Will In-Place Recovery Ever Replace the Need for Flotation?
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The history of mineral processing in general and flotation in particular is long and has always been tied to mining methods of the day. Building on the ever-improving fundamental understanding of the underlying science, the most significant trend in flotation has been the putting into practice the learnings from trailblazers such as Professor Fuerstenau that has given the confidence that enabled an ever-increasing scale of operations. There is, however, doubt this ongoing trend is enough to maintain the economics against global trends such as that of falling grades, increasing mining costs, pressure on water supply and demand, rising energy demands needed for mineral processing, and a focus on whole of life value and mine legacy issues.
In addition, we see that globally, the social license to operate for mining (and hence mineral processing) is far from secure and, at the very least, is under much more rigorous scrutiny.
In this paper, we comment on the ramifications of broader uptake of more sustainable mining for mineral processing methods and address the specific question of whether recent progress in in-place recovery will lead to a timely breakthrough. The answer proposed is that this is possible in the next 10–20 years but in the meantime, the focus is just as likely to be on removal of waste (beneficiation) much earlier in circuits. Either way, mineral processing and flotation, as we know it, will change significantly.
KeywordsIn place Recovery Mineral processing Trends
Mineral processing has a long history well covered in a publication by Habashi  which points out “the ancient Egyptians knew already that it would be easier to melt an earth rich in gold particles than another which is poor.” As a result, all efforts were made to enrich the gold by washing away the light gangue minerals. Similarly, another ancient method for enriching gold particles from a river stream was by means of fleece, hence the Greek myth of the “golden fleece.” Since the Middle Ages, striving for improved economics has driven a string of innovative developments in milling and separation. The reader is again referred to the informative and illustrative text by Habashi .
The point is that developments in mineral processing have, since ancient times, been driven by the availability and nature of the minerals delivered from the mine. The ancient Egyptians did not have access to iron and steel and yet a dagger found in the tomb of the pharaoh Tutankhamen is made of an iron-nickel alloy . The source is from a meteorite, again illustrating the point that mineral processing is very much a function of the source of the material to be processed.
2 Mineral Processing and Mining Interact
When we turn to the primary sources of materials that are mined or recovered and sent for mineral processing, it is informative to analyze recent trends. The first we might consider is the incremental improvements to existing methods of mining. Overwhelmingly, the main trend has been one of increasing scale, ever since the breakthrough of open cut mining first practiced at Bingham Canyon in 1906 . Various mines have at times held the world record for size of excavation or daily capacity with Panguna and Freeport featuring, but eventually eclipsed by Escondida.
As such, to maintain (or increase) production, the amount of material to be treated by mineral processing is rapidly increasing and with it are the corresponding energy and water demands and hence costs and carbon footprint. This has led to similarly problematic, parallel massive increase in waste and tailing generation, storage costs, risks, and occasional disasters (see for example Bingham Canyon landslide  and Bento Rodrigues tailings dam failure [11, 46]).
Increasingly new types of equipment promise finer comminution and lower power consumption. Some of these developments are at the small tonnage scale , while others are still in development . There is little, however, that promises to halve energy costs and water consumption, what some estimate as necessary within 20 years to maintain present consumption levels.
A complication that operators are increasingly aware of is the level of impurity in the ore. As grade drops, the relative level of problematic impurities is often increasing. An example of this would be arsenic in many copper sulfide ore bodies. High levels of impurities, such as arsenic, can be of health and safety, and economic concerns, with limits and penalties being imposed in most smelter off-take agreements.
Uncomfortable as it is, we might conclude that chasing economies and efficiencies through the ever-increasing scale of mineral processing unit operations is not keeping up with the requirements to reduce water, energy, and costs.
Finally, we might consider whether the trend to “geometallurgical processing” will deliver the needed reductions in energy and water consumed in mining and mineral processing. This approach to mineral processing goes beyond the “mine to mill” stage and takes a form of selective mining to its ultimate conclusion where much finer parcels of mineralized material are mined and appropriately sorted (as near to source as possible) and then sent for finely tuned mineral processing. The benefits are quite significant, and some mineralizations that were uneconomic using conventional mine planning and mineral processing are now considered economic. Further, by introducing bulk sorting of some parts of an ore body, quite significant improvements in operating costs have been demonstrated, see for example Carrasco et al . The goal, to remove gangue earlier and not to send as much gangue for milling in the first place, has been captured in the concept of Grade Engineering and is being developed collaboratively through CRC Ore [9, 45]. There are also good indications from the CRC Ore and its partners that a more open approach to innovation and cross-industry sharing of developments can help bring down the energy and water demands as well as the costs. The paper by King and Adair  notes a string of improvements that have resulted in the Minera San Cristóbal mine in Bolivia achieving a first quartile position, despite having some of the lowest head grades in the world.
