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Frost, Ray L. and Keeffe, Eloise C. and Reddy, B. Jagannadha (2010) Characterisation of Ni carbonate-bearing minerals by UV-Vis-NIR spectroscopy. Transition Metal Chemistry, 35(3). pp. 279-287.

© Copyright 2010 Springer Verlag

1

Characterisation of Ni carbonate-bearing minerals by UV-Vis-NIR spectroscopy 1

2

B. Jagannadha Reddy, Eloise C. Keeffe and Ray L. Frost 3

4

Inorganic Materials Research program, School of Physical and Chemical Sciences, 5

Queensland University of Technology, GPO Box 2434, Brisbane Queensland 4001, 6

Australia. 7

Abstract 8

9

Four nickel carbonate-bearing minerals from Australia have been investigated 10

to study the effect of Ni for Mg substitution. The spectra of nullaginite, zaratite, 11

widgiemoolthalite and takovite show three main features in the range 26720-25855 12

cm-1(1-band), 15230-14740 cm-1(2-band) and 9200-9145 cm-1(3-band) which are 13

characteristic of divalent nickel ion in six-fold coordination. Crystal Field 14

Stabilization Energy (CFSE) of Ni2+ in the four carbonates is calculated from the 15

observed 3A2g(3F) 3T2g(

3F) transition. CFSE is dependent on mineralogy 16

crystallinity and chemical composition (Al/Mg-content). The splitting of 1-band and 17

3-band and non-Gaussian shape of 3-band in the minerals are the effects of Ni-site 18

distortion from regular octahedron. The effect of structural cation substitutions (Mg2+, 19

Ni2+, Fe2+ and trivalent cations, Al3+, Fe3) in the carbonate minerals is noticed on 20

band shifts. Electronic bands in the UV-Vis-NIR spectra and the overtones and 21

combination bands of OH and carbonate ion in NIR show shift to higher 22

wavenumbers and shift is more significant in the case of widgiemoolthalite and 23

takovite. 24

25

26

Keywords: Inorganic compounds; Near-infrared spectroscopy; Crystal fields; Optical 27

properties 28

29

30

31

32 Author for correspondence (r.frost@qut.edu.au)

2

1. Introduction 33

34

Nullaginite Ni2(CO3)(OH)2 and zaratite Ni3(CO3)(OH)4.4H2O are the two 35

hydroxy nickel carbonate minerals. Nullaginite belongs to rosasite group [1-8] and is 36

found to form in the oxidised zone of nickel rich hydrothermal ore deposits. Zaratite 37

is of an unknown structure and is an uncommon secondary mineral formed by 38

alteration of chromite, pentlandite, pyrrhotite and millerite in ultramafic rocks. 39

Widgiemoolthalite (Ni,Mg)5(CO3)4(OH)2.4-5H2O, a new Ni analogue of 40

hydromagnesite associates with hydrothermal nickel deposit [9] and takovite is a 41

nickel hydroaluminate with composition Ni6Al2(CO3,OH) (OH)16.4H2O [10,11]. 42

There are a significant number of nickel carbonates with mixed cations especially 43

with a layered double hydroxide (LDH) structure which include carboydite, 44

comblainite, mountkeithite, reevesite and takovite [12-18]. It is important to study the 45

gaspeite-hellyerite-nullaginite assemblage and the relative stability of the minerals. 46

The reason is that these minerals are the stable minerals at one atmosphere. 47

48

Nullaginite Ni2(CO3)(OH)2 is closely related to rosasite and glaukosphaerite, 49

occurs as bright green nodular grains in a Ni-rich assemblage from the Otway deposit, 50

Nullagine district, Western Australia [1]. Several phases can be grouped into the 51

malachite-rosasite group minerals, with a general formula M22+(CO3)(OH)2 that 52

includes malachite (M22+ = Cu) and rosasite ( M2

2+ = Cu,Zn) together with rare species 53

like mcguinnessite (Mg,Cu), glaukosphaerite (Cu,Ni), nullaginite (Ni) and zaratite 54

