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 in the environment are directly affected by reduction and oxidation reactions. For example, Cr is insoluble (immobile) under reducing (anaerobic) conditions. In con- trast, Fe and Mn are insoluble under oxidizing (aerobic) conditions but are quite soluble (mobile) under anaerobic conditions. Environmental mobility of other potentially hazardous metals, such as Cd, Ni, and Zn, is indirectly related to redox conditions because these metals form ionic complexes and solid precipitates with redox-sensitive elements. Redox conditions regulate many of the biogeochemical reactions in the soil system. However, in order to achieve these conditions a number of factors must be simulta- neously fulfi lled in soil system (Trolard and Bourrie 2008 ) : – excess of water; – restriction of the oxygen sources;

Table 11.1 Redox-sensitive Elements Redox state elements potentially present Arsenic (As) III, V as contaminants in the environment (Essington 2004 ) Nitrogen (N) −III, 0, III, V Carbon (C) −IV to IV Molybdenum (Mo) III, IV, V, VI Chromium (Cr) III, VI Selenium (Se) −II, 0, IV, VI Copper (Cu) I, II Sulfur (S) −II to VI Iron (Fe) II, III Vanadium (V) III, IV, V Manganese (Mn) II, III, IV Antimony (Sb) III, V 11 Fe–Mn Concretions and Nodules to Sequester Heavy Metals in Soils 447

Fig. 11.2 Transformations of the redox sensitive elements under aerobic and anaerobic soil conditions

– presence of bioavailable substrates as electron donors; – temperature conditions favorable to microfl ora activity; – presence of elements with changeable oxidation state as electron acceptors Electron donors in soils are: (a) organic matter and organic compounds and (b) reduced forms of inorganic compounds (Fig. 11.2 ). Electron acceptors are − 3+ 4+ oxidized forms of inorganic compounds such as O2 , NO 3 , Fe , Mn (Fig. 11.2 ). Anaerobic environments such as wetland soils are usually limited by electron accep- O tors especially 2 and have an abundant supply of electron donors. Once oxygen is consumed, alternative electron acceptors are used with the follow descending − 4+ 3+ 2− sequential order: NO3 , Mn , Fe , SO 4 and CO2 (Vepraskas 2001 ) . Redox reac- tions in soils are mainly controlled by microbial activity and the presence of a supply of carbon for the microbes; during respiration, these organisms use organic sub- stances as electron donors (Fiedler et al. 2007 ) . There is a wealth of literature on specifi c research topics, as well as a comprehensive review specifi cally directed to the fi eld of organic matter dynamics in anaerobic soils like paddy soils (Kögel- Knabner et al. 2010 ) . The soil system is in a steady struggle between oxidation, driven by oxygen in the atmosphere and its diffusion in soil pores and water fi lms, and reduction, driven by organisms and organic matter availability. When a soil environment is converted form aerobic to anaerobic drastic changes occur. Prolonged anaerobic conditions change biogeochemical processes in the soil. The solubility of some compounds increase, nutrients can be leached out and toxic compounds may be formed. Both pH and redox potential have long been considered as critical parameters controlling the fate of pollutants in the environment, especially affecting the pollutants reactions on the soil–water interface (Davranche and Bollinger 2000 ) . 448 D. Gasparatos

