smaller dust particles to become airborne more easily, as a result of the increased air flow and speed of the system. A fugitive dust issue is thus created and needs to be addressed throughout the entire system.
of water can be made more effective by atomising the water used, as well as adding a surfactant to change the water’s chemical make-up. The principle of surface tension can be seen when liquid spreads onto a surface. An example is water Dust control techniques spreading over an area of perfectly clean glass. The There are a variety of dust control techniques used degree of wetting is a balance between two forces to curb the amount of fugitive dust generated from a within the liquid. The liquid’s adhesive force (attraction mining operation. Water sprays are the most common to another substance) encourages it to spread onto the and effective method employed. They can be used glass while the liquid’s cohesive force (attraction to the for both dust suppression and re-directing air flow. same substance) tries to form into a ball. Surfactants With this in mind, they are installed to suppress dust (also known as wetting agents) have a direct effect on at all major dust sources, including: cutting, loading, these forces. Surfactants increase the adhesive force and material transportation sites. While operational and lower the cohesive force which allows the liquid to changes and mechanical means are standard for most easily spread. The effects any surfactant has on these operations, the use of chemical suppressants should forces can be measured by determining the surface be considered to compliment engineering controls. tension of the liquid. There are various types of chemistries used to control Water typically maintains a surface tension dust dependent upon the application. Though there of approximately 72 dynes/cm, depending on its are several combinations of chemicals used to achieve temperature. By adding the appropriate amount of the desired results, all products primarily try to bind surfactant to the system, surface tension can be reduced dust particles together, create a seal over the dust, or below 45 dynes/cm, considered the point where increase the weight of the particles to the point that maximum wetting of dust occurs. When the surface they cannot become airborne. tension is reduced, it will allow the droplet to absorb many small particles of dust and wet them more easily. Water spray This will increase the weight of the dust particles and For conveying applications, dust is generally controlled reduce their ability to become airborne. When enough with a water spray system that continuously wets small particles of dust stick together, they increase in the material throughout the transportation process. weight and fall to the ground. In a normal spray system, Though effective in most circumstances, increased the size of a water droplet can remain large and collide amounts of water can affect moisture specifications with or create a slipstream effect with smaller dust and the ability to transport the ore efficiently. The use particles, limiting its effectiveness. Reducing surface tension also has an atomising effect on water droplet size, effectively reducing overall circumference. The Table 1. Respirable dust weight and size of the dust particle are not able overcome the surface tension of the water droplet Prior to After Applications DUSTGRIP® JFP-95 DUSTGRIP® JFP-95 and, in some cases, the water droplet may increase the suspension process. Continuous 0.221 miner operation 0.326 Shuttle car
0.317
0.169
Shuttle car
0.350
0.221
Scoop
0.372
0.152
Roof bolter
0.228
0.168
Table 2. Quartz
Prior to After Applications DUSTGRIP® JFP-95 DUSTGRIP® JFP-95 Continuous 5% miner operation 33.8%
30
Shuttle car
6.9%
4.3%
Shuttle car
22.9%
4.1%
Scoop
4.4%
4.1%
Roof bolter
14.2%
7.1%
WORLD COAL ISSUE 2 2021
Surfactants In practice, both liquid and solid forms of surfactants are commonly used, dependent upon available equipment and operation preference. Both forms have the same function and are applied via dilution in the water source that supplys the spray nozzles. The process can be introduced in a mine wide water system to control dust in all areas of the mine, or locally to control one specific area. In a conveying system, transfer points become a focal point for fugitive dust as the material is agitated during the process. This is the area at which the mined material becomes airborne itself when it transfers from one conveyer to the next. At most 90˚ transfers, the mined material impacts a deflector plate that is used to direct the flow of material onto the centre of the next conveyer. The physical movement of the material allows untreated dust particles to become airborne and create float dust. Though water sprays are used
