Environmental Engineering Reference
In-Depth Information
Kamali (2003), which used wastes such as potato peels, leaves, corn husks, and wood shav-
ings and different auxiliary processes to evaluate eficiency and/or reduction in costs,
found maximum solubilization of 68%, 46%, and 34% for copper, zinc, and nickel, respec-
tively (Figure 5.3). Additionally, iron co-dissolution was minimized with only 7% removal.
Rhamnolipid biosurfactants (biodegradable and of low toxicity) have also been added
to mining oxide ores, to enhance metal extraction (Dahr Azma and Mulligan, 2004). Batch
tests were performed at room temperature. Using a 2% rhamnolipid concentration, 28%
of the copper was extracted. Addition of 1% NaOH with the rhamnolipid enhanced the
removal up to 42% at a concentration of 2% rhamnolipid but decreased at higher surfac-
tant concentrations. Sequential extraction studies were also performed to characterize the
mining ore and to determine the types of metals being extracted by the biosurfactants.
Approximately 70% of the copper was associated with the oxide fraction, 10% with the
carbonate, 5% with the organic matter, and 10% with the residual fraction. After washing
with 2% biosurfactant (pH 6) over a period of 6 days, it was determined that 50% of the
carbonate fraction and 40% of the oxide fraction were removed by the biosurfactant.
Further experiments have been performed with biosurfactants and mining residues in
relation to arsenic (Arab and Mulligan, 2013). Results indicated that washing the mine tail-
ing samples with 1% rhamnolipid or sophorolipid arsenate As(V), the dominant species of
arsenic, to As(III). By comparing the reduction power of these two biosurfactants we can
conclude that sophorolipids are more successful in converting As(IV) to As(III) (the more
soluble form of arsenic). Rhamnolipids with different concentrations were able to mobilize
higher amounts of arsenic from the mine tailing than the sophorolipids. There was also a
positive correlation between mobilization of arsenic and iron. The results from the present
study show sophorolipids and rhamnolipid as highly eficient agents for the removal of
arsenic and other heavy metals from soil and mine tailings. However, there is a need for
further research on enhancing the process of arsenic and heavy metal mobilization.
100
Medium 3
80
60
Medium 2
40
Medium 1
Control
20
0
0
5
10
15
20
Time (days)
FIGURE 5.3
Effect of dilute acid pretreatment on leaves and sawdust on copper removal by A. niger. The control is dilute
acid, with medium 1 (40 g/L potato peels and dilute acid), medium 2 (40 g/L sawdust and dilute acid), and
medium 3 (40 g/L leaves with dilute acid) (Mulligan and Kamali, 2003).
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