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GRAVITY SEPARATION The Benefits of Using Gravity The leading suppliers offer their outlook on the current state of gravity-separation technology By Simon Walker, European Editor With its Apic jigs, Delkor is now the lead supplier of jigging technology within the Tenova Mining & Minerals group. With the possible exception of visual sorting—"this one's green, this one's not," or however the Bronze Age equiv- alent ran—being able to separate min- erals using differences in their density is the most ancient mineral-processing technique known to man. It is, after all, emulating the natural processes that formed the alluvial deposits in which gold and other dense minerals such as cassiterite were first found and, because of its effectiveness, it still plays a valuable role in a variety of modern mineral-recovery circuits. Panning and vanning, later upgraded by mechanization into shaking tables and jigs, formed the main means of recovering dense minerals for centuries, and it was only the advent of flotation for sulphide ores and cyanidation for 54 E&MJ; • NOVEMBER 2012 gold that relegated gravity separation to a minor place in the processing hierar- chy. By contrast, its use in coal wash- ing—initially using jigs then with en- hanced process capabilities through the introduction of dense-medium sys- tems—began in the late 19th century and has remained a washery mainstay ever since. Likewise the use of spirals for iron ore beneficiation. The big inno- vations in the past 25 years have been the development of 'assisted gravity' equipment, such as bowls for gold recovery, and the transfer of jig technol- ogy to a range of other minerals. Here, the contrast is that the concentrate is formed from sink material whereas in coal washing, the sinks are waste. As the Australian company, Gekko Systems, notes, in recent years flow- sheet designers have been reassessing gravity-separation systems for cost and environmental reasons, since they do not use increasingly expensive chemi- cal reagents. And, the company says, there are many situations where a sig- nificant proportion of the valuable min- erals in run-of-mine ore can be recov- ered into a pre-concentrate, thereby cutting subsequent mineral-processing costs. Jigging Applications Range Extends One of the most widely used gravity- separation technologies, jigging, has extended its range of applications sig- nificantly over the past quarter-century. Originally used almost exclusively in coal washing, jigging is now a recog- www.e-mj.com