Niobium pentachloride

Hydrolysis

Description of key information

This study covers the quantitative determination of dissolved niobium 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 niobium at the solubility limit upon mixing NbCl5 with water in a non-buffered system, determined in triplicates at nominal loading rates of 9.1 - 14.0 g/L varied between 1.3 - 2.3 g Nb/L (hypothetically corresponding to 3.74 - 6.79 g NbCl5/L), demonstrating an average recovery of 43.6 ± 4.3 % (relative to loading). The mean recovery values (triplicates each, given together with their standard deviation) of dissolved niobium in buffered solutions was found to be 90.6 ± 0.3 % in citrate buffer (at pH 4), 1.5 ± 1.2 % in phosphate buffer (at pH 7), and 0.02 ± 0.02 % in borate buffer (at pH 9). The mean recovery values of dissolved niobium in water after pH-adjustment to the pH-values 4 and 9 (triplicates each) was found to be < 0.1 % relative to the applied loading. The calculated average recovery of dissolved niobium (triplicates, given together with its standard deviation) in water after pH-adjustment to pH-value 7 was found to be 1.2 ± 1.2 % relative to the applied loading.

Additional information

A validated method, developed in the context of this study, was used for the quantitative determination of dissolved niobium 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 niobium at the solubility limit upon mixing NbCl5 with water in a non-buffered system, determined in triplicates at nominal loading rates of 9.1 - 14.0 g/L varied between 1.3 - 2.3 g Nb/L (hypothetically corresponding to 3.74 - 6.79 g NbCl5/L), demonstrating an average recovery of 43.6 ± 4.3 % (relative to loading). 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 niobium in buffered solutions was found to be 90.6 ± 0.3 % in citrate buffer (at pH 4), 1.5 ± 1.2 % in phosphate buffer (at pH 7), and 0.02 ± 0.02 % in borate buffer (at pH 9). The Nb concentrations in water after pH-adjustment to equivalent pH-values differed considerably from those in buffer. The mean recovery values of dissolved niobium in water after pH-adjustment to the pH-values 4 and 9 (triplicates each) was found to be < 0.1 % relative to the applied loading. The calculated average recovery of dissolved niobium (triplicates, given together with its standard deviation) in water after pH-adjustment to pH-value 7 was found to be 1.2 ± 1.2 % relative to the applied loading.