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Original source: Filella, M., May, P.M., 2020. The aqueous solution thermodynamics of niobium under conditions of environmental and biological interest. Applied Geochemistry 122, 104729.

Best stability constant values for niobium species, 25 °C and I 0 mol L-1:

Reaction log K
Nb(OH)5(am.,s) = Nb(OH)50 –7.510
Nb2O5(s) + 5 H2O = 2 Nb(OH)50 –18.31
Nb(OH)50 + H+ = Nb(OH)4+ + H2O 1.603
Nb(OH)50 + H2O = Nb(OH)6 + H+ –4.951
Nb6O198– + H+ = HNb6O197– 14.95
HNb6O197– + H+ = H2Nb6O196– 13.23
H2Nb6O196– + H+ = H3Nb6O195– 11.73
HNa7Nb6O19 ·5H2O(s) = 7 Na+ + HNb6O19 11.85


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