Simulated seawater

Vanadium is resistant to attack by hydrochloric or dilute sulfuric acid and to alkali solutions. It is also quite resistant to corrosion by seawater but is reactive toward nitric, hydrofluoric, or concentrated sulfuric acids. Galvanic corrosion tests mn in simulated seawater indicate that vanadium is anodic with respect to stainless steel and copper but cathodic to aluminum and magnesium. Vanadium exhibits corrosion resistance to Hquid metals, eg, bismuth and low oxygen sodium. 

Photoactivation analysis has also been used to determine fluoride in seawater [73]. In this method a sample and simulated seawater standards containing known amounts of fluoride are freeze-dried, and then irradiated simultaneously and identically, for 20 min, with high-energy photons. The half-life of 18F (110 min) allows sufficient time for radiochemical separation from the seawater matrix before counting. The specific activities of sample and standards being the same, the amount of fluoride in the unknown may be calculated. The limit of detection is 7 ng fluoride, and the precision is sufficient to permit detection of variations in the fluoride content of oceans. The method can be adapted for the simultaneous determination of fluorine, bromine, and iodine. 

A hanging mercury drop electrodeposition technique has been used [297] for a carbon filament flameless atomic absorption spectrometric method for the determination of copper in seawater. In this method, copper is transferred to the mercury drop in a simple three-electrode cell (including a counterelectrode) by electrolysis for 30 min at -0.35 V versus the SCE. After electrolysis, the drop is rinsed and transferred directly to a prepositioned water-cooled carbon-filament atomiser, and the mercury is volatilised by heating the filament to 425 °C. Copper is then atomised and determined by atomic absorption. The detection limit is 0.2 pg copper per litre simulated seawater. 

Schoenfeld and Held [539] used a spectrochemical method to determine rubidium in seawater. They determined concentrations of rubidium in the range 0.008-0.04 p,g/ml in the presence of varying proportions and concentrations of other salts as internal standard. The coefficient of variation ranged from 7 to 25% for simulated seawater standards. 

Two excellent examples of this membrane system have been developed, NS-lOO and PA-300 (5,15). The NS-lOO membrane was made by impregnating a polysulfone support with a 0.67 percent aqueous solution of polyethylenlmine, draining away excess reagent, then contacting the film with a 0.1 percent solution of toluenediisocyanate in hexane. An ultrathln polyurea barrier layer formed at the interface. This membrane was then heat-cured at 110°C. A later version of this membrane was developed (designated NS-101), which used isophthaloyl chloride in place of toluenedilsocyanate, producing a polyamide (16). With either type of membrane, salt rejections in simulated seawater tests at 1000 psi exceeded 99 percent. 

Table 6 lists several of the salient properties of this new composite membrane. When salt rejection was evaluated at different pressures in simulated seawater trials, potable water (containing less than 500 ppm dissolved salts) was generated at as low as 600 psi, with very good flux (12 gfd) at that pressure. In spiral-wound membrane element trials on actual 33,000 ppm seawater, potable water was obtained even at 500 psi, albeit at low flux. These results surpass by far the capabilities of any of the "NS" series of membranes. 

The FT-30 membrane was found to be resistant to swelling or salt rejection losses at high feedwater temperatures. In simulated seawater tests, the membrane had stabilized at about 99 percent salt rejection at temperatures of 40°C and higher. 

Figure 2. Exposure of FT-30 membranes to 100 ppm chlorine in water at different pH levels. Effect on salt refection in simulated. seawater reverse osmosis tests (0) pH 1 Cn pH 5 (O) pH 8 (A) pH 12.

Water temperatures in the Gulf of Mexico can be as high as 30°C along the coast during the summer. Use Table 8.3 to estimate the vapor pressure of seawater at that temperature and at 100°C and 0°C, assuming that a 0.50 m NaCl(aq) solution simulates seawater. 

Barcelo, D., G. Durand, V. Bouvot, and M. Nielen (1993). Use of extraction disks for trace enrichment of various pesticides from river water and simulated seawater samples followed by liquid chromatography-rapid-scanning UV-visible and thermospray-mass spectrometry detection. Environ. Sci. Technol., 27(2) 271-277. 

An example of the use of EIS measurements to make long-term corrosion predictions for polymer coated metals is shown in Fig. 46 (110). In this plot, the ASTM D610 and D714 visual rankings of corrosion damage after 550 days of exposure in simulated seawater are plotted against a protection index, < (/), determined after only 10 days of exposure. The damage protection index is determined from the breakpoint frequency, /, as... 

Wagh et al. [9] tested their Ceramicrete formulation for offshore wells by using simulated seawater. The composition of this water is given in Table 15.5, and the results are presented in Table 15.6. 

