Mineral Processing and Extractive Metallurgy: Transactions of the Institutions of Mining and Metallurgy

This paper describes the technical development of the Newman beneficiation plant over its 23 years of operation and how this development relates to the mine ore reserves of high grade and low grade ore. It also discusses the importance of the beneficiation product grades in the overall blending of shippable products from a range of mines to optimise overall ore resource utilisation. Also discussed is the importance of the ore reserve reconciliations in resource utilisation.

Data are provided on the capacity and quality improvement results of the plant upgrade, carried out in 1999. This shows how the original capacity upgrade targets have been exceeded and the additional quality benefits that have been obtained from this capacity.

Although cyclones have been around in their current form since the early 1890s, there have been some exciting new developments, which have extended their efficiency/operation. These developments have taken place with both dense medium and classification cyclones. The more noteworthy developments are inlet design, secondary offtake, water injector, 3 in 1 cyclone, and the Rejector.

Inlet design is the determining factor in classification cyclone capacity and efficiency. The recently developed ribbon inlet with patented pressure bulge has not only resulted in increases in capacity, but also in efficiency. Sharpness of separation corresponding to an alpha value of greater than 4 has been achieved.

One of the factors leading to reduced cyclone efficiency is the presence of coarse particles in the cyclone overflow. The secondary offtake has been developed specifically to scavenge these particles from the cyclone overflow with great success. The other major factor resulting in reduced cyclone efficiency is the presence of misplaced fine particles in the cyclone underflow. The water injector, which has been around for many years in various forms, can reduce this short circuit fraction by up to 50%. The 3 in 1 cyclone combines the inlet design, secondary offtake and water injector into a single unit resulting in the most efficient classification cyclone available in the market.

Iron ore has a high yield to underflow and traditional dense medium cyclones have always been spigot constrained. The Rejector is an exciting new development whereby the spigot capacity has been increased substantially. The application of the Rejector results in fewer/smaller cyclones being required for a given duty resulting in efficiency gains and reductions in both operating and maintenance costs.

BHP Billiton Iron Ore has replaced the conventional product quality control batch system at Yandi with the continuous stockpile management system (CSMS) centred on a fully integrated ‘continuous’ stockpile flow from mine planning through to port reclaiming. With increasing tonnage rates, tight operational coupling associated with the original batch system caused production interference which achieved final product quality but in an increasingly inefficient manner. This innovative approach places a continuous emphasis on product grade control and takes full advantage of the most appropriate blending opportunities of the mine to port planning and production system to reduce the natural variability of the ore to an acceptable level. To implement continuous control, product variability throughout the process is classified as long term and short term. Long term variability is best controlled through the monthly mine planning process which determines monthly grade targets while taking into account optimum mine development. In the past, attempts to control long term variability were made at the port through selective stockpiling and reclaiming, which reduced operational efficiency. Short term variability is best controlled around the monthly mine grade target by daily mine production scheduling, train sequencing, stacking into port stockpiles of appropriate size and systematic stockpile reclaiming. The implementation of the new system has maintained customer accepted shipping grades and has provided significant improvements in resource utilisation, operational efficiencies and costs.

Improved understanding of the variables that influence hydrocyclone performance is of increasing interest to the iron ore industry, where hydrocyclones are widely used to deslime fine ore. In many cases, the impact of particular variables is not sufficiently quantified experimentally to ensure that industrial performance matches expectations. The current work has focused on developing and implementing a systematic methodology to evaluate and compare the performance of four different hydrocyclones in a desliming application. A critical component of the project was the design and construction of a pilot scale hydrocyclone rig using state of the art monitoring and sampling methods. A wide ranging test programme was conducted to quantify the effect on metallurgical performance of the key hydrocyclone variables such as pressure, feed density, vortex finder size, spigot size and hydrocyclone make/overall design. Details of the experimental approach are presented, together with a discussion of the sizing analysis methods used.

Performance criteria were established to assess the four hydrocyclones. The effects of each major variable were quantified over a wide range of conditions. The results show that clear performance differentiation was achieved, enabling the selection of the optimum configuration. The results from this work demonstrate the benefit of objectively assessing the performance of nominally equivalent units in selecting an optimum configuration that best satisfies the performance criteria.

Regulations on the emission of particulates from sinter plant stacks are becoming increasingly stringent and reducing these emissions by improving gas cleaning systems is a significant cost to the sinter plants. This paper describes an investigation into the emission of particulate matter from an iron ore sinter bed during the sintering of a Japanese Steel Mill (JSM) style ore blend in a 300 mm diameter pot grate test facility.

Several techniques were trialled to determine a reliable method to sample the quantity of dust emitted and determine the mechanism of dust emission from the sinter bed. The nature of the dust was also examined using chemical and size analysis as well as optical and scanning electron microscopy. The paper discusses the techniques used to carry out the programme as well as results on dust loading measured during sintering and the nature of the dust captured.

Market forces, particularly iron ore prices, demand that plant operators achieve higher throughput in the World's iron ore beneficiation plants without compromising yields or efficiency. This means that production cost per tonne is of paramount importance and that all major pieces of processing equipment have come under close scrutiny to improve throughput at their most efficient performance levels and for the longest possible continuous running time. Without doubt the use of modern engineering standards and materials of construction has contributed to matching these throughput, efficiency and availability demands.

