Proxan-sodium

Mode of degradation in actual use

Administrative data

Endpoint:

mode of degradation in actual use

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

This report reviews available degradation data on xanthates focusing on the seasonal variation in Swedish tailing ponds in subarctic climate. The results summarise available scientific infromation applying it to realistic conditions in tailing ponds and are therefore rated as scientifically acceptable.

Data source

Reference

Reference Type:

publication

Title:

Water Quality Simulations for Tailings Ponds in Cold Regions

Author:

Faellmann et al

Year:

1988

Bibliographic source:

Licentitate thesis 1988: O3L, Report Series A No. 167

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

The degradation of xanthates were simulated using realistic conditions (monthly water temperatures and inflow rates) in tailing ponds in central Sweden. The impact of alternative technologies to xanthate concentrations in the tailings pond water and discharge was estimated by a numerical model. For xanthates, both a (conservative) constant degradation half-life of 47 days (B), and a calculated temperature-dependant half-life (C) was used. They were compared to a conservative non-degradable substance (A) with t1/2 of 100000 days. Re-generation from dixanthogen was excluded from the modelling. The simulations were not verified with measurements (as it was not known how much dixanthogen was formed and at which rate at it was degraded).

GLP compliance:

no

Type of study / information:

A review of available publications on (hydrolytical) degradation of xanthates. The impact of pH and temperature on degradation half-lives in pure solutions have been recalculated based on literature data, and compared to modelled data in tailings water. Abiotic and/or biotic reaction processes in tailings pond are additionally simulated based on the key parameters obtained from literature.

Test material

Test material information

Constituent 1

Reference substance name:

Proxan-sodium

EC Number:

205-443-5

EC Name:

Proxan-sodium

Cas Number:

140-93-2

Molecular formula:

C4H8OS2.Na

IUPAC Name:

sodium O-isopropyl dithiocarbonate

Test material form:

solid: compact

Details on test material:

- Name of test material (as cited in study report):sodium isopropyl xanthate
Examples of alkyl xanthates used: sodium isopropyl xanthate, (potassium) isobutyl xanthate, (potassium) amyl xanthate. A single rate is proposed for all xanthates.

Results and discussion

Any other information on results incl. tables

In summary, the modelled concentrations of xanthates in the tailings pond 0.14 - 0.22 mg/L for a conventional treatment method at dose of 1 g xanthate/ton ore (see Table below).

A very coarse calculation for the concentration in discharge water would end up in concentrations < 1 µg/L.

With three different treatment tehcniques, the concntrations of xanthates in the tailings pond can either increase or decrease ranging 0.05 - 0.23 mg/L. More importantly, these techniques decreased the amount of xanthates discharged 0 - 50 %.

 

The author referred to measured levels of Walterson (1984) in Swedish tailing ponds. Levels of 0.02 - 42 mg/L xanthates in tailing ponds and 0 - 16800 µg/L in discharge water (calculated as –OCS₂equivalent xanthate weight without the carbon chain). This kind of modelling provides a good tool to study the impact of key parameters like temperature, annual precipitation of rain and snow and their seasonal variations. The possibility of a separate biological tratment was pointed our as one possibility to further reduce the xanthate discharges to the surface water.

 

Table. Summary of xanthate concentrations measured and simulated at the Swedish tailing ponds.

	Measured (Walterson 1984) *	Simulated conventional (35 % recycled water)	Simulated reduced drainage	Simulated thickened disposal	Simulated thickened disposal with reduced drainage
Dose	11 - 162	1 g/tonne ore	1 g/tonne ore	1 g/tonne ore	1 g/tonne ore
Concentr. in pond (mg/L)	0.02 – 42	0.14 – 0.22	0.15 – 0.23	0.05 - 0.14	0.06 – 0.18
Concentr. in discha rge water (µg/L)	0 - 16800	calc. (0.07 – 0.36)	10 – 20 % of conventional	23 – 30 % of conventional	0 – 50 % of convention al

*as –OCS₂equivalent xanthate weight without the carbon chain

Applicant's summary and conclusion

Conclusions:

Measured levels of xanthates in Swedish tailing ponds have ranged 0.02 - 42 mg/L in tailing ponds and 0 - 16800 µg/L in discharge water (calculated as –OCS2 equivalent xanthate weight without the carbon chain).

The modelled concentrations of xanthates in the tailings pond were 0.14 - 0.22 mg/L for a conventional treatment method at dose of 1 g xanthate/ton ore. A rough calculation of xanthate concentrations was < 1 µg/L.. Three different treatment tehcniques either increased or decreased xanthate concentrations in the tailings water (0.05 - 0.23 mg/L). More importantly, these techniques decreased the amount of xanthates discharged to surface water 0 - 50 %. The simulation confirms that annual temperature and seasonal variations in the rain or snow deposition are extremely important parameters when considering the use of treatment technologies for reducing xanthate levels from tailings water.

Executive summary:

This report reviews available degradation data on xanthates focusing on the seasonal variation in Swedish tailing ponds in subarctic climate. Temperature, pH and the concentration of the xanthate are among the key factors determining the degradation of xanthates in tailing ponds.

Measured levels of xanthates in Swedish tailing ponds have ranged 0.02 - 42 mg/L in tailing ponds and 0 - 16800 µg/L in discharge water (calculated as –OCS2equivalent xanthate weight without the carbon chain).

The modelled concentrations of xanthates in the tailings pond were 0.14 - 0.22 mg/L for a conventional treatment method at dose of 1 g xanthate/ton ore. A rough calculation of xanthate concentrations was < 1 µg/L. Three different treatment tehcniques either increased or decreased xanthate concentrations in the tailings water (0.05 - 0.23 mg/L). More importantly, these techniques decreased the amount of xanthates discharged to surface water 0 - 50 %. The simulation confirms that annual temperature and seasonal variations in the rain or snow deposition are extremely important parameters when considering the use of treatment technologies for reducing xanthate levels from tailings water.

The results summarise available scientific infromation applying it to realistic conditions in tailing ponds in subarctic climate and are therefore rated as scientifically acceptable.