The NS-100 membrane is capable of giving salt rejections in excess of 99% in tests on salt solutions simulating seawater (18 gfd, 3.5% synthetic seawater, 1,500 psi, 25°C). If the polyurea interfacial reaction step is omitted, and the polyethylenimine-coated polysulfone film is heat-cured as usual, a crosslinked polyethylenimine semipermeable barrier film is generated. This membrane gives 70% salt rejection and 55 gfd water flux under the same test conditions as above. Also, if the fully formed NS-100 membrane is dried at 75°C, which is too low a temperature to effectively crosslink the amine layer, the resulting film will exhibit a salt rejection of 96% or less. 

The initial studies by Cadotte on interfacially formed composite polyamide membranes indicated that monomeric amines behaved poorly in this membrane fabrication approach. This is illustrated in the data listed in Table 5.2, taken from the first public report on the NS-100 membrane.22 Only the polymeric amine polyethylenimine showed development of high rejection membranes at that time. For several years, it was thought that polymeric amine was required to achieve formation of a film that would span the pores in the surface of the microporous polysulfone sheet and resist blowout under pressure However, in 1976, Cadotte and coworkers reported that a monomeric amiri piperazine, could be interfacially reacted with isophthaloyl chloride to give a polyamide barrier layer with salt rejections of 90 to 98% in simulated seawater tests at 1,500 psi.4s This improved membrane formation was achieved through optimization of the interfacial reaction conditions (reactant concentrations, acid acceptors, surfactants). Improved technique after several years of experience in interfacial membrane formation was probably also a factor. 

The most outstanding property of the NS-200 membrane was its extremely high salt rejection. In simulated seawater tests, salt rejection levels of 99.8 to 99.9% were rountinely observed. Typical performance in a 1,500 psi test on 3.5% synthetic seawater at 25°C was 20 gfd and 99.9% salt rejection. In a few instances, laboratory samples of NS-200 membranes with fluxes of 40 to 50 gfd under these same test conditions were obtained. 

Figure 4.42. Demonstration of the efficiency of the incorporation of an ion-exchange preconcentration column into a FIA system for the determination of lead by atomic absorption spectrometry. In (A) is shown the recordings obtained for a series of aqueous lead standards in the range 25-100 xg/L, using the manifold depicted in Fig. 4.41 comprising a dual-column system, that is, the twin peaks for each concentration refer to the outputs for reactors A and B respectively. (B) is the output for a 100 tig/L lead solution prepared in a matrix simulating seawater. For comparison the response of the same instrument, operated under conventional experimental conditions of direct continuous aspiration, but without the inclusion of the on-line preconcentration column, is shown in (C).

Although the number of studies of fluorapatite growth kinetics is smaller than for hydroxylapatite, they have particular relevance to sedimentary apatite formation. Amjad et al. (1981) repeated the experiments of Koutsoukos et al. (1980) (pH = 7.40, T = 37°C, S = 10-30) for fluorapatite and similarly found that the rate equation held for FAP with an apparent reaction order of 1.25 indicating a spiral growth mechanism. Van Cappellen and Berner (1991) conducted seeded fluorapatite growth rate experiments in a carbonate-free simulated seawater solution at different degrees of saturation, S. They fit their growth rate data with an empirical rate law of the form... 

For marine applications, pH-stable EAPs have been investigated. Double-stranded PANI has been coated onto A1 alloys (458) immersion tests in simulated seawater showed improved corrosion resistance as compared to control samples (epoxy coating) (459). Recently, poly(bis-dialkylamino)phenylene vinylene) (BAM-PPV) was shown to adhere to A1 alloy in an immersion test using simulated seawater (pH 8) to retard corrosion (460,461). Quantitative evidence was obtained to show corrosion inhibition as compared to noncoated A1 alloys. 

Figure 10.58 Overlaid chromatograms of simulated seawater and simulated seawater spiked with Be(ll). Separator column IDA-func-tionalized silica (8 pm) eluent 0.4mol/L KNO3 adjusted to pH 3.0 with HNO3 flow rate 1 mL/ min detection photometry at 590 nm after...

Fig. 7.4 Five year sorption data for AS4/3501-6 and IM7/8551-7 coupons immersed in simulated seawater at 34°C (note weight losses recorded after 4 years of exposure)...

Fig. 4(b) Time-dependent change in absorption ratio (in simulated seawater). 

Meyers, P.A., and T.G. Oas. 1978. Comparison of associations of different hydrocarbons with clay particles in simulated seawater. Environmental Science and Technology 12 934-937. 

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