Science of the Total Environment · Kinetics and mechanisms of the interaction between the calcite (10.4) ... Mineral dissolution, commonly presenting in weathering crust, plays signiﬁcant

Science of the Total Environment 668 (2019) 602–616

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Science of the Total Environment

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Kinetics and mechanisms of the interaction between the calcite (10.4)surface and Cu2+-bearing solutions

Hongmei Tang a,b,c, Haiyang Xian a,c,⁎, Hongping He a,b,c, Jingming Wei a,b,c, Hongmei Liu a,b,c,Jianxi Zhu a,b,c, Runliang Zhu a,b,c

a CAS Key Laboratory of Mineralogy andMetallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences,Guangzhou 510640, Chinab University of Chinese Academy of Sciences, Beijing 100049, Chinac Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China

H I G H L I G H T S G R A P H I C A L A B S T R A C T

• Both anion types and Cu2+ concentra-tions impact calcite dissolution.

• Inhibited spreading rates at csalt ≤0.1 mM result from the coverage ofsurface-active sites.

• Ca-OH and ion pairs cause enhanced ki-netics at 1 mM ≤ cCu2+ ≤ 10 mM.

⁎ Corresponding author at: CAS Key Laboratory of MiGeochemistry, Chinese Academy of Sciences, Guangzhou

E-mail addresses: [email protected] (H. Tang), x(J. Zhu), [email protected] (R. Zhu).

https://doi.org/10.1016/j.scitotenv.2019.02.2320048-9697/© 2019 Elsevier B.V. All rights reserved.

a b s t r a c t
a r t i c l e i n f o
Article history:Received 5 November 2018Received in revised form 26 January 2019Accepted 15 February 2019Available online 28 February 2019

Editor: Xinbin Feng

Calcite dissolution, occurring in rocks, soils and sediments, is essential to indicate element cycles and local envi-ronments in the lithosphere, biosphere, hydrosphere and atmosphere. Calcite dissolution strongly depends onmetal ions in aqueous solutions. Previous studies showed that aquatic Cu2+, a typical bio-toxic metal ion, canalter the calcite dissolution behavior. However, wide concentration ranges of Cu2+ coexistingwith ubiquitous an-ions in local environments, such aswaterways in the oxidation zones of copper deposits and soils nearmetal pro-cessing industry, was overlooked. When a considerable amount of aquatic Cu2+ ions are released into theenvironment, they migrate, diffuse, and hence become an environmental pollutant. Therefore, we focused onthe interaction between calcite dissolution andwide concentration ranges of Cu2+-bearing solutions with differ-ent types of anions (SO4

2−, Cl− and NO3−). Comprehensive approaches including in situ atomic force microscopy

(AFM), X-ray photoelectron spectroscopy (XPS), transmission electronmicroscope (TEM), and density functionaltheory (DFT) calculationswere employed to investigate kinetics andmechanisms of the interaction between thecalcite (10.4) surface and Cu2+-bearing solutions. Results demonstrated that both anion types and Cu2+ concen-trations dramatically affect calcite dissolution. The morphology of etch pits generated in CuSO4 solutions can befan-shaped but changed to tear-shaped in Cu(NO3)2 or CuCl2 solutions. Calcite dissolution kinetics is inhibited atcCu2+ ≤ 0.1 mM, caused by the coverage of active sites on calcite surfaces. As the Cu2+ concentration increases(1 mM ≤ cCu2+ ≤ 10 mM), calcite dissolution kinetics is enhanced due to the coupling effect of Cu2+-

Keywords:Calcite dissolutionCu2+ concentrationsAnion typesCoupling effectToxic element migration

neralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of510640, [email protected] (H. Xian), [email protected] (H. He), [email protected] (J. Wei), [email protected] (H. Liu), [email protected]

http://crossmark.crossref.org/dialog/?doi=10.1016/j.scitotenv.2019.02.232&domain=pdf

https://doi.org/10.1016/j.scitotenv.2019.02.232

[email protected]


http://www.sciencedirect.com/science/journal/00489697

603H. Tang et al. / Science of the Total Environment 668 (2019) 602–616

incorporated surface structure and solution chemistry. These results revealed the interactive mechanism be-tween calcite dissolution and the migration of toxic Cu2+ in waterways, provided a practical consideration indealing with the local environment.

© 2019 Elsevier B.V. All rights reserved.

1. Introduction

Mineral dissolution, commonly presenting in weathering crust,plays significant roles in environmental interfacial reactions and geo-chemical cycling of elements (Zhu et al., 2017; Kang et al., 2018). Calcitewith an abundance as high as 20% in carbonateminerals is ubiquitous inrocks, soils and sediments. Therefore, calcite dissolution directly affectsglobal carbon cycles, climate changes and the development of ecosys-tem (Alkattan et al., 2002; Villiers, 2005). For example, when the rateof marine calcification is at Gigaton (GT) per year level in the ocean sur-face, the sedimentary reservoir of CaCO3 precipitation is about 48 × 106

GT of carbon over geological time (Sigman and Boyle, 2000; Subhaset al., 2015). However, no more than 30% of the CaCO3 is buried in sed-iments while the rest is dissolved in the water column at sediment-water interface or in the upper portion of the sediment column(Feelym et al., 2004). Additionally, calcite is the primary component inexoskeletons and tissues of invertebrates, and these coastal organisms(e.g. corals and coralline algae) with biomineralization of calcite areclosely associated with the environmental ecosystem (Teng and Dove,1997). Because of the research significance andwide distribution of cal-cite in the earth's crust, its dissolution reactions have beenwidely inves-tigated in the past decades (Compton and Unwin, 1990; Shiraki et al.,2000; Giudici, 2002; Vinson et al., 2007; Kowacz and Putnis, 2008; Xuet al., 2010; Vavouraki et al., 2010).

Metal ions in environments are considered as one type of the mostactive factors that can influence calcite growth and dissolution(Reeder, 1996; Godelitsas et al., 2003a, 2003b; Davis et al., 2004; Freijet al., 2005). Previous studies mainly focused on two major aspects.On the one hand, because the transformation of calcite into dolomiteis unclear, effects of Mg2+ on calcite growth have been widely investi-gated (Zhang et al., 2013). Hong et al. (2016) discovered a mosaic-likesurface segmentation on calcite (10.4) surfaces under conditions with

varying saturation indexes SI ¼ logðΩÞ ¼ logðaCa2þ aCO2−

3Ksp

Þ (where Ω N 1)

andMg2+/Ca2+ ratios in solutions. They also classified etch pits formedon calcite surfaces into three types according to modified morphologiesand proposed that morphological changes were related to the incorpo-ration ofMg2+ into calcite lattice.Moreover, the presence ofMg2+ in so-lutions significantly altered dissolution kinetics of calcite anddramatically distorted morphologies of etch pits (Alkattan et al., 2002;Xu and Higgins, 2011). On the other hand, interactions between toxicmetal elements (such as Cd2+ and Co2+) and calcite have been exten-sively investigated since calcite growth or dissolution directly impacton the immobilization and release of elements, which is associatedwith the ecological risks such as soil contamination and bio-toxicity(Martin-Dupont et al., 2002; Freij et al., 2004; Pérez-Garrido et al.,

2007). Besides, the incorporation of metal ions into calcite lattice is cru-cial to reveal the relationship between calcite dissolution and epitaxialgrowth of crystals. Xu et al. (2014, 2015; M. Xu et al., 2017; H. Xuet al., 2017) discovered that certain edges of etch pits formed on calcite(10.4) surfaces became curved in Cd2+ (cCd2+=0.1mM),Mn2+ (cMn2+

b 0.25 mM) and Co2+ (cCo2+ b 0.2 mM) solutions, and they noticed pre-cipitations of CdCO3 and MnCO3 were produced along the direction of[421] whereas CoCO3 precipitations grew randomly.

As one of the predominant factors, aquatic metal ions with differentconcentrations can vastly inhibit, inmost cases, calcite dissolution. For ex-ample, the dissolution of calcite in Li+ (cLi+ b 100 mM), Mn2+ (cMn2+ b

0.02 mM) or Mg2+ (cMg2+ b 1 mM) solutions is inhibited (Arvidsonet al., 2006; Vinson et al., 2007; Ruiz-Agudo et al., 2010; Xu and Higgins,2011). However, Ruiz-Agudo et al. (2009) noticed that calcite dissolutionat neutral pH is inhibited at low Mg2+ concentrations (cMg2+ b 50 mM)but accelerated at high Mg2+ concentrations (cMg2+ N 50 mM). Gledhilland Morse (2004) also investigated the surface dissolution of calcite inbrine environments, discovering the inhibition of SO4

2− on calcite dissolu-tion was augmented with the increase of Ca2+ or Mg2+ concentrations.Although it is widely accepted that metal ions, such as Li+, Mn2+ andMg2+, heavily affect dissolution features of calcite, the influence of aquaticCu2+ on the dissolution behavior of calcite is still not very clear.

Aquatic Cu2+ is one of themost typical toxic metal elements in geo-chemical environments (Foster et al., 1978; Lukin et al., 2003; Torreset al., 2013; Perlatti et al., 2014; Panfili et al., 2017). Despite its low con-tents (ppb level) in most waterways and soil sediments, the concentra-tions in the groundwater of the oxidation zone of copper deposits aresurprisingly high in the range of 0.5–200 ppm and even reach up tohundreds of ppm in the soil near metal processing industry (Beuset al., 1976; Kashem and Singh, 1999; Lee et al., 2005; Kouzmanovet al., 2009; Oh et al., 2016; Spahić et al., 2018). Nevertheless, the nar-row concentration range of Cu2+ (cCu2+ b 1mM) in previous studies as-sociated with calcite dissolution is incomplete, causing an inaccuratereflection on calcite dissolution in the specific natural environmentsmentioned above (Terjesen et al., 1961; Salem et al., 1994; Gutjahret al., 1996).

