Infiltration Leaching

Any variety of configurations of injection wells, horizontal wells, trenches, infiltration galleries, aboveground sprayers or leach fields, and extraction wells, open ditches, or subsurface collection... 

Minimize infiltration of precipitation into the waste to control potential leaching of contaminants from the waste. 

Infiltration and percolation rates also determine which salts have been leached out of the soil. For instance, high infiltration and percolation rates leach calcium and magnesium out of soil and they become acidic. Where calcium and magnesium are not leached out, the soils are neutral or basic. Thus, the type and amount of salts present will affect a soil s pH, which will in turn affect the solubility and availability of both natural and contaminating inorganic and organic compounds. 

Tables 12.2 and 12.3. The effect of vertical variability is shown in Table 12.2, while the lateral spatial variability is shown in Table 12.3. The vertical and lateral spatial variabilities were defined on the basis of either the measured adsorption coefficient K), as generated from adsorption isotherms on soil profiles, or on adsorption coefficients on soil organic matter calculated as adsorption on organic carbon per unit weight of soil. We see that both vertical (Table 12.2) and lateral (Table 12.3) variability of soil affect the adsorption coefficients. A comparison between the bromide (conservative) and the two nonconservative herbicides distributions with depth after about 900mm of leaching is shown in Fig. 12.3. We see that, in the case of bromide, there is a continuous displacement of the center of mass with cumulative infiltration. In contrast, the bulk of the herbicide contaminant mass remains in the upper soil layer, with very little displacement.

An important factor of the surface s role in the water balance is infiltration of precipitation into the soil both during rainfall and in run-off. The rate of water take-up by soil wSH is described by the formula wsll = ksl, where ks is the coefficient of filtration, and l is the hydraulic slope. Let us denote the volume mass of the soil as k, which, on average, varies from 1.4g/cm3 to 1.5g/cm3, then for ks it is convenient to use the Azizov formula ks = 256.32k-7 28-1.27k1 14 (cm/da). The parameter / can be calculated using formula l = (z0 + zj + z2)/z0, where z0 is the depth of the column that leaches out, zx is the capillary pressure, and z2 is the height of the... 

Early reports on electrospun scaffolds described poor cellular infiltration [175], Frequently, cells adhered at the surface and thus coated the nano- or submicrometer-scaled electrospun meshes due to the small pore size. In order to overcome this limitation, pore sizes were increased by combining ES with other methods. These approaches included the coating of microfibers with nanofibers [183], Other strategies combine ES with leaching [184, 185], freeze-drying [186], blowing agents [187], or ice templates [188],... 

Figure 6. A comparison of leaching rates of sulfur-infiltrated and -uninfiltrated concrete cylinders by acids of different concentrations...

Figure 7. Leaching of 3-in. cylinders of infiltrated concrete by aggressive media. (leH) I.5N HCl solution removed CafOHL deeply, leaving a yellowish rim of sulfur and silicates (right)...

The effect of pH on the stability of infiltrated concrete in acids is not yet known, pending a study with buffered solutions or partly dissociated acids. A leaching experiment using silage liquor with a pH of 4 has shown no effect after three months. 

These tests indicated that sulfur-infiltrated concrete still loses abundant sulfur when immersed in neutral and sulfatic solutions, even though the reaction is localized and relatively slow. Compression tests of a few cylinders showed there had been little reduction in strength over several months. Examination of sawn surfaces revealed no clearly leached zone, but the specimens had turned a mottled blue, except near the center. Faint peripheral fractures had developed, and coherence of the infiltrated matrix near the surface had decreased, suggesting that some leaching had taken place. 

A Study of Leaching of the Infiltrated Concrete. The distilled water experiments provided the most information for examining the reactions involved in the leaching of sulfur-infiltrated concrete in aqueous media. Products selected from the specimens were analyzed, and the experiment was continued in a controlled environment. One specimen was partly immersed in distilled water under a nitrogen atmosphere. Fragments of the concrete were also sealed in a test tube. 

Analyses of Immersion Liquids and Precipitates. The experiment under nitrogen provided vital information on the stability of the concrete-water system and the reactions taking place. Under a normal atmosphere, sulfur leached from the infiltrated concrete was deposited on the surface as described or was precipitated as a fine mud in the immersion water, together with minor gypsum and calcite. Under nitrogen, however, the liquid turned yellow to pale orange, its pH rose to 11 or more, and precipitation ceased. When the solution was exposed to air, it turned colorless and precipitated sulfur rapidly. This was accompanied by a pH drop to a normal 7.3 level. 

The Final Analysis. The SEM analysis of the liquid extrusion shows that sulfur is present in quantities much greater than the monosulfide of calcium could provide. The most probable explanation is that part of the sulfur is present in polysulfide anions, as the infiltration conditions appear to favor their formation (18). A sample of the yellow solution obtained by leaching fragments under nitrogen was therefore analyzed by laser Raman spectrometry to determine if the absorption... 

Hypothesis of the Leaching Process. The results of these various analyses and observations permit formulation of a hypothesis of sulfur leaching from infiltrated portland cement concrete by aqueous media. 

The inherent instability of sulfur-infiltrated concrete in aqueous media illustrated in this study may be the most important factor in utilization, because it will affect long-term durability of the concrete in many natural settings. The Ca(OH)2 produced by the hydration of portland cement is a principal reactant in the leaching process, and while it remains sulfur could be extracted, leaving the matrix vulnerable to other destructive processes. The removal rate of sulfur will vary greatly, depending mostly upon the pH of the immersion medium thus, the concrete deteriorates in alkaline sulfatic soils but is relatively stable in the corrosive neutral sulfatic solutions from the sodium sulfate plant. 

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