Reaction mass of cobalt olivine and crystalline silicon dioxide

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2012-07-19 to 2012-08-23

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Series on Testing and Assessment No. 29 (23-Jul-2001): Guidance document on transformation/dissolution of metals and metal compounds in aqueous media

Version / remarks:

2001

Deviations:

yes

Remarks:

The 28-day test with a loading of 1 mg/L was conducted at pH 6 instead of 5.5

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2011-02-07

Type of method:

flask method

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

60.3 µg/L

Element analysed:

Cobalt

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 6

Remarks on result:

other: S.D.: ± 1.52 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

101 µg/L

Element analysed:

Cobalt

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 6

Remarks on result:

other: S.D.: ± 3.81 µg/L

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

138 µg/L

Element analysed:

Cobalt

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 6

Remarks on result:

other: S.D.: ± 6.36 µg/L

Details on results:

Temperature
The mean temperature recorded by the data logger from day 4 until day 28 is 21.0 ± 1.1 °C. The mean temperature recorded by the pH-meter during the complete study is 22.2 ± 0.2 °C. Therefore, the mean temperature is in agreement with the OECD guidance document 29.

pH
According to the guidance, the solution pH can be expected to remain constant (± 0.2 units) during most tests. The solution pH remained relatively constant during the 28 days in vessels containing the test item and in method blanks, pH ranged from of 5.7– 6.2.

Oxygen
Oxygen levels in all test vessels and 1 mg /L loadings were in the range recommended by the OECD Test Guidance 29 during the test: above 70 % of oxygen saturation at 8.5 mg/L (70 % of 8.5 mg/L = 6 mg/L).

Mass balance
After 12h of digestion with aqua regia, insoluble residues were not observed in any test vessel, indicating a complete dissolution of the test item. The recovery of cobalt was in the range of 93.1 – 98.0 %.

Method validation summary (ICP-MS)

validation parameter	results	comment
selectivity	similar data with at least two different isotopes for ICP-MS method	no interferences observed, measurements with best recoveries of reference material were used for calculation
Linearity	applied calibration functions were linear	correlation factor at least 0.9994
limit of detection	0.001 – 0.014 μg/L
limit of quantification	0.004 – 0.042 μg/L
method blanks (total: 48 samples)	12 samples < LOD 2 samples > LOD and < LOQ 34 samples > LOQ	method blanks with Co levels >LOQ are below Co concentrations in test sample (at least by a factor of 332 lower)
accuracy	mean recovery for CRM TMDA- 70 (285 μg Co/L, dilution factor 5): 108 ± 1.8 % (n = 2)	mid concentration range of samples (diluted 57 μg Co/L)
accuracy	mean recovery for CRM TMDA- 70 (285 μg Co/L, dilution factor 2): 115 ± 5.2 % (n = 2)	high concentration range of samples (diluted 145 μg Co/L)
accuracy	mean recovery for CRM TM-DWS.2 (64.4 μg Co/L, dilution factor 20): 103 ± 1.8 % (n = 8)	low concentration range of samples (diluted 3.22 μg Co/L)
accuracy	mean recovery for CRM TM-DWS.2 (64.4 μg Co/L, dilution factor 5): 100 ± 0.3 % (n = 6)	mid concentration range of samples (diluted 12.9 μg Co/L)
accuracy	mean recovery for CRM TM-DWS.2 (64.4 μg Co/L, dilution factor 2): 108 ± 0.3 % (n = 2)	mid concentration range of samples (diluted 32.2 μg Co/L)
accuracy	mean recovery for CRM TM15.2 (15.1 μg Co/L, dilution factor 5): 105 ± 3.0 % (n = 14)	low concentration range of samples (diluted 3.02 μg Co/L)
trueness	mean recovery for CPI recalibration standard (100 μg/L): 102 ± 3.7 % (n = 12)	high concentration range
trueness	mean recovery for Merck IV recalibration standard (50 μg/L): 100 ± 2.1 % (n = 2)	mid concentration range
trueness	mean recovery for Merck IV recalibration standard (100 μg/L): 107 ± 0.4 % (n = 2)	high concentration range
trueness	Recovery fortification samples: 103 – 115 %
reproducibility	mean recovery for CRM TMDA- 70 (285 μg Co/L, dilution factor 5): 108 ± 1.8 % (n = 2)	mid concentration range of samples (diluted 57 μg Co/L)
reproducibility	mean recovery for CRM TMDA- 70 (285 μg Co/L, dilution factor 2): 115 ± 5.2 % (n = 2)	high concentration range of samples (diluted 145 μg Co/L)
reproducibility	mean recovery for CRM TM-DWS.2 (64.4 μg Co/L, dilution factor 20): 103 ± 1.8 % (n = 8)	low concentration range of samples (diluted 3.22 μg Co/L)
reproducibility	mean recovery for CRM TM-DWS.2 (64.4 μg Co/L, dilution factor 5): 100 ± 0.3 % (n = 6)	mid concentration range of samples (diluted 12.9 μg Co/L)
reproducibility	mean recovery for CRM TM-DWS.2 (64.4 μg Co/L, dilution factor 2): 108 ± 0.3 % (n = 2)	mid concentration range of samples (diluted 32.2 μg Co/L)
reproducibility	mean recovery for CRM TM15.2 (15.1 μg Co/L, dilution factor 5): 105 ± 3.0 % (n = 14)	low concentration range of samples (diluted 3.02 μg Co/L)

