EP5 - Mobile Mixed Phases


Aims

Nanoparticulate natural mineralorganic mixed phases, composed of minerals like e.g. secondary oxihydroxides, carbonates, clay minerals, as well as organic components, which are present in natural systems are commonly known as natural colloids. Because of small size, between 1 and 1000 nm, the Brownian movements prevent the sedimentation of these particles, making them mostly mobile. That is why mobile colloids can be used as tracer of specific aquifers to find out the genesis of groundwater and which stratigraphic entities have it flowed through. The idea behind it is that via particles created through chemical erosion of mineral phases or reshaped into secondary mineralization (e.g. clay minerals, iron-, aluminum- and manganese oxides) and together with non-dissolved organic residuals can be used as tracer for specific stratigraphic entities. The goal is to verify and characterize mobile colloids in form of singular particles or small aggregates found in different groundwater samples.

Working area

The natural samples are from:

  • Scientific borehole, Erfurt
  • Hainich, close to Kammerforst
  • Tannroda Saddle, around Bad Berka

Methods

Mobile mixed phases have to be extracted from groundwater samples to be able to characterize their structure, morphology and chemistry. We use filtration method through silver filters to collect colloidal particles and then scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) to characterize them. To verify the place of origin of captured on silver filters particles the drill core material from filtered range is used. Three separate fractions of the drill core material are analyzed using x-ray powder diffraction (XRD) and fourier transformed infrared (FTIR) spectroscopy. The first fraction corresponds to the original material, the second fraction is composed of non-dissolved residual material and the third fraction is composed of secondary minerals, which have been enriched on open gap areas. For the first and second fractions are used only areas of the drill core, which are free from microscopic cracks, gaps and erosion symptoms.

Results

We have found that especially aggregates from the silicate rich material, most likely clay minerals, are present on the silver filters (Fig.1a). The EDX analysis shows that these silicates are very magnesium rich. Besides magnesium rich silicates we have found small amounts of nanocrystals of iron oxides (Fig.1b) and aluminum oxides (Fig.1c). The structural characterization of unweathered Trochitenkalk material (fraction 1) showed that calcite is the main component of it. Minor quantities of quartz und dolomite were measured. These results are congruent with EDX analysis of the same material, which is mostly composed of calcium carbonates. Because of high amount of calcite in unweathered Trochitenkalk material, we were unable to make any assumptions about mobile colloids in this fraction. The second fraction of non-dissolved residual material was composed mostly of quartz, feldspar and clay minerals. These particles correspond in size, shape und chemical composition to particles found in groundwater samples on silver filters. To characterize secondary minerals material for third fraction was prepared from gap areas of drill core without any chemical preparation. All results show, that all nanoparticles of iron oxides from gap areas can be transported with groundwater in colloidal form, which is confirmed by presence of morphologically similar rion oxides on silver filters.

Figure1_EP5

Figure 1: SEM pictures and corresponding EDX spectra of a) silicates/clay minerals, b) iron oxides and c) aluminum oxides, which were present after filtration of groundwater from Trochitenkalk aquifer on silver filters.

Team

Members of the Team EP5 you will find here.