Tailings have historically been a liability for the mining industry, comprising massive volumes of slurry or sludge-like process waste that has to be safely contained for decades, constantly monitored, and isolated from the surrounding natural environment. The weight of accountability continues to press heavily on the industry, amplified by public outrage over a series of catastrophic tailings dam failures.
The spotlight of concern focused on tailings management has illuminated the need for better planning, engineering and upkeep of tailings storage facilities. It has also highlighted opportunities for producers and industry suppliers to develop and apply new equipment, systems and technologies that can, for instance, reduce the cost and complexity of tailings pumping facilities, handle dewatering of high-volume process-waste flows in large concentrators, and even recoup economic value by recovering metal values from fresh tailings. Here are three recent examples:
Coarse Particle Flotation to Scavenge Copper Tails
Conventional stirred tank flotation cells have been the dominant workhorse for economically concentrating low-grade mineral deposits such as copper-bearing sulphide ores. This technology enabled the expansion of copper supply at an affordable price. Despite the great success of conventional flotation, it is known and reluctantly accepted that this technology is very poor for extracting target minerals outside of a narrow particle size range. Typically 5%-15% of recoverable copper is lost due to this inefficiency.
Eriez Flotation recently developed the HydroFloat, a fluidized bed assisted flotation cell, which has proven effective at floating coarse ore particles up to two to three times the size limit of conventional flotation. This technology was first introduced at a commercial scale for base metal sulphides at Newcrest’s Cadia Valley operation in Australia. Newcrest very recently announced its plan to expand the application of this technology. There are now other completed HydroFloat installations and a number of additional installations are in the works.
Cadia uses HydroFloat to scavenge fresh plant tails enriched in coarse ore because conventional stirred tank cells are very poor at floating coarse ore. The HydroFloat is an adjunct to the conventional flowsheet and can operate independently from conventional roughers, although they may share the same cleaner circuit. A side benefit of implementing a coarse particle tail scavenging plant is that the mill circuit’s grinding target can be increased without losing recovery. Therefore, the mass throughput can be increased with existing assets.
The business case for a tail scavenging application is primarily based on the additional recovery of lost coarse pay-metals, which Eriez reported is typically 3%-5% of total plant production. Based on this potential, Metallurgical Superintendent Umut Erol of Capstone’s Pinto Valley operation worked with Eriez Flotation to determine whether the HydroFloat technology would be appropriate for their flowsheet.
Pinto Valley is a porphyry copper mine and concentrator, wholly owned by Capstone Mining and located east of Phoenix, Arizona. As part of their PV3 Optimization Strategy, Pinto Valley is investigating capital improvements to increase overall recovery of copper and to increase mill capacity. The HydroFloat in tail scavenging mode offers the possibility to achieve both.
Since every ore is unique, the metallurgical performance of the HydroFloat is assessed by a continuous 6-in.-diameter lab unit, which can be run at Eriez’ full service test lab in Erie, Pennsylvania, or through an approved commercial lab. The scale-up of the results to commercial-scale equipment has been validated on multiple copper porphyry samples.
Preliminary results with Pinto Valley mill tails indicate that more than 50% of the copper and more than 30% of the molybdenum in the final tail should be recoverable with a commercial HydroFloat installation. On the basis of these results, Capstone and Eriez are moving forward quickly to conduct a HydroFloat pilot plant on tails at Pinto Valley later this year to confirm that these results can also be achieved under plant conditions. Lab test work suggests an improvement in global copper recovery of 6%.
Another important result — and a part of the PV3 optimization objectives — is to increase overall mill throughput capacity. This is possible by increasing the target mill grind size since coarse material that does not float in conventional flotation will be picked up downstream in the HydroFloat plant. The results of this pilot campaign could provide the basis for a decision to add a coarse particle flotation circuit at Pinto Valley.
