TREATMENT OF MINERAL-METALLURGICAL RESIDUES FOR THE RECOVERY OF USEFUL SPECIES AND THE REUSE OF PROCESS WASTE

Millions of tons of mining waste now represent a huge ecological challenge, perhaps also an economic opportunity. This paper illustrates and discusses an innovative approach in the reclamation of old mining areas, which is inspired by the principle of circular economy and considers the waste from old mining and mineral processing activities as potential secondary raw materials.The research proposes to apply the technique of flotation to extract from solid mining residues fractions of useful but polluting species, obtaining the double result of downgrading the material below the CSC (Contamination Threshold Concentration) and extracting a concentrate with commercial characteristics. The materials of potential interest are those of which the dumps from the cultivation and processing of the ores of Pb and Zn are composed. The establishment of the Centre of Excellence for Environmental Sustainability (CESA) has enabled an experimental activity based on the treatment of various mining residues in the Sulcis Iglesiente Guspinese area. The results obtained appear to be important in terms of both technological feasibility and costs compared to those of a Permanent Safety Deposit [1] [2]. The project has been developed, with reference to a pilot basin; the studies carried out so far have concerned samples taken from the Montevecchio Levante mud basin on which batch flotation tests were carried out for the reconstruction of a two-section plant flowsheet, one for the recovery of Zn sulphide and the second for the separation of the oxidized fraction from the final waste. Starting from feed concentrations around 2% Zinc, three products were obtained: a commercial Zn sulphide concentrate with 50% content; a final waste with heavy metal concentrations (Zn and Pb) lower than the CSC for industrial sites; and an intermediate concentrate (not marketable) whose residual Pb and Zn content requires inerting or disposal in a collection site. The collaboration with the Geological Survey of Finland (GTK), Europe's leading competence center for the evaluation and sustainable use of geological resources, has allowed the realization of a project aimed at the implementation of high quality data that have highlighted important characteristics of mineralogical composition of the treated material.