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TAILINGS MANAGEMENT SEPTEMBER 2017 • E&MJ; 55 www.e-mj.com weight percentage, which is the weight of water over the total weight of the sample. The percentage used by geotechnical en- gineers is the weight of the water over the weight of the solids. To counter the wetter filter cake, the EcoTails team proposed a method of mixing waste rock to add strength to the composite. Essentially, the EcoTails concept filters fast with less machines and adds strength by co-mingling it with waste rock. "We have trademarked two names: EcoTails, which is the project and process, and GeoWaste, which is the composite material — the comin- gled waste rock with the filtered tails," Wisdom said. Miners have been co-mingling materi- als forever, but they have mostly done it on a small scale with trucks and shovels to mix and move materials. That won't work for 150,000 mt/d. Placing the ma- terial on a conveyor with some specially designed transfer chutes would work and, at the end of the process, a completely mixed material can be placed on the TSF. "Most conveyors are moving material at a velocity of 4 m/second (s) to 6 m/s so there is a fair amount of kinetic energy at the transfer point," Wisdom said. "If the system is designed correctly, we can use that energy to mix the materials." The Advantages of a Less Permeable Pile In addition to strength, GeoWaste has other advantages. By filling the voids in the waste rock with filter cake, the permeability of the waste rock pile will be greatly reduced. "The coarse rock particles give the pile a higher density, which provides quicker self-weight consolidation, adding more strength more quickly in the TSF," Wisdom said. From a safety perspective, the water on top of the TSF dam and the whole dles this through location-to-location precedencies between the dam and the basin, such that the dam is completed prior to the basin becoming available. This arrangement allows for all possible destinations of waste material to be considered when optimizing the total mine sequence problem, and all the associated costs of doing so, along with known design/storage capacity limitations that re- strict the solution. Optimization of the Model In seeking maximum NPV, the model will assess all possible destinations of material with consideration of this import- ant tailings design requirement. Since the mill is the sole revenue-producing agent in this model, and given the power of discounting, the model will seek to construct that embank- ment structure as soon as possible, and this will influence the overall sequence of the pit such that the critical materi- al types are made available that enable this among the other competing factors. Planners can check to ensure a model is working through eval- uation of multiple dashboards. The 3-D visualization can show the progress of the waste placement in each of the three locations. The effect of the delay at the mill can be seen through a move- ment chart indicating mill tonnages or tailings tonnages. They can interrogate the buildup of volume to reach design capacity in each of the waste locations, including the tailings dam, using the remaining reserves table and dump tables. If one runs out of capacity in the tailings basin, the mill will stop producing; likewise, if one does not have enough material to construct a tailings dam structure, the mill will never operate. This simple example illustrates just how important it is to consider all the interdependent components — including tail- ings — throughout the scheduling process in order to achieve the best possible value. The effect of the delay at the mill can be seen through a movement chart indicating mill tonnages or tailings tonnages.