Modification of complex recycling slags

In addition to the main product, the pyrometallurgical production of metals also produces unavoidable by-products such as slags or dust. These often still contain high residual contents of metals. However, as in most cases it is nether ecologically nor economically viable to recover these, the majority of them are sent to landfill. In addition to the high costs for companies due to transport and landfill costs, this can also cause negative effects on the environment. Possible environmentally harmful compounds, e.g. heavy metal oxides, can be released into the environment through uncontrolled leaching reactions, with unpredictable consequences. For these reasons, this PhD-thesis focuses on the possible demobilisation of environmentally harmful compounds and the utilisation of slags from the lead industry for other sectors. By modifying the still liquid slags with various cost-effective additives, an attempt is made to reduce the leachability of the oxides of lead, zinc and barium in such a way that they can be used in construction industry without impairing the environment or the mechanical properties of the end products. Due to the low cementitious properties of these slags, the aim was to use them as a substitute for sand. The tests carried out for this purpose show that an appropriate modification by adding slag formers, in particular CaO and Al2O3, can result in a significant reduction in the leaching values of lead, zinc and barium. The pH-value of the leaching medium and the existing morphology play a major role here. As leaching of the heavy metals into the mortars cannot be completely avoided, care must be taken to limit the degree of substitution. The corresponding heavy metal ions delay the curing reaction of the Portland cement, which can result in a shortfall in the legally prescribed minimum strengths. Due to legal regulations, it is not yet possible to use slags from the lead industry as a substitute material in the construction industry. On the one hand, these determine a maximum leaching value, which the mixtures produced fall below, in some cases significantly. On the other hand, a maximum concentration is also defined in the input materials, which exceeds the existing residual materials by a factor of more than 100. This had the benefit of making it easier for producers of building materials to integrate recycled materials into the manufacturing process. In times of raw material scarcity and climate change, however, it is necessary to re-evaluate this aspect.