Sub-project 4:

Kinetics of leaching processes on natural and synthetic lead-zink-ores and related ore-minerals

May 1ˢᵗ 2013 – June 30th 2018
Responsible professor and other scientist:
Students on the project:
B.Sc. Antonia Korda
Aim of sub-project:
The aim of the sub-project is the development of a better understanding and clarification of the primary mechanisms of natural weathering and the controlled microbial leaching of sulphides, in particular the mineral sphalerite (ZnS). Aspects of the kinetics (weathering or leaching rates) will be investigated in the implementation of dissolution experiments. These experiments will be done with real samples preferably from the Erzgebirge and also synthetic samples with chemically - mineralogically pure mineral phases and with doping minor and trace elements for example rare elements such as indium.
Ongoing work and results:
Dissolution experiments were employed to investigate the leaching kinetics of polished cross sections of Indium-bearing sphalerite. Chemical and biological leaching experiments gave similar results and indicate a new stability sequence. The size of triangular etch pits varies with iron content in solution pointing towards different leaching kinetics. An increasing redox potential and decreasing pH-value indicated microbiological activity in biotic approaches.
For a better understanding of the complex leaching behaviour, dissolution experiments require a reference material of high availability with a reproducible composition and homogeneity. Commercially offered ZnS is unsuitable as reference material and homogeneous natural ZnS is very rare. Four different methods were used to produce a synthetic, doped sphalerite: 1) tempering in a furnace, 2) chemical transport reaction, 3) spark plasma sintering and 4) high-pressure-high-temperature (HPHT) treatment. The comparison of the different synthesis methods show that only during the HPHT treatment defect-free and additionally homogeneously doped sphalerite was synthesized. This material is planned to be used as reference material for geochemical analysis and to calibrate microbiological leaching experiments.
Publications from sub-project:
J. Heinrich, M. Schwarz, G. Heide, Z. Kristallogr. Supplement 36 (2016)
Student theses related to sub-project:
  • Bachelor Thesis A. Korda (2016): Research of chemical and biotic leaching on ore mineral cross sections from the polymetallic “kb” ore-type, Wilhelm Stehender Nord, Freiberg District, Germany
  • Bachelor Thesis B. Bethge, R. Häckh (2015): Sequential extraction on tailing material from El Toqui mine, Chile.
Possible additional student projects:
­Literature cited:
  • Baacke, D. 2000. Geochemisches Verhalten umweltrelevanter Elemente in stillgelegten Polysulfiderzgruben am Beispiel der Grube „Himmelfahrt“ in Freiberg/Sachsen. Dissertation TU Bergakademie Freiberg.
  • Heidel, C. 2011. Sulphide oxidation investigations on oxygen and sulphur isotopes. Dissertation TU Bergakademie Freiberg.
  • Klemm, W., Schlothauer, T. 2007. Mineralogisch-geochemische Untersuchungen zur Arsen-Schlema-Alberoda unter besonderer Berücksichtigung der Oxydationsprodukte. Forschungsbericht im Auftrag der Wismut GmbH, TU Bergakademie Freiberg.
  • Alpers, C. N., Blowes, D. W. 1994. Environmental geochemistry of sulfide oxidation. American Chemical Society Series.
  • Etzel, K., Huber, H., Rachel, R., Schmalz, G., Thomm, M., Depmeier, W. 2007. Pyrite surface alteration of synthetic single crystals as effect of microbial activity and crystallographic orientation. Advanced Materials Research: 20-21, 350-353.
  • Acero, P. Cama, J., Ayora, C. 2007. Sphalerite dissolution kinetics in acidic environment. Applied Geochemistry: 22, 1872-1883