October 2015

The critical importance of optimising performance

  • By Ralph J Holmes FAusIMM(CP) and Liming Lu, CSIRO Mineral Resources Flagship

Making the most of new technologies to maximise productivity in the iron ore sector

The theme of the recently held Iron Ore 2015 conference was ‘Optimising Performance’, which is particularly relevant at present as new projects and expansions have bedded down after an unprecedented period of major growth and iron ore market conditions have become
more volatile. 

Over the last 40 years, considerable changes have occurred in the iron ore resources available throughout the world, especially to steel mills in East Asia. Figure 1 shows the change in iron ore sources used by the Japanese steel industry during the period 1971 to 2007 (Lu and Ishiyama, 2015). The usage of Australian iron ore has been increasing steadily over this period, changing from hard hematitic to more goethitic ore types, such as pisolitic and Marra Mamba ores, with corresponding changes in the chemical and physical composition of the ores, particularly alumina content, loss on ignition (LOI) and particle size. The level of impurities, LOI and fine material has a significant impact on sinter quality and sintering performance. Hence, understanding the technologies used throughout the iron ore supply chain is of increasing importance in tailoring products to better suit the needs of end users.

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It is therefore timely that a new book, Iron Ore – Mineralogy, Processing and Environmental Sustainability,  edited by Dr Liming Lu from CSIRO has just been published. The book  aims to provide all involved in the various stages of the iron ore supply chain, from those who initiate the development of a resource to those involved in various end user market activities, with information on the latest practices and expert views on available technologies, including the research and technology development trends.

The introduction to the book briefly sets out the current status of the industry and the current challenges the industry is facing. While the iron ore industry is sometimes viewed as a simple quarrying operation, the industry is fiercely competitive internationally and is under considerable pressure at present to reduce costs due to the massive fall in iron ore prices over the last year or so. Consequently, the technology being used by the industry is in actual fact quite advanced, including recent leading edge developments to reduce operating costs such as the introduction of driverless trucks at a number of Australian Pilbara operations, and in the longer term, the introduction of driverless trains.

Furthermore, surface miners are being used in Australia instead of the conventional drill and blast method where the ore is free digging and the development and implementation of technologies for remote control of mining and processing operations in Australia and Sweden is also undoubtedly at the leading edge in terms of technologies used in the iron ore mining industry. The Rio Tinto and BHP Billiton remote operation centres in Perth enable the total supply chain to be controlled in real time, enabling metropolitan-based operators to make timely decisions and improve productivity while simultaneously removing them from high-risk locations.

These facilities utilise leading edge technologies for haul truck control and management, train control and control of fixed plant in mine and port operations, as well as CCTV and radio systems to communicate with remote sites. Both FMG and Roy Hill Iron Ore are in the process of establishing similar remote operation centres. New sensing technologies for downhole logging, in situ analysis on the drill rig, drill core logging, face analysis and online analysis are also being utilised, as well as robotic sample preparation and analysis laboratories with the long-term objective of reducing operating costs and making the workplace safer and less laborious. Other technologies being used to reduce costs and improve the grade and recovery of concentrates include stirred milling for fine grinding, micro-screening to remove gangue minerals, coarse and fine particle flotation, with the potential application of biotechnologies under evaluation.

Technology challenges

Despite these developments, substantial challenges still face the international iron ore industry. Over the next 10-20 years, alternative ore types will need to be developed to replace current resources. These include hematite/goethite ores, magnetite ores and polymetallic ores, such as those currently being exploited in China, that are low in grade, complex in mineralogy and fine grained. In specific instances these ores will require crushing and grinding to liberate the valuable minerals followed by concentration processes such as gravity separation, magnetic separation, flotation, leaching and bioprocessing to produce high-grade products suitable for subsequent downstream processing.

Consequently, there will be a continuous need to improve grinding and separation efficiencies to maximise productivity and reduce production costs, as well as reduce the production of waste products, water consumption and greenhouse and other gaseous emissions. More specifically, some of the key challenges facing the iron ore industry are as follows:

  • developing more efficient mining and transport methods
  • reducing energy consumption in grinding ores prior to beneficiation, particularly for magnetite and polymetallic ores
  • developing more efficient beneficiation processes for removing gangue components such as alumina, silica and phosphorus while minimising the loss of iron units
  • developing economic dewatering and drying processes for the new ore types – due to their high porosity – as mining moves progressively below the water table in some countries
  • minimising water consumption in arid environments during beneficiation of low grade ores, particularly in India
  • developing dry processing methods for beneficiation of iron ore where water is scarce
  • developing improved methods for counteracting the adverse effect of alumina content on sinter quality
    and productivity
  • reducing toxic emissions in sintering and pelletising iron ores, including dioxins, as well as reducing CO2 emissions and carbon footprints
  • minimising dust generation during handling and processing due to ever-increasing environmental constraints
  • improving mine site rehabilitation to mitigate the environmental, social and economic impacts on local communities.

