Lignosulfonates (LS) are a by-product of the paper and pulp industry in the process of bisulfite pulping of wood, pure cellulose fibers are separated by dissolution of hemicellulose and lignin.
The parent source of the lignin in LS is only 1 –2 % of the 50 – 70 million tons of lignin produced annually. Currently, LSs account for 90% of the total market of commercial lignin and has an annual production of 1.8 million tons per year. The conditions affecting use of LS in dust suppression include:
In the 1980s, LS were known to have the ability to create certain bonds among the particles of the mechanical soil stabilization which eventually led to dust suppression.
WHAT ARE
On spraying onto dirt roads, LSs become viscous as water evaporates during drying; this traps the dust and prevents particulate air pollution. When used as a dust suppression agent, the lignin polymers work by binding soil particles together through film formation. The chemical reaction involves; firstly a protonated H+ that dissociated from water which is followed by neutralization with the negative charges on particle surfaces leading to a reduction in the double layer thickness and form bindings.
Emulsified LSs can perform as dust suppressants in unbound gravel materials. They are by-products from sulphite paper and timber-making processes in which sulfonated lignin a polymer built up of phenyl propane subunits is dispersed in an aqueous solution. Their composition depends on tree species feedstock and chemicals used to extract cellulose, with neutralized lignin sulfuric acid containing sugar as their active ingredient.
Calcium, sodium, and ammonium lignosulfonates represent the most common types with calcium lignosulfonate used as a dust suppressant. Initially, lignosulfonate is mixed in with topical spraying as a maintenance measure and rehabilitation. In its emulsified state, lignosulfonates consist of 50% solids by weight. Application rates vary from 2.3 – 4.5l/m2 with up to 2 treatments recommended per season.
When it comes to weather conditions, the applications are only effective under dry conditions with low humidity. Lignosulfonate has low-cost, non-corrosive, considered fast acting with no interruption of mining activities when used to suppress haul mine road dust, non-hygroscopic hence create long-lasting protection, suitable for arid regions owing to good water solubility and their high organic matter content allows for good revegetation.
There are also significant limitations associated with in situ material; if the wearing course contains little fine material or excessive loose gravel, these dust suppressants are not suitable and have shown poor adaptability to wet conditions, as they resolubilise and wash away – contaminating receiving waters and leaving the material untreated. They also have a reputation for becoming slippery as they build up – leading to incidents onsite. As such, although lignin is an effective dust control measure, there are limitations to its applicability.
GRT is a world leader in innovative and superior dust suppression systems. GRT’s dust suppression systems use less water and offer a cost-effective, site-specific solution.
GRT’s dust suppression system includes the dust suppression product, SMART dosing units, the GRT dust management app, technical support, site visits, and much more.
Always at the forefront of innovation, GRT’s solar-powered SMART dosing units capture and use powerful data to improve water cart fleet management while cost-effectively eliminating dust. These autonomous Dosing Units are the key hardware component of GRT’s industry-leading dust suppression systems offering the most effective haul road management and dust control.
GRT provides dust suppression systems for different applications ranging from mines, logistics yards, dual-track light rails, haul roads, festival grounds, lodge access roads, and maintenance yards.
| Factor | Lignosulfonates | GRT systems |
| Variation in composition | Precursor dependent | Consistent feedstock |
| Longevity | Limited | Extended |
| Crust formation | Prone to water ingress | Seals water out |
| Adsorption behaviour | Limited | Multivariate |
| Water usage | Surface pre-wetting | No need to pre-wet surface |
| Toxicity | Concentration dependent | Benign |
| Biodegradability | Product chemistry dependent | Degrade with ease |
| Presence of electrolyte | Precipitates with pH change | Stable under pH changes |
| Dosage (dilution factor) | High | Low |
| Haul, LV and dirt roads | Destabilizes easily | Stable |
LS composition is precursor-dependent, hardwood and softwood LSs exhibit slight differences in solubility. At different optimum mix ratios of LS combinations, they perform better than individual applications of LS. Other factors that can influence the composition and characteristics of LS are the reaction conditions during the sulfonation reaction, fractionation, and purification procedures, as well as chemical modifications.
GRT products are formulated from a consistent feedstock that does not change based on a precursor, instead, our product development works on a cradle-to-cradle approach with the same composition and chemical characteristics. That gives the confidence of consistency in product over different batches without remnants from the chemical interactions like is the case with LS.
Although road preparation (blading and rolling) will increase the quality of the road and its longevity, LS can be used for ungraded areas and just applied topically. LS doesn’t get lasting results, so must be reapplied, over and over, racking up costs. The site requires daily applications of LS. Synergistic application of LS increase crust longevity and dust control performance. At limiting concentrations LS provides better water retention with higher LS concentrations.
GRT crusting technologies rely on polymeric moieties with a backbone and functional groups that bind and attach to the soil particles of different sizes through a long chain polymer technology and locks the soils particles down and away from being dislodged to generate dust. This enables use of GRT: Haul-Loc at a dilution factor which enables you to reduce your water truck loads for dust suppression by 65%.
