When, in 2019, FLSmidth launched MissionZero, a sustainability programme to enable customers to move towards zero water waste, zero energy waste and zero emissions in mining by 2030, it was only natural that tailings solutions would feature prominently.

The imperative to reduce water consumption is now greater than ever before, according to Ken Rahal, director of tailings solutions at FLSmidth.

"With all the tailings issues that have been seen around the globe, even those outside the industry are becoming aware of the hazards of large tailings impoundments and the risks associated with storing large bodies of water with your tailings," Rahal said.

"As ore grades decline, more water is needed to process more material just to keep up with production rates. We've been looking at how do you improve the dewatering to get the benefits of a more stable tailings facility, to be able to recycle more of your water for reuse, and to therefore reduce the need for freshwater."

FLSmidth says sustainable water use and smart tailings management can cut risks and costs for miners. Through solutions that eliminate wet tailings dams, it is helping mining companies minimise environmental risks to their operations, comply with tightening regulations and maintain a social licence to operate.

The firm stresses that MissionZero is not a silver bullet; it is a process with a defined timeline and goals, and refrains from prescribing any one solution. It recognises that mines are complex - that they vary from region to region, from commodity to commodity, and that each mine and tailings facility has different characteristics and needs.

Looking at the entire flowsheet

Due to this complexity, MissionZero focuses on the entire flowsheet - with an emphasis on areas with the most potential to reduce water use, energy consumption, emissions and waste.

When assessing a tailings facility, "we start from the point at where the ore is brought up all the way through to the crushing area", Rahal said.

"We look at which newer technologies we can apply upstream to reduce the amount of fines generated - from high-pressure grinding rolls and vertical roller mills to coarse air flotation and reflux flotation cells for fines - because fines often have the largest impact on dewatering and on the material properties during placement.

"After going through the upper portions of the flowsheet, we look at what are the best dewatering solutions to achieve the required moisture for disposal. We look at everything from different types of thickeners to different filter technologies."

FLSmidth uses high-rate or high-density thickeners to recover water in tailings prior to disposal, resulting in 50 to 65% solids. Derived from Dorr-Oliver and EIMCO technologies, its thickening equipment includes bridge-supported and column-supported designs to suit mines with smaller and larger throughputs. High-rate thickeners are designed to provide around 12 times the throughput of conventional machines of similar size, ensuring maximum capacity, improved control, increased underflow density and lower flocculant dose. Recent improvements to the firm's thickening technology include low-torque rake arms and spiral rakes that improve underflow density.

When it comes to filtering technologies, FLSmidth offers a broad range of options, including centrifuges, belt presses, dewatering screens, vacuum filters and pressure filters. Technology selection is affected by variables unique to each site, such as particle size distribution, mineralogy and target moisture. Decisions are based upon the need to maximise performance at the optimal investment and ensure site needs for waste recovery, cake moisture and availability are met.

For example, the high-efficiency, large-capacity AFP2525 Automatic Filter Press allows miners to recycle and reuse a significant amount of water in their operations, reducing the need for freshwater intake and cutting costs for the mine site.

Another part of the flowsheet where FLSmidth has had success is in evaluating whether to process coarse and fine waste materials or combine them. To this effect, it has introduced a proprietary co-mingling solution named EcoTails which blends "fast-filtered" tailings with waste rock in transit to create a trademarked geotechnically stable product it has named GeoWaste.

"With the reduction of fines, we have seen significant improvements in the dewatering capabilities, but we've also seen improvements in the material properties - these have been evaluated geotechnically and geochemically by customers using large test pads. Without the fines, you get a more stable material for stacking, so there's less chance of liquefaction," Rahal said.

Digitalising for the future of tailings

As a part of its forward-looking approach, FLSmidth has also developed a digital control system that combines smart thickening and smart filtration controls to improve the stability of the operation.

The Dewatering Expert assists operators in dealing with variability in the process, ensuring that the materials being stacked meet all geotechnical requirements.

The system incorporates a range of technologies, including Intelliplate, which allows the control system to detect media failures so that the media can be changed out prior to damage occurring to the more expensive plate. The filtration inputs that need to be monitored for variability include feed density, flow rate, mineralogy and pressure. Operators are automatically notified if any of these variables are detected to be outside a pre-set operating range or limit.

It is designed to be capable of handling large numbers of inputs and outputs, ensuring smooth operations, maximum availability and consistent achievement of moisture targets. For example, the primary outputs that must be monitored are cake moisture and filter throughput. This has seen FLSmidth develop a new cake-moisture sensor that can be used to give real-time readings for feedback to the control system.

According to FLSmidth, the system results in a better operating dewatering system and improves the results of the dewatering. The firm's embrace of its customers' digitalisation also extends to other aspects of tailings, including its SmartCyclone monitoring and a control solution that improves the performance and life of cyclones in all applications.

Despite the heavy focus on digitalisation, Rahal emphasises that this works not in isolation, but as part of the overall MissionZero approach to tailings.

"When you tie it all together, better engineered tailings dewater better, they behave better, and, along with digitalisation, this leads to an overall system that is lower in power usage, lower in water usage, produces lower emissions and is easier to control."