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Gravity separation has been enjoying something of a renaissance in recent years, having previously lost ground to froth flotation in many, though by no means all, ore beneficiation flow sheets since the 1920’s. Major reasons for this renewed interest are, on the supply side, availability of new and improved types of compact separator capable of high throughput rates – especially devices utilising enhanced gravity – and, on the demand side, the advantages of intrinsically less-polluting process technologies that are likely to be more acceptable to those charged with minimising adverse environmental impacts of industry. Linking with this second advantage is a growing realisation that more and more minerals processing will have to done in regions that are short of water.
So that’s fine then? Well yes, but as Dr Barry Wills pointed out when opening the Minerals Engineering International Gravity 04 Conference in Perth, Australia on March 22nd 2004, the benefits that new separators can offer are almost certainly not as widely recognised as they deserve to be. As well as providing networking opportunities, the conference, and the resulting refereed special issue of Minerals Engineering in which the papers will be published, are intended to draw more attention to the advantages of gravity separation and to the work being done to improve our understanding of this branch of minerals processing. Industry support for this MEI initiative was clear from the sponsorship made available - by Falcon Concentrators, based in Canada, the Australian manufacturers Gekko Systems and Roche Mining (Mineral Technologies), and the Perth-based Minerals Gazette. One reason for backing collaborative promotion is that most of the companies which have developed and marketed the new equipment designs are relatively small outfits with limited budgets, though it must be said they have been rather good at spreading the word.
Cutting to the paper chase, designing more capacity into and optimising the performance of a given unit size were key themes. John Elder of Outokumpu Technology introduced the H9000W, a new commercial high capacity spiral featuring wash water supply, and also discussed its potential applications. The Multi-Cell Jig, at an earlier stage of development albeit with a substantial body of comparative test results already collected, was discussed at the conference by its inventor, Dr Yang, head of Mineral Technologies International based in the USA. The Reflux Classifier, developed by a team at the University of Newcastle in Australia, has now been built at full-scale as the RC1800, reported Keith Galvin. In both the Yang Jig and the RC1800 sloping plates are used to increase capacity in a given machine volume. Also new and also an Australian innovation, but not a separator, is an automatic pycnometer developed at the JKMRC as a safe, rapid and cost effective tool for measuring specific gravity. The device has been licenced to Ultrasort for commercialisation.
Two speakers reported on commercial applications of enhanced gravity separators. In a paper co-authored with Peruvian mining company Minsur, Rob Longley of Gekko Systems explained the part played by the InLine Pressure Jig in the latest modernisation of Minsur’s San Rafael tin plant. John Botha discussed enhancements to gold recovery achieved at the Avgold Target Gold Mine in South Africa, the most recently developed large gold mine in that country. Here a Gekko Inline Leach Reactor is used to treat Knelson Concentrator product. Two other papers from South Africa reported research projects. Paul van der Plas of the Cape Technikon discussed optimisation of InLine Pressure Jig operation through characterisation of the pulse wave, while Brian Loveday reported on studies at the University of KwaZulu Natal concerning the modification of heavy medium viscosity by using the surface active chemical calcium lignosulphate.
Day Two was devoted to several aspects of the optimal application and operation of enhanced gravity separators, with both the Canadian and both the Australian manufacturers to the fore. Russell Heins from Gekko Systems discussed the use of a decision matrix to assist the selection of optimal feed characteristics for specific gravity circuits while Terry Jones reviewed applications of the Kelsey Jig, now a product of Roche Mining (Mineral Technologies), in the treatment of tailings. Steve McAlister of Falcon Concentrators examined strategies for sample testing ahead of full-scale gravity circuit design and Ish Grewal from Vancouver neighbours Knelson outlined the application of particle size distribution modelling to circuit optimisation. Modelling was also the theme of a paper presented by Nimal Subasinghe, covering work at Murdoch University in Australia on the Knelson Concentrator. Rob Dunne from Newmont’s Australian team closed the conference with an examination of the options for economically recovering fine gold from enhanced gravity separator concentrates.
One point stressed by the manufacturers present was that collaboration with the academic research community as well as with customer companies is undoubtedly beneficial. Given an attendance of 70 delegates from 15 countries, this Gravity Conference certainly succeeded in facilitating the exchange of ideas and experience. It deserves to be repeated, and it will be – Gravity 06 will be held in Western Australia in March that year.
Kyran Casteel, World Mining Equipment
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