Tailings management is no longer an afterthought in mine planning, operations and closure – it’s climbed the list of critical issues related to sustainable mining, and tailings processing technology is rapidly advancing.

Tailings management has become a critical aspect of mining operations globally, with an increased focus on water recovery, safety and sustainability. Combined with the stringent accountability that mine operators have to local communities, tailings management is now a significant consideration, with processing requirements and technology changing rapidly. Traditionally involved in the pumping of tailings, Weir Minerals recently noted it has extended its expertise into this area to encompass the entire tailings process. From dewatering to transport, disposal, and the conversion of tailings into a resource, the company said it can provide customers with an end-to-end tailings and pipeline solution.

“Our holistic solutions-based approach to tailings management strengthens our relationship with customers and adds value to their operation beyond pumping,” said Hoosen Essack, process manager for Weir Minerals Africa. “In light of water conservation, operational sustainability and safe deposition of tailings, it’s important that we invest in this area to help solve crucial issues within the mining sector.”

Weir Minerals said its extension into the tailings processing field means the company is now involved in the production of the material, as opposed to simply transporting it. Through consultation, site visits and audits, Weir Minerals ascertains customers’ objectives and recommends optimal solutions to meet their needs, including dewatering equipment, piping, pumps, valves and instrumentation.

This approach, according to the company, is a departure from the traditional industry practice of sourcing components from multiple suppliers, which can be challenging to integrate. Weir Minerals pointed out that its research and development capabilities allow it to provide a spectrum of tailings management options not limited by a particular type of technology or equipment. This involves assessing the variations in capital and operating expenditure along with the overall and long-term benefits of each, providing a customized solution. Prior to implementation, rigorous testing and trials are conducted to assess viability and performance ahead of final selection, detailed design, and engineering, delivery and commissioning.

“Weir Minerals can provide a variety of processing systems, including equipment and infrastructure to achieve the final tailings product that is required by the customer, from thickening to create a paste or applying a filter to produce a product that can be dry deposited. As tailings management evolves, the industry is moving toward the latter for increased safety and stability, and in the process, maximizing water recovery,” Essack explained.

The company said as mine operators become more vigilant in managing their tailings, new processing technology is continually being developed from sources such as the Weir Technical Centre (WTC) tailings research facility in Australia. In late 2017, Weir Minerals explained the facility’s unique setup for evaluating tailings solutions, with the center’s general manager–operations and development, Nils Steward, stating that, “We have the technology to test pipeline and tailings solutions for our customers before they are installed on site. By testing materials and equipment, we can fully understand the performance of the selected pumps when transporting solids, which provides us with valuable insight into pump performance, efficiency and predictive maintenance. Mineral slurries vary in many ways — mineralogy, particle-size distribution, solids concentration and chemistry — and thus each slurry behaves differently when in a pipe system. Therefore, the relatively simple task of pilot test work is a very important activity as it helps to determine the best solution for our customers’ sites while reducing the overall design risk.”

Pipeline selection — in terms of size, material and possible lining types — is essential to ensuring overall pipeline transport success, efficiency and system longevity. The selection of pipe size, together with pump and motor specifications, pose the greatest risk to any pumping operation, said Weir, and the WTC can assist with the correct slurry characterization and pipeline pressure gradient data to reduce, or remove, this process risk to the operator.

Weir Minerals said by using the data generated at the WTC, its can specify tailings handling products and processes to suit operators’ site-specific environmental and operational conditions. This helps mine operators minimize power and water consumption as well as the risk associated with design.

European Consortium Studies Fine-particle Flotation

Critical raw materials such as copper, cobalt and rare earths are of strategic importance to the European economy. However, the ore grain size of many of these metals remaining in available deposits is too small to be separated using conventional flotation.

“Froth flotation is the most important way of recovering valuable raw materials from ores,” explained Dr. Martin Rudolph from the Helmholtz Institute Freiberg for Resource Technology (HIF). “However, recovery of particles below 20 micrometers in size, which is less than half the thickness of a human hair, is beyond the capabilities of current flotation technologies.”

As part of an effort known as the FineFuture project, a consortium of 16 partners from the European industry and science sectors plan to explore the fine-particle flotation phenomena and develop new technological solutions for this process. The three-year project has received more than 6.2 million (US$6.9 million) in funding from the European Union. FineFuture is coordinated by Helmholtz-Zentrum Dresden-Rossendorf (HZDR), a German research center.

Europe accounts for just 3% of global mine production — compared to 40% in the early 1900s — but there are some signs of a turnaround due to rising commodity prices and the growing global demand for strategically important metals. Deposits previously considered uneconomic to mines are now becoming the focus of the mining industry: low-grade, finely dispersed ores.

Professor Kerstin Eckert of the Institute of Fluid Dynamics at HZDR said, “With the consortium’s combined expertise, we have the chance to make substantial improvements in the yield and recovery rate.” The FineFuture project involves cooperation between partners from 11 countries. The aim is to combine progressive facility design and process innovations to achieve a 30% higher recovery rate in the future. In addition, more efficient techniques involving fewer process steps should reduce water and energy consumption and minimize the discharge of chemicals to the environment.

Dr. Rudolph, who leads the Processing department, asked, “How can effective collisions between fine particles and bubbles be induced? How do the different reagents affect the overall process? And how can non-target particles be removed from the froth?” These questions have yet to be answered before mineral particles in the range of 0.1 to 20 micrometers can be separated on an industrial scale in the future. Such a technology would also be of major importance for recycling or for recovering raw materials from old heaps.

Research undertaken by the nine academic project partners mainly focuses on developing a better understanding of the mechanisms and microprocesses involved in fine particle flotation: two of the nine work packages concentrate on the physico-chemical and hydrodynamic aspects of processing. These include the binding mechanisms and frothing characteristics of the valuable particles, and turbulent flows in the flotation tank. The latter influence the collision frequency of particles and bubbles: adhesion is only possible when air bubbles come into contact with hydrophobized mineral particles.

Three groups at the HZDR are working to improve the yield of fine particle flotation: Eckert’s team, as well as others from the Department of Computational Fluid Dynamics and a research group led by Martin Rudolph. Using model experiments, newly developed measurement methods and computer simulations, they are investigating flow conditions in the flotation bath and how particles, fluids and gas bubbles interact.

The partners hope their research results will enable them to derive approaches, such as innovative hydrodynamic concepts, that can be used to increase the probability of bubbles colliding with fine particles. The researchers want to exploit insights into interface interactions to improve the adhesion of ultra-fine valuable particles to the gas bubbles by optimizing reagents. The technologies will then be tested and optimized in simulated environments, in the lab and in pilot plants.

In addition to research institutions, seven companies from the mining, materials processing and machinery, and plant engineering sectors are involved in FineFuture, including KGHM, one of the largest mining groups and copper mine operators, and three other raw materials companies. Besides achieving higher recovery rates, these companies hope to develop processes that are more sustainable and generate fewer flotation residues. Many waste heaps contain valuable fine particles, which they wish to exploit. This development could decrease the size of tailings sites, resulting in reduced land consumption and environmental dangers. BASF, a manufacturer of flotation chemicals, is also a member of the project and is focused on developing optimized reagents that are more economical, effective and environmentally friendly.