Redox conditions of soil govern metals chemistry. Many important redox sensitive metals such as As Cr and Se undergo redox transformation and some metals such as Pb, Cd and Zn are affected indirectly form dissolution of Fe-Mn oxides. Redox processes can play a role in soil remediation by either removing inorganic contaminants from soil solution or immobilizing them in the solid phase (fi xation) or enhancing mobility in the soil profi le so that the contaminants can be removed from the system. Thus the redox process may directly or indirectly lead to soil reme- diation via: (a) changes in speciation to a lower toxicity (b) Solubility decrease to immobilize contaminants or solubility increase to leach out contaminants and (c) adsorption impacts on contaminant mobility. Redox processes are also responsible for Fe and Mn segregation in the form of Fe–Mn oxide coatings or Fe-Mn concretions-nodules. Among natural particles, Fe and Mn oxides have long been recognized as playing an important role in control- ling the cycling of nutrients and trace elements especially in seasonally saturated soil containing naturally high concentrations of trace metals (Chen et al. 2006 ) . Several examples from the literature will confi rm that many studies has been dedicated to the development of the quantitative understanding of contaminant fate in fully aerobic soils (Alloway 1995 ) or permanently reducing subsurface environ- ments (Reddy and Delaune 2008 ) . Far less research has addressed the biogeochemi- cal functioning of environments characterized by fl uctuating redox conditions which lead to the formation of Fe-Mn concretions and nodules (Clausnitzer et al. 2003 ; Thompson et al. 2006 ; Gasparatos 2007 ) . An understanding of soil redox processes is crucial for predicting and protecting environmental health and can provide new opportunities for engineered remediation strategies.

11.3 Genesis and Properties of Pedogenic Fe-Mn Concretions and Nodules

11.3.1 Formation Process and Environmental Conditions

Since their discovery in marine sediments during the scientifi c expeditions of the H.M.S. Challenger, iron – manganese concretions and nodules have been studied in a wide range of natural geochemical systems. Fe – Mn concretions and nodules have been observed in oceans (Koschinsky and Halbach 1995 ; Banerjee et al. 1999 ) , lakes (Schwertmann et al. 1987 ; Belzile et al. 2001 ) , rivers (Halbach 1976 ) and soils (Palumbo et al. 2001 ; Cornu et al. 2005 ) . They are relatively common in soils through- out the world and their presence became known in the late of 1930s with the classic work of Wheeting (1936 ) , Winters ( 1938 ) and Drosdoff and Nikiforoff (1940 ) . Soil Fe-Mn concretions and nodules are discrete bodies formed in the soil system under alternating oxidizing and reducing conditions. These fi rm to extremely fi rm subrounded morphological features are formed by the processes of reduction, trans- location, and oxidation of Fe and Mn (Zhang and Karathanasis 1997 ; Zaidelman 11 Fe–Mn Concretions and Nodules to Sequester Heavy Metals in Soils 449 and Nikiforova 1997 ; Vepraskas 1999, 2001 ; Gasparatos et al. 2005b ; Chen et al. 2006 ; Zaidelman et al. 2009 ) . During wet periods, Fe(III) and Mn(III/IV) are reduced and dispersed throughout the soil matrix, while during drying periods when the soil environment becomes more oxidized and oxygen levels gradually increase, they reprecipitate lining or fi lling matrix pores. The concretions and nodules always have inclusions of the soil matrix and contain soil materials such as skeletal grains, clay minerals and pores cemented together under the infl uence of Fe and Mn oxides. Therefore Fe-Mn concretions and nodules are characterized by a greater concentration of Fe and Mn oxides than the surrounding soil matrix (Childs 1975 ; Sidhu et al. 1977 ; Ram et al. 2001 ; Gasparatos et al. 2004a ; Aide 2005 ) . Different terms are often used in the literature to describe them as glaebules, septaria, gravels, ferricrete (Brewer 1964 ; Singh and Gilkes 1996 ; Matchavariani 2005 ) , but in recent years the terms concretions and nodules are longer accepted (King et al. 1990 ; White and Dixon 1996 ; Kanev and Kazakov 1999 ; Liu et al. 2002 ; D’Amore et al. 2004 ; Aide 2005 ) . As noted by Vepraskas (1999, 2001 ) these terms have been used interchangeably. However recent studies have shown that as opposed to nodules, concretions have a distinct internal structure with well -expressed concentric rings around a point or plane, and, thus these two redoximorphic features refl ect different pedogenetic specifi cs which can describe the course of soil formation (Gasparatos 2007 ; Hickey et al. 2008 ) . Soil Fe-Mn concretions and nodules have been found to be widespread in soils with some internal drainage restrictions (Vidhana Arachchi et al. 2004 ; Zhang and Karathanasis 1997 ) and have been studied in different soil types (Cornu et al. 2005 ; Liu et al. 2002 ; Pai et al. 2003a, b ; Palumbo et al. 2001 ; Latrille et al. 2001 ; Sanz et al. 1996 ) . Soil Fe- Mn concretions and nodules formed gradually in the long-term soil pedo- genetic processes and they refl ect the specifi c features of the current soil formation. Their shape, structure and elemental composition were the products of soil – forming and environmental conditions. Therefore the elemental composition and distribution characteristics within Fe-Mn concretions and nodules may refl ect their forming redox history of the pedoenvironment. However, the effect of concretion accumulations on soil chemical properties may be signifi cant at high concentrations, depending on the chemistry and mineralogy of their oxide components (Gasparatos et al. 2005b ) .

