Weathering of metallurgical slag heaps: multi-experimental approach of the chemical behaviours of lead and zinc

摘要

The production of lead and zinc in the Lead Blast Furnaces of metallurgical factories produces a huge amount of slags. These slags are a Pb-Zn-rich vitreous material with a CaO-SiO_2-FeO-rich glass matrix containing metallic lead droplets and Fe oxides. The resulting slag heap is exposed to weathering and can be a source of chemical pollution. In this study, different experiments allow the study of the behaviour of Zn and Pb during the weathering of slags. First, a Teflon leaching column (ascending flux) equipped with samplers in order to collect the fluid inside and at the outlet of the column was used. The second experiment was a pure water flow on a polished section of slag. The third system was an outdoor experiment where the slag was exposed to natural weathering comparable to the heap. ICP-AES and ESEM-EDS have been used to follow the evolution of the water chemistry and the slag compositions and textures during the experiments. Two episodes of Pb and Zn releases were noticed at the column outlet. A first brief episode might be caused by some colloids or slag dust releases. The second episode essentially results from glass and metallic lead dissolution. Hydrocerusite locally appeared in the column. Investigations carried out on the polished sections show complex alteration patterns. They suggest that the behaviour of the glass and of minor phases is closely linked to the local structure and composition at the slag surface. Outdoor experiments show slower kinetics than in the other experiments, but the alteration type is similar despite some differences.