Iron silicate sorption

Actinide and Technetium Sorption on Iron-Silicate and Dispersed Clay Colloids... 

Figure 1. Sorption of 237Pu and 233U by Iron Silicate (top) and Na Bentonite (bottom) Colloids at 25°C.

The results of additional experiments conducted with 85Sr and 137Cs spikes are shown in Figure 4. The well known sorption characteristics of bentonite for Sr and Cs ions is apparent (7). The sorption properties of bentonite are reduced at low pH, which is consistent with an electrostatic concept. 137Cs sorption on the iron silicate colloids is considerably less than that observed with bentonite, even though the colloid zeta potentials are similar, which suggests that mechanisms other than simple electrostatic concepts may be involved. Also, the linear trend of data for Sr in iron silicate systems is considered to represent precipitation rather than sorption. 

Figure 3. Sorption of 95mTc and 235Np on Iron Silicate and Na-Bentonite Colloids at 25°C and Comparison with Possible Tc and Np Speciation.

Figure 4. Sorption of 137Cs and 85Sr by Colloidal Iron Silicates and Na Bentonite at 25°C.

The processes described and their kinetics is of importance in the accumulation of trace metals by calcite in sediments and lakes (Delaney and Boyle, 1987) but also of relevance in the transport and retention of trace metals in calcareous aquifers. Fuller and Davis (1987) investigated the sorption by calcareous aquifer sand they found that after 24 hours the rate of Cd2+ sorption was constant and controlled by the rate of surface precipitation. Clean grains of primary minerals, e.g., quartz and alumino silicates, sorbed less Cd2+ than grains which had surface patches of secondary minerals, e.g., carbonates, iron and manganese oxides. Fig. 6.11 gives data (time sequence) on electron spin resonance spectra of Mn2+ on FeC03(s). 

Rates of sorption and desorption of phosphate. Eur. J. Soil Sd. 48 101-114 Strens, R.G.S. Wood, B.J. (1979) Diffuse reflectance spectra and optical properties of some iron and titanium oxides and oxyhydr-oxides. Min. Mag. 43 347—354 Stumm, W. Eurrer, G. (1987) The dissolution of oxides and aluminum silicates Examples of surface-coordination-controlled kinetics. 

Takematsu, N. (1979) Sorption of transition metals on manganese and iron oxides and silicate minerals. J. Oceanogr. Soc. Japan 35 ... 

For each nuclide studied, the sorption distribution coefficients appeared to result from a minimum of two separate mechanisms. In all cases, one mechanism appears to be an ion-exchange phenomena associated with the silicate phases and appears to have a relatively much larger sorption capacity than the other mechanism. In the case of cesium (and probably rubidium) the second mechanism appears to also be related to the silicate phases and may or may not be an ion-exchange phenomena. However, for the other elements studied, the second mechanism appears to be related to the hydrous iron and manganese oxides and again may or may not be an ion-exchange process. 

Silicate, chromate, molybdenate, and humic acids also may create significant interferences with the sorption of As(V) and As(III) on zerovalent iron (Su and Puls, 2001b Giasuddin, Kanel and Choi, 2007). Interferences from borate and sulfate, however, were negligible with As(V) and only minor with As(III). Some interferences with As(III) and As(V) sorption occurred with carbonate and nitrate (Su and Puls, 2001b). Similarly, Farrell et al. (2001) concluded that carbonate and nitrate could hinder the efforts of zerovalent iron to lower As(V) concentrations in water to below 5 pgL-1. 

Zhang et al. (2004) estimated the sorption capacity of an Australian hematite iron ore as 0.4 mg As(V) g-1 ore (Table 7.2). The presence of silicate and phosphates in the ores hindered As(V) sorption, whereas sorption was slightly enhanced by water-soluble sulfate and chloride. Zhang et al. (2004) found... 

Zachara, J.M., Smith, S.C., Resch, C.T. and Cowan, C.E. (1992) Cadmium sorption to soil separates containing layer silicates and iron and aluminium oxides. Soil Sci. Soc. Am. J., 56, 1074-1084. 

Toxic trace elements were isolated from water samples by extraction with di-ethyldithiocarbamate (Table 2.1.2). Following this pre-concentration step the metal ions were adsorbed on a cation-exchange resin using a mixture of tetrahydro-furan-methylglycol-6 M HCl as sorption solution. The succesive elution was treated with 6 M HCl, 1 M HCl and 2 M HNO3 for fractional separation. In another application hexane-isopropanol-HCl mixture was used as the adsorption medium An analytical scheme which provides quantitative results, is described for ion-exchange separation of fifteen major, minor and trace elements in silicates For concentration and separation of copper, chromium, lead and iron an ion-exchanger in phosphate or OH -form was used in various combinations ... 

The sorption of uranium from acid sulfate leach liquors by strong base anion exchange resins is unusual since complexes of the type [U02(S04) ] " may be sorbed by both ion exchange and addition mechanisms. High concentrations of other species are present in the leach solution due to dissolution of pyritic and siliceous components of the ore, but, apart from iron, they do not interfere with the sorption of uranium as a complex anion. Iron(III) also forms an anionic sulfate complex, but is only weakly held by the resin and is displaced ahead of the uranium. The sorption of uranium may be represented by equations of the type ... 

A conceptual and mechanistic model of particle interactions in silica-iron binary oxide suspensions is described. The model is consistent with a process involving partial Si02 dissolution and sorption of silicate onto Fe(OH)3. The constant capacitance model is used to test the mechanistic model and estimate the effect of particle interactions on adsorbate distribution. The model results, in agreement with experimental results, indicate that the presence of soluble silica interferes with the adsorption of anionic adsorbates but has little effect on cationic adsorbates. 

Ca3(P04)2. Rapid sorption of iron by coastal sludge was observed after authorized discharge of Fe from an English nuclear power station, and re-mobilization of these anthropogenic iron traces was slow (Warwick etal. 2001). Correspondingly, the industrial Fe, Cr, and Ni load was associated with aluminum-silicate lattice in sediments of a Greek river estuary (Dassenakis et al. 

Nanocomposites of iron oxide and silicate were also synthesized for the degradation of azo-dye Orange II (see Table 7) [388, 389]. To improve the sorption capacity, clays were modified in different ways (e.g. treatment by inorganic and organic compounds). Organoclays have recently attracted lots of attention in a number of applications, for example, dithiocarbamate-anchored polymer/organosmectite for the removal of heavy metal ions from aqueous media (see Table 7) [390]. 

In a study of copper sorption to ternary systems composed of organic matter (leaf compost), ferrihydrite and montmorillonite (Martfnez-Villegas and Martmez 2008), and its time evolution over 8 months, it was found that copper sorption followed the order organic matter > silicate clays > iron oxides (Figure 14.11a). Within each solid... 

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