It is relatively early days for this approach, and Grade Engineering with more open innovation will help but we conclude that in-place mining will be necessary to cater for the lower grades of 2028.
3 The Central Role of Flotation to Date
It is interesting to consider the state of the art and the predictions made at the Centenary of Flotation Conference held in Brisbane. Perusal of the volume  is noteworthy for the number of references over a long period of time to the work of D. C. Fuerstenau. Perhaps the most obvious conclusion is that then, and now, and as noted above, flotation maintains a dominant role in mineral processing with the scale of operations still trending upwards. As M.W. Fuerstenau summarizes  despite its maturity, the field of flotation is quite active and rapidly changing.
As noted by one of the authors [4, 5], there is a deep understanding of the fundamentals, e.g., of bubble attachment, foam behavior, turbulence, and flow fields, and this contributes to the successful and relentless trend to larger unit operation sizes. At the same time, the boundaries of what can be separated by flotation are being pushed, especially in terms of both finer and coarser sizes, compatible with the trend to eliminate gangue minerals earlier in a flow sheet.
With such a robust base of large-scale practice and underlying technological support, flotation is unlikely to be replaced with an alternative technology soon. What is more likely to drive change is the societal push for much lower environmental footprints associated with mining and associated mineral processing. While small-scale opportunities exist, large-scale application of comminution and flotation underground seems unlikely if the prime driver is less footprint on the surface. In summary, it is more likely to be issues of the social license to operate than technological advances that render flotation obsolete.
4 The Social License to Operate
Mineral processing as a key part of mining has always been subject to a social license to operate. The revolution that closed the Panguna mine is but one reminder that the license to operate can be abruptly withdrawn . Many argue and indeed demonstrate that understanding and engaging stakeholders are the keys to obtaining and maintaining the license to operate, e.g., Reggio and Lane . There is excellent recent work on testing just how much and what form of engagement is the most effective in obtaining and holding the social license to operate . This work from CSIRO used engagement for a hypothetical mine and observed that the most effective route in winning trust was not just provision of an overview of the project but also a commitment to engage, a demonstration of adherence to prevailing regulations and requirements and, importantly, also allowing the community an opportunity to contribute. This suggests that the more novel practices of in-place recovery have a reasonable chance of gaining acceptance provided best practice of engagement is followed.
Although not discussed in this paper, there is a similar complex challenge for regulators to better understand future novel approaches to value extraction (such as being pursued by Mining3) and develop appropriate regulations and approaches to their permitting.
What is clear  from an analysis of projects worldwide is that conflict with local communities translates directly into delays and business costs. This study is based on a direct empirical analysis of 50 projects around the world, and they report an estimated cost of $20 million per week in delayed production and stoppages for mines with capitalization of between $3 and $5 billion. Most companies experience these costs as delays in production, but in some cases, projects are abandoned altogether after investing significant costs. Interestingly, in addition to these costs, the study also found that the average time taken for projects to come on line (and approach name-plate capacity) has doubled in the last decade and that non-technical risks represented around half of the total risks faced by companies.
While it is uncomfortable for many associated with mineral processing, there has been considerable activity suggesting that mining, as we know it, is dead and that a new approach is needed [20, 21, 48].
5 In-Place Mining as the Next Generation
While it is clear that mineral processing will adapt and change in response to changes in mining processes and that this is nothing new, the focusing question of this paper is when mineral processing per se will no longer be associated with mining. Is this a pipe dream or can we expect progress within the next 20 years? As an aside, this is not to suggest that mineral processing disappears. The advent of the circular economy and the drive to recycle materials will always require “mineral processing” to help sort and concentrate mixed streams, whether plastics, building materials, domestic waste, or contaminated soils. For many of these, the equipment used is derived in the first instance from mineral processing but evolves to be fit for purpose. The crushers developed in Russia for comminuting reinforced concrete to allow easy separation of the steel are a good example.
In terms of in-place extraction of components, nature has been demonstrating this for a long time. The original “Rio Tinto” is a river in southwestern Spain where the red color of the water is from acidic dissolution of iron minerals. The blue-green color of the stream that runs to the ocean from the abandoned Panguna mine on Bougainville Island is another example of in-place dissolution of metals, in this case, from waste dumps, rainfall, and exposed sulfides—a classic example of acid mine drainage. The lithium-bearing salars of South America can also be considered a natural example of value extraction occurring without traditional mining, comminution, or flotation.
