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Environmental fate & pathways

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The most important fate process of the substance is hydrolysis. Based on the knowledge of the degradation reactions of xanthates and the half-lives at the relevant environmental conditions, the hydrolysis cannot be considered to be rapid. In biodegradation screening tests xanthates have been found to be readily/inherently biodegradable. However, in the relevant environmental conditions of tailings ponds biodegradation is not expected to be a relevant degradation process.

 

The weight-of-evidence data consistently show PIAX to be hydrolytically degradable. During dissolution, potassium isoamyl xanthate dissociates to potassium cation and xanthate anion, which hydrolyses to xanthic acid, and further to (1) 3-methylbutan-1 -ol and pentan-1 -ol and (2) carbon disulphide. Under neutral to slightly alkaline solution, carbon disulphide is neutralised to further reaction products (3): carbonate and thiocarbonate anions. In strongly alkaline media, all carbon disulphide can be neutralised to carbonate and sulphide anions.

In addition to pH, temperature, concentration of potassium isoamyl xanthate and availability of other reactive substances in solution are important factors affecting the reactions and their rates.At pH 5.5, hydrolysis is rather rapid (half-life = 7 - 14 d at 15 - 25 degr. C). Under neutral to slightly alkaline conditions it is considerably slower (pH 7 -7.5, half-life = 45 - 67 d at 15 - 17 degr. C), and additionally a neutralisation mechanism takes place. In very alkaline solution, all carbon disulphide can be consumed in these secondary reactions (pH 8 - 11, half-life = 22 - 28 d at 25 degr. C). The most realistic half-life for potassium isoamyl xanthate in tailings pounds is 47 d at pH 7.5 at 17 ˚C. When the temperature decreases from 17 to 0 ˚C or less, hydrolysis half-lives increase from 47 to 274 days and more, respectively.

The major hydrolysis product carbon disulphide will volatilise to air, where it degrades within a week or two. Evolution of another potential degradation product, hydrogen sulphide gas, is not expected at the operational pH range of the tailings pond (6 – 9.5).