Post on 11-Dec-2020
ORIGINAL ARTICLE
An experimental study on dynamic coupling process of alkalinefeldspar dissolution and secondary mineral precipitation
Meirong Li1 • Chenchu Li2 • Juntao Xing2• Xiuting Sun1
• Guanghui Yuan3•
Yingchang Cao3
Received: 5 July 2018 / Revised: 27 December 2018 / Accepted: 24 February 2019 / Published online: 6 March 2019
� Science Press and Institute of Geochemistry, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract In order to clarify the dynamic process of feld-
spar dissolution–precipitation and explore the formation
mechanism of secondary porosity, six batch reactor
experiments were conducted at 200 �C and pH = 7 mea-
sured at room temperature. Temporal evolution of fluid
chemistry was analyzed with an inductively coupled
plasma optical emission spectrometer (ICP-OES). Solid
reaction products were retrieved from six batch experi-
ments terminated after 36, 180, 276, 415, 766 and 1008 h.
Scanning electron microscopy (SEM) revealed dissolution
features and significant secondary mineral adhered on the
feldspar surface. The process of feldspar dissolution–pre-
cipitation proceeded slowly and full equilibrium was not
achieved after 1008 h. Saturation indices suggested that the
albite and K-feldspar dissolution occurred throughout the
experiments. The average dissolution rates for albite and
K-feldspar were 2.28 9 10-10 and 8.51 9 10-11
mol m-2 s-1, respectively. Based on the experimental
data, the reaction process of alkaline feldspar was simu-
lated and the secondary porosity had increased 0.3% after
the experiment.
Keywords Alkaline feldspar � Dissolution rate �Precipitation � Mineral conversion � Secondary porosity
1 Introduction
Alkaline feldspar is regarded as amongst the most abundant
minerals in the crust of the Earth. Therefore, providing a
reasonable explanation for the process of alkaline feldspar
dissolution–precipitation is essential for many fundamental
geological processes. The dissolution and secondary min-
eral precipitation of alkaline feldspar are complicated
processes of mineral chemical weathering and hydrother-
mal metamorphism. All kinds of feldspar in the presence of
acidic media conditions are prone to dissolve and form
secondary pores (Huang et al. 2009; Yuan et al. 2015). In
the oil and gas reservoirs, the formation of secondary pores
can improve the porosity and permeability of sandstone
reservoirs, especially for sandstone reservoirs with low
porosity (Higgs et al. 2007; Liao et al. 2014; Baruch et al.
2015). A great number of geochemists have designed many
experiments under all kinds of different conditions to
measure the dissolution rate of silicate minerals in the past
30 years (Nagy and Lasaga 1992; Burch et al. 1993;
Hellmann 1994; Oelkers et al. 1994; Gautier et al. 1994; Fu
et al. 2009; Peng et al. 2015). However, the rates of mineral
dissolution obtained by most studies were carried out under
dynamic and stable chemical conditions. Under these
experimental conditions, silicate minerals (mainly feldspar)
are dissolved away from equilibrium conditions by
adjusting the chemical composition of the circulating fluid
phase and the rate to avoid secondary mineral precipitation
(Burch et al. 1993; Devidal et al. 1997; Hellmann and
Tisserand 2006; Hellmann et al. 2010). Obviously, these
experimental results provide us with the mineral dissolu-
tion rate under a large number of physical and chemical
conditions for the establishment of foundations to the later
dissolution rate equations (Lasaga 1984; Steefel and
Lasaga 1994; Xu et al. 2005; Hellevang et al. 2013;
& Meirong Li
lmrong888@163.com
1 College of Science, China University of Petroleum,
Qingdao 266580, China
2 College of Chemical Engineering, China University of
Petroleum, Qingdao 266580, China
3 College of Geosciences, China University of Petroleum,
Qingdao 266580, China
123
Acta Geochim (2019) 38(6):872–882
https://doi.org/10.1007/s11631-019-00326-0
Maskell et al. 2015). However, it is not possible to give a
reasonable explanation for the dynamic transformation of
minerals in the process of dissolution–precipitation and the
weathering rates of silicate minerals observed in the labo-
ratory are significantly higher than those in the field. Based
on this, six batch experiments were conducted at 200 �C
and near neutrality. The aim of this study was to clarify the
coupling process of alkaline feldspar dissolution and sec-
ondary mineral precipitation, to calculate the dissolution
rate of alkaline feldspar at conditions far from equilibrium
and neutral environment, then to identify the difference
between laboratory measurements and field measurements.
2 Experiments
2.1 Alkaline feldspar pre-treatment
Alkaline feldspar minerals used in the batch experiment
were obtained from the corporation of WARD’S Science.
The rock samples were crushed by iron mortar. For the
freshly ground material, there were a large number of
submicron particles that adhered to the surface of large
grains. Dissolution of these particles will lead to a sudden
increase in the reaction rate at the beginning (Peng et al.
2013; Zhu et al. 2016). To remove these particles, the
alkaline feldspar sample was ultrasonically rinsed with
ethanol three times for about 20 min per treatment and then
repeatedly rinsed with deionized water, dried in an oven at
105 �C overnight before the reaction. After the pretreat-
ment, 50–60 mesh particles were selected as the object of
dissolution. Major elemental content of alkaline feldspar
was determined by X-ray Fluorescence (Axios PW4400).
Samples and methyl cellulose were mixed in 3:1 ratio, then
tableted and analyzed. The results were in atomic % and
shown in Table 1. Meanwhile, the alkaline feldspar sample
also contained a small fraction of Ca and Fe. The multi-
point N2 gas adsorption isotherm of the alkaline feldspar
was measured to acquire the specific surface area of
0.18 m2/g (± 5%) by ASAP-2020.