In the Works: World’s Largest Filter Press
Diemme Filtration, a business unit of Aqseptence Group GmbH, is developing a jumbo-sized version of its GHT-F filter press for high-volume tailings dewatering applications. The new model, known as the GHT.5000.F, has a plate size of 5 x 5 m and total filtration surface of more than 3,000 m2. The GHT.5000.F’s plate dimensions are twice that of the company’s largest GHT-F model. E&MJ’s editor-in-chief Steve Fiscor recently spoke with Andrea Pezzi, Diemme’s sales director for North America and U.K., to get details about what the company claims will be the largest machine of its kind in the market.
E&MJ: How did this machine evolve?
Pezzi: It is an outcome of our industry experience over the course of the last 20 years, as process facilities have increased in size and throughput tonnage. High-volume facilities would require a significant number of filtration lines when using standard machine sizes, adversely affecting the overall attractiveness of the investment. Larger plate size translates into a reduction in the number of filtration lines and improves project economics. For example, we’ve gone from a standard 2- x 2-m plate size to 2.5 x 2.5 m, and with our GHT.5000.F, we now have a plate size of 5 x 5 m. The GHT.5000.F will have 141 of these plates. It is 37 m long, more than 9.5 m wide and more than 7 m high.
When we begin a major project like this, we work closely with consultants and clients in order to identify the targets that need to be set and achieved. In other words, we want to ensure that what we offer is suitable for the needs of the client’s site. Once we identify the basic requirements, we can determine the proper pressure setting, for example. With the GHT.5000.F, we can achieve maximum pressure of 15-16 bar, but it can operate at lower pressures as well. We also have the choice of plate types to achieve a specific moisture content.
The “F” in GHT.5000.F stands for fast, and the machine is designed to minimize cycle times. If you have what we’d regard as a fast-filtration product, you will be able to achieve cycle times of 12 to 15 minutes, which translates into four or five cycles per hour.
Tons per cycle, of course, is dependent on the product that is being filtered. In the case of copper tailings, for example, we assume tonnage rates of 140-150 metric tons per cycle.
We are designing the GHT.5000.F to be a “smart” filter press that will work within the Industrial Internet of Things, or IIoT. We think that the opportunity to compile data on a constant basis from its operations will result in better maintenance planning decisions and lower operating costs for the customer. We also intend to apply its IIoT capabilities to maximize the process efficiency and optimize power consumption.
E&MJ: What were some of the major design challenges?
Pezzi: With a machine this size, one of the biggest challenges is in terms of logistics. We had to find ways to maintain the robustness of the overall machine design yet optimize the quantity of steel required because the machine may have to be transported and assembled in a remote location.
We had to plan carefully in terms of worker safety when maintaining the machine or changing the filter cloths. We paid close attention to identifying the parts of the machine that need frequent access for inspection or maintenance, and we’ve provided access points to make the job quicker, which over time provides the customer with lower opex requirements. The GHT.5000.F includes an overhead work platform, complete with safety guards and handrails, that extends the length of the machine and offers a safe place for workers to carry out their jobs. The filter cloths hang from the top of the plate and have no other point of attachment, making cloth changes quick and easy with the machine’s cloth removal tool.
Finally, the machine is designed for fast-fill operations with large feed ports and multiple outlets. Our challenge was to optimize the fill rate without causing excessive wear and abrasion to the valves, piping and filter cloths. We’ve also included two separate washing systems: a low-pressure wash that occurs at the end of each cycle for removing residual filtrate, and a high pressure wash — at about 50 bar or 725 psi — that takes place at an interval set by the operator to keep the filter media clean and optimize filter cloth service life. We understand water conservation is important, and the system we are providing is designed to reuse wash water, minimizing overall water usage and providing advantages from both economic and social points of view.
E&MJ: What is the next step in development?
Pezzi: We are planning to assemble and test the machine next year before shipping it to a customer’s site in South America during summer 2021. This will be accompanied by a virtual launch event that will be available worldwide. We are extremely excited about the project, because it gives us an opportunity to present our company as a solutions provider for an industry that’s very important — mining. We want to make people aware that mines are looking beyond conventional approaches for tailings management — some of which haven’t worked out so well — and are receptive to new ideas and systems like large-scale filtration and dry stack tailings storage that can reduce their risk. Systems that result in risk reduction are always a good investment.
