Dewatering of Mine Tailings Slurries Using Superabsorbent Polymers (SAPs) Reclaimed from Industrial Reject of Baby Diapers: A Preliminary Study

Traditional deposition of tailings slurry in a tailings storage facility (TSF) can create risks of dike failure. In order to minimize these risks and slurry spillage, the surface deposition technique of densified tailings (DT) through dewatering of the slurry has emerged. The DT technique has the potential to maximize water reuse, improve the shear strength of surface tailings, and reduce the ecological footprint of TSF. The consistency of DT covers a continuum ranging from thickened state, to paste state, to dry state. Despite its efficiency and economic feasibility, DT densification using thickeners sometimes proves unable to achieve the design target solids mass concentration (Cw%). Hence, the use of superabsorbent polymers (SAPs) seems to represent a promising alternative, owing to their higher water absorbent capacity. In this paper, superabsorbent polymers (SAPs) reclaimed from industrial reject of baby diapers (Na-polyacrylates) are explored as a promising alternative to mine tailings slurries dewatering. To this end, laboratory-scale dewatering tests have been performed using two grades of Na-polyacrylate SAPs (grade 1 SAP = SAG-A06P coarse-grained, and grade 2 = SAG-M01P-100 medium-grained) for the tailings slurries densification. A higher water absorbency (or swelling capacity) was observed using the coarser SAPs (SAG-A06P) compared to the finer SAPs (SAG-M01P-100). The preliminary results showed that a SAP volume dosage in the range 10–13 kg of SAP/m3 of slurry allowed achieving a final solids mass concentration (Cw%_final) ≥ 70%, despite the occurrence of gel-blocking phenomenon

Oxygen diffusion and consumption in unsaturated cover materials

Résumé: Dans plusieurs problèmes de géotechnique environnementale, les ingénieurs doivent analyser des situations d’écoulement simultané d’eau et de gaz. C’est typiquement le cas lorsque des couvertures en sol sont conçues pour des sites d’entreposage de rejets. Étant placés bien au- dessus de la surface phréatique, les matériaux de recouvrement sont non saturés, et ils peuvent permettre à des composés gazeux (tels que l'air et le méthane) d’entrer ou de s’échapper du site. Comme c’est le cas avec l’eau, le flux de gaz doit habituellement être contrôlé par le recouvrement. Une application particulière à cet égard concerne les couvertures construites pour limiter le flux d’oxygène vers les résidus miniers sulfureux, qui peuvent générer un lixiviat acide. Dans cet article, les auteurs présentent une a pproche pour évaluer ce flux et les paramètres de contrôle, incluant le coeffi cient de diffusion effectif D e et le coefficient du taux de réaction (ou de consommation) K r . Un procédé expérimental pour la mesure simultanée de ces deux paramètres en laboratoire est décrit, et une procédure d’in terprétation avec quelques résultats d'essais sont présentés. Des solutions analytiques sont de plus développées pour calculer le flux d’oxygène à travers des systèmes de recouvrement. Ces solu tions sont comparées aux résultats obtenus d'un traitement numérique des lois de Fick modifiées . Diverses applications spécifiques de la méthode de conception des barrières à l'oxygène sont présentées et discutées. ---------- Abstract: In many environmental geotechnique problems, engineers must analyse situations where water and gas can move simultaneously. Such is typica lly the case when soil covers are designed for waste disposal sites. Being located well a bove the phreatic surface, cover materials are unsaturated and may allow gaseous compounds (such as air and methane) to flow in or out from the disposal facilities. As is the case for water, the flow of gas must usually be controlled by the cover. A particular application in that rega rd relates to covers built to limit oxygen flux to reactive sulphidic tailings, which can be the source of an acidic leachate. In this paper, the authors present an approach to evaluate the oxygen flux with the controlling parameters, including the effective diffusion coefficient D e and the reaction (consumption) rate coefficient K r . An experimental procedure to determine these two parameters simultaneously during laboratory experiments is described, and sample results are presented with the proposed interpretation. Analytical solutions are further developed to calculate oxygen flux through cover materials. The proposed solutions are compared to calculation results ensuing from a numerical treatment of modified Fick’s laws. A vari ety of specific applications of the method for designing oxygen barriers are also presented and discussed

Mine Backfilling in the Permafrost, Part II: Effect of Declining Curing Temperature on the Short-Term Unconfined Compressive Strength of Cemented Paste Backfills

When cemented paste backfill (CPB) is used to fill underground stopes opened in permafrost, depending on the distance from the permafrost wall, the curing temperature within the CPB matrix decreases progressively over time until equilibrium with the permafrost is reached (after several years). In this study, the influence of declining curing temperature (above freezing temperature) on the evolution of the unconfined compressive strength (UCS) of CPB over 28 days’ curing is investigated. CPB mixtures were prepared with a high early (HE) cement and a blend of 80% slag and 20% General Use cement (S-GU) at 5% and 3% contents and cured at room temperature in a humidity chamber and under decreasing temperatures in a temperature-controlled chamber. Results indicate that UCS is higher for CPB cured at room temperature than under declining temperatures. UCS increases progressively from the stope wall toward the inside of the CPB mass. Under declines in curing temperature, HE cement provides better short-term compressive strength than does S-GU binder. In addition, the gradual decline in temperature does not appear to affect the fact that the higher the binder proportion, the greater the strength development. Therefore, UCS is higher for samples prepared with 5% than 3% HE cement. Findings are discussed in terms of practical applications