Complete Column Trials for Water Refinement Using Titanium(IV

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Complete column trials for water refinement, using titanium(IV) phosphate sorbents Mylène Trublet, and Daniela Rusanova ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b04823 • Publication Date (Web): 28 Mar 2018 Downloaded from http://pubs.acs.org on April 9, 2018

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ACS Sustainable Chemistry & Engineering

Complete column trials for water refinement, using

1

titanium(IV) phosphate sorbents

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3

Mylène Trubleta*, Daniela Rusanovaa

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a

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*Correspondence to: [email protected], +46-(0)920-493448

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ABSTRACT

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A titanium phosphate sorbent with linked active units (LTP) is synthesized. XRD, 31P MAS NMR,

10

and TGA techniques are used to disclose the relation between the ion-exchange units of –HPO4

11

(crystalline α-TiP) and of –H2PO4 (amorphous TiP1) type. The published kinetics data of TiP1

12

sorbent in batch mode have been re-processed according to the non-linear approach in order to

13

explore further the sorption mechanism, and it was found that the data could be well described by

14

the pseudo-second order model in the case of Ni2+ ions. Consequently, fixed-bed column sorption

15

experiments of Ni2+ ions on LTP were designed and the effects of both the amount of nickel(II)

16

ions in the feed solution and of the flow rates on the sorption equilibrium were studied. The ion-

17

exchange capacity is estimated to be 1.6 meq.g-1 during the first four cycles before decreasing to

18

1.2 meq.g-1 for cycles five and six. The experimental data were simulated following the Thomas

19

model and desorption experiments with HCl were performed. Observations show that regeneration

20

and reutilization of the LTP ion-exchanger is possible through at least six cycles. It is revealed that

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the sorption performances in column conditions could be undoubtedly predicted from the

22

corresponding batch sorption data.

Chemistry of Interfaces, Luleå Univeristy of Technology, 97187 Luleå, Sweden

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ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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KEYWORDS

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Titanium phosphate, ion-exchanger, column, nickel, sorption

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INTRODUCTION

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The presence of nickel ions and other pollutants in the surface and groundwater water is a major

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concern for the environmental commission due to their adverse effects on public health and on

29

ecological systems (the terms nickel and nickel ions will be used interchangeably in the text and

30

the forms will be distinguished when necessary) 1.

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The accumulation of nickel can cause infertility, cutaneous sensitivity, nausea, liver and kidney

32

diseases, cancer, etc., in humans when exposed to concentrated doses and/or long-term exposure

33

at minimal concentration. The release of nickel ions in the environment is mainly caused by

34

wastewater spillage 2. The primary source of nickel in drinking water originates from leaching of

35

Ni-containing metal parts that are in continuous contact with water, such as pipes and fittings.

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Nickel metal has many applications and has been extensively used in alloys production of various

37

types, i.e. stainless steel, non-ferrous alloys and super alloys 3. Discharge of such waste increases

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the nickel concentration in soil and groundwater and creates the need for a more permanent solution

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to lower this concentration below the European regulations 4–9.

40

Different treatment techniques have been employed for removing nickel and heavy metals ions

41

from wastewaters 10. Each treatment process has been designed for specific geographic areas and

42

has its own advantages and disadvantages. For example, chemical precipitation and sedimentation

43

are favored processes due to inexpensive running costs and their simplicity but they are not suitable

44

when contaminants are present at trace level. These treatments can also result in the production of

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large amounts of sludge that would need to be further treated. On the other hand, the ion-exchange 2


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and sorption techniques have high treatment capacities but are often expensive and require

47

regeneration of the material using chemical reagents which can in turn produce secondary pollution

48

4

. More efforts are put into finding low costs ion-exchangers that can efficiently remove heavy

49

metal ions from drinking and waste waters, although their regeneration can be an issue.