Noting the leaching that occurs in nature, there have been many efforts to directly leach valuable minerals: copper as a prime example. The early efforts at Bingham Canyon were not successful as many of the minerals in the waste dumps are not amenable to simple acid leaching. Indeed, the track record for in-place leaching (or in situ recovery) of copper has had many attempts but until relatively recently, few successes . Most of the abundant copper minerals (particularly sulfides) are simply too slow to leach at reasonable temperatures. The more readily leachable minerals have been mined and heap leached so that the chemistry and kinetics are well known. Indeed, heap leaching operations can be very large. What is now apparent is that oxide copper deposits are now being targeted for leaching in situ and with good environmental performance and with the necessary social license to operate. In Arizona, two copper ISR projects, the Excelsior company’s Gunnison project  and the Florence Copper project , are both progressing well through approvals and into demonstration. While in Russia, Uralgidromed OAO, built by the Russian Copper Company in 2005, operates an in situ recovery facility from the Gumeshevskoye deposit and appears to be in commercial production . Indeed in Australia, the level of interest in in situ recovery for non-uranium opportunities has never been as keen, and both copper and gold targets are currently under consideration by a number of companies.
To some extent, the spate of interest in in-place recovery of copper should come as no surprise. References to in situ recovery date back to 177 BC, and the Chinese are known to have won copper by in situ recovery in 907 AD. While applications in deep hard rock are still to become common place, porous soft rock deposits have been routinely mined by in situ recovery for soluble salts (e.g., potash), uranium, gold, and lithium.
Indeed, the low cost and environmentally sound nature of an ISR approach to the process of extracting values is illustrated well in the world of uranium mining where around 50% of the world’s uranium is extracted using an ISR approach and the all of the lowest 1/3 cost uranium producers are all using an ISR approach . New low-cost uranium ISR opportunities continue to be established although (at the time of writing) the value of the uranium product is a major hurdle to raising capital for investment .
6 Next Steps for the Mine of the Future
There have been many visionary projections for the mine of the future, including one of the present authors at the IMPC in 2003  and a recent update . The authors contend that there are two pathways to in situ recovery (ISR) of values from hard rock minerals located deep underground. Both are evolutionary on existing practices.
The first path involves brownfield deposits and shallower mineralizations. There is rapid development of enabling technologies that allow solution mining (or ISR) practices to extend into a broader range of ore bodies [24, 26, 34, 35, 36, 37]. The challenges are numerous but include the following: advanced in situ ore body characterization tools, robust self-sufficient and wireless metal-specific sensors for environmental and production monitoring, controllable fracturing technologies and improved in situ target mineral liberation, and advanced lixiviants (more robust but environmentally benign and target metal selectivity). In parallel greater understanding of and the ability to measure and model fracture networks and ore body porosity, lixiviant flow, and soluble metal pathways, economic outcomes (costs and production) will occur and improved confidence in ISR will grow . This will likely depend on some early successes that demonstrate the progress. In particular, brownfield use of an ISR method for mine life extension and increased value recovery, e.g., around or in open pits and underground mines (operating or abandoned), will give operators confidence to move into green field projects [26, 36].
Just as hydraulic fraccing has revolutionized the production of natural gas and changed the world order in terms of oil and gas production, so as application of the similar stimulation processes to increase in situ access to target mineral surfaces for solution mining practices will be a key step in enabling the mine of the future.
It should be noted that in situ recovery differs quite significantly from conventional mining which primarily targets at various scales the geology and structure of a mineralization. ISR by comparison requires a different approach, essentially eliminating conventional mining and mineral processing, but requiring even more detailed understanding of the underlying characteristics of the mineral system, its geology, mineralogy, setting, and hydrology. The two key (and interconnected) challenges in establishing initial potential for an in situ recovery approach involve (1) ensuring adequate and sustainable fluid pathway and in situ access for a lixiviant to the target mineral systems; considering inherent and induced porosity, permeability, value mineral liberation, and exposure, while also considering boundary geology, potential natural attenuation, and potential flow barriers (natural and introduced) and (2) development of improved lixiviant systems and lixiviant delivery, involving both solubilizing reagents and, as needed, oxidants, buffers, and other chemicals that accelerate dissolution and maintain favorable solution chemistry (including avoiding detrimental lixiviant/gangue chemistry).
