Germanium hydroxide oxides, amorphous silica and sodium chloride, recovery products from germanium refining

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:

10-21/12/2017

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:

To assess the solubility of the test item water, the pH of 6 was selected because the metals of concern are rather soluble at lower pH than at higher pH. Moreover, the substance has been filtered between pH 8-10 (which assumes lowest overall solubility in that range).

GLP compliance:

yes

Type of method:

flask method

Specific details on test material used for the study:

The test item, RESM1, as received was a pasty granulated material and did not fulfil the <1 mm size condition. To make the test item suitable for the study, it was dried for 14 hours at 100 °C until constant weight as proposed by the Manufacturer. This drying process would not affect the inherent properties of the test material. During the drying process coagulated porous structures were formed. These coagulates were crushed between two 1 cm thick polycarbonate sheets to get a more or less fine powder that could easily pass the 1 mm sieve.

Key result

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

ca. 12.9 mg/L

Element analysed:

germanium

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

at nominal pH 6

Remarks on result:

other: standard deviation: 0.5 mg/L

Key result

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

ca. 9.38 mg/L

Element analysed:

silicon

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

at nominal pH 6

Remarks on result:

other: standard deviation: 1.33 mg/L

Details on results:

Based on the element contents in the test item and the average dissolved element concentrations in the test solutions:
• a release of 38 % of germanium content (i.e. 34.1 % Ge),
• a release of 72 % of silicon content (i.e. 13.0 % Si),
could be calculated at the 24 hours endpoint in test medium at pH 6.

Conclusions:

During this study on RESM1 at a loading of 100 mg/L, it was shown that:
• For germanium, an average concentration of 12.9 mg/L Ge (CVoverall = 4 %; N = 9) was measured at pH 6 (i.e. 38 % germanium release),
• For silicon, an average concentration of 9.38 mg/L Si (CVoverall = 14 %; N = 9) was measured at pH 6 (i.e. 72 % silicon release),
after 24 hours of exposure to the test medium at pH 6.
The pH rose after administration of the test item up to pH 6.72 but was back to normal (pH 6 ± 0.2) at the end of the 24 hours experiment.

Executive summary:

The objective of this study was to obtain information about the dissolution characteristics of RESM1. The pH-dependent extent of dissolution of RESM1 was tested in standard aqueous solutions at pH 6 (0.5 % CO2-buffering) for 24 hours at an agitation speed of 100 revolutions per minute (rpm). The extent of the transformation/dissolution was measured as the dissolved germanium and silicon concentrations obtained after 24 hours. This study has been performed according to OECD Test Guidance No.29, as laid down in the Study Plan and performed according to the SOPs as established by ECTX.

The test medium at the start of the test and the blank control vessels during the test showed concentrations below the limits of detection of 0.04 μg/L Ge and 0.03 mg/L Si. The limits of detection were determined as the rounded up values of three times the standard deviation of each element of all blank measurements in this study at pH 6. For the test at nominal pH 6 at a loading of 100 mg/L RESM1, average dissolved concentrations of:

- 12.9 ± 0.5 mg/L germanium (CVoverall= 4 %; N = 9),

- 9.38 ± 1.33 mg/L silicon (CVoverall= 14 %; N = 9),

were found at the 24 hours endpoint.

Based on the element contents in the test item and the average dissolved element concentrations in the test solutions:

- a release of 38 % of germanium content (i.e. 34.1 % Ge)

- a release of 72 % of silicon content (i.e. 13.0 % Si)

could be calculated at the 24 hours endpoint in test medium at pH 6.

Description of key information

During this study on RESM1 at a loading of 100 mg/L, it was shown that:

• For germanium, an average concentration of 12.9 mg/L Ge (CVoverall = 4 %; N = 9) was measured at pH 6 (i.e. 38 % germanium release),

• For silicon, an average concentration of 9.38 mg/L Si (CVoverall = 14 %; N = 9) was measured at pH 6 (i.e. 72 % silicon release),

after 24 hours of exposure to the test medium at pH 6.