Flotation has been a mainstay of mineral processing for the best part of a century, and the technology continues to develop. E&MJ asked some of the world’s suppliers of equipment and reagents for their insights on current and future trends.

Flotation is one of the key technologies within the mineral processing catalogue. And while the concepts have remained more or less unchanged since the concept was first introduced, there have been some very significant developments in the areas of both technology and reagents over the years. Take, for example, the introduction of column cells, which at the time was considered revolutionary. Today, column cell technology is widely used throughout the industry. Or the continuing trend toward larger and larger flotation units, as concentrators are designed for ever-increasing throughputs of lower head-grade ores.



Flotation testwork at one of Clariant Mining Solutions’ laboratories; the first stage.
 

For this article, E&MJ sought the expert views of some of the companies who supply the world's mines with flotation reagents, not only in terms of the chemistry involved but also where operators can improve their flotation performance and, hence, their profitability. We also asked a number of the world's leading suppliers of flotation equipment for their technology news and for their views on what the future may hold in terms of applications and unit sizing.

Reagents: Turning to the Experts

The Danish chemicals company, Cheminova, manufactures the Danafloat product range, which is used as collectors in the flotation of sulphide and oxidized mineral ores. Its responses to E&MJ's questions were provided by Thomas Velgaard, global manager for fine chemicals.

Texas-based Clariant Mining has an extensive range of reagent chemistries for the flotation of sulphide ores and industrial minerals. Its views were voiced by Paul Gould, global head of marketing and application development.

Kenneth Lee is a customer solutions specialist at Orica, the Australian-domiciled international chemicals company. Orica's product portfolio includes flotation, leaching and dewatering reagents, as well as blasting products and grinding media.

Headquartered in Illinois, USA, Nalco offers a broad range of collectors and frothers for applications in both base metals and coal. Steven Paulson is the company's global marketing director for mining and mineral processing.

While essentially an equipment manufacturer, Westpro Machinery discussed the reagent questions with representatives of Quadra Chemicals. Brock Taplin, Westpro's manager of mineral processing, provided their responses.

The final set of responses, from Eric Wasmund, global managing director for Eriez Flotation Division (EFD)-formerly known as Canadian Process Technologies-provides another equipment company's perspective of reagent usage and trends.

Regent Chemistry Development

The first question E&MJ posed to the panel of flotation reagent manufacturers looked at any major advances that have been made in reagent chemistry over the past 10 years.

For Cheminova, Velgaard said that from an innovative molecule basis, the industry has not invested in the development of new flotation chemistries per se for the past three decades. Essentially, all its efforts have been focused on learning to understand better flotation collector responses to different mineralogy species, and tailoring collector combinations to enhance process performance for the more complex ores and difficult processing conditions the industry is experiencing.

According to Gould (Clariant), the most recent reagent advances have been in the fields of the flotation of phosphate and iron ore. For the beneficiation of low-grade phosphate ores containing low silica, ferric oxide, aluminum oxide, magnesium oxide, and calcium oxide contaminants, Clariant has developed new anionic collectors that provide higher recoveries and grades than the traditional fatty acid anionic collectors commonly used around the world for semi-soluble salt minerals.

Clariant's new chemistries provide an alternative to commonly used fatty acids and their salts (carboxylates), with a higher ROI for the plant, Gould added, with the company specializing in the development of reagents for the reverse flotation of phosphate and iron ore.

Lee (Orica) looked at a different aspect of technology developments. A major improvement in flotation optimization has been the increasing use of automated quantitative ore characterization to assist in tailoring flotation reagent schemes for specific mine operations. Automated mineralogy analytical techniques typically involve Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS), he said.

For Nalco, Paulson told E&MJ that important developments have included the development of reagents that provide greater selectivity as well as improved combination collectors for copper and molybdenum circuits. Another advance, he added, has been the development of collectors with improved health and safety characteristics, such as the company's CoalEx collectors for coal flotation.

Westpro's Taplin commented that new frother developments have been the key chemistry change in the past 10 years, from its experience. The movement away from the typical alcohol-based MIBC to more aggressive high-molecular structure glycol-based frothers has allowed milling operations to grind coarser but still have high metal recovery. Bubble strength has been enhanced because of the nature of the glycol-based frothers.

