Valorization of Sulphidic Mine Tailings as Artificial Aggregate: Implementation in Cement-Based Materials

Abstract

Mine tailings are significant environmental liabilities worldwide. This adds up to the increasing depletion of non-renewable resources for use as construction materials. Valorization of such wastes as secondary raw materials is an effective environmental-friendly strategy. This paper presents an investigation on the valorization of low-grade sulphidic mining waste in the shape of cold-granulated artificial aggregates. The study was carried out in the framework of the NEMO project (EU Framework Programme Horizon 2020, Grant Agreement No 776846). Results reveal the efficient immobilization of heavy metals in addition to the possibility of partial replacement of aggregates in mortar mixes. The optimized granulation process, based on intensive mixing with minimal contents of cement as binder, was demonstrated in pilot production, and the artificial aggregate in sizes 0–4 mm and 0–10 mm was afterwards implemented in mortar mixes at replacement ratios of 17 and 32% of natural aggregate. Limited affectation of compressive strength and workability by the substitution with secondary aggregate was resolved through optimization of the superplasticizer dosage. The hydrated cement contained in the granules demonstrated no perceptible interference with the fluidifying action of the superplasticizer. The results reveal that despite their porous nature the granules are feasible to be used in non-structural or low-grade cement-based mixes. A notable contribution is therefore made for the valorization of the mine tailings as artificial granules with a comparable cement consumption to that required in landfilling.