Mining operations are under pressure to demonstrate more sustainable management of water resources and mineral processing by-products, known as mine tailings. Dry tailings (filtered tailings) can have significant economic and environmental benefits, particularly if the transportation and final placement of the material is done continuously with highly mechanised and automated equipment.
Mining operations face challenges in managing wet tailings, which pose environmental and safety risks. Dry tailings, or filtered tailings, offer a sustainable alternative by significantly reducing water use and improving storage stability through mechanized handling and stacking techniques.
By Gabriel Moniz
Processing raw materials such as copper, iron and gold often produces wet tailings as a by-product. This slurry consists of crushed rock, water, trace quantities of metal and, in some cases, chemical additives used during ore processing. Transporting and storing wet tailings safely presents significant challenges for mining operations, primarily due to the potential for geochemical and geotechnical instability.
Wet tailings are conventionally stored in specially designed dams, so that the stored (supernatant) water can be recovered for reuse later. However, wet tailings are more conducive to acidic drainage, which can pollute surface and groundwater, threatening aquatic life and ecosystems. The weight of wet tailings can also put immense pressure on containment structures. There are several well-documented cases of wet tailings storage facilities failing, with catastrophic consequences for nearby communities, wildlife, and the local environment.
Many mining operators are considering dry tailings as a more economical and sustainable alternative to wet tailings storage and treatment.
Dry tailings have much of the contained water removed before they are placed at the tailings storage facility (TSF). The direct freshwater consumption in ore processing can be drastically reduced by up to 85%, depending on the filtration system and the actual dry tailings handling process.
Some moisture content is typically retained during the process, so ‘dry’ tailings is not an entirely accurate description. Filtered tailings is more technically correct. Whatever description you prefer, the tailings are dewatered to a target water content that is dependent on transportation parameters and the geotechnical requirements of the storage facility.
Rather than using dams and containment ponds, a dry tailings operation is essentially an earthworks project. The tailings are transported using familiar open-pit mining equipment, such as fixed and mobile conveyors, tipper cars and spreaders, to deposit tailings to a predetermined plan. The terrain is reshaped by placing large volumes of dry tailings to create a geotechnically and geochemically stable landform that meets closure requirements and minimises the associated capital and operating costs.
Rio Tinto and BHP are two of the world’s largest mining companies that are actively evaluating dry tailings as a tailings management alternative. In 2022, Rio Tinto and BHP established a partnership to enhance technology for recovering water from mine tailings. The initiative aimed to mitigate safety hazards and environmental impacts associated with a TSF, including the transportation and stacking of tailings, which are critical factors affecting project cost and feasibility.
The project involved the development of a materials handling solution for stacking dry tailings efficiently, tailored to the mine’s operating parameters, unique topography, and TSF geotechnical requirements. It features a single-flight overland conveyor linking the filter plant to the TSF, and two pairs of shiftable conveyors and tripper cars at the TSF. A mobile stacking bridge undertakes the final deposition of the material.
This design ensures high system availability with built-in redundancy that minimises the need for frequent equipment relocation. It also handles material with varying moisture content, allowing for the construction of structural and non-structural zones of the TSF using the same equipment set. Operational safety is enhanced through retreat stacking, which allows time for the freshly stacked dry tailings to settle before the conveyor operates on top of them.
In this instance, the continuous automated handling system resulted in a significant net present cost reduction when compared to traditional truck-based or hybrid solutions. While this system has proven effective for the application presented by Rio Tinto and BHP, it is important to note that adaptations would be necessary for implementation in other mines, taking into account their unique requirements and terrain.
Dry tailings stacking is a well-established process of tailings management that can help mining projects meet their environmental, social, and economic objectives. TSF design and construction are primarily guided by geotechnical factors, so efficient materials handling is key to economic success. Conveyor-based materials handling systems can offer significant cost advantages over traditional truck haulage systems, especially at higher throughputs. These benefits are further enhanced when the system layout, stacking plan, and selected equipment are customised to the site’s topography, material, and geotechnical requirements.
The collaboration between Rio Tinto and BHP has shown that conveyor-based materials handling can make dry tailings a more attractive and sustainable option, but it is essential to engage materials handling specialists early in the project to optimise the benefits and develop a solution that aligns with the specific needs of the operation.
