Lignosulfonate Used in Dust Control ,The overall impact on the environment from applying lignosulfonates to roads is negligible. They are safer to use for stabilization and dust control than any competing class of chemicals.
The manufacture of lignin involves evaporation; the evaporation process drives off any volatile contaminants such as acetic acid. Corrosion and toxicity towards plants can be readily minimised by pH control and lignosulfonates are non-toxic to animals.
Lignosulfonate have been applied to roads, used in animal feeds and converted into human foods
for more than 30 years without problem. This comes as no surprise after learning that the products
Lignosulfonate Used in Dust Control have the following properties:
x No dioxins present. No other organics present at hazardous levels
x Toxic trace minerals are below EP Toxicity limits
x Low order of toxicity towards fish
x Non-toxic orally and non-irritating to the skin or eyes of animals
x No human health problems attributed to exposure
x Very low toxicity towards plants
x Residuals are resistant to decay
When spread on land, there is no risk of contaminating ground water. Published data indicate that at less than 10 kgs per square meter, no problems arise. This is much above the 1 kgm/square meter required for stabilisation and 0.3 kgm used for dust control.
The non-hazardous features and abundant supply of lignosulfonate make it a good material for treating roads (1). It is widely used in Sweden and California – two of the world’s most environment-conscious areas.
PRODUCTION
In the sulfite pulping of wood, lignin – nature’s binder – becomes soluble and is separated from the pulp fibers as spent liquor (SSL). This liquor also contains the naturally occurring wood sugars.
Dilute SSL at 12% solids is treated and concentrated to 50 – 60% solids by evaporating water.
Starting from this base material, a family of chemicals has been developed. They are known as lignins or lignosulfonates.
They are used in the following applications:
Water Treatment Chemicals Oil Well Drilling Mud Additives
Components of Adhesives Textile Dye Dispersants
Animal Feed Pellet Binders Gypsum Dispersants for Wallboard
Concrete Additives
Leather Tanning Agents
Road Binders Dispersants for Brick Clay
Feed Molasses Additives Battery Plate Expanders
Of the 1.32 million tons of lignosulfonate sold worldwide, 150,000 tons are sold for application to roadways – 80,000 tons in North America and 70,000 tons in Europe and Australia.
The product used on roads is the base product that has not been chemically modified and may be the calcium, sodium or ammonium form depending on the pulp mill (36). Complex lignofsulfonates are sophisticated, high technological content chemicals, showing all the chemical complexity of the
naturally occurring lignin from which they were derived.
SUGARS
The types of sugars present in lignosulfonate will change depending on the kind of wood pulped.
Wood from needle-bearing trees yield predominantly the hexoses-mannose, glucose and galactose.
Wood from leaf-bearing trees yield predominantly the pentoses-xylose and arabinose. We do not pulp maples!
ENVIRONMENTAL EFFECTS
(a) Dioxins:
During the evaporation of spent liquor, SO2 and any volatile components are removed.
However, with attention recently focused (38) on the presence of dioxins in paper mill effluents, the U.S. Environmental Protection Agency approved laboratory – Enseco Inc., was contracted to determine the dioxin content of SSL roadbinder. Results from analysing a 7-day composite of Lignosol B, (a calcium lignofsulfonate) (37) show that it contains no detectable amounts of 2, 3, 7, 8 – tetrachloro dibenzofuran or 2,3 7, 8 – tetrachloro dibenzo p-dioxin.
This is not surprising as chlorinated organic contaminants require the presence of substantial chlorine concentrations.
This can come from:
x Using chlorinated biocides after bleaching
x Bleaching fibers with chlorine, hypochlorite or chlorine dioxide
But the Quebec mill (REED) does not bleach. Mills that do bleach only do so after the lignosulfonate has been separated and removed from the system.