Abstract
Abstract Tailings storage facilities are disposal systems for storing the waste products of the mining industry consisting of a slurry mixture made of soil, rock and water that remain after the mineral values have been removed from the patent ore. Tailings dams are supposed to last forever, so after their deposition, tailings can experience aging processes with physical and chemical changes depending on the interactions between local conditions and source mineralogy. The consequences of these aging processes are increased interlocking of particles and oxidation processes, sometimes making previously safely held contaminants available and mobile. Among the long-term aging processes, the natural ionizing radiation (from radioactive isotopes of the soils, cosmic rays, and also ultraviolet rays from the sun) can be considered, as proposed in the current research. Furthermore, in many countries, tailings are beginning to be re-used as backfill, landscaping material or feedstock for cement and concrete. So if any, the long-term physical and chemical modifications could affect the hydraulic and mechanical behaviour of tailings with relevant economic consequences. For these reasons, wet and dry silty samples of tailings spilled out after the failure of the Stava tailings dam (Trentino Alto Adige, Italy) were exposed to gamma rays, as an accelerated aging technique to simulate the natural ionizing radiation, and then characterized. The modifications on physical and chemical properties were observed and, despite certain chemical stability, some physical changes were observed, particularly in terms of size particle distribution, inner porosity of the particles and specific surface.
Highlights
Tailing dams are complex geotechnical structures that should be designed taking into account long-term stability and long-term properties of materials (DME, 1999; Szymanski, 1999; ONTARIO, 2000; Silva et al, 2003; Xendis et al, 2004; Bjelkevik, 2005; Jantzer and Knutsson, 2010; ANCOLD, 2011; ICOLD 2013)
Little variations of mineral constituents before and after the treatment suggest no modifications occurred after irradiation
Indirect aging tests were performed on silty samples of Stava tailings dams, by means of gamma radiations bombardment carried out at Centro de Desenvolvimento de Tecnologia Nuclear in Belo Horizonte (Brazil)
Summary
Tailing dams are complex geotechnical structures that should be designed taking into account long-term stability and long-term properties of materials (DME, 1999; Szymanski, 1999; ONTARIO, 2000; Silva et al, 2003; Xendis et al, 2004; Bjelkevik, 2005; Jantzer and Knutsson, 2010; ANCOLD, 2011; ICOLD 2013). Troncoso et al (1988) studied the cyclic resistance on aged copper tailing samples by performing cyclic triaxial tests. They estimated that cementation between particles can increase the cyclic liquefaction resistance of the impoundment more than 250% over 30 years. The results of cyclic triaxial tests on the 30,5 and 1-year old quartz tailings samples are shown in Fig. 1a in terms of cyclic stress ratio (defined as the ratio of amplitude of cyclic axial stress to twice the initial confining stress) required to produce 5% double amplitude axial strain
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