Modern Mining May 2016

feature CRUSHING, SCREENING AND MILLING

Correct screen media selection now

Asset optimisation has always been a primary objective for all mining houses – the more so in the present tough conditions facing the mining sector. A major asset for all mines, of course, is the minerals processing plant and optimising its operation will vary from commodity to commodity and frommine resource to mine resource, with the selection of the correct screen media being an important part of the process.

R hodes Nelson, MD of Multotec Manufacturing, tells Modern Mining that some iron ore mines are focusing on increasing the throughput volume because their business model is based on the cent per ton calculation. Other mines are using the differ- ences in their geological resource characteris- tics and therefore have to look at optimising the product quality to create differentiation. “The same is true in the diamond sector where mines producing gem quality stones are increasing throughputs to increase yields while those producing industrial type application diamonds are trying to reduce the cent per ton model,” Nelson says. He notes there has also been a major increase in waste dumps being recycled across a range of commodities. “This,” he explains, “is another opportunity to squeeze volume out without having to deal with the mining constraints and allows miners to meet long term contractual requirements.” Although greenfield capital project plants have largely dried up, there remain brown- field opportunities within existing operations – including the recycling of dumps – and these present the need to optimise plants to adapt to the changing throughput and grades required by customers. Market conditions coupled with the ongo- ing drive to optimise minerals process plants have led to a situation where the control of the changes in the orebody is heightened more so than in more economically relaxed times. “This has made the selection of screen media more important than ever to make sure that it will fit into the ‘sweet spot’ for the plant because of this variability. Add to this, the sweet spot is a constantly moving target and where, in previous years, a screen media solu- tion supplied would have stayed in place for

extended periods, today this is no longer the case,” says Roy Roche, Vice President Screen Media at Multotec. He cautions, however, that changing the throughput on a screen is not the simple exer- cise that many mines believe it is. “It requires the input of skilled process engineers who can recognise that there are a number of factors that need to be considered.” In previous years, there would probably have been just one type of screen media on the screen. This has changed dramatically in the drive to optimise screening operations and has led to increased innovation and out-of-the-box thinking in terms of applying fit-for-purpose solutions to screens. Roche says that in some applications today there are up to nine types of panels on a screen deck. “Another example would be where a combi- nation of compression moulded and injection moulded rubber panels is used along with diverters to ensure optimum throughput with well over 95 % screening efficiency,” he says. An example would be where specially engi- neered screen panels which combine Hardox ® embedded in rubber have been installed on the feed sections of screens in an iron ore applica- tion. These panels are capable of handling the impact of the 600 mm top size. On the same screen bed, high impact slotted skid bar pan- els, known as Multotec Ratel panels, are used to reduce channelling and ensure accurate cut size while providing maximum screen panel life. In this self-same screening application, Rhodes Nelson, MD of Multotec Manufacturing, and Roy Roche, Vice President Screen Media at Multotec, inspecting a newly designed screen panel.

44  MODERN MINING  May 2016