Defeating the Deleterious
Whether at the head of a circuit or scavenging tailings, today’s flotation innovations address challenges presented by declining grades, rising costs and aging plants
By Jesse Morton, Technical Writer
At the time, flotation, as a discipline, was in its infancy. The solution, being trialed at a couple of mines in the United Kingdom, represented a much-needed first and a “great success.” It piped oil into a watery ore slurry and agitated the mix. After that, “the oil with its charge of mineral is separated from the water and waste rock by running the whole into a large pointed box, from the bottom of which the rock and water flow, while the oil and mineral float on the top and overflow for subsequent treatment.”
Word got around and the Elmore method took off. By late 1916, it was in use by just under a dozen sizeable copper mines around the world, a big chunk of the total in existence back then. It was an example of the speed at which a flotation innovation that meets the pressing needs of the day can go from prototype testing to market acceptance. Today’s innovations and improvements follow a similar trajectory. What has changed is how “in recent times, ore is becoming more complex,” according to flotation expert Virginia Lawson. “It is not as simple as it used to be.”
Growing challenges only intensify the race for viable solutions and ensure the demand for those with a successful track record. Reports from some of the more prominent innovators in the space provide examples.
Certainty Over Probability
With the 30th anniversary of the first deployment of a Jameson Cell imminent, research and development for the fifth generation of the solution is under way, said Lawson, technology manager, Glencore Technology. “Every 10 years or so, you are looking for some changes to address anything that you’ve learned over the previous 10 years,” she said. “So we are just stepping into the Mark V and looking for areas that would improve the performance of the cells for end users.”
With customers dotting the globe and with the solution deployed to a sizeable sample of the full range of conditions and grades found in the sector, feedback from the field will guide any design changes, Lawson said. “We are always looking for ways to improve the cell and make it more operator-friendly,” she said. “And right now, we are seeking feedback from operations on improving the designs for future cells.”
The solution is described as a high-intensity froth flotation cell typically used as part of the cleaning circuit in a concentrator plant. It creates a high-pressure jet of mixed air and slurry, which shoots through a pipe, called the downcomer, that penetrates and empties into the flotation column. The downcomer is where particle and bubble contact first occurs. “The plunging jet of liquid shears and then entrains air, which has been naturally aspirated,” Glencore Technology personnel reported in a white paper. “Due to high mixing velocity and a large interfacial area, there is rapid contact and collection of particles.”
In the tank, secondary bubble-particle contact occurs. “The velocity of the mixer and large density differential between it and the remainder of pulp in the tank results in recirculating fluid patterns, keeping particles in suspension without the need for mechanical agitation,” the company reported.
The bubbles gather on the surface of the column, and the resulting froth is removed by froth drainage or froth washing. The key technology in the system is the downcomer, which features no moving parts and is based on simple physics to optimize efficiency and cost effectiveness, Lawson said. “You create a hydraulic field and the slurry is drawn up into the downcomer because there is a pressure difference as that plunging jet goes through that orifice,” she said. “It naturally draws air from the atmosphere, so you don’t actually have to use compressors, or any energy associated with compressing air.” The original seed idea for the downcomer is attributed to a laureate professor, Graeme Jameson of the University of Newcastle. In search of a means to optimize flotation performance of a lead/zinc concentrator, he was commissioned by Mount Isa Mines, in Queensland, Australia, to develop the idea, which he patented in 1986 on behalf of Newcastle Innovation Ltd. That year, the resulting pilot cell was tested. Three years later, two full-scale cells were installed in the lead-zinc concentrator at the mine. Two more were built that year for a similar concentrator at nearby Hilton mine.
From there, the technology gained in popularity and demand, seeing relative widespread adoption in Australia first before going global. In the roughly three decades that followed, the cells were adopted and deployed to plants processing precious and base metal ores, coal, industrial metal ores and oil sands. In 2013, Jameson was named New South Wales Scientist of the year. That year, Jameson Cells at Australian sites were credited with recovering some $30 billion in export coal. In 2015, the solution won the Prime Minister’s Award for Innovation for its role in the Australian economy.