In this study, we used AFM, XPS, TEM and DFT calculations to in-vestigate effects of Cu2+-bearing solutions with the presentation ofSO4

2−, Cl− or NO3− on dissolution features of calcite (10.4) surfaces,

in which the Cu2+ concentrations range from 0 to 10 mM at pH 4.5and 2.6. In addition, we also discussed the kinetics and mechanismof calcite dissolution in Cu2+-bearing solutions. We have noticedthat both the type of anions and the concentration of Cu2+ can signif-icantly alter dissolution features of calcite. Besides, surface structureand solution chemistry codetermine calcite dissolution in Cu2+-bearing solutions.

2. Experimental section

2.1. Calcite substrate and solution preparation

An optical-quality Iceland Spar (collected from Guizhou, China) waswashed by ethanol andMilli-Qwater (resistivity= 18.2MΩ cm−1). Then, itwas driedwith N2 and smashed to small sized samples using a hammer. Small crystal grains (3 × 3 × 2 cm3) were chosen and then cleaved by a scal-pel along (10.4) cleavage surfaces. The cleaved fragments with sizes of approximately 2 × 2 × 1mm3were handled with tweezers to avoid any con-taminations, and a jet of N2was applied to remove debris from the cleaved surfaces. Afterwards, theprepared sampleswere glued on steel puckswithcyanoacrylate.

604 H. Tang et al. / Science of the Total Environment 668 (2019) 602–616

Solutions were prepared from high-purity Cu(NO3)2, CuCl2, CuSO4, K2SO4 and KCl (Guangzhou Chemical Reagent Factory or Kermel, Tianjin) dis-solved in deionized water. The concentrations of solutions ranged from 0 to 10 mM with the pH adjusted to determined values (4.5 and 2.6) byadding reagent grade KOH or HNO3, HCl and H2SO4 solutions. Because we focused on actual environmental issues, solution conditions deviatedfrom saturation. Solution chemistry in the system is constrained by the amounts of Cu2+, ∑CO2 and pH. Consider the following equilibria:

Cu2 OHð Þ2CO3 þ 2Hþ↔2Cu2þ þ CO2−3 þ 2H2O Ksp−1; ð1Þ

Cu3 OHð Þ2 CO3ð Þ2 þ 2Hþ↔3Cu2þ þ 2CO2−3 þ 2H2O Ksp−2; ð2Þ

Cu OHð Þ2 þ 2Hþ↔Cu2þ þ 2H2O Ksp−3; ð3Þ

CuCO3↔Cu2þ þ CO2−3 Ksp−4; ð4Þ

Cu2 OHð Þ3Clþ 3Hþ↔2Cu2þ þ Cl− þ 3H2O Ksp−5; ð5Þ

Cu4 OHð Þ6SO4 þ 6Hþ↔4Cu2þ þ SO2−4 þ 6H2O Ksp−6; ð6Þ

Cu2 OHð Þ3NO3 þ 3Hþ↔2Cu2þ þNO−3 þ 3H2O Ksp−7; ð7Þ

H2CO3↔Hþ þHCO−3 Ka1; ð8Þ

and

HCO3−↔Hþ þ CO2−

3 Ka2: ð9Þ

From the definition of Ksp, we derived

log Cu2þ� � ¼ 12

logKsp−1 10−2pH þ 10−3pH=Ka2 þ 10−4pH=Ka1Ka2

h iP

CO2

0@

1A ð10Þ

log Cu2þ� � ¼ 13

logKsp−2 10−8pH=Ka1

2Ka22 þ 10−10pH=Ka1

2Ka24 þ 10−12pH=Ka1

4Ka24

h i

∑CO2ð Þ2þ

0@ 2 10−9pH=Ka1

2Ka23 þ 10−10pH=Ka1

3Ka23 þ 10−11pH=Ka1

3Ka24

� �

∑CO2ð Þ2

1A

ð11Þ

log Cu2þ� � ¼ −2pHþ logKsp−3 ð12Þ

log Cu2þ� � ¼ logKsp−4 1þ 10−pH=Ka2 þ 10−2pH=Ka1Ka2

h iP

CO2

0@

1A ð13Þ

log Cu2þ� � ¼ 12

−3pHþ log Ksp−5� �

− log Cl−ð Þ� � ð14Þ

log Cu2þ� � ¼ 14


− log SO42−

� �h ið15Þ

log Cu2þ� � ¼ 12


− log NO3−ð Þ� � ð16Þ

where (Cu2+) represents the activity of Cu2+, and∑CO2 is the total concentration of carbonate species. Eqs. (10) to (16) define the stability fields ofmalachite, azurite, Cu(OH)2, CuCO3, atacamite, brochantite and Cu2(OH)3NO3, respectively, in the two-dimensional stability diagram of log (Cu2+)–pH (Fig. 1). According to the concentration of Ca2+ (8 × 10−6 M) after the dissolution of calcite in Cu2+-bearing solutions at pH 4.5, we assumed∑CO2 = 8 × 10−6 M. The concentrations of Cl−, SO4

2− and NO3− in these equations were determined based on added amounts.

2.2. Experimental procedure and in-situ AFM imaging

O-ring and probe were installed on the cleaned liquid cell which was then placed on the top of calcite (10.4) surfaces to form a closed re-action environment. We selected a relatively flat area and pumped solutions into the fluid cell. Then, flatjaw pinchcocks were closed understatic conditions or kept the flow rate at 0.5 mL min−1 under flowing conditions, during which surfaces of calcite were mapped continuallywith AFM.

The analysis was carried out on a Bruker Nanoscope IVa scanning probemicroscope (Digital Instruments, Santa Barbara, CA) at the room temper-ature (25 °C) in contact mode with a J-type scanner (maximum scan area of 125 × 125 μm2) and gold-coated Si3N4 tips with a nominal spring con-stant of 0.06 N/m. Scan rates and resolutions were set to 1.0–4.0 Hz and 512 × 512 in AFM images. The point voltage was set to minimum values toassure the tip would not affect the dissolution morphology of calcite cleavage surfaces. The spreading rate of etch pits (vsum) was calculated by themeans of angle method which has more advantages to reduce measuring errors than the step displacement method especially in conditions for

Fig. 1. Stability diagram ofmalachite, azurite, Cu(OH)2 and Cu2(OH)3NO3 (a); atacamite (b); brochantite (c)with respect to Cu2+ activity and solution pH. Illustrations in the bottom rightcorner are partial enlarged drawings. The asterisk symbols mark the compositions of experimental solutions in this study.


rapid dissolution (Teng, 2005). Besides, we measured aspect ratios from AFM images to analyze morphological changes of etch pits in different so-lutions. It is defined by the equation:

λ ¼ xy

ð17Þ

where λ denotes the aspect ratio; x and y represent the max lengths perpendicular and parallel to c-glide plane of etch pits in the 2D direction,respectively.

2.3. XPS and TEM analysis

Samples were collected for X-ray photoelectron spectroscopy (XPS) analysis on a K-alpha XPS instrument equipped with Al Kα source(1486.8 eV). The base pressure in the spectrometer analyzer chamber was 10−8 mbar, and the charge neutralizer filament was used during thewhole processes to control charging of calcite surfaces. Finally, the Carbon C 1s core level at 284.8 eVwas used as the reference to correct the chargingeffect of other spectra.

Transmission electron microscope (TEM) was used to observe precipitations on calcite surfaces. We prepared samples by crushing them along(10.4) cleavage surfaces, and then dispersed them into the deionized water and 1 mM Cu(NO3)2 solution, respectively. Then, we added a fewdrops on grids to make TEM observations. This analysis was carried out using a FEI Talos F200S high resolution TEM (operated at 200 kV) equippedwith HAADF detector and energy dispersive spectrometer.

2.4. Computational details

To further clarify the AFM results, we performed DFT under periodic boundary conditions (PBC), as executed in the Vienna Ab initio SimulationPackage (VASP) (Kresse and Furthmuller, 1996) with the projector augmented wave (PAW) method (Kresse and Joubert, 1999). Similar standardand parameters with Sánchez andMiranda (2014) and Bruno et al. (2010) were considered to perform energy calculations and geometry optimiza-tions by means of the conjugate gradient (CG) method. The Perdew-Burke-Ernzerh (PBE) function (Perdew et al., 1996) was used to describe theexchange correlation energy. Only Γ point was used during the geometry optimizations. Besides, the carbonate-terminated polar surfaces,i.e., (01.2)CO3 and (00.1)CO3, were considered, on which the Ca2+ vacancy was occupied by Cu2+, as the surface stability of (01.2)Ca and (00.1)Ca isless than that of (01.2)CO3 and (00.1)CO3, respectively (Bruno et al., 2013). Calculations were done by considering the (01.2)CO3 and (00.1)CO3 slabswith vacuum thickness of 20 Å. The (01.2)CO3 and (00.1)CO3 surfaces were all represented as four-layers of structural units, with 2 × 1 and 2 × 2


supercells, respectively. Moreover, net charge was calculated by Bader charge analysis (Bader, 1990) with the code developed by Henkelman et al.(2006).

The surface substitution reaction is expressed as:

surf−□Ca2þ þ Cu2þ→surf−Cu2þ ð18Þ

Adsorption energy is defined by the equation:

Eads ¼ Eaft−Cu−Ebef−Cu ð19Þ

where Eads denotes adsorption energy; Ebef-Cu and Eaft-Cu represent adsorption energies before and after the adsorption of Cu2+ into Ca2+ vacancy.We also investigated effects of\\OH on (01.2)Ca and (01.2)Cu. The surface adsorption reactions are:

surf−Ca2þ þ OH→surf−Ca−OH; ð20Þ

and

surf−Cu2þ þ OH→surf−Cu−OH ð21Þ

Similarly, adsorption energies are defined by equations:

Eads ¼ Eaft−Ca−OH−Ebef−Ca−OH ð22Þ

and

Eads ¼ Eaft−Cu−OH−Ebef−Cu−OH ð23Þ

where Ebef-Ca/Cu-OH and Eaft-Ca/Cu-OH represent adsorption energies before and after the adsorption of\\OH on (01.2)Ca and (01.2)Cu. Eads/A value indi-cates the change of adsorption energy per unit area, where A is the cross-section area of the (01.2) or (00.1) surfaces.

