Deep-Sea Research I 54 (2007) 85–98 Geochemistry of lithium in marine ferromanganese oxide deposits Xuejun Jiang a,b, , Xuehui Lin b , De Yao c , Shikui Zhai a , Weidong Guo d a College of Geoscience, Ocean University of China, 266071 Qingdao, China b Qingdao Institute of Marine Geology, 266071 Qingdao, China c Shandong University of Technology, 255049 Zibo, China d Department of Oceanography, Xiamen University, 361005 Xiamen, China Received 11 December 2005; received in revised form 15 September 2006; accepted 5 October 2006 Abstract We have measured lithium content of marine ferromanganese oxide deposits of different origins and conducted a sequence of selective dissolution experiments on them. There is more lithium in diagenetic and transitional marine ferromanganese nodules than in hydrogenic ferromanganese crusts. Lithium in diagenetic and transitional nodules is in the 10 A ˚ -manganate phase rather than in the lithiophorite or other phases, as shown by the sequential selective dissolution results. The different contents of lithium in the different generic types of marine ferromanganese oxide deposits are attributed to the varying mineralogy. Ten A ˚ manganates, the main minerals in diagenetic and transitional marine ferromanganese nodules, can incorporate significant amounts of lithium because of their distinct structure and can be regarded as an important scavenger of lithium in the oceans. The diagenetic and transitional marine ferromanganese nodules may play a role in the mass balance of lithium in the oceans. On the other hand, it appears that lithium is present in hydrogenic marine ferromanganese crusts in an aluminosilicate phase rather than in other phases such as vernadite (d- MnO 2 ) or ferric oxide/hydroxide. Vernadite (d-MnO 2 ) and ferric oxide/hydroxide adsorb very small amounts of lithium in the oceans. r 2006 Elsevier Ltd. All rights reserved. Keywords: Lithium; Selective dissolution experiment; Diagenetic ferromanganese nodules; Hydrogenic ferromanganese crust; Existing phase 1. Introduction The lithium concentration of seawater has not varied significantly over the last 40 Ma (Delaney and Boyle, 1986), while rivers discharge a large quantity of lithium into the oceans (Stouffyn-Egli and Machenzie, 1984) and hydrothermal activity at ridge crests supplies a considerable amount of lithium to oceanic waters (Edmond et al., 1979). Lithium is regarded as a sensitive indicator of sediment–water interaction, and the significance of sediment diagenesis and adsorption as sinks of oceanic Li has been evaluated (Zhang et al., 1998). Stouffyn-Egli and Machenzie (1984) suggested that basalt–seawater reactions play an important role in ARTICLE IN PRESS www.elsevier.com/locate/dsr 0967-0637/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.dsr.2006.10.004 Corresponding author. Present address: Qingdao Institute of Marine Geology, China Geological Survey, Qingdao 266071, China. Tel.: +86 532 85755851; fax: +86 532 85773903. E-mail address: [email protected] (X. Jiang).
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0967-0637/$ - see
doi:10.1016/j.ds
�CorrespondiMarine Geolog
China. Tel.: +8
E-mail addre
Deep-Sea Research I 54 (2007) 85–98
www.elsevier.com/locate/dsr
Geochemistry of lithium in marine ferromanganeseoxide deposits
Xuejun Jianga,b,�, Xuehui Linb, De Yaoc, Shikui Zhaia, Weidong Guod
aCollege of Geoscience, Ocean University of China, 266071 Qingdao, ChinabQingdao Institute of Marine Geology, 266071 Qingdao, China
cShandong University of Technology, 255049 Zibo, ChinadDepartment of Oceanography, Xiamen University, 361005 Xiamen, China
Received 11 December 2005; received in revised form 15 September 2006; accepted 5 October 2006
Abstract
We have measured lithium content of marine ferromanganese oxide deposits of different origins and conducted a
sequence of selective dissolution experiments on them. There is more lithium in diagenetic and transitional marine
ferromanganese nodules than in hydrogenic ferromanganese crusts. Lithium in diagenetic and transitional nodules is in the
10 A-manganate phase rather than in the lithiophorite or other phases, as shown by the sequential selective dissolution
results. The different contents of lithium in the different generic types of marine ferromanganese oxide deposits are
attributed to the varying mineralogy. Ten A manganates, the main minerals in diagenetic and transitional marine
ferromanganese nodules, can incorporate significant amounts of lithium because of their distinct structure and can be
regarded as an important scavenger of lithium in the oceans. The diagenetic and transitional marine ferromanganese
nodules may play a role in the mass balance of lithium in the oceans. On the other hand, it appears that lithium is present
in hydrogenic marine ferromanganese crusts in an aluminosilicate phase rather than in other phases such as vernadite (d-MnO2) or ferric oxide/hydroxide. Vernadite (d-MnO2) and ferric oxide/hydroxide adsorb very small amounts of lithium in
quantity of lithium into the oceans (Stouffyn-Egliand Machenzie, 1984) and hydrothermal activity atridge crests supplies a considerable amount oflithium to oceanic waters (Edmond et al., 1979).Lithium is regarded as a sensitive indicator ofsediment–water interaction, and the significanceof sediment diagenesis and adsorption as sinks ofoceanic Li has been evaluated (Zhang et al., 1998).Stouffyn-Egli and Machenzie (1984) suggested thatbasalt–seawater reactions play an important role in
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the mass balance of dissolved Li in the oceans. Thealteration minerals of submarine basalts canincorporate lithium from seawater (Chan andEdmond, 1988). Many reports have assumed thatauthigenic clays such as smectite and phillipsite canremove lithium from seawater by isomorphic sub-stitution of Mg2+ and Li+ for Al3+ or of Li+ forMg2+ or Fe2+ in the octahedral positions of layersilicates (Huh et al., 1998; Stouffyn-Egli andMachenzie, 1984) to play an important role in themass balance of lithium (Pistiner and Henderson,2003; Chan et al., 1992; Zhang et al., 1998; Huh etal., 1998). One important type of authigenicstructure, marine ferromanganese oxide deposit,has been overlooked in the studies of the massbalance of lithium in the oceans. Also overlookedhas been the geochemistry of lithium in the oxidedeposits themselves.
