Traditional Approach – Water

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. Understanding dust suppression products and their chemistries is core to developing greener, water sparing and fit for purpose alternatives. The article takes a closer look into highly refined synthetic fluids from green feedstocks, ionic surface-active agents, and liquid polymers. Renewable source origins and circular economy incentives to highly refined synthetic fluids make them more palatable although surfactants and polymers perform distinctively in their various applications.  

Challenges with Water

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Applications such as quarrying, mining and road construction utilize water mostly on hydrophobic surfaces and the smartest way to change the surface charges and make water work is to super activate water. Super activation of water is achieved through reactions with surface active agents normally known as surfactants. Surfactants can be ionic or non-ionic and for this application the focus will be on ionic surfactants. Instead of repetitive use of water to achieve intended wetting of the hydrophobic surfaces, the amphophilic nature of surfactants enable them to reduce the surface tension between hydrophobic surfaces and water. This is achieved through the chemical structure of the surfactant which consists of a hydrophobic tail and a hydrophilic head. The hydrophilic head interacts with the water, which on contact with the hydrophobic surface the hydrophobic tail interacts with the surface which allows the binding of the fugitive dust particles in the process. 

Overcoming these challenges

The adsorption of ionic surfactants at hydrophobic solid surfaces is driven by the transfer of the surfactant hydrocarbon part from an aqueous environment to the apolar environment in the adsorbed layer. This is accompanied by the attraction of its counterion to the surface, as a result of the complete dissociation of the surfactant in the bulk solution. The hydrophobicity of the super-activated water in GRT: Activate enables water to timeously coat airborne dust particles, leading to them to succumb to the force of gravity from their suspension in air through immobilizing elusive dust. Effective at the coalface and utilized in the coal industry without effect on the calorific value is another GRT product known as GRT: Activate UG. Coal is hydrophobic and it’s finest particles if not bound on spray applications can lead to health problems hence the super-activated water interacts with the particles enabling efficiency of existing spray infrastructure and systems. 

GRT Water Truck

Polymer Binders

Binding and coating of surfaces to control dust can be achieved through use of liquid polymers in water. The monomeric units in liquid polymers can either be hydrophilic such as in polyethylene glycol. On the other hand, triblock copolymerization enables combination of hydrophilic and hydrophobic monomeric moieties with a typical example of poly(ethylene oxide-b-propylene oxide-b-ethylene oxide). 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. 

In dust suppression applications the choice of liquid polymer is based on biocompatibility, water solubility, phase at room temperature and how environmentally friendly it is. Interestingly, liquid amphiphilic polymers show significant dust control relative liquid hydrophilic polymers owing to the dual effect of the liquid state and the amphiphilicity of the polymer. GRT: Haul-Loc is the mining and resource sector version of liquid polymer available. It reduces the water required by 50% with up to five-fold improved duration of dust control sustenance compared to use of water alone. Another product GRT 7000 provides a robust liquid polymer solution for nearly all soil surfaces with up to 99% suppression of dust particles. 

Plant-Based Alternatives

Highly refined synthetic fluids from can be used as dust suppressants. Lignocellulosic organic matter available on a renewable basis has been recognized as the most reasonable carbon-based source for a range of materials. Depending on plant species, lignocellulose consists of cellulose, hemicellulose, and lignin with building blocks of glucose polymeric units, xylose and cross-linked aromatic based heteropolymers respectively. Due to their differences in composition and reactivity, fractionation is key before further processing. Of major interest, is lignin which consists of three phenylpropanoic monomers connected by carbon-carbon and ether bonds. The liquification process of lignocellulosic biomass is performed through oxypropylation via grafting propylene oxide through catalysis or activation of biomass in ethanol solution. Unfortunately these chemistries are water-soluble and breakdown and wash away in the rain – which can be slippery in industrial applications and require premature reapplication.

Long term, waterless options

Another potential renewable raw material that has been utilized to generate bio-based self-healable polymeric networks is environmentally friendly oil. Vegetable oils are known to consist of triglycerides formed between glycerol and various fatty acids. The ability to functionalize vegetable oils at their ester groups, unsaturated double bonds, and allylic hydrogen atoms creates opportunity for diverse chemical reactions. Some other potential feedstocks include sunflower, castor oil plant and palm trees. The variation of the chemical composition of triglycerides between and within a particular crop source poses a challenge, as does the rapid speed of biodegradation. Synthetic oils avoid this shortcoming. On the market currently, a GRT product, GRT: Wet-Loc is available and produced from green feedstock. GRT: Wet-Loc adsorbs to the treated surface offering long term performance on a wide variety of surfaces in addition to its self-healing and workability properties. The formulation suppresses the buoyancy and collisions of dust particles in air through size increase whilst deterring evaporation or freezing unlike what is experienced when using water or water-borne solutions.

A broad environmental outlook

The factors contributing to sustainable product development of dust suppressants include design for water efficiency, use of renewable feedstocks, less hazardous chemical syntheses and inherently safer chemistry for the environment. As seen above, some factors, which may tick the environmental box, can actually impact safety. Terms like biodegradability can seem to be inherently positive environmentally – however the difference between readily biodegradable and ultimately should be considered, particularly when a long-term single application is required. The onus is on the formulation chemists and engineers to think green from conception to application of dust suppressants. 

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