If these challenges can be overcome in laboratory and demonstration scale, then before field trials and application start, there is the necessary establishment of environmental monitoring and risk mitigation strategies (proactive and reactive), lixiviant system design and flow optimization, barrier/boundary monitoring and accurate fluids flow modeling, production well monitoring and extraction optimization, regulatory requirements, and very importantly, the social license to operate as additional factors that need to be considered and addressed.
The challenges with in situ recovery should not be underestimated, especially given the public concerns about water management and water rights, fracking, and the possibilities and dangers of groundwater contamination. In situ recovery is more about reservoir engineering than mineral processing. A strong understanding of local geology and hydrogeology is essential. New technologies are being developed and varyingly being demonstrated at scale that can assist with establishing improved and more extensive fluid pathways (within the ore body) while introducing barriers around the target mineral system. A range of management techniques over extraction and flow gradient management is also needed. In-place monitoring wells are still critical together with a plan of what to do when or if an excursion is identified. To eliminate any delay in leakage excursions being identified, real-time standalone sensors are necessary and examples of such solid-state sensors are being demonstrated on a working ISR operation in a monitoring role at the time of writing .
The second and parallel path to the mine of the future involves deep mineralizations. While deep rock mining is never easy, one notes that there are many developments in sampling, analyzing, and understanding the nature of rock masses. There are good reviews on this in the set of articles in the August 2017 edition of “Engineering” with its focus on efficient exploitation of deep mineral resources .
So, we conclude that it is only a matter of time before in situ recovery becomes standard, thus changing the whole nature of mineral processing.
7 Recent Initiatives That Suggest In Situ Recovery Will Be Commonplace Within 20 years
The development of knowledge and enabling technologies that would create the opportunities for broader application of an in situ recovery (ISR) approach are being promoted and pursued by Mining3, a partnership formed in July 2016 that brings together researchers, technology developers, and operating companies in a collaborative manner.
Mining3 is a world-leading research organization, directed by its global mining industry members to develop and deliver transformational technology to improve productivity, sustainability, and safety. Its world-class researchers and engineers develop tangible solutions to industry-identified challenges using both fundamental and applied research as well as leveraging off an extensive history of impact through a Cooperative Research Center (CRC) for Mining and the research partners. As well, Mining3 is a partner with Environmental Copper Recovery, Thor Mining, and Terramin Exploration in a further CRC grant targeting ISR at the Kapunda site in South Australia. Mining3 has a track record of successful delivery of real-world solutions from its research (commercialization), ensuring they are available as rapidly and effectively as possible.
The second step towards ISR is what we call in-mine recovery. In this case, an ore body is fragmented, either by removing a small amount of rock as in the starting of a block cave or alternatively, treating a mineralization already caved. Fresh leaching agent is delivered through a borehole and pregnant liquor collected at draw points and pumped to the surface through a borehole. The benefits are a much-reduced energy demand, improved resource utilization, less infrastructure, and minimal surface waste with no tailings. Fracture modeling is a key enabling technology as are hydraulic hoisting and fluid management, leaching and metal extraction technologies, wireless detonation, and smart blasting together with remote and automated rock breakage.
Such innovative alternative value extraction approaches will enable the profitable extraction of many currently uneconomic ores, both greenfield and at existing operations (open pit or underground) where increased value recovery, mine life, and longer lasting jobs would result. They are also the stepping stones to a wider application of ISR in hard rock mining.
Since antiquity, mineral processing has always been linked to the methods of mining. While some would argue that mining as we know it is dead, a more reasonable approach is that with falling grades, ever more costs for energy and water and a much more focused requirement for the public license to operate, mining must achieve the extraction of metal values with less than half the energy and water requirements seen today. Such a drastic change is unlikely to be met just by incremental improvements in mining and mineral processing.
The most likely 20-year scenario is that there will be significant adoption of in situ recovery of values from deep, hard rock deposits with very little surface footprint or impact. The Mining3 initiative described in this paper is a good step in expediting the process of change. This will be complemented by more and more examples of solution mining of shallow deposits.
The precise nature of the geology, chemistry, rock properties, hydrogeology, and other local factors combine to suggest that not all mineralizations will be suitable for in situ recovery. As such, mineral processing and flotation will still play a role in mining that will complement their role in the recovery of value in recycling as the world moves more towards a circular economy.
The authors acknowledge useful discussion with colleagues, in particular, Ben Adair, CEO of the CRCORE.
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