Non-segregated tailings placement using shallow injection deposition

The discharge of tailings slurry using either sub-aerial or sub-aqueous deposition methods often results in particle-size segregation within the tailings mass. As predicted by Stokes Law, segregation occurs because coarse particles settle quicker than fine particles. As a result, when tailings are discharged, coarse tailings are deposited very near the discharge point while fine tailings are deposited further away.
This paper presents a novel approach to tailings deposition method in which a non­segregated tailings mass is developed from tailings slurry without use of specialized equipment. The tailings deposition concept consists of shallow injection of tailings slurry into the tailings mass via a tremie pipe. The injection of the tailings slurry into the tailings mass prevents dilution of the tailings slurry in the water column, which has been observed with typical sub-aqueous deposition techniques, and gives rise of two mechanisms that lead to the formation of non-segregated tailings. The first mechanism is the development of counter-current fluidization near the tremie tube. Counter-current fluidization consists of the upward movement of tailings water from the injected slurry while tailings solids are moving downward from gravitational forces. The counter-current fluidization causes the slurry to density as free water is lost. The second mechanism is the development of a mobilized thickened slurry which moves away from the injection point. As the thickened slurry moves away from the deposition point, the slurry density is high enough to settle as a hindered (non-segregated) mass.
To test the shallow injection concept, a full-scale field test was conducted at the JEB Tailings Management Facility at the McClean Lake mine site in Canada, which traditionally employed sub-aqueous deposition methods. The field test was conducted for a period of seven weeks, during which observations were made using an underwater camera. After the field test, sampling was conducted to evaluate segregation in the deposited tailings.
Field test observations and sampling verified the presence of counter-current fluidization and hindered settling sedimentation during deposition. The sampling also demonstrated the presence of non-segregated tailings developed from slurry injection.