2.2 Solutions
Acetic acid was selected as the acid solution because it is
the highest content of organic acids in the stratum. The
concentration, salinity, and pH of the reaction solution
were set as 30, 100 mmol kg-1 (NaCl) and 7 at room
temperature, respectively. The pH of the reaction solution
was adjusted by NaOH solution with 1250 mmol kg-1.
2.3 Experimental setting
Six batch experiments involving alkali feldspars dissolu-
tion in Na-bearing (* 100 NaCl mmol kg-1) solution,
with different run times of 36, 180, 276, 415, 766 and
1008 h, were performed at 200 �C. The pretreated alkaline
feldspar and the prepared solution were loaded into a
Teflon-lined hydrothermal reactor with a solid–liquid ratio
of 1:40.
After the reaction the solid needs to be filtered, cleaned
and dried for a series of pretreatment operations. Then a
variety of analytical techniques including XRD (X’Pert Pro
MPD), XRF (Axios PW4400) and SEM–EDS (JEM-
5410LV) were used to characterize solid reactants and
experimental products. The main ions (Na?, K?, Cl-,
Al3?, SiO2) in the sample were analyzed on an inductively
coupled plasma optical emission spectrometer (Agilent
5100). For each sample, the standard and blank investiga-
tion were repeated five times to determine the average and
standard deviation of the quality of each selected element.
The uncertainty of all elements is calculated to be
within ± 1%. The pH of all samples was measured using a
pH meter (PHS-3C) at room temperature (25 �C).
The calculation of equilibrium constants for aqueous
speciation was calculated using a modified version of
SUPCRT92 (Johnson et al. 1992). Mineral saturation state
and derive ion-activity diagrams were accessed from
PHREEQC (Parkhurst 1995).
Table 1 Major elemental content of alkaline feldspar
Element K Al O Si Na
Content (%) 11.16 9.08 47.15 31.92 0.68
Table 2 The changes of major composition with time in the solution
Reaction time (h) Cl- K? SiO2 Na? Al3? pH
mmol kg-1 25 �C
36 97.8 0.73 0.33 102.3 0.32 6.99
180 98.6 0.92 1.34 101.6 0.27 6.72
276 97.3 0.92 1.5 102.5 0.21 6.65
415 98.5 1.09 1.82 102.6 0.11 6.86
766 99.2 1.31 2.76 101.8 0.014 6.67
1008 98.8 1.42 3.05 99.8 0.0098 6.65
Acta Geochim (2019) 38(6):872–882 873
123
3 Results
3.1 Anions, cations, and dissolved SiO2
The time series changes in the chemical composition of the
reaction solution after the experiment are listed in Table 2
and illustrated in Fig. 1. The relative abundance of the fluid
and mineral composition used in the experiment indicated
that the dissolved Cl- concentrations were relatively
stable. However, the concentration of dissolved Na? ten-
ded to decrease, although the degree of decrease is rela-
tively small compared to the amount of addition
(100 mmol kg-1). During the 1008 h of the experiment,
the dissolved concentrations of K?, Al3?, and SiO2 in the
solution changed significantly with the continuous process
of dissolution–precipitation of alkaline feldspar. The dis-
solved SiO2 increased rapidly to 1.34 mmol kg-1 during
the first 180 h, and then slowly increased to
3.05 mmol kg-1 after the next 586 h of reaction (Fig. 2).
The change of dissolved concentration of K? was consis-
tent with the change of SiO2 concentration. The concen-
trations of Al3? decreased slowly during the first 276 h of
the reaction, and then decreased sharply to
0.14 mmol kg-1 at 766 h, and finally decreased to
0.0098 mmol kg-1.
During the 1008 h experiment, the pH decreased from
6.99 to 6.65 (Table 2). Through the study of the kinetics of
silicate minerals in aqueous solutions by the majority of
geological chemists (Oelkers et al. 1994; Luo et al. 2001;
Wild et al. 2016), the conclusions suggested that pH plays
an extremely important role in the rate of mineral disso-
lution–precipitation processes. The dissolution rate curves
showed a U-shaped (Hellmann 1994) or a V-shaped
(Brantley 2008) relationship with pH from acidic to basic.
3.2 Characteristics of the mineral surface
after dissolution
The surface morphology of the alkaline feldspar was
observed by SEM (JEM-5410LV) operated at 20 kV before
and after the reaction. From Fig. 3a–c, obvious dissolution
features (laminar channels and etch pits) were observed on
the surface of feldspars, demonstrating the intensive dis-
solution of alkaline feldspar. At the same time, a large
number of slices and regular hexagonal secondary precip-
itations were observed on the pits and feldspar platform
(Fig. 3b, c). From the result of EDS exhibited in Fig. 3d,
we found that the regular hexagonal crystals are albite,
which indicated the albitization of K-feldspar by cation
replacement is easy to occur in the conditions of partial
neutral, 200 �C and rich in Na?. The relative positions of
primary and secondary minerals suggested that the albiti-
zation of K-feldspar through dissolution-crystallization
mechanism rather than through transformation of the
crystal structure of primary minerals (Alekseyev et al.
1997). The conversion formula was shown in Eq. (1)
(Schmidt et al. 2017).
KAlSi3O8ðK � feldsparÞ þ Naþ
¼ NaAlSi3O8ðAlbiteÞ þ Kþ ð1Þ
In addition, similar dissolution phenomenon was
observed by Fu et al. (2009) at pH = 3. Zhu et al.
