Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr
Issue link: https://emj.epubxp.com/i/94438
GRAVITY SEPARATION nized concept for separating a much wider range of minerals. The concept of the jig is based on synthesizing natural processes of strati- fication in which denser material is concentrated below the less-dense in a water bath—comparable to the forma- tion of alluvials but in a controlled process that can handle large through- puts. And whereas the original jig designs used mechanically induced pulsing to assist in stratification, mod- ern systems use air-pulsing to achieve the same effect, but with much greater control and efficiency. E&MJ; asked one of the major sup- pliers of jig technology for minerals separation, Delkor (now a Tenova Mining & Minerals company), to ex- plain in more detail how jig applica- tions have been extended in the recent past. The company's product manager for jig technology, Anup Dutta, con- firmed how in earlier times jigs were only used for coal processing, but that in the past 20–30 years under-bed pulsed jigs have become used increas- ingly for separating hard and dense materials such as iron ore, diamonds, gold, manganese ore, barite and heavy- mineral sands. "Jigs have also been used very successfully to recover met- als such as ferrochrome and ferro-man- ganese from slags, at size ranges vary- ing from 0.5 to 30 mm at varying gran- ulometry," he added. Dutta went on to explain how Delkor is now taking the lead within Tenova Mining & Minerals in terms of its jig- ging technology. "Bateman developed its proprietary technology known as the Apic jig," he said, "which was a tech- nologically advanced version of some of the older air-driven jigs. It successfully commissioned Apic jigs in coal and heavy minerals such as iron ore and manganese ore, along with ferro- metal slag applications. Since Tenova acquired Bateman and Delkor in early 2012, its jig technology has been con- solidated under Delkor, with its prod- ucts now being marketed as Delkor Apic jigs." Benefits claimed for Apic jigs include their ability to deal with both fine and coarse material effectively and efficiently, and that they can concen- trate either lighter float or heavier sink material in a wide range of particle sizes. Delkor also points out that they www.e-mj.com can cope with a wide range of deslimed and non-deslimed feed and discharge rates, as well as continuously varying feed grades. Another significant advan- tage is that their operating costs are lower than competitive separation tech- nologies, while there is no loss of heavy media since none is used. "Compared to other separation tech- nologies, and specifically to dense- media processes, jigging has the edge in terms of its energy usage," said Dutta. "Generally speaking, jigging has a spe- cific power consumption of around 2.75–3.25 kWh/mt of raw material feed, while dense-media systems need 3.75–5 kWh/mt, depending on the design con- siderations and the technology applied in relation to the feed characteristics and the throughput." From Coarse to Fine Dutta also explained that the sizing and design of a jig plant is very sensitive to the nature and beneficiation character- istics of the raw material to be pro- cessed. "Although attempts have been made to standardize the design, we feel that some design changes or modifica- tions will be needed for each kind of feed. This will optimize the efficiency for that particular material, or if the system needs to be flexible enough to handle material coming from a number of feed sources." To illustrate this, Delkor now pro- duces jigs in sizes ranging from 500 mm to 8 m wide, covering applica- tions ranging from pilot plants to full industrial installations. The number of jigging chambers, from two to seven, is also dependent on the required separa- tion efficiency and the number of prod- ucts, with individual unit capacities varying from 10 to 1,000 mt/h for coal plants and from 10 to 350 mt/h for heavy-mineral applications. In terms of particle size-handling capabilities, the company's fines jigs operate in the range 0.5–20 mm, medium-grain jigs from 20 to 80 mm and coarse-grain jigs from 75 to 125–150mm. Today's jigging technology has be- come much more sophisticated and con- trollable through the use of systems such as Delkor's Jig Scan PLC software. By controlling parameters such as the pul- sation frequency, stroke and pattern, this in turn means that the separation cut point can be fine-tuned more effectively. Optimizing the cut point depends on achieving proper settling of the sink material, Dutta told E&MJ;, which requires uniform feed distribution as well as controlling the specific through- put relative to the jig width, and the jig- ging air quantity and pressure. It is also important to have accurate measure- ments of the settled bed height, with advances in instrumentation and ultra- sonic sensors having improved this. In addition, he said, the sink-discharge mechanism plays an important role in obtaining better cut-point control. One of the biggest changes in jig applications has been the transfer of the concept from essentially coarse feed material, in which the density differ- ences between float and sink con- stituents are clearer, to its use for sepa- rating fines. As Delkor notes, for exam- ple, jigging iron-ore fines is very diffi- cult, and factors such as fluctuating pulse frequencies, pulse dampening, the extraction methods and dead areas on the jigging surface—which can be neglected in the case of coarse iron-ore jigging—can have a significant effect on the jig performance in this situation. Bateman installed two of its Apic jigs for handling iron-ore fines. The first, at Corumba in Brazil, was subse- quently optimized with Delkor applying the changes made to the next installa- tion at an Indian iron ore operation. In both cases, the systems have worked well, Dutta said. Changes made included reducing the bed depth in the first two jig com- partments, allowing the jig pulse to dilate all parts of the jig bed effective- ly. This improved the unit's perform- ance and the product grade, but at the expense of lower recovery, so Delkor then cut the velocity of the hutch water over the end weir to thicken the reject layer and prevent scouring of the jig bed. Finally, the company optimized the control settings on the jig, and the height of the chamber levels, testwork having indicated that recovery could be improved by around 8% by running chamber levels high compared to low. An Australian Viewpoint E&MJ; also sought the views of Gekko Systems' business development direc- tor, Sandy Gray, on the way in which the use of jig technology has extended in the recent past. "Gekko has seen pro- NOVEMBER 2012 • E&MJ; 55