Use of a new leaching test framework for evaluating alternative treatment processes for mercury-contaminated soils

A new framework for evaluating leaching of wastes was used for assessing the efficacy of potential treatment processes for mixed wastes (radioactive and hazardous) that contain mercury. This framework is based on measurement of intrinsic leaching properties of the material of concern and using the testing results in conjunction with assumed management scenarios and mass transfer models to estimate release of constituents of potential concern over a defined time period. Two mercury-contaminated soils (ca. 4500 mg/kg) were used for the demonstrations. Four candidate treatments were examined: vacuum thermal desorption, encapsulation and amalgamation with sulfur polymer cement, and two forms of solidification/stabilization. Fundamental leaching properties (i.e., acid neutralization capacity of the materials, mercury solubility as a function of pH and mercury release rates) were measured. Testing results provided valuable information on the response of the materials to the impact of stresses that may be encountered under different management scenarios. Mercury release estimates for percolation and mass transfer-controlled scenarios were compared to release estimates based on total content and Toxicity Characteristic Leaching Procedure (TCLP) results. Results showed that testing over a range of conditions and evaluation of test results for assumed management scenarios using simple mass transfer models, provides release estimates that are much more reflective of the waste and its plausible management than release estimates based on total content or single batch test results.