selected option to help reduce the increased stresses imposed on the underlying slimes.
For environmental reasons, it was also decided that the future facility would have to be constructed upon a geosynthetic liner which would be overlain by an underdrain system. The selection of filtered tailings greatly simplified the design.
The area is environmentally sensitive with migratory fauna that required protection from the presence of process water ponds.
The second facility design was carried out for Nevada Copper’ s Pumpkin Hollow project to store combined waste and tailings in a single facility in the western US. The filtered tailings option was selected by the owner as a preferred approach in consideration of limited available water leases for use in their mining operation. The operation would combine filtered tailings produced at the rate of up to 60,000 t / d, possibly together with waste rock, both of which are chemically benign. The authors’ involvement in this project was limited to the early planning stages, and thus additional design details are not available for this paper. What is notable for this project is the magnitude of materials that would be involved in the operation.
The third facility design was carried out for a confidential client is in Latin America and is now an operating facility. Several practical lessons have been learned since the facility came into operation. The facility is situated in a V-shaped valley and the design includes separate areas for placement of material during the rainy season and dry season. The pre-deposition construction work included the construction of a series of underdrains, a starter berm and a seepage / sedimentation pond. As the facility gains height, a rocky rind is placed on the outer slope. The rock shell serves to provide erosion protection from precipitation, and a drain into which any water seeping from the deposit may be safely conveyed to the sedimentation pond which is situated at the toe of the facility.
As with many similar facilities, the operation includes delivery of the filtered tailings by conveyor to a central point. From the conveyor, the material is pushed into place by a dozer before being compacted by subsequent dozing activities. These activities would tend to drive off moisture, especially in the furthest reaches from the conveyor, in this case near the outer containment structure.
Start-up of the facility commenced during unseasonal precipitation events, and, since the facility is situated in a north-south oriented V- shaped valley, the facility is exposed to sunshine for only a limited amount of time each day when there is no precipitation. In addition, the filter plant was not functioning optimally at start-up, and the filter cake produced was higher than the design value. This combination
of factors hampered the early development of the facility to a point where some alternative arrangements were needed to get the operation to function adequately. Continual monitoring at that site is still underway.
Environmental prizes
As previously discussed, there are several environmental benefits associated with the use of filtered tailings, including a reduced footprint, reduced water consumption, and improved closure opportunities. The improved closure opportunities include the ability to begin the closure work essentially at the cessation of operations( and concurrently on side slopes).
Conclusions
Filtered tailings facilities are becoming more and more common as technological advances make this application increasingly feasible as a viable tailings storage option. As with other such disposal options, the decision to select filtered tailings should be made on site-specific requirements and considerations, including capital, operating and closure costs, but also based on other matters such as the outcome of a risk assessment, water usage and availability and environmental matters. IM
A full reference list is available from Bryan Ulrich at bulrich @ knightpiesold. com
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JUNE 2017 Supplement | International Mining P3