(2004a, 2006) observed massive amorphous layers with
nanometers thick on the surface of feldspar. However, it is
still ambiguous whether the amorphous layer is caused by
leaching or the result of secondary mineral precipitation
(Hellmann et al. 2003, 2004). All above of the experiments
indicated that the dissolution–precipitation of alkaline
feldspar is extremely complex coupling process with
0 200 400 600 800 1000
0.1
1
10
95
100
1.05E2
gK.lom
m(/snoitartnecnoC
-1)
Time/h
Cl-1
Na+
SiO2
K+
Al3+
Fig. 1 The change curve of the concentration of K?, Cl-, Na?, Ca2?,
Al3?, and SiO2 with time for the alkali feldspar dissolution
experiments
Fig. 2 SEM image of alkaline feldspar surface before reaction
(100 lm)
874 Acta Geochim (2019) 38(6):872–882
123
inhomogeneous dissolution and secondary mineral precip-
itation in the natural diagenetic environment.
3.3 Analysis of mineral composition change
after dissolution
The results of X-ray powder diffraction spectrometer
(X’Pert Pro MPD) before and after the reaction were shown
in Fig. 4. The power XRD analysis was equipped with a Cu
anode operated at 40 kV and 40 mA. The scanning angle
(2h) ranged from 5.008� to 74.992�, with scan steps of
0.026�. The main component of alkaline feldspar was
K-feldspar before the reaction. However, alkaline feldspar
minerals contained K-feldspar and minute quantities of
boehmite after the reaction.
The changes in the elements of the alkaline feldspar
before and after the reaction are listed in Table 3. The K/Al
molar ratio was decreased from 1.23 to 1.09, while the Al/
Si molar ratio increased from 0.28 to 0.32. At the same
time, the DAl/DSi value of 0.63 was greater than the sto-
ichiometric ratio of 0.33. These data fully confirmed the
selective dissolution of alkaline minerals and the genera-
tion of secondary mineral boehmite during the dissolution
process.
4 Discussion
4.1 Albite dissolution and precipitation
According to the distribution of aqueous species calcula-
tion at corresponding experimental conditions, saturation
states of mineral were determined during the experiments
(Table 4). The calculated saturation indices (SI, SI = log
Q/K) indicated that the SI of albite is always negative
throughout the experiments.
Therefore, it is predicted that the hydrolysis of albite
occurs during the whole experiment. Meanwhile,
Fig. 3 SEM images of alkaline feldspar surface after 1008 h (a–c) and the EDS map of hexagonal secondary mineral (d)
Acta Geochim (2019) 38(6):872–882 875
123
secondary mineral precipitation like boehmite, kaolinite
and muscovite are possible to form after 36-hour reaction
on account of the negative value of SI. However, the result
of SEM (Fig. 3a, b) and XRD (Fig. 4) demonstrate that
only the boehmite was generated after the reaction, is
consistent with previous observations (Lagache 1976;
Bevan and Savage 1989).
4.1.1 Albite conversion process
Hydrolysis reaction of albite can be illustrated by the fol-
lowing equation (Zhu and Lu 2009):
NaAlSi3O8ðAlbiteÞ þ 4Hþ ¼ 2H2Oþ Al3þ þ Naþ
þ 3SiO2ðaqÞ ð2Þ
With the concentration of Al3? and SiO2 reach to the
state of oversaturation for secondary minerals (boehmite,
kaolinite, paragonite, silicate), those minerals will be
formed theoretically. Generally, boehmite and gibbsite are
formed in the first stage of albite dissolution (Zhu and Lu
2009). From our simulation experiments, we can see the
form of boehmite clearly (Fig. 3a) at the time of 1008 h
after the reaction and the corresponding equation for pre-
cipitation is as follows:
Al3þ þ 2H2O ¼ AlOðOHÞðBoehmiteÞ þ 3Hþ ð3Þ
In the acidic environment, feldspar is able to form
kaolinite when the temperature reaches 200 �C and pH = 3
in the batch system, and the process can be represented by
Eq. (4) (Fu et al. 2009). However, kaolinite was not
identified in our simulation experiment which conducted in
the near-neutral condition. In fact, because of the high
value of log aNa?/aH?, the reaction path will pass the
stable area of paragonite instead of kaolinite by the phase
figure of mineral conversion (Fig. 5). The reaction can be
described by Eq. (5).
2Alþ3 þ 5H2Oþ2SiO2 ¼ Al2Si2O5ðOHÞ4ðKaoliniteÞþ 6Hþ ð4Þ
20 25 30 350
10000
20000
30000
40000
50000
60000
Inte
nsity
2-Theta/degree
before
K-fe
ldsp
ar
20 25 30 350
500000
1000000
1500000
2000000 after
Inte
nsity
2-Theta/degree
Boe
hmite
K-f
elds
par
Fig. 4 X-ray diffraction patterns of alkaline feldspar before and after the reaction. Boehmite and K-feldspar were identified
Table 3 The content of
alkaline feldspar before and
after the reaction
K Na Al O Si K/Al Al/Si
Content (%) Mole ratio
Initial alkaline feldspar 11.16 0.68 9.08 47.15 31.92 1.23 0.28
After the reaction minerals 10.67 0.69 9.74 48.14 30.88 1.09 0.32
Table 4 The changes of
mineral saturation (log Q/K)
with time during alkaline
feldspar dissolution
Sample Time (h) Minerals
K-feldspar Albite Boehmite Kaolinite Muscovite
1 36 - 3.67 - 2.87 2.68 4.35 3.25
2 180 - 1.82 - 1.13 2.60 5.41 4.93
3 276 - 1.79 - 1.09 2.49 5.28 4.74
4 415 - 1.74 - 1.12 2.21 4.90 4.24
5 766 - 2.01 - 1.47 1.32 3.46 2.17
6 1008 - 2.00 - 1.51 1.16 3.24 1.87
876 Acta Geochim (2019) 38(6):872–882
123
3Al3þ þ Naþ þ 3SiO2 þ 6H2O
¼ NaAl3Si3O10ðOHÞ2ðParagoniteÞ þ 10Hþ ð5Þ
Evidently, the dissolution of albite releases SiO2 and
Na? into the solution mainly by consuming H?. In the
batch system, the concentration of dissolved SiO2 and Na?
will increase while H? decreases. Therefore, the changes of
log aNa?/aH? and log aSiO2 (aq) over time provide a
method for assessing the mineral conversion path (Fig. 5)
(Fu et al. 2009).
