Geoscience Reference
In-Depth Information
line represents the best fit of the data with a slope of
2 dictated by
Reaction
(4.25)
. The solubility is shown in this figure to be reversed by a back titration
(inverse triangles) with a basic titrant causing ZnO to precipitate.
The dissociation quotients of
Reaction (4.25)
were regressed against a variety of
temperature
2
ionic-strength functions using the ORGLS (software developed at
Oak Ridge National Laboratory, USA) general least squares program of Busing and
Levy
[99]
. At infinite dilution, good agreement is obtained with previous experi-
mental and model values (i.e., Khodakovsky and Yelkin
[100]
, Ziemniak
[101]
)
except for the values obtained which deviate from the values at 250 and 250
C.
In this figure, comparison is also made between these solubilities and those
obtained in experiments performed by titration of solution containing chloride (dia-
mond) and sulfate (circle) into the cell. It is clearly shown that the effect of addi-
tion of either chloride or sulfate is to increase the concentration of zinc. At this
temperature, ionic strength, and stability constants of the reactions:
Zn
2
1
1
SO
2
4
!
ZnSO
4
ð
4
:
26
Þ
Z
2
1
1
Cl
2
!
ZnCl
1
ð
4
:
27
Þ
Zn
2
1
1
ZnCl
2
2C1
2
!
ð
4
:
28
Þ
were obtained. The dashed curves in
Figure 4.14
are generated from these stability
constants and are shown to reproduce the experimental points
[98]
. For
Reaction
(4.26)
, there are no published experimental data with which to compare these
results. In order to compare with literature data, the constants for
Reactions (4.27)
and (4.28)
are extrapolated to infinite dilution at 200
C. Good agreement with
Bourcier et al.
[102]
and Ruaya and Seward
[103]
is obtained for the dichloro-zinc
complex stability constant. However, the result for the monochloro-zinc complex
disagrees markedly.
Solubility of Malachite
The growth of malachite single crystals has posed a challenge in the past decade.
Several original methods, which allow nearly all textural varieties found in natural
malachite, have been devised. Malachite solubility in pure water and in electrolytic
aqueous solutions has not been understood precisely. Symes and Kester
[104]
stud-
ied the peculiarities of malachite dissolution in pure and seawater in order to reveal
the conditions necessary for its precipitation. Sulyapnikov and Shtern
[105]
deter-
mined the maximum copper concentration during malachite dissolution in solutions
of NaHCO
3
and KHCO
3
of different concentrations at temperatures up to 200
C
and different amounts of CO
2
. Their data has shown that, under normal conditions,
the copper content in these solutions changes, strongly depending on the time of the
solution mixing with the powder of the basic copper carbonate. Balitsky and
Bublikova
[106]
have investigated malachite solubility in 1,2,3 M solutions of
ammonium hydroxide at temperatures 20, 25, 50, and 75
C(P
5
1 bar).
Figure 4.12