Marine ferromanganese deposits can be groupedinto nodules and crusts according to their morphol-ogy. Although the marine manganese minerals havelow crystallinity, sub-micro size and intergrowthand are hydrous (Burns et al., 1983; Burns andBurns, 1977; Ostwald, 1984), the mineralogy is oneof the most important criteria used for determiningthe origin of marine ferromanganese deposits (Usuiet al., 1993). Many studies, therefore, classifymarine ferromanganese deposits into the diagenetic,hydrothermal and hydrogenic according to themineralogy (Halbach et al., 1988; Skornyakovaand Murdmaa, 1992; Jeong et al., 1994; Jung etal., 1998), the classification being based on threeprincipal minerals: diagenetic (buserite (10 A man-ganates)), hydrogenic (d-MnO2) and hydrothermal(todorokite) (Burns et al., 1983; Stouff and Boule-gue, 1988; Usui et al., 1989). The basal d-spacings ofdiagenetic 10 A manganates that are poor intransition metals other than Mn in the interlayerscontract from about 10 and 5 A to about 7 and3.5 A after drying at 110 1C, while the 10 Amanganates with sufficient amounts of interlayertransition metal cations remain structurally unal-tered (Mellin and Lei, 1993; Usui et al., 1989). Onthe other hand, the structure of todorokite dried at110 1C remains unaltered (Arrhenius and Tsai, 1981;Usui et al., 1989, 1997). Diagenetic nodules withabrasive and gritty surfaces enriched in Mn, Ni, Cuand 10 A manganates are generally embedded insurface sediments (Jeong et al., 1994; Aplin andCronan, 1985; Martin-Barajas et al., 1991; Kastenet al., 1998; Bonatti et al., 1972; Dymond et al.,1984; Halbach et al., 1982) and have a high ratio of
Mn/Fe(44 generally) ( Usui et al., 1993; Skornya-kova and Murdmaa, 1992). Hydrogenic nodulesand crusts, which are composed mostly of d-MnO2
and ferric hydroxide, are generally exposed on theseafloor to seawater containing abundant Fe andCo (Jeong et al., 1994; Martin-Barajas et al., 1991;Kasten et al., 1998), have a low ratio of Mn/Fe(o2.5 generally) and are poor in Cu, Ni and Zn(Jeong et al., 1994). Hydrothermal nodules arecharacterized by a high ratio of Mn/Fe and by beingpoor in Cu, Ni and Co relative to the diagenetic andhydrogenic counterparts (Usui et al., 1997; Hod-kinson et al., 1994; Hein et al., 1987; Moorby et al.,1984; Moorby and Cronan, 1983). In addition to thethree types mentioned above, a transitional manga-nese nodule occurs. Its chemical composition andminerals vary depending on contact with eithersurface or deeper sediments (Moore et al., 1981;Reyss et al., 1985). At the bottom the chemicalcomposition and minerals are similar to those ofdiagenetic manganese nodules, while at the top thechemical composition and minerals are similar tothose of the hydrogenic nodules and crust (Skor-nyakova and Murdmaa, 1992; Jeong et al., 1994).
Many elements, such as transitional elements Cu,Co, Ni and Zn, have different geochemistries indifferent types of ferromanganese oxide deposits.We will investigate the geochemistry of lithium inthe ferromanganese deposits in terms of chemistryand mineralogy.