(Ni) [19]. The crystal structure determination of rosasite and mcguinnessite from 55

powder data shows they are isostructural, with space group P21/a, and cell constants a 56

= 1.2898, b = 0.9371 and c = 0.3162 nm for rosasite and a = 1.2918, b = 0.9392 and c 57

= 0.3162 nm for mcguinnessite. It has been shown that the structures of both 58

malachite and rosasite are built up by “octahedral” walls of edge-sharing M22+ 59

polyhedra, linked together through corner sharing to form infinite layers, and 60

“triangular” CO3 groups, which assure their interlayer connection. Two distinct 61

models are realised in this mineral group and are denoted as malachite-like and 62

rosasite-like structures [20]. 63

64

Four samples of natural takovite from different origins were examined by X-65

ray powder diffraction and chemical analysis. The observed cell parameters are 66

3

closely similar to those of pyroaurite and hydrotalcite [11]. The XRD pattern of 67

widgiemoolthalite, from Western Australia [9] suggests a high degree of structure 68

disorder and the cell parameters similar to that of hydromagnesite with a = 1.006, b = 69

0.875 and c = 0.832 nm. The minerals of the pyroaurite and sjogrenite group 70

represented by a common formula Mg6Fe2(OH)16(CO3).4H2O form hexagonal, platy 71

crystals. In other members of the group, Mg2+ may be replaced by dipositive cations 72

of similar size for example, Ni2+ and Fe3+ by suitable tripositive cations like Al3+, Cr3+ 73

[21]. 74

Infrared and Raman spectroscopy have been applied to investigate carbonates. 75

A detailed single crystal Raman study of selected mineral carbonates has been 76

undertaken [22-28]. This would seem to be important in the context of the stability of 77

the hydroxy carbonates of Ni, Zn, Cu and Pb. However electronic and vibrational 78

spectroscopy of many carbonates of Ni has not been undertaken. This may be due to 79

the unknown structure of some nickel hydroxy carbonates. Few infrared spectral 80

studies of related minerals such as the rosasite group have been forthcoming [29-31]. 81

82

Carbonate minerals produce absorption features from visible-near-infrared to 83

thermal infrared spectral regions. Structural variations accompanied by the 84

substitution of Mg2+ or Ca2+ by other divalent cations like Cu2+ , Co2+, Ni2+, Fe2+ can 85

be studied through the electronic spectral features in UV-Vis-NIR region. These 86

spectra can be used for the determination of the coordination state of transition metals 87

in minerals [32-36]. Several strong bands due to vibrations of the carbonate radical 88

and OH units occur in NIR and IR regions [37-40]. Recent studies have shown that 89

the formation of secondary precipitates plays an important role in the retention of Ni 90

and Co by clay minerals. It is evident that a precise knowledge of the nature of these 91

precipitates is crucial to predict the fate of Ni and Co in the environment, because of 92

the solubility of the precipitates strongly depends on their structure and composition 93

[41-43]. Several studies have already been reported concerning optical absorption 94

spectra Ni-hydrous silicates [44-46] and Ni-carbonate minerals of zaratite and 95

takovite have been published [47]. Subsequently Ni in clay minerals has been 96

preciously studied to know the mechanism of Ni-Mg substitution [41,48]. 97

98

Spectroscopic properties of nickel bearing carbonates and silicates are still 99

quite lacking. In this paper we present the results of a systematic study of nickel-100

4

bearing carbonate minerals and compare the spectral properties with their structure 101

and composition. 102

103

2. Experimental 104

105

2.1. Sample description 106

107

The minerals used in this work are nullaginite (bright green), 108

widgiemoolthalite (bluish green) and takovite (pale green) were kindly supplied by 109

CSIRO, Australia and zaratite (green) was procured from Mineralogical Research 110

Co., U.S.A. The characterisation and composition of these minerals has already been 111

established and published. 112

113

2.2. UV-Vis spectroscopy 114

115

A Varian Cary 5000 UV-Visible NIR spectrophotometer, equipped with 116

Diffuse Reflectance Accessory (DRA) was employed to record the electronic 117

spectrum of the samples in the region between 200 and 1100 nm (50,000-9090 cm-1). 118

