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