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Environmental fate & pathways

Hydrolysis

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Description of key information

A validated method, developed in the context of this study, was used for the quantitative determination of dissolved tantalum as hydrolysis/transformation product of the test item by ICP-MS in non-buffered water, buffered solutions (pH 4, 7, and 9) and aqueous solutions after pH adjustment (pH 4, 7, and 9). The test item showed a rapid hydrolysis in contact with water and a strong temperature rise during the addition of water was observed due to the exothermic reaction. The resulting turbid solution was strongly acidic (pH-value < 1) and contained an insoluble residue. The concentration of dissolved tantalum at the solubility limit upon mixing TaCl5 with water in a non-buffered system, determined in triplicates at nominal loading rates of 8.9- 13.5 g/L varied between 2.0-3.5 g Ta/L (hypothetically corresponding to 3.92- 6.91 g TaCl5/L), demonstrating an average recovery of 49.3 ± 4.6% (relative to loading). The mean recovery values (triplicates each, given together with their standard deviation) of dissolved tantalum in buffered solutions was found to be 38.1 ± 8.1 % in citrate buffer (at pH 4), 12.8 ± 2.3% in phosphate buffer (at pH 7), and 0.02 ± 0.02% in borate buffer (at pH 9). The Ta-concentrations in water after pH-adjustment to equivalent pH-values differed considerably from those in buffer. The mean recovery values of dissolved tantalum in water after pH-adjustment to the pH-values 4 and 7 (triplicates each) was found to be < 0.1 % relative to the applied loading. The calculated average recovery of dissolved tantalum (triplicates, given together with its standard deviation) in water after pH-adjustment to pH-value 9 was found to be 0.7 ± 1.0% relative to the applied loading.

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Additional information

A validated method, developed in the context of this study, was used for the quantitative determination of dissolved tantalum as hydrolysis/transformation product of the test item by ICP-MS in non-buffered water, buffered solutions (pH 4, 7, and 9) and aqueous solutions after pH adjustment (pH 4, 7, and 9). The test item showed a rapid hydrolysis in contact with water and a strong temperature rise during the addition of water was observed due to the exothermic reaction. The resulting turbid solution was strongly acidic (pH-value < 1) and contained an insoluble residue.

The concentration of dissolved tantalum at the solubility limit upon mixing TaCl5 with water in a non-buffered system, determined in triplicates at nominal loading rates of 8.9- 13.5 g/L varied between 2.0-3.5 g Ta/L (hypothetically corresponding to 3.92- 6.91 g TaCl5/L), demonstrating an average recovery of 49.3 ± 4.6% (relative to loading). For an additional validation of method precision, six aliquots, obtained from one sample preparation procedure, were used for analysis via ICP-MS and the determined average recovery of tantalum was found to be 53.4 ± 0.8 (standard deviation, SD) % (in % of loading) with a coefficient of variation (CV) of 1.4 %.

Whereas the solutions after addition of water became strongly acidic (pH-value < 1), the buffer capacity was sufficient to maintain the desired pH-value when samples were prepared in buffered solutions. In both procedures, insoluble residues occurred which in some cases showed a slightly turbid filtrate even after membrane filtration of supernatants using filters with pore size 0.45 µm. The mean recovery values (triplicates each, given together with their standard deviation) of dissolved tantalum in buffered solutions was found to be 38.1 ± 8.1 % in citrate buffer (at pH 4), 12.8 ± 2.3% in phosphate buffer (at pH 7), and 0.02 ± 0.02% in borate buffer (at pH 9). The Ta-concentrations in water after pH-adjustment to equivalent pH-values differed considerably from those in buffer. The mean recovery values of dissolved tantalum in water after pH-adjustment to the pH-values 4 and 7 (triplicates each) was found to be < 0.1 % relative to the applied loading. The calculated average recovery of dissolved tantalum (triplicates, given together with its standard deviation) in water after pH-adjustment to pH-value 9 was found to be 0.7 ± 1.0% relative to the applied loading.