Tailings are transported to their final storage place in a number of different ways. The most common is slurry transportation in a pipeline from the thickeners (normally located at the processing plant) to deposition points located within or around a surface tailings storage facility. The tailings properties, tonnage and site topography dictate the type of transportation system required to manage the tailings both cost effectively and efficiently.
The types of tailings transportation systems used today are as follows:
Tailings pumping systems can be complex. The tailings properties and flow rate for a mining operation are never uniform and so a system has to be installed that allows for variation. Today, with the increase in popularity of High Density Thickened Tailings (HDTT) and paste, these pumping systems are more advanced as principally higher pressures are required to transport a material that is less viscous. In conventional tailings systems, the higher volumes of water (i.e. lower % solids concentration of the slurry) reduces the yield stress of the tailings where-by the water acts as a transporter for the tailings solids. This can be observed in tailings facility failures, where a breach of the facility due to high volumes of water (e.g. overtopping) generally have large run out distances as the water is transporting the tailings solids. In tailings facility breaches where the water contained was not greater than normal conditions (e.g. seismic trigger failure), the run out distances are usually much less.
Pumping using centrifugal style pumps are still the most common type of pumping system used in tailings slurry transportation. Quite often, when a tailings trade-off study for different tailings discharge techniques is performed for a proposed storage facility, the limits of centrifugal pumping are almost always more cost effective than paste transportation (particularly for high tonnage operations). However, there are site specific factors that dictate this (e.g. limited land and water availability where paste is the only viable option).
Paste tailings can be pumped by centrifugal pumps, up to a limit, which is normally determined by the yield stress in the first instance which is a function of the %solids concentration of the slurry. Beyond the limits of centrifugal pumps, positive displacement pumps are required for paste tailings. This is typical done using piston diaphragm or hydraulic piston pumps. Peristaltic (hose) pumps may be used for very low tonnage systems.
Filtered tailings (dry stacking) style of tailings storage is becoming more popular mainly due to the growing need to reduce makeup water costs in the mining industry. Over the recent years there has been a significant advancement in the field of dewatering of tailings using pressure and vacuum filtration techniques. Typical disadvantages to filtration are the associated power and maintenance costs (e.g. filter cloth replacement) that can vary depending on the tailings properties. For this reason it is important to consider laboratory or pilot testing to determine the feasibility of filtration for a particular type of tailings.
The transportation of wet cake tailings is typically achieved by conveyor or truck transportation. Conveyor systems require a minimum tonnage per hour to be economical to install and operate, where-by truck transportation becomes more feasible.
Typically there are two types of conveyor systems used for delivery of wet cake tailings. These are similar to the style of conveyors systems used for stacking and reclaiming coal (bucket wheel excavators), but usually on a much smaller scale:
For more information regarding dry stacking of tailings, see the relevant page here.