February 2017

Is column flotation still relevant?

  • By Greg Harbort FAusIMM(CP), Technical Director – Process, Amec Foster Wheeler, Australia East and Tony Lipiec, Director – Process Engineering, Amec Foster Wheeler, Canada

An overview of column flotation in Australia and globally

Australia has had a long association with flotation columns (or pneumatic flotation cells as they are also sometimes known). Currently, Australia ranks third in terms of installed column flotation area behind China and Canada (Figure 1). Almost 15 per cent of the world’s flotation column capacity is installed in Australia.

The popularity of column flotation reached a peak in Australia between 2005 and 2007. Except for a minor resurgence in 2012 and 2013, the rate of flotation column capacity installed after 2007 has been roughly one quarter of this peak. Since 2014, the capacity of flotation columns installed in Australia has continued to decline significantly. This trend has also been evident globally.

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Column flotation in Australia

Figure 2 shows the flotation column capacity in Australia as a percentage of total installed flotation capacity. Flotation capacity variations include new greenfield capacity, brownfield capacity increases or decreases and mine closures (Harbort et al, 2016).

Historically, installations in the 1960s and 1970s were dominated by lead and zinc. In the 1980s, gold flotation led to a decade of column flotation popularity, together with an increasing number of installations in lead, zinc and copper operations. In terms of total flotation capacity, the use of flotation columns in Australia has increased linearly since 1985. In the 1990s, coal operations took over as the dominant user of column flotation. It would remain in this position for the next 20 years. However, the industry downturn in the 2010s resulted in a collapse in the installation of flotation columns in coal. The last several years have seen a tentative return of column flotation to the Australian metalliferous industry, with copper the dominant commodity being treated. Columns currently account for ~35 per cent of installed flotation capacity in Australia. The majority of this is in coal flotation, which accounts for 28 per cent of installed capacity. Base metals accommodate a relatively small proportion, together comprising only five per cent of installed capacity, while flotation of pyrite/gold comprises another one per cent.

The strong presence of flotation columns in coal processing is by no means guaranteed. There is increasing opinion that flotation columns and mechanical flotation cells can provide similar technical performance given optimal operation. Experience has indicated that there are issues with the complex nature and broad size distribution of the feed in coal flotation, making it difficult to obtain optimal results from a single-step process such as flotation columns. The current depressed state of the coal industry in Australia may also lead to increased mine closures, resulting in high-capacity column flotation circuits being taken off-line and representing a lower proportion of the remaining capacity.

Within metalliferous flotation, the proportion of use has varied over the last 30 years. Between 1985 and 1994, column flotation capacity as a percentage of total metalliferous flotation capacity increased linearly to approximately three per cent, where it remained until 2015. The level of use reflects the role of column flotation installations in cleaning operations, which is likely to continue. In the medium term, it is expected that flotation columns will continue to account for between three and five per cent of metalliferous flotation capacity.

Column flotation globally

Globally, the majority of flotation column capacity is installed in coal operations (42 per cent of total column capacity). The majority of these installations are in the USA, China and Australia. There are a number of reasons for this, including the dilute nature and high volume of coal feeds, changing mining methods that generate more fines and the increased need for flotation, stringent contaminant requirements for coking coal and increasingly stringent product specifications in thermal coal for environmental reasons.

Copper also makes a major contribution, with 21 per cent of column flotation capacity installed since 1961 being in this commodity. These installations have primarily occurred in the large porphyry operations of Chile, Peru and the USA.

Flotation column capacity in iron ore has also been significant, representing nine per cent of the installed column total. The majority of this is in Brazil (67 per cent of installed iron ore column flotation capacity), with the other countries utilising columns for iron ore flotation including China, Peru, USA, Russia, India, Mexico, South Africa, Venezuela and Chile.

The other major commodity that utilises column flotation is phosphate, which represents four per cent of total installed column flotation capacity. An assortment of commodities including zinc, molybdenum, potash, gold, niobium, lead and fluorite represent a further ten per cent of installed capacity. The remaining column flotation capacity is spread over more than 60 other commodities.

Flotation columns installed in the 1960s were overwhelmingly in base metals, with 45 per cent in lead, 25 per cent in zinc and 20 per cent in copper operations. The remaining ten per cent of flotation columns were installed in coal. In the 1970s, there was a major transition away from column flotation use in both zinc and lead, although its use did increase slightly in copper operations. Column use in coal increased dramatically during the decade, representing 30 per cent of installed capacity. Increased use in both phosphate and molybdenum was also apparent, with each amounting to approximately five per cent of the installed capacity during the decade. The 1970s also represented a period of experimentation, with 20 per cent of flotation columns treating minor commodities.

