Adsorption onto ferric oxides

Figure 7. Langmuir isotherms for adsorption of pyridine from cyclohexane onto ferric oxide. Conditions heat of adsorption, —8.8 kcal/mol and area per pyridine, 87 A2. Key A, 45°C and O, 25°C. (Reproduced, with permission, from Ref. 33. Copyright 1981, NACE.)...

Typically limit to 0.5 ppm total Fe maximum in the cooling water. Above this level, phosphonate can be used to control problems initiated by iron. However, if the total Fe rises to 3.0 ppm, adsorption of the phosphonate onto the iron takes place and a loss of inhibitor function can occur. Iron salts present a serious fouling risk in cooling systems. Dissolved iron quickly oxidizes (especially where chlorine, bromine, or other oxidizing biocides are used) and forms ferric oxide/hydroxide, which acts as a flocculant,... 

Wilkie, J.A. and Hering, J.G. (1996) Adsorption of arsenic onto hydrous ferric oxide effects of adsorbate/adsorbent ratios and co-occurring solutes. Colloids And Surfaces A-Physicochemical and Engineering Aspects, 107, 97-110. 

Other Controls on Mobility. The mechanism of adsorption of As onto hydrated ferric oxide surfaces has not yet been elucidated. 

Table 7.10. Results of minteqa2 calculations of adsorption onto hydrous ferric iron oxide (HFO).

Doyle et al. (1994) used the triple layer model of Davis et al. (1978) to model surface adsorption of arsenic onto amorphous ferric oxides. Copper smelting has produced... 

The authors found that the model-predicted As concentration is close to the leachate concentrations from the column packed with dust from the continuous reactor (1 120 H.gL-1 versus 1 330 xgL-1), when the solubility product of scorodite from Robins (1990) and the triple layer model is used. Only 11% As in the system was sorbed onto hydrous ferric oxide surfaces. Arsenic concentrations in the leachate are largely controlled by scorodite solubility. It should also be pointed out that simulations using solubility only and without including surface adsorption resulted in a closer match (1 270 n-gL-1 versus 1330 piglA1). For the simulation of the column experiments using wastes from the batch-reactor, the triple layer model predicted too low an As concentration (33 jigL-1 versus 120 pigL-1). 

These observations indicate that reduction of As(V) to As(III) does not, in itself, result in the mobilization of arsenic. This conclusion is supported by laboratory adsorption studies showing similar affinities of As(III) and As(V) for hydrous ferric oxide, goethite, and magnetite.16 However, outstanding questions remain regarding the factors that control the rate and extent of the reductive dissolution of iron in these sediments and whether the arsenic (and iron) that is released into the porewater is (re)sorbed onto the residual iron oxyhydroxides in... 

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... 

Precipitation reactions cannot decrease dissolved arsenic concenPations below that in equilibrium with the solid. In contrast, the dissolved arsenic concentrations controlled by equilibrium sorption will decrease with increasing sorbent concenPation. This effect is illusPated in Figure 3, which shows the calculated disPibution of As(V) between sediment and porewater where this disPibution is controlled by As(V) adsorption onto hydrous ferric oxide (HFO). Increasing the concenPation of iron (present as HFO) in the sediment from 1 to 1.5 mg/g significantly decreases the predicted concentration of As(V) in the porewater. This modeling follows the approach used by Welch and Lico (33) except that we have used a published constant for the sorption of silica on ferrihydrite (114) rather than the estimated constants used by Welch and Lico (33). The choice of the... 

JA Wilkie, JG Hering. Adsorption of arsenic onto hydrous ferric oxide Effects... 

The essential aspects of mechanism are the dissociative adsorption of water on ultrafine gold particles, followed by the spillover of active OH groups onto adjacent sites of the ferric oxide. The formation and decomposition of intermediate species are accompanied by redox transfer of Fe Fe in Fe304 and the reverse step during the dissociation of water molecule. 

The type of substrate the metal is bound to, determines its propensity to be mobilized under completely specific conditions - the metal co-precipitated with carbonates can reach the water environment due to the decrease of a pH, while ions sorbated onto hydrous ferric oxides will be mobilized if there is a decrease in the redox potential, etc. On the other hand, the strength of the connection which the ion of a heavy metal establishes with its substrate will directly determine its mobility - the ion bound by weak, adsorptive connections to some substrate will easily convert into a solution, while the huminous associated metals will be firmly bound to... 

J.A. Wilkie and J.G Hering, Adsorption of Arsenic onto Hydrous Ferric Oxide Effects of Adsorbate/Adsorbent Ratios and Co-occurring Solutes. Colloids cavi Surfaces, A Physicochemical and Engineering Aspects, 107,97-110 (1996). 

The adsorption of heavy metals onto amorphous or crystalline forms of iron oxide and clays occurs in nature and is phenomenologically related to the binding of contaminant to the superhcial ferric and/or aluminium ions. Although, this behavior explains the concentration of metal contaminants in soils, it does not constitute a viable method for trapping low concentrations of contaminants from aqueous streams because of its limited adsorption capacity. 

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