2. Sample description
Locations and descriptions of the ferromanganeseoxides deposits studied here are given in Tables 1and 2, and locations of the sampling sites shown inFig. 1. The ferromanganese crust was discoveredand collected by dredging on a seamount surfaceduring cruise DY-10 with the ‘‘Haiyang VI’’ in2002. Obvious ripples of surficial sediments on theseamount surface, caused by currents, were ob-served with an underwater camera. The diageneticferromanganese nodule, which was buried under thesediments, was collected by dredging, andthe transitional nodule, which was embeddedin the uppermost sediment was collected from theabyssal plain with free-fall grab during a cruise ofthe ‘‘Dayang I’’ in 2003.
The hydrogenic ferromanganese crust, with asmooth dark gray surface, was about 5.2 cm thickwith seven visible layers. Samples were taken fromeach layers (Table 2, Fig. 2).
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Table 2
Descriptions of the samples collected from the crust and the diagenetic nodule
Samples Property Thickness
Mn-Fe-Cru-1 Dark gray 0.4
Mn-Fe-Cru-2 Dark gray with clay interlayer in brown 0.5
Mn-Fe-Cru-3 Brownish-yellow with loose structure 0.5
Mn-Fe-Cru-4 Dark gray with brownish-yellow 0.6
Mn-Fe-Cru-5 Grayish-yellow with brownish-yellow interlayer 0.5
Mn-Fe-Cru-6 Dark gray with fine brownish-red vein and a little clay in yellow, loose structure 1.4
Mn-Fe-Cru-7 Dark gray with pitchy luster 1.3
Mn-Fe-Nod-1 The spherical core in brownish-yellow with dense structure 0.6
Mn-Fe-Nod-2 Gray with intercalated ooze and somewhat loose structure 0.5
Mn-Fe-Nod-3 The same as Mn-Fe-Nod-2 1.2
Mn-Fe-Nod-4 The same as Mn-Fe-Nod-2 0.9
Mn-Fe-Nod-5 Dark gray with dense structure 0.8
Table 1
Details of the managaese nodules and crust analysed in this investigation
Samples Location Sediment type Water depth (m) Depth of nodule
X. Jiang et al. / Deep-Sea Research I 54 (2007) 85–98 87
The diagenetic nodule was spherical with a radiusof 4.0 cm and an abrasive and gritty surface coveredby yellow clays. There were five laminations fromthe center to the periphery (Table 2, Fig. 2). Besidesthe 5 diagenetic samples, a transitional nodulesample of ellipsoid shape with micro-axis, mean-axis and minor-axis of 3.5, 2.2 and 1.1 cm,respectively, was collected to compare the amountof lithium and 10 A manganates to those of thediagenetic nodule sample.
3. Experimental details
Samples were dried in air and finely ground in anagate mortar for chemical analysis. The powdersproduced by grinding were digested with HCL,HNO3 and HClO3 to determine the macro and traceelements by inductively coupled plasma/atomicemission spectrometry (ICP/ES) (Table 3), while Siwas determined by atomic absorption spectroscopy(AAS). The mineral composition of nodule andcrust samples was determined on the powder afterair-drying at room temperature. The nodule sam-ples were also analyzed after heating at 110 1C withan X-ray diffractometer (XRD) (Fig. 3, Fig. 4).
We analyzed the existing phases of lithium invarious ways because of the great differences oflithium concentration among the ferromanganesedeposits. It is difficult to analyze the lithium phasein the hydrogenic crust by chemical methods be-cause of the very small amounts of lithium (Table 3),though the statistics are available and are useful tosome extent. On the other hand, the lithium phase inthe diagenetic and transitional nodules could beanalyzed by chemical methods because of thehigh content. The analytical methods were basedon the following strategy: first, to determinewhether the lithium is present in the lithiophoritephase in the diagenetic and transitional nodules,because lithiophorite is an important mineralbearing some lithium; second, if the lithium wasnot present in the lithiophorite phase, the selectivedissolution experiments were conducted further toinvestigate the existing phase.
A selective dissolution experiment was conductedas a reference (Tokashiki et al., 2003) to determinewhether the lithiophorite was present: 50mg of theo2 mm diagenetic and transitional ferromanganesenodule samples were placed in each of six 50mlTeflon centrifuge tubes, and 40ml of 0.1M hydro-xylamine hydrochloride solution was put into each
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Fig. 1. Location map of the nodule samples Fe–Mn-Nod and Fe–Mn-TranNod in a manganese nodule province and the crust sample
Fe–Mn-Cru near Line Island. Contours with hatched lines denote 6000m water depth and others 4000m.
Fig. 2. Morphology of manganese deposits. Both of the samples are greyish black. (A) The crust sample has seven visible layers and
samples were taken from each. The layers in the actual sample were far more distinct than in the photo. (B) The nodule sample has five
discernible laminations from the center to the periphery, and each was sampled.
X. Jiang et al. / Deep-Sea Research I 54 (2007) 85–9888
tube; the tubes were shaken for 30min at ambienttemperature (16–25 1C) and centrifuged at 2000g for10min; the supernatant was decanted for analysisby ICP/ES with the results shown in Table 4.