A copper miner, therefore, would enjoy a higher probability of bubble-particle attachment in a single stage, she said. “You’ve got the ability to soft wash, which will improve your concentrate grade, and because the Jameson Cell has such small bubbles, it has a much greater ability to recover tons of concentrate,” Lawson said. “In the same footprint, you are able to recover significantly more tons of concentrate, making it a more efficient use of capital.”
For a molybdenum miner, the downcomer doesn’t allow the target particles to behave the way they normally would in a conventional cell. “Moly flakes tend to be long and skinny and very flat,” Lawson said. “Particles of that shape have a habit of just following streamlines in the water. The beauty of the Jameson Cell is it doesn’t allow a Moly particle to behave according to its shape.”
For a gold miner, the downcomer ensures rapid particle-bubble attachment, which prevents the deposition of calcium on the surface of the gold. “You need to recover it as quickly as possible by using a Jameson Cell at the head of the circuit,” Lawson said. “Those gold particles are recovered fresh out of grinding or regrinding before they have an opportunity to have the calcium deposit on their surface.” Headlines reveal the technology is currently seeing sustained demand. In the last few years, even amid the bust and aftermath of the super cycle, a handful of majors and juniors adopted the solution as a part of brownfield projects.
Telson Mining Corp. announced in the third quarter of 2018 it will test zinc flotation using Jameson Cell technology, hoping to increase zinc recoveries and zinc concentrate grade at the Campo Morado mine, in Guerrero, Mexico.
In July 2017, Glencore Technology reported it sold two Jameson Cells to Toronto’s First Quantum Mineral’s Cobre Panama mine in Panama. At the time, the company reported that cells were also being installed at McArthur River mine, located roughly 600 miles from Darwin in Australia’s Northern Territory, on a zinc-cleaning circuit.
In December 2016, Glencore Technology reported two cells were being installed on a copper/molybdenum circuit at the Collahuasi mine in Chile. In the same report, the company stated Jameson cells had been installed and commissioned at Newmont’s Cadia copper/gold operations. Two more cells were reportedly being built for the Cadia operation, along with “several” others for an African copper miner. It also reported an earlier model cell was being upgraded at a coal operation in Bowen Basin, Queensland.
Those deployments add to the roughly 350 units that were already operating in almost 30 countries around the globe. In each case, the cells were selected as technical solutions to technical problems, increasingly relating to grade, Lawson said. “Deleterious elements are there because of entrainment, and our technology is essential to eliminate those deleterious elements,” she said.
Deleterious means beyond the capability of smelters to handle, she said. “Things like fluorine and uranium and other gangue species too abundant for smelters to deal with,” Lawson said. “In those cases, we are an absolutely excellent solution because, with the froth washing, we can eliminate those materials or those minerals that are there accidentally, and produce very high concentrate grade and improve their return from the smelter.” Lawson said the cells are ideally situated at the head of a circuit “where you might have half your minerals liberated and then we could remove half of those liberated minerals to final concentrate, making the rest of the circuit smaller.”
Adoption is easy as the Jameson Cell “has direct scale-up from pilot testing,” she said. “So, if you have an existing operation and we pilot on your site, then we will know exactly how our Jameson Cell will operate.” With four generations in operation, three decades of history, and field results from around the world attesting to the viability of the solution, the primary barrier to adoption now is normalcy bias, Lawson said. “We just have to get over some of those barriers that people have to adopting something different,” she said. “The technology does it, and it speaks for itself. They just need to be willing to listen and to adopt change.”
Last month, Glencore Technologies announced a 25% capital back performance guarantee on the cells. The guarantee formalizes the confidence the company has in how well the cells will perform, Lawson said. “Work with us and we will demonstrate what can be done and that we are willing to stand by it,” she added.