Measured dissolved Co concentrations (loading of 1 mg/L at pH 6)

sample	LOD [μg/L]	LOQ [μg/L]	mean Co conc. all vessels ± SD [μg/L]
1, 2, 3 - 2h	0.014	0.042	9.71 ± 1.05
1, 2, 3 - 6h	0.014	0.042	25.5 ± 2.90
1, 2, 3 - 24h	0.005	0.015	60.3 ± 1.52
1, 2, 3 - 96h	0.005	0.015	87.2 ± 7.39
1, 2, 3 - 168h	0.005	0.015	101 ± 3.81
1, 2, 3 - 336h	0.005	0.015	117 ± 3.50
1, 2, 3 - 504h	0.001	0.004	131 ± 8.38
1, 2, 3 - 672h	0.001	0.004	138 ± 6.36

Test summary

Under the described conditions of this test with IPC-2013-006-01 (Olivine, cobalt silicate blue), the following dissolved concentrations were measured at the respective loading, exposure and solution pH:

1 mg/L loading at pH 6 after 7 days: Cobalt: 101 ± 3.81 µg/L

1 mg/L loading at pH 6 after 28 days: Cobalt: 138 ± 6.36 µg/L

 

The OECD Series 29 requires a limit of 20 % and 10 % for the between-vessel and within vessel variation, respectively.

The observed variations within the test flasks were in compliance with the guidance except for the within-vessel variations of vessel 1 and 2 (11.5 % and 12.3 %) after 2 h and vessel 2 (12.7 %) after 96 h. The observed variations between the test flasks over the experimental period were in the range of 2.5 – 11.4 %.

Conclusions:

Under the described conditions of the transformation/dissolution test according to OECD series 28 with IPC-2013-006-01 (Olivine, cobalt silicate blue), the following dissolved cobalt concentrations were measured at the respective loading, solution pH and exposure:
- 1 mg/L loading at pH 6 after 7 days: 101 ± 3.81 µg/L cobalt
- 1 mg/L loading at pH 6 after 28 days: 138 ± 6.36 µg/L cobalt

Description of key information

The solubility of Reaction mass of cobalt olivine and crystalline silicon dioxide is ~10 wt% at a 1mg/L loading.

Transformation/dissolution at a loading of 1 mg/L at pH 6, the pH that maximises dissolution, after 7 and 28 days resulted in dissolved cobalt concentrations of 101 µg Co/L and 138 µg Co/L, respectively. (Knopf, 2014).

The particle size of the tested sample (BET surface area 16 m2/g) is representative for the particle size on the market. Thus, the extent to which "Reaction mass of cobalt olivine and crystalline silicon dioxide" can produce soluble available ionic and other metal-bearing species in aqueous media is limited.