Dust Control Handbook for Industrial Minerals Mining and Processing

Grinding circuits and buildings should be designed so that they can be washed down forcleaning.A vacuum system should be installed and used for cleanup. Equipment should not be dryswept or brushed off because of the possibility of dust liberation. Never use compressedair to clean equipment or work areas.Upper levels around process equipment should have solid floors. If a spill or leak were tooccur over a solid floor, it immediately piles up instead of falling towards the next levelwhere it will become airborne and contaminate the mill.Sections of the milling process should be isolated to improve containment efforts.Examples include uncovered storage, bagging areas, and bulk load out areas.Above freezing conditions, floors should be kept wet so that any falling dust willimmediately hydrate and be trapped.Whole room ventilation with at least 10 air changes per hour (acph) is recommended.For classifier circuits, vendor guidelines should be followed for ducting and airflow toachieve optimum classification results. With other components of the grinding/loadoutoperation, the containment, pickup points, and ducting should be designed so that areaswith high air movement do not occur at transfer points and other potential disturbanceareas where the air stream will entrain product.When new or recently lined tumbling mills are started up for the first time, the air leavingthe mill is fairly humid until the grinding action builds up enough heat to drive off themoisture out of the curing grout. This can lead to a buildup of moist material in ductingand may cause blinded bags and cartridges in the dust collectors. These problems willtypically be resolved once the mill reaches operating temperature and the grout has cured.SCREENINGScreening operations can produce high levels of dust because smaller sized material is handled.Airborne dust is generated from the vibrating screen decks that accomplish the size separation.Additionally, material must fall some distance as part of the separation process, and some dustwill be suspended by this process.Dust control for screening systems is similar to that for crushers, although wet systems aregenerally not used due to blanking of the screen openings by the wet material. Also, screens arenot normally subject to large surges of material flow as are crushers. This is due to the fact thatscreens operate most efficiently within a designed flow range. Overloading screens, whetherthrough excessive feed rate or large surges of material, can cause accelerated wear ofcomponents, reducing the efficiency of the operation and potentially increasing dust emissions.Screens should be totally enclosed, and water suppression systems (when compatible with theprocess) or dust collection and exhaust systems should be incorporated. Necessary openings inthe screen enclosure must be minimized, and inspection and maintenance openings must beprovided with tight-fitting closures.Flexible materials (e.g., rubber or synthetic sheeting) must be used to seal openings between themoving screen components and stationary equipment and structures. Because the seal betweenmoving and stationary components is under dynamic stresses whenever the screen is operating, itCrushing, Milling, and Screening 125