11.3.2 Morphological Properties

Soil Fe- Mn concretions and nodules are morphological characteristics with signifi cant heterogeneity in relation to the surrounding soil material and can easily be isolated from it and even seen with the naked eye. There is wide variety in shape, colour and size depending on the soil properties and the conditions under which they formed. Soil Fe-Mn concretions and nodules can occur in several forms, including spherical (Phillippe et al. 1972 ; Palumbo et al. 2001 ; Gasparatos et al. 2005b ) , oval (Latrille et al. 2001 ) , subangular (Childs and Leslie 1977 ) , tubular (Gaiffe and Kubler 1992 ) and 450 D. Gasparatos irregularly shaped (Ojanuga and Lee 1973 ; White and Dixon 1996 ) with size ranging from a few millimetres (0.25 mm) up to some centimetres (4 cm). Several researchers are studying the size distribution of concretions and nodules in sand size fractions from 0.5 to 2 mm (Rhoton et al. 1991, 1993 ) and in gravel size fractions (>2 mm) (Zhang and Karathanasis 1997 ; Gasparatos et al. 2004a ) . Their colour also varies considerably, with black (black, dark gray) and brown (brown, rusty) colour domi- nating the majority of studies. Rhoton et al. ( 1993 ) found in Glossic Fragiudlafs, Fe-Mn nodules with dominant brown hue 7.5 YR. Liu et al. ( 2002 ) observed Fe-Mn nodules of reddish brown colour (2.5 YR 5/4) in an Orthic Agrudalf and Pai et al. ( 2003b ) found Fe nodules in a colour range from reddish yellow to reddish brown in a Typic Paleudult. Manganese is the main factor affecting the colour of concre- tions and nodules because of the dark colour of Mn oxides (Rabenhorst and Parikh 2000 ) . Generally the darker concretions and nodules appear to have higher Mn content than the red, yellow, orange and/or brown hues and high chromas which indicate dominance of Fe oxides (Phillippe et al. 1972 ; Sanz et al. 1996 ; Zhang and Karathanasis 1997 ; Ram et al. 2001 ) . The morphology of the Fe-Mn concretions and nodules not only varies between soils but also between the horizons of the same soil profi le. Phillippe et al. (1972 ) found that at the surface soil horizons in a hydrosequence spherical Fe-Mn concre- tions prevailed whose shape became more irregular with increasing depth. Schwertmann and Fanning ( 1976 ) studying two hydrosequences in western Germany found that in soils with better drainage, Fe-Mn concretions exhibited an irregular shape, with moderate hardness, brown (rusty) coatings around a black core, while in soils with impermeable horizons, black spherical concretions with high hardness dominated in surface horizons. In Glossic Fragiudalfs, shape and size of Fe nodules is infl uenced by the position of the fragipan horizon in the soil profi le. The size of the nodules was larger and their shape changes gradually from sub-spherical to sub- angular within and just above fragipan (Lindbo et al. 2000 ) . Gasparatos et al. (2004a, 2006 ) and Gasparatos (2007 ) studied Fe-Mn concretions and nodules from Alfi sols under the stereolight microscope. Fe-Mn concretions were somewhat spherical in shape and have a 10 YR 4/6 surface coating, encasing a very dark gray (N 3/0) core (Fig. 11.3a ) while Fe-Mn nodules show darker colours (Fig. 11.3b ). Research on the role of Fe-Mn concretions and nodules in adsorption of metals has shown the need for the expansion of knowledge on the morphology and fabric characteristics of these soil constituents (Gasparatos et al. 2006 ) . A usually optical microscope observation shows that the concretions and nodules contain grains of primary minerals cemented with an ochreous – brown or dark matrix which consists by Fe – Mn oxides and clay minerals (Fig. 11.4 ). Optical microscope observations showed that the Fe-Mn concretions have a differentiated fabric and more specifi cally a concentric internal structure in which the constituents are arranged in zones or bands around a nucleus, often a primary mineral grain or a void (Fig. 11.5 ) (Latrille et al. 2001 ; Gasparatos et al. 2006 ) . However, the degree of expression (number and thickness) of these concentric rings in individual concretions is quite variable. On the contrary Fe – Mn nodules lack well – developed bands and no visible zoning was observed by optical microscope (Fig. 11.6 ). 11 Fe–Mn Concretions and Nodules to Sequester Heavy Metals in Soils 451

