Dust control methods are techniques used to control particulate matter emissions from land surfaces.

Dust consists of small airborne particles and occurs primarily due to wind and traffic movements. The dust particle sizes differ according to the nature of activity that generated them. There are different dust control techniques used in mining and construction sites.

The top 10 dust control methods are:

  1. Water
  2. Salts and brines
  3. Bitumen emulsions 
  4. Surface active agents 
  5. Lignosulfonates
  6. Liquid polymers
  7. Highly refined synthetic fluids  
  8. Polymer emulsions 
  9. Petroleum derivatives
  10. Vegetable oils 

The severity of influence on health depends on the type of dust, concentration, exposure duration, etc. Apart from disturbing respiratory system processes by mechanical properties of particles, dust also has a negative influence due to its chemical characteristics. Dust can be toxic to a certain extent if it contains metal, PAHs (polycyclic aromatic hydrocarbons), other organic compounds, endotoxin, etc. These compounds can be contained in almost every type of dust: soil dust, construction dust, dust from mines and quarries, etc. The possible precise consequences of dust exposure in everyday life are hard to determine. Therefore, dust control is crucial for human health protection. Besides the impact on human health, dust decreases visibility in traffic and work sites, contaminates surrounding environment, contributes to the deterioration of roads by mitigating from the road surface, etc.

Chemical products used for dust suppression include water, products manufactured specifically as dust suppressants, natural or synthetic compounds, and waste or by-products from other uses and manufacturing processes. The products are usually provided as a concentrate. Water dilution for application varies from 1:1 to 1:20 depending on the type of dust suppressant and site conditions.

Water is the most widely used dust suppressant. To date, the most widely utilized dust control measure has been particle agglomeration through the capillary effect of water. The balance between its efficacy and sustainability remains a cause for concern. Single application has a very short-lasting effect, so watering is a meaningful method if dust control is needed for a short period. The application rate is important since a heavy application may turn the road into the mud and thus destroy the soil structure and make it non-suitable as a sub-grade.

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Salts and brines applications are the next most common dust control methods. Calcium chloride and magnesium chloride are the major products in this group. Calcium chloride is a by-product of the ammonia-soda process and a joint product from natural salt brines. Magnesium chloride is produced through seawater evaporation or from industrial by-products. These dust control methods stabilize the soil surface by absorbing atmospheric moisture, so it is critical for a target region to have sufficient humidity levels of 30-80%. Salts such as calcium chloride, magnesium chloride and sodium chloride have the ability to absorb water and significantly increase surface tension of water film between particles therefore slowing down evaporation but require minimum humidity levels to absorb moisture from the air.  

Bitumen emulsions are formulated from water, neat of bitumen in the presence of a surfactant to form either a water in oil or oil in water emulsion. The dispersed phase of bitumen is in the continuous phase of water in the presence of surface active agents which reduce the surface tension between bitumen and water. Bitumen emulsion binds and agglomerates surface particles because of bitumen adhesive properties. It also serves to waterproof the surface. The limitations include possible release of polycyclic aromatic hydrocarbons as a result of runoff into waterbodies which could result in genetic defects amongst many other problems associated with bitumen chemistry when exposed to the environment owing to its non-biodegradability. Bitumen emulsion applications can be limited as a result of too many fines relative to high asphaltene content of the bitumen which can lead to crust formation and fragmentation under traffic and in wet weather. The phase chemistry of bitumen emulsion also makes applications difficult to maintain. 

Lignosulfonate is a polyelectrolyte polymer that has good water solubility and its aqueous solution consists of a mass of anions. It is a by-product of the chemical pulping industry. Its advantages include cementing soil grains together, formation of a crust which renders a strong structure and is effective in resisting external erosion. It can also be used as a clay dispersant which reduces void volume in soil and increases the structure strength. On the downside, in the presence of rainfall it tends to leach away consequently leading to its significant reduction in concentration within the surface layer or pavement layer. Lignosulfonates are known to be corrosive to some metals and their alloys as well.

Liquid polymers are used to bind and coat surfaces to control dust. Synthesis of the polymeric component is performed to target saturation, penetration and bonding on the top layer even after water evaporates. The greatest motivation to use of liquid polymers has been the reduction in volume of water used which in the process saves time and costs. The need to prolong moist conditions has seen the use of biocompatible liquid polymers with success observed in post evaporative moisture compared to conventional water treatment.  

Highly refined synthetic fluids are the latest environmentally friendly dust control products which works through adsorption onto the treated surface, making dust particles heavy to be airborne. 

Synthetic polymer emulsions bind surface particles together via their adhesive properties which increases the shear strength of the material but are difficult to maintain as a hard surface and are susceptible to photodegradation. This group of emulsions is made by monomer polymerization in an aqueous medium. Their mechanism of action relies on evaporation kinetics, where removal of water leads to a transition from flocs into a film as a result of coalescence. The 40-60% solids by weight content are responsible for particle encapsulation and formation of a binding network adhering soil grains together. 

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Many dust control methods involve petroleum derivatives such as mineral oil and Vaseline. They are both produced from highly refined crude oil. The drawbacks are that they evaporate and break down quickly, and are expensive. Also in the petroleum category are waxes, which are sprayed onto the surface to form a bond with sand particles. They are also prone to evaporation and UV breakdown, and additionally to melting. Mineral oils and base oils agglomerate surface particles and are applied in their neat form hence do not require any dilution with water and have been used with great success to access extended dust control applications.

Applications of vegetable oils such as soybean, cottonseed and canola oil are common dust control methods. Molasses provide temporary binding of surface particles but have limited availability whereas vegetable oils agglomerate the surface particles but oxidize rapidly and become brittle. These substances are environmentally safe and biodegradable. However, they also evaporate easily and thus are short-lasting solutions. Both petroleum-based and vegetable oils are applicable when used on a surface that is all or mostly sand. Mixing oil with a soil that has a high content of silt and clay will produce a slick mess. As with water, frequent light applications are needed.

Many years of research on Global Road Technology made dust control methods environment-friendly and cost-effective. GRT offers dust control products applicable and effective under extreme conditions. Costs savings of 30-40% are accomplished due to the removal of daily watering and grading, less wear and tear on vehicles, improved haul times, elimination of downtime during and after wet weather (independently verified by Deloitte). GRT products are certified environment-friendly by Environmental Resource Management (ERM).

For more information regarding Global Road Technology or dust control methods please contact us.

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REFERENCES 

Ball, G.F.A., Herrington, P.R., Patrick, J.E. 2008. Environmental Effects of Emulsions. Land Transport New Zealand Research Report 343. 

Ding, X., Xu, G., Kizil, M., Zhou, W., and Guo, X. 2018. Lignosulfonate Treating Bauxite Dust Pollution: Effect of Mechanical Properties and Wind Erosion Behavior. Water Air Soil Pollut. 229:214. 1-13.

Hossain, S.Z., Mumford, K.G., and Rutter, A. 2017. Laboratory study of mass transfer from diluted bitumen trapped in gravel. Environmental Science: Processes & Impacts.

Jones, D. Holistic Approach to Research into Dust and Dust Control on Unsealed Roads. Transportation Research Record 1652

Jones, D., James, D., Vitale, R. 2008. Road Dust Management: State of the practice. In Proceedings of 1st Road Dust Management Conference, 13-14 November, San Antonio, Texas