Additional dissolution experiments were con-ducted to investigate the phase of lithium in thediagenetic and transitional nodule samples. A two-step procedure was used.
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Table 3
Concentrations of the elements in transitional nodule Mn-Fe-TranNod, diagenetic nodule Mn-Fe-Nod and hydrogenic crust Mn-Fe-Cru
Samples Mn (%) Fe (%) Ca (%) Mg (%) Al (%) Na (%) Li (10�6) K (%) Si (%) Ni (%) Cu (%) Co (%)
Fig. 3. The powder XRD patterns of nodule samples (A: Mn-Fe-Nod-1; B: Mn-Fe-TranNod; C: Mn-Fe-Nod-2. Because the samples from
Mn-Fe-Nod-2 to Mn-Fe-Nod-5 have the same XRD patterns except the ratio of 10 A manganates/d-MnO2, the XRD patterns of Mn-Fe-
Nod-2 to Mn-Fe-Nod-5 are not shown here.)
X. Jiang et al. / Deep-Sea Research I 54 (2007) 85–98 89
Step 1. Elements in soluble, exchangeable orcarbonate states.To each of six 50-ml Teflon centrifuge tubes weadded 200mg of o2 mm powder from each of thesix diagenetic and transitional nodule samples
and 20ml 1M acetic acid. The six tubes wereplaced on a mechanical shaker at ambienttemperature and at medium speed for 20min.The solid and liquid phase were thenseparated by centrifuging at 1500g for 10min.
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Fig. 4. The XRD patterns of sample Fe–Mn-Nod-3 (A: air drying at room temperature; B: drying at 110 1C for 4 h. The 10 A spacing of
the 10 A manganates remained unaltered after heating at 110 1C with a slight decrease in the ratio 10 A/7 A. Other nodule samples have
almost the same patterns despite various slight decrease in the ratio 10 A/7 A, only Fe–Mn-Nod-3 is shown here).
Table 4
Bulk chemical composition and amounts of elements leached with hydroxylamine hydrochloride of the diagenetic and transitional nodule
samples
Elements Bulk chemical composition Amounts of elements Leached with hydroxylamine hydrochloride
Li (ppm) Mn (%) Fe (%) Al (%) Li (ppm) Mn (%) Fe (%) Al (ppm)
X. Jiang et al. / Deep-Sea Research I 54 (2007) 85–9890
The supernatants were decanted for analyzingthe elements, and the residues were then rinsedwith 10ml distilled water and centrifuged again.The supernatants were discarded. The solidresidues were reserved for the next step of theselective dissolution experiments.Step 2. Elements bound to manganese oxides.Twenty ml 0.1M NH2OH �HCL–0.01N HNO3
was poured into each of the six Teflon centrifugetubes holding the solid residues reserved from
Step 1. The tubes were placed on the mechanicalshaker at ambient temperature and at mediumspeed for 30min. The solid and liquid phase werethen separated by centrifuging at 2500g for15min. The supernatants were decanted foranalysis.
The chemical compositions of the supernatantsfrom Steps 1 and 2 were analyzed by ICP/ES(Table 5).
X. Jiang et al. / Deep-Sea Research I 54 (2007) 85–98 91
4. Results
The manganese contents of the nodule samplesranged from 25.46 to 34.68wt% with an average of30.66wt%, whereas the averages for Fe and Al were5.35 and 2.38wt%, respectively; the Mn/Fe ratioranged from 3.49 to 11.58 (Table 3). The contents ofFe and Al as well as the Mn/Fe ratio were all higherthan those of hydrothermal nodules (Table 6). Niand Cu contents ranged from 0.84 to 1.72wt%,distinctively different from those of hydrothermalMn deposits (Table 6). Hydrothermal deposits are,in general, markedly enriched in Mn but depleted inFe, Al, Co, Cu and Ni compared with hydrogeneticor diageneitc manganese deposits. These composi-tional features indicate that the nodule samples arein categories other than hydrothermal.
XRD analysis of the nodule samples, measuredafter air drying, shows that they are composedmainly of 10 A manganates with minor d-MnO2 andminimal 7 A manganates, quartz and feldspar(Fig. 3). The nodule samples are diagenetic andtransitional manganese deposits according to che-mical composition, mineral constituents and mor-phology. The X-ray intensity ratio 10 A/7 A isvariable among the six nodule samples but withina narrow range. The thermal treatment at 110 1C, todiscriminate todorokite from buserite, revealed thatthe 10 A spacing is retained with a slight decrease inthe ratio 10 A/7 A (Fig. 4). The stable structure of10 A manganates indicated that the 10 A manga-nates have incorporated sufficient amounts of theinterlayer transition metal cations, such as Cu andNi, to retain the structure unaltered after heating at110 1C (Mellin and Lei, 1993; Martin-Barajas et al.,1991; Usui et al., 1989).
