Foam-Delivery of Remedial Amendments for Enhanced Vadose Zone Metals and Radionuclides Remediation -9465

Abstract

ABSTRACT The remediation of metals and radionulides contamination, such as Cr(VI), Tc-99, and Sr-90 in the U.S. DOE Hanford Site vadose zone is a critical need. Water-based remedial amendments delivery to the deep vadose zone is facing significant technical challenges. Water-based delivery will easily leach out the highly mobile pollutants therefore contaminate the underlying aquifer. Preferential flow of the amendment-laden solution in the vadose zone due to the formation heterogeneity is difficult to overcome, resulting in bypassing of the less permeable zones. Foam has unique transport properties in the vadose zone that enable mitigation on the mobilization of mobile contaminants and enhance the sweeping over heterogeneous systems. Calcium polysulfide (CPS) is a remedial amendment that can be used to reduce and immobilize hexavalent chromium [Cr(VI)] and other redox-sensitive radionuclides/metals in the vadose zone. The delivery of CPS to the vadose zone using foam and the immobilization of Cr(VI) via reduction by the foam-delivered CPS was investigated in this study. Batch tests were conducted to select the foam-generating CPS-surfactant solutions, to determine the solution foamability and the reducing potential of CPS-containing foams, and to study the influence of foam quality, surfactant concentration, and CPS concentration on foam stability. Column experiments were performed to test the foam delivery of CPS to sediments under conditions similar to field vadose zone, to study the foam transport and interaction with sediments, and to determine the extent of Cr(VI) immobilization using this novel delivery approach. CPS-containing foams with high reducing potential were prepared based on the batch tests. Sediment reduction by foam-delivered CPS was observed in the column studies. Significant mobilization of Cr(VI) from sediments occurred when CPS was delivered in aqueous solution. The Cr(VI) mobilization was minimized when CPS was delivered by foams, resulting in significant Cr(VI) in-situ immobilization. Foam delivery of citrate-phosphate mixture to vadose zone sediments for apatite precipitation was also tested in preliminary column and 2-D flow cell tests. The results of this study demonstrated for the first time that foam injection can be successfully used for CPS delivery and that foam-delivered CPS can be applied for Cr(VI) immobilization in contaminated vadose zones. A second solution (Ca-citrate-PO 4 ) was also foam-delivered into vadose zone sediments. This sediment will result in precipitation of apatite, which then adsorbs and incorporates Sr (and Sr-90) into the structure. 1-D and 2-D foam injection experiments resulted in a wide area of apatite precipitate

    Similar works

    Full text

    thumbnail-image

    Available Versions