Seawater elements from

The elements listed in the table of Figure 15.2 are of importance as environmental contaminants, and their analysis in soils, water, seawater, foodstuffs and for forensic purposes is performed routinely. For these reasons, methods have been sought to analyze samples of these elements quickly and easily without significant prepreparation. One way to unlock these elements from their compounds or salts, in which form they are usually found, is to reduce them to their volatile hydrides through the use of acid and sodium tetrahydroborate (sodium borohydride), as shown in Equation 15.1 for sodium arsenite. 

Plants developed from photosynthetic bacteria. As we have explained in Chapters 5 and 6, bacteria could evolve on the top surface of the Earth by increasing their ability to capture light (energy) and by obtaining and using more effectively 15-20 elements from seawater, later the seabed and land, and with three or four from the atmosphere, while utilising novel chemistry. The need to adapt to oxygen later forced the development of compartments already seen in differentiated ... 

Ion exchange chromatography using Chelex 100 resin has been used for the concentration of rare earth elements from large volumes of seawater, with recoveries of 85-112% [636]. 

Nakashima et al. [719] detail a procedure for preliminary concentration of 16 elements from coastal waters and deep seawater, based on their reductive precipitation by sodium tetrahydroborate, prior to determination by graphite-furnace AAS. Results obtained on two reference materials are tabulated. This was a simple, rapid, and accurate technique for determination of a wide range of trace elements, including hydride-forming elements such as arsenic, selenium, tin, bismuth, antimony, and tellurium. The advantages of this procedure over other methods are indicated. 

Mujazaki et al. [733] found that di-isobutyl ketone is an excellent solvent for the extraction of the 2,4-pyrrolidone dithiocarbamate chelates of these elements from seawater. 

Greenberg and Kingston [821,822] used a solid Chelex 100 resin to preconcentrate these elements from 100-500 ml of estuarine and seawater prior to their determination. A procedure is described for the preconcentration of 100 ml of estuarine and seawater into a solid sample using Chelex 100 resin. This solid sample weighs less than 0.5 g, and contains the transition metals and many other elements of interest, but is essentially free of alkali metals, alkaline earth metals, and halogens. 

Riccardo et al. [841] showed that chitosan is promising as a chromatographic column for collecting traces of transition elements from salt solution and seawater, and for recovery of trace metal ions for analytical purposes. Traces of transition elements can be separated from sodium and magnesium, which are not retained by the chitosan. 

Most of the trace elements are present in concentrations well below those that should result from the maintenance of simple equilibria with mineral phases. Clearly some other processes are effectively removing these elements from seawater. As it turns out, all of these processes involve incorporation of the trace metals into sinking particles. 

Vander Sloot, H. A. Nieuwendijk, B. J. T. 1985. Release of trace elements from surface-enriched fly ash in seawater. Wastes Ocean, 4, 449-465. 

Riley, J.P. and Taylor, D. (1968) Chelating resins for the concentration of trace elements from seawater and their analytical use in conjunction with atomic absorption spectroscopy. Anal. Chim. Acta, 40, 479-485. 

Table 9.16. Estimates of fluxes involving exchange reactions between seawater and solids and biological and chemical removal of some elements from seawater. Units of 10 2 moles y1.

Ordinary anion and cation ion-exchange resins are of limited use for the analytical concentration of trace elements from water, because of their lack of selectivity. This is especially so with strong electrolytes such as seawater. In this case the major ions sodium, magnesium, calcium and strontium, are retained preferentially. However, the recent advent of commercial chelating resins based mainly on iminodiacetic acid-substituted cross-linked polystyrene, makes it possible to concentrate trace elements from waters. In consequence, a number of researchers have used chelating resins for trace-metal preconcentration from seawater and natural waters. 

Kelp, a type of seaweed, is a popular source of iodine, since it absorbs the element from seawater. IMAGE COPYRIGHT 2009, EPIC STOCK. USED UNDER LICENSE FROM SHUTTERSTOCK.COM. 

Trace Elements from Seawater, Geochim, Cosmochim. Acta (1968) 28,... 

Salinity is a measure of the mass of salts dissolved in seawater. It is usually measured in grams of salt per kilogram of seawater. The average salinity of ocean water is about 35 g per kg, so ocean water contains about 3.5% dissolved salts. Most of these salts dissociate in water and are present in the form of ions. Table 26-2 lists the ions in seawater. Note that chlorine and sodium are the most abundant ions in seawater. Although Earth s oceans are vast, the proportions and quantities of dissolved salts are nearly constant in all areas. Indeed, they have stayed almost the same for hundreds of millions of years. Why is this so As rivers, volcanoes, and atmospheric processes add new substances to seawater, elements are removed from the oceans by biological processes and sedimentation. Thus, the oceans are considered to be in a steady state with respect to sahnity. 

Extrapolated from study of the Endevor Ridge. Although the ocean volume is cycled through the plume in 2.8 x 103 years, the rate of reaction of the plume with seawater is much slower. To strip the reactive elements from seawater it is necessary to cycle the ocean volume approximately 100 times through the plume (2.4 x 105yr). 

The chemistry of hydrothermal fluids indicates that basalt-seawater interactions are a source of some elements that have been stripped from ocean crust and injected into seawater. Data from hydrothermal fluids show that both Ca2+ and dissolved silica are concentrated in the hydrothermal waters compared with seawater (Table 6.6). Calcium is probably released from calcium feldspars (anorthite) as they are converted to albite by Na+ uptake, a process called albitization. Silica can be leached from any decomposing silicate in the basalt, including the glassy matrix of the rock. Globally, basalt-seawater interaction seems to provide an additional 3 5 % to the river flux of Ca2+ and silica to the oceans. 

Koschinsky, A. and Hein, J.R., 2003. Uptake of elements from seawater by ferromanganese crusts solid-phase associations and seawater speciation. Marine Geology, 198 331-351. 

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