Wasmund (Eriez) pointed out that continued improvement in selectivity is a major advance. "As we continue to consume the ‘easier' orebodies, it is becoming necessary to continually develop reagents that are more selective with regards to complex mineralogy," he said.


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A Metso 300-m3 cell. The company is currently designing cells with capacities of up to 660 m3.
 

Increased Ore Complexity

Gould: As ores become more complex, separation requires more selective collectors to operate in more complex flowsheets. Reagents are being developed that are more selective in the roughers, and especially more selective in the cleaners and scavengers. This has become a major area of research.

Taplin: One of the key areas is the development of new collectors due to the limited number of high-sulphide copper orebodies, and the increasing amount of oxide ore blended with sulphides. New collector development is targeted to allow for better recoveries using DTP, mercaptons and hydroxamate chemistries, increasing the typical low recoveries associated with oxide-blended ores.

Paulson: The increased complexity of orebodies and higher variability in mineralogy drives the need for more customized programs. Nalco is addressing this by performing detailed mineralogy studies and then developing tailored reagents with improved performance for a given set of conditions. This gives the operator flexibility in changing reagents as the mine plan progresses.

Wasmund: The industry is addressing complex mineralogy by conducting more bench-top and laboratory-scale flotation evaluations, both on new projects and existing concentrators.

It is an adage in our business that the best metallurgical results are obtained by a simultaneous optimization of ore characteristics, reagent chemistry and flotation equipment, and this is especially true for complex mineralogy.

Lee: Oxide flotation and reverse flotation techniques are increasingly being used to maximize mineral recovery in more complex orebodies. This has led to the development of novel collectors such as hydroxamates for oxide flotation and amine-based collectors for reverse flotation in the iron-ore industry.

Traditionally controlled potential sulphidization (CPS) has also been used successfully to recover oxide and surface oxidized minerals using conventional sulphide collectors, which is a more complex processing route when compared to the novel oxide collectors but normally is more cost-effective.

Velgaard: The reagent strategy is dependent on the source of the complexity, which can include the particle liberation size, the types and qualities of any interfering minerals or water-chemistry impacts. In addition, the range of ore responsewithin the same orebody can vary widely, posing flotation chemical suite optimization challenges.

There is usually no single "magic bullet" flotation reagent chemistry suite combination that will be the optimum, so it is incumbent on suppliers to test and develop flotation reagent suites that offer the best response to individual ores.

Tailor-made Reagents

E&MJ then asked the respondents for their advice on how reagent suppliers can best tailor their products to meet the needs of individual mines.

Paulson: Knowing the mineralogy as well as the process and operational conditions to then combine chemistries that suit the specific ore type. And also, to provide timely technical assistance when changes or adjustment in the programs are needed, he added.

Paulson: Knowing the mineralogy as well as the process and operational conditions to then combine chemistries that suit the specific ore type. And also, to provide timely technical assistance when changes or adjustment in the programs are needed, he added.

Taplin: The key before tailoring any chemical cocktail is to understand fully what needs to be floated. More and more mining operations use the following three factors before making any reagent decision:

  • Ore-the mineralogy, liberation, particle size and variability;

  • Chemistry-particle hydrophobicity and contact angle, selectivity, water chemistry, pulp pH and Eh, and the reagents- the collector, frother, depressants and dispersants; and

  • The machine-the type, design, bubble size, gas hold-up, carrying capacity, lip length and mixing intensity.

Gould: As orebodies become more complex and of poorer grade, the need for more tailored reagents is becoming more and more common.

It is not often appreciated what chemical suppliers need to do in order to bring a new product to market. Not only do they need to create a new chemistry, but also create a repeatable manufacturing procedure, source secure quantities of raw materials and satisfy regulatory requirements.

Wasmund: We have found that working closely with both reagent suppliers and mines can provide great dividends. While the miner understands the overall goal, the reagent vendor has an innate understanding of the complex surface chemistry, and the equipment supplier knows the limits of their machine. When working together, this is a powerful team.

Velgaard: As noted earlier, the chemical supplier's focus must be on providing technical support in defining the optimum combination of collectors, frothers, and flotation modifier chemistries and combinations. Because chemical suppliers are focused on how flotation reagent chemistries impact the process response, they are the application experts-or should be. Suppliers must develop a good understanding of how their chemistries impact flotation performance, and importantly develop methodologies for creating the product combinations and blends that will be best for the individual customer.

