, the decrease in Kads with an increase in ionic strength Indicates that DPM is competing with the metal ions in seawater for adsorption sites. The increasing nonlinearity of adsorption isotherms with increasing suspended humic acid concentration is also similar to results obtained for metal ion adsorption. 

P.A.KAVAKLI, N.SEKO, M. TAMADA, O. GUVEN, Synthesis of a new adsorbent for uptake of significant metal ions in seawater by radiation induced graft polymerization , to be published in Polymer (2004)... 

The Pb imprinted resins were then applied to chemical analysis [26]. Experiments were carried out to determine and compare percent recoveries of Pb from the seawater samples by using different ion exchange resins, such as Chelex-100, Duolite GT-73, a proprietary NASA resin, and the Pb imprinted ion exchange resin. The percent recoveries from the Pb imprinted resin were greater than 95% over a broad range of pH. The Pb imprinted ion exchange resin did not suffer from interferences from other metal ions in seawater matrix. The Pb imprinted resin gave superior performance when used for separation and preconcentration prior to analysis by either AAS or spectrophotometry. The utility of the Pb imprinted resin was demonstrated by analysis of a standard reference material. Coastal reference seawater (CASS-3). The resin extract was of suificient purity to be analyzed by spectrophotometry with the nonspecific indicator dithizone. 

Bilinsld, H. and Branica, H. (1966) Precipitation and hydrolysis of metallic ions in seawater. I. Ionic state of zirconium and thorium in seawater. Croat Chem. Acta,... 

Autoxidation of DMS DMS is autoxidized by 02 very slowly in solution at ordinary temperatures but the reaction is catalyzed by metal ions. In a saline solution of pH 8, Brimblecombe and Shooter (University of East Anglia, unpublished data) obtained a first order rate constant of 2.2 x 10-8 s-1 at 20 C and an activation energy of 78 kJ. The rate was also found to decrease with pH (but not linearly dependent on the H+ ion concentration). In the presence of Cu(II) ions (10-4 M) at pH 5.6 and temperatures at 20° C, a tenfold increase in first order rate constant was observed (ka = 2 x 10-7 s-1). Reactions in NaG solutions were found to be nearly an order of magnitude slower than in seawater and at least an order of magnitude faster than in distilled water. 

The interaction between sodium and alkaline-earth metal ions and borate has attracted recent attention, particularly from the point of view of association of ions in seawater. Several studies (69, 114,168, 169, 340) have shown that the boron content of seawater (4-5 x 10 4 M) is too low to support appreciable concentrations of polyborate species. The increase in acidity of boric acid in the presence of metal ions results from ion-pair formation ... 

For substances which are not present in the atmosphere but in the ocean, we can take the reference species of zero exergy level at the most stable state of their existence in seawater. For example, metallic sodium takes its reference level at the state of sodium ions in seawater and the standard chemical exergy e a of metallic sodium is equivalent to the free enthalpy... 

With these data we can now calculate the distribution of the major species on the surface of goethite in seawater. This approach will form the basis for modeling trace metal adsorption in seawater and determining the competitive effects of the major ions with each other and with trace metals. 

Today, metals are scavenged from water by extremely sophisticated biochemical processes (Morel and Price, 2003). Thus, seawater can have very low ambient levels of metal ions. Early Archean seawater would likely have been much richer in trace metals. But given that early organisms presumably had very unsophisticated processes for capturing metals, even in seawater rich in metal it would have been difficult to access the metal. Perhaps the earliest distribution of organisms was very restricted, with few cells living away from locations such as volcanoes that had readily accessible metals. Only the evolution of effective metal-gaining siderophores would have allowed the spread of life. There is thus reason to believe that, even if the last common ancestor was not hyperthermophile but lived... 

Life evolved in seawater. Therefore a consideration of the relative compositions of seawater and extracellular and intracellular fluids is relevant to an analysis of metal ion utilization. Seawater contains a high concentration of sodium ions, and, in lesser amounts, potassium, calcium, and magnesium ions. These cations are also found in living cells in varying amounts. It is necessary, however, for the cell to maintain pumps to keep the individual concentration of these ions within it to appropriate limits. For example, sodium ions are found in high concentrations in seawater and in extracellular fluids, but potassium ions are concentrated within living cells. Sodium ions must be pumped out of the cells, and systems are available to do this. Pumps are also available to control the intracellular concentrations of other cations. The transition metal ions, such as zinc, are also found in seawater, but in much, much lower concentrations, and they are, as described above, equally rare within cells. 

In order to carry out most biochemical reactions, metalloenzymes generally utilize the rarer transition metal ions. Elements such as zinc, copper, iron, nickel, and cobalt are found in low concentrations in plasma and seawater and yet the enzyme has to select the appropriate metal ion from them. There is evidence for the existence of proteins that can chaperone specific metal ions to their appropriate sites in apoenzymes, protecting the metal ions from adverse reactions as they are guided to their required location [5]. How does the enzyme attempt to select out the one metal ion it requires The answer is that the chemistry of the metal ion is used as a basis for selection. Each metal ion has some property that is different from that of most others, but, in fact, there is often considerable overlap in these properties so that a given enzyme may bind one of several different cations in one specific site. Some relevant data are provided in Tables 1 and 2. The metalloenzyme contains within its overall design an arrangement of preferred side-chain functional groups with the correct size hole to bind the required metal ions in an appropriate hydrophobic or hydrophilic environment. Thus the metalloenzyme binds metal ions... 

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