This study investigated the influence of
flushing duration, [S,S]-ethylenediaminedisuccinic
acid (EDDS) dosage,
humic acid and various combinations of
ethylenediaminetetraacetic acid (
EDTA), EDDS and
tetrasodium pyrophosphate (Na(4)
P(2)O(7)) on
metal extraction during soil
flushing, through column experiments. A lesser extent of enhancement in
metal extraction efficiencies was found when the
flushing duration and the dosage of EDDS was doubled, compared to their efficiencies measured at pore volume 100.
Metal extraction efficiency was mainly influenced by the initial
metal distribution in the
soils rather than the
flushing duration and the EDDS-to-
metal molar ratio.
Humic acid of less than 10mg/L as
dissolved organic carbon (DOC) posed an insignificant effect on
metal extraction during EDDS enhanced soil
flushing. The extraction rate of Ni by
EDTA and EDDS was time dependent, and was initially fast in the case of EDDS, whereas it was slow for
EDTA. However, the overall Ni extraction efficiency by
EDTA was higher when the
flushing time was longer. Na(4)
P(2)O(7) promoted the
mineral dissolution which enhanced the
metal extraction as a result of soil disruption. The order of
metal extraction by Na(4)
P(2)O(7) was Ni>Cr>Cu, probably be due to the different affinities between metals and P(2)O(7)(4-).