The hydrogenic ferromanganese crust sampleswere composed mainly of d-MnO2, amorphousferric oxide/hydroxide with minimal quartz,goethite and silicate minerals and were enriched inMn and Fe with minor Al, Ca, Na, K, Co and traceelement Li (Table 3, Fig. 5). Unlike the diageneticnodule samples, each layer of the hydrogenicferromanganese crust had very similar chemicalcompositions and minerals.
There is more lithium in the nodules than in theferromanganese crust, and the average abundanceof lithium in the crust samples is only about 1% ofthat in the diagenetic nodule samples. Lithiumconcentrations in the laminations of the diageneticnodule samples ranged from 95.4 to 318.7 ppmwith an average of 229.1 ppm (s ¼ 80.2). In the
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Fig. 5. Mineralogy of the sample Mn-Fe-Cru-2. The sample was composed mainly of d-MnO2 and amorphous ferric oxides and
hydroxides (no peaks) with minor quartz, feldspar, goethite and chlorite. Only the XRD pattern of Mn-Fe-Cru-2 is shown, other crust
sample patterns are similar.
Table 6
Average chemical composition of the hydrothermal marine Mn deposits
Areas Mn (%) Fe (%) Ca (%) Mg (%) Al (%) Na (%) Li (10�6) K (%) Ni (%) Cu (%) Co (%)
aPitcairn Is. hot spot, S. Pacific. N ¼ 10. Hodkinson et al. (1994).bMariana arc, W. Pacific. N ¼ 5–11. Hein et al. (1987).cHavre rift, S. Pacific. N ¼ 24. Moorby et al. (1983).dGalapagos rift, EPR. Moorby and Cronan (1983).
X. Jiang et al. / Deep-Sea Research I 54 (2007) 85–9892
transitional nodule sample lithium concentrationreached 143.5 ppm, far higher than that of thehydrogenic crust samples, which have an average of2.27 ppm (Table 3). This feature is related closely tothe mineralogy of the two types of ferromanganeseoxides and will be discussed later.
An average of 95% of the lithium and 91% of theMn were extracted by 0.1M hydroxylamine hydro-chloride solution at 18 1C from the diagenetic andtransitional nodule samples. On the other hand, theaverage percent of Fe and Al extracted by 0.1Mhydroxylamine hydrochloride solution was only2.8% and 0.4%, respectively. The average concen-tration of lithium present in soluble, exchangeable or
carbonate (extracted in step 1) was 56% of the totalamount of lithium, while the average value of lithiumpresent in manganese oxide states reached 43% ofthe total amount of lithium (Table 5). Only about0.4% (average) of the Mn was extracted in Step 1 byacetic acid, while about 92.1% of the Mn wasextracted in Step 2. This indicates that the experi-ments were effective, because the Mn and Li wereseparated completely from other minerals or oxides.
Each lamination of the diagenetic nodule samplescan be considered as a different nodule, and so caneach layer of the ferromanganese crust sample. Thiscan help us to treat the data on the basis ofstatistics.
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5. Discussion
5.1. Geochemistry of lithium in the diagenetic and
transitional ferromanganese nodules
It appears that the lithium in the diagenetic andtransitional nodules was held in the manganeseoxides rather than ferric oxide or other minerals.This is indicated by the nearly complete extractionof lithium and manganese from the diagenetic andtransitional nodules by 0.1M hydroxylamine hy-drochloride (Table 4).
Lithiophorite (LiAl2[Mn(IV) Mn(III)]O6(HO)6)(Post, 1999) is commonly found in weathered zonesof Mn deposits, ocean-floor manganese crust,certain acid soils and low-temperature hydrother-mal veins (De Villers, 1983; Post and Appleman,1994). Published chemical analyses of lithiophoritesamples from a variety of localities show that the Licontent ranges from 0.2 to 3.3 oxide weight percent(Ostwald, 1988). It is difficult to differentiatebetween lithiophorite and 10 A manganates by X-ray diffraction because of the overlap of theirdiffraction peaks. On the other hand, the chemicalmethod is available to determine whether lithio-phorite is present. It is impossible for lithiophoriteto be dissolved in hydroxylamine hydrochloridesolution below 25 1C (Tokashiki et al., 2003).Because almost all of the lithium in the nodulesamples was extracted by 0.1M hydroxylaminehydrochloride solution below 20 1C, it can beconcluded that the lithium was present in a phaseother than lithiophorite.
Little lithium is adsorbed by suspended particlesbecause of the low energy of adsorption of thiselement onto clay minerals and colloidal particles(Lebedev, 1957; Grim, 1968). This has beenconfirmed by laboratory experiments that showedthat the Li concentrations of seawater samples is notaffected by even large amounts of clay (1 g/L) oriron hydroxide (E4mg/L) in suspension (Egli,1979). The extremely low lithium concentration(average 2.27 ppm (s ¼ 1.55)) in the hydrogeniccrust also reveals that d-MnO2 and ferric oxide/hydroxide can adsorb only a very small amount oflithium. This indicates that the lithium in thediagenetic and transitional nodules was in closeassociation with the 10 A manganates rather thanother minerals or oxides.
