The feasibility of using biodegradable biosurfactants to remove heavy metal
s from an oil-contaminated soil was evaluated by batch washes with surfacti
n, a rhamnolipid and a sophorolipid. The soil contained 890 mg/kg of zinc a
nd 420 mg/kg of copper with a 12.6% oil and grease content. Highest levels
of zinc removal were obtained using 12% rhamnolipid (19.5% of the zinc) and
4% sophorolipid/0.7% HCl (15.8% of the zinc). Highest copper removal rates
were achieved (greater than 25%) with 12% rhamnolipid or with 2% rhamnolip
id/1% NaOH or 0.25% surfactin/1% NaOH. A series of five batch washes remove
d 70% of the copper with 0.1% surfactin/1% NaOH while 4% sophorolipid/0.7%
HCl was able to remove 100% of the zinc. Sequential extraction procedures s
howed that the carbonate and oxide fractions accounted for over 90% of the
zinc present in the soil and the organic fraction in the soil constituted o
ver 70% of the copper. Sequential extraction of the soil after washing with
the surfaction or rhamnolipid (both with 1% NaOH) indicated that these sur
factants could remove the organically-bound copper and that the sophorolipi
d with acid could remove the carbonate and oxide -bound zinc. In conclusion
, the results clearly indicated the feasibility of removing the metals with
the anionic biosurfactants tested even though the exchangeable metal fract
ions were very low.