50

Titanium phosphates (TiP) are a group of inorganic ion-exchangers that have demonstrated to have

51

very good cationic sorption properties in batch experiments. It has been proven that the ion-

52

exchange capacity (IEC) is dependent on the degree of TiP crystallinity, the Ti:P molar ratios and

53

the sorbents' stability and that all these factor should be taken into account when designing new

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TiP ion-exchangers. Recent studies have reported very promising ion-exchange properties of an

55

amorphous TiP material with chemical formula TiO(OH)(H2PO4)•H2O (TiP1) 11–13 . The material

56

has been found to be the most chemically stable TiP ion-exchangers at a pH range of 2-10. The

57

maximum hydrolysis of P-units (2.5 %) was observed at pH = 10 while the hydrolysis of T-units

58

remained negligible in the whole pH range. With the presence of two exchangeable protons, TiP1

59

has displayed a maximum ion-exchange capacity (expressed as sodium uptake) of 6.3 meq.g-1 which

60

is the highest recorded so far for amorphous TiP materials. The actual ion-exchange capacity (IEC)

61

has been estimated to be around 3.1 meq.g-1 towards transition metal ions and is among the highest

62

values reported for TiP ion-exchangers 12.

63

Crystalline TiP ion-exchangers are usually obtained at harder synthetic conditions. One of the most

64

studied crystalline TiP is α-TiP (Ti(HPO4)2•H2O). It can be obtained in an autoclave at 200 °C for

65

3 hours 14 or at lower heat (between 50 and 80 °C) combined with a very long reaction time (from

66

12 h to 4 days) or/and under refluxing conditions 15,16. Crystalline TiP have shown to have higher

67

Na+ uptakes but a considerably lower IEC towards metal ions in solution than amorphous TiP 17.

68

Despite their proven sorption properties in batch conditions, TiP ion-exchangers have not been

69

thoroughly studied in continuous column experiments. Among the few data found in the literature, 3



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70

it has been observed that the ion-exchange performances of amorphous TiP materials depended on

71

the ion-exchange form (proton or alkaline) it had been converted to. It has also been shown that

72

amorphous Na-TiP (in sodium form) was increasing the sorption capacity of the material towards

73

divalent metal ions, in batch and in column experiments, when compared to amorphous H-TiP (in

74

proton form) 13,18. Other forms of amorphous TiP have been studied (Mg-TiP and Ca-TiP) and it

75

was found that ion-exchange performances of TiP was increasing in the order: Ca-TiP < Mg-TiP

76

< Na-TiP 19. Another advantage in using the sodium form of LTP is the fact that the pH during the

77

sorption process will remain in the same range, while the proton form would result in a pH drop

78

due to the proton exchange.

79

To the best of our knowledge, no complete studies on the sorption behavior of TiP in column

80

conditions (influence of the concentration, flow rate of the feed solution, regeneration of the

81

material, modeling) have been published and data on a direct relation between batch and column

82

tests are missing.

83 84

In this work, the sorption behavior of the Linked Titanium Phosphate ion-exchanger (LTP),

85

composed of two types of ion-exchange units: amorphous –H2PO4 groups and crystalline –HPO4

86

groups, was studied in continuous column conditions. The structural properties of LTP were first

87

characterized by XRD,

88

determined by the sodium uptake. Column experiments were designed based on batch data and

89

sorption of Ni2+ ions onto Na-LTP (sodium form) were conducted under different working

90

conditions varying the nickel(II) ions concentration in the feed solution as well as the flow rates.

91

Desorption experiments were also performed to investigate the regeneration and reutilization of

92

the ion-exchanger.

31

P MAS NMR, and TGA and the maximum sorption capacity was

93 4


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94


EXPERIMENTAL SECTION Synthesis

95 96 97

The linked titanium phosphate (LTP) ion-exchanger in this study was synthesized as follow: 50

98

mL of a solution of TiOSO4•(H2SO4)x from Sigma Aldrich (containing 27-31% H2SO4 basis and

99

ca 5% Ti) was heated up to 80 °C and mixed with the corresponding amount of 85% H3PO4 so that

100

the molar ratio TiO2:P2O5 = 1:1. The mixture was kept under heating for about 24 h before being

101

filtrated and washed with 5% H3PO4. The obtained white precipitate was then dried at 60 °C for ca

102

5 h. The post synthetic treatment consisted in successive washings with diluted HCl and deionized

103

water.

104

The synthesis of TiP1 follows similar procedure as for LTP at the condition that the temperature

105

of 80 °C is switched off within the 30 min after adding 85% H3PO4 11.

106 107

Characterization

108 109

The titanium phosphate ion-exchanger synthesized in this study (LTP) was characterized using 31P

110

MAS NMR, XRD and TG.

