several month) and the use of Mn oxides can reduce the half-life of As(III) at
10–20 min (Johnson and Pilson 1975).
7.4.2 Use of Mn Oxides as Sorbent Agents for Trace Metals
and Metalloids
A major remediation potential of Mn oxides involves their sorption capacities, as
discussed and reviewed in Sect. 7.2. Such properties are generally considered for the
immobilization of metals and metalloids: As, Sb, Se, Pb, Cu, sometimes after an
oxidation step (e.g., As(III)—see Sect. 7.4.1).
7.4.2.1 Efficiency
The Mn oxides are particularly efficient (i.e., more efficient than Fe oxides) for Pb
sorption (Kumpiene et al. 2008; Michalkova et al. 2014; O’Reilly and Hochella Jr
2003; Wang et al. 2012). This particularity is due to the presence of internal reactive
sites in the structure of some Mn oxides. Layer structures such as birnessite have the
highest Pb sorption efficiency, followed by tunnel structure such as cryptomelane
(O’Reilly and Hochella Jr 2003). The sorption efficiency of birnessite specifically on
Pb rather than other trace metals could be explained by the fact that Pb
2+ occupies
both interlayer and surface edge sites, whereas Cu
2+ , Zn
2+ , and Cd
2+ occupy mostly
interlayer sites (Wang et al. 2012).
The pH at the point of zero charge (pH PZC ) of several types of Mn oxides such as
birnessite, ramsdellite, or cryptomelane has been reported to be <4.7, with values
below three for birnessite (Liu et al. 2009; Tripathy and Kanungo 2005). Thus, Mn
oxides are responsible for the uptake of cations in a wide range of pH.
Nevertheless, soil remediation of metals by Mn oxides needs specific care since
the stability of some Mn oxides (e.g., amorphous oxides) is pH dependent (Della
Puppa et al. 2013; Ettler et al. 2015). The immobilization of trace metals by these
minerals is more favorable in acidic conditions, i.e., below pH 6. However, it is
interesting to note that adding exogenous Mn oxide in soils either has no effect on
microbial functioning or increases the activity of soil microorganisms, partly due to
the increase of dissolved organic carbon due to dissolution of soil organic matted
after Mn oxide addition (McCann et al. 2015; Michalkova et al. 2014).
The efficiency of Mn oxides on Zn and Cd is still under debate: it is generally
admitted that Cd and Zn have a lower sorption capacity than Cu and Pb on Mn
oxides (Della Puppa et al. 2013), and that remediation with Mn oxides does not
reduce significantly the mobility of Cd (Ettler et al. 2015; Wang et al. 2012).
However, Michalkova et al. (2014) demonstrated that application of amorphous
Mn oxides to contaminated soils significantly decreases exchangeable metal fractions, with, respectively, 92%, 92%, and 93% decreases of Cd, Cu, and Pb soluble
416
S. Grangeon et al.
10–20 min (Johnson and Pilson 1975).
7.4.2 Use of Mn Oxides as Sorbent Agents for Trace Metals
and Metalloids
A major remediation potential of Mn oxides involves their sorption capacities, as
discussed and reviewed in Sect. 7.2. Such properties are generally considered for the
immobilization of metals and metalloids: As, Sb, Se, Pb, Cu, sometimes after an
oxidation step (e.g., As(III)—see Sect. 7.4.1).
7.4.2.1 Efficiency
The Mn oxides are particularly efficient (i.e., more efficient than Fe oxides) for Pb
sorption (Kumpiene et al. 2008; Michalkova et al. 2014; O’Reilly and Hochella Jr
2003; Wang et al. 2012). This particularity is due to the presence of internal reactive
sites in the structure of some Mn oxides. Layer structures such as birnessite have the
highest Pb sorption efficiency, followed by tunnel structure such as cryptomelane
(O’Reilly and Hochella Jr 2003). The sorption efficiency of birnessite specifically on
Pb rather than other trace metals could be explained by the fact that Pb
2+ occupies
both interlayer and surface edge sites, whereas Cu
2+ , Zn
2+ , and Cd
2+ occupy mostly
interlayer sites (Wang et al. 2012).
The pH at the point of zero charge (pH PZC ) of several types of Mn oxides such as
birnessite, ramsdellite, or cryptomelane has been reported to be <4.7, with values
below three for birnessite (Liu et al. 2009; Tripathy and Kanungo 2005). Thus, Mn
oxides are responsible for the uptake of cations in a wide range of pH.
Nevertheless, soil remediation of metals by Mn oxides needs specific care since
the stability of some Mn oxides (e.g., amorphous oxides) is pH dependent (Della
Puppa et al. 2013; Ettler et al. 2015). The immobilization of trace metals by these
minerals is more favorable in acidic conditions, i.e., below pH 6. However, it is
interesting to note that adding exogenous Mn oxide in soils either has no effect on
microbial functioning or increases the activity of soil microorganisms, partly due to
the increase of dissolved organic carbon due to dissolution of soil organic matted
after Mn oxide addition (McCann et al. 2015; Michalkova et al. 2014).
The efficiency of Mn oxides on Zn and Cd is still under debate: it is generally
admitted that Cd and Zn have a lower sorption capacity than Cu and Pb on Mn
oxides (Della Puppa et al. 2013), and that remediation with Mn oxides does not
reduce significantly the mobility of Cd (Ettler et al. 2015; Wang et al. 2012).
However, Michalkova et al. (2014) demonstrated that application of amorphous
Mn oxides to contaminated soils significantly decreases exchangeable metal fractions, with, respectively, 92%, 92%, and 93% decreases of Cd, Cu, and Pb soluble
416
S. Grangeon et al.