Adsorption isotherms seawater

In Kaw = 11.27 - 3230/(T/K) measured range 5-33°C (seawater, multiply equilibrium-GC, Hunter-Smith 1983) 3060 (adsorption isotherm, Urano Murata 1985)... 

Adsorption isotherms and conditional adsorption constants (Kads) were determined for the adsorption of diphenyl mercury and phenylmercurie ion (introduced as phenylmercuric acetate) from a seawater matrix onto several solid phases. Diphenyl mercury was found to adsorb onto humic acid, but no adsorption was detected onto bentonite, amorphous FeCOH) or hydrous MnO,. The value of Kads was found to decrease with increasing ionic strength for the diphenyl mercury - humic acid system in seawater. As the concentraction of suspended humic acid increased, the nonlinearity of the diphenyl mercury - humic acid system became more pronounced at an increasingly lower diphenyl mercury concentration. Phenylmercuric ion adsorbed most strongly onto humic acid although adsorption onto FeCOH) and MnO was detected and Kads values were determined. Kads values for PMA with humic acid, MnO and Fe(OH) were found to decrease with decreasing salinity. 

The effect of concentration of suspended adsorbent on sorptive behavior in a seawater matrix was studied by determining adsorption isotherms for DPM and 94, 150, 200,400, and 1000 ppm humic acid. The corresponding values of Kads (Table III) show no definite trend with respect to Increased adsorbent concentration. This is not totally unexpected in view of O Connor and Connolly s observation that systems with low Kads values do not show dramatic changes of Kads with changes in suspended matter concentrations 9). Only systems with high Kads values typically show definite decreases in Kads with increases in adsorbent concentration. 

Phenylmercuric ion was introduced to the various solid phase-seawater suspensions as an aqueous solution of phenylmercuric acetate (PMA). Adsorption of phenylmercuric ion onto all solid phases studied, except bentonite clay, was noted at solid concentrations of 150 ppm (suspended). Adsorption isotherms for humic acid, hydrous MnO and amorphous Fe(OH)2 are shown in Figure A. Values of Kads for phenylmercuric ion and these solid phases are listed in Table IV. 

Figure 3. Adsorption isotherms for DPM and various concentrations of suspended humic acid in seawater.

Figure 4. Adsorption isotherms of PMA and solid phases in seawater.

Conclusions. Diphenyl mercury, a neutral organometallic compound, which does not contain any markedly acidic or basic functional groups was found to adsorb only onto humic acid. No sorptive behavior could be detected with respect to bentonite, MnO or Fe(OH)-. The rather low value of Kads indicates a simple molecular attraction. However, the decrease in Kads with an increase in ionic strength Indicates that DPM is competing with the metal ions in seawater for adsorption sites. The increasing nonlinearity of adsorption isotherms with increasing suspended humic acid concentration is also similar to results obtained for metal ion adsorption. 

I if>urc 3. Adsorption isotherms of model surfactants (sodium dodecyl sulphate (SDS), egg albumin. iml lecithin) and their mixtures (SI >S and leicthin, concentration ratio 1 5, and albumin and lecithin, (iiux-ntration ratio I I) in seawater. Dashed lines correspond to calculated isotherms. (Cosovic et al.,... 

The preferential sorption-capillary flow model starts from the consideration of the solid-liquid interface. For example, aqueous sodium chloride solution is in contact with a solid surface. Sodium chloride solution represents the reverse osmosis system where the separation of solute (sodium chloride) flrom solvent (water) occurs. This system also represents one of the most important applications of reverse osmosis, i.e., seawater desalination. A concentration gradient should inevitably appear at the solution-solid interface, as shown in Figure 6.1. The Gibbs adsorption isotherm... 

Pigna M, Colombo C, Violante A (2003) Competitive sorption of arsenate and phosphate on synthetic hematites (in Italian). Proceedings XXI Congress of Societa Italiana Chimica Agraria SICA (Ancona), pp 70-76 Quirk JP (1955) Significance of surface area calculated from water vapour sorption isotherms by use of the B. E. T. equation. Soil Sci 80 423-430 Rancourt DG, Fortin D, Pichler T, Lamarche G (2001) Mineralogical characterization of a natural As-rich hydrous ferric oxide coprecipitate formed by mining hydrothermal fluids and seawater. Am Mineral 86 834-851 Raven K, Jain A, Loeppert, RH (1998) Arsenite and arsenate adsorption on ferrihydrite kinetics, equilibrium, and adsorption envelopes. Environ Sci Technol 32 344-349... 

Figure 1. Freundlich isotherm for the adsorption of DPM onto 150 ppm humic acid in 50% seawater.

Diphenyl Mercury Adsorption. Adsorption of DPM from seawater onto amorphous iron hydroxide, manganese oxide and bentonite clay was not detected in this study. A comparison of standard diphenyl mercury solutions in seawater with Identical solutions to which sediment phase had been added and shaken for 48 hours was routinely performed as part of the isotherm determination. There was no significant difference in the concentration of dissolved diphenyl mercury for standard. versus standard plus solid phase for any of the suspensions of amorphous, Fe(OH)-, MnO, or bentonite in seawater, implying no significant adsorption of DPM from seawater onto these phases under the concentrations studied. If lower concentrations of DPM could have been used (ppb or lower) it is possible that adsorption might have been detected. 

Adsorption of DPM from seawater by humic acid was recorded and the value of Kads was determined by a simple least squares analysis of the linear portion of the isotherm to be 1.11 for a 150 ppm suspension of humic acid in seawater (Table II). This low value of Kads is not unexpected, since one would expect the interaction between the neutral nonpolar DPM molecule and the suspended humic acid to be due to a rather weak molecular attraction. 

FIGURE 5.13 Ca-Fe(II) exchange isotherms (plotted as amount sorbed) on montmoril-lonite, a layered clay mineral (see Chapter 8). ( ) Ca + sorbed (0) Fe(II) sorbed lines nonpreference isotherms. (With kind permission from Springer Science+Business Media Aquat. Geochem., Charlet, L., C. Tournassat, Fe(II)-Na(I)-Ca(II) cation exchange on montmorillon-ite in chloride medium Evidence for preferential clay adsorption of chloride - metal ion pairs in seawater, 11, 2005, 115-137.)... 

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