3. Results

3.1. Effects of Cu2+-bearing solutions with different types of anions on cal-cite dissolution

3.1.1. Morphology of etch pits in Cu2+-bearing solutions with differenttypes of anions

Before carrying out dissolution experiments of calcite in Cu2+-bearing solutions, we used deionized water to dissolve calcite to serveas a morphological reference (Fig. 2A1, A2; Figs. S1). The morphologyof etch pits is consistent with previous results, namely, the two adjacentsides [441]+ and [481]+ fail to cross at a particular point and form a cur-vilinear boundary instead in deionized water under static conditions

Fig. 2. AFM deflection images of the calcite (10.4) surface in different concentrations of CuCl2flowing, (B1) 0.1 mM in static, (B2) 0.1 mM in flowing, (C1) 1 mM in static, (C2) 1 mM in flowin

(Fig. 2A1), whereas the morphology of etch pits recovered to the rhom-bic shape when hydrodynamic state was changed to flow (Fig. 2A2; Wuet al., 2012). After introducing CuCl2, CuSO4 or Cu(NO3)2 solutions, weobserved particles precipitation on calcite surfaces (Figs. 2–4). Understatic conditions, the [421] steps were produced with the increase ofCuCl2 concentration (Fig. 2B1–E1). After changing the hydrodynamicstates to flow, both [421] and [010] steps of etch pits emerged inCuCl2 solutions with higher concentrations (Fig. 2C2–E2).

Themorphological features of etch pits generated in CuSO4 solutionsare totally different from those observed in CuCl2 solutions. The mor-phology of etch pits emerged in most of CuSO4 solutions with differentconcentrations is similar to that generated in deionized water. Never-theless, when the concentration of CuSO4 solution increased

solution under static/flowing conditions at pH 4.5 with (A1) 0 mM in static, (A2) 0 mM ing, (D1) 5 mM in static, (D2) 5 mM in flowing, (E1) 10mM in static, (E2) 10mM in flowing.

Fig. 3.AFMdeflection images of the calcite (10.4) surface in different concentrations of CuSO4 solutions under static/flowing conditions at pH4.5with (A1) 0.1mM in static, (A2) 0.1mM inflowing, (B1) 1 mM in static, (B2) 1 mM in flowing, (C1) 5 mM in static, (C2) 5 mM in flowing, (D1) 10 mM in static, (D2) 10 mM in flowing.


progressively from 0.1 to 10 mM, the [010] steps were observed in0.1 mM and 1 mM solutions under flowing conditions (fan-shaped)(Fig. 3A2, B2).

The dissolution features of calcite in Cu(NO3)2 solutions resemble tothose in CuCl2 solutions (tear-shaped), while they are totally differentfrom those in CuSO4 solutions. The presence of Cu(NO3)2 under staticor flowing conditions showed highly selective effects on the +/− cor-ners which joint acute and obtuse of etch pits. Under static conditions,the [421] steps were kept in Cu(NO3)2 solutions (Fig. 4A1–D1). Afterflowing the 0.1 mM Cu(NO3)2 solution over the (10.4) surface, dissolu-tion took place with the feature of unsharp edges (Fig. 4A2). Further in-creasing the concentration of Cu(NO3)2 solutions to 1, 5 and 10mM, weinvestigated the evolution of surface morphology of calcite dissolution.On reacting with the 1 mM Cu(NO3)2 solution, the morphology ofpreexisting steps turned into round shape with noticeable [010] and

Fig. 4.AFMdeflection images of the calcite (10.4) surface in different concentrations of Cu(NO3)in flowing, (B1) 1 mM in static, (B2) 1 mM in flowing, (C1) 5 mM in static, (C2) 5 mM in flowin

[421] steps (Fig. 4B2). Interestingly, [010] steps disappeared when theconcentration of Cu(NO3)2 solutions was increased to 5 mM or 10 mM(Fig. 4C2–D2).

3.1.2. Step kinetics of etch pits in Cu2+-bearing solutions with differenttypes of anions

The spreading rates of etch pits (vsum) formed in the calcite (10.4)surface were used to reflect the dissolution kinetics process. The vsum(nm s−1) obtained from vsum = (v++v−) (where v+ and v− refer tothe retreat velocities of + and - steps, respectively) was calculated mea-suring the length increase per unit time between opposite parallel stepsin sequential images. The vsum values acquired in 0mMCuSO4, Cu(NO3)2and CuCl2 solutions (pH was adjusted to 4.5 using acid or base) understatic conditions, were 1.47, 2.84 and 3.52 nm s−1, respectively. Keepingthe concentration of Cu2+-bearing solutions at cCu2+ ≤ 0.1 mM, lower

2 solution under static/flowing conditions at pH 4.5with (A1) 0.1mM in static, (A2) 0.1mMg, (D1) 10 mM in static, (D2) 10 mM in flowing.

Table 1Etch pit spreading rates of calcite (nm s−1) under static conditions as a function of salt concentration (mM) for different Cu2+/K+ salts.

CuSO4 CuCl2 Cu(NO3)2

C (mM) v+ v− v+/v− vsum Std C (mM) v+ v− v+/v− vsum Std C (mM) v+ v− v+/v− vsum Std

0 0.36 1.11 0.32 1.47 0.22 0 0.73 2.78 0.26 3.52 0.86 0 0.53 2.31 0.23 2.84 0.220.0001 0.27 0.40 0.68 0.67 0.38 0.0001 0.28 2.20 0.13 2.50 0.49 0.0001 0.45 0.62 0.73 1.07 0.440.001 0.35 0.59 0.59 0.93 0.70 0.001 0.22 2.87 0.08 3.09 0.83 0.001 0.45 0.53 0.85 0.98 0.590.01 0.31 0.44 0.70 0.76 0.40 0.01 0.85 1.29 0.66 1.65 0.33 0.01 0.53 0.62 0.85 1.15 0.810.1 0.37 2.40 0.15 2.77 1.12 0.1 0.36 1.40 0.26 1.95 0.40 0.1 0.60 1.58 0.38 2.18 0.881 4.76 2.93 1.62 7.69 0.62 1 0.89 2.32 0.38 3.20 0.97 1 0.31 2.27 0.14 2.58 0.495 11.37 2.80 4.06 14.17 0.41 5 2.27 5.35 0.42 7.62 0.90 5 1.00 2.70 0.37 3.7 0.4710 14.53 3.03 4.80 17.57 1.82 10 2.37 6.93 0.34 9.31 1.25 10 0.98 2.98 0.33 3.96 0.90

K2SO4 KCl

C (mM) v+ v− v+/v− vsum Std C (mM) v+ v− v+/v− vsum Std

0 0.36 1.11 0.32 1.47 0.22 0 0.73 2.78 0.26 3.52 0.860.0001 0.36 0.84 0.43 1.20 0.22 0.0002 0.36 0.36 1.00 0.71 0.430.001 0.27 0.53 0.51 0.80 0.19 0.002 0.71 0.36 1.97 1.07 0.440.01 0.22 0.49 0.45 0.71 0.36 0.02 0.36 0.53 0.68 0.89 0.600.1 0.27 0.58 0.47 0.84 0.30 0.2 0.61 1.79 0.34 2.40 0.801 0.53 0.48 1.10 1.01 0.66 2 0.67 1.87 0.36 2.53 0.385 0.29 0.35 0.83 0.64 0.26 10 0.79 0.92 0.86 1.71 0.5210 0.27 0.44 0.61 0.71 0.11 20 0.64 1.22 0.52 1.86 0.63


vsum values than those in deionized water were observed. With the in-crease of Cu2+ concentration to 0.1 mM, these vsum varied to 2.77, 2.18and 1.95 nm s−1 in CuSO4, Cu(NO3)2 and CuCl2 solutions. With the fur-ther increase of solution concentration to 1, 5 and 10mM, vsum increasedto 17.57, 3.96 and 9.31 nm s−1, which are all higher than those acquiredin deionizedwater (Table 1).We also discovered that vsum valueswere inthe order of CuSO4 N CuCl2 N Cu(NO3)2 in 1 mM ≤ cCu2+ ≤ 10 mM Cu2+-bearing solutions at pH 4.5 under static conditions (Fig. 5).

3.1.3. Comparison of dissolution characteristics of calcite in Cu2+-bearingwith those in K+-bearing solutions

To highlight effects of Cu2+ on the dissolution reaction, we com-pared the dissolution features of etch pits in Cu2+-bearing solutionswith those in K+-bearing solutions, while the anion types and concen-trations are not changed. Etch pits formed on the surface of calcite inK2SO4 and KCl solutions exhibited a similar rhombic shape to thoseemerged in deionized water (Fig. S2). On the other hand, the spreadingrate (vsum) changedwith the type of salts, in the order of CuSO4 N K2SO4

and CuCl2 N KCl in 0.1mM ≤ csalt ≤ 10mMsalt solutions under static con-ditions (Fig. 5). Besides, the average v+/v− ratios in CuSO4 solutionswith the concentrations of 1 mM ≤ cCu2+ ≤ 10 mM are higher (N 1),

Fig. 5. Average spreading rate of etch pits nucleated on the calcite (10.4) surface in thesolution of pH 4.5 under static conditions vs. concentration (mol L−1) of (□) CuSO4, (○)CuCl2, (Δ) Cu(NO3)2, (◊) K2SO4, and (∇) KCl solutions.

whereas those ratios in CuCl2, K2SO4 and KCl solutions are lower (al-most all b1) (Table 1).

3.2. Dissolution features of calcite in Cu(NO3)2 solutions

It can be seen from the above results that morphological features ofetch pits formed in CuSO4, CuCl2 and Cu(NO3)2 solutions varied fromsimple to complex. Therefore, the Cu(NO3)2 solution was selected to in-vestigate effects of concentrations, hydrodynamic states and pH condi-tions of Cu(NO3)2 solutions on the morphology of etch pits and themechanism of Cu2+ interactions with calcite (10.4) surface.