Reclaiming Tailings Sustainably With a Mobile Pumphouse
Water requirements for intensive applications such as hard rock mining and oil sands processing have historically been supplemented by local water sources. Today, these applications face new challenges as the focus shifts to how operations can minimize their environmental footprint but continue to improve productivity while also complying with new regulations.
Weir Minerals suggests the best way forward is not limited to installing energy-efficient products, but also includes working in partnership with companies that can design engineered-to-order solutions.
One of the ongoing challenges for customers is tailings reclamation. The question of how best to reduce dependence on tailings ponds yet expedite reclamation of both water and product in the process was top of mind for one Weir Minerals customer.
Pumping stations are a critical element of tailings management, providing the energy needed to drive the downstream processes. Static slurry pumphouses have until now been the norm, but they are costly and present many limitations when considering alternate tailings processing techniques.
When the customer approached the Weir Minerals Canada dewatering team with a vision to mobilize the pump system for their new tailings treatment process, initially they didn’t know if it was even possible.
“The sheer size and energy requirements of the equipment needed for the application meant that this was a huge undertaking from the beginning. You don’t normally think of 3,500 horsepower pumps and 160 tons of equipment as mobile,” explained Kris Kielar, product manager for Dewatering Engineered to Order Solutions at Weir Minerals Canada.
The Weir Minerals team worked directly with the customer to design an innovative booster pumphouse, engineered especially to manage the Non-Segregating Tailings (NST) on site. The proposed solution was an integral piece to reduce the tailings pond footprint on site through accelerated fines capture and decreased fluid tailings production, thus releasing more water for recycling thereby reducing necessary water intake from local sources. This in turn would expedite reclamation to create landforms that support wetlands and self-sustaining forest ecosystems.
This solution dramatically reduced tailings residence time with a total solution realized through Weir Minerals equipment. Multiflo pump barges mounted with Hazleton submersible slurry pumps extract the target fluid tailings that feed high-powered, land-based, Weir relocatable pump houses. Inside the pump houses, Warman slurry pumps boost recovered tails from the pond to drive the new tailings treatment process plant.
Weir Minerals said its dewatering team designs solutions that also can add value to a customer’s site process. For example, the entire module of the Weir mobile pumphouse can be built offsite at a much lower cost than traditional pumphouses, which are built in-situ. Building a pumphouse in-situ is time-consuming and expensive, as the method requires skilled trades to work for extended periods of time in remote locations.
“Competitor pumphouses built using in-situ construction methods can more than double the construction time and costs compared to the steel fabrication methods we have used,” said Peter Pavlin, Weir Minerals’ North America general manager of Engineering.
The Weir mobile pumphouse is an innovative solution that provides a variety of pumping possibilities for intensive tailings applications. It’s designed to relocate across the site using especially engineered, military-style skid and “jack-and-roll” elements and a novel patent-pending pump/motor suspension system, providing a unique advantage in mobile pumphouse technology. These advances provide operators with distinct advantages over traditional fixed-in-place designs, creating a more agile and cost-effective solution.
“Our ground-breaking design sets a new standard for tailings management applications. Other pumphouses in the market are static and often cause difficulties for operators when they wish to expand into new areas, as they must discontinue service, resulting in a large capital expenditure. Our solution has overcome these limitations by providing the customer with the tools to rapidly reconfigure a changing pumping network and move it to other sections of the tailings pond,” Pavlin said.
The Weir mobile pumphouse incorporates an integral gland water supply system and a separate eHouse for power control and remote communication. A patent-pending, three-point pump base mounting system allows the base and skid to act independently, minimizing the risk of pump and motor shaft misalignment during operation and the relocation process.
“Establishing relationships with our customers is just the beginning,” Kielar said. “By working closely together over several years, we learn the ins and outs of their operation. We hear feedback directly from the people who work with our equipment, and that helps us create even better solutions.”