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Grinding technology trimmed in at the Laiva mine
After working in mining projects across the globe for 37 years, it took leading edge grinding mill technology to tempt Australian project manager Mike Gunn to Finland to oversee the start-up of the gold production process at the Laiva mine. “I wanted to learn more about this innovative grinding process that saves both costs and the environment,” he says.
Asking what the escape plan was when he headed a mining project in politically unsettled conditions in Tajikistan, he was pointed towards the mountains leading into Afghanistan -which was being bombed by the US at the time. Compared to that experience – as well other adventurous mining projects in countries ranging from Mexico and Mali to Mongolia – the Laiva mine in central Finland appears as a textbook case of effectivity to Mike Gunn.
- Everything is so shiny and new, he says and looks admiringly around in the processing plant, which is being trimmed in at the moment. - In many of the projects where I’ve been, a lot of second-hand equipment has been used – but here you can mirror yourself in the machinery, he says. But it wasn’t the spotlessness that made Mike Gunn pack his bags from his base in Brisbane, Australia, and head for the north to accept the offer to oversee the start-up of the gold production process at Nordic Mines’ Laiva mine.
- What really tempted me was to see for myself how the technology being used for the grinding mills works in practice. Traditionally, steel balls are used to grind the rock. But here stones are used instead, which leads to a number of advantages.
- Steel balls are expensive and can only be used once. They give off remnants that can disturb the leaching. And producing steel consumes a lot of energy – which means a negative impact on the environment, Mike Gunns says.
In the processing plant at the Laiva mine, the ore is crushed and ground until all particles measure less than 0.1 mm. This takes places in several stages, using stones to crush stones. The mills have been designed by Outotec, one of the leading suppliers of ore grinding mills in the Nordic region. Outotec is also responsible for the technology and installation of the mills. The technology is called autogenous grinding. The mills have a capacity of grinding 250 tonnes of ore per hour. The gold is present in small quantities in the ore. Two tonnes of ore are required to produce gold equivalent to a wedding ring weighing approximately 4 grams.
- But compared to many other profitable gold mining projects, this is by no means low quantities – several mines are operating with less than half of this grade, Mike Gunn points out.
He knows what he is talking about. Mark Gunn has more than 35 years’ experience in the mineral processing industry, specializing in operations and process design. He gained operating experience with Anglo American in Zambia, CRA in Bougainville, then with RGC, Selwyn and Ok Tedi in Australasia –and then feasibility study and process design skills working with Minproc Engineers. Lately, he has been consulting to major engineering and consulting groups, including Metso, one of the major suppliers for the Laiva mine project and responsible for the start-up. He has undertaken a broad range of mineral processing and hydrometallurgy design and process consulting assignments worldwide, largely in base metals and gold. He holds a B.App.Sc. in Metallurgy from the University of New South Wales.