| Summary: |
The mining industry is a fundamental pillar of modern society, providing the minerals for energy transition and digitalisation that comprise the European plan to recover from the COVID-19 crisis towards green and digital industries. This is in line with Portugal aspiration to explore lithium. The supply of mineral raw materials requires an adequate management of tailings, the fine material discarded after ore extraction, traditionally disposed in dams raised by tailings hydraulic fill.
The increasing number of catastrophic accidents in tailings dams demonstrates that the stability of these structures constitutes a geotechnical engineering challenge for which an urgent solution is needed. An alternative deposition in dry stacks has been used compacting filtered tailings (with less water) in massive embankments. However, accidents were observed in these structures during heavy rain periods, indicating that more robust solutions are needed especially in a climate change scenario.
INPROVE proposal is to build structural zones with cemented filtered tailings to improve the stability of dry stacking embankments or to reinforce existing facilities at risk. This is very important: in new facilities, to re-mine existing facilities with historical accumulated resources, and for remediation and closure plans of existing facilities. These latter often include the reanalysis of potential vulnerability and eventual stabilisation or improvement with structural zones (usually not cemented). Due to climate change, storms are becoming frequent and stronger, turning these structures even more instable. For these reasons, advanced hydromechanical analysis are required with constitutive models capable of simulating the evolution of the material during construction history and the softening behaviour associated to the tailings brittle response. Up to now, these advanced analysis were mostly used to identify the causes of accidents rather than for design purposes. Considering the ca  |
Summary
The mining industry is a fundamental pillar of modern society, providing the minerals for energy transition and digitalisation that comprise the European plan to recover from the COVID-19 crisis towards green and digital industries. This is in line with Portugal aspiration to explore lithium. The supply of mineral raw materials requires an adequate management of tailings, the fine material discarded after ore extraction, traditionally disposed in dams raised by tailings hydraulic fill.
The increasing number of catastrophic accidents in tailings dams demonstrates that the stability of these structures constitutes a geotechnical engineering challenge for which an urgent solution is needed. An alternative deposition in dry stacks has been used compacting filtered tailings (with less water) in massive embankments. However, accidents were observed in these structures during heavy rain periods, indicating that more robust solutions are needed especially in a climate change scenario.
INPROVE proposal is to build structural zones with cemented filtered tailings to improve the stability of dry stacking embankments or to reinforce existing facilities at risk. This is very important: in new facilities, to re-mine existing facilities with historical accumulated resources, and for remediation and closure plans of existing facilities. These latter often include the reanalysis of potential vulnerability and eventual stabilisation or improvement with structural zones (usually not cemented). Due to climate change, storms are becoming frequent and stronger, turning these structures even more instable. For these reasons, advanced hydromechanical analysis are required with constitutive models capable of simulating the evolution of the material during construction history and the softening behaviour associated to the tailings brittle response. Up to now, these advanced analysis were mostly used to identify the causes of accidents rather than for design purposes. Considering the carbon footprint of Portland cement (OPC), a more sustainable binder generated by the alkaline activation of industrial by-products (AAB) is highly convenient. However, conversely to OPC, there is no rational methodology to define the mixture dosage in soils stabilised with AAB which has prevented its large scale application.
To address these challenges, INPROVE provides the following innovations:
i) an integrated solution that comprises not only the material development and binder optimisation but also a rational methodology to define the best mixture dosage taking into account the tailings in situ water content, density of the treated layer after compaction, and required mechanical performance at a given curing period.
ii) a systematic approach to link laboratory characterisation with advanced constitutive model parameters capable of reproducing the post-peak behaviour associated to bond degradation. This is important to numerically analyse the influence of the structural zone on the tailings deposit stability.
iii) design charts for dry stacks relating the mixture dosage and the thickness of the stabilised berm for a given embankment height and a typical slope angle.
The approach is based on a mixture index that includes the effect of binder dosage and mixture compaction degree. After obtaining a clear relation between this mixture index and the mechanical behaviour of the material, this index will be related to constitutive model parameters. For this purpose INPROVE comprises: i) statistical analysis based on design of experiments (DoE); ii) advanced laboratory characterisation on the stabilised tailings; iii) hydromechanical numerical analysis in models previously calibrated with centrifuge tests.
The objective is to establish a simplified calibration procedure relating mixture dosage, mechanical behaviour and constitutive model parameters for tailings stabilised with AAB. This is expected to have a major impact on a wider use of sustainable AAB, enabling the numerical simulation of tailings storage facilities with structural stabilised berms to reinforce and contain possible localised liquefaction failures occurring on the unreinforced area.
FEUP has been working together with UPC on the calibration of advanced constitutive models to reproduce the tailings behaviour. INPROVE benefits not only from this work, but also from the team expertise on statistical models for cementitious materials, tailings geomechanics, and AAB for soil improvement.
INPROVE addresses the concerns of the mining industry shared by the scientific community, both supporting the present application as expressed by two support letters from Mafalda Oliveira (from SOMINCOR mining company) and TAILENG consortium (https://taileng.ce.gatech.edu/). |