Todorokite shows much the same interlayerstrength as marine high-temperature hydrothermaland metal-rich diagenetic 10 A manganates (Usui
et al., 1989; Mellin and Lei, 1993). Burns et al.(1983) summarized the observations of tunnelstructures of both terrestrial and marine 10 Amanganates and recommended that the nametodorokite be universally adopted for the predomi-nant marine 10 A manganates. Lei (1996) suggestedthat marine and synthetic 10 A manganates andterrestrial todorokite have similar tunnel structures.As a matter of fact, buserite can be transformed intotodorokite (Shen et al., 1993). The heating experi-ment revealed that the 10 A spacing of the 10 Amanganates remained unaltered after heating at110 1C. It appears that the initial 10 A manganatesobtain structural stability by incorporation oftransition metals, the oxidation of Mn2+ to Mn4+
ions and the simultaneous change of OH� to O2�
ligands in the walls of the tunnel structure of the10 A manganates (Lei, 1996).
Diagenetic ferromanganese nodules enriched inCu, Ni and 10 A manganates are formed fromreprecipitation of the remobilized manganese ionsfrom solid Mn4+ to soluble Mn2+ in the interstitialwater due to the reduced micro-environment in thesediments where the diagenetic nodules are formed(Dymond et al., 1984; Halbach et al., 1981;Calvertand Price, 1977). In the structure of 10 A manga-nates, ½Mn4þO2�
6 � octahedral layers are orderlystacked along the C-axis to form the ceiling orfloor of the tunnel, while the wall of the tunnel isconstructed of three edge-shared octahedral stringsconstructed by two [(Mn4+, Me(2+,3+),Mn2+)O2�
3þxðOH�Þ3�x] octahedra (0pxp3) with a[(Mn4+, Me(2+,3+), Mn2+)O2�
2x ðOH�Þn�2x] unit(n ¼ 6 or 8) (Fig. 6) (Lei, 1996). The ½Mn4þO2�
6 �
octahedral layers of the 10 A manganates are boundby hydrated interlayer cations with Van der Waal’sforces and weak coordination links (Mellin and Lei,1993). The tunnel is filled by water (Feng et al.,1998; Post et al., 2003) and ions with a large radiussuch as Na+, Ca2+, K2+ and Mg2+ (Lei, 1996; Postet al., 2003; Shen et al., 1993). The magnesium ionsare located at both tunnel sites (Post et al., 2003;Shen et al., 1993) and octahedral Mn sites (Post andBish, 1988; Post et al., 2003; Feng et al., 1998). Theions Cu2+, Co2+ and Ni2+ can substitute for Mg2+
and Mn2+ in the octahedral [(Mn4+, Me(2+,3+),Mn2+)O2�
3þxðOH�Þ3�x] and [(Mn4+, Me(2+,3+),Mn2+)O2�
2x ðOH�Þn�2x] in the walls, resulting inhigher crystal field stabilization energy (CFSE)and shorter coordination bonding bridges between½Mn4þO2�
6 � octahedral layers, thus enhancing thestability of early formed 10 A manganates (Mellin
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Fig. 6. The model for the structural frameworks of marine diagenetic 10 A manganates (Lei, 1996) (Highly hydrated Cu2+ and Ni2+ ions
can enter the walls of the tunnel to stabilize the structure; lithium ions can fill in the tunnel to substitute to form [Li+(H2O, OH�)6] and can
substitute for many Mg2+ ions in the walls of the tunnel in the form ½Mg2þO2�3þxðOH�Þ3�x� (0pxp3) or ½Mg2þO2�
2x ðOH�Þn�2x� (n ¼ 6 or 8)
to form ½LiþO2�3þxðOH�Þ3�x� (0pxp3) or ½LiþO2�
2x ðOH�Þn�2x� (n ¼ 6 or 8).
X. Jiang et al. / Deep-Sea Research I 54 (2007) 85–9894
and Lei, 1993; Martin-Barajas et al., 1991; Shenet al., 1993).
