Dust Control Handbook for Industrial Minerals Mining and Processing

soil surface becomes compact and mechanically stable, thus becoming more resistant towind erosion. The soil must have an appropriate amount of fine material in order to bindthe larger materials to form the crust. However, the degree of cementation is hard todetect, making it difficult to measure the amount of cementation required for windresistance, i.e., the number of wet/dry cycles required to prevent erosion (Chepil 1958).The amount of moisture in the soil also affects the erodibility of soil. Basically, as themoisture is increased, the erodibility of the soil decreases [Chepil 1956]. This is importantfor dust control of open areas. However, it has been shown that even soils with highmoisture contents can be susceptible to wind erosion. With loose soil, with a depth of 5cm, the erodibility of a moist soil can be similar to that of a dry soil if the wind speedapplied to the moist soil is 15–20 mph more than that applied to the dry soil [Cowherd andGrelinger 1996]. Therefore, while wetting is a good dust control measure, the area muststill be monitored to maintain the proper amount of moisture to prevent erosion.CoatingsCoatings as a dust control method generally include water or a myriad of chemicalstabilizers in commercial production. The best coatings that prevent wind erosion form acrust on the surface of the material or soil. Additionally, the best coatings are nontoxic toplants, water permeable, and allow the material to be handled easily. The drawbacks tocoatings are that they are expensive, and once the crust created by the coating ispenetrated, erosion readily resumes [Diouf et al. 1990; Armbrust and Dickerson 1971;Lyles et al. 1969].Mixing bentonite clay with soil is a dust control for open areas. Water is applied,allowing the soil-bentonite mixture to form a crust on only the top of the mixture.Beneath the crust the material is unconsolidated, as water is not able to penetrate the crust.Bentonite concentrations that are too high leave easily erodible sand particles (