3.2.1.Morphological changes of etch pits formed in Cu(NO3)2 solutionswithdifferent concentrations, hydrodynamic states and pH conditions

The presence of Cu(NO3)2 solutions with different concentrationshad strong impacts on morphological changes of etch pits. When theconcentration of the Cu(NO3)2 solution was kept at 1 mM under staticconditions, [421] steps emerged at the joint between the obtuse andacute angle edges, and the average aspect ratio ( _λ) was 1.40 (Figs. 6A,8). Upon increasing the concentration of the Cu(NO3)2 solution to10 mM, [421] steps became more obvious, and _λ was increased to2.13 (Figs. 6D, 8; Table S1).

We also took the hydrodynamic states into consideration on the in-fluence of calcite dissolution. When the hydrodynamic state was staticin the 1 mM Cu(NO3)2 solution, we noticed the nucleation and spreadof etch pits which had a different morphology from the rhombic shapegenerated in deionized water on calcite (10.4) surface. Although theoverall morphology of etch pits was still symmetrical along c-glideplane, the rounded shape indicated the generation of [42 1 ] steps(Fig. 6A). When the hydrodynamic state was changed from static toflowing conditions (flowing rate 0.5 mL min−1), [421] and [010] stepsof etch pits emerged over time, and _λ dropped to 0.92 (Figs. 6B, 8;Table S1). Changing the hydrodynamic state from flowing to static, [421] steps remained, but [010] steps disappeared (Fig. 6B–C). In the sameway, we observed similar phenomena in the 10 mMCu(NO3)2 solution,yet [010] steps of etch pits disappeared under flowing conditionswith _λchanged to 1.32 (Figs. 6D–F, 8; Table S1). In different hydrodynamicstates of Cu(NO3)2 solution, [421] stepswere preserved in the entire dis-solution process, suggesting its incomplete reversibility. Nevertheless,[010] steps could only be generated in the 1 mM Cu(NO3)2 solutionunder flowing conditions, which disappeared when the concentration

Fig. 6. AFM deflection images of the calcite (10.4) surface in Cu(NO3)2 solutions at pH 4.5 with concentration of 1 mM under (A) static conditions, (B) flowing conditions, (C) conditionschanged from flowing to static, and with concentration of 10 mM under (D) static conditions, (E) flowing conditions, and (F) conditions changed from flowing to static.


or hydrodynamic state of Cu(NO3)2 solution was changed, indicating itscomplete reversibility.

Apart from concentrations and hydrodynamic states, pH values alsomightily affect morphological changes of etch pits. At pH 2.6 understatic conditions, the dissolution morphology of etch pits generated oncalcite (10.4) cleavage surfaces was regular rhombus in deionizedwater (Fig. 7A). Increasing the concentration of Cu(NO3)2 solution to

1 mM, these etch pits became rounded with [421] and [010] stepsemerged, and newly formed etch pits nucleated on the surface(Fig. 7B–H). In comparison, when the Cu(NO3)2 solution concentration

Fig. 7. AFM deflection images of the calcite (10.4) surface in 1 mM Cu(NO3)2 solution under sta(E) 28 min, (F) 35 min, (G) 42 min, (H) 49 min.

was increased to 10 mM, only [42 1 ] steps of etch pits existed(Fig. S3A), and _λ (1.46) was much higher than that measured in the1 mM Cu(NO3)2 solution (0.74) (Table S1).

Morphological changes of etch pits formed in different Cu(NO3)2 so-lution conditions can be semi-quantitatively analyzed by (average as-pect ratio) _λ values (Table S1). On the one hand, a higher _λ valuecould be acquired in the Cu(NO3)2 solution with a higher concentrationor pH value. The _λ values of etch pits measured in 1mMCu(NO3)2 solu-tions were smaller, which are only 50.68–69.70% of those in 10 mM Cu(NO3)2 solutions (Fig. 8). When the pH dropped from 4.5 to 2.6 under

tic conditions at pH 2.6, with time prolonged (A) 0 min, (B) 7 min, (C)14min, (D) 21min,

Fig. 8. Average aspect ratios (λ) of etch pits under different dissolution conditions.


static conditions, the _λ values of etch pits decreased by 45.39% and34.29% in the 1 mM and 10 mM solutions, respectively (Fig. 8). On theother hand, _λ values of etch pits measured in the solution under staticconditions were higher than those obtained under flowing conditions.Changing the hydrodynamic state from static to flowing and againback to static conditions, the _λ value gradually decreased and then re-covered to the initial values (Fig. 8). In addition, aspect ratio values(λ) gradually increased and kept unchanged under static and flowingconditions over time, respectively (Table S1).

3.2.2. XPS and TEM of calcite exposed to Cu(NO3)2 solutionsThe signal of Cu 2p core level could not be detected on the fresh

cleavage surfaces or those dissolved in deionized water, but it emergedon those dissolved in Cu(NO3)2 solutions at both pH 4.5 and 2.6 (Fig. 9).The shake-up satellite peaks in the XPS narrow spectra of Cu 2p corelevel at around 940.4 eV, 944.2 eV and 963.0 eV indicated an unfilledCu 3d9 shell and the existence of Cu2+ in the sample (Ghijsen et al.,

Fig. 9.XPS spectra of Cu2p core levels of the calcite (10.4) surface after reactingwith the (A) 1msolution at pH 2.6, and (D) 10 mM Cu(NO3)2 solution at pH 2.6; XPS spectra of Cu 2p core leve

1988; Borgohain et al., 2002). Four obvious signals generated in Cu 2pcore level at 932.8 ± 0.1 eV, 952.3 ± 0.1 eV and 935.0 ± 0.1 eV, 954.6± 0.2 eV suggested the variety of Cu-bearing phases. With the concen-tration of Cu(NO3)2 solutions changed from 1 to 10 mM, the intensitiesof the former two signals increased while the latter ones relatively de-creased (Fig. 9). In addition to Cu 2p XPS spectra, Ca 2p and O 1s XPSspectra could also be utilized to characterize the surface chemical envi-ronment of calcite. Compared with samples that had a fresh cleavagesurface or emerged in deionized water, new signals of Ca 2p (348.0 ±0.3 eV and351.5±0.3 eV) core levels emerged at higher binding energyin those reacted in Cu(NO3)2 solutions, indicating a new Ca-phaseformedon or near surfaces of calcite (Fig. 10; Fig. S4). Similarly, after cal-cite surfaces were dissolved in Cu(NO3)2 solutions, the signal of O 1 s(532.8 ± 0.1 eV) core level suggested the formation of a new chemicalenvironment for O (Fig. 10; Fig. S4). Finally, from the valence band spec-tra, we discovered that the (10.4) surfaces reacted with Cu(NO3)2 solu-tions had broader bandwidth than those of fresh ones (Figs. S4–5). Thus,there might exist newly formed substance and valence electrons trans-formation in the reaction system (Fig. S5).

TEM results showed that a smooth surface of calcite wasmaintainedwhen dispersed in deionized water. Amorphous Cu-bearing nanoparti-cles generated on these smooth surfaceswhen dispersion time of calcitein 1 mM Cu(NO3)2 solution was extended from 15 min to 1 month(Fig. S6). Further prolonging dispersion time to 10 months, Cu-bearingminerals which were identified as azurite by selective electron diffrac-tion (SAED) were produced around calcite (Fig. 11A, B, D). Combinedwith the consequence of high-resolution transmission electron micro-scope (HRTEM), multiple crystal particles with different orientationswere generated, which further formed polycrystalline aggregations byparticle attachment (Fig. 11C).

3.2.3. Adsorption energy and Bader charge distributionIn order to clarify effects of Cu2+ on surface stabilities and Bader

charge distributions of (01.2)CO3 and (00.1)CO3 surfaces, we calculatedsurface energies and Bader charges after Cu2+ was adsorbed into Ca2+

MCu(NO3)2 solution at pH4.5, (B) 10mMCu(NO3)2 solution at pH4.5, (C) 1mMCu(NO3)2ls of (E) Cu(OH)2, and (F) Cu2(OH)2CO3. The star symbol (☆) represents satellite peak.

Fig. 11. Results of calcite dispersed in the 1mMCu(NO3)2solution at pH4.5 after 10months (A) TEM image; (B) HAADF STEM–EDXmapping image; (C)HRTEM image, and the FFT image

of these colored particles displayed in the illustration; (D) SAED image of azurite which is the labeled area in (B).

Fig. 10.XPS spectra of Ca 2p (a) andO 1s (b) core levels of the calcite (10.4) surface after reactingwith the (A) deionizedwater at pH 4.5, (B) 1mMCu(NO3)2solution at pH4.5, (C) 10mM

Cu(NO3)2solution at pH 4.5, (D) deionized water at pH 2.6, (E) 1 mM Cu(NO

3)2solution at pH 2.6, and (F) 10 mM Cu(NO

3)2solution at pH 2.6.


Table 2The adsorption energy after one of Cu2+ was adsorbed into Ca2+ vacancy of the calcite(01.2)CO3 and (00.1)CO3 surfaces, and the adsorption energy of\\OH on (01.2)Ca and(01.2)Cu surfaces.

Surfaces Eads. (eV) Eads/A. (eV Å−2)

(01.2)CO3 −6.37 −0.10(00.1)CO3 −6.99 −0.08(01.2)Ca-OH −6.12 −0.10(01.2)Cu-OH −3.51 −0.06

Notes: Eads/Ab0 means that occur the reaction spontaneously.


vacancies on these two surfaces. After Cu2+ occupied Ca2+ vacancies,adsorption configurations of (01.2)CO3 and (00.1)CO3 surfaces were to-tally different (Fig. 12A–B). Based on stable adsorption configurations,we obtained that Eads/A values of (01.2)CO3 and (00.1)CO3 were−0.10 eV Å−2 and−0.08 eV Å−2, respectively (Table 2). In addition, al-though the charge distribution of Ca and C were not intensely affectedby the occupation of Ca2+ vacancy by Cu2+, the average charge of O in-creased from−1.17 e to−1.03 e after occupation (Fig. 12A–B). Further-more, effects of \\OH on Ca and Cu of calcite (01.2) surface wereconsidered, and we therefore concluded that Eads/A values of (01.2)Ca-OH and (01.2)Cu-OH were−0.10 eV Å−2 and−0.06 eV Å−2, respectively(Table 2). Based on adsorption configurations, we found that the coordi-nation number of O (from\\OH) is 3 for (01.2)Ca-OH yet it decreased to 2for (01.2)Cu-OH (Fig. 12C–D).