This technique allows the study of the reflectance spectra of the samples in the 119

powder form. The DRA consists of a 110 mm diameter integrating sphere, featuring 120

an inbuilt high performance photomultiplier. Each sample was placed in a powder cell 121

specifically designed for the instrument. Initially a base line was recorded using a 122

polytetrafluoroethylene (PTFE) reference cell covering the reflectance port. The 123

sample is then mounted over the port and the reflection off the sample surface was 124

collected by the sphere. The reflectance was therefore measured relative to the PTFE 125

disk. The diffuse reflectance measurements were converted into absorption (arbitrary 126

units) using the Kubelka-Munk function (f (R ) = (1- R )2/2R ). Data manipulation was 127

performed using Microsoft Excel. 128

2.3. Near-infrared (NIR) spectroscopy 129

130

NIR spectra were collected on a Nicolet Nexus FT-IR spectrometer with a Nicolet 131

Near-IR Fibreport accessory (Madison, Wisconsin). A white light source was used, 132

with a quartz beam splitter and TEC NIR InGaAs detector. Spectra were obtained 133

5

from 13,000 to 4000 cm-1 (0.77-2.50 µm) (770-2500 nm) by the co-addition of 64 134

scans at a spectral resolution of 8 cm-1. A mirror velocity of 1.266 m sec-1 was used. 135

The spectra were transformed using the Kubelka-Munk algorithm to provide spectra 136

for comparison with published absorption spectra. 137

138

Spectral manipulation such as baseline adjustment, smoothing and 139

normalisation were performed using the Spectracalc software package GRAMS 140

(Galactic Industries Corporation, NH, USA). Band component analysis was 141

undertaken using the Jandel ‘Peakfit’ software package which enabled the type of 142

fitting function to be selected and allows specific parameters to be fixed or varied 143

accordingly. Band fitting was done using a Lorentz-Gauss cross-product function with 144

the minimum number of component bands used for the fitting process. The Gauss-145

Lorentz ratio was maintained at values greater than 0.7 and fitting was undertaken 146

until reproducible results were obtained with squared correlations of r2 greater than 147

0.995. 148

149

3. Results and discussion 150

151

3.1. Nullaginite and zaratite 152

153

The six-fold coordination of Ni2+ in serpentine and talc [49], chrysotile [50], 154

nickel antimony sulphide mineral, ulmannite [51] and gaspeite [52] was established 155

from the study of optical absorption spectra of Ni-bearing minerals. The reflectance 156

spectra of the four Ni carbonate minerals were recorded using Varian Cary 5000 UV-157

Visible NIR spectrophotometer and transformed into absorbance coefficients using 158

the Kubelka-Munk function. The spectra have been decomposed by Gaussian analysis 159

to obtain each spectral feature corresponding to a band component and are illustrated 160

(for each sample). Three bands are expected for Ni2+ in an octahedral field [53]: 161 3A2g(

3F) 3T1g(3P) (1 band), 3A2g(

3F) 3T1g(3F) (2 band) and 3A2g(

3F) 3T2g(3F) 162

(3 band). The spectra of nullaginite and zaratite show three main features which are 163

characteristic of the presence of divalent nickel ion in six-fold coordination. The 164

spectral patterns of the two minerals are shown in Figs. 1, 2 and 3. Three broad 165

intense bands centred at 25955, 15230 and 9190 cm-1 in nullaginite are assigned to 166

6

spin-allowed transitions, 3A2g(3F) 3T1g(

3P), 3A2g(3F) 3T1g(

3F) and 3A2g(3F) 167

3T2g(3F). In addition, a prominent shoulder on the low wavenumber side of 2 band 168

arising from the spin-forbidden transition 3A2g(3F) 1Eg(

1D), invariably appeared in 169

all the four Ni-carbonates. For nullaginite the spin-forbidden transition is located at 170

