concentrations. Nevertheless, careful is needed regarding these relative efficiencies
because they are strongly dependent on the target metal concentrations.
For As and sometimes Sb removal, the use of Mn oxides (natural or engineered)
significantly decreases their mobility and bioavailability (Bagherifam et al. 2014),
even if Fe oxides often remain more efficient for As sorption. However, mixing
MnO 2 with another adsorbant can be a more powerful solution to treat soluble As in
soils (Gupta et al. 2011; Lenoble et al. 2004; Luo et al. 2012; Yu et al. 2015). In this
case, Mn oxides are generally used for their oxidizing properties (i.e., transformation
of As (III) in As(V), see above) in a two-step treatment: As(III) oxidation followed
by As(V) immobilization.
A promising soil remediation technique for selenite [Se(IV)] involves Fe-Mn
binary oxide nanoparticles (Xie et al. 2015). It was found that in a Se(IV)-spiked soil
treated in situ with starch-stabilized nanoparticles, >90% water leachable Se
(IV) was transferred to the nanoparticle phase, retained in the downstream soil
matrix. This technique is interesting since the sorption capacity is efficient in a
wide range of pH (4–8) and does not show important anion competition [i.e., is very
specific to Se(IV)].
7.4.2.2 Feedback on a 50-Year-Old Case Study
The presence of Mn oxides in industrial waste, heavily contaminated with metals,
can decrease their toxicity and can lead, for example, to plant colonization when
deposited on land. This is the case for sludge resulting from wet cleaning of blast
furnace gases of steel production. Huot et al. (2014) showed the appearance of a
forest since the end of the industrial activity about 50 years ago, on a sludge resulting
from manganese steel production. In comparison, no forest was observed on sludge
of the same age and the same region resulting from classical steel production as
illustrated in Fig. 7.7. The first one contains between 10 and 20% of Mn while the
second one less than 0.2%. Their total contents in Pb and Zn are similar and often
exceed several % in mass. Using spectroscopic techniques, Huot et al. (2014) clearly
show that poorly crystallized Mn oxides are the major scavengers of metals in the
Technosol developed on sludge from the manganese steel production.
7.4.3 Use of Mn Oxides as Reactive Sorbent Agents
for Specific Organic Compounds
Finally, Mn oxides can act as reactive sorbents for the decontamination of persistent
chemical warfare agents and organophosphates pesticides (Mahato et al. 2010;
Prasad et al. 2007a, b; Šťastný et al. 2016; Stengl et al. 2012; Verma et al. 2016).
Particularly, Mn oxides with large specific surfaces and structure defects make them
effective to treat chemical warfare agents such as sarin, agent VX, sulfur mustard or
7 The Nature of Manganese Oxides in Soils and Their Role as Scavengers of Trace. . .
417
because they are strongly dependent on the target metal concentrations.
For As and sometimes Sb removal, the use of Mn oxides (natural or engineered)
significantly decreases their mobility and bioavailability (Bagherifam et al. 2014),
even if Fe oxides often remain more efficient for As sorption. However, mixing
MnO 2 with another adsorbant can be a more powerful solution to treat soluble As in
soils (Gupta et al. 2011; Lenoble et al. 2004; Luo et al. 2012; Yu et al. 2015). In this
case, Mn oxides are generally used for their oxidizing properties (i.e., transformation
of As (III) in As(V), see above) in a two-step treatment: As(III) oxidation followed
by As(V) immobilization.
A promising soil remediation technique for selenite [Se(IV)] involves Fe-Mn
binary oxide nanoparticles (Xie et al. 2015). It was found that in a Se(IV)-spiked soil
treated in situ with starch-stabilized nanoparticles, >90% water leachable Se
(IV) was transferred to the nanoparticle phase, retained in the downstream soil
matrix. This technique is interesting since the sorption capacity is efficient in a
wide range of pH (4–8) and does not show important anion competition [i.e., is very
specific to Se(IV)].
7.4.2.2 Feedback on a 50-Year-Old Case Study
The presence of Mn oxides in industrial waste, heavily contaminated with metals,
can decrease their toxicity and can lead, for example, to plant colonization when
deposited on land. This is the case for sludge resulting from wet cleaning of blast
furnace gases of steel production. Huot et al. (2014) showed the appearance of a
forest since the end of the industrial activity about 50 years ago, on a sludge resulting
from manganese steel production. In comparison, no forest was observed on sludge
of the same age and the same region resulting from classical steel production as
illustrated in Fig. 7.7. The first one contains between 10 and 20% of Mn while the
second one less than 0.2%. Their total contents in Pb and Zn are similar and often
exceed several % in mass. Using spectroscopic techniques, Huot et al. (2014) clearly
show that poorly crystallized Mn oxides are the major scavengers of metals in the
Technosol developed on sludge from the manganese steel production.
7.4.3 Use of Mn Oxides as Reactive Sorbent Agents
for Specific Organic Compounds
Finally, Mn oxides can act as reactive sorbents for the decontamination of persistent
chemical warfare agents and organophosphates pesticides (Mahato et al. 2010;
Prasad et al. 2007a, b; Šťastný et al. 2016; Stengl et al. 2012; Verma et al. 2016).
Particularly, Mn oxides with large specific surfaces and structure defects make them
effective to treat chemical warfare agents such as sarin, agent VX, sulfur mustard or
7 The Nature of Manganese Oxides in Soils and Their Role as Scavengers of Trace. . .
417