Lee: Suppliers need to work with customers' mill operations personnel to understand fully their specific needs, in order to develop jointly a tailored reagent solution to maximize recovery.


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A bank of Tenova Delkor BQR flotation cells, which the company makes in sizes from 0.5 m3 to 150 m3.
 

So What's Going Wrong?

Given the strong relationship between reagent suppliers and flotation operators, E&MJ asked the experts if there are any particular problems that they see regularly in terms of poor practice in mineral flotation, and if so, what advice can they give to plant operators to help them put these right.

Gould: Commonly seen issues are:

  • Frother under-dosing, causing unstable froth and large bubbles;

  • Over-dosed frother, causing froth that is too stable and small bubbles;

  • Air rate too low, causing low recovery, slow froth and small bubbles; and

  • Feed conditions that have changed, but the flotation process has not been recalibrated.

Lee: Occasionally mine operations may base their future metal production budgets on historical metallurgical data, with insufficient metallurgical test work completed to define optimal operating parameters accurately for future ores. This can lead to a need to adjust processes and reagents on-the-run as the ore quality changes, potentially resulting in suboptimal recoveries and higher, unbudgeted operating costs.

Paulson: Poor control or adjustment of reagent dosing with respect to process-condition changes such as ore mineralogy, particle sizing and water chemistry, as well as operational conditions.

Taplin: New flotation operators or ‘green' employees seem to be the biggest challenge for the industry. We have lost the experience of key operators who can visually see changes happening on their float circuit, and are able to adjust on-the-fly. Froth cameras and viscosity tools help, but nothing will replace a trained operator.

Wasmund: Too many times, we see that the answer to a mechanical deficiency isto simply ‘turn up the chemical.' For instance, when there is poor coarse particle recovery in a flotation circuit, many times the collector rate is increased along with the extender (i.e., oil) in an effort to overcome a mechanical process issue. In reality, choosing the correct technology for a particular size class or orebody may be the best approach. By utilizing the best-in-class technology, it has been found that recoveries can improve while simultaneously optimizing reagent consumption.

Velgaard: As implied in the question, in fact flotation chemicals are only one facet of the ‘flotation system,' where ore conditions, mineralogies, process-system as-pects, how the process is operated, and other factors, define the process capabilities. There are plenty of opportunities for improved flotation performance; we consider the main ones to be training, particle liberation and maintenance.

Since an operator's ability and process understanding has an overwhelming impact on process capability, there is a lot of ‘low-hanging fruit' from having well-trained operators who are also well-coordinated with the other plant personnel. A second area is to have sufficient mineralogical and morphological understanding of the ore being processed, as good separation and recovery is dependent on having sufficient liberation to achieve metallurgical targets.

And finally, properly maintained and optimized equipment is necessary for good process control.

Optimizing Reagent Usage

What are the key factors that flotation plant operators need to consider in order to optimize their reagent use and overall operating costs?

Velgaard: Once a reagent suite has been defined and proved through laboratory work, and confirmed by plant testing as being the best for a particular application, the operational key is to avoid under- and overusing reagents. There is an optimal range where the metallurgy is maximized. Operations should be adjusting their reagent dosages based on variations in tonnage throughput rates but also, often overlooked, varying mineral content.

Unfortunately, defining the optimum dosage is a bit of a moving target since different ores within an orebody inevitably require different reagent dose levels. Finally, operators should make evaluating defining a proper reagent suite and combinations as well as appropriate dosage points an ongoing quest to optimize their mill's metallurgical performance.

Taplin: Changing ore provided by the mining operations seems to be the biggest challenge for any plant operator. If operators know what is expected, they can key or dial in their process and reagent usage and optimize all elements to run a smooth operating circuit. However, if the ore changes on a daily or hourly basis, this will be difficult to manage, and the end result will be higher reagent usage and poor recovery.

Wasmund: The biggest factor to consider is choosing the correct technology for the various size classes treated. Conventional cells are tailored for the “bulk” of the typical size distribution that occurs generally between 50 and 200 ?m. Unfortunately, a significant part of the flotation feed lies outside this range. As such, the operator must have an understanding of their feed ore and understand that they may not be able to simultaneously optimize the separation across the entire particle-size spectrum.

