Adsorption mercury

Few comprehensive classification schemes for CCP exist. The American Society for Testing and Materials (ASTM 1994) classifies two catgories of fly ash (Class F and Class C) based upon chemical and physical properties of the fly ash (the total amount of Si + A1 + Fe, sulphate, loss on ignition). This classification system was developed for the use of fly ash as an admixture in concrete. More recently, new classification schemes have been developed that place emphasis on textural descriptions, the form of carbon (or char ), and the surface properties of fly ash (Hower Mastalerz 2001). These new classification schemes for fly ash may be the result of growing concern over mercury emissions from coal-fired boilers. Studies have shown that mercury adsorption onto the surface of fly ash particles is a function of both the total carbon content and the gas temperature at the point of fly ash collection (Hower et al. 2000). 

Hower, J. C., Finkelman, R. B., Rathbone, R. F. Goodman, J. 2000. Intra- and inter-unit variation in fly ash petrography and mercury adsorption examples from a western Kentucky power station. Energy and Fuels, 14, 212-216. 

The mercury adsorption mechanism was equilibrium controlled Until these conditions have been achieved the rate of mercury adsorption on the walls will not equal the rate of desorption. The first two conditions were approximated in most of the tests reported. A second assumption in the mass balance was that the air utilized in the combustion process does not contribute a significant quantity of mercury to the system. 

Azimonti, G., Bidoglio, G., Righetto, L., and Bellobono, I. R. (1994). Cobalt and mercury adsorption on alumina colloids in the presence of humic substances. In Humic Substances in the Global Environment and Implications to Human Health, Senesi, N., and Miano, T. M., eds., Elsevier, Amsterdam, 1079-1084. 

Keywords heavy metal ions MCM-41 MCM-48 mercury adsorption mesoporous organosilicas ordered mesoporous silicas SBA-15... 

Sample BET specific surface area (m7g) Total pore volume (cm3/g) Pore width (nm) Mercury adsorption capacity (g/g) C>,g (mmol/g) Reference to data... 

The most consistent results seem to be the ones for mercury adsorption. For example. Huang and Blankenship ]221] have reported pronounced uptake max-... 

Adsorption kinetics. Figures 1 and 2 show the mercury adsorption kinetics at 20°C on cellulose and corn-stick powder which have been chemically modified. 

The adsorption mechanism of mercury by modified cellulose seems to be related to the number of proton present in solution. This kind of phenomenon was already observed by Miyamoto [8] who studied mercury adsorption by keratine gel and by Marchant [17] who utilized cellulose modified with thiol groups. 

Adsorption losses to the sample container during storage (22, 23, 24). These investigations suggest that under nonacidified conditions, mercury adsorption to the container walls is rapid enough to affect mercury concentrations within a sampler during a hydrocast. 

Diphenyl Mercury Adsorption. Adsorption of DPM from seawater onto amorphous iron hydroxide, manganese oxide and bentonite clay was not detected in this study. A comparison of standard diphenyl mercury solutions in seawater with Identical solutions to which sediment phase had been added and shaken for 48 hours was routinely performed as part of the isotherm determination. There was no significant difference in the concentration of dissolved diphenyl mercury for standard. versus standard plus solid phase for any of the suspensions of amorphous, Fe(OH)-, MnO, or bentonite in seawater, implying no significant adsorption of DPM from seawater onto these phases under the concentrations studied. If lower concentrations of DPM could have been used (ppb or lower) it is possible that adsorption might have been detected. 

Figure 3. Relationship between mercury adsorption and mercury concentration in solution at pH 4.0 ( ) and pH 9.6 (O) [30].

Walcarius, A.. Devoy. J., and Bessiere. J.. Electrochemical recognition of selective mercury adsorption on minerals. Environ. Sci. Technol.. 33, 4278, 1999. 

