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TERRESTRIAL FATE:

 

Xanthates are dithiocarbonates which are used in the flotation processes for most sulfide minerals, the metallic elements such as copper, nickel, lead, zinc, silver and gold, and a number of oxidized minerals oflead and copper. Flotation is a physiochemical method of concentratingfinely ground ores. The process involves chemical treatment of an ore pulp to create conditions favorable for the attachment of certain mineral particles to air bubbles. The air bubbles carry the selected minerals tothe surface of the pulp and form a stabilized froth which is skimmed off while the other minerals remain submerged in the pulp. Xanthates fit in to this process by functioning as "collectors. " Collectors aid in the attachment of a mineral particle to an air bubble.Sodiumethyl xanthate is one of the most commonly used xanthates.

 

Reaction mass of SEX is hydrolytically unstable when exposed to acidic conditions, reverting rapidly to alcohol, carbon disulphide and caustic soda, and therefore will not persist in the acidic environment of tailings dams. If discharged to waterways, the chemical would be likely to persist for at least some days, hydrolysing only slowly in this more neutral environment. However, it is not expected to bioaccumulate in view of its ionic character. Reaction mass of SEX is not expected to contaminate the environment where ore tailings are confined to well constructed tailings dams. Most will be retained on sulphide minerals and destroyed when they are dried after flotation. Minor residues that remain associated with tailings will be destroyed by hydrolysis intailings dams.

 

Based on estimated Koc value of 4 L/kg, indicates that Reaction mass of SEX is expected to have very high mobility in soil.

 

Volatilization of Reaction mass of SEX from moist soil surfaces is not expected to be an important fate process given a estimated Henry's Law constant of 7.494E-016 atm-m3/mole (7.593E-011 Pa-m3/mole). The estimated Henrys Law Constant (25 deg C) measured by calculation from EPI SuiteTM v4.1, HENRYWIN v3.20 Program was (7.593E-011 Pa-m3/mole) , which is almost zero.

 

Xanthates have not been subjected to regulatory action in any country except. No further investigations were conducted as several xanthates were nolonger used inworld. Use of those that remained was not widespread, being confined to a few users in the mining industry.

Assuming a treatment rate of 500 gms Reaction mass of SEX per tonne of feed, 1% loss to tailings and 30% solids content in the tailings slurry, the concentration of Reaction mass of SEX in the slurry will be in the order of 5 gms in 3.3 tonnes, or about 1.5 ppm. Concentrations of Reaction mass of SEX likely to be found in the tailings slurry may be moderately toxic to aquatic fauna. Such waste streams should therefore not be discharged to waterways.

When suitable precautions are taken to avoid entry of tailings to waterways, the environmental risk of sodium ethyl xanthate can be described as minimal in view of the low environmental exposure and limited persistence.