## 4 Results
### Campaigns with Industrial Residues in a Muffle Furrace  
The calculated valex values in Figure 6a,b show that MgCl\({}_{2}\)-6H\({}_{2}\)O is the most effective chlorination agent for jarosite and calcined jarosite at the base chlorine addition factor. For all reaction systems, the yield is increased with rising temperature; when using FeCl\({}_{3}\)-6H\({}_{2}\)O, it appears to be significantly increased by higher rates in the mixture (except for calcined jarosite at 900 \({}^{\circ}\)C). AlCl\({}_{3}\)-6H\({}_{2}\)O shows the poorest outcome with very low valex values of slightly over 0.3 for the base chlorine addition. For goethite and calcined goethite (Figure 6c,d), the valex values are generally higher and less diverse with base chlorine addition; trials at 1100 \({}^{\circ}\)C again deliver better results compared to those at 900 \({}^{\circ}\)C. Yields are increased to over 90% when tripling the base addition of FeCl\({}_{3}\)-6H\({}_{2}\)O for both residues. In mixtures with MgCl\({}_{2}\)-6H\({}_{2}\)O, the multimetal recovery is higher when doubling the chlorineFigure 7 shows the individual extraction rates of the elements in trials at 1100 \({}^{\circ}\)C. Every column is dedicated to a certain addition rate of the chloride (2 Mg being the two-fold of MgCl\({}_{2}\)-6H\({}_{2}\)O e.g.). Some elements such as gold and bismuth are generally very easily extracted by both MgCl\({}_{2}\)-6H\({}_{2}\)O and FeCl\({}_{3}\)-6H\({}_{2}\)O. Indium, zinc, and lead are preferably extracted in the presence of MgCl\({}_{2}\)-6H\({}_{2}\)O from all investigated residues. Silver is hard to extract from jarosite as well as calcined jarosite, but high yields are achieved with all three chlorides from goethite. Tin is almost entirely extractable with higher additions of FeCl\({}_{3}\)-6H\({}_{2}\)O from jarosite.  
Nickel extraction (Figure 8a) via chlorination from original nickel jarosite is generally low with 35% being the highest yield when using the base addition of MgCl\({}_{2}\)-6H\({}_{2}\)O at 1100 \({}^{\circ}\)C and 38% for the three-fold rate in the mixture. The valex values when using FeCl\({}_{3}\)-6H\({}_{2}\)O are significantly increased by higher additions from 7% (base) to 32% at the three-fold base addition in the mixture. AlCl\({}_{3}\)-6H\({}_{2}\)O reveals poor results with extraction rates of up to 18%. Extraction rates from calcined materials (Figure 8b) are lower with values of 24% and 27% for two-fold and three-fold MgCl\({}_{2}\)-6H\({}_{2}\)O addition.  
For all given trials, the extraction rates of iron and chlorine were furthermore calculated. Iron extraction is fluctuating whereby it is higher for trials with goethite materials. The average iron extraction over all trials is 15%. Hereby, the selective chlorination of the valuable elements is confirmed. As the chlorination of iron results in the generation of FeCl\({}_{3}\), which was proven to be an effective reaction agent, it is not interpreted to have a negative impact on the process performance.  
In general, chlorine is entirely removed for most trials. However, for experiments with MgCl\({}_{2}\), it was observed that significant amounts remained in the material, especially for  
Figure 6: Calculated valex values of trials with precipitation residues from the zinc industry at 900 and 1100 \({}^{\circ}\)C. (**a**) Jarosite; (**b**) Jarosite calcined; (**c**) Goethite; (**d**) Goethite calcined.  
trials with jarosite and calcined jarosite from the zinc industry. When treating nickel jarosite (both original and calcined), chlorine was removed entirely in all trials.