Large-Strain Consolidation Behaviour of Uranium Mill Tailings from Northern Saskatchewan, Canada

Imteaz Bhuiyan, Shahid Azam

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Mining Geotechnics

ABSTRACT: The objective of this research was to investigate the large-strain consolidation behaviour of uranium mill tailings samples. During self-weight and load-induced consolidation the interface height reduction were found to be 30% to 42%. The change in void ratio was higher for 4% mill tailings (e = 2.5) than 5% and 6% mill tailings (e = 1.3~1.7). The lowest measurable effective stress was 0.3 kPa for all mill tailings. The void ratio at the effective stress of 1 kPa was found to be 3.8, 3.1 and 3.4 respectively. The k values showed an initial scatter before attaining a steady value and found to be ranging from approximately 10-7 m/s to 10-8. RÉSUMÉ L'objectif de cette recherche était d'étudier le comportement de consolidation d'échantillons de résidus d'uranium sous grande tension. Au cours de la consolidation induite par l'auto- chargement, la réduction de la hauteur de l'interface a varié entre 30 et 42 %. Le changement de taux de vide était plus élevé pour les résidus de 4 % (e = 2.5) que les résidus de 5 % et 6 % (e = 1,3 ~ 1,7) . La contrainte efficace la plus faible qui pouvait être mesurée était de 0,3 kPa pour tous les résidus. Pour une contrainte effective de 1 kPa, les valeurs des rapports de vide étaient égales à 3,8, 3,1 et 3,4 respectivement. Les valeurs de k ont montré initialement une dispersion avant d'atteindre une valeur stable comprise entre environ 10-7 et 10-8m/s. 1 INTRODUCTION The Key Lake operation in Northern Saskatchewan, Canada is the world largest uranium producer. By the end of October 2009, the facility had produced more than 170 x 106 kg of uranium concentrate from on-site ore deposits and ore from the nearby McArthur River mine (Cameco, 2010a). The tailings management is an essential activity related to ore processing at the Key Lake mill. Mill tailings refer to the solid waste materials that result from the processing of the uranium ore. From initial mill start-up in 1983 to 1996, tailings were discharged into the Above Ground Tailings Management Facility (AGTMF). Since 1996, tailings are pumped from the mill to a thickener and subsequently to the Deilmann Tailings Management Facility (DTMF) for deposition. By the end of October 2009, the total volume of sediments in the DTMF was calculated to be 6.7 X 106 m3 (Azam et al., 2014). To reduce environmental footprint by large amount of tailings, the current uranium tailings management practice emphasises on non-segregating deposit and higher degree of consolidation by depositing the slurry in a engineered containment facility equipped with adequate drainage system (Mittal and Landine, 2013). The storage capacity of the tailings management facility depends on the consolidation behaviour of the deposited material (Ito and Azam, 2013). Therefore, an effective tailings management during operation, closure, and reclamation requires a clear understanding of tailings consolidation. The Objective of this study was to investigate large-strain consolidation behaviour of uranium mill tailings from Northern Saskatchewan, Canada. A detailed laboratory investigation program was developed to understand consolidation behaviour of three types of uranium mill tailings. First, a large strain consolidation test equipment was designed and fabricated. This is followed by the tests at for three types of slurries in the consolidation cell. Upon completion of self-weight consolidation tests, load-induced consolidation tests were conducted applying loads on each sample. Finally, the hydraulic conductivities were measured after completion the each consolidation tests. 2 URANIUM MILL TAILINGS 2.1 Production of Mill tailings Figure 1 shows conceptual mill process and the production of uranium mill tailings. The separation between milling and tailings management can be clearly distinguished from this diagram. In tailings management scheme, the primary ingredients in tailings are solids residue from the leaching process and barren waste solution. The solids residue is primarily fine ground rock material that did not dissolve during the leaching process, so this is material that is not amenable to dissolution in highly concentrated acid. The barren waste solution contains everything that did dissolve, without the uranium, and any process reagents used along the way. The barren waste solution is neutralized in a series of to produce the precipitate slurry. The residue (lime neutralized solids) and precipitates (waste solution) are combined in a tailings thickener to produce a combined product (mill tailings) with a specified solids density.

RÉSUMÉ: -Strain Consolidation Behaviour of Uranium

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Imteaz Bhuiyan; Shahid Azam (2014) Large-Strain Consolidation Behaviour of Uranium Mill Tailings from Northern Saskatchewan, Canada in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper166,author = Imteaz Bhuiyan; Shahid Azam,title = Large-Strain Consolidation Behaviour of Uranium Mill Tailings from Northern Saskatchewan, Canada ,year = 2014}