4. Discussion

4.1. Comparison with previous studies

The results obtained in Cu2+-bearing solutions at lower concentra-tions (cCu2+ ≤ 0.1 mM) are in accordance with previous phenomenathat calcite dissolution is inhibited in most metal ion solutions (Leaet al., 2001; Hay et al., 2003; Ruiz-Agudo et al., 2010), while the spread-ing rate is accelerated when the concentration of Cu2+-bearing solu-tions is controlled at 1 mM ≤ cCu2+ ≤ 10 mM in our study. We useHSAB (hard and soft acids and bases) theory (Pearson, 1963) to analyzethe effects of different ions on calcite dissolution in the followingcontext.

Since the softness of Lewis acids determines their chemical reactiontypes, different acid softness indexes of divalent cations are likely toexert diverse influences on calcite dissolution (M. Xu et al., 2017; H.Xu et al., 2017). Effects of hard acids, such as Ca2+, Sr2+, Ba2+ Mn2+,and Mg2+, on calcite dissolution have been widely investigated in pre-vious studies, and all of them show inhibition (Sjöberg and Rickard,1985; Gutjahr et al., 1996; Lea et al., 2001; Hay et al., 2003). Arvidson

Fig. 12. Bader charge distribution diagrams of (01.2) surface viewed along the [010]direction (A) before Ca2+ was desorbed, (B) after Cu2+ was adsorbed into the Ca2+

vacancy. And adsorption configurations of (C) (01.2)Ca-OH surface, (D) (01.2)Cu-OH surface.

et al. (2006) discovered an inhibition effect of Mg2+ on calcite dissolu-tion at solution pH-1–3. Nevertheless, Ruiz-Agudo et al. (2010) pro-posed that the concentration of Mg2+ also dramatically influencescalcite dissolution at pH N 6.8. When the Mg2+ concentration is keptat cMg2+ b 50 mM, calcite dissolution is inhibited. With the increase ofthe Mg2+ concentration to cMg2+ N 50 mM, the dissolution is acceler-ated, although the spreading rate is still inhibited. Accordingly, solutioncomponents, such as pH and ion concentrations, are extremely crucialto calcite dissolution.

In terms of effects of borderline acids, such as Cd2+, Zn2+ Hg2+ andCu2+, which display an inhibition on calcite dissolution have been stud-ied (Gutjahr et al., 1996; Cubillas et al., 2005). We noticed that concen-trations of these Lewis acids are almost at cMe2+ b 1 mM and mostcalcite samples are powders in these experiments (Table 3). Accordingto our results, calcite dissolution is inhibited at lower Cu2+ concentra-tions (cCu2+ ≤ 0.1 mM), which is consistent with previous conclusions(Terjesen et al., 1961). Additionally, the spreading rate (vsum) of etchpits on calcite (10.4) surfaces is accelerated at higher Cu2+ concentra-tions (1 mM ≤ cCu2+ ≤ 10mM). Consequently, it is the different attribu-tion of Cu2+ and Mg2+, assigned to borderline acid and hard acidrespectively, that possibly makes a different dissolution behavior oncalcite.

4.2. Effects of surface structure on calcite dissolution

4.2.1. Site-specific and non-specific effectsMorphological reversibility is useful to determine site-specific and

non-specific effects (Ruiz-Agudo and Putnis, 2012; Wu et al., 2012). Be-cause the morphological change is attributed to effects of mass transferand surface reaction, the expression of [421] steps is controlled by hy-drodynamic states although it does not entirely depend on them(Ruiz-Agudo and Putnis, 2012). The expression of [421] steps understatic conditions is more obvious than that under flowing conditions,suggesting interactions between Cu2+ and calcite (01.2) surfaces in-clude both site specific and non-specific effects with the former as thepredominant one. Additionally, [010] steps, dramatically influenced byhydrodynamic states and concentrations of solutions, disappearedwhen either of these two factors is altered, indicating interaction be-tween Cu2+ and calcite (00.1) surfaces is mainly site non-specific effect.

Although (01.2) and (00.1) surfaces are unstable in the natural envi-ronment, as confirmed by the ubiquity of (00.1) contact twins and(01.2) polysynthetic twins of calcite in the nature, they are well pre-served in Cu(NO3)2 solutions (Kitamura et al., 1979; Bruno et al.,2010). Stabilization of (01.2) and (00.1) surfaces is consistent with thedevelopment of [421] and [010] steps of etch pits during dissolution, be-cause the directions of new edges correspond to the intersection of(01.2) and (00.1) surfaces with the cleavage rhombohedron (10.4) sur-face, respectively (Ruiz-Agudo et al., 2010; Wu et al., 2011). Comparedwith [42 1 ], [010] steps are more sensitive to concentrations, pHvalues and hydrodynamic states, showing a stronger correlation be-tween Cu2+ and (01.2) surfaces. From atomic structure arrangement,the Ca\\Ca distances along the [010] and [421] steps are 4.99 Å and4.05 Å respectively, suggesting the Ca atomic density on the (00.1) sur-face is lower than that on the (01.2) surface (Wu et al., 2012). Hence, the

Table 3Studies of calcite dissolution behaviors in different softness of Lewis acids.

Lewis acids CMe2+. (mM) pH Sample types Inhibitor/accelerant References

Hard acids

Ca2+ 1 b c b 10 6–8.3

(10.4) plane Inhibitor

Sjöberg and Rickard (1985)Sr2+ 0.01 b c b 1

c b 0.024c b 1

6–98.8–9

pH-stat

Hay et al. (2003)Lea et al. (2001)

Gutjahr et al. (1996)Ba2+ c b 1 pH-stat Gutjahr et al. (1996)Mn2+ c b 0.02 8.8–9 Lea et al. (2001)Mg2+ c b 1 −1–3 (10.4) plane Inhibitor Arvidson et al. (2006)

c b 50 N6.8 Inhibitor Ruiz-Agudo et al. (2010)c N 50 Accelerant

Borderline acids Cd2+ c b 0.050.01 b c b 1c b 0.16

5.656–9

(10.4) plane Inhibitor Pérez-Garrido et al. (2007)Hay et al. (2003)

Cubillas et al. (2005)6.18–9 PowderZn2+ c b 0.001 pH-stat Powder Gutjahr et al. (1996)Hg2+ c = 5 3.5 (10.4) plane Godelitsas et al. (2003a)Cu2+ c b 0.001

c b 0.005c b 1

pH-stat9.2–

Powder Inhibitor Gutjahr et al. (1996)Salem et al. (1994)

Terjesen et al. (1961)c ≤ 0.1 4.5 (10.4) plane Inhibitor This study

1 ≤ c ≤ 10 4.5 Accelerant


(01.2) surface, supplying more defect vacancies for Cu2+, is more suit-able for Cu2+ to incorporate, which is in accordancewith our adsorptionenergy calculations. Based on results of calculations, after the adsorptionof Cu2+ into the Ca2+ vacancy, the Eads/A value of the (01.2) surface is−0.10 eV Å−2, smaller than that of the (00.1) surface (−0.08 eV Å−2).Therefore, it is concluded that Cu2+ prefers to be adsorbed on the(01.2) rather than (00.1) surfaces, which is consistent with our AFM re-sult that [421] steps are expressed more easily than [010] steps in Cu(NO3)2 solutions.

The spreading rate of calcite dissolution is interpreted based onsurface-active sites. When concentrations of Cu2+ are kept at cCu2+ ≤0.1mM, vsum values are inhibited comparedwith thosemeasured in de-ionized water. The inhibition effect is ascribed to the coverage ofsurface-active sites i.e. steps and kinks by Cu2+ hydrated ions and com-plexes, decreasing the energy of dissolution system. Therefore, the cov-erage of active sites increaseswith Cu2+ concentrations, causing a lowervsum (Xu and Higgins, 2011).

4.2.2. The occupation of Cu2+ into Ca2+ vacancies and the hydroxylation ofCa2+

Defect vacancies have significant effects on the stabilization of polarsurfaces and the hydroxylation of Ca2+ (Pokrovsky and Schott, 2002;Ruiz-Agudo et al., 2010). First of all, the generation of defects favorsthe dissociation of water molecules, boosting the hydroxylation of cat-ions bonded on calcite surfaces. In the O 1s core level of calcite surfaces,the newly formed signal at higher binding energy (532.8± 0.2 eV) wellcorresponds with the formation of S∙Ca-OH (Stipp and Hochella, 1991).Besides, the occupation of Ca2+ vacancies by Cu2+ would produce(CuxCa1-x)CO3 and cause electron loss of oxygen, making the signal ofO1s core level to shift to higher binding energy, too. Furthermore,Bader charge distribution and XPS analysis both support charge transfertrends in general (Patterson et al., 2013). Comparedwith the charge dis-tribution after the adsorption of Cu2+ into the Ca2+ vacancy, the chargedensity of oxygen reduced 0.15 e, which supported the observation thatnewly formed signal of O 1s core level emerged at 532.8±0.2 eV.More-over, on the basis of previous studies, Ca 2p core levels at 346.9 eV and

Table 4Diffusion coefficients, D (Awakura et al., 1988; Ruiz-Agudo et al., 2011) and ion energyconstants, ΦK (Fersman, 1937).

