J Solution Chem (2011) 40: 680–702
DOI 10.1007/s10953-011-9670-x
Solubility Measurements of Crystalline NiO in Aqueous
Solution as a Function of Temperature and pH
Donald A. Palmer · Pascale Bénézeth · Caibin Xiao ·
David J. Wesolowski · Lawrence M. Anovitz
Received: 24 March 2010 / Accepted: 17 September 2010 / Published online: 17 March 2011
© Springer Science+Business Media, LLC 2011
Abstract Results of solubility experiments involving crystalline nickel oxide (bunsenite)
in aqueous solutions are reported as functions of temperature (0 to 350 °C) and pH at
pressures slightly exceeding (with one exception) saturation vapor pressure. These exper-
iments were carried out in either flow-through reactors or a hydrogen-electrode concentra-
tion cell for mildly acidic to near neutral pH solutions. The results were treated success-
fully with a thermodynamic model incorporating only the unhydrolyzed aqueous nickel
species (viz., Ni
2+
) and the neutrally charged hydrolyzed species (viz., Ni(OH)
0
2
). The
thermodynamic quantities obtained at 25 °C and infinite dilution are, with 2σ uncertain-
ties: log
10
K
o
s0
= (12.40 ± 0.29), Δ
r
G
o
m
=−(70.8 ± 1.7) kJ·mol
−1
; Δ
r
H
o
m
=−(105.6 ±
1.3) kJ·mol
−1
; Δ
r
S
o
m
=−(116.6 ± 3.2) J·K
−1
·mol
−1
; Δ
r
C
o
p,m
= (0 ± 13) J·K
−1
·mol
−1
; and
log
10
K
o
s2
=−(8.76 ± 0.15); Δ
r
G
o
m
= (50.0 ± 1.7) kJ·mol
−1
; Δ
r
H
o
m
= (17.7 ± 1.7) kJ·mol
−1
;
Δ
r
S
o
m
=−(108 ± 7) J·K
−1
·mol
−1
; Δ
r
C
o
p,m
=−(108 ± 3) J·K
−1
·mol
−1
. These results are
internally consistent, but the latter set differs from those gleaned from previous studies
recorded in the literature. The corresponding thermodynamic quantities for the formation
of Ni
2+
and Ni(OH)
0
2
are also estimated. Moreover, the Ni(OH)
−
3
anion was never observed,
even in relatively strong basic solutions (m
OH
− = 0.1 mol·kg
−1
), contrary to the conclusions
drawn from all but one previous study.
Keywords Nickel oxide · Bunsenite · Ni(II) · Solubility · Thermodynamics · Hydrolysis ·
Aqueous solutions · Temperature · pH
D.A. Palmer ( ) · D.J. Wesolowski · L.M. Anovitz
Chemical Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge,
TN 37831-6110, USA
e-mail: Solution_Chemistry@comcast.net
P. Bénézeth
Geosciences Environnemental Toulouse (GET), UMR-5563 CNRS/IRD/Université de Toulouse,
14 Avenue Edouard Belin, 31400 Toulouse, France
C. Xiao
Barclay Water Management, Inc., 150 Coolidge Ave., Watertown, MA 02472-2815, USA