Coarser is Better
Newcrest Mining Ltd. announced the commissioning of its Coarse Ore Flotation plant at Cadia Valley Operations in central west New South Wales. The plant was calendared to reach full capacity in December, according to the miner’s quarterly report released in September. The miner credited the new plant with helping to improve its numbers. Newcrest reported that “while total mine production was 8% higher than the prior quarter,” Cadia’s “gold production for the September quarter was 37% higher.” The increase in gold production was driven primarily by a return to “access to full processing capacity” after an embankment slump limited mill throughput. It was “also,” however, “assisted by increased head grade … and higher plant recovery due to debottlenecking work in the flotation circuit and the commissioning of the Coarse Ore Flotation plant.”
In its Newcrest 2018 Investor Day Market Release, the miner declared the commissioning of the plant had produced “positive results” and the plant would “support the life-of-mine (LOM) gold recovery improvement.” In the 2018 Investor Day Briefing Book, it attributed possible “energy saving(s)” to the new circuit. The plant cost roughly $30 million, and trial operations began in July 2018, according to Newcrest. It centers on two technologies sold by Eriez, Cross- Flow and Hydrofloat.
The former “is a fluidized-bed classifier,” Eriez reported. In the CrossFlow, feed particles sink through rising waters piped in at the base of the main separator housing. Smaller particles that fail to sink are “carried over the top of the separator,” Eriez reported. Bigger, coarser particles settle and form a fluidized bed that is piped out through the underflow control valve.
Thus, the CrossFlow is used to coarsen feed for the HydroFloat Separator, which floats “liberated and semi-liberated particles at a much coarser size than that which can be achieved using conventional flotation,” Eriez reported. The separator combines “flotation with gravity concentration” for an outcome “that cannot be achieved by either approach alone,” Eriez reported.
The inverted cone shape of the separator tank interior helps provide the “gravity concentration.” Bubbles “dispersed by the fluidization system, percolate through the hindered-settling zone and attach to the hydrophobic component altering its density and rendering it sufficiently buoyant to float and be recovered,” Eriez reported. “The use of the dense phase, fluidized bed eliminates axial mixing, increases coarse particle residence time and improves the flotation rate through enhanced bubble-particle interactions.”
Newcrest reported in the 2018 Investor Day Briefing Book it is considering putting a coarse ore flotation system ahead of its flash float/gravity circuit. Possible advantages include energy efficiency, low operating cost, and a small footprint, the miner reported. At an estimated capital cost of roughly $70 million, the system could possibly contribute as much as two to three percentage points to the targeted percentage increase in LOM total gold recovery, helping, along with other improvements, to raise the target LOM gold recovery rate from 72%, as determined by the prefeasibility study, to possibly 79%, the miner reported. The disadvantage is the newness of the technology, Newcrest reported.
The idea, one of two reported as possible LOM recovery improvement projects, would be subject to the completion of a feasibility study and attainment of the requisite permits and approvals.
Recovering Single Particles
Minerals Refining Co. (MRC) reported it is planning to pilot test its Hydrophobic-Hydrophilic Separation (HHS) system at an American copper mine in the second quarter of 2019. The system, originally developed and pilot-plant-proven to capture and dry the smallest coal fines, will be tested at processing roughly 50 to 100 pounds per hour of ore solids comprised of less than 10 micron particles otherwise destined for the thickener, Stan Suboleski, Ph.D., president, MRC, said. “After the concentrating plants do multiple flotation steps and give up on the ore that is too fine for flotation, that is the ideal place to put HHS,” he said.
Currently, MRC is lab-trialing the system using cleaner-tailings samples from four copper and nickel mines. “Once we are satisfied that HHS works well on all four, we will probably be at the point where we can schedule the pilot test at one of them,” Suboleski said. The goal, he said, is to produce a concentrate that is 20% copper. “At that point, it becomes something that refineries would love to have.”