13200 cm-1. The crystal field and Racah parameters, Dq and B are determined from 171

the observed band positions using the energy expressions [54]: 172

173 3A2g(

3F) 3T1g(3P): 15Dq + 13.5B = 25955 cm-1 (1) 174

3A2g(3F) 3T1g(

3F): 15Dq + 1.5B = 15230 cm-1 (2) 175

and 3A2g(3F) 3T2g(

3F): 10Dq = 9190 cm-1 (3) 176

B = 894 cm-1 is obtained from the relation, 1 - 2 = (25955 - 15230 cm-1) = 12B and 177

Dq = 919 cm-1 is a direct measure of crystal field parameter from 3. The ratio of 178

Dq/B has been used to determine the transition for the 29830 cm-1 band in the UV 179

region from the energy level diagram of d8 configuration (Ni2+) as 3A2g(3F) 1Eg(

1G) 180

[55]. 181

The spectral patterns of the two minerals look similar. The position and 182

intensity of the bands slightly vary from one another. Zaratite bands observed at 183

25855 (1-band), 14740 (2-band) and 9145 cm-1 (3-band) are assigned to the three 184

spin-allowed transitions of 3A2g(3F) 3T1g(

3P), 3A2g(3F) 3T1g(

3F) and 3A2g(3F) 185

3T2g(3F). The shoulder band extended to the 2 main band at13380 cm-1 is identified as 186

3A2g(3F) 1Eg(

1D) transition. The parameters evaluated from the zaratite bands are 187

Dq = 915 and B = 926 cm-1. The 1- and 3-bands show pure Gaussian shape as 188

observed in nickel hydroxide and nickel-doped ammonium-magnesium double 189

sulphate ( Tutton salt) and the absence of splitting confirms a regular octahedral 190

symmetry (Oh) for Ni2+ [56]. The line shape of the 3-band is particularly sensitive to 191

the site symmetry because of its dependence on the crystal field. The half-width (2800 192

cm-1) of 3 band in zaratite is slightly more than the half-width (2700 cm-1) observed 193

for nullaginite (Fig. 3). The result of non-Gaussian shape and splitting of the 3 band 194

into two main component bands; 9190 and 7880 cm-1for nullaginite and 9145 and 195

7910 cm-1 in zaratite may be assigned to the lowering of Ni-site to either tetragonal or 196

trigonal. 197

198

7

The spectra of the two hydroxyl-bearing nickel carbonates presented in Figs. 3 199

and 4 show OH overtone and combination bands resulting from structural hydroxyls 200

and water. A single band at 6845 cm-1 for OH overtone is seen in zaratite where as in 201

nullaginite this band appeared with structure at 7185-6745 cm-1. The difference in the 202

spectra may be explained by the compositional variations between the two carbonates 203

[57]. An observation of two strong OH vibrational modes in IR at 3600-3400 cm-1 and 204

the overtones of OH fundamentals around 7000 cm-1 in near-IR have been made in a 205

number of carbonate minerals [58-62]. Visible and near-infrared spectra of minerals 206

and rocks reported by Hunt and Salisbury [63] show a strong band at 5260 cm-1 which 207

is used as evidence of liquid water in minerals. Near-IR spectra in Fig. 4 show a broad 208

band from 4945-5155 cm-1 due to the presence of water both in nullaginite and 209

zaratite. The carbonate ion displays a strong absorption feature in the low 210

wavenumber region. The unsymmetrical band near 4300 cm-1 assigned to the 211

combination of the vibrational modes of CO32- is evidence for the reduction in 212

symmetry for carbonate ion. 213

214

3.2. Widgiemoolthalite and takovite 215

216

The electronic and vibrational spectra in the UV-Vis and NIR regions are 217

shown in Figs. 5, 6, 7 and 8. Notably, as can be expected from their structural 218

formulae difference, the spectral features of the carbonates-widgiemoolthalite 219

(Ni,Mg)5(CO3)4(OH)2.5H2O and takovite Ni6Al2(CO3,OH)(OH)16.4H2O are not 220

similar. The spectra in Fig. 5 allow us to extract cation-ordering information relevant 221

to the samples. The decomposition of the spectral patterns of widgiemoolthalite 222

exhibits three main bands in at 26200 (1), 15010 (2) and 9185 cm-1 (3), together 223

with spin-forbidden bands of low intensity band in the visible range at 20580 and the 224

shoulder to 2 band appear at 13760 cm-1. For takovite, the 1, 2 and 3 bands are 225

observed at 26720, 15140 and 9200 cm-1 while the spin forbidden bands appeared at 226