SO42− NO3

− Cl− K+ Cu2+

D (10−5 cm2·s−1) 0.70–1.50 1.92 1.77 1.83 0.53–0.58ΦK 0.70 0.18 0.25 0.36 2.10

350.4 eV observed on calcitewere assigned to Ca binding to theO in car-bonate (Christie et al., 1983; Demri and Muster, 1995). Signals at 348.0±0.3 eV and 351.5± 0.3 eV of Ca 2p core levels are different from thoseof its polymorphisms, such as aragonite (347.2 eV and 350.7 eV) andvaterite (346.6 eV and 350.1 eV) (Chu et al., 2013), also indicating thegeneration of S∙Ca-OH caused by foreign Cu2+. Finally, since there areno direct bonding between Ca\\Cu and C\\Cu, the charge density ofthe neighboring Ca and C around Cu only fluctuated slightly (b0.01 e).Therefore, these obvious changes emerged in Ca 2p core levels of calcitesurfaces dissolved in Cu(NO3)2 solutions arise from the dissociation ofwater molecules enhanced by Cu2+ occupation on calcite surfaces(Lardge et al., 2009, 2010).

Additionally, Cu 2p core levels of calcite surfaces showed differentCu-bearing phases. These signals at lower binding energy (932.8 ±0.1 eV and 952.3 ± 0.1 eV) are ascribed to CuO which is produced bythe decomposition of Cu(OH)2 (Moretti et al., 1989). Signals at 935.0± 0.1 eV and 954.6 ± 0.2 eV suggest the existence of Cu(OH)2, Cu2

(OH)2(CO3)2, Cu2(OH)2CO3 and (CuxCa1-x)CO3 (Wagner, 1979; Elzingaand Reeder, 2002; Elzinga et al., 2006; Deroubaix and Marcus, 2010)which are likely precursors of granular azurite identified by TEM(Fig. S6; Fig. 11). These amorphous Cu-bearing phases detected by XPSand TEM are consistent with precipitated particles observed in AFM(Fig. 4; Figs. 6, 7). Konrad-Schmolke et al. (2018) also proposed that pre-cipitations of minerals occur directly by repolymerization of the

Fig. 13. Etch pit spreading rates (vsum nm s−1) on the calcite (10.4) surface of selected ionsas a function of the difference in the diffusion coefficients (ΔD) of ions composing therespective salt.

Scheme 1. Schematic representation of calcite dissolution in Cu2+-bearing solutions.


amorphous material at the product surface, which perfectly explainsour results.

The incorporation of Cu2+ into Ca2+vacancies changes the reactivityof calcite surfaces. Since Cu2+ is a borderline Lewis acid while Ca2+ is ahard Lewis acid, Cu2+ is softer than Ca2+ (Hancock and Martell, 1996).Similarly, the softness of base follows the order OH– N CO3

2– (M. Xu et al.,2017; H. Xu et al., 2017). Hence, it is common to form OH-bearing car-bonate phases for Cu2+ instead of anhydrous Cu-carbonate like Ca2+

(Pearson, 1963; Usman, 2008). When Cu-OH is formed on calcite sur-faces, the\\OH will be shared by neighboring Ca2+ (Fig. 12D). Besides,on the basis of calculations, the adsorption energy of (01.2)Cu-OH ishigher than that of (01.2)Ca-OH, and thus the configuration of the formeris less stable (Fig. 12C–D; Table 2). Therefore, the formation of Cu-OHwill change the behavior of neighboring Ca2+, which contributes to cal-cite dissolution at 1 mM ≤ cCu2+ ≤ 10 mM.

4.3. Effects of solution chemistry on calcite dissolution

When the pH of solutionwas kept at 4.5, the reaction system is a hy-brid control model with both mass transfer control and surface control.We discovered that dissolution rates of etch pits on calcite surfaces areincreased with higher Cu2+ concentrations (1 mM ≤ cCu2+ ≤ 10 mM),which is similar to the conclusion of Yoshino and Kagi (2008) that thedissolution rate constant of calcite is affected by the concentration ofaspartic acid. Therefore, the mass transfer control is likely to be a pre-dominance at higher Cu2+ concentrations, leading to a higher dissolu-tion rate constant increased by mass transfer control than the onedecreased by surface control.

To investigate effects of different ion types in solutions on calcite dis-solution, differences in diffusion coefficient (ΔD) of the ionic salt con-stituents in solutions and ion energy constants (ΦK) of ions areutilized to characterize various ions involved in this study (Table 4).Etch pits spreading rates (vsum) were plotted against the difference inthe diffusion coefficient of the ionic salts constituents (ΔD) (Fig. 13),which is a measure of ion separation in solution (Ruiz-Agudo et al.,2010). A lower ΔD value represents more paired ions and less non-paired ions during calcite dissolution. Non-paired ions in electrolyte so-lution inhibit calcite dissolution by electrostatic interaction which is as-cribed to the stabilization of the hydration layer of Ca2+ on calcitesurfaces (Ruiz-Agudo et al., 2010). The number of non-paired ions inthese three types of Cu2+-bearing solutions is in the order of Cu(NO3)2 N CuCl2 N CuSO4, and thus vsum of etch pits formed on calcite (10.4)

surfaces is in the opposite order. Similarly, the quantity of non-pairedions in copper salt solutions is less than that in potassium solutions,which both contain the same anion types and concentrations, leadingto the decreased order of vsum as CuSO4 N K2SO4 and CuCl2 N KCl(Fig. 13). Interestingly, whatwe observed in calcite dissolution is similarto the phenomena of dolomite dissolution (Ruiz-Agudo et al., 2011).

The increase of ΦK is generally in accordance with the decrease ofsolubility (Perel'man, 1968). In the condition of low ionic strength(0.3–30 mM) of Cu2+-bearing solutions, a less ΦK of ions means agreater solubility of corresponding ionic salt, indicating less pairedions and more non-paired ions (Collins, 1997), and therefore etch pitsspreading rate (vsum) is smaller in this case (Fig. S7).

It is noteworthy that calcite dissolutionwith increase of the local sat-uration index contributes to variation of the Ca2+ activity, which also af-fects the spreading rate of calcite dissolution in CuSO4 solutions at 1mM≤ cCu2+ ≤ 10mM. Because Ca2+ and SO4

2− are ascribed to hard Lewis acidand base respectively, it is easy for them to form strong ion pairs CaSO4

(aq) or complex (Hancock and Martell, 1996). Thus, the activity of dis-solved Ca2+ decreases, which promotes the release of Ca2+ from calcitesurfaces.

4.4. The mechanism of calcite dissolution in Cu2+-bearing solutions andimplications

The coupling effect of surface structure and solution chemistry de-termines calcite dissolution behavior. Calcite dissolution is inhibited atcCu2+ ≤ 0.1 mM, which is influenced by the coverage of active sites,namely, surface structure. Additionally, when the concentration of Cu2+-bearing solutions is controlled at 1 mM ≤ cCu2+ ≤ 10mM, the spread-ing rate is positively related to the increase of solute concentrations. Inthis case, both surface structure and solution chemistry accelerate therelease of Ca2+ from calcite surfaces, promoting dissolution-precipitation (the formation of Cu-bearing precipitations) (Scheme 1).

The coupling effect disclosed for the Cu2+ and calcite dissolution inour study is likely to provide important insights into carbonate biomin-eralization. For example, the growth of coastal organisms may also beinfluenced by both their surface structures/properties (e.g. exposure ofactive sites/defects/hydroxylation) and solution chemistry (e.g. diffu-sion of organic molecules/inorganic ions). Another interesting implica-tion of our discoveries is that the dissolution rate of calcite depends onanion types and metal ion concentrations, suggesting that we need to


consider various factors as much as possible when the dissolution rateof global carbonate is estimated.

5. Conclusions

In situ atomic force microscopy measurements of the interactionsbetween calcite dissolution and SO4

2−, Cl− andNO3− of Cu2+-bearing so-

lutions at acid pH (4.5 and 2.6), combined with DFT calculations, XPSand TEM characterization, lead to the following conclusions.

(1) Anion types of Cu2+-bearing solutions strongly impact the mor-phological features of etch pits. Etch pits generated in CuSO4 so-lutions express unstable [010] steps under certain conditions,whereas the morphological characteristics of these etch pitsformed in CuCl2 and Cu(NO3)2 solutions are similar, both emerg-ing [421] and [010] steps.

(2) [421] and [010] steps of etch pits formed in Cu2+-bearing solu-tions are attributed to the stabilization of (01.2) and (00.1)polar surfaces with the former and the latter controlled by sitespecific and non-specific effects, respectively. The coverage ofsurface-active sites constrains calcite dissolution at lower Cu2+

concentrations (cCu2+ ≤ 0.1 mM).(3) The occupation of Cu2+ into Ca2+ vacancy and the formation of

ion pairs both impact calcite dissolution at higher Cu2+ concen-trations (1 mM ≤ c Cu2+ ≤ 10 mM). Incorporated Cu2+ shares\\OH with neighboring Ca2+, resulting in the removal of Ca2+.The formation of CaSO4 (aq) ion pairs in CuSO4 solution also en-hances calcite dissolution. Besides, spreading rates of etch pits(vsum) are negatively related to the difference in the diffusion co-efficient of the ionic salts constituents (ΔD), i.e., vsum is in theorder of CuSO4 N CuCl2 N Cu(NO3)2.

(4) Both concentrations and anion types of Cu2+-bearing solutionsshould be considered when calcite dissolution, carbonate min-erals transformation and Cu2+ migration are concerned.

Acknowledgments

The authors gratefully acknowledge the National Key R&D Programof China (Grant No. 2017YFC0602305), the Science and TechnologyPlanning Project of Guangdong Province, China (Grant No.2017B030314175), the National Natural Science Foundation of China(Grant No. 41825003) and China Postdoctoral Science Foundation(Grant No. 2018M643220). This is a contribution of No. IS-2667 fromGIGCAS.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.scitotenv.2019.02.232.

References

Alkattan, M., Oelkers, E.H., Dandurand, J.L., Schott, J., 2002. An experimental study of cal-cite dissolution rates at acidic conditions and 25 °C in the presence of NaPO3 andMgCl2. Chem. Geol. 190, 291–302.

Arvidson, R.S., Collier, M., Davis, K.J., Vinson, M.D., Amonette, J.E., Luttge, A., 2006. Magne-sium inhibition of calcite dissolution kinetics. Geochim. Cosmochim. Acta 70,583–594.

