Extraction from seawater

Seawater. The world s oceans contain ca 4 X 10 t of uranium (32). Because the uranium concentration is very low, approximately 3.34 ppm, vast amounts of water would be required to recover significant amount of uranium metal, ie, 10 m of seawater for each metdc ton of U. Significant engineering development and associated environmental concerns have limited the development of an economic means of uranium extraction from seawater (32) (see Ocean RAWMATORiALs). 

Seawater. Salt extraction from seawater is done by most countries having coastlines and weather conducive to evaporation. Seawater is evaporated in a series of concentration ponds until it is saturated with sodium chloride. At this point over 90% of the water has been removed, and some impurities, CaSO and CaCO, have been crystallized. This brine, now saturated in NaCl, is transferred to crystallizer ponds where salt precipitates on the floor of the pond as more water evaporates. Brine left over from the salt crystallizers is called bitterns because of its bitter taste. Bitterns is high in MgCl2, MgSO, and KCl. In some isolated cases, eg, India and China, magnesium and potassium compounds have been commercially extracted, but these represent only a small fraction of total world production. 

The high sensitivity and selectivity of some gas chromatographic detectors are used to advantage in the measurement of organic mercury compounds. In the simplest approach, methyl mercury is extracted from seawater and converted to the iodide for electron capture gas chromatography [74],... 

Similar elements also occur in the same natural environment. For instance, the halogens are markedly concentrated in seawater. (The major salt in ocean brines is sodium chloride.) The other halogens are extracted from seawater that has been further concentrated—bromine from salt beds formed by evaporation and iodine from kelp, which grows in oceans. 

IP LLE methods are generally employed for the extraction of LASs from river waters and the solvent sublation method of Wickbold is still used for their extraction from seawater [85]. SPE methods making use of C18 and C8 phases are largely employed [85]. The amount of sorbent is optimized as a function of the degree of pollution and the average composition of river waters [85]. The performances of C18 disks and C18 cartridges are compared [85]. 

Alternatively, potable water can be extracted from seawater by freezing salts, which depress the freezing point of water, remain in the liquid phase. Generally, though, it is more practical to remove the relatively small amount of solutes (typically, 0.02% for river water) from the great excess of water, rather than vice versa. Seawater is an exceptional case, with about 3.5% dissolved solids. Water softening is concerned primarily with removal of Ca2+ and Mg2+, but for some purposes removal of all dissolved solids (deionization or demineralization) is necessary. 

Although fission reactors do not generate chemical pollution, they do produce highly hazardous radioactive waste. However, another kind of nuclear reaction is essentially free of long-lived waste products, and its abundant fuel is readily extracted from seawater. The reaction is the fusion of hydrogen nuclei to form helium nuclei. 

The commercial production of bromine from salt-well brines or from seawater depends on the fact that chlorine is capable of displacing bromine from its salts. Bromine is extracted from seawater by a process involving the following steps ... 

For Balanus amphitrite, a waterborne settlement inducer that is more active than the surface-associated settlement factors has been extracted from seawater conditioned with adult barnacles.53 The cyprid settlement responses could be stimulated by peptides bearing C-terminal arginine or lysine residues.54 102 Interestingly, the same barnacle settlement-inducing peptides attract a variety of barnacle predators such as oyster drills.53103... 

In the process used by Norsk Hydro, magnesium hydroxide extracted from seawater with the aid of calcined dolomite is mixed with charcoal and magnesium chloride brine and is heated to 1000-1200°C in the presence of chlorine produced during subsequent electrolysis of magnesium chloride. The main reactions are [266]... 

Suzuki, T, Mitsuya, T, Matsubara, H., and Yamasaki, M. 1998. Determination of pectenotoxin-2 after solid-phase extraction from seawater and from the dinoflagellate Dinophysis fortii by liquid cbromatography with electrospray mass spectrometry and ultraviolet detection. Evidence of oxidation of pectenotoxin-2 to pectenotoxin-6 in scallops. J ChromatogrA 815, 155-160. 

The production of fusion energy would begin, of course, with fuel. In a fusion reactor, the most promising fuels are deuterium and tritium, the heavy isotopes of hydrogen, both of which can be extracted from seawater. Deuterium s potential as a plentiful energy source is easily understood when one considers that a small amount can produce the equivalent of some 300 gallons of gasoline when it is burned off. 

The world s oceans hold 1.37x10 of water (97.2% of the total amount of water of the hydrosphere). They cover 71% of the earth s surface, are actually the biggest reservoir on our planet, and contain many important minerals. The overall content of mineral matter in the oceans is estimated to be about 5 x 10 tons [1,2]. The seas contain virtually all of the naturally occurring elements and are the only universal source of mineral wealth that is available to most nations. For some of them it is the only source. Yet, most of the elements, the microelements, are available in very low concentrations, i.e., in parts per billion (ppb). The products being extracted from seawater with economic profit at present are sodium chloride, magnesium compounds, and bromine [2-4]. During the last two decades there has been growing interest in the possibility of commercial recovery of additional minerals from seawater [5] and brines [6]. 

Detailed information on the research carried out in the field of uranium extraction from seawater up to 1984 are given in reviews [ 164, 191-198]. The most intensive investigations are being carried out in Japan in institutes dedicated to uranium recovery firom seawater [196]. 

Transuranic elements are extracted from seawater by coprecipitation with either ferric hydroxide or calcium/strontium oxalate or are leached from sediments with 8M nitric acid. Radiochemical separations are used to aruilyze PUy... 

The transuranic elements extracted from seawater or sediments are further purified such that ... 

High ash contents for yellowish-brown organic matter extracted from seawater have been attributed to inorganic impurities in the carbon sorbent used (Jeffrey and Hood, 1958). These authors recommend extraction of carbon with phenol prior to use to remove these inorganic impurities. A more serious problem is the possibility of chemical alteration of organic matter on the surface of carbon (Jeffrey, 1969). 

A similar study has hitherto not been carried out of the extraction from seawater of the compotmds of interest (LAS, NPEO, AP, LABs, etc). Preliminary results, however, show differences in extraction efficiencies between LLE and sorption by Amberlite XAD-2 (Table I). The more hydrophilic compotmds (i.e. LAS and NP, log Kow=2.0) were recovered with high efficiency by the XAD-2 coluitm (95-97%) whereas the hydrophobia ones (i.e LAB, log Kow=8.8) were recovered only by LLE. Intermediate results were obtained for NPEO and AP. 

Sodium is present in many compounds that have great economic importance. One of the most well-known compounds is salt, or sodium chloride (NaCl). Approximately 20 million tons of salt is produced every year through the mining of salt deposits all over the world. Salt is also extracted from seawater, although in lower amounts than are available from salt mine deposits. 

Magnesium chloride is extracted from seawater or brine, of which it is a component, and from minerals, such as carnal-lite (KCl-MgClj-HjO) and bischofite (MgCl2,6H20). The usual procedure is to treat seawater, brine, or the mineral with lime (CaO), calcined dolomite (CaO-MgO), or caustic soda (sodium... 

Free fatty acids, hydroxy acids and their esters may be extracted from seawater after filtration with various organic solvents in high yields after acidification to pH 2—3 or extraction at pH 8 and subsequent acidification to pH 2—3 (A. Saliot, pers. comm., 1979). Chloroform is the most commonly employed extracting solvent, three repeated extractions being sufficient to quantitatively extract 1—2 1 of seawater (Treguer et al., 1972). 

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