Figure la shows a quick fall of the mercury concentration in the mercury solution to the end of one hour of treatment this could be explained by mercury adsorption on different immobilization supports and also to mercury adsorption on the bacteria cellular envelope due to the peripheral charges and functional groupings present in the envelope and also to absorption phenomena by which these the bacteria accumulates the metals inside the cell by active or passive transport (Jairo-Alberto, 1990). Then we are witnessing a progressive decrease of the load polluting and this for the different effectuated experiences due to mercury detoxification. In fact mercury can bind with cell surface proteins, highly specific transport of Hg2+ into the cell in the protein-bound form. 

Figure 9. Plots of 0 vs.. cj (o o o and —) and (AG a)/RT vs., ( and —) due to ethylene glycol adsorption on a Hg electrode at concentrations 2, 1.6, 1.2, 1.0, 0.7, 0,5 and 0.2 mol dm (from top to bottom). Points are experimental data reprinted from J. Electroanal. them., 28, S, Trasatti, Effect of the Nature of the Supporting Electrolyte on the Thermodynamic Analysis of the Adsorption of Organic Substances on Mercury. Adsorption of Ethylene Glycol form 0.1 m Aqueous Solutions of Halides, p. 257, Copyright 1970, with permission from Elsevier Science. Curves were calculated from Eqs. (16), (21), and (23) using the parameters given in text.

In the second step of the process, the metallic mercury is adsorbed on the CMG273 trapping mass (metal sulfide supported on alumina). The mercury adsorption can be also modeled, with the same kinetic model (Fig. 18.33). 

Reimers, R.S., P.A. Krenkel, 1974, Kinetics of Mercury Adsorption and Desorption in Sediments, Water Pollution Control Federation,... 

Materials with SH groups were treated with an aqueous solution of HgCla at room temperature. It was observed that the ratio of metal ions per thiol moieties was found to be around 1/3, confirming the high mercury adsorption capacity (2.3 mmol of Hg per gram). These values are high in comparison with most of those obtained for thiol-modified mesoporous silica described in the literature. " ... 

Seigner C, Abeck H, Chia G, Reinhard M, Bloom NS, Prestbo E, Saxena P (1998) Mercury adsorption to elemental carbon (soot) particles and atmospheric particulate matter. Atmos Environ 32 2649-2657... 

Although the higher concentrations of tannic acid showed increased removals over those produced by activated carbon alone, the increase was not as high as in the case of 1 mg/L concentration of tannic acid. The presence of calcium ions in aqueous solutions also enhanced the adsorption of Hg(II) ions (Figure 6.18). The mercury adsorption increased by between 10 and 20% as the concentration of calcium ions was increased from 50 mg/L to 200 mg/L. This was attributed to a reaction between the calcium ion in solution with the surface groups on the carbon surface in such a way that new adsorption sites are aeated in the process. When both calcium ions and tannic acid were present, the removal of Hg(ll) ions was almost doubled, even with smaller amounts of the activated carbon. 

Sulfur-impregnated activated carbons has been shown to be an effective sorbent for the removal of vapor-phase Hg< from CFPP and MWC flue gases [3,12,14,20-26]. This material has a large mercury adsorption capacity, but the addition of sulfur to activated carbon requires additional production cost. To avoid such processing steps, it may be possible to produce activated carbons from a precursor that already contains sulfur. 

To examine the role of film mass transfer (the maximum mass transfer flux), assume C Cg at all positions in the duct (this means that mercury adsorption capacity of the carbon and the carbon reactivity are not limiting the mass transfer rate). Equation (4) is obtained by integrating equation (2) using the following boundary conditions 1) at z = 0 ( entrance), Cg=Co 2) at z = L (outlet), Cg=Cg. 

Bench-scale experiments were performed in a 5-cm ID fluidized-bed reactor (FBR). These experiments were intended to 1) prepare carbon products with varying ash content, sulfur content, surface area, pore volume and production yield, 2) identify optimum conditions for producing activated carbon samples with desired properties for removal of various mercury species from utility flue gas, 3) evaluate the influence of inherent sulfur of the coal precursors on the mercury adsorption reactivity and capacity of the resultant activated carbon products, and 4) obtain scale-up date for producing larger quantities of carbon products in a pilot-scale FBR. 

Figure 4. Bench-scale, fixed-bed mercury adsorption apparatus.

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