Fig. 11.3 Spherical Fe–Mn concretions (a ) and nodules (b ) sample from Greek Alfi sols (Gasparatos 2007 )

Over the last 30 years the use of scanning electron microscopy (SEM) for micromorphological study of soils has become an important technique to assess the size, morphology, structure of soil minerals (primary and clay minerals) and their interaction with the soil solution (Sposito and Reginato 1992 ) . 452 D. Gasparatos

Fig. 11.4 Thin section of Fe–Mn concretions and nodules viewed by optical microscopy. Their internal structure displays abundant primary mineral grains (Gasparatos 2007 )

Fig. 11.5 Photomicrograph showing Fe-Mn concretions from Greek Alfi sols characterized by a differentiated fabric (Gasparatos et al. 2006 )

Analysis of Fe-Mn concretions and nodules using electron microscopy was originally based on the study of their morphology, their components at high magni- fi cations as well as the qualitative elemental analysis (Cescas et al. 1970 ; Pawluk and Dumanski 1973 ) . Most recent studies includes the identifi cation of specifi c 11 Fe–Mn Concretions and Nodules to Sequester Heavy Metals in Soils 453

Fig. 11.6 Photomicrograph showing Fe-Mn nodules from Greek Alfi sols characterized by homogenous fabric (Gasparatos 2007 )

minerals, quantitative elemental analysis and specifi cation of the structure of Fe-Mn concretions and nodules (White and Dixon 1996 ; Palumbo et al. 2001 ; Liu et al. 2002 ; Cornu et al. 2005 ; Gasparatos et al. 2005b ; Gasparatos 2007 ) . SEM examination shows that Fe-Mn concretions exhibited a differentiated structure by well-expressed bands whereas Fe-Mn nodules a homogeneous fabric without any specifi c pattern (Palumbo et al. 2001 ; Liu et al. 2002 ) . Recently Gasparatos et al. (2005b ) showed that Fe–Mn concretions have a distinctive concentric structure of alternating Fe- and Mn-rich zones (Fig. 11.7 ) while Fe-Mn nodules are characterized by homogeneous distribution of elements (Fig. 11.8 ). The concentric internal structure of the Fe-Mn concretions indicates a mode of formation in waves as the result of alternating wet and dry periods (Zhang and Karathanasis 1997 ; Gasparatos et al. 2005b ) . Soil redox changes signifi cantly infl uence the geochemical behavior of Fe and Mn compounds which are reduced during wet periods and dis- persed in pore waters, while they reprecipitate during dry periods, lining or fi lling soil pores. Contrasting Fe and Mn concentrations in concretions are attributed to the higher oxidation potential of Mn because of variations in the air movement into the soil pores imposing specifi c oxidation – reduction conditions (Huang et al. 2008 ; Aide 2005 ) . The repetition of these cycles leads to the development of an onion like internal structure of Fe-Mn concretions suggestive of seasonal growth (Manceau et al. 2003 ) . Each ring most likely represents the precipitation of soluble soil con- stituents due to suitable local chemical conditions and a phase in the development of the accretionary material. 454 D. Gasparatos