A 20-t/h commercial HHS system for capturing coal fines is calendared for commissioning prior to the end of 2019. The technology has reportedly been developed to a point where the miner can recover coal fines that are now being pumped to the impoundment as waste. The product, on average, is of a higher quality than that produced by the plant. The system also enables the miner to “dial” in the water content, usually in the single digits, Suboleski said. Those capabilities suggest the tech could be deployed for similar applications in the hard rock space, he said. “We think on the mineral side it might have a future going after really small particles,” Suboleski said. “We’ve recovered particles down to single micron size, and even smaller than that when we were trying it out on rare earths,” he said. “We don’t know how fine we can go with this technology, and that is probably going to be pretty important on the metals side.”
HHS shares characteristics with traditional flotation systems. Instead of being aerated, the slurry is mixed with an oil. Oil molecules simply perform better at grabbing hydrophobic particles, Suboleski said. “It is a matter of contact angle,” he said. “We can recover particles that are both larger and smaller than flotation can.” The system employs several steps. In the first step, the oil and slurry are mixed mechanically. “We have to mix this stuff pretty thoroughly, because if we don’t get the oil on the coal or the mineral particle, it doesn’t get recovered,” Suboleski said. The mix is then piped to a second tank. “These oil-covered particles are attracted to each other,” Suboleski said. “They bump into each other and they form agglomerates.”
Those agglomerates ensconce water droplets. “The impurities are hydrophilic, so they want to go where the water goes,” Suboleski said. “And when the moisture is trapped inside, it also raises the impurity level, lowering the ore grade, which is the reason that agglomeration has not been used widely in the past, even though it was first discovered in the early 1900s.”
The patented method for agitating the mix to release trapped water and waste particles was discovered and invented by Dr. Roe-Hoan Yoon, director, Center of Advanced Separation Technologies, Virginia Polytechnic Institute and State University (Virginia Tech). “It largely involves the application of the correct amount of energy, although other factors are involved as well,” Suboleski said.
The agglomerate-breaking component that is the heart of the technology is called the Morganizer, after MRC Board Chairman E. Morgan Massey, and former CEO of the A.T. Massey Coal Co. “The name came from the developers of the initial unit several years ago and has stuck, somewhat to Mr. Massey’s embarrassment,” Suboleski said. In sync, the oil-coated ore particles rise to the top and the impurities and water are drain from the bottom of the Morganizer. The oil-ore mix is then piped into a vacuum filter, and then put through an evaporator, which enables the process to capture and recycle the oil.
The final product, which has, at times, been of a reportedly high enough quality to be categorized as “pure carbon,” emerges dry from a chute. It is the result of roughly seven years of research and development. MRC began brainstorming and testtube scale tests on the technology in 2011. A proof-of-concept unit was constructed the next year. “Based on results of tests from seven different coal plants, we went ahead and commissioned a company that specializes in building pilot plants to build one for us,” Suboleski said. “The design and construction consumed all of 2014 and the first part of 2015.”
The pilot plant was tested for two years. The feed averaged 58% ash, and the resulting clean coal averaged between 4% and 4.5%. “We discovered then that we could control the moisture,” Suboleski said. MRC stopped testing in late 2017 and “started our initial commercial plant design,” Suboleski said. “We now have our first plant under contract,” he said. And because it uses minimal water and otherwise is self-contained, it will operate under the existing permits for the plant.
Meanwhile, the idea was bandied about that HHS could be used in the process of recovering rare earths from coal waste. That in turn pushed the envelope to develop it for hard rock mining applications, which ran into inevitable hurdles. “Everybody who worked on this thing is a coal person,” Suboleski said. The idea, however, had legs, and labscale testing of HHS at recovering copper from what was otherwise considered waste has proven successful thus far. “We’re getting good results from samples of cleaner- stage flotation tails,” Suboleski said. “Now we want to broaden out to test samples from more processing plants — and ore types — and make sure it is not a fluke.”