Seawater sources salinity

Reverse osmosis membranes can be divided into subclasses according to their solute/water selectivity and operating pressure regimes. Figure 30 shows a number of commercial membranes developed for seawater and brackish desalination, and for nanofiltration. These include cellulose ester and polyamide asymmetric membranes available since the 1960s, and high-performance composite membranes developed in the 1970s. Collectively, they make it possible to produce potable water from virtually all saline water sources. 

Seawater desalination is the production of fresh, low-salinity potable or industrial-quality water from a saline water source (sea, bay, or ocean water) via membrane separation or evaporation. Over the past 30 years, desalination technology has made great strides in many arid regions of the world such as the Middle East and the Mediterranean. Today, desalination plants operate in more than 120 countries worldwide, and some desert states, such as Saudi Arabia and the United Arab Emirates, rely on desalinated water for over 70% of their water supply. According to the 2004 desalination plant inventory report prepared by the International Desalination Association (Wagnick Consulting, 2004), by the end of 2003 worldwide there were over 17,000 desalination units with total installed treatment capacity of 37.8 million m /day. Seawater desalination plants contribute approximately 35% (13.2 million m /day) of this capacity. 

TABLE 3.2 Salinity and Temperature of Various Seawater Sources"... 

Brine Sources. Lithium occurs naturally in brines from salars, saline lakes and seawater, od-fteld waters, and geothermal brines. Of these sources, lithium is produced only from brines of two salars. 

Common salt, or sodium chloride, is also present in dissolved form in drilling fluids. Levels up to 3,000 mg/L chloride and sometimes higher are naturally present in freshwater muds as a consequence of the salinity of subterranean brines in drilled formations. Seawater is the natural source of water for offshore drilling muds. Saturated brine drilling fluids become a necessity when drilling with water-based muds through salt zones to get to oil and gas reservoirs below the salt. 

Because seawater signatures of temperature and salinity are acquired by processes occurring at the air-sea interface we can also state that the density characteristics of a parcel of seawater are determined when it is at the sea surface. This density signature is locked into the water when it sinks. The density will be modified by mixing with other parcels of water but if the density signatures of all the end member water masses are known, this mixing can be unraveled and the proportions of the different source waters to a given parcel can be determined. 

All soils contain soluble salts, but their concentration is low. The salt content of most arid soils is, however, much higher. Salts in desert soils are usually derived from three main sources (1) deposition of wind-blown salt spray or dust (2) in situ weathering of salt-containing rocks or sediments, and (3) upward movement with the capillary flow from a shallow salty groundwater. Along the coastline, some salinization may occur through intrusion and flooding by seawater. 

Figure 6.2. (a) The effects of salinity on the sensitivity of standard additions of ammonia in laboratory mixed waters ( ) and in waters from the Tamar estuary (A) expressed as percentage of response in river water. For comparison, the salt error curves reported by Loder and Gilbert [3] are also shown (... and —, respectively), (b) Contribution of reactive index and organic absorbance to the optical blacks in the Chemlab Colorimeter. = River water-seawater mixture, o = De-ionized water-seawater mixture. Source [2]... 

Annually averaged salinity of surface seawater In the world s oceans. Source-. After Levltus, S. (1982). Climatological atlas of the world ocean. NOAA Professional Paper 13, U.S. Government Printing Office, Washington, DC. (See companion website for color version.)... 

This is why the salinity of seawater is nearly the same throughout the open ocean, varying by only a few parts per thousand. (As per Figure 3.3, 75% of seawater has a salinity between 34 and 35 %o.) The small degree of spatial variability is a consequence of geographic variations in the balance of evaporation versus precipitation in the surface waters. Recall that these surface waters are the source waters for intermediate and deep water masses. Since shifts in the relative rates of evaporation versus precipitation involve only addition or removal of water, the major ion ratios are unaltered. This is why the major ion ratios do not exhibit little if any spatial differences within the open ocean. 

Sodium chloride is widely distributed in nature. Oceans are the vast source of sodium chloride. It occurs in seawater at an average concentration of 2.68 wt%. It also occurs in many inland saline waters and in salt deposits in sedimentary rocks, as the mineral hahte. 

As previously mentioned, the primary processes responsible for variations in the deep sea C02-carbonic acid system are oxidative degradation of organic matter, dissolution of calcium carbonate, the chemistry of source waters and oceanic circulation patterns. Temperature and salinity variations in deep seawaters are small and of secondary importance compared to the major variations in pressure with depth. Our primary interest is in how these processes influence the saturation state of seawater and, consequently, the accumulation of CaC03 in deep sea sediments. Variations of alkalinity in deep sea waters are relatively small and contribute little to differences in the saturation state of deep seawater. 

Land (1987) has reviewed and discussed theories for the formation of saline brines in sedimentary basins. We will summarize his major relevant conclusions here. He points out that theories for deriving most brines from connate seawater, by processes such as shale membrane filtration, or connate evaporitic brines are usually inadequate to explain their composition, volume and distribution, and that most brines must be related, at least in part, to the interaction of subsurface waters with evaporite beds (primarily halite). The commonly observed increase in dissolved solids with depth is probably largely the result of simple "thermo-haline" circulation and density stratification. Also many basins have basal sequences of evaporites in them. Cation concentrations are largely controlled by mineral solubilities, with carbonate and feldspar minerals dominating so that Ca2+ must exceed Mg2+, and Na+ must exceed K+ (Figures 8.8 and 8.9). Land (1987) hypothesizes that in deep basins devolatilization reactions associated with basement metamorphism may also provide an important source of dissolved components. 

The Black Sea is the world s largest semienclosed marginal sea with permanent anoxic zone (about 85% of the total water volume). Its physical and chemical structure is determined by its hydrophysical balance [1]. The narrow (0.76-3.60 km) and shallow (< 93 m) Bosporus Strait provides the only pathway of water exchange between the Black Sea and the Mediterranean. The sill depths of the Bosporus are 32-34 m at the southern end and 60 m at the northern end [2,3]. The seawater that flows out of the Bosporus Strait is the only source of salty water to the basin. Deep-water salinity values increase to S = 22.33 psu. Freshwater inflow from several European rivers (especially the Danube, Dniester, and Dnieper) and brackish water inflow from the Sea of Azov keep the salinity low in the surface layer (S 18.0-18.5 psu in the central region). As a result, the water column is strongly stratified with respect to salinity, and thus density. 

Potential external sources of concentrated fluids can be found on and adjoining every crystalline rock mass on the planet. Seawater and the derivatives of seawater such as evaporite deposits and sedimentary basin brines are the primary candidates for the external sources of salinity. Dilute seawaters from the Yoldia and Litorina stages of the Baltic Sea (<10" yr) are recorded as entering crystalline rocks along coastal sections of the... 

Strontium isotopes have also been used to identify allochthonous sources for saline waters in crystalline rock. Sr/ Sr ratios for deep, saline waters of the Vienne granites (France) show a value that is consistent with Jurassic seawater and not consistent with values expected from equilibration with the rock. A mixing model between Jurassic seawater and crustal end-members can explain the origin of these deep saline ground-waters (Casanova et al., 2001 Negrel et al., 2001). 

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