Diphenyl mercury adsorption isotherm

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 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. 

S represents the concentration of the adsorbate in the solid phase, while C represents the equilibrium concentration in the bulk solution. The adsorption isotherm of diphenyl mercury and humic acid is illustrated in Figure 1. 

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. 

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See also in sourсe #XX -- [ ]

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