Fig. 11.7 Representative SEM photomicrograph image showing the internal fabric of a Fe-Mn concretion sample and X-ray mapping of Fe, Si, Ti, Mn, Al and Mg (Gasparatos et al. 2005b ) 11 Fe–Mn Concretions and Nodules to Sequester Heavy Metals in Soils 455

Fig. 11.8 Representative SEM photomicrograph image showing the internal fabric of a Fe-Mn nodule sample and X-ray mapping of Si, Al, Mn, Fe, Ca and Na (Gasparatos 2007 ) 456 D. Gasparatos

Table 11.2 Literature review of the mineralogical composition of soil Fe – Mn concretions and nodules Secondary minerals Primary minerals Clay minerals Iron oxides Manganese oxides Gasparatos ( 2007 ) Quartz, albite Illite, kaolinite, Goethite, Vernadite smectite ferrihydrite Aide (2005 ) Quartz – Goethite, – ferrihydrite Cornu et al. (2005 ) Quartz, feldspars, Kaolinite Goethite, – micas ferrihydrite Vidhana Arachchi – Vermiculite, Goethite Lithiophorite, et al. ( 2004 ) illite, birnessite kaolinite Gasparatos et al. Quartz, feldspars Illite Goethite, – (2004a ) ferrihydrite Liu et al. (2002 ) Quartz Illite, kaolinite Goethite, Lithiophorite, ferrihydrite vernadite Ram et al. (2001 ) Quartz, feldspars, Kaolinite Goethite, M anganite micas ferrihydrite, lepidocrocite Palumbo et al. (2001 ) Quartz Kaolinite – – Zhang and Quartz, micas Kaolinite Goethite – Karathanasis (1997 ) Sanz et al. (1996 ) Quartz, feldspars, Chlorite Goethite Birnessite, micas, calcite vernadite White and Dixon Quartz, micas Smectite, – – ( 1996 ) kaolinite Singh and Gilkes Quartz Kaolinite Goethite, hematite, (1996 ) maghemite Rhoton et al. (1993 ) Quartz, feldspars Vermiculite, Goethite – illite, kaolinite Gaiffe and Kubler Quartz, musco- Kaolinite Goethite, hematite, – (1992 ) vite, feldspars maghemite Sidhu et al. (1977 ) Quartz, feldspars Illite – – Childs ( 1975 ) Quartz, feldspars – – –

