Interpretations of Column Experiments

A large, pilot scale column measuring 671 cm in height and 66 cm in diameter was used to study this decommissioning option. Broken but uncrushed ores of about 6 inch size were placed in a column, and rinsing studies commenced after the completion of the copper extraction experiments. Clean water was fed into the top of the column, and leachate was collected weekly at the bottom of the Gaspe Large Column 2. 

The authors concluded that the leachate reached equilibrium with silica and gypsum because the SI values of these two minerals are constant and close to zero despite the orders of magnitude of concentration differences in sulfate. Solubility control by gypsum also explains the calcium concentration increase at the early washing stage. Calcium concentrations were depressed at first because of the high sulfate concentrations. With the sharp decrease of sulfate concentrations, calcium concentrations increased in response to the decrease in sulfate in the solution. 

The solubility control of iron concentrations is evident by the constant SI of goethite 

The interpretation by Li et al. (1996) was that Al was controlled by A1(0H)S04 solubility at low pH but that this phase was depleted as the washing proceeded. The authors also interpreted the wide range of SI values for jarosites to be a result of the absence of jarosite in the column. 

Besides geochemistry, transport processes also exert significant controls on effluent concentrations. The dual porosity model (Decker, 1996 Dixon et al., 1993) for 

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Passivation of iron granulates in permeable barriers used for in situ groundwater remediation may result in a shorter life time and in contaminant breakthrough earlier than expected. Therefore, mineral reactions or generally the effect of other groundwater constituents on the long term reactivity of iron is of major interest for the application of this technology in environmental clean up. For interpretation of column experiments it is also important to estimate the effect of flow velocity on the extent of passivation due to mineral reactions. 

From the interpretation of the values with respect to "elution yield" can be derived that for a good "elution yield ( 70%) a combination with 0.1-5 would be needed. Complexing agents meeting this criterion, namely THI0, TRIS, PAH, GTT, MPG and TM were further tested in column experiments. 

Specification of boundary conditions for interpreting column experiments and... 

In interpreting the results of advection-dominated column experiments, it is essential that a mass-conserving entrance boundary condition be utilized (e.g., as discussed by Parker and van Genuchten, 1984) ... 

Solubility estimates made by the techniques discussed above are reported in the last column of Table H. In addition to the limited number of such measurements, the results do not compare favorably in all cases with the theoretical values listed. This fact is hardly surprising considering the recognized limitations in the thermodynamic data base and difficulties encountered in interpreting results of solubility experiments. Furthermore, the theoretical estimates are based on the assumption that the thermodynamically most stable solid for a radionuclide controls its solubility. The effects of metastability are not included and, in this sense, theoretical solubility estimates are not conservative. A series of sorption-type experiments designed to yield solubility estimates for a number of the radionuclides included in this paper is in progress, and the results will be reported at a later date. 

The table is organized as follows Column 2 lists methods used to complement the XRD experiments. It is obvious from the analysis of the literature that most investigations have required (within the same report) the availability of complementary data for the interpretation of the XRD results. By far the most common complementary techniques are EXAFS and XAS to characterize the evolution of short- and long-range ordering simultaneously. The pairing of this very important basic information about the constitution of a catalyst has even led to the construction of a combined synchrotron-based experiment whereby both techniques were used with catalysts in complex reaction atmospheres (Clausen et al., 1993 Dent et al., 1995 Grunwaldt and Clausen, 2002 Sankar et al., 2000). 

Therefore, we have to analyse the variation of the rate of permeation according to the temperature (zj), the trans-membrane pressure difference (Z2) and the gas molecular weight (Z3). Then, we have 3 factors each of which has two levels. Thus the number of experiments needed for the process investigation is N = 2 = 8. Table 5.13 gives the concrete plan of the experiments. The last column contains the output y values of the process (flow rates of permeation). Figure 5.8 shows a geometric interpretation for a 2 experimental plan where each cube corner defines an experiment with the specified dimensionless values of the factors. So as to process these statistical data with the procedures that use matrix calculations, we have to introduce here a fictive variable Xq, which has a permanent +1 value (see also Section 5.4.4). 

The control over the uptake experiment in a chromatographic column and interpretation of results is even more difficult than with static experiments. For example the pH in dynamic experiments varies not only as a function of time but also spatially (as a function of the position in a column). On the other hand, chromatography is an efficient method to entirely remove certain solutes from solution, it is also used to simulate migration of pollutants in natural systems. 

The interpretation of rate coefficients for chemical change induced by discharges is hampered by the lack of auxiliary data these circumstances are illustrated below in discussing Kirkby s data for positive column reaction. Two principal questions are (1) can the primary and rate-determining step in the reaction mechanism be identified and (2) can a rate coefficient based on that primary step be computed from theory in quantitative agreement with that derived from experiment for the final reaction product. 

For Reaction R4 the rate coefficient Pxx+A computed from Formulae 2.1 and 10 agrees closely with the values found from experiment (usually denoted as a/n or a/p) and long known as the Townsend coefficient of ionization (24). For Reaction R5 and for similar reactions generating the radiative species H2 (a 3V) and N2 (C 3nu), a similar concordance is found between experiment and the predictions of theory (16, 58, 59, 61, 74). In discussing possible interpretations of Kirkby s data for positive column reaction, it is assumed that the Maxwellian form for /(E) is a valid approximation to the true distribution. 

If the surface is first saturated with a monolayer of protein exposed to steady-state concentration cQ, and then is exposed to a second treatment at concentration 2c0, a second front emerges. The second profile represents the situation where no net protein is adsorbed and thus, in principle, is representative of the diffusion-shifted flow pattern of the nonadsorbed protein. Figure 7 shows both the initial (cQ) and second (2c0) fronts and the subtraction curve which is very close to the ideal step function. If the data are interpreted as solution-borne molecules passing over an inert surface, then (a) adsorption must be essentially instantaneous and (b) the surface must become covered by exhausting the concentration of solute at the front as it moves down the column. The slope of the difference profile should represent the rate of uptake of material on the column, and that is essentially infinite on the time scale of the experiment. The point of inflection of the subtracted front indicates the slowing of the sorption process due to filling of sites on the surface. 

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