Chapter 11 Fe–Mn Concretions and Nodules to Sequester Heavy Metals in Soils Dionisios Gasparatos Contents 11.1 Introduction ..................................................................................................................... 444 11.2 Redox Process and Environmental Issues ....................................................................... 446 11.3 Genesis and Properties of Pedogenic Fe-Mn Concretions and Nodules ......................... 448 11.3.1 Formation Process and Environmental Conditions ........................................... 448 11.3.2 Morphological Properties .................................................................................. 449 11.3.3 Mineralogical Composition ............................................................................... 456 11.3.4 Geochemistry .................................................................................................... 457 11.4 Role of Pedogenic Fe-Mn Concretions and Nodules in the Environmental Geochemistry of the Soil ................................................................................................ 460 11.4.1 Iron .................................................................................................................... 460 11.4.2 Manganese......................................................................................................... 461 11.4.3 Copper ............................................................................................................... 462 11.4.4 Zinc ................................................................................................................... 463 11.4.5 Cobalt ................................................................................................................ 463 11.4.6 Nickel ................................................................................................................ 464 11.4.7 Lead ................................................................................................................... 464 11.4.8 Chromium ......................................................................................................... 465 11.4.9 Arsenic .............................................................................................................. 466 11.5 Application of Pedogenic Fe-Mn Concretions and Nodules to Remediating Metal Contaminated Soils ..................................................................... 467 11.6 Conclusions ..................................................................................................................... 468 References .................................................................................................................................. 469 D. Gasparatos ( *) Laboratory of Soils and Agricultural Chemistry , Agricultural University of Athens , Iera Odos 75 , Athens , 11855 , Greece e-mail: [email protected] E. Lichtfouse et al. (eds.), Environmental Chemistry for a Sustainable World: 443 Volume 2: Remediation of Air and Water Pollution , DOI 10.1007/978-94-007-2439-6_11, © Springer Science+Business Media B.V. 2012 444 D. Gasparatos Abstract Over the last two decades, considerable attention has been paid to the management of metal-contaminated soils. Fe-Mn concretions and nodules can be used to sequester metals by adsorption. Fe-Mn concretions and nodules are discrete bodies with variable compositions formed in the soil system under alternating oxidizing and reducing conditions. This chapter highlights the high adsorption capacity of soil Fe-Mn concretions and nodules for many metal contaminants. The geochemical association of various metals with either Mn or Fe rich phase in Fe-Mn concretions and nodules are a primary environmental procedure that controls the dynamics of these contaminants in the soil system. The formation of Fe-Mn concre- tions and nodules is the most effi cient and durable process for metal contaminants sequestration in the soils. Since the formation of soil concretions has a potentially benefi cial effect on metals availability, the application of these environmental materials as geochemical reactors to improve the effi ciency of in situ technologies for remediating metal contaminated soils is strongly recommended. Keywords Soil • Contamination • Redox process • Fe – Mn oxides • Heavy metals • Remediation technologies • Fe-Mn concretions and nodules • High sorption capacity • Arsenic • Toxic metal sequestration • Environmental geochemistry • Lead • Chromium 11.1 Introduction In terrestrial ecosystems the soil is of central signifi cance because as a very important “ecological crossroad” it is the place where many kinds of interactions take place between solids, liquids, gases and the biota (Fig. 11.1 ). Soil, in an environmental context, is not only a sink to dispose off undesirable materials, but also a transmitter of many contaminant chemicals as metals to surface-ground water, atmosphere and living organisms (Kabata-Pendias 2001 ; Gasparatos et al. 2005a ) . Therefore the metal contaminants content of soil governs the composition of these elements in plants and animals. As a consequence of industrialization during the last centuries, the contamina- tion of soils with toxic metals has become a major environmental concern in many parts of the world. These metals are considered as hazardous pollutants with a long residence time in soils due to their toxicity and lack of biodegradability (Alloway 1995 ; Adriano 2001 ) . Toxic metals may be retained by soil components through a number of processes such as electrostatic adsorption, formation of inner-sphere sorption complexes or multinuclear surface complexes, and precipitation of new mineral phases. In soil, Fe and Mn oxides, oxyhydroxides and hydroxides (for the sake of brevity all are called oxides) constitute only a small fraction of the total solid phase but with their high sorption capacity often control the location, mobility and bioavailability of metal contaminants (McKenzie 1980 ; Contin et al. 2007 ; Manceau et al. 2007 ) . Because of their high surface area and high surface-charge density, the Fe and Mn compounds 11 Fe–Mn Concretions and Nodules to Sequester Heavy Metals in Soils 445 Fig. 11.1 Schematic view of the soil as an “ecological crossroad” – it is the place where many kinds of Atmosphere interactions take place between solids (Lithosphere), liquids (Hydrosphere), gases (Atmosphere) and the biota (Biosphere) (Adapted from Lin et al. 2005 ) BiospherePedosphere Hydrosphere (Soils) Lithosphere are useful for retarding transport of inorganic contaminants in groundwater systems (Stipp et al. 2002 ) and to some extent for purifying the soil fi nes from heavy metals (Lombi et al. 2002, 2004 ) . Since Fe and Mn oxides are able to bind metals, the use of Fe- Mn rich materials could be appropriate to treat soils contaminated with toxic metals (McKenzie 1980 ; Mench et al. 1994 ; Puschenreiter et al. 2005 ) . Natural Fe and Mn compounds in soils may display several features with a wide variety of sizes and shapes such as nodules, concretions, coatings, laths, spindles etc. (Latrille et al. 2001 ; Manceau et al. 2007 ) . Among them, a special place is occu- pied by the group of Fe-Mn concretions and nodules due to the ability of their Fe and Mn oxides to concentrate and control the distribution and mobility of metals in soils (Childs 1975 ; Suarez and Langmuir 1976 ; Zaidelman and Nikiforova 1998 ) . A number of investigations have focused on soil Fe-Mn concretions and nodules (Dawson et al. 1985 ; Palumbo et al. 2001 ; Liu et al. 2002 ) . Furthermore, several studies have shown the high adsorption capacity of soil Fe-Mn concretions and nodules for many toxic metal pollutants and in some cases they are considered the primary environmental material that controls metal dynamics in the soil system (Manceau et al. 2003 ; Gasparatos et al. 2005b ; Gasparatos 2007 ) . This review was compiled in an effort to assess the general extent of scientifi c knowledge regarding the properties of Fe-Mn concretions and nodules and their role in the metals sequestration. A literature research was conducted in order to identify (a) the ability of Fe-Mn concretions and nodules on metals immobilization and (b) potentially viable in situ remediation technologies using the Fe – Mn oxides (main components of concretions and nodules) for soils where metals are the principal contaminants of concern. 446 D. Gasparatos Over 100 papers were reviewed and synthesized to summarize the geochemical role of Fe – Mn concretions and nodules to control metals dynamics in the soil system. 11.2 Redox Process and Environmental Issues Redox-related environmental issues have increased in importance in the last decades. The importance of the redox potential, as a main biogeochemical variable, in con- trolling the speciation and toxicity of a wide variety of elements have been recently reviewed (Borch et al. 2010 ) . Redox processes are chemical reactions that include a transfer of electrons and consequently a change in valence state of elements that are either oxidized to a higher valence state or reduced to a lower valence state. Oxidation – reduction reactions in soils affect the biogeochemical cycles of many major and trace elements. Many elements can exist in nature in more than one valence or oxidation state. Elements that occur in more than one valence state in natural environments and may be present as contaminants are listed in Table 11.1 . The chemical speciation, bioavailability, toxicity, and mobility of these elements