Leaching, pore-water characterization

Despite the drawbacks of leaching, it is still a useful and in some instances the only method that can be used for pore-water characterization. It is important, however, that its limitations are recognized. 

Two different approaches have been taken by researchers to determine the secondary mineralogy of CCBs (1) direct observation, which is accomplished via analysis of weathered ash materials, and (2) prediction, based on chemical equilibrium solubility calculations for ash pore-waters and/or experimental ash leachate or extractant solutions. Because the secondary phases are typically present in very low abundance, their characterization by direct analysis is difficult. On the other hand, predictions based on chemical equilibrium modelling or laboratory leaching experiments may not be reliable indicators of element leachability or accurately indicate the secondary phases that will form under field conditions (Eighmy et al. 1994 Janssen-Jurkovicova et al. 1994). 

In this study, the practicalities of three methods for extracting and characterizing pore-waters from potential containment materials are discussed. These are (i) mechanical squeezing using a hydraulic press (ii) centrifugation using a heavy liquid displacent and (iii) aqueous leaching of residual salts from crushed core material. 

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