20540 and 13380 cm-1. Dq and B parameters obtained from the observed energies of 227

the bands are 918 and 932 cm-1 for widgiemoolthalite whereas in takovite these values 228

are 920 and 965 cm-1. The half-width of 3 band measured for widgiemoolthalite as 229

3150 cm-1 is larger than that for (2700 cm-1) takovite (Fig. 7). 230

231

8

The relative values of ∆○ obtained from the energy of the 3A2g(3F) 3T2g 232

transition allow us to calculate Crystal Field Stabilization Energy (CFSE) of nickel in 233

the four samples studied. There are two main features in the NIR spectra (Fig. 8) as a 234

function of band frequency in the ranges: >5000 and <4500 cm-1. In the former region 235

we observe absorptions due to occupied water molecules in the minerals and the 236

latter, strong absorption band is due to CO32- ion. The splitting of 1 and 3 bands and 237

non-Gaussian shape of 3-band in the minerals are the effects of Ni-site distortion 238

from the regular octahedron. For each band, the values obtained notably, wavenumber 239

are nearly similar but relative intensity is different for the two carbonates (Table 2 and 240

3). The small differences can be attributed to the main reasons: (1) the slight chemical 241

differences between the samples [9,11] and (2) the structural cation substitution 242

(Mg2+, Ni2+, Fe2+) and trivalent cations like Al3+, Fe3+. The absence of UV band in 243

takovite may be explained by the presence Al significantly in the mineral [11]. The 244

position and assignments of the bands of Ni-bearing carbonates are compared with the 245

data reported for other carbonates, zaratite: Oxford serpentine quarry, Texas, USA; 246

takovite: Carr Boyd Nickel Mine, Australia; nickel hydroxide and kerolite from New-247

Caledonia in Table 2 and crystal field parameters in Table 3. The structural cation 248

substitutions, like Mg2+, Ni2+, Fe2+ and trivalent cations, Al3+, Fe3 in the Ni-249

carbonates cause band shifts to high wavenumbers with reference to nickel hydroxide 250

(Table 2) and the shift is more significant for widgiemoolthalite 251

(Ni,Mg)5(CO3)4(OH)2.5H2O and takovite Ni6Al2(CO3,OH)(OH)16.4H2O. Table 3 252

shows the CFSE values vary in the range >10560 and <11040 cm-1. The increase of 253

CFSE value indicates the intensity of distortion of Ni-site in the carbonate minerals 254

studied. 255

256

257

4. Conclusions 258

259

Spectroscopic analysis of Ni carbonates is in harmony with chemical 260

composition confirming the presence of both molecular water and carbonate ions in 261

the mineral structure. Three broad intense bands centred at 26720-25855 cm-1(1), 262

15230-14740 cm-1(2) and 9200-9145 cm-1(3) are assigned to spin-allowed 263

transitions, 3A2g(3F) 3T1g(

3P), 3A2g(3F) 3T1g(

3F) and 3A2g(3F) 3T2g(

3F). In 264

9

addition, a prominent shoulder on the low wavenumber side of the 2 band arising 265

from the spin-forbidden transition 3A2g(3F) 1Eg(

1D), invariably appeared in all the 266

four Ni-carbonates. The relative values of ∆○ obtained directltly from the observed 267

energy of the 3A2g(3F) 3T2g(

3F) transition allow us to calculate Crystal Field 268

Stabilization Energy (CFSE) of nickel in the four mineral samples studied. The value 269

of CFSE indicates the degree of distortion of Ni-site in the carbonate minerals studied. 270

The result of non-Gaussian shape and splitting of the 3 band around 9200 cm-1 in 271