Lithium is an alkali metal, but because of its smallionic radius it behaves more like Mg2+ in nature. Itsubstitutes for Al3+, Fe2+ and especially Mg2+ incrystal structures rather than for Na+ (Huh et al.,1998). Li+ has the weakest sorption chemistry of allthe alkalis (Heier and Billings, 1978), and theenrichment of lithium is considered to be due toisomorphic substitution. Although the ionic radius ofLi+ (0.76 A, octahedral coordination (Shannon,1976)) is similar to that of Mn2+ (0.83 A, octahedralcoordination (Shannon, 1976)), Li+ can’t substitutefor Mn2+ because of the valence state difference andthe different ionic configuration. In addition, theCFSE of Li+ in octahedral coordination can beregarded as zero and is lower than that of many
transitional ions, such as Mn2+ and Mn4+, which arethe dominant ions, and Cu2+, Co2+ and Ni2+, whichare the main substitutional transitional ions. On theother hand, Li+ can substitute for a small amount ofMg2+ in the wall to form ½LiþO2�
3þxðOH�Þ3�x� (0px
p3) or ½LiþO2�2x ðOH�Þn�2x� (n ¼ 6 or 8), and this
may result in further imbalance of the charge of thestructure and enhance the absorbability of largecations into the tunnel. It is difficult for H+ tosubstitute for the Li+ ions located in the octahedralstrings, and this part of the lithium wasn’t extractedby acetic acid solution. Of course, the amounts of theLi+ ions in the octahedral strings vary greatly,depending on different individual nodules anddifferent formation conditions, such as the numberof Mg2+ ions in the octahedral strings and thenumber of Li+ ions supplied by the ocean.
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Although the ionic radius of Li+ is smaller thanthose of Na+, Ca2+ and K+, all alkali metals canenter the tunnel of the structure (Feng et al., 1998).Lithium ions can enter the tunnel to form[Li+(H2O, OH�)6] as other metal ions such asNa+, Ca2+, K+ and Mg2+ do. However, it isimpossible for Li+ ions to enter the tunnel withoutlimit because of the low concentration of lithiumin seawater (about 0.18 ppm (Stouffyn-Egli andMachenzie, 1984; Gieskes et al., 1998)) and in porewaters of the upper sediments on the bottom of theoceans (Zhang et al., 1998) compared to those ofNa+, Ca2+, K+ and Mg2+. The low valence of Li+
ions is a disadvantage to the balance of the chargeof the structure, and mg2+ ions are more suitablefor the tunnel because of the high valence, whichcan bring about the charge balance of the structure.The size of the tunnel is more suitable for caitonswith large ionic radius such as Na+, Ca2+, Ba2+
and K+. The metal ions in the tunnel can bereplaced during ion exchange (Shen et al., 1993) andcan be easily extracted by acid treatment (Feng etal., 1998). Lithium ions in the tunnels in theoctahedral [Li+(H2O, OH�)6] can be extracted byacetic acid. This part of the lithium can be regardedas soluble or exchangeable Li in the diagenetic andtransitional ferromanganese nodules.
The interstitial water Li concentrations within theupper 10m of marine sediments sometimes is onlyabout half of the seawater value (Zhang et al., 1998;Gieskes et al., 1998). On the other hand, Liconcentrations in the diagenetic and transitionalnodules can reach several hundreds of ppm in wt%,and this value is one to two thousands times as largeas in the interstitial water. This indicates that thediagenetic nodules take up Li, and this is attributedto the incorporation capability of 10 A manganates.The 10 A manganates of the diagenetic and transi-tional ferromanganese nodules can be regarded asan important scavenger of lithium in the ocean.
The Li fluxes into and out of the ocean have beenestimated, and it has been concluded that the uptakeby weathered basalt is insufficient to balance theriverine and hydrothermal inputs (Seyfried et al.,1984; Stouffyn-Egli and Machenzie, 1984). Themaximum diffusive flux into the sediment due tovolcanic matter alteration can be no more than 5%of the combined inputs from rivers and submarinehydrothermal solutions (Zhang et al., 1998). It isgenerally believed that the deficit is balanced bymarine sediments, possibly with authigenic clays asthe dominant sinks (Stouffyn-Egli and Machenzie,
1984). However, the incorporation of Li intoauthigenic clay minerals from volcanic matteralteration in the sediment column and Li adsorptionon sediments are relatively minor sinks (Zhang etal., 1998). It seems that other sinks should beexplored. The diagenetic and transitional ferroman-ganese nodules may play a role in the mass balanceof lithium in the oceans.
5.2. Geochemistry of lithium in the hydrogenic
ferromanganese crust
The lithium content of the layers of the hydro-genic crust samples ranging from 5.68 to 1.25 ppm,with an average of 2.27 ppm (s ¼ 1.55), is about 1%of the average value of the diagenetic nodulesamples. The coefficients of correlation between Liand Al, Mn, Fe, Si are 0.98, �0.94, �0.07 and 0.89,respectively, indicating that there is not anyrelationship between Li, Mn and Fe in the hydro-genic crust samples. The presence of Li in thehydrogenic crust is not attributed to the d-MnO2 orthe amorphous or crystalline ferric oxide/hydroxide.The low concentration of lithium in the crustindicates that d-MnO2 and amorphous or crystallineferric oxide and hydroxide are incapable of adsorb-ing lithium.
