Stabilisation of CCA-contaminated soil: assessment of amendments for immobilization of chromate cupper arsenate (CCA)

Stabilisation of trace element contaminated soil is a soil remediation method used to reduce the mobile fraction of critical elements in the soil using soil additives (amendments). The stabilisation of trace elements occurs through i.e. sorption, co-precipitation or complex formation. In this work, different amendments and combinations of amendments have been added to chromate cupper arsenate (CCA) contaminated soil collected at a former wood preservation site at Robertsfors works, Sweden. The amendments used in the experiments were blast furnace slag (BFS), zerovalent iron (Fe0), blaster sand (BS), coal fly ash (CFA) and peat. The changes in the element mobility were tested performing standard compliance batch leaching tests at L/S (liquid to solid ratio) 2 and 10.

The purpose of the investigation was to increase knowledge about the behavior of the trace elements occurring in CCA contaminated soil when adding different amendments. One goal was to identify an amendment or combination of amendments that effectively stabilized the contaminants (reducing the mobility of the contaminants). A second goal was to test how the effectiveness of the selected amendment changed in different geochemical environments. To vary the geochemical environment the parameters pH, amount of water added to the soil and redox potential were controlled. The evaluation of the results was based on the leaching of As, but the behavior of the other trace elements e.g. chromium, copper was also considered.

All amendments added alone decreased the mobility of As, except for peat which increased the amount of As in the leachate about 4 times. The most effective amendment to decrease the leaching of As was Fe0 alone. Fe0 also decreased the leaching of Cr, Cu and Zn. A combination of amendments that effectively reduced the mobility of the trace elements was Fe0 and BFS together. When more water was added to the soil (L/S 10) it was observed that Fe0 alone worked more effectively than the combination of BFS and Fe0.

Further investigations were made for the soil treated with Fe0. The effect of redox could not be evaluated because the treatment with nitrogen gas of the samples during the leaching did not permit to reach low redox potential, i.e. to reach oxygen free conditions. The amount of water that was in contact with the soil had less effect on the mobility of As than the pH in the leachant. The pH was kept constant at pH 3, 5 and 8. The least amount of As was leached from the soil when pH was kept at 5.

Author: Lundberg, Eleonor

Source: LuleƄ University of Technology

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