Iron Oxide Adsorption

Chang Y., Benjamin M.M, (1995), A combined iron oxide adsorption and ultrafiltration process for natural organic matter removal and fouling control, Proc. AWWA Annual Conference, Anaheim, 0, 657-666. 

The examples in the preceding section, of the flotation of lead and copper ores by xanthates, was one in which chemical forces predominated in the adsorption of the collector. Flotation processes have been applied to a number of other minerals that are either ionic in type, such as potassium chloride, or are insoluble oxides such as quartz and iron oxide, or ink pigments [needed to be removed in waste paper processing [92]]. In the case of quartz, surfactants such as alkyl amines are used, and the situation is complicated by micelle formation (see next section), which can also occur in the adsorbed layer [93, 94]. 

Adsorption Processes. The processes based on adsorption of hydrogen sulfide onto a fixed bed of soHd material are among the oldest types of gas treating appHcations (4). Two common sorbent materials for low concentration gas streams are iron oxide and zinc oxide. 

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 ... 

Fig. 1. Iron oxide process where Kl represents the iron oxide sorbent bed ( ), the adsorption system and (-...

As shown in Figure 2, adsorption of dispersants on particle surfaces can increase 2eta potential further, enhancing electrostatic repulsion. Increased repulsion between particles is evidenced by lower viscosity in concentrated slurries, or decreased settling rates in dilute suspensions. The effect of added dispersants on settling of (anhydrous) iron oxide particles is shown in Figure 3. 

As a possible method of concentrating trace amounts of bioactive organic compounds occurring in the hydrosphere, adsorption properties of various compounds have been explored by employing hydrous metal oxides as the adsorbents. To date, a family of organophosphoms compounds and carbonic acids were adsorbed onto hydrous iron oxide, along with the adsoi ption of monosaccharides onto hydrous zirconium oxide. 

They also provide useful corrosion inhibition by the adsorption of calcium phosphonate onto iron oxide corrosion products, thus reducing the ferrous metal corrosion rate. Phosphonates can be described as cathanodic corrosion inhibitors. 

Fig. 15-17 The effect of chloride on adsorption of mercury by hydrous iron oxide at constant total mercury concentration of 3.4 x 10 M. The lines represent the predicted adsorption assuming that Hg-Cl complexes do not sorb at all. (Reprinted with permission from P. V. Avotins, Adsorption and coprecipitation studies of mercury on hydrous iron oxides," 1975, Ph.D. dissertation, Stanford University, Stanford, CA.)...

Nitrogen adsorption experiments showed a typical t)q5e I isotherm for activated carbon catalysts. For iron impregnated catalysts the specific surface area decreased fix>m 1088 m /g (0.5 wt% Fe ) to 1020 m /g (5.0 wt% Fe). No agglomerization of metal tin or tin oxide was observed from the SEM image of 5Fe-0.5Sn/AC catalyst (Fig. 1). In Fig. 2 iron oxides on the catalyst surface can be seen from the X-Ray diffractions. The peaks of tin or tin oxide cannot be investigated because the quantity of loaded tin is very small and the dispersion of tin particle is high on the support surface. 

The effects of the removal of organic matter and iron oxides on Zn adsorption on soils are also influenced by Zn concentration. At low concentrations (5-10 mg L initial concentration), both treated soils (removed organic matter and iron oxides) behaved similarly. At high Zn concentration, however, treated soils behaved differently. When the initial Zn concentration was between 5 and 10 mg kg-1, adsorption of Zn by soils without organic matter and without both organic matter and iron oxides were 2-2.5 times that of the untreated soil. With an increase in initial Zn concentration, the soil without both iron oxides and organic matter adsorbed more Zn than the soil without organic matter. This indicates that the available sites for Zn decrease with increases in the initial Zn concentration. 

Borggaard O K. Influence of iron oxides on cobalt adsorption by soils. J Soil Sci 1987 38 229-238. 

Shuman L.M. Zinc adsorption isotherms for soil clays with and without iron oxides removed. Soil Sci Soc Am J 1976 40 349-352. 

Hongshao Z, Stanforth R (2001) Competitive adsorption of phosphate and arsenate ongoethite. Environ Sci Technol 35 4753—4757 Hsia TH, Lo SL, Lin CF, Lee DY (1994) Characterization of arsenate adsorption on hydrous iron oxide using chemical and physical methods. Colloid Surface A 85 1-7... 

Lafferty BJ, Loeppert RH (2005) Methyl arsenic adsorption and desorption be-hatior on iron oxides. Environ Sci Technol 39 2120—2127 Le XC (2002) Arsenic speciation in the environment and humans. In Frankenberger WT Jr (ed) Environmental chemistry of arsenic. Marcel Dekker, Inc. New York, pp 95-116... 

Liu F, De Cristofaro A, Violante A (2001) Effect of pH phosphate and oxalate on the adsorption/desorption of arsenate on/from goethite. Soil Sci 166 197-208 Livesey NT, Huang PM (1981) Adsorption of arsenate by soils and its relation to selected properties and anions. Soil Sci 131 88-94 Manceau A (1995) The mechanism of anion adsorption on iron oxides Evidence for the bonding of arsenate tetrahedra on free Fe(0, OH)6 edges. Geochim Cosmochim Acta 59 3647-3653. 

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