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• The reversibility time-dependent property of CTB mixtures was observed. • A novel rate equation of structural parameter was proposed. • A thixotropic model with 8 parameters for CTB mixtures was established. • The proposed model exhibited good correlations with experimental results. The thixotropic properties of fresh cemented tailing backfill (CTB) pastes applied in underground backfilling are investigated. Reversibility of thixotropy, equilibrium rheology, and stress decay curves of CTB pastes are discussed. A constitutive model that contains an evolution equation of structural parameter and a constitutive equation for shear stress is proposed. Modifications are made to incorporate the steady-state rheological model and the evolution equation of structural parameter. The proposed model has 8 parameters that are easily determined by fitting experimental data from a series of constant shear rate tests. The good agreement between the predicted and experimental shear stress responses suggests that such a thixotropic model is validated for CTB pastes. Compared to existing thixotropic models, the proposed constitutive model is simple and distinct, showing the novelty of the evolution equation of structural parameter. [ABSTRACT FROM AUTHOR]

The technique of mixing mine waste rock and tailings for disposal has the potential to avoid the problems of acid rock drainage and tailings liquefaction. This paper presents a rational basis for the design of mixtures based on particle packing theory and laboratory investigations. Mixtures were conceptualized using a particle model that allows mixture design and interpretation of behaviour. Laboratory investigations included examination of tailings rheology, mixture trials, and compressibility testing of waste rock, tailings, and mixtures of waste rock and tailings. Results indicate that mixture design governs mixture structure, and consequently also compressibility behaviour. A method is presented to predict mixture compressibility from mixture ratio and the properties of the parent waste rock and tailings. The study provides theory for the design and evaluation of mixtures as a mine waste disposal technique and demonstrates that the design of geotechnical properties is possible for homogeneous mixtures of mine wastes at the laboratory scale. [ABSTRACT FROM AUTHOR]

• Continuous physical, mineralogical, geochemical data recorded in waste-rock pile. • Multi-scale heterogeneities in alteration resembling hardpan formation in tailings. • Secondary mineral assemblages and weathering mechanisms in reactive and inert zones. • Mineralogical controls on leachate composition and metal mobility in waste-rock pile. Mine waste rock is typically stored on-site in large piles that are heterogeneous in terms of material composition and grain size. This leads to variable reactivity within the pile and makes prediction of drainage quality difficult. Here, we present data from two >100 m continuous boreholes through an operational waste-rock pile at the Antamina mine (Peru). Reactive zones with elevated sulfide and metal content exhibited increased temperatures, reduced oxygen content, as well as pervasive secondary mineral precipitation. Sharp contact between altered and unaltered layers at the meter to centimeter scale indicated strong variability in mineral reactivity. Unaltered waste rock persisted within high-sulfide zones due to low oxygen levels, and surface passivation and galvanic interactions between sulfide couples also limited alteration. Waste-rock layers with gradated alteration that resemble hardpans, as observed in tailings, were in direct contact with non-altered, less-permeable layers. Finally, leaching tests show that sulfate, Cu and Zn were efficiently leached from reactive and mineralogically altered zones, whereas As and Fe were retained through sorption, surface passivation, or secondary mineral formation. This study shows that, over and above bulk geochemical and lithological data, waste-rock reactivity may also be defined by mineralogical data and thereby contribute to improved drainage quality predictions. [ABSTRACT FROM AUTHOR]