Dust Control Handbook for Industrial Minerals Mining and Processing

Figure 2.3. Contact angle resulting from a liquid meeting a solid surface [NDT 2009].The use of surfactants increases the rate at which the droplets are able to wet or coat dustparticles; thus less moisture is used to produce the same effects as a typical water application.Small amounts of surfactants can be injected into the spray water, typically in a dilution range of1:700 to 1:1500, to improve the wetting and subsequent control of dust particles [Swinderman etal. 2002]. Despite the effectiveness of chemical additives, it must be noted that they are notoften used in the metal/nonmetal mining industry based upon several limitations.Surfactants are significantly more expensive than a typical water application.They can alter the properties of the mineral or material being processed.They can damage some equipment such as conveyor belts and seals.Surfactant systems require more upkeep and maintenance than typical water systems.Surfactants have limited usefulness in the metal/nonmetal mining industry, as opposed toin the coal industry, since ore or stone are much easier to wet than is coal due to itshydrophobic nature [NIOSH 2003].The effectiveness of chemical additives depends on:the type of wetting agent;hydrophobic nature of the mineral particles;dust particle size;dust concentration;water pH; andminerals present in the water used [Rocha 2005c].NOZZLE TYPES AND SPRAY PATTERNSSpray nozzles are categorized by the type of atomization method used and by the spray patternsthey produce. The most commonly used spray nozzles produce full cone, hollow cone, round, orflat fan patterns. Air atomizing nozzles (which utilize compressed air) are typically used toproduce round or flat fan spray patterns, while hydraulically atomizing nozzles are typically usedto produce full or hollow cone spray patterns; however, some hydraulically atomizing nozzlescan also produce flat fan spray patterns.Wet Spray Systems 65