Awakura, Y., Doi, T., Majima, H., 1988. Determination of the diffusion coefficients ofCuSO4, ZnSO4, and NiSO4 in aqueous solution. Metall. Trans. B 19, 5–12.

Bader, R.F.W., 1990. Atoms inmolecules: a quantum theory. International Series of Mono-graphs in Chemistry 22. Oxford University Press, Oxford.

Beus, A.A., Grabovskaya, L.I., Tikhonova, N.V., 1976. Environmental Geochemistry. Nedra,Moscow.

Borgohain, K., Murase, N., Mahamuni, S., 2002. Synthesis and properties of Cu2O quantumparticles. J. Appl. Phys. 92, 1292–1297.

Bruno, M., Massaro, F.R., Rubbo, M., Prencipe, M., Aquilano, D., 2010. (10.4), (01.8), (01.2),and (00.1) twin laws of calcite (CaCO3): equilibrium geometry of the twin boundaryinterfaces and twinning energy. Cryst. Growth Des. 10, 3102–3109.

Bruno, M., Massaro, F.R., Pastero, L., Costa, E., Rubbo, M., Prencipe, M., et al., 2013. New es-timates of the free energy of calcite/water interfaces for evaluating the equilibriumshape and nucleation mechanisms. Cryst. Growth Des. 13, 1170–1179.

Christie, A., Lee, J., Sutherland, I., Walls, J., 1983. An XPS study of ion-induced composi-tional changes with group II and group IV compounds. Appl. Surf. Sci. 15, 224–237.

Chu, D.H., Vinoba, M., Bhagiyalakshmi, M., Baek, I.H., Nam, S.C., Yoon, Y., et al., 2013. CO2

mineralization into different polymorphs of CaCO3 using an aqueous-CO2 system. RSCAdv. 3, 21722–21729.

Collins, K.D., 1997. Charge density-dependent strength of hydration and biological struc-ture. Biophys. J. 72, 65–76.

Compton, R.G., Unwin, P.R., 1990. The dissolution of calcite in aqueous solution at pHb4:kinetics and mechanism. Philos. Trans. R. Soc. 330, 1–45.

Cubillas, P., Köhler, S., Prieto, M., Causserand, C., Oelkers, E.H., 2005. How domineral coat-ings affect dissolution rates? An experimental study of coupled CaCO3 dissolution—CdCO3 precipitation. Geochim. Cosmochim. Acta 69, 5459–5476.

Davis, K.J., Dove, P.M., Wasylenki, L.E., De Yoreo, J.J., 2004. Morphological consequences ofdifferential Mg2+ incorporation at structurally distinct steps on calcite. Am. Mineral.89, 714–720.

Demri, B., Muster, D., 1995. XPS study of some calcium compounds. J. Mater. Process.Technol. 55, 311–314.

Deroubaix, G., Marcus, P., 2010. X-ray photoelectron spectroscopy analysis of copper andzinc oxides and sulphides. Surf. Interface Anal. 18, 39–46.

Elzinga, E.J., Reeder, R.J., 2002. X-ray absorption spectroscopy study of Cu2+ andZn2+ adsorp-tion complexes at the calcite surface: implications for site-specific metal incorporationpreferences during calcite crystal growth. Geochim. Cosmochim. Acta 66, 3943–3954.

Elzinga, E.J., Rouff, A.A., Reeder, R.J., 2006. The long-term fate of Cu2+, Zn2+, and Pb2+ ad-sorption complexes at the calcite surface: an X-ray absorption spectroscopy study.Geochim. Cosmochim. Acta 70, 2715–2725.

Feelym, R.A., Sabine, C.L., Lee, K., Berelson, W., Kleypas, J., Fabry, V.J., et al., 2004. Impact ofanthropogenic CO2 on the CaCO3 system in the oceans. Science 305, 362–366.

Fersman, A.E., 1937. Geochemistry. Third ed. Goskhimizdat, Moscow.Foster, P., Hunt, D.T.E., Morris, A.W., 1978. Metals in an acid mine stream and estuary. Sci.

Total Environ. 9, 75–86.Freij, S.J., Putnis, A., Astilleros, J., 2004. Nanoscale observations of the effect of cobalt on

calcite growth and dissolution. J. Cryst. Growth 267, 288–300.Freij, S.J., Godelitsas, A., Putnis, A., 2005. Crystal growth and dissolution processes at the

calcite–water interface in the presence of zinc ions. J. Cryst. Growth 273, 535–545.Ghijsen, J., Tjeng, L.H., Elp, J.V., Eskes, H., Westerink, J., Sawatzky, G.A., et al., 1988. Elec-

tronic structure of Cu2O and CuO. Phys. Rev. B 38, 11322.Giudici, G.D., 2002. Surface control vs. diffusion control during calcite dissolution: depen-

dence of step-edge velocity upon solution pH. Am. Mineral. 87, 1279–1285.Gledhill, D.K., Morse, J.W., 2004. Dissolution kinetics of calcite in NaCl–CaCl2–MgCl2 brines

at 25 °C and 1 bar pCO2. Aquat. Geochem. 10, 171–190.Godelitsas, A., Astilleros, A., Hallam, J.M., Löns, K.R., Putnis, J., 2003a. Microscopic and

spectroscopic investigation of the calcite surface interacted with Hg(II) in aqueoussolutions. Mineral. Mag. 67, 1193–1204.

Godelitsas, A., Astilleros, J.M., Hallam, K., Harissopoulos, S., Putnis, A., 2003b. Interaction ofcalcium carbonates with lead in aqueous solutions. Environ. Sci. Technol. 37,3351–3360.

Gutjahr, A., Dabringhaus, H., Lacmann, R., 1996. Studies of the growth and dissolution ki-netics of the CaCO3 polymorphs calcite and aragonite II. The influence of divalent cat-ion additives on the growth and dissolution rates. J. Cryst. Growth 158, 310–315.

Hancock, R.D., Martell, A.E., 1996. Hard and soft acid-base behavior in aqueous solution:steric effects make some metal ions hard: a quantitative scale of hardness-softnessfor acids and bases. J. Chem. Educ. 73, 654–661.

Hay, M.B., Workman, R.K., Manne, S., 2003. Mechanisms of metal ion sorption on calcite:composition mapping by lateral force microscopy. Langmuir 19, 3727–3740.

Henkelman, G., Arnaldsson, A., Jónsson, H., 2006. A fast and robust algorithm for Bader de-composition of charge density. Comput. Mater. Sci. 36, 354–360.

Hong, M., Xu, J., Teng, H.H., 2016. Evolution of calcite growth morphology in the presenceof magnesium: implications for the dolomite problem. Geochim. Cosmochim. Acta172, 55–64.

Kang, X., Hu, W., Cao, J., Jin, J., Wu, H., Zhao, Y., et al., 2018. Selective dissolution of alkalifeldspars and its effect on Lower Triassic sandy conglomerate reservoirs in theJunggar Basin, northwestern China. Geol. J. 53, 475–499.

Kashem, M.A., Singh, B.R., 1999. Heavy metal contamination of soil and vegetation in thevicinity of industries in Bangladesh. Water Air Soil Pollut. 115, 347–361.

Kitamura, M., Hosoya, S., Sunagawa, I., 1979. Re-investigation of the re-entrant corner ef-fect in twinned crystals. J. Cryst. Growth 47, 93–99.

Konrad-Schmolke, M., Halama, R., Wirth, R., Thomen, A., Klitscher, N., Morales, L., et al.,2018. Mineral dissolution and reprecipitation mediated by an amorphous phase.Nat. Commun. 9, 1637–1646.

Kouzmanov, K., Moritz, R., Quadt, A.V., Chiaradia, M., Peytcheva, I., Fontignie, D., et al.,2009. Late cretaceous porphyry Cu and epithermal Cu–Au association in the SouthernPanagyurishte District, Bulgaria: the paired Vlaykov Vruh and Elshitsa deposits. Min-eral. Deposita 44, 611–646.

Kowacz, M., Putnis, A., 2008. The effect of specific background electrolytes on water struc-ture and solute hydration: consequences for crystal dissolution and growth. Geochim.Cosmochim. Acta 72, 4476–4487.

Kresse, G., Furthmuller, J., 1996. Efficiency of ab-initio total energy calculations for metalsand semiconductors using a plane-wave basis set. Comput. Mater. Sci. 6, 15–50.

Kresse, G., Joubert, D., 1999. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 59, 1758–1775.



http://refhub.elsevier.com/S0048-9697(19)30730-2/rf0005




























































































































Lardge, J.S., Duffy, D.M., Gillan, M.J., 2009. Investigation of the interaction of water withthe calcite (10.4) surface using ab initio simulation. J. Phys. Chem. C 113, 7207–7212.

Lardge, J.S., Duffy, D.M., Gillan, M.J., Watkins, M., 2010. Ab initio simulations of the inter-action between water and defects on the calcite (10.4) surface. J. Phys. Chem. C 114,2664–2668.

Lea, A.S., Amonette, J.E., Baer, D.R., Liang, Y., Colton, N.G., 2001. Microscopic effects of car-bonate, manganese, and strontium ions on calcite dissolution. Geochim. Cosmochim.Acta 65, 369–379.

Lee, Y.J., Elzinga, E.J., Reeder, R.J., 2005. Cu(II) adsorption at the calcite–water interface inthe presence of natural organicmatter: kinetic studies andmolecular-scale character-ization. Geochim. Cosmochim. Acta 69, 49–61.

Lukin, A., Dauvalter, V., Kashulin, N., Yakovlev, V., Sharov, A., Vandysh, O., 2003. Assess-ment of copper-nickel industry impact on a subarctic lake ecosystem. Sci. Total Envi-ron. 306, 73–83.

Martin-Dupont, F., Gloaguen, V., Granet, R., Guilloton, M., Morvan, H., Krausz, P., 2002.Heavy mental adsorption by crude coniferous barks: a modelling study. J. Environ.Sci. Health A 37, 1063–1073.