However, often not enough attention is paid to the ‘insignificant elements’ connecting this metallurgical equipment, such as chutes, pipes or other conveying systems, and particularly to the sufficient protection of their wearing surfaces. The result can be an unplanned and expensive outage caused by the wear related failure of such components. The present paper discusses the theory of wear and the multiple factors of material and design that contribute to a reduction in wear and the combinations of modern wear resistant materials available to today's engineer and how, by intelligent selection and correct application, plant availability can be optimised. Examples are given outlining how these principles have been applied in South Africa, showing some improvements leading to increased plant availability.

The beneficiation of heavy metal oxides, such as iron ore, is usually performed with heavy medium separation in cyclones, static baths and lately with Larcodems. Atomised ferrosilicon is most suitable as a heavy medium at densities above 3600 kg m^-3, whereas a mixture of milled and atomised ferrosilicon is suitable at densities below 3600 kg m^-3. When operating a beneficiation plant at densities higher than 3600 kg m^-3 the quality of the ferrosilicon particles is an important factor that influences the control of the beneficiation process. The present paper considers how the rheology is affected by ferrosilicon quality, since this also influences the control of the process at these elevated densities.

In the iron ore industry significant emphasis is placed throughout the mining process on meeting chemical composition specifications for the export of fine ores. However, little has been published on the implications of ore chemical composition for iron ore sinter and pellet product quality. The ore bulk composition and the nature of the minerals in the fine ore both play a critical role in determining the type of high temperature bonding phases that form during sintering and pelletising. This paper uses the experimental determination of phase relations in model sinter and pellet systems such as Fe₂O₃-CaO-SiO₂ (FCS) and Fe₂O₃-Al₂O₃-CaO-SiO₂ (FACS) to examine the links between iron ore chemical composition and the temperatures used during sintering and pellet firing. The phase relations help to establish the critical thermal and compositional parameters that control the bonding phase chemistry, which in turn influences the physical characteristics of the sinter or pellet matrix. Results show that lower Fe grade (<62%Fe) ores and concentrates will typically form SFCA as part of the final assemblage, medium grade (62-65%Fe) ores will form a mixture of SFCA and SFCA-I, while high grade (65-68%Fe) ores will form largely SFCA-I. The SFCA-I phase is the most desirable bonding phase in iron ore sinter and pellets since microstructures composed entirely of SFCA-I show higher physical strength and higher reducibility than microstructures composed predominantly of SFCA.

Massive hematite ore (MHO) is a special high grade iron ore used as lump ore in the process of obtaining direct reduced iron (DRI). The influence of porosity on the reducibility has been investigated using optical and scanning electron microscopes. Hematite is the main component of the samples and occurs as granular crystals (10 μm), microplates (1 μm) and euhedral martite (10-30 μm). Quartz, maghemite, kenomagnetite and goethite are minor components. Primary micropores (Å to 1 μm) are associated with microplaty crystals that fill cavities between granular hematite. Secondary micropores (Å to 5 μm) related to euhedral martite crystals are the most important. The total porosity of weathered samples, measured using nitrogen adsorption and mercury injection, attains values up to 18%, whereas unweathered samples have a porosity less than 2·5%. Varajão et al. showed that reducibility is strongly enhanced by porosity and this work shows that reducibility can be indirectly evaluated by bulk density.

All major companies now operating in the production of iron ore in Brazil currently employ or are planning to employ some sort of concentration method to upgrade their fine sized products (sinter feed fines and pellet feed fines). The criteria for the selection of the most adequate concentration method for each application include a series of parameters, the most important among them being related to ore mineralogy. This paper reviews the concentration operations currently employed in Brazil and shows how ore mineralogy plays a fundamental role in the selection of a given method. Examples involving gravity concentration (jigs and spirals), magnetic separation (Rare Earth wet drums, ferrous wheel, and Jones type magnetic separators) and flotation (especially column flotation) are discussed. Fundamentally important for the selection of a concentration method is the mineralogy of iron bearing minerals and gangue minerals presented to the feed to the concentration unit operation. For instance, the presence of liberated quartz as the major gangue mineral for a pellet feed size stream generally indicates that flotation will be the best selection for the concentration of that stream. However, even if magnetite is present only in the form of crystal relicts within hematite grains, it may lead to the selection of either magnetic separation alone or a combination of magnetic separation and flotation for concentrating such material. Presence of gibbsite and/or kaolinite as the major phase containing alumina will also affect the selection of the concentration method in all cases. Again for the case of pellet feed size streams, kaolinite does not interfere with flotation whereas gibbsite tends to contaminate flotation concentrate (pellet feed fines) as it is depressed together with iron oxides and hydroxides during the reverse cationic flotation process.

A higher bed height - up to 680 mm, including a 30 mm hearth layer of sized return sinter - and high suction below the grate bars up to 1400 mm WG have resulted in increasing productivity to 33 t m^-2/day and have reduced the coke rate to a level of 46 kg t^-1 sinter. Ferro wastes such as blue dust, flue dust, mill scale, collection from dust catcher and gas cleaning plant, have been successfully added to the charge mix to produce quality sinters. In this paper, work carried out at the Regional Research Laboratory (CSIR) over the last few years is briefly descibed and two case studies are discussed, including the successful development of pan sintering units.