One of the environmental concerns associated with mining waste is the contamination of
soil. This study addresses the decontamination of soil, particularly of Co and Ni using
Berkheya coddii (B. coddii). B. coddii is a hyperaccumulater plant that is able to
decontaminate Co and Ni from the contaminated land. The use of B. coddii to
decontaminate soil or waste must be based on a cognizance of the complicated, integrated
effects of pollutant sources and soil-plant variables.
Phytoextraction pot trials using B. coddii were carried out under green house condition,
with controlled watering. A contaminated metallurgical waste residue known as
Rustenburg Base Mine Refineries waste (RBMR waste soil) collected from Rustenburg
while a serpentine (native) soil (N soil) where B. coddii grows naturally was collected
from Mpumalanga. The experiment involved the addition of sulfur doses to both soils in
order to test whether acidification and higher sulfur availability could enhance the uptake
of both Co and Ni by B. coddii. The results indicate that the addition of sulfur from 2.0 to
8.0 g per kilogram decreased pH in both substrates. RBMR waste soil pH was found to
have decreased from 7.8 to 7.4 while the N soil pH was found to have decreased from 6.4
to 4.7. The reduction oxidation potential (redox potential) in both substrates was observed
to have decreased along with the increase in sulfur dosage. The mean redox potential for
RBMR waste soil was found to be 350 mV and 506 mV for the N soil after the addition
of sulfur. Conductivity increased along with the increase in sulfur dosage in both
substrates. The mean conductivity for the N soil was found to be 961 μS/cm while that of
the RBMR waste soil was found to be 1453 μS/cm after the addition of sulfur.
The decrease in soil pH was significant (p = 0.00115) in the N soil than RBMR waste
soil. Despite the increase in sulfur dosage and decrease in soil pH in both substrates, B.
coddii observed growing. Although it was evident that B. coddii is able to grow in the
RBMR waste soil, it was observed that the RBMR waste soil limits the root depth of the
B. coddii, reducing chances for the roots to penetrate into the ground especially when dry.
The RBMR waste soil becomes more compacted than the N soil when dry. It is therefore crucial to ensure that there is enough moisture to allow for the B. coddii being able to
survive effectively in the RBMR waste soil. B. coddii plant height in the RBMR waste
soil after four months was observed to be in the range of 190 to 200 mm tall. This was
found to be less than the height observed for the B. coddii planted in the N soil, which
was in the range of 350 to 400 mm.
Nonetheless, plants grown in both substrates were able to absorb Ni and Co into their
tissues. More Co and Ni were found to have accumulated into the leaf tissues than in
other parts of the plant. This could be an advantage since one would harvest only the leaf
part or the canopy (shoots) and allow B. coddii to resprout in order to continue taking up
more Co and Ni from the same waste substrate to remediation levels that could be
stipulated by Government as desirable for the ecosystem and the protection of human
health. Although the accumulated Ni and Co can be recovered from biomass, this alone
might not provide sufficient economic justification for phytoextraction due to the low
concentrations that could be recovered.
B. coddii was found to absorb higher concentrations of Co and Ni from the N soil than
from the RBMR waste soil. However, the results found in this study may not be
conclusive. This could be due to many variables that could control metal uptake which
were not investigated. These include mycorrhizal fungi and metal forms in the soil.
Moreover, this study was performed in a green house and not in the outdoor environment.
Ni is generally toxic to most plants, hyperaccumulators (i.e. B.coddii) contain elements that
nullify the toxic effect of nickel, and in this case the accumulated nickel is bound to malate to
form a harmless nickel complex which could be absorbed by the plants as nutrients.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/11940 |
| Date | 12 September 2012 |
| Creators | Nethengwe, Thendo Peterson |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf, application/pdf |
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