NIR spectra of the Ni-carbonates suggests lowering of Ni-site from regular octahedral 272

to either tetragonal or trigonal. A broad unsymmetrical band in the NIR spectra 273

centred in the range 4225-4425 cm-1 is the result of symmetry distortion of CO32- ion 274

in the Ni-carbonate-bearing minerals. Band shifts are caused due to structural cation 275

substitutions (Mg2+, Ni2+, Fe2+ and trivalent cations, Al3+, Fe3) in the carbonate 276

minerals studied and shift is more significant for widgiemoolthalite 277

(Ni,Mg)5(CO3)4(OH)2.5H2O and takovite Ni6Al2(CO3,OH)(OH)16.4H2O. 278

279

Acknowledgements 280

281

The financial and infra-structure support of the Queensland Research and 282

Development Centre (QRDC-Alcan) and the Queensland University of 283

Technology Inorganic Materials Research Program of the School of Physical and 284

Chemical Sciences is gratefully acknowledged. The Queensland University of 285

Technology is also acknowledged for the award of a Visiting Fellowship to B. 286

Jagannnadha Reddy. 287

288

289

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[60] R. L. Frost, D.L. Wain, W.N. Martens, B. J. Reddy, Spectrochim. Acta Part A 369

66 370

(2007) 1068. 371

[61] R. L. Frost, B. J. Reddy, D.L. Wain, W.N. Martens, Spectrochim.Acta Part A 66 372

(2007) 1075. 373

[62] R.L. Frost, D. L. Wain, W.N. Martens, B. J. Reddy, Polyhedron 26 (2007) 275. 374

[63] G.R. Hunt, J.W. Salisbury, Mod. Geol. 5 (1976) 211. 375

[64] A. Manceau, G. Calas, A. Decarreau, Clay Miner. 20 (1985) 367. 376

377

378

379

13

380

Code

Mineral

Colour

Formula

Origin

Ni-1

Nullaginite

Bright green

Ni2(CO3)(OH)2

Otway Prospect, Nullagine Region,

Western Australia

Ni-2 Zaratite Green

Ni3(CO3)(OH)4.4H2O

Lord Brassey Nickel Mine,

Heazlewood, Tasmania, Australia

Ni-3 Widgiemoolthalite Bluish green

fibres

(Ni,Mg)5(CO3)4(OH)2.5H2O

132 North Nickel Mine,

Widgiemooltha, Co., Western Australia

Ni-4 Takovite Pale green Ni6Al2(CO3,OH)(OH)16.4H2O

Perseverance Nickel Deposit, Agnew,

Western Australia

381

382

Table 1 Table of the Ni carbonate-bearing minerals, their origin and formula 383

14

Nullaginite Ni2(CO3)

(OH)2

(cm-1)

Present study

Zaratite Ni3(CO3)

(OH)4.4H2O

(cm-1)

Present study

Widgiemoolthalite

(Ni,Mg)5(CO3)4

(OH)2.5H2O

(cm-1)

Present study

Takovite

Ni6Al2(CO3,OH)

(OH)16.4H2O

(cm-1)

Present study

Nickel

hydroxide

Ni(OH)2

(cm-1)

Reported [64]

Kerolite

(Mg,Ni)3Si4O10

(OH)2.H2O

(cm-1)

Reported [64]

Zaratite Ni3(CO3)

(OH)4.4H2O

(cm-1)

Reported [47]

Takovite

Ni6Al2(CO3,OH)

(OH)16.4H2O

(cm-1)

Reported [47]

Suggested assignment

29830

30970c

29660

30490

nd

3A2g(3F) 1Eg(

1G) t

25955

25855

26200

25410c

26720

23860c

25700

23560

25800

23900

23805

26665

3A2g(3F) 3T1g(

3P) t

nd

nd

20580

20540

22300

22340

21735

24095

3A2g(3F) 1T2g(

1D) t

15230

14740

15010

15140

15040

17320

15380

14285

15380

3A2g(3F) 3T1g(

3F) t

13200sh

13380sh

13090sh

13380sh

13240

13580

nd

14930

3A2g(3F) 1Eg(

1D) t

9190

7880sh

9145

7910sh

9185

7820sh

9200

8075sh

8800

8950

8195

10000

8200

3A2g(3F) 3T2g(

3F) t

15

7185c

6745

6845

6785

6405

6885

6505sh

nr nr 7140 7-90 22 a

22 a

22 a

5085

5155

4945sh

5645sh

5130

5380sh

5155

4910sh

nr

nr

nr

nr

(2 + 3) a

(2 + 3) a

(2 + 3) a

4315 4225 4425 4310 nr nr nr nr (23 + 24) b

384 t Electronic transition of Ni2+ 385 a Overtones and combination modes of OH fundamentals; 3 and 2 observed in IR at 3500-3300 and 3000-2800 cm-1. 386 b Overtones and combination modes of (CO3)