On the other hand, understanding the orebody and the deportment of the values as it pertains to the various size classes can help the operator identify other technologies that may be able to better treat their ore.

Gould: When reagents are selected, it is important to look at the Return on Investment (ROI) of the complete process: the return from the recovery and grade that is generated by the total chemical package. For example, it is best to consider the frothers and collectors in combination, and not as isolated systems.

Paulson: Operators need to select compatible collectors and frothers to match up with changes in ore characteristics, while the automation of reagent addition will help optimize usage.

Lee: It is important to define the problem. Make distinct changes in the plant and see how they influence flotation performance before making any further changes. There needs to be closer communication between the technical staff and operations to define outcomes and measure process improvements when evaluating any reagent change or projects aimed at reducing operating costs.


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A Westpro Machinery conventional flotation circuit at Mina San Rafael in Guatemala.
 

Looking Ahead

Finally, E&MJ asked the experts for their views on what the main trends are likely to be in relation to the development and introduction of new reagents.

Paulson: With the processing of highly variable and more complex ores, customers are demanding faster responses to their ore changes. We expect the development and introduction of new reagents to be much faster than the current development time-frame. New products will include environmentally friendly reagents with non-carcinogenic effects and biodegradables, and there will be better dosage control of collectors and frothers via automation.

Gould: The key trends are toward higher mineral selectivity and greener chemistries. Currently flotation reagents are dominated by chemistries that are decades old, and in some cases more than a century old. These reagents were developed in a time when mineral head grades were much higher and environmental impacts were less of a concern.

Velgaard: Because the development of new flotation chemistries is a high-risk business proposition with low expected returns, we think it very unlikely that chemical companies will invest in the search for new chemical families.

We expect that over the next 10 years, the bulk of product development efforts will be related to a better understanding of chemical-metallurgy responses, improving the quality of existing products, and focusing on developing product blends that provide improved metallurgical performance in general-and blended specifically for individual mills.

Lee: A likely trend will be the improved application and fine-tuning of existing reagent chemistries based on empirical and fundamental research. Improvements will be driven by a more thorough understanding of the surface interaction of existing commercial reagents with ores, via the use of enhanced analytical technologies to better define metallurgical characteristics and issues for an operation.

Taplin: More and more frother and collector improvements will be coming to the market, as well as enhanced flocculants and depressants used to control clays, pyrite and other challenging elements that new orebodies are presenting to the mining world.

Wasmund: We think the reagent suppliers will continue to offer more specially tailored chemicals that target the desired ore surface very selectively. Again, as orescontinue to become more complex, the reagent chemistry gets that much tougher. Another big trend is environmentally friendly reagents.


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Eriez Flotation Division’s HydroFloat Separator combines traditional teeter-bed separator technology with flotation cell selectivity for coarse particle recovery.
 

The Machines Get Bigger...

Not only are the chemical companies involved in a continuing search for new reagents and applications, but the equipment manufacturers are also investing in developing the technology to optimize recoveries and handle ever-increasing throughput requirements.

In a paper presented at the last SME meeting, Devan Govender and others from FLSmidth provided an overview of the forces driving increases in cell capacities, with available cell volumes having quadrupled over the past decade as high copper prices coupled with lower grades have brought requirements for ever-higher plant throughputs. In addition, they said, higher-capacity individual cells offer proportionately lower capex and power costs than their smaller counterparts for a given throughput, while from a construction perspective, larger cells do not need much more headroom for either installation or maintenance.

The company told E&MJ that economies of scale are forcing flotation cells to keep getting bigger-and more efficient. With concentrators now being designed for a capacity of 200,000 mt/d and more, new trends in flotation plant design mean that instead of having a large number of cells per row, the average concentrator has between five and seven high-capacity units. In addition, these cells are attractive where existing high-capacity plants have limited room for expansion.

To design the 600-m3 machines, FLSmidth made computational fluid dynamics (CFD) models of existing cells, and scaled them up using dimensionless and hydrodynamic analysis. The 600 Series SuperCell uses WEMCO and Dorr-Oliver mechanisms, with an XCell 600 Series machine to be developed later.

According to Metso's global manager for flotation, Thierry Monredon, the company recently reorganized its long-standing flotation equipment business, such that it can now compete effectively in providing complete concentrator packages from crushing to product dewatering. In addition, he said, Metso is now one of the few companies that can supply both mechanical cells for roughers and scavengers, as well as column cells for cleaners.