Hydrogenic crusts are formed from the directprecipitation of colloidal metal oxide of the sea-water (Dymond et al., 1984; Halbach et al., 1981;Calvert and Price, 1977) under oxic conditions(Skornyakova and Murdmaa, 1992; De Carlo,1991). The oxides are composed principally of d-MnO2 with amorphous ferric oxide/hydroxide(Alvarez et al., 1990; Martin-Barajas et al., 1991;De Carlo, 1991; Dymond et al., 1984;Halbach et al.,1981). In addition, minor quartz, feldspar, goethiteand chlorite are present in the crust samplesanalysed in this paper (Fig. 4).
d-MnO2 is formed by the edge-shared ½Mn4þO2�6 �
layers and is disordered in the layer-stackingdirection (Giovanoli and Arrhenius, 1988; Giova-noli, 1980) with no vacancy in the structure(O’Connor et al., 2003; O’Connor et al., 2004).There is no tunnel structure in d-MnO2; thereforethere is no site for Li to occupy d-MnO2 cannotincorporate any Li+ into its structure. d-MnO2
can’t adsorb any Li+ into the structure during itsformation because of the greatly different charge,type and radius between Li+ and Mn4+. On theother hand, laboratory experiments have confirmedthat the Li concentration of seawater samples is not
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affected by large amounts of clay (1 g/L) or ironhydroxide (E4mg/L) in suspension (Egli, 1979). Itis reasonable to assume therefore, that lithium in thehydrogenic crust is present in states other than theiron oxide and hydroxide phases.
The high coefficients of correlation between Liand Al (0.98) and Si (0.89) indicates that Li in thehydrogenic crust is incorporated into certain typesof minerals enriched in Al and Si. The coefficient ofcorrelation between Al and Si in the hydrogeniccrust reached 0.92, indicating that Li in thehydogenic crust may occur in an aluminosilicatephase. In addition, the XRD peaks (Fig. 5)probably reveal the presence of small amounts ofclay minerals despite the fact that clay and ironhydroxide adsorb little Li in seawater (Egli, 1979).Li is believed to substitute for Mg2+ and Fe2+ inthe octahedral site of chlorite and smectite or for Nain zeolite (Berger et al., 1988). It can also occupyexchangeable positions in interlayers of these layeraluminosilicates (Berger et al., 1988). Therefore, it isreasonable to assume that clay minerals, such aschlorite, can to some extent adsorb a little lithium,i.e., the lithium precipitated first in the clay mineralsand then was deposited with the manganese andiron oxide/hydroxide in the ferromanganese crust.This is in agreement with the coefficient of correla-tion between Li and Al (0.98), Si (0.89) in theferromanganese crust, and it is very different fromthe geochemistry of lithium in the diageneticferromanganese nodules. On the other hand, theclay minerals can adsorb relatively very little lithium(Grim, 1968), and the average concentration oflithium in the ferromanganese crust sample is nomore than 2.27 ppm(s ¼ 1.55).
6. Summary and conclusions
Lithium shows different geochemistry in differentorigin of marine ferromanganese deposits. There isfar more lithium in diagenetic and transitionalnodules than hydrogenic crust.
Lithium in diagenetic and transitional ferroman-ganese nodules is not in lithiophorite phase, whichbears a certain amounts of lithium according to theresult of the selective dissolution experiment. Thediagenetic and transitional nodules strongly incor-porate lithium due to the presence of 10 Amanganates, which are able to incorporate lithiuminto their structure via ion exchange and substitu-tion. Lithium enters 10 A manganates structure tofill in the tunnel and be present at octahedral sites in
the walls. However, 10 A manganates cannot uptakelithium without limit because the radius of lithiumions is less than that of Na+, Ca2+ and Ba2+ thatare more suitable for the tunnel, and the low valenceof Li+ is a disadvantage to the charge balance of10 A manganates structure. The 10 A manganatescan be regarded as an important scavenger oflithium in the oceans. Diagenetic and transitionalnodules may play a role to some extent in massbalance of lithium in the oceans.
Neither d-MnO2 nor iron oxide/hydroxides offerromanganese crust adsorbs lithium in seawater.It appears that lithium is present in hydrogenicmarine ferromanganese crusts in an aluminosilicatephase due to their capacity of ion exchange. Thealuminosilicates that adsorb a little lithium pre-cipitate into the ferromanganese crust with themanganese and iron oxide/hydroxides. However itis very difficult to confirm the phase of the lithium inthe hydrogenic ferromanganese crust because of itsextremely low concentrations. Here we suggest thepresent phases of the lithium in the hydrogenicferromanganese crust by the correlation betweenlithium and other elements.
Acknowledgements
We thank the officers, crews and scientists of the‘‘Haiyang IV’’ and ‘‘Dayang I’’ for exemplarycooperation during long cruises. We also express ourappreciation to the anonymous reviewers for theirthoughtful comments. Thanks are given to Dr.Michael P. Bacon for deliberate suggestions andcomments on my manuscript. This research was supp-orted by the National Nature Science Foundation ofP.R. China Grant 40076015 and China OceanMineral Resources R & D Association.
References
Alvarez, R., De Carlo, E.H., Cowen, J., Andermann, G., 1990.
Micromorphological characteristics of a marine ferromanga-