Trace element accumulation in Mn—Fe—oxide nodules of a planosolic horizon

Abstract

The aim of this work was to determine the importance of nodule formation on the dynamics of major and trace elements (TEs) along a Planosol toposequence developed in metamorphic parent material at La Châtre (Massif Central, France). The different horizons were sampled within three pits and analysed for major and trace element contents. The nodule-rich horizon was studied more closely. A simplified sequential extraction scheme, X-ray diffraction (XRD) and microscopic approaches were used in order to determine the individual phases containing TE in nodules.Along the slope, the nodule-rich horizon varies in thickness, is composed of different oxide fractions and has different scavenging efficiencies according to the TE considered. Iron was found to accumulate in the middle of the slope, while Mn accumulated at the base. The scavenging effect is only evident for Ni in profile 1. For Fe and Cu, it is maximal in profile 2 where the nodule-rich horizon is the thickest. For Pb and Mn, maximal scavenging effect is recorded for both profiles 2 and 3, in the lowest part of the slope. Cr is not accumulated at all. This was related to the water dynamic and the hydromorphic conditions prevailing along the slope.Results obtained by sequential extractions and associated X-ray diffraction on the different nodule size fractions and those obtained by electron microprobe allow inference of the TE distribution in nodules. Nodules were mainly composed of three to four types of cements surrounding grains of quartz, feldspars, micas and accessory minerals: iron-rich cements, Si-and Al-rich cements, Mn-rich cements and Ti-rich cements in places.The iron-rich cements consist of poorly crystalline goethite and possibly some ferrihydrite. Ferrihydrite is associated with Cr as demonstrated by extractions. Goethite contained Mn and most of the TE extracted except for Ni and Pb.Fine-grained Si-and Al-rich cements were also observed. They contain variable amounts of Ti and Mn. 0016-7061/$ -see front matter D Geoderma 125 (2005) 11 -24 www.elsevier.com/locate/geodermaMn-rich cements were not present in all the nodules and were mainly linked to the dark zones of the nodules. The nature of these Mn oxides could not be determined. They were found to contain Co, Ni, Cu and probably Pb. D

Mobility of major-, minor- and trace elements in solutions of a planosolic soil: Distribution and controlling factors

“…1b). The gravelly and concretion-rich horizon below comprises concretions which are mainly composed of several types of cements (Fe-rich, Si-and Al-rich, Mn-rich and Ti-rich) surrounding grains of quartz, feldspars, micas and accessory minerals (Salvador-Blanes, 2002;Cornu et al, 2005) …”

Enrichment of trace elements in ferromanganese concretions from terra rossa and their potential desorption

“…Lead Childs (1975) and Rankin and Childs (1987) pointed to higher concentrations of Pb in FMCs than in the corresponding surrounding soil materials. Cornu et al (2005) found that accumulation of Pb in the ferromanganese nodules was due to the high specific adsorption of Pb by the Mn oxides. In contrast, Palumbo et al (2001) reported that Pb appeared to be associated with the Fe-rich phase…”

“…Mn and Fe are important elements for plant and animal nutrition (Liu et al, 2002). In addition, oxides and/or hydroxides of both Mn and Fe are the main Mn-Fe phases in the soils, and they often act as strong scavengers of trace elements during weathering and pedogenesis (Burns, 1976;McKenzie, 1980;Bellanca et et al, 1985;Latrille et al, 2001;Liu et al, 2002;Cornu et al, 2005), few have focused on the distribution of trace elements in FMCs at different depths in the soil profile (Feng, 2010(Feng, , 2011. There is also a lack of information both on the direct quantitative relationship between MnFe phases and trace elements, and on the comparative capacities of the Mn-and Fe-phases to retain trace elements in FMCs at different depths and in various pedoenvironments (Chao and Theobald, 1976).…”

Distribution, geochemical fractionation and sorption of Cu and Pb in soils characteristic of Hungary

“…This fraction is primarily expected to dissolve soil iron oxides, and the high affinity of trace metal to these phases in soils is a well-known phenomenon (e.g. Cornu et al 2005). Both metals show similar reducible ratios for both soil groups: 7.7 ± 6.8% and 10.5 ± 10.2% for Cu, and 28.9 ± 12.4% and 29.9 ± 9.6% for Pb in the Luvisols and non-Luvisols, respectively.…”

“…On the other hand, both Cu and Pb were also found to be of high affinity to soil iron oxides. However, Cornu et al (2005) found that metals forming stable hydroxide and carbonate complexes are preferentially bound to the (slightly) positively charged iron oxide surfaces. As Pb is much more able to form such complexes (hydroxide complexes in the acid Luvisol and carbonate ones in the alkaline non-Luvisol environments) than Cu, its higher affinity to iron oxides in the studied soils is expected.…”