Research is currently in progress in all these areas to assist in meeting the key industry challenges. For example, a review of recent advances in iron ore sintering was presented by L Lu and O Ishiyama at the recent Iron Ore 2015 conference (Lu and Ishiyama, 2015). A key aspect of this topic is new coating and granulation technologies to counteract the adverse effects of the alumina content and finer particle size of current iron ore product offerings on sinter strength and sintering productivity. In the past, sintering productivity depended mainly on the combustion efficiency of the fine coke added to the raw materials (Sakamoto, 2002). However, coating the surface of quasi-particles with fine coke and segregation of coke particles vertically in the sinter bed significantly reduced the coke consumption. Hence, the permeability of the sinter bed is now a key focus for maximising sintering productivity.

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Figure 2. Process flow sheet for the limestone and coke breeze coating granulation technology installed on the JFE Kurashiki No 2 sinter machine in Japan, including schematic diagrams of the granulated particle and sinter structures for the conventional and new granulation methods.

To improve coke combustion and control melting, JFE Steel Corporation in Japan developed the limestone and coke breeze coating granulation technology installed on the JFE Kurashiki No 2 sinter machine, shown schematically in Figure 3 (Oyama et al, 2005; Oyama, Takeda and Fujii, 2008). This technology controls the melting reactions of the iron ore and limestone by distributing the coke breeze and limestone on the surface of the quasi-particles. This improves the sintering productivity and sinter reducibility, because it retains finely-porous and highly reducible primary hematite relict particles and maintains product yield by forming a strong calcium-ferrite matrix that bonds together the primary hematite relict particles (Figure 2).

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Figure 3. Schematic diagram of the NKK Hybrid Pelletised Sinter (HPS) process

An approach to enable use of larger proportions of fine iron ore in sinter blends, including pellet feed with high iron content, is the Hybrid Pelletised Sinter (HPS) process developed by NKK (now JFE Steel Corporation) in Japan, in which the conventional processes for production of both sinter and pellets are utilised as shown in Figure 3 (Niwa et al, 1993). In contrast to the conventional sintering process, the blended ore, limestone and burnt lime are first mixed and pelletised in the HPS process using disc pelletisers to produce green pellets, which are then coated with coke breeze in a drum mixer before feeding to the sinter machine. With this process, it was possible to successfully operate the No 5 Sinter Plant at the NKK Fukuyama Steel Works at high productivity using a sinter blend comprising 60 per cent fine iron ore, including pellet feed.

Regarding counteracting the adverse effects of alumina content, a selective granulation method for fine clayish iron ores has been developed by Nippon Steel Corporation (now Nippon Steel and Sumitomo Metal Corporation, NSSMC) in Japan to improve the sintering performance of sinter mixtures containing high proportions of limonitic ore (Haga et al, 1997a, 1997b). In this process, the ore is first screened at 2-4 mm to take out the fine material, which often has a high alumina content. This undersized material is then pelletised to make pseudo-particles, which are then mixed with the oversized material and the other raw materials in the sinter mix. Figure 4 shows the conceptual design of the selective granulation method, in which the green pseudo-particles are strong enough to retain their integrity during handling and hence segregate the high alumina material from the bonding forming material. This reduces the amount
of fine material in the granulated sinter mix and results in improved permeability, sintering productivity and sinter quality.

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Figure 4. Selective granulation method developed by Nippon Steel and Sumitomo Metal Corporation

Conclusion

After an unprecedented period of major growth and prosperity coupled with high iron ore prices, the iron ore industry is now facing significant challenges following the emergence of volatile iron ore market conditions. Consequently, the focus is now on ‘optimising performance’ in an all-out effort to reduce costs. Over the next 10-20 years, alternative ore types will also need to be developed to replace current resources as they are slowly depleted. Development of new and improved technologies will play an important role in this process to accommodate changes in the chemical and physical composition of these alternative ores, such as alumina content, LOI and particle size, which impact on sinter quality and sintering performance. 

References

Lu L and Ishiyama O, 2015. Recent Advances in Iron Ore Sintering, in Proceedings Iron Ore 2015, pp 61-67 (The Australiasian Institute of Mining and Metallurgy, Melbourne).

Sakamoto N, 2002. Iron ore granulation model supposing the granulation probability estimated from both properties of the ores and their size distributions, ISIJ International, 42(8): 834-843.

Oyama N, Sato H, Takeda, K Ariyama T, Masumoto S, Jinno T and Fujii N, 2005. Development of Coating Granulation Process at Commercial Sintering Plant for Improving Productivity and Reducibility, ISIJ International, 45(6): 817-826.

Oyama N, Takeda K and Fujii N, 2008. Development of New Coating Granulation Technology of Limestone and Coke Breeze, JFE Technical Report, 22: 32-37.

Niwa Y, Sakamoto N, Komatsu O, Noda H and Kumasaka A, 1993. Commercial Production of lron Ore Agglomerates Using Sinter Feeds Containing a Large Amount of Fine Ores, ISIJ International, 33(4): 454-461.

Haga T, Ohshio A, Hida Y, Fukuda H and Ogata N, 1997a. Improvement of the Melting Reaction in Sintering Process by the Fine Part Selective Granulation of Clayish Iron Ores, Tetsu-to-Hagane, 83(4): 233-238.

Haga T, Ohshio A, Nakamura K, Kozono T and Uekawa K, 1997b. Control Technique of the Melting Reaction in Sintering Process by the Fine Part Selective Granulation of Clayish Iron Ores, Tetsu-to-Hagane, 83(2): 103-108.

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