Moretti, G., Fierro, G., Lo Jacono, M., Porta, P., 1989. Characterization of CuO–ZnO catalystsby X-ray photoelectron spectroscopy: precursors, calcined and reduced samples. Surf.Interface Anal. 14, 325–336.

Oh, C., Han, Y.S., Park, J.H., Bok, S., Cheong, Y., Yim, G., et al., 2016. Field application of se-lective precipitation for recovering Cu and Zn in drainage discharged from an operat-ing mine. Sci. Total Environ. 557-558, 212–220.

Panfili, I., Bartucca, M.L., Ballerini, E., Del, B.D., 2017. Combination of aquatic species andsafeners improves the remediation of copper polluted water. Sci. Total Environ.601, 1263–1270.

Patterson, M.C., Nie, X., Wang, F., Kurtz, R.L., Sinnott, S.B., Asthagiri, A., et al., 2013. Growthand structure of Cu and Au on the nonpolar ZnO (10.0) surface: STM, XPS, and DFTstudies. J. Phys. Chem. C 117, 18386–18397.

Pearson, R.G., 1963. Hard and soft acids and bases. J. Am. Chem. Soc. 85, 3533–3539.Perdew, J.P., Burke, K., Ernzerhof, M., 1996. Generalized gradient approximation made

simple. Phys. Rev. Lett. 77, 3865–3868.Perel'man, A.I., 1968. Geochemistry of Epigenetic Processes (Hypergenesis Zone). Nedra,

Moscow.Pérez-Garrido, C., Fernández-Díaz, L., Pina, C.M., Prieto, M., 2007. In situ AFM observations

of the interaction between calcite surfaces and Cd-bearing aqueous solutions. Surf.Sci. 601, 5499–5509.

Perlatti, F., Otero, X.L., Macias, F., Ferreira, T.O., 2014. Geochemical speciation and dynamicof copper in tropical semi-arid soils exposed to metal-bearing mine wastes. Sci. TotalEnviron. 500-501, 91–102.

Pokrovsky, O.S., Schott, J., 2002. Surface chemistry and dissolution kinetics of divalentmetal carbonates. Environ. Sci. Technol. 36, 426–432.

Reeder, R.J., 1996. Interaction of divalent cobalt, zinc, cadmium, and barium with the cal-cite surface during layer growth. Geochim. Cosmochim. Acta 60, 1543–1552.

Ruiz-Agudo, E., Putnis, C., 2012. Direct observations of mineral fluid reactions usingatomic force microscopy: the specific example of calcite. Mineral. Mag. 76, 227–253.

Ruiz-Agudo, E., Putnis, C., Jiménez-López, C., Rodriguez-Navarro, C., 2009. An atomic forcemicroscopy study of calcite dissolution in saline solutions: the role of magnesiumions. Geochim. Cosmochim. Acta 73, 3201–3217.

Ruiz-Agudo, E., Kowacz, M., Putnis, C.V., Putnis, A., 2010. The role of background electro-lytes on the kinetics and mechanism of calcite dissolution. Geochim. Cosmochim.Acta 74, 1256–1267.

Ruiz-Agudo, E., Urosevic, M., Putnis, C.V., Rodríguez-Navarro, C., Cardell, C., Putnis, A.,2011. Ion-specific effects on the kinetics of mineral dissolution. Chem. Geol. 281,364–371.

Salem, M.R., Mangood, A.H., Hamdona, S.K., 1994. Dissolution of calcite crystals in thepresence of some metal ions. J. Mater. Sci. 29, 6463–6467.

Sánchez, V.M., Miranda, C.R., 2014. Modeling acid oil component interactions with car-bonate reservoirs: a first-principles view on low salinity recovery mechanisms.J. Phys. Chem. C 118, 19180–19187.

Shiraki, R., Rock, P.A., Casey, W.H., 2000. Dissolution kinetics of calcite in 0.1 M NaCl solu-tion at room temperature: an atomic force microscopic (AFM) study. Aquat.Geochem. 6, 87–108.

Sigman, D.M., Boyle, E.A., 2000. Glacial/interglacial variations in atmospheric carbon diox-ide. Nature 407, 859–869.

Sjöberg, E.L., Rickard, D.T., 1985. The effect of added dissolved calcium on calcite dissolu-tion kinetics in aqueous solutions at 25 °C. Chem. Geol. 49, 405–413.

Spahić, M., Sakan, S., Cvetković, Ž., Tančić, P., Trifković, J., Nikić, Z., et al., 2018. Assessmentof contamination, environmental risk, and origin of heavymetals in soils surroundingindustrial facilities in Vojvodina, Serbia. Environ. Monit. Assess. 190, 208–228.

Stipp, S.L., Hochella, M.F., 1991. Structure and bonding environments at the calcite surfaceas observed with X-ray photoelectron spectroscopy (XPS) and low energy electrondiffraction (LEED). Geochim. Cosmochim. Acta 55, 1723–1736.

Subhas, A.V., Rollins, N.E., Berelson, W.M., Dong, S., Erez, J., Adkins, J.F., 2015. A novel de-termination of calcite dissolution kinetics in seawater. Geochim. Cosmochim. Acta170, 51–68.

Teng, H.H., 2005. AFM measurement of step kinetics for the growth and dissolution ofcrystallites. Spectroscopy 20, 16–20.

Teng, H.H., Dove, P.M., 1997. Surface site-specific interactions of aspartate with calciteduring dissolution: implications for biomineralization. Am. Mineral. 82, 878–887.

Terjesen, S.G., Erga, O., Thorsen, G., Ve, A., 1961. Phase boundary processes as rate deter-mining steps in reactions between solids and liquids: the inhibitory action of metalions on the formation of calcium bicarbonate by the reaction of calcite with aqueouscarbon dioxide. Chem. Eng. Sci. 14, 277–288.

Torres, E., Ayora, C., Canovas, C.R., García-Robledo, E., Galván, L., Sarmiento, A.M., 2013.Metal cycling during sediment early diagenesis in a water reservoir affected by acidmine drainage. Sci. Total Environ. 461-462, 416–429.

Usman, A.R.A., 2008. The relative adsorption selectivities of Pb, Cu, Zn, Cd and Ni by soilsdeveloped on shale in New Valley, Egypt. Geoderma 144, 334–343.

Vavouraki, A.I., Putnis, C.V., Putnis, A., Koutsoukos, P.G., 2010. Crystal growth and dissolu-tion of calcite in the presence of fluoride ions: an atomic force microscopy study.Cryst. Growth Des. 10, 60–69.

Villiers, S.D., 2005. Foraminiferal shell-weight evidence for sedimentary calcite dissolu-tion above the lysocline. Deep-Sea Res. I 52, 671–680.

Vinson, M.D., Arvidson, R.S., Luttge, A., 2007. Kinetic inhibition of calcite (10.4) dissolutionby aqueous manganese (II). J. Cryst. Growth 307, 116–125.

Wagner, C.D., 1979. Handbook of X-Ray Photoelectron Spectroscopy: A Reference Book ofStandard Data for Use in X-Ray Photoelectron Spectroscopy. Physical Electronics Di-vision, Perkin-Elmer Corp, Eden Prairie.

Wu, C., Wang, X., Zhao, K., Cao, M., Xu, H., Xia, D., et al., 2011.Molecular modulation of cal-cite dissolution by organic acids. Cryst. Growth Des. 11, 3153–3162.

Wu, C., Zhao, K., Wang, X., Cao, M., Xu, H., Lu, J.R., 2012. Dissolution of the calcite (10.4)face under specific calcite–aspartic acid interaction as revealed by in situ atomicforce microscopy. Cryst. Growth Des. 12, 2594–2601.

Xu, M., Higgins, S.R., 2011. Effects of magnesium ions on near-equilibrium calcite dissolu-tion: step kinetics and morphology. Geochim. Cosmochim. Acta 75, 719–733.

Xu, M., Hu, X., Knauss, K.G., Higgins, S.R., 2010. Dissolution kinetics of calcite at 50–70 °C:an atomic force microscopic study under near-equilibrium conditions. Geochim.Cosmochim. Acta 74, 4285–4297.

Xu, M., Kovarik, L., Arey, B.W., Felmy, A.R., Rosso, K.M., Kerisit, S., 2014. Kinetics andmech-anisms of cadmium carbonate heteroepitaxial growth at the calcite (10.4) surface.Geochim. Cosmochim. Acta 134, 221–233.

Xu, M., Ilton, E.S., Engelhard, M.H., Qafoku, O., Felmy, A.R., Rosso, K.M., et al., 2015. Hetero-geneous growth of cadmium and cobalt carbonate phases at the (10.4) calcite sur-face. Chem. Geol. 397, 24–36.

Xu, M., Riechers, S.L., Ilton, E.S., Du, Y., Kovarik, L., Varga, T., et al., 2017. Manganese-calcium intermixing facilitates heteroepitaxial growth at the (10.4) calcite-water in-terface. Chem. Geol. 470, 152–163.

Xu, H., Xu, D.C., Wang, Y., 2017. Natural indices for the chemical hardness/softness ofmetal cations and ligands. ACS Omega 2, 7185–7193.

Yoshino, T., Kagi, H., 2008. Effects of aspartic acid on calcite dissolution rate and solubility.Chem. Lett. 37, 508–509.

Zhang, F., Yan, C., Teng, H.H., Roden, E.E., Xu, H., 2013. In situ AFM observations of Ca–Mgcarbonate crystallization catalyzed by dissolved sulfide: implications for sedimentarydolomite formation. Geochim. Cosmochim. Acta 105, 44–55.

Zhu, J., Tang, C., Wei, J., Li, Z., Laipan, M., He, H., et al., 2017. Structural effects on dissolu-tion of silica polymorphs in various solutions. Inorg. Chim. Acta 471, 57–65.





























































































































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Science of the Total Environment · Kinetics and mechanisms of the interaction between the calcite (10.4) ... Mineral dissolution, commonly presenting in weathering crust, plays signiﬁcant