The addition of LS has virtually no influence on the density of the formed crust, but the crust thickness reduces with the increase of LS concentration. However, the thinner crust formed by higher LS concentration has better penetration resistance, which indicate that higher LS concentration possesses lower infiltration ability.
The chemistry of GRT crusting technologies (such as GRT: Soil-Loc, GRT: Ore-Loc, and GRT: DC Binder) is formulated with the application in mind. The agglomeration of the soil particles by the liquid polymers continues without a limiting concentration as that is catered for in the dilution factor. Application happens to specific thickness and consistency based on product dosing
Adsorption of lignosulfonates on solid surfaces has been stated to follow the Langmuir isotherm. Straight-chain alcohols can enhance this adsorption. Hydrophobic interactions and cation−π interactions were dominant rather than electrostatic interactions.
The polymer backbone of the GRT crusting technology is loaded with chemical functional groups that cater for both hydrophilic and hydrophobic interactions with the surfaces. Predominantly, hydrophobic interactions create an impervious crust which prevents erosion by water or infiltration of water that can break the crust.
In preparation for applying LS as a dust suppressant, roads should first be re-crowned with a grader. Pre-wetting the road is recommended for best results. Lignin can also be applied without pre-wetting if water is not accessible, although results will vary depending on moisture content of the road base.
GRT’s film forming technologies offer a solution which does not require any pre-wetting of the road to achieve best results. This reduces water expenditure in preparation for dust suppression and also for the dust suppression itself.
No human health problem has been attributed to exposure to LS. Evaporating water and volatiles from dilute calcium and sodium LS substantially reduces toxicity to the point where fish can tolerate. In some instances, biomass of herbaceous plants was significantly decreased only at the two highest application rates. The effect of lignosulfonate on groundwater is related to concentration. It is considered nontoxic, non-hazardous, noncorrosive, and generally environmentally benign polymeric compound.
GRT liquid polymer and refined fluid technologies are environmentally benign. Our water-saving technologies do not rely on water evaporation to reduce toxicity, they are formulated with environmental inertness in mind which eliminates the unsurety of post product residency in the environment.
Lignosulfonate is considered biodegradable; therefore, its presence in the environment could be considered harmless. The application of LS as a soil additive has negligible impact on the environment and it is safer to use for stabilization and dust control than any competing class of chemicals.
The extent to which biodegradability progresses is product chemistry dependent. The presence of acid type of chemicals in LS can proliferate longer residency times in the soil due to the inability of microorganisms to further break down the spent 3D backbone that is lignin. GRT offers solutions that biodegrade with ease and provide targeted lifespans based on the application need.
The presence of electrolytes can induce LS precipitation, during which flocculates are formed, which have dimensions much larger than LS aggregates. An increase in pH was reported to lead to size expansion by structural unfolding of both dissolved and aggregated LS because of ionization of weakly hydrophilic groups. The carboxylic groups were stated to
ionize at about pH 3−4, whereas the phenolic groups may ionize at around pH 9−10.
The spectrum of pH dependency of GRT products varies in comparison to LS. For example, GRT: Wet-Loc is neutral under any pH changes which makes it a formidable chemical technology which can be used in making it perfect for packing and loading yards, container yards and ports, livestock yards, pens, stables, racetracks, horse arenas, underground mining, heavy machinery yards, and access roads.
Penetration resistance of sandy soil increases with higher spray rate and stabilizer concentration, and this improvement is more remarkable at higher LS concentration. When LS is first applied it has a dark brown colour that lets the public and your crew know where it has been applied. The colour will fade as traffic and rain slowly wear down the application. For dust control, only 2.5 tons of solids per mile are sprayed on premoistened dirt roads. This total amount is usually applied in two applications.
Although the application rates differ, a range between 0.2 – 1.6 l/m2 over two applications means more water, more truck loads, more fuel used to deliver LS product. In applications that require frequent application, GRT: Haul-Loc is applied at a dilution factor of 1:7000 which goes a long way in reducing the product used for dust suppression. There is no need to premoisten the surface with GRT: Haul-Loc which also contributes to saving water.
LSs cement soil, improve surface strength, reduce road surface fines, reduce surface erosion caused by rainfall and temperature change, and improve road stability. Mechanical bonding and ion exchanges are the two mechanisms for haul road dust suppression.
The former is the dominant one, which is achieved by forming a crust with certain strength and thickness on the treated surface to improve cohesion force between particles. However, a major disadvantage of LSs usage in this area is their water solubility. In this case, LSs may leach from the surface of the road during heavy rainfalls. This further caused destabilization of the haul roads and makes them slippery. In most cases, use of LS accelerates the falling apart of the wearing course which negatively impacts haul road performance.
As a solution to haul roads, GRT: Haul-Loc liquid polymer technology forms an impenetrable crust which is impervious to the effects of water solubility experienced by LS. On the LV roads and dirt roads topical application of GRT: Wet-Loc develops into film of bound and dispersed soil particles in a continuous phase of a highly refined fluid. The film is very effective in areas where a lot of turning and breaking of the wheel track induce stress on the LV and dirt roads.
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