Characterisation and Metallurgical Treatment of Jarosite Residues from Zinc and Platinum Production
Research output: Thesis › Doctoral Thesis
Metallurgical by-products are often regarded as waste ending up in dumps, even though they may bear considerable amounts of different valuable metals. This does not only cause potential value losses, but also increasing problems of landfilling due to stringent environmental regulations. Adapting or developing processes which allow the treatment of such residues requires detailed knowledge of all properties concerning the material and its components. This study deals with the characterisation of hydrometallurgical by-products out of zinc and platinum production (jarosite) and the development of a characterisation procedure for similar materials. By-products of different zinc smelters were investigated. These are usually mixtures of residues from various process steps. The main part of the residue is the precipitation product, consisting of jarosite group minerals [(K,Na,NH4)Fe3+3(SO4)2(OH)6]. Referring to this main component, the whole material is commonly called “jarosite” as well. Furthermore, a similar residue from platinum production was investigated. Many different analytical methods were tested on these residues for their applicability. Starting with sample preparation and chemical bulk analysis, electron beam methods and the determination of the mineralogical composition were in focus. Identification of valuable phases was of prime importance. Thereby, the limits and benefits of different methods were demonstrated. In close cooperation with the research fields “nonferrous metallurgy” and “mineral processing,” numerous experimental trials were performed. The (intermediate-) products generated were also characterised in detail for process optimisation. The jarosite residue from zinc production contains various valuable metals, with zinc (2.2-6.6 %), lead (4.0-7.1 %) and silver (80-219 ppm) being the most important. Copper is commonly around several tenths of a per cent and therefore only of minor importance. Gold concentrations around 1 ppm are due to its heterogeneous distribution (nugget effect). The small grain size is a challenge for mineralogical characterisation. Grain size analyses showed a distribution of 90 % <30 µm and 57 % <10 µm for the jarosite from zinc production and 100 % <40 µm and 45 % <10 µm for the jarosite from platinum production, respectively. Jarosite group minerals comprise a main value-bearing phase in the residue from zinc production, as they often contain several per cent of both lead and zinc. Further phases containing considerable amounts of these metals are zinc ferrite (franklinite), sphalerite, galena, anglesite and litharge. Silver appears mainly associated with copper as inclusions in quartz, feldspar and sphalerite particles. The jarosite residue from zinc production was successfully treated in pyrometallurgical trials in order to produce a slag (low content of heavy metals), a Pb, Ag, Cu, Au- containing metal alloy and an off-gas that contains zinc as zinc oxide. The slag was successfully tested for replacing natural sand in concrete. The jarosite residue from platinum production is simpler in its mineralogical composition, as it is only a precipitation product and not a mixture of different residues like the jarosite from zinc production. Nickel is the only valuable element (3.7-8.4 %). This material was treated in the same pyrometallurgical process as the jarosite from zinc production. These trials were also successful. The metal alloy in this case consisted of Fe and Ni. Intermediate and final products of all trials were characterised for process optimisation. With the insights from the extensive characterisation of these residues, a characterisation procedure for such and similar materials was defined. Such a procedure is of major importance to evaluate the chemical and especially the mineralogical composition of unknown materials in the forefront of a possible (metallurgical) treatment.
|Translated title of the contribution||Charakterisierung und metallurgische Verwertung von Jarositrückständen aus der Zink- und Platinproduktion|
|Publication status||Published - 2020|