The test data of dissolution for a large number of alu-
minosilicate minerals usually show an inconsistency with
the stoichiometric amount, mostly due to the formation of
secondary mineral precipitation during the dissolution
process and preferentially released reactive ion (Brantley
2003). The composition of the solution coexisting with the
mineral also results in the dissolution of the mineral non-
stoichiometric amount (Casey et al. 1988). The dissolution
of feldspar and the precipitation of boehmite in a moder-
ately acidic aqueous fluid can be described by Eq. (3)
(Stillings and Brantley 1995).
The composition of the solution began to gradually close
to the paragonite stable region and eventually stabilized in
the paragonite phase area (Fig. 5). The mineral conversion
occurred in the process of forming paragonite can be
expressed by the following reaction:
NaAlSi3O8 þ 2Al3þ þ 4H2O
¼ NaAl3Si3O10ðOHÞ2ðParagoniteÞ þ 6Hþð6Þ
3AlOðOHÞ þ Naþ þ 3SiO2
¼ NaAl3Si3O10ðOHÞ2ðParagoniteÞ þ Hþð7Þ
However, the calculated saturation indices of boehmite
and paragonite in the solution (Table 4) indicate that the
composition of the solution is supersaturated for both.
Obviously, the dissolution of albite is still sufficient to
maintain the supersaturation of boehmite and kaolinite,
despite the continued presence of secondary mineral and
precipitated mineral during the dissolution reaction.
According to the dynamic changes of ionic concentra-
tion in the solution during the dissolution–precipitation
process, the prediction of the reaction process is in accor-
dance well with that of the solid phase prediction. For
example, after the 1008 h experiment, the XRF data shows
that the K/Al molar ratio decreases from 1.23 to 1.09 and
the Al/Si molar ratio increases from 0.28 to 0.32, in
agreement with the observed phenomena.
4.1.2 Albite dissolution rate
Generally, the change of dissolved SiO2 concentration with
time can be used to calculate the rates of mineral disso-
lution–precipitation process during the 42-day experiment,
the corresponding calculation equation is as follow (Fu
et al. 2009):
r ¼wPi
11cDmSiO2ðaqÞt
ð8Þ
where r represents the dissolution rate of SiO2, w is the
mass of solution, DmSiO2ðaqÞ is the change of dissolved SiO2
for each process of dissolution or precipitation, c is the
stoichiometric coefficient of SiO2 in the reaction, l is the
number of reaction stage for the entire simulation
experiment.
In our experiments, alkaline feldspar consisting of both
albite and K-feldspar was selected as the reactant for dis-
solution experiments. But the relative content of albite is
low. Therefore, the amount of SiO2 released by alkaline
feldspar can’t be used to calculate the dissolution rate of
albite.
Since the release of Na? was generated by the dissolu-
tion of albite, the dissolution rate of albite can be calculated
by the change of Na? concentration in the solution. Our
experimental data indicated that the dissolved Na? in the
solution reached the maximum at the time of 415 h, and
then gradually decreased with the formation of the sec-
ondary mineral. Therefore, the dissolution rate of albite is
2.28 9 10-10 mol m-2 s-1 according to the change of
Na? at 415 h after the reaction. The calculated value is
well consistent with those measurements from Hellmann
(1994) for a similar temperature and surface area.
4.2 K-feldspar dissolution and precipitation
4.2.1 K-feldspar mineral conversion process
By Table 4, we found that the calculated saturation indices
(SI) of K-feldspar is always negative. Therefore, K-feld-
spar hydrolysis was predicted to occur throughout the
-4.0 -3.5 -3.0 -2.5 -2.0 -1.5-1
0
1
2
3
4
5
6lo
g aN
a+ /aH+
log aSiO2(aq)
Boehmite
Kaolinite
Paragonite Albite
Pyrophyllite
200
Fig. 5 The system of Na2O-Al2O3-SiO2-H2O-HCl
Acta Geochim (2019) 38(6):872–882 877
123
experiment. In the first 276 h, the release rate of SiO2 was
8.51 9 10-11 mol m-2 s-1 higher than any other reaction
stages obviously in the whole 1008 h due to the rapid
decrease of chemistry diving force with the release of SiO2,
Al3?, K?. Therefore, we defined the time before 276 h as
the first stage. At this stage, K-feldspar will dissolve and
release SiO2, Al3?, and K? into the solution by consuming
H?. When the concentration of Al3? arrives at the state of
oversaturation to the boehmite, the secondary mineral
boehmite will be formed. Therefore, we can consider that
mineral conversion process happened in this stage is from
K-feldspar to boehmite. The corresponding equations can
be illustrated as follows (Giles and De Boer 1990; Zhu and
Lu 2009):
KAlSi3O8ðK � feldsparÞ þ 4Hþ
¼ 2H2Oþ Al3þ þ Kþ þ 3SiO2ðaqÞ ð9Þ
Al3þ þ 2H2O ¼ AlOðOHÞðBoehmiteÞ þ 3Hþ ð10Þ
KAlSi3O8 þ Hþ ¼ AlOðOHÞðBoehmiteÞ þ Kþ þ 3SiO2
ð11Þ
Dissolution of K-feldspar releases SiO2 and K? into the
solution by consuming H? and achieve K-feldspar-boeh-
mite equilibrium, then to the stable region of K-feldspar
and muscovite (Fig. 6) till the end of the reaction. The
formation of muscovite minerals can be expressed as fol-
lows (Fu et al. 2009):
KAlSi3O8 þ 2Al3þ þ 4H2O
¼ KAl3Si3O10ðOHÞ2ðMuscoviteÞ þ 6Hþð12Þ
3AlOðOHÞ þ Kþ þ 3SiO2
¼ KAl3Si3O10ðOHÞ2ðMuscoviteÞ þ Hþð13Þ
At the same time, since the mineral transformation
phase diagram (Fig. 6) does not take into account the ions
outside the equilibrium system, the process of ion dynamic
change in the solution fails to exhibit the transformation
between K-feldspar and albite, especially in the case of a
higher content of Na? in the solution (Wilkinson et al.
