Engineering & Mining Journal

MAR 2017

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

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ENERGY EFFICIENCY 48 E&MJ • MARCH 2017 alent amount. Using existing tech- nology, this means the energy require- ment for grinding and flotation will in- crease as well. Eric Bain Wasmund, global managing director of Eriez's Flotation Division, explained to E&MJ that his division is developing and com- mercializing new products based on metallurgical first principles that will actually allow the energy requirements to be dramatically decreased. These im- provements, said Wasmund, are not the kind of incremental second order im- provements achieved by simply making bigger unit operations based on current technology, but major first order ad- vancements that are possible through a major re-think of the flotation process, which hasn't changed fundamentally in more than 100 years. The first of these, according to Was- mund, is the HydroFloat, a high-effi- ciency, aerated, fluidized-bed flotation cell that is capable of recovering coarse, semiliberated particles. Benchmark- ing the performance of the HydroFloat against a conventional stirred tank cell in a number of studies has shown a dramat- ic improvement in the flotation of coarse particles, as illustrated in a recent pa- per.* This approach allows for recovery at a much coarser size (and rejection of a coarse tail), which results in a significant reduction in grinding, the major energy consumer in the concentrator. The po- tential benefits of reducing comminution energy consumption are now well-accept- ed, and major mining companies are now looking at the HydroFloat as a type of ore sorter to develop a coarse throwaway tail, Wasmund explained to E&MJ. Another technology that is being com- mercialized for base metals is the Stack- Cell, which was introduced a decade ago into the U.S. coal industry. Developed by Dr. Michael Mankosa and Dr. Gerald Luttrell, the StackCell is a two-stage flotation device. A cross-section of the StackCell is shown below. The first stage (center of tank) is an energy-intensive, low-residence-time chamber consisting of a rotor-stator (4) that creates high turbulence to mix air and feed slurry to- gether (1). In this stage, the kinetics for particle-bubble collection are maximized in a zone that can flow in one direction into the second stage, with no short cir- cuiting. The second stage is a settling tank with overflow launders (2) and wash water (7) that allows for bubble-particle separation from the pulp into the froth phase in a fluid environment that allows for froth washing and minimizes particle bubble detachment. A campaign using a train of three 0.60-m-diameter StackCells in series for a low-grade copper ore was reported at the 2016 Denver SME conference.** (A similar installation is shown in the ac- companying photo.) The objective was to evaluate the StackCell as a low-energy, high-capacity alternative for a multistage rougher application for slow-floating ores and to compare the kinetics (recovery and grade) with a Denver lab cell, which is the industry-accepted standard for scaling up conventional stirred flotation cells. Results from this campaign are shown in the accompanying graph as residence time versus cumulative recovery for both the StackCell and the lab Denver tests. An estimate of the curve showing expect- ed performance for a full-scale conven- tional circuit is also shown. According to Wasmund, the commercial units are sized using the industry-accepted practice of multiplying the required retention time by 2–2.5 times to account for performance losses in scale-up. "By drawing horizontal tie-lines at any target recovery, we can see the advantag- es of the StackCell technology, compared with the incumbent technology. For exam- ple, 40% recovery can be achieved in 2.5 minutes with a train of three StackCells, or about 9 minutes in the batch Denver test. Using the standard scale-up rules, this Principal components of an Eriez StackCell. A three-stage StackCell pilot plant.

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