Residual adsorption capacity

Sacco, A. Chung, B and Aksoy, Y., Nondestructive method to measure residual adsorption capacity of charcoal filters, Chem. Eng. Commun., 17(1), 43-56 (1982). 

Bac, N. Sacco, A., and Hammarstrom, J.L., Measurement of residual adsorption capacity of charcoal filters under conditions of variable humidity, Chem. Eng. Common., 24(4), 205-214 (1983). 

It is important to note that adsorption does not necessarily lead to a catalytic reaction but the surface catalyzed reactions always occur through adsorption. In their catalytic action, the surfaces are specific in nature. Ni and Cu surfaces are very good catalysts for hydrogenation processes. The physical nature of a surface also influences its catalytic efficiency. Those atoms, which are at the peaks, edges etc. have high residual fields and are likely to have greater adsorption capacity. Taylor (1925) postulated that the adsorption and subsequent reaction takes place preferentially on certain parts of the surface, which are called active centers. The active center may constitute a small portion only of the total surface. Moreover, all active centers where adsorption occurs are not always catalytically effective. 

Various well-known industrial and municipal waste products particularly those from the base metal industry, contain appreciable amounts of Fe oxides which may make them suitable for remediation purposes. Two examples from industry are the residues from the alumina and the titanium industries. The extraction of either Al or Ti from the natural ores (bauxite and ilmenite/rutile, respectively) leaves behind an alkaline and acidic (sulphuric) residue, respectively, in which Fe oxides are enriched, as indicated by their names Red Mud and Red Gypsum . A sample of Red gypsum is reported to contain ca. 35% of Fe oxide consisting of goethite and hematite, half of which was oxalate soluble (Fauziah et al., 1996). As expected, this material had an appreciable adsorption capacity for phosphate and heavy metals and, if added to soils, could confer these properties on them (Peacock Rimmer, 2000),... 

By way of comparing the capacity data derived from the present experiments with capacity data obtained by other investigators for the same solute, a plot of an experimental isotherm presented by Aly and Faust for adsorption of 2,4-D on powdered carbon indicates an adsorption capacity of 80 mg./gram corresponding to a residual concentration... 

Example 8.5 A wastewater containing [C ] = 25 mg/L of phenol is to be treated using PAC to produce an effluent concentration [C] = of 0.10 mg/L. The PAC is simply added to the stream and the mixture subsequently settled in the following sedimentation tank. The constants of the Langmuir equation are determined by rnnning a jar test prodncing the resnlts below. The volnme of waste snbjected to each test is one liter. If a flow rate of Q of 0.11 mVs is to be treated, calcnlate the quantity of PAC needed for the operation. What is the adsorption capacity of the PAC Calcnlate the qnantity of PAC needed to treat the inflnent phenol to the ultimate residual concentration. 

R.T.Yang et.al. [6] studied the influence of residual water on the adsorption properties of LiLSX. They removed water out of hydrated LiLSX by heating at different temperatures. Their results showed that very small amounts of water in LiLSX have a significant effect on the adsorptive capacity. The nitrogen adsorption capacity dropped from -17.4 N2 molecules/u.c. (per unit cell) for the fully dehyc ted LiLSX to <2 N2 molecules/u.c. when the sample contained about 32 water molecules/u.c.. They pointed out that this also could be well correlated to the Li population of Sill sites in LiLSX. Li at Sill sites preferred to attract H2O molecules over N2 molecules, because of the much stronger interaction between H2O and Li. When H2O molecules were adsorbed on Li at Sill sites, they would block the adsorption of other molecules. This explains why it took only 32 H2O molecules to significantly diminish the N2 adsorption capacity. 

Figure 2. Nitrogen adsorption capacity versus water content, (a) samples with residual water ...

The isotherm parameters were determined using Nelder Mead simplex method by minimizing the sum of residual, namely, the differences between experimental and estimated adsorption amount. Figure 2 showed the adsorption isotherms of TCE on MCM-48 at 303, 308, 313, 323 K. As one can be expected, the adsorption capacity was decreased with increasing temperature. The hybrid isotherm model for a pure adsorbate was found to fit the individual isotherm data very well. The parameters of the hybrid equations are listed in Table 1. 

This retardation is caused by adsorption on clays and organic materials. The adsorption capacity is in turn a function of the surface area and availability of these materials to the adsorbing species in question. In real soils, and especially those of sedimentary origin, the adsorbant components are to be found as discrete lenses of low permeability rather than as an evenly distributed phase as is essentially assumed in the laboratory methodologies for determining the retardation factors. In these lenses penetration to the bulk of the adsorption sites is restricted to diffusion and the small residual convection fluxes. 

For these experiments the maximum adsorption capacities measured are about 30 mg TOC per gram of 400-carbon and about 20 mg TOC per gram of J 23-carbon at equilibrium TOCs of respectively 18 and 16 mg L . These capacities are not only low but they also drop very quickly to values lower than 10 mg TOC per gram when at equilibrium with TOC concentration of about 10 mg L". For both carbons a residual nonadsorbable fraction of about 10 mg (45%) is left in solution. When using UV 254 absorption, the same results are obtained. The ratio U.V.-absorbance over TOC is almost constant during adsorption ( +5.0 mg L m ). 

VijTTolf (6, 7) set forth that the transformation of Type 4A zeolite by thermal treatment at 600°C begins at the periphery of the crystal. This opinion is related to the decrease of water adsorption capacity at 600°C observed by Milton (2) and the abrupt disappearance of activity in the sample at 670°C pointed out by Piguzova (5), while an x-ray crystallographic analysis indicates the presence of a large quantity of untransformed zeolite. In order to show clearly the mechanism of thermal transformation of a Type 4A zeolite, we decided to determine the quantity of residual zeolite and the possible macroporosity at each step of the... 

The 3 essential points of our study are the following The solid B formed by thermal treatment masks the adsorption properties of the residual zeolitic phase. The adsorption capacity reappears with the grinding of the sample. The transformation of the zeolite occurs with the appearance of a closed macroporosity. 

To explain the total suppression of adsorption capacity from the moment of disappearance of half of the zeolitic phase and the appearance of a closed macropososity, it seems necessary to invoke the hypotheses of Wolf (6, 7) the solid-solid transformation begins at the periphery of the particle and progresses toward the center. It is sufficient to cause the shell of product B to break in order to bring about the residual zeolitic phase and thus find the properties of the microporous solid. After thermal treatment at 670 °C, calculation indicates the presence of 37 volume % of solid B. If a cubic particle with an edge equal to 1 micron is considered, the thickness attained by the layer of solid B impervious to water is close to 0.1 micron. 

The thermal transformation of Type 4A zeolite begins at 550°C, as indicated by the decrease of water vapor adsorption capacity. This capacity is nonexistent after a thermal treatment at 670°C. We have demonstrated that, after grinding the samples which have been heated previously at this temperature, half of the zeolitic phase, characterized by its water retention capacity, remained. The residual zeolite is thermally unstable. It has the same x-ray diffraction pattern as the initial zeolite, but should not have the same chemical composition. We have shown that the solid-solid transformation is accompanied by a closed macroporosity which disappears gradually with sintering. There is every reason to believe that the solid-solid transformation begins at the periphery of the particles and progresses towards the center. 

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