Reference: Galvin, K.P., Roberts, A., Loo, C.E., Evans, G.M., Williams, K., Iveson, S.M., Australian Research Council Research Hub for Advanced Technologies for Australian Iron Ore – An Introduction, 7-12, Iron Ore 2015, Perth, AusIMM, 13th-15th July 2015. Keynote paper.
The ARC Research Hub for Advanced Technologies for Australian Iron Ore is focussed on developing innovative approaches for creating enhanced value across the full value chain, through beneficiation, raw materials handling and the characterisation of the different ore types and end-use functionality.
Iron Ore Beneficiation
Beneficiation is concerned with recovering and concentrating the valuable ore from the run-of-mine feed, with different technologies applied to specific particle size ranges. Fine particles are usually well liberated, and thus have the potential to produce high grade concentrate. However, this theoretical potential is not realised in practice due to the presence of the colloquially termed ‘slimes’, including clays which report with the water that associates with the product. The performance of existing beneficiation technologies such as spirals deteriorates below 75 µm, while reverse flotation starts to rapidly deteriorate below particle sizes of 20 µm.
The REFLUX™ Classifier (FIG 1) consists of a set of parallel inclined channels mounted above a vertical fluidised bed. These channels create a large effective settling area via the so-called Boycott effect (Boycott, 1920), greatly increasing the capacity compared to a conventional fluidised/teetered-bed separator. The inclined channels produce a high shear rate, resuspending the low-density particles, in-turn transporting these particles to the overflow, thus promoting a density-based separation (Galvin and Liu, 2011). The technology was developed through collaboration between Ludowici Australia and the University of Newcastle. Initially commercialised in 2005, further research led to a new mechanism for separation, and the launch of a new design in 2009. By working closely with an equipment manufacturer, engineering design company, and an end-user, the research was successfully translated into industry, with more than 80 full-scale units installed in 8 countries.
FIG 1a: Laboratory-scale REFLUX™ Classifier
FIG 1b: Full-scale RCTM3000 unit with a 3m diameter (Courtesy FLSmidth).
Existing installations of the REFLUX™ Classifier have focussed on the beneficiation of particles in the 0.250 to 2.0 mm size range. Significant interest has emerged in the coal industry in the processing of particles up to 4.0 mm in size, with new research funding directed to the establishment of a full-scale facility (FIG 2), located at a plant just one hour from the University. Again, collaboration has involved input from university researchers, equipment manufacturers, engineering design companies, and end-users.
FIG 2a: REFLUX™ Classifier 3-D design concept
FIG 2b: Plant for testing of the REFLUX™ Classifier at full-scale on particles up to 4mm in size.
The high fines and moisture content of future ores may create problems with stickiness. In the export of iron ore, the mine-to-port chain of operations includes numerous storage and handling steps during the various mining, overland transport and ship loading stages. In such a system, the overall performance is only as good as the weakest link. So, for example, a blockage in a single transfer chute can seriously disrupt the entire system, leading to significant delays and lost production costs. While the cost of a belt replacement is ~ AU$1M, the associated costs due to downtime can be up to a staggering AU$70M. Similarly, incorrectly designed storage bins, chutes, feeders and belts can experience severe wear, which causes further production losses due to the more frequent stops for maintenance work. “Silo quaking” during discharge from hoppers can cause structural support problems. At sea, the liquefaction potential of iron ores needs to be identified and managed to mitigate the potential loss of ship and crew. Hence the bulk properties of these systems need to be quantified to ensure robust design of handling, storage, transport, and dust-suppression equipment.
TUNRA Bulk Solids (TBS), the consulting arm of the Centre for Bulk Solids and Particulate Technologies (CBSPT) was established in 1975. Since then TBS has completed more than 4000 projects for clients from over 40 countries. Recent work has included Discrete Event Modelling (DEM), Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) simulation to gain greater understanding of the mechanisms of wear and dust control, which has enabled the design of more reliable conveying, feeding and transfer systems (Donohue et al., 2012; Chen et al., 2012; Goniva et al., 2012). This work has led to many innovations in iron ore handling, such as successful improved stock pile reclamation. In addition, TBS has built its capability in developing the understanding of the liquefaction potential of bulk solids, and the mechanisms by which they may liquefy (Williams et al., 2015).
