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Lehrstuhl für Geologie und Lagerstättenlehre

Characterisation of by-products of the Metal producing Industry

Gustav Hanke

 

Introduction

Every day, large amounts of by-products of the metal processing industries are dumped as waste. Due to the lack of suitable processing techniques these dumps still contain high concentrations of precious and critical metals. In connection with the ever growing demand on raw materials and the ubiquitous search for deposits, these dumps become increasingly important as secondary deposits. Besides the continuously formed residues, there is also a high number of ancient dumps from mining, processing and metallurgical activities. These commonly contain an even higher amount of various metals because of less developed processing methods of the past.

One main field of research are jarosite dumps of the zinc producing industry. Today the major part of the world’s zinc output is produced through the conventional hydrometallurgical route. Jarosite dumps are formed as a precipitation residue after leaching processes. The mineral jarosite proper, an iron sulphate (KFe3+3(OH)6(SO4)2), is of lower importance than other phases that occur in these dumps. The precipitation residue theoretically consists of jarosite and gypsum, but is usually dumped together with the leaching residue; this significantly increases the amount of precious metals. Scanning-electron-microscopic investigation and chemical analysis of various jarosite dumps show variable concentrations of Fe (<20 wt. %), Zn (< 7 wt. %) and Pb (<6 wt. %), as well as considerable amounts of copper, nickel, gallium, germanium, indium, gold and silver. As jarosite dumps have to be treated as hazardous waste, the advantage of the reprocessing is not only the production of metals, but also a decrease of the total waste tonnage, respectively a transformation of the waste to a less problematic material.

Additionally many other residues, like slags and dusts are also of interest and will be part of further research.

Aims

Detailed mineralogical and chemical characterisation is of importance to develop appropriate mineral processing recipes and methods to recover the metals of interest. The following questions need to be answered:

- Which particles contain the metals of interest?

- What is the concentration of the metals in these particles?

- What is the morphology and grain size of the particles?

- What are the intergrowth relationships?

Due to the small grain sizes of the material (<10 µm) the optical characterisation and quantification is difficult, even when using a scanning electron microscope.

The development of a characterisation receipt for a systematic and partly automatic characterisation, suitable for different by-products, is the final aim of the research.

Close cooperation with other institutes and industrial partners allows a practical research at the end of which a method will be developed that allows a fast and reliable characterisation of different processing- and mine wastes. The emerging knowledge of the properties of the material will allow adjusting the processing methods and will subsequently convert dumps to new deposits.

 

 

SEM-image of a typical jarosite sample.