Iron oxides adsorption capacity

The sulfur is thus removed from the gas stream and trapped in the sorbent as iron sulfide [1317-37-9]. Over time all of the iron oxide becomes sulfided and the adsorptive capacity of the sorbent becomes exhausted. The bed can be partially regenerated by oxidation, as follows ... 

In Skirmer, H.G.W. Fitzpatrick, R.W. (eds.) Biomineralization processes of iron and manganese. Catena Verlag, Cremhngen-Destedt, Catena Suppl. 21 75—99 Ghoneimy, H.F. Morcos.T.N. Misak, N.Z. (1997) Adsorption of Co and Zn ions on hydrous Fe(lll), Sn(lV) and mixed Fe(lll)/ Sn(IV) oxides. Part 1. Characteristics of the hydrous oxides, apparent capacity and some equilibria measurements. Colloids Surfaces A. 122 13-26... 

Colloidal saccharated iron is sometimes used in place of ferric hydroxide as an antidote in arsenical poisoning, but its adsorptive capacity depends on the alkalinity of the medium.4 Thus a commercial preparation containing 0-75 per cent, of sodium hydroxide was found to adsorb 12-57 per cent, of arsenious oxide (reckoned on the amount of iron present) addition of alkali increased the adsorption until, with 1-28 per cent, of sodium hydroxide present, there was a maximum adsorption of 27 per cent. The addition of acid correspondingly diminished the adsorption. A gel of ferric magnesium hydroxide, if prepared without boiling, also adsorbs arsenic from sodium arsenite solutions.5... 

Whereas several specific soil attributes are advocated as being responsible for DOC sorption in the mineral soil (Table V), it appears that the greater the clay or aluminum and iron oxide content of a soil, the greater its adsorptive capacity for DOC. For example, there is a positive correlation between m (the measure of the affinity of a substance for the sorbent or the partition coefficient) and soil clay content, dithionite extractable iron (Fej), and oxalate extractable aluminum (Al0) (Moore et al., 1992 Nelson et al., 1993 Kaiser and Zech, 1998). Direct measurements of the surface area of soil particles also correlate very well with DOC adsorption capacity (Nelson et al., 1993). Furthermore, Nelson et al. (1993) report that riverine DOC concentrations are negatively correlated to the clay content of watershed... 

EC is a simple, efficient, and promising method to remove arsenic form water. Arsenic removal efficiencies with different electrode materials follow the sequence iron > titanium > aluminum. The process was able to remove more than 99% of arsenic from an As-contaminated water and met the drinking water standard of 10p,gL 1 with iron electrode. Compared with the iron electrodes, aluminum electrodes obtained lower removal efficiency. The plausible reason for less arsenic removal by aluminum in comparison to iron could be that the adsorption capacity of hydrous aluminum oxide for As(III) is much lower in comparison to hydrous ferric oxides. Comparative evaluation of As(III) and As(V) removal by chemical coagulation (with ferric chloride) and electrocoagulation has been done. The comparison revealed that EC has better removal efficiency for As(ni), whereas As(V) removal by both processes was nearly same (Kumar et al. 2004). 

Zhang and Itoh (2006) described a low-cost, environmentally friendly adsorbent for As(III) photocatalytic removal, formed by a mixture of Ti02 and slag-iron oxide obtained from an incinerator of solid wastes. Arsenite is first oxidized to arsenate in a fast process, followed by a slow adsorption of arsenate, although the material shows an adsorbent capacity higher than that of pure anatase. 

Reaction of phosphate with calcite surfaces appears likely in hard water areas, but low adsorption capacity and slow kinetics of the phosphate-calcite reaction under natural conditions probably prevent calcite mediated phosphorus mineralization from becoming a greater phosphorus sink than binding to the amorphous iron oxides. 

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. 

Soil-leaching studies indicate that some silica is released from soil rather rapidly. McKeague and Cline (20) have shown that in soil—water mixtures at 100% water saturation, the silica in solution after 5 minutes was approximately half as great as that after 10 days. After the first day or two the silica concentration increased very slowly. They also demonstrated that pH has a marked effect on silica concentrations in soil solutions (21). These authors attributed the control of silica concentration to pH-dependent adsorption and indicated that, of the common soil minerals, iron and aluminum oxides have appreciable adsorption capacity. Jones and Handreck (22, 23) studied the effects of iron and aluminum oxides on silica concentrations in soil solutions and concluded that both caused a significant reduction in dissolved silica, with aluminum oxides being most effective. Minimum silica concentrations occurred at pH 9-10 in solutions in contact with iron and aluminum oxides. Harder and Flehmig (24) reported that the hydroxides of iron, aluminum, and other elements could remove silica from solutions containing as little as 0.5 mg/liter SiOo. 

Unfortunately, no nitrogen contents of the carbons used for H2S adsorption are cited in the literature. The good performance of nitrogen-containing carbons was ascribed to their basic properties [58], H2S will dissociate at the basic surface sites, their hydrophilicity would provide for adsorbed water. An adsorbent prepared from bituminous coal with the addition of basic oxides such as CaO and MgO and of iron oxides has a much higher capacity than that of Centaur [136],... 

The presence of ash can also influence the adsorption mechanism either via ion exchange or due to the catalytic effect of an inorganic matter. The adsorption feature of activated carbon combined with iron oxides in composites have been reported for a wide range of contaminants in water. The cmnposites materials show high adsorption capacities fiir phenol, chloroform, chlorobenzene and organic %es in aqueous solution [353]. 

Activated carbon does not seem to be a good adsorbent of ammonia present in air. Thus, in order to increase the adsorption capacities of such a material, an impregnation with metal or metal oxides is performed. Iron, copper or other metal-impregnated activated carbons are commonly used. 

Iron-oxide-coated sand is another recently introduced arsenic adsorbent that has been shown to have promise for arsenic removal (8,9). However, because the effective adsorption area is only on the surface of the particle, minimal capacity should be expected compared with adsorbents that are pure hydrated iron oxide and are truly porous. An example of the latter type of adsorbent is granular ferric hydroxide (5). 

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