Frequently Asked Questions
Q How much thickening is required for a Tailings Management System?
A For typical base metal tailings between 50 and 70 percent solids, for extremely fine tailings (for example bauxite residue) 30 to 50 percent solids.
Q How much smaller is the quantity of process liquid or water being discharged with the tailings by the TMS?
A For tailings slopes of 2.5% to 5%, liquid discharged by TMS is only 12 to 36 percent of that discharged into a conventional pond. Consequently, discharge pipelines are also substantially smaller in size.
Q Are the tailings still fluid enough to be pumped at the above consistencies?
A Yes, some coarse tailings have been pumped at consistencies as high as 74 percent with centrifugal pumps. Depending on topographical positions of the plant disposal area
and viscosity, the pumps may be either centrifugal or positive displacement.
Q Can the tailings be hydrocycloned instead of being thickened for the TMS?
A No. Hydrocycloning merely separates the coarse fraction from the fines. The coarse fraction may stack, but the fines and liquid still require a conventional pond.
Q How steep a slope can be attained using the TMS?
A In wet to moderate climates slopes of 2% to 6% are recommended. In dry climates steeper slopes could be used.
Q What about erosion of the tailings slopes?
A During active mining, in wet climates, it is recommended to limit the slopes to 2% to 3.5% to reduce erosion. However, erosion is not critical in most cases, because the deposit continues to expand, and the eroded tailings at the toe will be buried by subsequent discharges. After termination of operations, and reclamation, erosion of such gentle slopes will be negligible.
Q Isn't the problem of dam stability still a critical issue?
A With the TMS, properly designed, the problem is much reduced. Dams will be much smaller and in some cases will be eliminated almost entirely.
Q Will the TMS deposit liquefy during earth tremors or earthquakes?
A Special design conditions are involved for such settings. However, a well-designed arrangement of discharge points will ensure that the tailings mass, layer by layer moisture contents lower than the the shrinkage limit. Any shear stress will induce negative pore pressures which then act to oppose the strains and prevent liquefaction.
Q It has been stated by some that the TMS requires a much larger surface area for disposal.
A This is a misconception. Thickened tailings form a cone or ridge - a convex deposit, whereas the conventional deposit is always concave. Therefore, per square unit of surface, TMS will always accommodate more tailings. For a given quantity of tailings in identical terrain TMS will require considerably smaller dams than the conventional system.
Q If there is no topographic 'high' from which to discharge tailings, how does one achieve a conical or ridged deposit?
A Initial discharge can be from a man-made ramp, or vertical tower (perforated pipe). Thereafter, the discharge line is extended over the previously deposited tailings, if necessary with the help of a layer of gravel or geotextile to act as roadway.
Q How difficult is it to adopt TMS to an on-going conventional disposal pond?
A All that is required is to progressively advance the thickened tailings discharge line onto the existing tailings. Simultaneously, the discharge ramp will be built-up progressively higher, thereby forming a ridge on top of the existing deposit. The plan could be developed to avoid any encroachment on the existing containment dams.
Q If the above approach was to be adopted, can the existing conventionally discharged loose tailings support the advancing new thickened tailings deposit?
A Generally, yes. Slopes of 2% to 6% are extremely gentle and the discharged tailings develop a 'bermed' support consisting of the surrounding gently sloping thickened tailings. A low mud wave may develop at the toe of the thickened tailings deposit as it expands.
Q Are there any advantages of using TMS in permafrost terrain?
A Yes. The reduced quantity of water in the thickened tailings slurry allows the discharged mass to freeze much quicker.