Cations in seawater

The concentrations of various cations in seawater, in moles per liter, are... 

Table 5.15. Miscellaneous solids used in the pre-concentration of cations in seawater...

Sediment deposition on the seafloor traps interstitial water. After deposition, complex reactions take place in the sediment, most of them fueled by the decay of organic matter, such as sulfate reduction, denitrification,... Because of fast diffusion rates of most cations in seawater, the presence of interstitial water makes exchange between overlying sedimentary layers a much easier process than if sediment deposition was dry. The book by Berner (1980) is entirely dedicated to these processes and only a short example is given here. 

The major anions and cations in seawater have a significant influence on most analytical protocols used to determine trace metals at low concentrations, so production of reference materials in seawater is absolutely essential. The major ions interfere strongly with metal analysis using graphite furnace atomic absorption spectroscopy (GFAAS) and inductively coupled plasma mass spectroscopy (ICP-MS) and must be eliminated. Consequently, preconcentration techniques used to lower detection limits must also exclude these elements. Techniques based on solvent extraction of hydrophobic chelates and column preconcentration using Chelex 100 achieve these objectives and have been widely used with GFAAS. 

Calcium compounds, essential for the formation of bones and teeth, are obtainable from limestone (CaCOs), gypsum (CaS04-2H20), and fluorite (CaF2) for use in water treatment, agriculture, construction (concrete), and the chemical industry, for which lime (CaO) is the least expensive source of alkali. Calcium is the third most common cation in seawater (400 mg kg-1). 

Potassium is found in feldspars and micas, and is the fourth most abundant cation in seawater (390 mg kg-1). Potassium compounds are usually obtained from evaporites (i.e., residues from evaporated water) as KC1 ( potash ) or carnallite, mainly for use in fertilizers. 

Other applications of high performance liquid chromatography to the determination of cations in seawater are tabulated in Table 4.10. 

The major cations in seawater are predominantly present as free aquo metal ions. This is understandable because they are A-type metals and... 

As Table 6.5 illustrates, most of the cations in seawater are present as free aquo cations. The concentration of associating SOj", HCOj. and CO is much smaller than that of major cations. 

Removal of dissolved C does not affect the amount of cations in seawater, so alkalinity (A) remains constant and Eqn 3.13 indicates that the concentration of carbonate ions will increase. Dissolved C02 levels decrease as both salinity and temperature increase (Weiss 1974) and, ultimately, seawater can become supersaturated with respect to calcium carbonate. Removal of CaC03 affects both alkalinity (because of the decrease in Ca2+ ions) and dissolved C concentrations. 

The molar concentration of uranium, 1.4 x 10 mol/m is about 1 part in 4 X 10 of that of magnesium, which is a representative bivalent cation in seawater. Extensive efforts have been exerted to develop an adsorbent capable of separating uranium from the other elements [79-88]. At present, a resin containing an amidoxime group (-... 

The parts of the earth s crust becoming the ocean bottom were likely to be highly alkaline because of NaO and MgO and, of much less importance, CaO (according to abundance of the cations in seawater. Table 2.9). Large amounts of soluble oxides led to dissolved Na , Mg and Ca " " and OH , which converts bicarbonate into less soluble carbonates (Eq. 2.30) as well as ammonium back to NH3 (Eq. 2.27) with subsequent degassing from the ocean. This is simply the explanation for the chemical composition of the seawater (Table 2.9). 

Next to sodium, magnesium is the most abundant cation in seawater. 

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