Studio di processi mineralurgici per il trattamento di residui da attività minerarie

Mining is one of the main industrial activities that has the greatest impact on the territory, both in terms of the major changes made to the morphology of the landscape and the pollution caused by the not always correct management of waste, reflecting on the quality of human health and ecosystems. The legacy left by the mining activity means a precious historical and cultural heritage to be safeguarded and mostly to be enhanced, through the recovery and reconversion of abandoned mining areas. The environmental issue linked to neglected sites stands for an emergency that finds multiple examples all over the world and whose serious negative effects are documented. In the mining sector, as in other industrial branches, the most effective intervention from the environmental point of view is the reuse of polluting waste; better if within the same area, and better if the reuse improves the landscape value and strengthens the testimony of the past industrial activity. In this context, the research aims to evaluate the applicability of flotation as a remediation technique by which declassify the waste, reducing the concentration of heavy metals. The applications presented refer to two types of materials: on the one hand, the Pb and Zn flotation tailings present in the Montevecchio Levante area, which represent the most important type of waste in the mining district of Sardinia, and on the other hand, the marine sediments of the industrial harbour of Portovesme, whose dredging is hindered by the presence of a layer of sediments contaminated by mining-metallurgical wastes. The objectives of the research, partly common to the two materials, were as follows. In the case of treatment of tailings: to verify the persistence of flotation conditions by a material already waste coming from the same process and at low concentration; research into the best treatment route (phases and reagent adjustments) for the purpose of achieving a final standard waste and a commercial concentrate; search for the best treatment route (including the possibility of recirculation of middlings) in order to reduce the inevitable presence of product; comparison of treatment flowsheet in the light of the products that can be obtained and the complexity of the process (simplicity of the process, as well as reducing investment and operating costs, benefits higher productivity). In the case of marine port sediments: to verify the flotability of the materials subjected to the combined sulphide-oxidised mineralurgical process; research of the best conditions for the environmental compatibility of the plant by simplifying the flowsheet and eliminating the phase using organic compounds. Finally, the work shows how the different purpose of application, decontamination associated or not with the production of a commercial product, conditions the structure of the treatment process.