Normalized leaching rate

Figure 4. Long-Term Normalized Leach Rates vs. Time.

Concentration of (ppm) in waste form (waste loading) Normalized leach rate (g/m day) in PCX Leachability index in ANS 16.1 test... 

Normalized Leaching Rates (g/cm day) for the Matrix Components in the Supernatant and Sludge Waste Forms. 

The amount of biocides needed in an antifouling paint will be determined by actual tests performed in real life. A rule of thumb says that the minimum level of protection with copper is a leaching rate of 10 pg/(cm2 day) (WHOI, 1952). The amount of cuprous oxide can be up to 40 wt % of an antifouling paint and it is normally assisted by booster biocides (5 to 10 wt %) to provide full protection against both animals and algae. The amount of biocides will be based on practical performance and, at the same time, be restricted to given legislation. 

Although there is plenty of experimental evidence that ultrasound improves leaching the exact mechanism is not fully understood. Swamy and Narayana [60] have suggested models for leaching in the presence and absence of ultrasound (Fig. 4.4). Normal leaching takes place as the solvent front moves inward and a steady state diffusion occurs through the depleted outer region and is equal to the rate of reaction within the reaction zone itself (Fig. 4.4a). 

An example of the kinds of data required for land disposal options would be Information on soll/pestlclde Interactions to determine the effect of the pesticide on the soil and soil on the pesticide. The physical composition of the soil and the physical properties of the pesticide and Its formulation will determine the adsorption, leaching, water dispersal, and volatilization of the pesticide which. In turn, determine the mobility of the pesticide In soil. Even pesticides of closely related structures may have very different soil retention properties. Much of this data will be available from that developed to meet other registration data requirements with the exception that disposal rates are often orders of magnitude higher than normal application rates and the difference must be considered. 

Fig. 7. Plot of the Pu leach rate as a function of time for pyrochlore- and zirconolite-rich LLNL-type waste forms in experiments performed at 90 CC in pure water (after Hart et al. 2000). Power law curve fits illustrate the normal trends for these materials initial rapid decrease in leach rates followed by slower release rales, which decrease to 10"5 g/m2/d or less after time periods of several months to one year.

In order to estimate the long-term durability of HT materials, leaching experiments need to be expressed in terms of apparent normalized release rates of elements (Perret et al. 2003). For comparison purposes (from element to... 

Gross dissolution of the waste can be measured from the loss of weight of the sample or by determination of the appearance in the leaching medium of the major matrix constituent e.g. glass). However, the selective leaching of important fission product elements has been observed in this work to be significantly different from that of the bulk waste matrix. The units normally used to describe leach rates, g/cm day, appear to imply... 

In leaching, there usually is a very rapid leach rate that occurs when the mineral is on the surface of the particle, but many times the internal diffusion of the solid through the solid particle becomes controlling, and mixer variables do not affect the leaching rate beyond that point. In studying the effect of mixing on leaching processes, it is normally desirable to run separate experiments with... 

Table IV is a summary based upon the total elemental recovery concentrations of calcium and magnesium leached from the five stone samples, their equivalent carbonate weights, and the total average sample leaching rate (normalized for surface area and rain depth) ...

Based on preliminary leaching results for TPD (Dacheux et al., in press), normalized dissolution rates are of the order of 10 g/m d for neutral solutions. These leaching data are comparable to those for monazite and better than those for apatite. Thomas et al. (2000, 2001) have completed detailed leaching studies of Th-TPD and Th-U-TPD solid solutions as a function of surface area, flow rate, temperature and pH of the solution. For the Th-TPD, remarkably low leach rates of 10 g/m d were measured. Th-concentrations in solution were controlled by the formation of a thorium phosphate phase, identified by HRTEM, with a solubility <10 M in solutions in contact with the Th-TPD. With the substitution of uranium, the Th-U-TPD shows a slight increase in leach rate, lO " g/m d. The saturation concentrations in solution for U and Th were controlled by the formation of (U02)3(P04)2 5H20 and Th2(P04)2(HP04)H20, respectively. 

If the concentration level of PCBs can be reduced to such an extent that subsequent leaching does not yield a concentration which is above the 500 ppm PCB limit imposed by the EPA 90 days after the process has been completed then, according to the letter of the law, the unit can be reclassified as PCB contaminated. However, experimental data on units which have been retrofilled with a simple vapor cleaning process have shown that the PCB leaching rate under normal load conditions is in the range of 1.5 2.5 ppm PCB per day. If the trapped PCBs are able to leach out into the bulk retrofill fluid at a rate of as little as 1 ppm PCB... 

The reaction proces.ses can be described by a combination of results from leach tests and SIMS. The nominal composition and leach rates (g in - d" ) of a glass formulation, PNL 76-68 (Pacific North-West Laboratories), used as the. standard high-level nuclear waste glass matrix [4], are shown in Table 4. The definition of leach rate u.sed normalizes the loss (in g) to the proportion of that element in the nominal bulk composition. It will be seen that the leach rates for Cs, Na, Mo, Si and B exceeded the overall rate of mass loss from the gla.ss surface, whereas the elements Fe, Zn and Ti did not show significant loss to solution under these conditions. There were also several elements, e.g.. Ca. Ba, Cd and Sr, that were neither rapidly leached nor apparently retained in the surface layers. Studies described in the above-mentioned reviews, using XPS, FTIR, SIMS, SEM and dissolution rates, have established clearly that the primary reaction occurring in solution is the bond-breaking attack by OH at Si (or Al and... 

It was estimated that the vitrification option would allow for a volume decrease of 0.75 as a conservative estimate, and that the actual volume decrease could be 0.50. Wastes would be treated in four equally sized melter systems, each of which would process about 80 tons per day. The project would be completed in about 10 years. The online operational rate is projected to be 75%, with three normally operating systems and one system down for maintenance. The produced glass does not require placement in containers, as it will pass leach test requirements in that form (D114432, Appendix A). 

---