During the 1980s, the popularity of flotation columns in copper and molybdenum operations increased significantly in North America (respectively accounting for 30 and 20 per cent of installed capacity over the course of the decade). Phosphate use also increased to approximately ten per cent due to the use of flotation columns in both USA and Brazilian phosphate operations.

A significant shift in the distribution of column use occurred in the 1990s, with coal increasing to 35 per cent of installed capacity, primarily in Australia, the USA and China. Copper continued to account for 30 per cent of installed capacity in this decade, which was largely due to use in South American porphyry copper mines. The 1990s also represented the first significant use of column flotation in the iron ore industry for the removal of silica. New column installation in iron ore comprised approximately ten per cent of new column capacity during the decade, largely in Brazil. In comparison with the 1980s, the use of column flotation in other commodities decreased significantly, with the most apparent decline occurring in molybdenum.

Phenomenal growth in the use of column flotation in China’s coal industry during the 2000s distorts the distribution for this decade, with coal representing 60 per cent of new installed capacity. The trends have returned to more normal levels during the last six years, with coal and copper representing the two most popular commodities for column flotation.

Fluctuations in column flotation popularity

The popularity of flotation columns has fluctuated significantly over the last five decades, with commodity price fluctuations possibly having the most pronounced impact (Figure 3). Declining commodity prices between 1988 and 1994 led to an increase in installed column flotation capacity in an effort to reduce operating costs. From 1995 to 2003, a period of low but relatively stable commodity prices, new installed column capacity decreased. This is potentially due to the lack of new mining operations and the reduced need to refurbish existing circuits. In Australia, these years also saw new base metals concentrators built without columns being installed. A number of reasons existed for this, including the perceptions that flotation column circuits were difficult to operate and that mechanical flotation cells could achieve the same performance as flotation columns.

Installed column flotation capacity increased sharply in 2002, some two years before the increase in commodity prices. This is considered a distortion brought about by the substantial changes in the Chinese coal industry. If the installations in Chinese coal are excluded, the underlying trend of installed column flotation capacity approximately follows commodity price increases between 2004 and 2007 and commodity price decreases between 2007 and 2009. The same can be said for rising and falling commodity prices between 2009 and 2014.

In 2015, the installed capacity increased sharply in a global context in direct contrast to the continuing fall in commodity prices. A number of installations planned or that have become operational in the last several years have been in copper to increase concentrate grade and decrease production costs.

Other reasons for fluctuations in flotation column popularity include:

  • Performance – flotation column performance has varied within individual commodity groups. It was found that columns used for cleaning duties often produced final concentrate grades with substantially less recleaning stages. However, enthusiasm sometimes resulted in flotation columns being installed in unsuitable duties or circuits. One example is molybdenum cleaning duties, where multiple flotation columns in series would often prove difficult to stabilise, generating high recirculating loads and recovery losses.
  • Market starvation – in numerous cases, flotation columns have been installed in areas where they are considered new technology. Where the installations are initially successful, there is often a rush to install despite a lack of understanding of the performance. This has led to poor installation and operations, ultimately leading to negative perceptions.
  • Market support – in comparison to large mechanical flotation equipment suppliers, many column flotation suppliers tend to be smaller companies with limited resources. It is traditional for flotation columns to have a substantial market support network in the country where they were first developed, with support for overseas installations either being from the home country or via a network of agents. Where sales reach a level suitable to support a local office, there is typically a significant increase in popularity as the supplier is seen to support both local industry and the local installations.
  • Vendor strategic changes – strategic changes by flotation column manufacturers can often have a dramatic but understated effect on flotation column popularity. These changes can be as small as changing the name of the flotation column, withdrawal from a specific market area or transferring ownership/marketing rights.

Is column flotation still relevant?

Since 1961, column flotation has gone through three distinct rises and falls in popularity. These fluctuations have largely been driven by commodity prices. Within these primary waves, there are secondary fluctuations in popularity driven by the rise and fall of individual flotation column manufacturers, the necessity for circuit refurbishment, commodity-specific requirements and the effect of capacity saturation, both within commodities and in individual countries.

The survival of column flotation technology through these fluctuations and recent increases in installation in defiance of the depressed minerals industry indicates that they are still considered relevant. This is expected to be especially so in areas where they have historically achieved wide popularity, including the Australian, Chinese and USA coal industries, the phosphate industries in the USA and Brazil and the iron ore industry in Brazil. Within the base metals industry, flotation columns are expected to maintain their relevance in the smaller-capacity cleaner roles.

References

Harbort G, Deonarain N, Frost D, Lipiec T and David D, 2016. Changing trends in column flotation use – their impact for Australian mill operators, in Proceedings 13th AusIMM Mill Operators’ Conference 2016, pp 93–104 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Feature image by Geomartin. Used under CC BY-SA 4.0

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