11.3.3 Mineralogical Composition

The mineralogical composition of Fe-Mn concretions and nodules is largely determined by the soil environment in which they are formed and the properties of their Fe – Mn oxides. Table 11.2 presents a literature review of the mineralogical composition of Fe-Mn concretions and nodules from various research papers published over the last 30 years. The majority of studies have shown that the primary minerals of the Fe-Mn con- cretions and nodules were quartz, feldspars and micas. The mineralogical similarity 11 Fe–Mn Concretions and Nodules to Sequester Heavy Metals in Soils 457 between the Fe-Mn concretions and nodules and the surrounding soil matrix indicates their pedogenetic origin and their in situ formation due to cementation of soil materials by Fe and Mn oxides (Manceau et al. 2003 ; Gasparatos 2007 ) . The nature of Fe and Mn oxides in soil concretions and nodules is of great interest from the viewpoints of both pedogenesis and environmental chemistry. The iron and manganese oxides in soil concretions have been reported to appear as x-ray amorphous or very poorly crystalline (Childs 1975 ) . In recent studies the main components of concretions where shown to be ferrihydrite and goethite or hematite with variable amounts of Al as substitutions (Liu et al. 2002 ; Cornu et al. 2005 ) . Gasparatos et al. (2004a ) concluded that the Fe-Mn concretions from Greek Alfi sols are only enriched in thermodynamically unstable Fe oxides. The associa- tion of the poorly crystalline goethite and ferrihydrite in the Fe-rich concretions of their study refl ect an environment containing Fe2+ , oxidized in the presence of factors that inhibit or retard the transformation of the poorly crystalline oxides to more stable forms. Mn oxides were found to be fi ne-grained with relatively diffuse XRD peaks (Rhoton et al. 1993 ; Zhang and Karathanasis 1997 ; Cornu et al. 2005 ) . Because of their low degree of crystallinity it is diffi cult to distinguish Mn oxides in soil Fe-Mn concretions and nodules. However efforts combining x-ray diffraction techniques and selective dissolution procedures have been successful in identifying and characterizing Mn minerals like lithiophorite and vernadite (Liu et al. 2002 ; Tokashiki et al. 1986, 2003 ; Vidhana Arachchi et al. 2004 ) .

11.3.4 Geochemistry

The study of the geochemical composition of Fe-Mn concretions and nodules origi- nally started with samples mainly from marine sediments (Li 1982 ) . The researchers found that the Fe-Mn nodules from the oceans contained signifi cant quantities of Ni, Cu and Co of economic value (Chauhan et al. 1994 ; Dutta et al. 2001 ) . The geochemical study of soil Fe-Mn concretions and nodules began in the mid 1970s (Childs 1975 ) and was expanded during the last decade (Ram et al. 2001 ; Cornu et al. 2005 ) . Table 11.3 presents data of enrichment factor (EF) for each element which calcu- lated as “element concentration in concretion-nodule/element concentration in surrounding soil” (Dawson et al. 1985 ; Gasparatos et al. 2004b ) . The EF data show that the degree of enrichment varies from element to element, with lower values of Si, Al concentrations in the Fe-Mn concretions and nodules than the soil matrix (EF < 1). On the contrary, concretions and nodules are enriched 30–60 times in Mn with respect to the host soil. They are moderately enriched in Fe, whereas they are in most cases depleted in major alkaline earth metals (Ca and Mg). According to the data in Tables 11.4 and 11.5 , Fe-Mn concretions and nodules are composed mainly of Si, Al, Fe and Mn. Liu et al. (2002 ) showed that Si, Al, Fe, Mn, Ca, K and Ti were the main elements presents in Fe-Mn concretions and nodules isolated from a Chinese Alfi sol. 458 D. Gasparatos

Table 11.3 A literature review of the enrichment factor (EF) for various elements in Fe-Mn concretions and nodules

EFSi EFAl EFFe EF Mn EF Ca EFMg EF K EFNa Tan et al. (2006 ) 0.70 0.78 2.11 57.8 2.29 0.77 0.66 1.49 Palumbo et al. (2001 ) 0.95 2.34 30.7 0.14 0.56 0.78 0.47 Zaidelman and Nikiforova (1998 ) 0.80 0.80 5.9 30.0 1.1 0.70 – – Childs (1975 ) 0.72 0.83 3.5 25.7 0.71 – 0.89 –

Table 11.4 Major (%) and trace element (ppm) composition of Fe- Mn concretions and nodules of different sizes from Greek Alfi sols (Gasparatos 2007 ) Fe-Mn concretions Fe-Mn nodules 4.76–2.00 mm 2.00–1.00 mm 4.76–2.00 mm 2.00–1.00 mm Total concentrations (%)

