7.5 Conclusion and Future Perspectives
The exceptional sorption and degradation properties of natural Mn oxides make that
these minerals control or influence the geochemical cycle of trace elements, including metals and organics. By extension, the properties of Mn oxides can be used for
soil remediation purposes.
The reactivity of Mn oxides depends on their structure, which could evolve with
time. This has an implication in terms of short- and long-term metal immobilization
processes, as well as on the nature of the products formed during the reaction of Mn
oxides and metals or organics. The nature of Mn oxides that exist in soils is
extremely large. Given that sorption and degradation properties depend on the
exact nature of the Mn oxide, determining the potential reactivity of soil Mn minerals
toward metals and organics require a sound description of their structure. This has
many implications. For example, this means that the results of wet sequential
extraction procedures, which are frequently used to determine associations between
trace metals and soil components, should as much as possible be complemented by a
mineralogical characterization.
Both natural and engineered Mn oxides have been already tested for soil remediation. They can be used as oxidative reagents for organic and inorganic substances,
sorption agents of trace metals and metalloids, and reactive sorbents for chemical
warfare agent and organophosphate pesticides. Birnessite-like structures seem to be
the most efficient Mn oxides for cleanup purposes. As we can see, efficiencies of
each technique are variables and specific care is needed regarding the degradation
products in the case of organic substances remediation. Thus, the use of Mn oxides is
more mature for trace metals and metalloids immobilization rather than for oxidation
of the organic pollutants. The next step would be now to develop an industrial outlet
of the use of Mn oxides in the field of soil remediation. Such technique would be an
advantage for the remediation of soils polluted by a combination of organic and
inorganic pollutants.
Acknowledgments S.G. acknowledges funding by the French national research agency (ANR-14CE01-0006) and thanks Julie Philibert for fruitful discussions. Special thanks are due to Patrick
Charbonnier (ArcelorMittal) and Hermine Huot (Sun Yat-Sen University) who provided the
pictures presented in Fig. 7.7.
References
Aplin AC, Cronan DS (1985) Ferromanganese oxide deposits from the Central Pacific Ocean,
II. Nodules and associated sediments. Geochim Cosmochim Acta 49(2):437–451
Appelo CAJ, Postma D (1999) A consistent model for surface complexation on birnessite (δ-MnO 2 )
and its application to a column experiment. Geochim Cosmochim Acta 63(19–20):3039–3048
Atkins AL, Shaw S, Peacock CL (2014) Nucleation and growth of todorokite from birnessite:
implications for trace-metal cycling in marine sediments. Geochim Cosmochim Acta
144:109–125
7 The Nature of Manganese Oxides in Soils and Their Role as Scavengers of Trace. . .
421
The exceptional sorption and degradation properties of natural Mn oxides make that
these minerals control or influence the geochemical cycle of trace elements, including metals and organics. By extension, the properties of Mn oxides can be used for
soil remediation purposes.
The reactivity of Mn oxides depends on their structure, which could evolve with
time. This has an implication in terms of short- and long-term metal immobilization
processes, as well as on the nature of the products formed during the reaction of Mn
oxides and metals or organics. The nature of Mn oxides that exist in soils is
extremely large. Given that sorption and degradation properties depend on the
exact nature of the Mn oxide, determining the potential reactivity of soil Mn minerals
toward metals and organics require a sound description of their structure. This has
many implications. For example, this means that the results of wet sequential
extraction procedures, which are frequently used to determine associations between
trace metals and soil components, should as much as possible be complemented by a
mineralogical characterization.
Both natural and engineered Mn oxides have been already tested for soil remediation. They can be used as oxidative reagents for organic and inorganic substances,
sorption agents of trace metals and metalloids, and reactive sorbents for chemical
warfare agent and organophosphate pesticides. Birnessite-like structures seem to be
the most efficient Mn oxides for cleanup purposes. As we can see, efficiencies of
each technique are variables and specific care is needed regarding the degradation
products in the case of organic substances remediation. Thus, the use of Mn oxides is
more mature for trace metals and metalloids immobilization rather than for oxidation
of the organic pollutants. The next step would be now to develop an industrial outlet
of the use of Mn oxides in the field of soil remediation. Such technique would be an
advantage for the remediation of soils polluted by a combination of organic and
inorganic pollutants.
Acknowledgments S.G. acknowledges funding by the French national research agency (ANR-14CE01-0006) and thanks Julie Philibert for fruitful discussions. Special thanks are due to Patrick
Charbonnier (ArcelorMittal) and Hermine Huot (Sun Yat-Sen University) who provided the
pictures presented in Fig. 7.7.
References
Aplin AC, Cronan DS (1985) Ferromanganese oxide deposits from the Central Pacific Ocean,
II. Nodules and associated sediments. Geochim Cosmochim Acta 49(2):437–451
Appelo CAJ, Postma D (1999) A consistent model for surface complexation on birnessite (δ-MnO 2 )
and its application to a column experiment. Geochim Cosmochim Acta 63(19–20):3039–3048
Atkins AL, Shaw S, Peacock CL (2014) Nucleation and growth of todorokite from birnessite:
implications for trace-metal cycling in marine sediments. Geochim Cosmochim Acta
144:109–125
7 The Nature of Manganese Oxides in Soils and Their Role as Scavengers of Trace. . .
421