Metso's product portfolio now includes cell capacities up to 660 m3, althoughthe current maximum installed capacity is 300 m3-with three active projects/operations in North America, Latin America and the CIS. However, Monredon said, producers and project developers are already looking for 600-m3 units.

Monredon also gave his views on the use of froth cameras-for which he said that the company is a market leader-integrated into its APC (Advanced Process Control) systems. By allowing cells fitted with advanced instrumentation and control to achieve a constant froth pull-out rate, plant operators can gain a 0.5%–1.5% increase in plant recovery, with a payback period of just a few weeks, he explained.

The need for higher plant throughputs is also bringing new design challenges, he added. Whereas up to now, plant capacities have largely been dictated by the ability of the grinding circuit to supply adequate flotation feed, the situation is now arising that flotation capacity is becoming a bottleneck as well-hence the demand for larger cells.


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An MBE-CMT Pneuflot installation at a Chilean iron-ore mine.
 

…As the Technology Evolves

Heiko Teuber, head of Tenova Delkor, told E&MJ that the company offers a comprehensive suite of flotation technologies including its BQR flotation cells, square cells and flash float cells. BQR cell technology is widely used in roughing, scavenging, cleaning and re-cleaning, unit and pilot cell applications, he said. Designed circular to reduce the dead zone volume compared to square cells, they have a much higher effective pulp volume, thereby increasing the effective energy input into the cell.

While the BQR1500 is currently the company's largest cell, Tenova Delkor is developing bigger units to meet increasing demand. Teuber said that the company is also seeing the next evolutionary stage in flotation technology, with fully automated flotation cells becoming more and more common, aided by smart control, online analysis and advances in software.

The Canadian equipment manufacturer, Westpro Machinery, told E&MJ that it has some 30 years of experience in the flotation field, having supplied systems ranging from individual components to complete modular circuits to the international market.

The Canadian equipment manufacturer, Westpro Machinery, told E&MJ that it has some 30 years of experience in the flotation field, having supplied systems ranging from individual components to complete modular circuits to the international market.

Westpro currently supplies two lines of flotation equipment-tank and conventional cells. Completely redesigned in 2012, its 10-model tank cell line-up offers sizes from 20 m3 (700 ft3) to 300 m3 (10,600 ft3). Its conventional cells are available in nine models from 0.014 m3 (0.5 ft3) to 14 m3 (500 ft3).

Westpro's conventional cells are a mechanically agitated, externally aerated design that has been proven in service over many years. Applications have included copper, lead, zinc, gold, silver, lithium and potash, the company said.

Its tank cells feature a completely new impeller-diffuser design, based on conventional hydrodynamics and CFD that provides effective solids suspension during operation and resuspension after shut-down. Current development work includes using CFD in an initial cost-benefit analysis on retrofitting the conventional cells with the new impeller-diffuser design from the tank cells.

Germany-based MBE-CMT offers its Pneuflot pneumatic flotation system, which can be used in coal washing as well as in mineral processing. The cell operates on the principles of mixing the air and pulp in a continuous stream, and ensuring that the correctly sized bubbles are fed into the pulp as it enters the cell. This maximizes the number of particle and bubble collisions, according to the company.

MBE-CMT claims that Pneuflot is more effective than other flotation technologies in terms of both energy consumption and operational performance. In addition, the vertical flow format ensures that the cell has a small footprint.

The company said that the ultra-fine bubbles produced in Pneuflot cells are a major advantage. Producing a very wide range of bubble sizes (5-1,000 μm, averaging at 300 μm), also gives a Pneuflot cell the capability to operate at all stages in a flotation circuit-rougher, cleaner and scavenger-while the system is easily adjusted

Cell capacities range from 8-12 m3/h for the smallest unit to 1,000-1,400 m3/h for the largest. MBE-CMT installed its most recent Pneuflot system at the Anjerskaya coal washery near Kemerovo, Russia.

Clearly, flotation technology is continuing to advance steadily in both equipment and reagent fields, with selectivity and cell size being leading drivers of development in the face of lower ore grades and more complex mineralogy. Success is being supported by better communication at all levels between mines, equipment manufacturers and chemical companies, with the overall aim being to optimize the recovery-cost equation.

 

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