Stabilization of CCA-contaminated soil with iron products - a field experiment

Abstract

Chemical stabilization of metals is lately considered as a possible pretreatment for soil
contaminated with average levels of trace elements. The element mobility in soil can be
altered by adding soil amendments that can adsorb, complex, or co-precipitate trace elements.
As a consequence, pollutant spreading from the contaminated soil and effect on the recipient
can be reduced. The different contaminants originating from wood impregnation chemicals,
e.g. Cu, Cr, and As limit the choice of amendments because e.g. large pH fluctuations and
consequent mobilization of Cu or As should be avoided. The results show that the leaching of
arsenic is lowest in the lysimeter with 15% Fe3O4. In both lysimeters with untreated soil and
with 1 % Fe 0, the arsenic leaching seems to decrease with the sampling depth. The leaching of
copper is generally low. Further the addition of iron seems to increase the leaching of
manganese and nickel but to reduce the leaching of zinc. Results from the laboratory
experiment show that the arsenic content in the leachate is lowest with the highest mixture of
magnetite. Mixing is one of the key issues when discussing the treatment efficiency and
possible use of the treated soil. The results so far indicate that magnetite can be used for
treatment of CCA contaminated soil also at a large scale. Reduction of both arsenic and
copper using a single amendment is challenging as they behave opposite. Magnetite seems to
be a promising amendment even though a high amount of amendment needs to be added.
Moreover, the potential establishment of reducing conditions at larger depths in the soil is of
concern since this might lead to a rapid increase in arsenic leaching