2001). In fact, it is apparent to observe that a large amount
of secondary mineral crystals were formed on the surface
from the SEM images (Fig. 3a) after the reaction. The
transformation process between K-feldspar and albite is
extremely complicated, containing breakdown and rebuild
of Al–O and Si–O bonds (O’Neil and Taylor 1967; O’Neil
1977). A strong driving force is provided for the formation
of secondary mineral due to the large amount of Na?.
Meanwhile, it is worth mentioning that we define the 766–
1008 h as the third stage because of a decrease in Na?. The
transformation equation is as follows:
KAlSi3O8ðK�feldsparÞ þ Naþ ¼ NaAlSi3O8ðAlbiteÞ þ Kþ
ð14Þ
Because the amount of preferential release of albite is
relatively low (Table 1), it can be concluded that the
release of SiO2 in the solution is mainly contributed by
K-feldspar under longer reaction time ([ 180 h), and the
K-feldspar dissolution rate is calculated as 8.51 9 10-11
mol m-2 s-1. Meanwhile, the calculated rate was not sig-
nificantly different from that researched by Peng et al.
(2015) when taking the mineral surface area and temper-
ature into consideration. The results of the 1008 h experi-
ment showed that the reaction eventually reaches
K-feldspar-muscovite-solution equilibrium phase (Fig. 6).
4.2.2 K-feldspar dissolution rate
Similar observations have been reported in the field and
experimental studies based on hydrothermal and diagenetic
systems for a long time (Ehrenberg 1991; Ehrenberg 1993).
The experimental results by Huang (1986) depicting con-
version of albite to illite showed that the formation of illite
occurred most effectively under near neutral pH conditions,
while boehmite and kaolinite were formed in an initially
acidic solution. In this experiment, relatively neutral fluid
chemistry initiates the dissolution of potassium feldspar in
the field of boehmite stability, which leads to the early
formation of boehmite, followed by muscovite. Although
the formation of muscovite in the course of the reaction has
always been the possibility of thermodynamics (Table 4),
the amount of muscovite production did not reach the
minimum detection limit. At the same time, the dissolu-
tion–precipitation process of K-feldspar can be divided into
three stages (Fig. 7), and the corresponding dissolution–
precipitation rate can be roughly estimated by the dynamic
change rule of the solution ion concentration, SEM char-
acteristics, and the whole mineral dynamic transformation
process, the results are shown in Table 5.-4.0 -3.5 -3.0 -2.5 -2.0 -1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
log
aK+ /H
+
log aSiO2(aq)
Boehmite
Kaolinite
K-feldspar
Pyrophyllite
Muscovite
Fig. 6 The system of K2O-Al2O3-SiO2-H2O-HCl
878 Acta Geochim (2019) 38(6):872–882
123
As can be seen from Table 5, the dissolution of
K-feldspar is mainly carried out in the initial stage of the
reaction (\ 276 h), and the corresponding dissolution rate
is 8.78 9 10-11 mol s-1. In the second stage of the reac-
tion (276–766 h), the dissolution rate of K-feldspar will
slow down due to the decrease of the thermodynamic
driving force. At this time, the precipitation will gradually
dominate the reaction, the rate is 4.42 9 10-12 mol s-1.
In the final stage (766–1008 h), due to the enrichment of
Na? in the solution, albitization of K-feldspar will occur,
the average rate is 1.83 9 10-11 mol s-1. Therefore, for
feldspar, the dissolution process is a complex process of
mineral conversion, involving feldspar dissolution and
secondary minerals (boehmite, albite) precipitation. The
effect of porosity enhancement caused by dissolution is
extremely weak, only 0.3%, which is much lower than that
from carbonation under the same conditions (Gong et al.
2008).
4.2.3 Comparison with previous data
The experimental result from this study demonstrated that
albite will convert to boehmite under neutral pH conditions
first, then with the reaction proceeding, paragonite will be
formed ultimately, and at the same condition, K-feldspar
will transform into boehmite in the first place, followed by
muscovite. Our experimental data was evidently different
from the result researched by Fu et al. (2009) designed in
an acidic environment. Meanwhile, the dissolution rate
of albite and K-feldspar calculated from the experiment
were 2.28 9 10-10 and 8.51 9 10-11 mol m-2 s-1
respectively.
Figure 8 compared alkaline feldspar dissolution rates
from the literature with those from this study plotted
pH,the dissolution rates were transformed into 200 �C
using Arrhenius’ s formula.
Our rate was one order of magnitude slower than those
from Burch et al. (1993) and two orders of magnitude
slower than Oelkers et al. (1994) and Gautier et al. (1994).
The major reason is probably due to pH. The values were
higher than that obtained from Fu et al. (2009) which is
probably due to the complex effect (Welch et al. 2000) and
salt effect (Ruckheim and England 1990).
