Seawater boron

Boron concentrations and isotopes are also useful geochemical tracers of contamination in MORB. Boron concentrations are low (<2 ppm) in unaltered ocean floor basalt but high in altered basalts (>8 ppm B) (Spivack and Edmond 1987 Ryan and Langmuir 1993). Goldstein et al. (1989) measured B concentrations in their samples and found them to be less than 1.6 ppm, inconsistent with contamination. More recently, B isotopes have been used to assess contamination since large differences in 5 B are known to exist between seawater, sediments, and unaltered MORB. Sims et al. (2002) reported that 6 B for their 9°N EPR samples were inconsistent with incorporation of any seawater or seawater-derived material. 

Spivack AJ, Edmond JM (1987) Boron isotope exchange between seawater and the oceanic crust. Geochim Cosmochim Acta 51 1033-1043... 

Various chromogenic reagents have been used for the spectrophotometric determination of boron in seawater. These include curcumin [108,109], nile blue [110], and more recently 3,5 di-tert butylcatechol and ethyl violet [111]. Uppstroem [108] added anhydrous acetic acid (1 ml) and propionic anhydride (3 ml) to the aqueous sample (0.5 ml) containing up to 5 mg of boron per litre as H3BO3 in a polyethylene beaker. After mixing and the dropwise addition of oxalyl chloride (0.25 ml) to catalyse the removal of water, the mixture is set aside for 15-30 minutes and cooled to room temperature. Subsequently, concentrated sulfuric-anhydrous acetic acid (1 1) (3 ml) and curcumin reagent (125 mg curcumin in 100 ml anhydrous acetic acid) (3 ml) are added, and the mixed solution is set aside for at least 30 minutes. Finally 20 ml standard buffer solution (90 ml of 96% ethanol, 180 g ammonium acetate - to destroy excess of protonated curcumin - and 135 ml anhydrous acetic acid diluted to 1 litre... 

Marcantoncetos et al. [112] have described a phosphorimetric method for the determination of traces of boron in seawater. This method is based on the observation that in the glass formed by ethyl ether containing 8% of sulfuric acid at 77 K, boric acid gives luminescent complexes with dibenzoylmethane. A 0.5 ml sample is diluted with 10 ml 96% sulfuric acid, and to 0.05-0.3 ml of this solution 0.1ml 0.04 M dibenzoylmethane in 96% sulfuric acid is added. The solution is diluted to 0.4 ml with 96% sulfuric acid, heated at 70 °C for 1 h, cooled, ethyl ether added in small portions to give a total volume of 5 ml, and the emission measured at 77 K at 508 nm, with excitation at 402 nm. At the level of 22 ng boron per ml, hundredfold excesses of 33 ionic species give errors of less than 10%. However, tungsten and molybdenum both interfere. 

Atomic absorption spectrometry has been used for the rapid determination of boron in seawater [113]. 

Tsaikov [ 114] has described a coulometric method for the determination of boron in coastal seawaters. This method is based on the potentiometric titra-... 

Marquis and Lebel [534] precipitated potassium from seawater or marine sediment pore water using sodium tetraphenylborate, after first removing halogen ions with silver nitrate. Excess tetraphenylborate was then determined by silver nitrate titration using a silver electrode for endpoint detection. The content of potassium in the sample was obtained from the difference between the amount of tetraphenyl boron measured and the amount initially added. 

Traces of boron in seawater have been determined by flow injection analysis with spectrophotometric detection at 415 nm using G 30 methine H. The linear range was 1 -10 mg/1 boron with a detection limit of 0.017 mg/1 [3]. 

Chemically, tungsten is rather inert, but it will form compounds with several other elements at high temperatures (e.g., the halogens, carbon, boron, silicon, nitrogen, and oxygen). Tungsten will corrode in seawater. 

