Leaching index

As mentioned in Section 17.3.1, retention of quadrivalent actinide oxides within the phosphate matrix is not a major issue because these oxides are insoluble in water, and all that is needed is their microencapsulation by the phosphate components of the matrix. This was demonstrated in a number of studies on UO2 and PUO2 and their surrogate Ce02. If the actinides are found in a trace amount in the waste, their chemical form is not so important because the phosphate matrix immobilizes them very efiectively. For example, the wastewater in the case study given in Section 16.3.2.2 contained 32 pCi/ml of and 0.6 pCi/ml of The ANS 16.1 tests conducted on the waste forms with 18.6pCi/g loading of combined U in the waste form showed that the leaching index was 14.52. XCLP tests also showed that levels in the leachate were below the detection limit of 0.2 pCi/ml. This implies that microencapsulation of trace-level U is very efiective in the Ceramicrete matrix. 

Figure 22 Predicted pattern of Holocene pedogenic carbonate accumulation in a cm column in a semi-arid, thermic climate (leaching index = 3.5 cm). External carbonate flux rate = 1.5 X 10 g cm yr PcOj = 1-5 X 10 atm in compartment 1 increasing to 10 atm in compartment 5 (20-25 cm). Below compartment 5, the pco decreases to a minimum value of 10 atm in compartment 20 (95-100 cm). Dotted line shows carbonate distribution at r = 0. Gray area indicates final simulated distribution. Depth = absolute infiltration depth in <2 mm fraction (McFadden et al, 1991) (reproduced by permission of Soil Science Society of America from Occurrence, Characteristics, and Genesis of Carbonate, Gypsum and Silica Accumulations in...

The LEACH index is a leaching index assessing the potential degree of groundwater and river water contamination [Laskowski, Goring et al, 1982]. It is defined as... 

Based on the Principal Component Analysis, the LIN index (leaching index) and the VIN index (volatility index) were defined in terms of the first and second PCs, respectively, explaining 92.7% of the total variance [Gramatica and Di Guardo, 2002]. PCs were calculated on a data set of 135 pesticides, described by vapour pressure (Vp), Henry s law constant (H), water solubility (Sw), and octanol/water (Kqw) and organic carbon (Kqc) partition coefficients. The LIN and VIN indices are defined as the following ... 

The Global Leachability Index (GLI index) [Papa, Castiglioni et al, 2004] was defined by Principal Component Analysis, condensing information derived from GUS index, modified LEACH index, and LIN index. 

LEACH index environmental indices (0 leaching indices)... 

Of course, water solubility alone is not an adequate criterion for soil movement, and must be tempered with a knowledge of soil sorption, volatility, and chemical reactivity, competing processes that can remove a chemical from the soil water phase, and the method of application to soil. An attempt to build in the important factors which govern leaching (as well as a similar approach to volatilization from soil) has been described (22). Their leaching index" can be calculated from the simple ratio ... 

Information about persistence is essential for the environment risk assessment of chemical substances. Persistence is needed as input for all predictive approaches, from simple leaching indexes to more complex models. Nevertheless, the availability of reliable persistence data is, at present, the weakest link in the prediction of the environmental fate of chemicals. 

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