Calcination of Sulfidic Tailings

Abstrakt

Metals play a fundamental role in modern society. However, large quantities of tailings are produced during their extraction. Some of these tailings contain large amounts of sulfides and heavy metals, which make their disposal challenging.
Nowadays, tailings are mainly deposited in tailings dams. These dams, can have a significant impact on local ecosystems, as they often lead to «acid main drainage» (ACM), contaminated groundwater due to heavy metals or even to catastrophic dam failures. Furthermore, tailings management is very costly. Based on these circumstances, this thesis tries to valorise the tailings of Neves-Corvo and to find an application for their reuse in order to reduce their environmental impact. In particular, it is investigated whether the calcination of tailings and the co-calcination of a mix of, tailings and calcium hydroxide (Ca(OH)2), can increase the activity of the minerals allowing to use them as supplementary cementitious material (SCM). Additionally, the eciency of the two mentioned processes in oxidising pyrite is investigated. The pyrite content is important as it can lead to major durability problems in concrete and the tailings investigated here have a very high pyrite content.
The results of X-ray powder diffraction (XRD), thermogravimetric analysis (TGA) and uniaxial compressive strength measurements, lead to the conclusion that the investigated tailings are not suitable for SCM. This is due in particular to the increased risk of durability problems in concrete or to the large SO2 emissions generated. Nevertheless, the use of co-calcination proved to be very promising for tailings with a lower proportion of pyrite and should be further investigated.