metals and other base metals. In South Africa, the country with the largest reserve
of chrome ore, the main seams include:
• Chromite: (Mg,Fe
2+ )(Cr,Al,Fe
3+ ) 2 O 4 , the main component of Merensky Reef of
the Bushveld Igneous Complex in South Africa (von Gruenewaldt and Hatton
1987; Wagner 1923)
• Barbertonite: Mg 6 Cr 2 (CO 3 )(OH) 16 .4H 2 O, the major component of the Eastern
Bushveld Igneous Complex (Meli 2009; Calas et al. 1984)
• Nichromite: (Ni,CoFe
2+ )(Cr,Fe
3+ ,Al,) 2 O 4 , which was discovered first in the Bon
Accord nickel deposit in Barberton District, South Africa (Tredoux et al. 1989)
In Brazil, the richest chrome ore seam is in the Campo Formoso layered
intrusion which also contains chromite (Cramer et al. 2004; Boukili et al. 1984).
Consequently, tailing dumps and process waste stockpiles at chrome mining and
ferrochrome processing sites contain significant levels of other platinum group and
rare earth metals (Chirasha and Shoko 2010; von Gruenewaldt and Hatton 1987).
Chromium in the tailing dumps can exist either as Cr(III) or Cr(VI) depending on
the environmental conditions within the dump. Interaction with other metals at
different oxidation states can influence the stability of the oxidation state of the
chromium species inside the waste dump and its ability to leach into the surrounding water bodies (Tiwary et al. 2005; Ma and Garbers-Craig 2006). In areas where
the leachate water enters agricultural supply water, there is a high risk of contamination of food products and bioaccumulation into higher order organisms
(Chirasha and Shoko 2010).
3 Metal Polluting Activities
Due to the wide range of uses of metals, pollution comes in many forms. The most
important feature is whether a metal poses a particular threat and how such a threat
could be best dealt with. In the following subsections, we classify pollutants based
on whether they are toxic to organisms due to chemical poisoning or radiation
poisoning. Chemical toxicity is best dealt with by neutralization using reducing or
oxidizing agents, whereas radiation toxicity, on the other hand, is remediated by
isolation of the radiation source and confinement for a period equivalent to the time
required for the radiation to dissipate.
3.1 Chemically Toxic Elements
There are various metallic elements that confer chemical toxicity. Technically, any
element at excessive loading can cause toxicity. For some metals, the levels at which
they produce observable negative impacts are very low. For metals such as Cr(VI),
2 Advances in Bioremediation of Toxic Heavy Metals and Radionuclides in. . .
23
of chrome ore, the main seams include:
• Chromite: (Mg,Fe
2+ )(Cr,Al,Fe
3+ ) 2 O 4 , the main component of Merensky Reef of
the Bushveld Igneous Complex in South Africa (von Gruenewaldt and Hatton
1987; Wagner 1923)
• Barbertonite: Mg 6 Cr 2 (CO 3 )(OH) 16 .4H 2 O, the major component of the Eastern
Bushveld Igneous Complex (Meli 2009; Calas et al. 1984)
• Nichromite: (Ni,CoFe
2+ )(Cr,Fe
3+ ,Al,) 2 O 4 , which was discovered first in the Bon
Accord nickel deposit in Barberton District, South Africa (Tredoux et al. 1989)
In Brazil, the richest chrome ore seam is in the Campo Formoso layered
intrusion which also contains chromite (Cramer et al. 2004; Boukili et al. 1984).
Consequently, tailing dumps and process waste stockpiles at chrome mining and
ferrochrome processing sites contain significant levels of other platinum group and
rare earth metals (Chirasha and Shoko 2010; von Gruenewaldt and Hatton 1987).
Chromium in the tailing dumps can exist either as Cr(III) or Cr(VI) depending on
the environmental conditions within the dump. Interaction with other metals at
different oxidation states can influence the stability of the oxidation state of the
chromium species inside the waste dump and its ability to leach into the surrounding water bodies (Tiwary et al. 2005; Ma and Garbers-Craig 2006). In areas where
the leachate water enters agricultural supply water, there is a high risk of contamination of food products and bioaccumulation into higher order organisms
(Chirasha and Shoko 2010).
3 Metal Polluting Activities
Due to the wide range of uses of metals, pollution comes in many forms. The most
important feature is whether a metal poses a particular threat and how such a threat
could be best dealt with. In the following subsections, we classify pollutants based
on whether they are toxic to organisms due to chemical poisoning or radiation
poisoning. Chemical toxicity is best dealt with by neutralization using reducing or
oxidizing agents, whereas radiation toxicity, on the other hand, is remediated by
isolation of the radiation source and confinement for a period equivalent to the time
required for the radiation to dissipate.
3.1 Chemically Toxic Elements
There are various metallic elements that confer chemical toxicity. Technically, any
element at excessive loading can cause toxicity. For some metals, the levels at which
they produce observable negative impacts are very low. For metals such as Cr(VI),
2 Advances in Bioremediation of Toxic Heavy Metals and Radionuclides in. . .
23