From 11th to 13th February, the SULTAN program Kick-off meeting was held in Leuven, where all partners and early stage researchers (ESRs) had the opportunity to meet each other and share information about the different work packages and the state of the research. On the third day, the ESRs were invited to visit the labs in the geology and chemistry buildings at KU Leuven.
KU LEUVEN GEO-INSTITUTE VISIT
The visit to the geology building started with a brief introduction of the type of mineralization found in Pb-Zn deposits such as Plombières. It was possible to observe the transition between the different types of rocks, finding first a banded primary ore consisting of a core of greyish galena (lead sulfide) and brownish sphalerite (zinc sulfide). The sphalerite varies from pale brown to dark brown, depending on the iron content, with a rhythmic banding. It is important to mention that these kinds of processes are formed at a depth of 1 – 3 km in the crust (by hot fluids). The primary ores were then brecciated and altered to form Calamine ores (hemimorphite, hydrozincite, and smithsonite) which were exploited in Belgium.
The Plombières tailings facility was built from tailings of the historical Pb-Zn mining and smelting in East Belgium, of ores like those shown above. It was shown that the stratigraphy of the tailing’s facility at Plombierès consists of, from the bottom to the top, green to gray clay, clay with millimeter-scale brick fragments and roots, brown clay with red brick fragments, greenish granular sand with brick fragments, limonite sand with grey galenite and green sand with few roots and millimeter-scale brick fragments. Lead and zinc are distributed variably throughout most of these layers, and some Germanium have been locally found.
Following this, one of the ESRs Srećko Bevandić, who is based at KU Leuven and working on the Plombierès tailings facility, demonstrated the methodology that he uses to prepare samples for particle size analysis. This method is called the Jackson method, and the steps are explained in the chart below:
|Jackson treatment (Modify version)|
|1st step (Carbonates)||2nd step (Organic matter)||3rd step (Fe-oxide)|
|6 g of sample + 70 ml Na acetate||Residue from sample + 50 ml Na acetate + 6 ml of H2O2||Residue from sample + 45 ml Na citrate|
|Leave it overnight or min. 12 h||Heat sample at 70°C and add 6 ml of H2O2||Heat sample at 75-80°C and mix it slowly|
|Add 70 ml of Na acetate||Add H2O2 until oxidation of organic matter stops||Add 1 g of Na dithionite after 5 min again and repeat that 3 times|
|Put in a sonic bath for 5 min||Heat samples at 70°C for 3 h don’t mix||Heat samples for 15 min|
|Heat and mix sample at 70-80°C for 30 min||Centrifuge sample at 2000 rpm||Centrifuge sample at 2000 rpm|
|Centrifuge sample at 2000 rpm||Pour out H2O2 from the beaker and add water||Pour out a mixture of solution from the beaker and add water|
|Pour out Na acetate from the beaker and add water||Centrifuge and pour out water||Centrifuge and pour out water|
|Centrifuge and pour out water|
For the particle size distribution to be accurately determined, the samples must first be prepared by using the Jackson treatment. Briefly described, this preparation involves breaking down aggregated or flocculated clay particles, which would cause an over-estimation of particle size. These aggregates are cemented by carbonates after deposition, so firstly the carbonates must be dissolved (Step 1). Organic material is then removed (step 2) and a combination of agitation and reagents are used for the Fe oxides removal (step 3). After the sample is dried, it can be measured to provide an accurate particle size distribution.
The third and final stage of the visit to the Geo-Instituut led us to the laboratory where we were taught about the technique for analyzing Particle Size Distribution of the samples. This is used to determine the fractions of different components, such as sand, silt and clay, whose particle sizes differ. The particle size distribution was measured with a laser diffraction particle analyzer. The particles are passed in front of a laser, which is diffracted by the path of the particle. A smaller particle will diffract the laser at a lower angle than a larger particle. The diffracted laser is measured with detectors to determine the diffraction angle and therefore estimate the particle size. This relies on the assumption that the particles are spherical and not agglomerated.
To sum up, we covered topics from the original Pb-Zn ore, to Calamine ore, to the mining, processing and smelting of the ore, to the Plombières tailings, and to the methods for determining the particle sizes of the material left in the Plombières tailings. Overall, this provided a brief yet well-packed exposure to aspects of geology and chemistry, particularly ones which may be helpful throughout the SULTAN project.
Authors: Ana Luiza, He Niu, Panagiotis, Raka, Srecko, Rosie, Alexandra