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Large volumes of waste rock (WR) are generated in open-pit mines. WR is characterised by high anisotropy in its physical, chemical, mineralogical, and hydrogeological properties. WR is often deposited in unsaturated piles on the mine surface. Mineralogical investigations defined the diameter of physical locking of sulphides (DPLS) allowing the WR to be separated into two fractions: i) a reactive fine fraction (<2.4 mm), and ii) an inert coarse fraction (>2.4 mm). Environmental desulphurisation carried out on the reactive fine fraction decreased the risk of contamination caused by WR oxidation. The geochemical behaviour of three benign desulphurised lithologies (altered greywacke (AGR), carbonated greywacke (CGR) and carbonated porphyry (CPO)) and their corresponding fine fractions (<2.4 mm) were assessed using kinetic weathering cells (WCs). These tests confirmed the effectiveness of environmental desulphurisation to prevent acid mine drainage formation. In fact, geochemical analyses of the leachates from WCs showed that pH values ranged between 7.4 and 8.9. Moreover, instantaneous concentrations of iron and zinc were below 0.5 mg/L and 3 mg/L, respectively. Pyrite oxidation rates, which represent sample reactivity, were higher for head samples (3.01, 4.86, and 2.54 μmol/kg/day for AGR, CGR, and CPO lithologies, respectively) in comparison to the benign desulphurised materials (2.32, 2.4, and 2.25 μmol/kg/day for AGR, CGR, and CPO lithologies, respectively). Pyrite in the dismantled material was only partially liberated or almost encapsulated, making it mineralogically unavailable for oxidation. The benign desulphurised material with low initial sulphide content was potentially non-acid generating at the long-term scale. Upstream environmental desulphurisation has been confirmed as an effective strategy for WR management and valorisation. • Pyrite oxidation rates were low for desulphurised materials in comparison with head samples. • Environmental desulphurisation allowed to prevent acid mine drainage formation. • The geochemical behaviour is an important aspect to be considered during waste rock management and valorisation. • Desulphurisation demonstrated its effectiveness to reduce risks related for WR. [ABSTRACT FROM AUTHOR]

Open-pit mining generates a large volume of waste rocks (WR) that are deposited as unsaturated piles on the surface. WR are mainly characterised by the high heterogeneity of their hydrogeological, mineralogical and physical proprieties. The main objectives of this study consist of: i) a detailed characterisation of WR from Canadian Malartic mine in Malartic city (Quebec, Canada), ii) the use of environmental desulphurisation of the three classified waste rocks main lithologies to reduce their acid generation potential and iii) the recovery of the residual precious metals (e.g. Au, Ag). The studied materials were sampled after blasting while ensuring their representativity. Each lithology was first screened based on the DPLS (diameter of physical locking of sulphides) to remove the inert fraction higher than 2.4 mm. Then, the fraction (<2.4 mm) was separated into two fractions to optimize their integrated management: 0–1 mm referenced as fine fraction and 1–2.4 mm referenced as coarse fraction. Chemical and mineralogical determinations showed that the three lithologies are more enriched in carbonates (mainly as calcite) than sulphides (mainly as pyrite). The acid base accounting (ABA) testing and the net acid generation (NAG) tests both showed that these lithologies (<2.4 mm) and their corresponding fractions are non-acid generating except three fractions that are uncertain. In order to reduce the sulphur content, desulphurisation applied on the fraction <2.4 mm using laboratory gravity separation (Knelson separator and Mozley table) was more efficient than flotation. All desulphurised materials from gravity and flotation methods were in the non-acid generating zone. The gravity method offered a sulphur recovery of about 84 wt%. The pyroanalysis of gold (Au) and silver (Ag) on the concentrate of desulphurisation with gravity methods display a gold content of 3,78 g/t and of 4,9 g/t for silver. The precious metals recovery could offset partially the costs related to the waste handling and reprocessing. • Studied lithologies were more enriched in carbonates in comparison to sulphides. • Sulphur recovery for the gravity method were better than the flotation process. • Desulphurised materials were in the non-acid generating zone (ABA tests). • Recovery of Au and Ag can offset partially the charges of gravity methods. • Approach proposed need a techno-economic evaluation (capital and operation costs). [ABSTRACT FROM AUTHOR]

The mining and ore processing of sulfide-bearing deposits generates large volumes of waste rock (WR) and tailings, which often contain barren and residual iron sulfides (e.g., pyrite and pyrrhotite). Sulfide oxidation under atmospheric conditions can generate acidic leachates loaded with high concentrations of dissolved metal(oid)s when the carbonate content is insufficient to buffer the produced acidity. The acid generation potential of mine waste is defined by its sulfide and carbonate occurrences. Nowadays, the environmental behavior of mine waste is a key factor for the economical and technical feasibility of mining projects from exploration to mine closure. Consequently, the prediction of mine drainage formation is crucial for the mining industry to identify the costs related to mine site reclamation. Prediction is often based on multiscale laboratory and/or field tests such as static tests, column-leach tests, humidity cells, and/or field-testing. The geochemical behavior of mine waste and its prediction are controlled by many intrinsic characteristics (e.g., particle size, mineralogy, chemical composition) and extrinsic factors related to the applied tests (e.g., test dimension, flushing frequency, liquid–solid ratio, climatic conditions). The prediction of mine drainage can be conducted using chemical and/or mineralogical static tests and/or kinetic tests. Static tests provide a simple and rapid overview of the type of mine drainage by comparing the neutralization and acidification potentials. However, static tests may show contradictory results for the same sample. For this reason, static tests can be used as a preliminary indicator. Kinetic tests are used to provide information about mineral reactivity and chemical species release rates. The accurate prediction of acid mine drainage and contamination generation must further consider the following aspects: i) an accurate sampling strategy, ii) the textural properties (mineral liberation and association) of the mine waste, and iii) the scale effect during kinetic tests. Finally, from a circular economy perspective, mine waste valorization is superior to conventional management. [Display omitted] • Representative sampling is a crucial step during environmental studies. • Static tests preliminary indicate the short-term AGP of mine waste. • High prediction confidence level is only ensured by kinetic field tests. • Mineralogical characterization is a key factor for environmental studies. • More efforts are needed to scale up results of laboratory tests to field conditions. [ABSTRACT FROM AUTHOR]