2- fundamentals observed in IR (1 = 1045, 2 = 830, 3 = 1510 and 4 = 740 cm-1) 387 Abbreviations: p-component; sh-shoulder; nd-not detected 388 389

390

391

Table 2 Assignments of the UV-Vis and NIR bands of Ni carbonate bearing-minerals and other Ni compounds. 392

16

Table 3 Comparison of crystal field parameters of Ni2+ in Ni-carbonates with 393

other complexes 394

395

Complex

Transition energy

[3A2g(3F) 3T2g(

3F)]

(10Dq = ∆○)

(cm-1)

CFSE

(6/5)∆○)

(cm-1)

Reference

Tutton salt

[M2M'(SO4)2.(H2O)6]

8850 10620 [63]

Nickel hydroxide

Ni(OH)2

8800 10560 [63]

Kerolite

(Mg,Ni)3Si4O10(OH)2.H2O

8950 10740 [63]

Gaspeite

Ni,Mg,Fe)(CO3)

8130 9756 [52]

Zaratite

Ni3(CO3)(OH)4.4H2O

8195 9834 [47]

Takovite

Ni6Al2(CO3,OH)(OH)16.4H2O

9100 10920 [47]

Nullaginite

Ni2(CO3)(OH)2

9190 11028 Present study

Zaratite

Ni3(CO3)(OH)4.4H2O

9145 10974 Present study

17

Widgiemoolthalite

(Ni,Mg)5(CO3)4(OH)2.5H2O

9185 11022 Present study

Takovite

Ni6Al2(CO3,OH)(OH)16.4H2O

9200 11040 Present study

396

397

398

399

400

18

List of Tables 401

402

Table 1 Table of the Ni carbonate-bearing minerals, their origin and formula 403

404

Table 2 Assignments of the UV-Vis and NIR bands of Ni carbonate bearing-405

minerals and other Ni compounds. 406

407

Table 3 Comparison of crystal field parameters of Ni2+ in Ni-carbonates with 408

other complexes 409

410

List of Figures 411

412

Fig. 1 UV-Visible-NIR spectra of nullaginite and zaratite: 300-420 nm region. 413

414

Fig. 2 UV-Visible-NIR spectra of nullaginite and zaratite: 550-800 nm region. 415

416

Fig. 3 Near-infrared (NIR) spectra of nullaginite and zaratite: 11000-6000 cm-1 417 region. 418

419

Fig. 4 Near-infrared (NIR) spectra of nullaginite and zaratite: 6000-4200 cm-1 420 region. 421

422

Fig. 5 UV-Visible-NIR spectra of widgiemoolthalite and takovite: 300-550 nm 423

region. 424

425

Fig. 6 UV-Visible-NIR spectra of widgiemoolthalite and takovite: 500-800 nm 426

region. 427

428

Fig. 7 Near-infrared (NIR) spectra of widgiemoolthalite and takovite: 11000- 429

6000 cm-1 region. 430

431

Fig. 8 Near-infrared (NIR) spectra of widgiemoolthalite and takovite: 6000-4000 432

cm-1 region. 433

434

19

435

436

437

438

439

440

441

442

443

20

444

Figure 1 445

446

447

448

449

450

451

452

453

454

21

455

456

Figure 2 457

458

459

22

460

461

462

Figure 3 463

464

23

465

466

Figure 4 467

468

24

469

470

471

472

473

Figure 5 474

475

476

25

477

478

Figure 6 479

480

26

481

482

483

Figure 7 484

485

486

27

487

488

Figure 8 489

490

491