Klochko K, Kaufman AJ, Yao W, Byrne RH, Tossell JA (2006) Experimental measurement of boron isotope fractionation in seawater. Earth Planet Sci Lett 248 276-285 Kloppmann Girard NSgrel P (2002) Exotic stable isotope composition of saline waters and brines from the crystalline basement. Chem Geol 184 49-70 Knauth LP (1988) Origin and mixing history of brines, Palo Duro Basin, Texas, USA, Applied Geochemistry 3 455 74... 

Sanyal A, Nugent M, Reeder RJ, Bijma J (2000) Seawater pH control on the boron isotopic composition of calcite evidence from inorganic caldte precipitation experiments. Geochim Cosmochim Acta 64 1551-1555... 

Spero HJ, Bijma J, Lea DW, Bemis BE (1997) Effect of seawater carbonate concentration on foraminiferal carbon and oxygen isotopes. Nature 390 497-500 Spivack AJ, Edmond JM (1986) Determination of boron isotope ratios by thermal ionization mass spectrometry of the dicesium metaborate cation. Anal Chem 58 31-35 Spivack AJ, Edmond JM (1987) Boron isotope exchange between seawater and the oceanic crust. Geochim Cosmochim Acta 51 1033-1043... 

Zachos J, Pagani M, Sloan L, Thomas E, BiUups K (2001) Trends, rhythms and aberrations in global climate 65 Ma to present. Science 292 686-693 Zeebe RE (1999) An explanation of the effect of seawater carbonate concentration on foraminiferal oxygen isotopes. Geochim Cosmochim Acta 63 2001-2007 Zeebe RE (2005) Stable boron isotope fractionation between dissolved B(OH)3 and BlOH). Geochim Cosmochim Acta 69 2753-2766... 

In water, boron readily hydrolyzes to form the electrically nentral, weak monobasic acid H3BO3 and the monovalent ion B(OH)4. Waterborne boron may be adsorbed by soils and sediments (USPHS 1991). The predominant boron species in seawater is boric acid (Thompson et al. 1976) concentrations are higher at higher salinities and in proximity to indnstrial waste discharges (Liddicoat et al. 1983 Narvekar et al. 1983). In seawater, borate or boric acid occurs naturally at... 

Boron, aluminum and gallium are all highly hydrolysed trivalent elements, but the extent of their hydrolysis in seawater is distinctly different. While all three elements exist as M(OH) and M(OH)4 in seawater, Al is much more weakly hydrolysed than either B or Ga. The free-to-total metal ratio for Al3+ is in the order of 10 9A at 25°C and pH 8.2, while for Ga the free-to-total metal ratio is in the order of 10 15 7. Owing to its high charge and small radius, boron does not form a simple cation (M3+) in aqueous solution and, in fact, forms of boron less... 

Thallium (Tl), which appears to exhibit conservative behaviour in seawater, has two potential oxidation states. As Tl1, thallium is very weakly complexed in solution. In contrast, Tl111 should be strongly hydrolysed in solution ([T13+]/[T13+]t — 10 20 5) with Tl(OH)3 as the dominant species over a very wide range of pH. The calculation of Turner et at. (1981) indicated thatTl111 is the thermodynamically favoured oxidation state at pH 8.2. Lower pH and p()2 would be favourable to Tl1 formation. Within the water column, pH can be considerably less than 8.2 and /)( )2 lower than 0.20 atm. In view of these factors, and the observation that redox disequilibrium in seawater is not uncommon, the oxidation state of Tl in seawater is somewhat uncertain. The existence of Tl in solution as Tl+, a very weakly interactive ion, would reasonably explain the conservative behaviour of Tl in seawater. However, the extremely strong solution complexation of Tl3+ suggests that Tl3+ may be substantially less particle reactive than other Group 13 elements (with the exception of boron). 

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 ... 

The boron problem still exists due to the low rejection of boric acid through the membranes, yet several other solutions exist, as described below. Final mixing of the water is advisable in some cases to increase salt concentration slightly. Small organic compounds dissolved in the feed water may also find their way into the water produced. Salt content depends on feed quality (brackish or seawater) and may vary between 50-600 ppm of TDS. A secondary stage may improve quality with only a... 

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