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This one day MEI meeting was attended by 20 delegates, representing Australia, Canada, China, Finland, Iran, Korea, South Africa, Turkey and UK.
Eight papers were presented during the day, 5 in the session on Magnetic Separation, and 3 in Electrical Separation and Combined Methods.
As discussed by James Watson of the University of Southampon, UK, the mineral processing industry is the largest user of magnetic separation. This market is largely made up of low-gradient separators using iron circuits. The Superconducting High Gradient Magnetic Separator (SHGMS), originally developed at English China Clays, has resulted in approximately 30 large machines using liquid helium, with separation channels of 0.5m to 1m diameter, distributed throughout the world.
Prof. Watson considered a few examples of where superconducting separators can be used to concentrate low grade minerals from mine dumps which exist across the world. Often the gangue materials are coated with small quantities of magnetite, which saturates at less than 2 Tesla but with 6 Tesla available from SHGMS there is a large difference in magnetic moment between the gangue materials and the value to be concentrated. He discussed the concentration of uranium and gold from the leached residues from the Witwatersrand, South Africa, dumps from other regions of South Africa for the concentration of platinum group metals, the treatment of complex ores from Gargill region, Canada with SHGMS, concentration of V, Pb and Zn from dumps of 8 million tonnes in Zambia, the recovery of U and Au from Olympic Dam, Australia and the extraction of Au from slag at Zalau, Romania.
Alan Jones, of Alcoa Australia, described investigations into processing Red SandTM through standard mineralogical processes (Low Intensity Magnetic Separator- LIMS and Wet High Intensity Magnetic Separator -WHIMS), to produce various fractions that have a higher potential value than the total sand fraction.
In recent years, the Chinese iron and steel industry has developed rapidly. There are abundant iron ore deposits in China but most of them are of low grade and need upgrading by either flotation or high intensity magnetic separation. SLon vertical-ring and pulsating high gradient magnetic separators have proven to be efficient and reliable, as discussed by Xiong Dahe, of Slon Magnetic Separators Ltd, China. 400 SLon magnetic separators have been applied in the Chinese oxidized iron ore, ilmenite and nonmetallic minerals processing industries.
The efficiency of a magnetic separation can be determined by measuring the magnetic properties of the different process streams. This measurement, if done at all, is performed by laboratory testing of spot samples from magnetic separators. This is an inherently slow process and, where feed grades are variable, optimum performance of separators is generally not achieved. Trevor Powell, of Ultra-Dynamics Pty Ltd, Australia, described on-line and laboratory measurements of the magnetic properties of process minerals. AC measurement techniques, including the analysis of the phase component of the magnetic vector; frequency dependent magnetic susceptibility and the effect of applied magnetic field strength were discussed. Industrial applications in mineral sands, coal processing, iron ore processing and copper smelting were reported.
Ilker Erkan of the Karadeniz Technical University, Turkey, described the magnetic separation of boron from plant tailings. A variety of boron minerals and boron-rich brines are used for the production of boron compounds, which are extensively used in many industries. Colemanite is one of the most important boron minerals of commercial interest. It is used mainly in the production of various intermediate boron compounds such as boric acid and borax, and preferentially in the textile and glass industries where sodium content is often undesirable.
Dolf MacHunter, of Roche Mining (MT), Australia, discussed modern mineral separation plant flowsheet design, incorporating the new generation electrostatic and magnetic separators. Since the introduction of new processing units, the latest drymill flowsheets have been significantly simplified and with the requirement for middlings recirculation having almost been eliminated the mineral separation plant will be easier to operate and control, leading to increased output. He compared the traditional flowsheet design with that of one incorporating new technology and process philosophy.
Peter Rozakeas of KEMENG, Australia, described how the application of electrokinetic techniques in the continuous flow of coal-water suspensions in various anode-cathode pipe geometries effectively causes a significant reduction in the wall shear stress. This reduction in the frictional force at the cathodic pipe wall surface is attributed to a decrease in the concentration of coal particles in this flow region caused by the migration of negatively charged coal particles towards the anodic surface(s). It is possible to reduce the specific pumping energy requirements of coal-water suspensions flowing in pipes by as much as an order of magnitude. The practical and economic implications of this work relate to an enhanced method of long distance transportation of slurries in pipes as well as an alternative technique for continuously separating solid-liquid suspensions.
In the final presentation, Hannu Kuopanportti of Mikkeli Polytechnic, Finland looked into the possibilities of reducing the heavy metal concentrations of fly ash by means of electrostatic precipitation. The utilisation of fly ash as fertiliser is hampered by its high concentrations of heavy metals, which are highly variable. Fly ash fractionation experiments were done using electrostatic precipitators at four power plants. The concentration of cadmium in fly ash used as fertiliser can be reduced by as much as 70% by applying electrostatic precipitation fractionation. The removal of other heavy metals is not as efficient as that of cadmium. The results show that electrostatic precipitation is an adequate method in the fractionating of fly ash to be used as a fertilizer or soil amendment.
The conference was followed by the 2-day Gravity Concentration ’06 symposium, at the same venue, and the Proceedings of Magnetic, Electrical and Gravity Concentration ’06 is available on CD-ROM. Details can be found at www.min-eng.com/magnetic06/paps.
B.A. Wills, Minerals Engineering International, UK.
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