Clays and Clay Minerals, Vol. 64, No. 5, 488–501, 2016. 1 1 2 2 3 XRD AND TEM STUDIES ON NANOPHASE MANGANESE OXIDES IN 3 4 FRESHWATER FERROMANGANESE NODULES FROM GREEN BAY, 4 5 5 6 LAKE MICHIGAN 6 7 7 8 8 S EUNGYEOL L EE AND H UIFANG X U* 9 9 NASA Astrobiology Institute, Department of Geoscience, University of Wisconsin Madison, Madison, 10 À 10 1215 West Dayton Street, A352 Weeks Hall, Wisconsin 53706 11 11 12 12 13 Abstract—Freshwater ferromanganese nodules (FFN) from Green Bay, Lake Michigan have been 13 14 investigated by X-ray powder diffraction (XRD), micro X-ray fluorescence (XRF), scanning electron 14 microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and scanning 15 transmission electron microscopy (STEM). The samples can be divided into three types: Mn-rich 15 16 nodules, Fe-Mn nodules, and Fe-rich nodules. The manganese-bearing phases are todorokite, birnessite, 16 17 and buserite. The iron-bearing phases are feroxyhyte, goethite, 2-line ferrihydrite, and proto-goethite 17 18 (intermediate phase between feroxyhyte and goethite). The XRD patterns from a nodule cross section 18 19 suggest the transformation of birnessite to todorokite. The TEM-EDS spectra show that todorokite is 19 associated with Ba, Co, Ni, and Zn; birnessite is associated with Ca and Na; and buserite is associated with 20 2+ +2 3+ 20 Ca. The todorokite has an average chemical formula of Ba0.28(Zn0.14Co0.05 21 2+ 4+ 3+ 3+ 3+ 2+ 21 Ni0.02)(Mn4.99Mn0.82Fe0.12Co0.05Ni0.02)O12·nH2O. Barium is the main cation in the structural tunnels of 22 the todorokite. The average chemical formula of birnessite and Ca-buserite are: 22 + 2+ 4+ 3+ 2+ 4+ 3+ 23 Na0.14Ca0.19(Mn1.48Mn0.52)O4·nH2OandCa0.27(Mn1.46Mn0.54)O4·nH2O, respectively. Most nodules have 23 24 a concretionary structure of alternating Fe/Mn layers, commonly with a core of reddish feldspar containing 24 25 hematite micro-crystals. Other cores consist of goethite, cristobalite, tridymite, hercynite, hematite- 25 bearing quartz, coal, and chlorite-bearing rock fragments. The hexagonal or hexagonal-like structures of 26 26 hematite micro-crystals and clay minerals in the cores may serve as heterogeneous nucleation sites for the 27 Mn-oxides and Fe-(oxyhydr)oxides. The alternating Fe/Mn layers in FFNs might be caused by oscillatory 27 28 redox condition fluctuations at the sediment-water interface due to changes in water level. 28 29 Key Words—Birnessite, Buserite, Ferromanganese Nodule, Green Bay, Heterogeneous Nucleation, 29 30 HRTEM, Lake Michigan, Todorokite, XRD. 30 31 31 32 INTRODUCTION 32 33 that constitute the bulk of glacial debris (Rossmann and 33 34 Freshwater ferromanganese nodules (FFN) are known Callender, 1968; Edgington and Callender, 1970). The 34 35 to occur in lakes throughout North America (Harriss and glacial materials are quite permeable and thus easily 35 36 Troup, 1970; Callender et al., 1973; Sozanski and weathered under temperate climatic conditions (Callender 36 37 Cronan, 1979; Stein et al., 2001), Europe (Calvert and et al., 1973; Robbins and Callender, 1975). 37 38 Price, 1970; Kuleshov and Sterenberg, 1988), Asia The purpose of the present paper is to offer further 38 39 (Amirzhanov et al., 1992; Tan et al., 2006), and Africa evidence of trace element binding behavior, nucleation 39 40 (Williams and Owen, 1992; Kalindekafe, 1993). sites,andgrowthofGreenBaynodulesbyusingX-ray 40 41 However, no detailed investigation has been reported powder diffraction (XRD), scanning electron microscopy 41 42 about nano-phase minerals and nucleation of ferroman- (SEM), high-resolution transmission electron microscopy 42 43 ganese nodules in freshwater environments. (HRTEM), and scanning transmission electron micro- 43 44 Green Bay FFN consist of alternating Fe/Mn layers scopy (STEM). The Mineralogy of Green Bay nodules is 44 45 around a central core, which undergo oscillatory changes todorokite, birnessite, buserite, feroxyhyte, goethite, 45 46 between reduced and oxidized conditions at the sediment- ferrihydrite, and proto-goethite with a guyanaite structure 46 47 water interface (Rossmann and Callender, 1968; Stein et (an intermediate phase between feroxyhyte and goethite) 47 48 al., 2001; Hlawatsch et al., 2002). Microbial communities (Lee et al., 2016). Given that the mineralogy of nanophase 48 49 are proposed to play a significant role in the mineraliza- Fe-(oxyhydr)oxides in Green Bay nodules were strongly 49 50 tion of ferromanganese nodules (Nealson and Myers, discussed in Lee et al., (2016), the present paper will 50 51 1992; Stein et al., 2001). The Mn(II) and Fe(II) in the focus on the mineralogy of nanophase Mn-oxides, the 51 52 nodules are derived from igneous/metamorphic minerals transformation pathways between birnessite, buserite, and 52 53 todorokite, and the associated trace elements Ba, Co, Ni, 53 54 and Zn. Furthermore, a model to describe Fe/Mn-mineral 54 55 * E-mail address of corresponding author: nucleation on core minerals was proposed and the texture 55 56 [email protected] of alternating Fe/Mn layers in Green Bay nodules was 56 57 10.1346/CCMN.2016.064032 described. 