Characterisation of wet sticky ores
The characterisation of bulk solids in relation to industrial bulk solids handling plant design and performance is now widely accepted and well proven in Australia and worldwide (Roberts, 2005). The work of TBS has extended the flow property test capability through the design of 300 mm diameter direct (FIG 3) and inverted shear cells which enable the testing of bulk mineral ores over more realistic size ranges relevant to mining operations as well as allowing adhesion and cohesion measurements to be obtained for transfer chute design. The foundation work in the development of the vibration shear test is of particular relevance (Roberts, 1997). Other developments include submerged shear tests for supersaturated bulk ore tests.
FIG 3: The 300 mm large direct shear testing cell.
Existing tests such as the Durham Cone are empirical and do not provide the quantified strength, and internal friction versus consolidation stress that is necessary for handling plant design and evaluation. An alternative to these so-called empirical tests is the “flowability” tester, developed by TBS (FIG 4). The principal aim is to characterise selected iron ore feeds employing the standard Jenike test along with the flowability test as well as selected empirical tests. One important aspect of the characterisation is the hitherto neglected correlation of the flow properties with relevant mineralogical properties of the ore and how these properties may have some bearing on moisture retention and release as well as bulk strength. Apart from the characterisation work, the application of the measured flow properties in conjunction with modelling and simulation aimed at optimising handling-plant performance will be undertaken.
FIG 4: The innovative “flowability” tester developed by TBS.
Wear minimisation, dust control, and adhesion characterisation
Here the emphasis will be on both abrasive and impact wear and passive dust control. Following a period of development work in abrasive tests for bulk solids applications, a new, improved annular abrasive wear tester of 2 m diameter has been designed and constructed. This machine has provision for 4 samples of lining materials or conveyor belts to be tested simultaneously over an extended period of time. Mass loss and surface roughness of the samples are progressively recorded and, apart from the measurement of wear, the measured data provide the basis for surface roughness and particle interaction studies. For impact wear, the aim is to improve the reliability and repeatability of impact tests by using a vertical circular bucket wheel to continuously drop material onto the sample. This work will lead to further development of transfer chute design.
Properties and End-Use Functionality
The value of an iron ore is closely related to its performance and impact on the blast furnace process. The iron ore raw material covers a very broad particle size range, necessitating very different forms of evaluation with respect to its end-use functionality in the blast furnace. While iron ore fines and concentrate must be processed into sinter and or pellet prior to use in the blast furnace, lump ore can be directly utilised without any further processing. For this reason, lump is inherently more valuable than fines.
Australian lump ore is widely utilised and valued by customers in markets such as Japan, Korea and Taiwan (JKT). In China, the utilisation of Australian lump is lower, due in part to China’s preference for prepared burden (sinter and pellet) but also its supply of domestic concentrate which lends itself to pelletising. There is therefore an opportunity to increase the utilisation of Australian lump by studying its behaviour in the furnace relative to sinter and pellet.
The aim of Program 3 is to study the properties of different ferrous materials using laboratory furnaces (FIG 5) and to investigate the link between these and their behaviour and performance in the blast furnace. While the program covers the efficacy of the fines in granulation and the preparation for sintering, the current emphasis is on the response of the lump ore to increased reduction time and the inclusion of hydrogen, especially at the stage when the ferrous burden softens and melts. Thus the program goes beyond standard testing. Tests will also include quenching beds of lump ore at different stages (FIG 6) in order to preserve changes in bed porosity and in turn permeability. The load acting on the sample will be altered to understand the effect of furnace size. Together with detailed mineralogical study of the reduction products, this project will provide firm conclusions about the role of lump ore properties in various furnaces.
FIG 5: High temperature furnaces are used to simulate the behaviour of iron ore fines during sintering, and lump ore, sinter and pellet in a blast furnace.
FIG 6: Quenched beds are used to explain the differences in softening and melting behaviour of individual ferrous material types and blends, and the effects of reduction degree and chemical composition. The beds shown were quenched at 1300°C.