A New In Situ Method to Analyze Mineral Particle Reactions in Soils

Abstract

We developed a simple method to monitorthe transformation of particles in soils under in situ conditions. The particles were fixed on small polymer supports (2 cm x 2 cm) with a thin film of epoxy resin. Attached to these carriers, the particles could be put into close contact with soil at a chosen site and easily recovered after extended periods of time. The method was tested with lead oxide and copper concentrate in the field. Quartz and copper oxide particles were used in preliminary laboratory experiments. The used particles sizes ranged from 20 to 200 microm. Laboratory and field experiments with acidic and calcareous soils showed that the PbO and Cu concentrate coated polymer supports were stable under field conditions for at least one year. Nondestructive X-ray fluorescence spectroscopy was used to quantify the metals before and after exposure. Scanning electron microscopy combined with energy-dispersive X-ray spectroscopy as well as micro-Raman spectroscopy was used to identify signs of dissolution and newly formed mineral phases. The mineral dissolution rate could be determined under field conditions. The new method has the potential to be used in other environmental media such as sediments or water to study the reactions of a variety of particles larger than 20 microm.

Bacteria-mediated reduction of As(V)-doped lepidocrocite in a flooded soil sample

“…Until recently, it was still a challenge to study the processes involved in bioreduction directly in soils despite a large set of experimental studies (Jorgensen and Willems, 1987;Voegelin et al, 2002;Jenkinson and Franzmeier, 2006). However, Fakih et al (2008) developed a method inspired from Birkefeld et al (2005) to monitor the transformation of Feoxides directly within soils and to quantify their reductive dissolution. Iron oxides are precipitated onto acrylic slides, which can be directly inserted into the soil.…”

Raman spectroscopy speciation of natural and anthropogenic solid phases in river and estuarine sediments with appreciable amount of clay and organic matter

“…Raman spectroscopy has been used, alone or with other analytical techniques, by some authors to search for small quantities of pyrite and amorphous iron sulfide(s) 9 or metal sulfides in anoxic sediments of the Seine estuary (northern France), 10 to analyse mineral particle reactions in soils, 11 to look for different classes of compounds on igneous sediments from a perennially ice-covered lake, including sediments from surface and bottom oxic and anoxic zones, as analogues of Mars paleolake environments 12 and to characterize metallic contaminants through the analysis of heavy particles separated from the stream, canal and estuarine sediments. 13 All these works have in common the absence of clay in the solid phases or the use of pre-treatment protocols to avoid the interference of clays.…”

The biogeochemistry of marine particulate trace metals

“…Incubation slides were designed after (Birkefeld et al, 2005), who immobilized a range of inorganic mineral particulates in epoxy resin (c.f. their Figs.…”

“…The spray pattern was no larger than the chamber aperture, indicating most, if not all, mineral sprayed had impacted the slide/epoxy surface. Microscopic imaging of the slide surfaces showed some finer particles were buried (inaccessible) beneath the epoxy resin, though most retained a slight (10-50%) surface exposure to the environment as in (Birkefeld et al, 2005). Epoxy was allowed to set for 3 days in a HEPA-filtered environment.…”

“…We synthesized two particulate mineral phases that were >96% 57 Fe:ferrihydrite, an Fe 3 oxy-hydroxide chosen to be reflective of poorlycrystalline suspended Fe(III) oxides commonly found in marine particle assemblages and the early authigenic phase formed after precipitation of dissolved Fe in oxygenated seawater; andfayalite, an Fe 2 + silicate chosen to be reflective of primary lithogenic silicates. Through immobilization of these phases onto acrylic slides after (Birkefeld 2005) and bottle incubation of the slides in iron-limited, whole seawater surface communities for 12-14d, we sought to ascertain whether biotic communities incorporated 57 Fe from source minerals into biomass via any combination of abiotic or biotic processes. 57 Fe-fayalite ( 57 Fe2SiO4) was prepared by petrogenic reduction of s 7 Fe 2 O 3 in the presence of quartz (Si0 2 ).…”