Traditionally, the process of feldspar hydrolysis is
considered as partial equilibrium between the solution
composition and secondary minerals (Crundwell 2015). If
the phenomenon of partial equilibrium can’t be viewed, the
real process of reaction may be different (Lasaga 1984).
Our study demonstrated that boehmite and paragonite
sustained metastable during the entire process of experi-
ment, which provided sufficient evidence to support the
model presented by Steefel and Cappellen (1990).
Moreover, the time series solution chemical composi-
tion and saturation indices of all kinds of minerals were
also in agreements with Lasaga’s cases. In fact, mineral
dissolution and precipitation are an extremely complex
process in the condition of natural reservoirs. However, it
is not possible to completely simulate field dissolution of
silicates, the differences include efficiency of solution/
mineral contact, aging of surfaces, formation of leached
Fig. 7 The sketch map of
dissolution process of
K-feldspar in this study
Acta Geochim (2019) 38(6):872–882 879
123
layers and solution chemistry in micro-pores (Ganor et al.
2007).
Although the simulated experiment time was up to
1008 h, the calculated SI (saturation indices) of alkaline
feldspar indicated that our experiment was still far from
equilibrium. Meanwhile, the dissolution rates we measured
were still up to a few orders of magnitude higher than those
measured in the field. Based on this, we thought about two
reasons to explain the gap between laboratory and field
rates: (1) Our dissolution rates were measured in far-from-
equilibrium, so our data were higher than those measured
in close-to-equilibrium in the field. (2) Owing to the slow
process of formation to secondary minerals, dissolution and
precipitation reaction is coupled, which is significant to
interpret the data from the field (Zhu et al. 2004a, b, c).
5 Conclusions
In this paper, we designed alkaline feldspar hydrolysis
experiments in a neutral environment to explore the dis-
solution–precipitation mechanism of alkaline feldspar and
determined the reaction rate. The results were as follows:
(1) Hydrolysis of albite fractions in alkaline feldspar results
in the formation of boehmite and then forms paragonite. In
the early stages of the experiment (\ 415 h), Na? release
was observed. When the mineral surface area, temperature,
and saturation state effects were taken into account, the
dissolution rate of albite was consistent with other studies;
(2) K-feldspar hydrolysis occurred throughout the experi-
ment. Meanwhile, during the 1008 h experiment, K-feld-
spar first achieved equilibrium with boehmite, then reached
the stable phase area of K-feldspar and muscovite until the
end of the reaction, a transformation between K-feldspar
and albite was taken place during the reaction. At the same
time, the dissolution–precipitation process of K-feldspar is
divided into three stages, and the dissolution and precipi-
tation rates were calculated; (3) For feldspar, the dissolu-
tion process is a coupled process of mineral transformation,
different mineral dissolution may occur at different stages
of the reaction, while generating boehmite, muscovite,
paragonite, albite, and other secondary mineral precipita-
tion. Therefore, the precipitation of secondary minerals
may weaken the effect of pore enhancement caused by
dissolution evidently. The value of the effect of pore
enhancement is 0.3% under the experimental condition,
which is much lower than that of carbonate minerals.
Acknowledgements This work was supported by the National Sci-
ence and Technology Major Project ‘‘Bohai Bay Basin deep oil and
gas geology and reserves increasing direction’’ (No. 2016ZX05006-
007) and the National Natural Fund (Youth) ‘‘Relationship between
rich feldspar sandstone reservoirs in feldspar alteration and pyrolysis
of hydrocarbons’’ (41602138).We appreciated the SEM–EDS analysis
by Guanghui Yuan from School of Geoscience at China University of
Petroleum. We thanked the Institute of Oceanology, Chinese Acad-
emy of Sciences for chemical analysis of fluid samples. At the same
time, we also thanked College of Chemical Engineering at China
University of Petroleum for the assistance with analysis of XRD,
BET, and XRF. We appreciate Juntao Xing in revising the manuscript
and data processing. Comments by reviewers were much appreciated
and helped improve this manuscript.
Table 5 The reaction stages of dissolution experiments in alkaline feldspar and corresponding key reactions and mineral dissolution/precipi-
tation rates
Stage Time Key reactions Reaction rates (mol s-1)
h Dissolution Precipitation
1 0–276 KAlSi3O8 þ Hþ ¼ AlOðOHÞ þ Kþ þ 3SiO2 8.78 9 10-11 (Kf) 8.78 9 10-11 (Bm)
2 276–766 KAlSi3O8 þ 2Al3þ þ 4H2O ¼ KAl3Si3O10ðOHÞ2 þ 6Hþ 4.42 9 10-12 (Kf) 4.42 9 10-12 (Mus)
3 766–1008 KAlSi3O8 þ Naþ ¼ NaAlSi3O8 þ Kþ 1.83 9 10-11 (Kf) 1.83 9 10-11 (Ab)
Ab albite, Bm boehmite, Kf K-feldspar, Mus Muscovite
7 8 9
-10.0
-9.5
-9.0
-8.5
-8.0
-7.5
-7.0
-6.5
-6.0
log
rate(
mol
m-2 s
-1)
pH
Burch(1993) Oelkers(1994) Gautier(1994) This study
Fig. 8 Comparison of alkaline feldspar dissolution rates from
literature
880 Acta Geochim (2019) 38(6):872–882
123
References
Alekseyev VA, Medvedeva LS, Prisyagina NI, Meshalkin SS,
Balabin AI (1997) Change in the dissolution rates of alkali
feldspars as a result of secondary mineral precipitation and
approach to equilibrium. Geochim Cosmochim Acta
61(6):1125–1142
Baruch ET, Kennedy MJ, Lohr SC et al (2015) Feldspar dissolution-
enhanced porosity in Paleoproterozoic shale reservoir facies
from the Barney Creek Formation (McArthur Basin, Australia).
