Metal adsorbents or complexing agents are materials that have the ability to bind with metals to form metal complexes. The carboxylate and sulfonate groups of lignosulfonates can act as potential complexation aids for metals.This occurs through cation-exchange mechanisms, in which the salt (e.g., sodium salt) of the functional group of lignosulfonates exchanges irreversibly with the metal contaminants in solution (e.g., Co2+ or Hg2+).
The increased sulfonation of the lignosulfonates can allow for better metal complexation because sulfonate groups have a higher affinity for adsorbing metals.
Lignosulfonates were used as corrosion inhibitors or iron in a potable water distribution system.The complexation efficiencies of lignosulfonates at 100 g L−1 dosage were 95 % with iron and copper and 70 % with zinc.
Increasing hydroxyl groups of lignosulfonates through hydroxymethylation allowed for an increased complexation ability of 23.3 % with zinc, 18.9 % with magnesium, and 24.9 % with copper The main contributor to the complexing ability lignosulfonates was derived from hydroxyl groups.
4.5 Dust suppressants
Lignosulfonates have also been used as dust suppressants. Lignosulfonates were sprayed onto dirt roads and became viscous as water evaporated during drying; this trapped dust and prevented air pollution from particulate.Lignosulfonates are better alternatives than other types of dust-prevention chemicals (i.e., calcium chloride) because they are more efficient. Lignosulfonates provide a better road-surface coverage and decreased maintenance requirements through improved surface drainage.
Lignosulfonates are also nontoxic, noncorrosive, and biodegradable; these factors reduce their potential environmental impact compared with synthetic alternatives. However, a major disadvantage of the use of lignosulfonates in this area is their water solubility. In this case, lignosulfonates may leach from the surface of the road during heavy rainfall.