Soil washing is an important method for the remediation
of contaminated
soil. This research presents the optimization of soil washing conditions
in the remediation of Zn-contaminated soils with water-soluble chitosan
(WSCS). Response surface methodology (RSM) was used to optimized the
washing conditions after single factor experiments. The central composite
design (CCD) with three factors and five levels was applied to the
optimization of the removal efficiency of Zn from soils, and WSCS
concentration, pH value, and washing time were evaluated variables
in the washing process. Results indicated that the pH value (p < 0.0001) was the most significant factor which mainly
affected the distribution and content of metal species in aqueous
solution, ion exchange and adsorption/desorption behavior of metals,
solubility of chelating agent, as well as readsorption of metal complexes.
The optimal conditions for the Zn removal from soils were WSCS concentration
of 1.5%, pH of 3.3, and washing time of 72 min. The removal efficiency
could reach 65.4% under the optimized conditions, which was close
to the predicted value of 68.3% by the response surface method. Therefore,
it could be found that the response surface methodology was an effective
method to determine the optimal conditions for the removal of metals
from contaminated soils by soil washing.
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