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46 E&MJ; • MARCH 2014 www.e-mj.com F I LT E R S A N D T H I C K E N E R S Dewatering: An Increasingly Important Mineral Process Efficiency improvements are always the goal in this vital equipment class, with the aim of optimizing the balance between residual moisture contents and the benefits gained from water recovery Filtration and thickening are areas of min- eral recovery technology that are often overlooked. Nonetheless, they represent an important component of the entire process, since without dewatering, it would be hard to produce concentrates to transport specifications while water recy- cling from tailings streams is becoming increasingly important as energy costs for pumping steadily increase. In addition, the benefits of dry tailings disposal are becoming increasingly appreciated from both environmental and social responsibil- ity perspectives. This review looks at some of the major players in the supply of both filtration and thickener equipment, companies that over the years have developed and improved upon the technologies and concepts involved. As with other areas of mineral processing technology, efficiency improve- ments are always the goal, with the aim of optimizing the balance between residual moisture contents and the benefits to be won from water recovery. The Benefits of a Joined-up Approach U.S.-based McLanahan Corp. has recently been doing a lot of work installing its deep- cone thickeners and filter presses together for several different mineral-processing customers. McLanahan's director of pro- cess engineering for mineral processing, Scott O'Brien, explained the rationale for using this approach to dewatering. O'Brien said while using a thickener on its own will enable an operator to recover 80%-90% of the water in a slurry, the underflow will still contain enough water to make it difficult to handle. Normally, he said, this would go to a pond for further consolidation of the solids, and perhaps to recover some reusable water. "However," he went on, "getting a per- mit for the pond might not be feasible or may just be very difficult. That's when a fil- ter press can be extremely useful. "The thickener underflow can go through a filter press to become a cake that can be picked up with a loader and transported. Since filter-press cakes contain such a high proportion of solids, they also stop water dripping all over the road during transport, which officials don't take kindly to." O'Brien went on to point out that pro- ducers who do not have a thickener, but do have a filter press, end up putting a dilute feed into the press. This greatly increases the cycle times because more water is going through the press. In addition, he said, longer cycle times of high-velocity water can cause faster wear on the filter cloths. The benefits of using a thickener and filter press combination can include better water recovery, the removal of permitting issues, lower operating costs since a tail- ings pond may not be needed, and better compliance with environmental require- ments, O'Brien suggested. Higher water-recovery rates mean that operations can cut their fresh-water demand, while stacked dry tailings are less likely to have dam-failure issues. McLanahan stated that interest in this type of combined dewatering system is increasing, with the concept becoming more accepted. It also points out that most mineral-processing plants already have some type of thickener, and with changes in regulations or plant-processing needs, a filter press can easily be added to treat the thickener underflow. The company added that it will be installing a number of press- es with existing thickeners in the U.S. and Russia over the next few months. Colossal Filter Recovers More Water FLSmidth reported that its paste thicken- ing equipment is used to maximize water WesTech Engineering's EvenFlo feedwell provides better feed distribution into a thickener, according to the company. By Simon Walker, European Editor EMJ_pg46-58_EMJ_pg46-58 2/28/14 3:10 PM Page 46