SiO2 61.90 57.85 56.63 54.80

Al2 O 3 10.50 10.45 9.88 11.22

Fe2 O 3 12.30 16.55 10.15 10.30 MnO 1.82 0.70 5.17 5.05 CaO 0.57 0.58 0.60 0.70 MgO 0.95 1.00 1.06 1.30

K2 O 1.70 1.57 1.80 1.70

Na2 O 2.30 2.55 2.30 2.30 Total concentrations (ppm) Ba 695–6,790 120–1,586 1,835–11,670 995–8,092 Co 191–622 115–226 786–1,198 595–1,280 Pb 302–395 350–640 375–735 450–943 Ni 201–592 186–332 506–1,874 515–3,360 Cr 155–351 337–529 144–230 188–302 Cu 35–48 35–67 41–96 54–97 Zn 80–244 87–109 80–161 84–526

Many studies have shown the general enrichment of Fe – Mn concretions and nodules in trace elements with respect to the surrounding soil matrix (Childs 1975 ; Sidhu et al. 1977 ; Dawson et al. 1985 ; Gasparatos et al. 2004b ) . For example, high enrichment factors were observed, in nodules from Sicilian soils for Mn (296), Co (93), Ce (45), Pb (31), Ba (18), Ni (17), Cd (15) and Fe (2.6) (Palumbo et al. 2001 ) . Figure 11.9 shows average enrichment factors of Ba, Co, Ni, Pb, Cr, Cu and Zn in the Fe-Mn concretions and nodules of different sizes from Greek soils (Gasparatos 2007 ) . The EF values vary from element to element and have a great range for elements such as Ba and Co. Childs and Leslie (1977 ) found that in each case, the Fe-Mn concretions from soils in New Zealand had high concentrations of Fe, Mn, Ti, Co, S, P, Mo, Cu, V in relation to the surrounding soil mass. Gasparatos et al. (2004b ) show that the Fe-Mn concretions absorbed signifi cant amounts of metals and especially Pb and Cd from the soil system. According to the enrichment factors, the affi nity of metals for the concretions due to the charged 11 Fe–Mn Concretions and Nodules to Sequester Heavy Metals in Soils 459

Table 11.5 Major (%) and Enrichment trace element (ppm) Element Soil Nodules factor composition of Fe- Mn (%) nodules from a lateritic SiO 31.94 14.67 0.46 subsoil (Neaman et al. 2004 ) 2 Al2 O3 27.98 12.55 0.45

Fe2 O3 18.36 41.88 2.28 MnO 0.91 13.00 14.29 MgO 0.20 0.22 1.10 CaO <0.01 <0.01 –

Na 2 O <0.01 <0.01 –

K2 O 0.17 0.32 1.88

TiO2 2.59 1.11 0.43

P2 O5 0.14 0.32 2.29 (ppm) As 288 1,252 4.3 Ba 176 2,435 13.8 Cd 0.3 2.8 9.3 Co 24.3 216 8.9 Cr 296 2,771 9.4 Cu 57.5 333 5.8 Mo 22.6 130 5.8 Ni 60.6 419 6.9 Pb 32.9 357 10.9 Zn 103 273 2.7

Fig. 11.9 Average enrichment factors of elements in the Fe-Mn concretions and nodules of different sizes from Greek Alfi sols (Gasparatos 2007 ) surfaces of Fe and Mn oxides, follow the order Pb > Cd > Mn > Co > Ni > Fe. McKenzie (1980 ) also found adsorption of Co, Mn, Ni and Pb at the same order on nine synthetic Mn oxides. In Fe-Mn nodules form nine main soils in China, Pb, Cd, Ba and Co had high accumulation, Ni moderate accumulation and Cu, Zn accumulated to a minor degree (Tan et al. 2006 ) . http://www.springer.com/series/11480