Abstract. On the basis of the nuclear magnetic resonance (NMR) relaxation of imbibed water, we evaluated the interparticle and intraparticle pore sizes in packed beds of silica materials of known particle sizes and microporous structure. The NMR relaxation distribution is scaled by the surface relaxivity parameter p, which incorporates a surface area to volume ratio (So/Vo) term, to yield a corresponding pore size distribution. The NMR-derived pore sizes of nonporous silica sand agreed with the expected interparticle pore sizes estimated from the morphology of a packed bed of spheres of comparably sized particles. The NMR-derived intraparticle pore size for porous silica was also in good agreement with reported values for the silica materials studied. Scaling of the NMR relaxation corresponding to interparticle water by the same surface interaction parameter to yield interparticle pore size in high-surface area porous silica material, however, grossly underestimated interparticle pore size. In these high-surface area materials the intraparticle micropores provide a higher contribution to the N 2 measured surface area relative to the contribution from interparticle macropores. When the NMR relaxation method was used to evaluate the pore space in the Borden Aquifer material, the NMRderived pore sizes agreed with those observed in scanning electron micrographs as well as pore sizes estimated from the morphology of packed beds of comparably sized particles. For soils and aquifer materials of low to moderate surface area the NMR-derived porosity determination may be used to adequately evaluate both solute transporting and sorbing pore sizes. IntroductionThe fate and transport of pollutants in terrestrial and aquatic ecosystems are influenced by the heterogeneity of the sotbent matrix. In modeling solute transport, assumptions regarding the sorption mechanisms and the microgeometry of sotbents must be made. Experimental data is needed to calibrate model parameters which describe the pore structure and hydraulic properties. There is, however, a lack of process- The principle methods for pore structure analysis are gas adsorption/condensation and mercury porosimetry [Gregg and Sing, 1977]. In heterogeneous porous media characterized by a broad range of pore sizes, the two methods are complementary [Ball et al., 1990] in that the former is capable of measuring sizes less than 0.05/xm and the latter is better suited to measure sizes greater than 0.05/xm. There are limitations inherent to each of these methods, however. Both gas adsorption and mercury porosimetry measure the smallest constriction in a porous matrix rather than the pore radius [Gallegos et al., 1988]. In addition, these methods require removal of the pore fluid prior to analysis. Desiccation may cause irreversible 2697

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Nuclear magnetic resonance spectroscopy (31P NMR) was used to characterize the phosphorus (P) extracted from selected municipal sewage sludges. Aqueous and nonaqueous extraction schemes were studied. The trichloroacetic acid/KOH two‐step extraction and the 0.5 M NaOH extraction were effective in recovering P from sludges. It was found that the P distribution pattern is sludges was affected by the sludge digestion processes. Almost all of the P in anaerobically digested sludges was inorganic. In the waste‐activated sludge and aerobically digested sludges, more than 50% of the total P was present as P‐monoesters and P‐diesters. Several experiments were conducted to confirm P‐diester peak assignment. Incubation of the sludge with ribonuclease caused a decrease of the peak in the P‐diester region, indicating that at least a part of the P‐diesters is in the form of RNA. Results of a dialysis experiment appeared to indicate that P‐diesters were broken down from the molecular weight >1000 material to their lower molecular weight components during sludge digestion. The peaks appearing in the 31P NMR spectra of sludge‐borne phospholipids were tentatively assigned to phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, and phosphatidylglycerol or diphosphatidylglycerol.

ABSTRACTduced amorphous Al and Fe oxides exhibiting high reactivity toward ion adsorption suggestive of high surface Surface area is a physical property of solids that has been used as area (Sims and Bingham, 1968;McPhail et al., 1972).an indicator of reactivity and as an input parameter in chemical surface complexation models of ion adsorption. This study was conducted to Sims and Bingham (1968), and Ͼ200 m 2 g Ϫ1 for Al oxide mesoporosity, were characterized using gas adsorption, mercury intruusing the preparation technique of McPhail et al. (1972).sion porosimetry, scanning and transmission electron microscopy, andWe attributed the differences in surface area of the Al The objectives of our study were (i) to identify the is needed at the time of reaction if thermodynamically unstable materifactors that affect surface area of synthetic amorphous als are used in adsorption studies.Al oxides, (ii) to evaluate whether surface area is a stable physical property of amorphous Al oxides, and (iii) to propose a synthesis methodology that produces D ue to their size, soil colloidal particles contain amorphous Al oxides having surface areas consistent a large amount of reactive surface. Various soil with their reactivity toward anion adsorption. physical and chemical properties, including ion adsorption capacity, are highly correlated with surface area.MATERIALS AND METHODS Amorphous particles are generally small in size, reactive, and have a large surface area. The predominant Oxide Synthesis Al and Fe oxide phases in soils are often the amorphous Aluminum oxides were synthesized and freeze-dried using species. These generally have larger surface area and four different methodologies. The synthesis for the lowest greater reactivity toward anion adsorption than the corsurface area material was repeated and the product was split responding crystalline mineral phases (Bohn et al., into two parts; one part was freeze-dried and the other was 1979). Because of their high reactivity, synthetic amorair-dried. In all methods, the AlCl 3 /NaOH ratio was constant phous Al and Fe oxides are often studied as reference at a value of 0.375. Aluminum/OH ratio is a very important variable affecting the end product in Al oxide synthesis. Table materials for the comparable amorphous minerals in 1 indicates the starting reagent concentrations for amorphous soils that are difficult to isolate in pure form.Al oxides of varying surface area. Using x-ray diffraction analSurface area is a physical property of solids that has ysis, we found that all Al oxides were amorphous. been used as an indicator of potential reactivity. Materials having higher surface area are considered to be more Characterization of Surface Area and Porosity reactive in retention of nutrient ions and toxic trace elements. Surface area is also an important input paramSpecific surface areas were determined using both singlepoint and multipoint Brunauer-Emmett-Teller (BET) N 2 adeter in chemical surface complexation models and transsorption and desorption isotherms obtai...

Nuclear magnetic resonance relaxation measurements were used to identify different characteristic porosity domains in soil and aquifer materials. The porosity distribution can be inferred from these measurements by a regularization method applicable to any nuclear magnetic resonance (NMR) relaxation, or by an analytic method applicable only to multiexponential relaxations (D'Orazio et al., 1989). The porosity distribution obtained from NMR relaxation measurements strongly depends on the pore shape factor. For the Borden aquifer material, both the regularized and the analytic pore size distribution obtained from NMR relaxation measurements are consistent with those obtained by Ball et al. (1990) using Hg porosimetry and N2 adsorption. For the Eustis and the Webster soils, the measured porosity domains are qualitatively consistent with those expected based on their respective composition. Our findings suggest that due to the long time required to saturate fine pores, NMR measurements of porosity distribution that are collected at short saturation times are biased toward larger pore sizes. Tikhonov, A. N., and V. Y. Arsenin, Solutions of Ill-Posed Problems, Winston and Sons, New York, 1977. Timur, A., Pulsed nuclear magnetic resonance studies of porosity, movable fluid, and permeability of sandstones, J. Pet. Technol., 246, 775-786, 1969. van Genuchten, M. T., and P. J. Wierenga, Mass transfer studies in sorbing porous media, I, Analytical solutions, Soil Sci. Soc. Am. J., 40, 473-480, 1976. van Genuchten, M. T., and P. J. Wierenga, Mass transfer studies in sorbing porous media, II, Experimental evaluation with tritium (3H20), Soil Sci. Soc. Am. J., 41,272-278, 1977. Woessner, D. E., An NMR investigation into the range of the surface effect on the rotation of water molecules, J. Magn.