Ferric hydroxide sorption onto

As an example of an equilibrium calculation accounting for surface complexation, we consider the sorption of mercury, lead, and sulfate onto hydrous ferric oxide at pH 4 and 8. We use ferric hydroxide [Fe(OH)3] precipitate from the LLNL database to represent in the calculation hydrous ferric oxide (FeOOH /1H2O). Following Dzombak and Morel (1990), we assume a sorbing surface area of 600 m2 g-1 and site densities for the weakly and strongly binding sites, respectively, of 0.2 and 0.005 mol (mol FeOOH)-1. We choose a system containing 1 kg of solvent water (the default) in contact with 1 g of ferric hydroxide. 

To see how this process works, we construct a model in which reaction of a hypothetical drainage water with calcite leads to the precipitation of ferric hydroxide [Fe(OH)3, which we use to represent HFO] and the sorption of dissolved species onto this phase. We assume that the precipitate remains suspended in solution with its surface in equilibrium with the changing fluid chemistry, using the surface com-plexation model described in Chapter 10. In our model, we envisage the precipitate eventually settling to the stream bed and hence removing the sorbed metals from the drainage. 

PROBABLE FATE photolysis . C-Cl bond photolysis is possible, could be important, may photolyze on the soil surface, when released to the atmosphere, it will react with photo-chemically produced hydroxyl radicals with an estimated half-life of 1.23 hr, adsorption onto atmospheric particles will increase this half-life oxidation , probably not important, photooxida-tion by u.v, light in aqueous medium 90-95°C, 25% CO2 formation 5.0 hr, 50% 9.5 hr, 75% 31.0 hr, oxidation rate constant 9.7x10 at pH 7, half-life 71.4 days hydrolysis , hydrolysis of sulfite group may be rapid, probably important above pH 7, hydrolyzed rapidly by alkalies, when released to water, hydrolytic half-life 37.5 and 187.3 days for pH 7 and 5.5 respectively, in the presence of ferric hydroxide, a higher rate of hydrolysis was observed at pH 7 and 20°C, in a solution of ferric oxide, hydrolysis half-life was 9.4 days volatilization could be important sorption sorption is an important process biological processes not important... 

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