A complete guide to surface disposal methods for tailings

In mining operations, proper disposal of tailings is a critical task. Surface disposal of tailings is usually done with the help of various types of dams and dikes to construct reservoirs to store tailings and factory wastewater. There are a variety of dike types to choose from, including single-layer water storage types and elevated dike types such as upstream, downstream, and centerline. Each type has its own unique construction methods, application conditions, advantages and disadvantages.

Upstream method: cost-effective but demanding

The construction of the upstream retaining wall begins with the starter dike at the downstream foot. During construction, the tailings are discharged from the top of the starter dike through a faucet or hydrocyclone, which forms a wide beach composed of coarse-grained material. This beach is significant not only as the surface slope of the tailings after being washed by water, but also as the basis for subsequent dike construction. In some cases, the dike is placed mechanically, and the discharge is only used to build the beach.

The elevated part of the dike can be filled with borrow soil or tailings can be excavated from the beach and placed by an excavator or front-end loader. Regardless of the method used, some degree of mechanical compaction of the dam structure is usually required before the next stage of dam construction.

The key to the upstream method is that the tailings beach must form a solid foundation that can support the next stage of dam heightening. However, in addition to the tailings gradation, there are many factors that limit the application of this method, such as water table control, water storage capacity, seismic liquefaction sensitivity, and the speed of dam heightening. Although the upstream method may have certain economic advantages, its strict requirements on tailings beach conditions and other factors make it need to be carefully evaluated in practical application.

Downstream method: strong stability but high planning requirements

The design requirements of the downstream construction method are similar to those of traditional impoundment dams. Like upstream construction, it also starts with the construction of a starting dam with compacted borrow material. However, the construction material selection of this starting dam is more flexible, and can be permeable gravel or silt and clay-based materials to minimize leakage from the dam. If the starting dam uses low-permeability materials, internal drainage systems must be included in the design.

The downstream method is so named because subsequent dam construction stages are supported on the top of the previous downstream slopes, and the centerline of the dam top moves downstream as the dam stages are gradually raised. In the downstream construction method, a variety of tailings deposition techniques can be combined, with peripheral pipe insertion of the tailings being the most common. Therefore, if coarse rock (run-of-mine waste) is used, filters or impermeable upstream membranes need to be installed on the upstream slope to prevent tailings from being discharged through the rock pipe.

The downstream construction method excels in stability, compaction capabilities, ease of use, and the ability to combine water table control measures, and the dam heightening is not structurally dependent on tailings deposits for foundation strength. However, this method requires careful planning, because the toe of the dam will expand outward as it increases in height, so sufficient space must be reserved when the initial dam is laid out to avoid dam encroachment on property lines and terrain restrictions. Restrictions at the toe often determine the final height of the dam. In addition, the downstream heightening method requires a large amount of fill to raise the dam, so planning must be done to ensure that the productivity of the fill can meet the needs throughout the life of the dam.

Centerline method: a compromise with advantages

The centerline method is a compromise between the upstream method and the downstream method. It combines the advantages of both methods to a certain extent while mitigating their disadvantages. Similar to the upstream method, the initial dam is built first, and the tailings are discharged from the outer perimeter of the dam to form a beach. Subsequent heightening is achieved by filling the beach and the downstream slope of the previous heightening. As the dam continues to move upward, the centerline of the heightened section coincides. The centerline method generally has good seismic resistance, and this method may be more advantageous in some areas that are more sensitive to earthquake factors.

In-pit deposition: environmentally friendly but with resource waste issues

Open-pit mining leaves cavities, and from an environmental perspective, storing tailings in these waste-generating cavities seems to be a good choice. Tailings can be placed in the completed open pit in the form of slurry, thickened or filtered, or mixed with waste rock. However, disposing tailings in a completed open pit may result in resource waste, and it may not be possible to rely solely on the open pit for tailings disposal during mining operations. In addition, open-air disposal usually has very few or even no walls (depending on the terrain), which also brings certain risks and management difficulties.

The ground disposal methods of tailings have their own advantages and disadvantages. In practical applications, it is necessary to comprehensively consider geological conditions, topographic factors, environmental protection requirements, cost budget and other factors to select the most suitable disposal method to achieve safe, environmentally friendly and economical disposal of tailings.