Aapg Bull 99(9):1745–1770
Bevan J, Savage D (1989) The effect of organic acids on the
dissolution of K-feldspar under conditio-ns relevant to burial
diagenesis. Mineral Mag 53(372):415–425
Brantley SL (2003) Reaction kinetics of primary rock-forming
minerals under ambient conditions. In: Drever, J.I. (Ed.), Sur-
face and Ground Water, Weathering, and Soils.Hol-
land, H.D., Turekian, K.K. (Eds.), Treatise o-n Geochem-
istry, Vol. 5, Pergamon Press, Oxford, 73–117
Brantley SL (2008) Kinetics of mineral dissolution. Springer, New
york, pp 151–210
Burch TE, Nagy KL, Lasaga AC (1993) Free energy dependence of
albite dissolution kinetics at 80 �C and pH 8.8. Chem Geol
105:137–162
Casey WH, Westrich HR, Arnold GW (1988) Surface chemistry of
labradorite feldspar reacted with aqueous sol-utions at pH, = 2,
3, and, 12. Geochim Cosmochim Acta 52(12):2795–2807
Crundwell FK (2015) The mechanism of dissolution of the feldspars:
part I. dissolution at conditions far from equilibrium. Hydromet-
allurgy 151:151–162
Devidal J, Schott J, Dandurand J (1997) An experimental study of
kaolinite dissolution and precipita-tion kinetics as a function of
chemical affinity and solution composition at 150 �C, 40 bars,
and pH 2, 6.8, and 7.8. Geochim Cosmochim Acta
61(24):5165–5186
Ehrenberg SN (1991) Kaolinized, potassium-leached zones at the
contacts of the Garn Formation, Haltenbanken, mid-Norwegian
continental shelf. Marine Pet Geol 8(3):250–269
Ehrenberg SN (1993) Depth-dependent transformation of kaolinite to
dickite in sandstones of the Norwe-gian continental shelf. Br J
Oral Maxillofacial Surg 28(3):325–352
Fu Q, Peng L, Konishi H et al (2009) Coupled alkaline feldspar
dissolution and secondary mineral pre-cipitation in batch
systems: 1. New experiments at 200 �C and 300 bars. Chem
Geol 258(3–4):125–135
Ganor J, Lu P, Zheng Z, Zhu C (2007) Bridging the gap between
laboratory measurements and field estimations of silicate
weathering using simple calculations. Environ Geol
53(3):599–610
Gautier JM, Oelkers EH, Schott J (1994) Experimental study of
K-feldspar dissolution rates as a fun-ction of chemical affinity at
150�C and pH 9. Geochim Cosmochim Acta 58:4549–4560
Giles MR, De Boer RB (1990) Origin and significance of redistri-
butional secondary porosity. Mar Pet Geol 7(4):378–397
Gong Q, Deng J, Wang Q et al (2008) Calcite dissolution in deionized
water from 50�C to 250�C at 10 MPa: rate equation and reaction
order. Acta Geol Sin 82(5):994–1001
Hellevang H, Pham VTH, Aagaard P (2013) Kinetic modelling of
CO2–water–rock interactions. Int J Greenh Gas Control 15:3–15
Hellmann R (1994) The albite-water system: part I. The kinetics of
dissolution as a function of pH at 100, 200, and 300 �C. Geochim
Cosmochim Acta 58:595–611
Hellmann R, Tisserand D (2006) Dissolution kinetics as a function of
the Gibbs free energy of reaction: an experimental study based
on albite feldspar. Geochim Cosmochim Acta 70(2):364–383
Hellmann R, Penisson J-M, Hervig RL, Thomassin J-H, Abrioux M-F
(2003) An EFTEM/HRTEM high-resolution study of the near
surface of labradorite feldspar altered at acid pH: evidence for
interfacial dissolution–reprecipitation. Phys Chem Miner
30:192–197
Hellmann R, Penisson J-M, Hervig RL, Thomassin J-H, Abrioux M-F
(2004) Chemical alteration-n of feldspar: a comparative study
using SIMS and HRTEM/EFTEM. In: Wanty RB, Seal RR
(Eds), Proceedings of the 11th international symposium on
water–rock interaction, Saratoga Springs, New York
Hellmann R, Daval D, Tisserand D (2010) The dependence of albite
feldspar dissolution kinetics on fluid saturation state at acid and
basic pH: progress towards a universal relation. C R Geosci
342(7–8):676–684
Higgs KE, Zwingmann H, Reyes AG et al (2007) Diagenesis, porosity
evolution, and petroleum emplacement in tight gas reservoirs,
Taranaki Basin, New Zealand. J Sediment Res
77(12):1003–1025
Huang WL (1986) The effect of fluid/rock ratio on feldspar
dissolution and illite formation under reservoir conditions. Clay
Miner 21(4):585–601
Huang S, Huang K, Feng W (2009) Mass exchanges among feldspar,
kaolinite and illite and their influe-nces on secondary porosity
formation in clastic diagenesis: a case study on the Upper
Paleozoic, Ordos Basin and Xujiahe Formation, Western
Sichuan depression. Geochimica 38(5):498–506
Johnson James W, Oelkers Eric H, Helgeson Harold C (1992)
SUPCRT92: a software package for calculating the standard
molal thermodynamic properties of minerals, gases, aqueous
species, and reactions from 1 to 5000 bar and 0 to 1000�C.
Comput Geosci 18(7):899–947
Lagache M (1976) New data on the kinetics of the dissolution of
alkali feldspars at 200 �C in CO2 charged water. Geochim
Cosmochim Acta 40(2):157–161
Lasaga AC (1984) Chemical kinetics of water-rock interactions.