57 Vol. 64, No. 5, 2016 Nanophase manganese oxides from Lake Michigan 489 1 MATERIALS AND METHODS Experimental methods 1 2 Freshwater ferromanganese nodules 2 3 Multipoint Brunauer-Emmett-Teller (BET) surface 3 4 Ferromanganese nodules, which were previously areas and Barrett-Joyner-Halenda (BJH) pore size 4 5 studied by Callender et al., (1973), were collected distributions were determined by N2-adsorption techni- 5 6 from the uppermost ~10 cm of lake-bottom sediments in ques using a Nova 4200e surface area and pore size 6 7 Green Bay, Lake Michigan. The samples vary in analyzer (Quantachrome instruments, Florida, USA) in 7 8 diameter from ~0.5 to ~5 mm and can be divided into: the Geoscience Department at the University of 8 9 Mn-rich nodules, Fe-Mn nodules, and Fe-rich nodules Wisconsin-Madison. Surface area analyses of a refer- 9 10 (Figures 1a, 1b, and 1c). Nodules from the northern area ence material (Cat. No. 2005, Quantachrome instru- 10 2 11 of Green Bay are primarily Fe-rich, whereas nodules ments, Florida, USA; 108.1 Ô 6.6 m /g) suggest that the 11 12 adjacent to the Menominee River are Mn-rich (Callender measurement error was within Ô 5%. 12 13 et al., 1973). Interestingly, the Fe/Mn ratios of FFNs Two types of samples were prepared: one sample as 13 14 increase from 0.7 in the central part of Green Bay to 10.8 polished thin sections (50 mm thickness) for in situ XRD; 14 15 in the north (Callender et al., 1973). and the other sample was crushed and colloidal particles 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 25 25 26 26 27 27 28 28 29 29 30 30 31 31 32 32 33 33 34 34 35 35 36 36 37 37 38 38 39 39 40 40 41 41 42 42 43 43 44 44 45 45 46 46 47 47 48 48 49 49 50 50 51 51 52 52 53 53 54 54 55 55 56 Figure 1. Optical images and element maps of Green Bay nodules: (a) Mn-rich nodules, (b) Fe-Mn nodules, (c) Fe-rich nodules, and 56 57 (dÀi) elemental maps and optical image of a nodule showing alternating Fe/Mn layers with an Fe-oxide-bearing quartz core. 57 490 Lee and Xu Clays and Clay Minerals 2 1 1 were collected from a suspension to eliminate possible the Mn-rich nodules, 120 and 132 m gÀ for Fe-Mn rich 1 2 1 2 large detrital grains, such as quartz, for use in heating nodules, and 100 and 114 m gÀ for Fe-rich nodules, 2 3 experiments. Mineral grains were also picked from cores respectively. Similarly, BJH adsorption surface areas 3 2 1 4 in the nodules for XRD analyses. XRD data were were 158 and 178 m gÀ for the Mn-rich nodules (inner 4 2 1 5 collected on a 2-D image-plate detector using a Rigaku part and outer layer), 144 and 165 m gÀ for the Fe-Mn 5 2 1 6 Rapid II instrument (Rigaku, Tokyo, Japan) using nodules, and 115 and 124 m gÀ for the Fe-rich nodules 6 7 Mo-Ka radiation in the Geoscience Department. Two (Figure 2). The increased Mn-oxide content was 7 8 dimensional images were converted to produce conven- proportional to the increased surface area. In addition, 8 9 tional 2y vs. intensity patterns using Rigaku’s 2DP the outer layers of FFN have slightly larger surface areas 9 10 software. Percentages of mineral phases in the sample than the inner portion, consistent with the outer layers 10 11 were calculated using the Rietveld method by using having more poorly crystallized minerals as young-stage 11 12 JADE 9 software (MDI, California, USA). A pseudo- precipitates. The BJH pore size distribution analyses 12 13 Voigt method (Thompson et al., 1987) was used for show that the surface areas were dominated by nanopore 13 14 fitting the peak profiles. surfaces (<10 nm) (Figure 2). 14 15 Samples for SEM analysis were mounted onto glass 15 16 slides, polished, and coatedwithcarbon(~10nm).All In situ XRD results 16 17 SEM images were obtained using a Hitachi S3400N Diffraction data for selected regions of the thin section 17 18 variable pressure microscope (Hitachi, Tokyo, Japan) (Figure 3) showed that Mn-rich nodules were composed 18 19 with an energy-dispersive X-ray attachment. of todorokite, birnessite, buserite, quartz, and orthoclase.