J Geophys Res Solid Earth (1978–2012) 89(B6): 4009–4025
Liao P, Wang Q, Tang J et al (2014) Diagenesis and porosity
evolution of sandstones reservoir from Chang 8 of Yanchang
formation in Huanxian–Huachi region of Ordos Basin. Zhongnan
Daxue Xuebao 45(9):3200–3210
Luo XJ, Dong YW, Xi LR et al (2001) Effects of pH on the solubility
of the feldspar and the development of secondary porosity. Bull
Mineral Pet Geochem 20(2):103–107
Maskell A, Kampman N, Chapman H et al (2015) Kinetics of CO2–
fluid–rock reactions in a basalt aquifer, Soda Springs, Idaho.
Appl Geochem 61:272–283
Nagy KL, Lasaga AC (1992) Dissolution and precipitation kinetics of
gibbsite at 80�C and pH 3: the dependence on solution saturation
state. Geochim Cosmochim Acta 56(8):3093–3111
Oelkers EH, Schott J, Devidal J-L (1994) The effect of aluminum,
pH, and chemical affinity on the rates of aluminosilicate
dissolution reactions. Geochim Cosmochim Acta 58:2011–2024
O’Neil JR (1977) Stable isotopes in mineralogy. Phys Chem Miner
2(1–2):105–123
O’Neil JR, Taylor HP (1967) The oxygen isotope and cation
exchange chemistry of feldspars. Am Mineral 52:1414–1437
Parkhurst DL (1995) User guide to PHREEQC-A computer program
for speciation, reaction path, advective-transport, and inverse
geochemical calculations. Center for Integrated Data Analytics
Wisconsin Science Center
Peng L, Qi F et al (2013) Coupled alkali feldspar dissolution and
secondary mineral precipitation in batch systems: 2. New
experiments with supercritical CO2 and implications for carbon
sequestration. Appl Geochem 30:75–90
Peng L, Konishi H, Oelkers E et al (2015) Coupled alkali feldspar
dissolution and secondary mineral precipitation in batch systems:
Acta Geochim (2019) 38(6):872–882 881
123
5. Results of K-feldspar hydrolysis experiments. Chin J
Geochem 34(1):1–12
Ruckheim J, England WA (1990) Organic geochemistry of petroleum
reservoirs. Org Geochem 16(1–3):415–425
Schmidt RB, Bucher K, Druppel K, Stober I (2017) Experimental
interaction of hydrothermal Na-Cl solution with fracture surfaces
of geothermal reservoir sandstone of the Upper Rhine Graben.
Appl Geochem 81:36–52
Steefel CI, Cappellen PV (1990) A new kinetic approach to modeling
water-rock interaction: the role of nucleation, precursors, and
Ostwald ripening. Geochim Cosmochim Acta 54(10):2657–2677
Steefel CI, Lasaga AC (1994) A coupled model fortransport of
multiple chemical species and kinetic precipitation/dissolution
reactions with application to reactive flow insingle phase
hydrothermal systems. Am J Sci 294(5):529–592
Stillings LL, Brantley SL (1995) Feldspar dissolution at 25�C and pH
3: reaction stoichiometry and the effect of cations. Geochim
Cosmochim Acta 59(8):1483–1496
Welch SA, Ullman WJ, Welch SA et al (2000) The temperature
dependence of bytownite feldspar dissolution in neutral aqueous
solutions of inorganic and organic ligands at low temperature
(5–35 �C). Chem Geol 167(3):337–354
Wild B, Daval D, Guyot F et al (2016) PH-dependent control of
feldspar dissolution rate by altered surf-ace layers. Chem Geol
442:148–159
Wilkinson M, Milliken KL, Haszeldine RS (2001) Systematic
destruction of K-feldspar in deeply buried rift and passive
margin sandstones. J Geol Soc 158(4):675–683
Xu T, Apps JA, Pruess K (2005) Mineral sequestration of carbon
dioxide in a sandstone–shale system. Chem Geol
217(3–4):295–318
Yuan G, Cao Y, Jia Z et al (2015) Selective dissolution of feldspars in
the presence of carbonates: the way to generate secondary pores
in buried sandstones by organic CO2. Mar Pet Geol
60(5):105–119
Zhu C, Lu P., 2009. Alkali feldspar dissolution and secondary mineral
precipitation in batch systems: 3. Saturation states of product
minerals and reaction paths. Geochim Cosmochim Acta,
73(11):3171-3200
Zhu C, Blum AE, Veblen DR (2004a) Feldspar dissolution rates and
clay precipitation in the Navajo aquifer at Black Mesa, Arizona,
USA. In: Wanty RB, Seal RI (Eds), Proceedings of the 11th
international symposium on water–rock interaction. A. A.
Balkema, New York, pp 895–899
Zhu C, Blum AE, Veblen DR (2004b) Feldspar dissolution rates and
clay precipitation in the Navajo aquifer at Black Mesa, Arizona,
USA. In: Eleventh international symposium on water-rock
interaction Wri, pp 895–899
Zhu C, Blum AE, Veblen DR (2004c) A new hypothesis for the slow
feldspar dissolution in groundwater aquifers V M Goldschmidt
Conference. A148
Zhu C, Veblen DR, Blum AE, Chipera SJ (2006) Naturally weathered
feldspar surfaces in the Navajo Sandstone aquifer, Black Mesa,
Arizona: electron microscopic characterization. Geochim Cos-
mochim Acta 70:4600–4616
Zhu C et al (2016) Measuring silicate mineral dissolution rates using
Si isotope doping. Chem Geol 445:146–163
882 Acta Geochim (2019) 38(6):872–882
123