111

The 31P MAS NMR spectra were obtained at 162.01 MHz on a Bruker Ascend Aeon WB 400 MHz

112

spectrometer (B0 = 9.48 T) using a 5 mm MAS probe and the samples were packed in standard

113

ZrO2 rotors. The spinning frequency was 12 kHz and all spectra were externally referenced to solid

114

NH4H2PO4 at 0.9 ppm. All data are reported with chemical shifts related to H3PO4 at 0 ppm and

115

single pulse experiments were used to investigate the samples. The pulse width and the pulse delay

116

were 1.5 μs and 5 s, respectively. 64 acquisitions were acquired to obtain the spectra. The NMR

117

spectra were processed and the deconvolution was performed with Topspin 3.5 software. 5



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118

The powder X-ray diffraction (XRD) patterns were recorded using a PANalytical Empyrean

119

diffractometer run in Bragg-Brentano geometry with Cu Kα radiation (λ = 1.5406 Å). The samples

120

were scanned in the 2θ range of 2-70 ° with a 2θ step size of 0.0260 ° and a scan step time of 3.3

121

min.

122

The thermogravimetric (TG) data of LTP were obtained using a thermogravimetric analyzer

123

(Perkin Elmer TGA 8000) under nitrogen atmosphere. The amount of weight loss and the heat flow

124

were recorded in the temperature range from 30 °C to 1000 °C with a temperature rate of 1 °C/min.

125

Sodium uptake

126 127 128

The maximum sorption capacity for TiP systems was determined as the sodium uptake (in meq.g1

). The studied ion-exchanger, LTP, was mixed with a solution of 0.5 M Na2CO3 following a mass

129

(g) to volume (mL) ratio of 1:50. The mixture was kept under stirring for 24 h at ambient

130

conditions. The sodium content was analyzed after filtration using an Inductive Coupled Plasm

131

Atomic Emission Spectroscopy (ICP-AES) by ALS Global Scandinavia, Luleå. The sodium form

132

of LTP (Na-LTP) was used for further sorption column experiments.

6


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133


Sorption-Desorption column experiments

134 135

The column experiments were carried out using a vertical glass column with an inner diameter of

136

1 cm. The column was filled with glass beads of 1 mm diameter, filter paper and glass wool before

137

loading the column with Na-LTP. About 5 g of the ion- exchanger Na-LTP was used which

138

corresponds to a bed height of about 10 cm and a bed volume (BV) of about 8 mL. Filter paper,

139

glass wool and glass beads were also added on the top of the sorbent. A schematic representation

140

of the column set up (Figure S2) can be found in the supporting information.

141

Solutions of NiSO4•7H2O at two different concentrations (2.5 mM and 5.0 mM) were pumped

142

through the column from the bottom to the top using a peristaltic pump at three different flow rates:

143

54, 78 and 96 mL.min-1. Details of the experiments (with fixed and variable parameters) are

144

described in the supporting information, Table S1.

145

Desorption studies were performed with HCl at two concentrations (0.05 M and 0.01 M) and two

146

flow rates (90 and 54 mL.min-1).

147

The LTP ion-exchanger was converted to its sodium form using a solution of 0.5 M Na2CO3 and

148

was further washed with deionized water until the pH at the outlet of the column was the same as

149

the inlet (pH. ~ 5.7). In total, six sorption-desorption cycles were performed. The pH of the

150

solutions at the inlet and outlet of the column were found to be between 5.0 and 5.5 during the

151

whole experiment (no further alteration of the initial pH was detected). This small pH window

152

ensures that no Ni(OH)2 precipitate can be formed as it would be expected only if the pH raised to

153

7.6-7.7 for the studied concentration ranges 20.

154

The concentration of Ni2+ in the filtrate after sorption was determined spectrophotometrically using

155

a standard procedure that was adapted to NiSO4•7H2O concentrations used in this work 21. Prior to

156

the analysis, the samples were diluted 50 times with deionized water. To 20 mL of this diluted Ni2+ 7



Page 8 of 34

157

ions solutions, 1mL of 10% Na2S2O8, 3 mL of 10% NaOH and 1 mL of 1% of dimethylglyoxime

158

in ethanol were added. The absorbance of the samples were measured using a UV-VIS

159

spectrometer at a wavelength λ = 465 nm.

160 161

BATCH EXPERIMENTS: REVISITED KINETICS

162

The majority of kinetics data on sorption experiments report linear regression approach in the

163

determination of kinetics parameters for the pseudo-first and pseudo-second order kinetics. As it

164

has been discussed by Simonin, these statistical treatments tend to favor the pseudo-second order

165

rate law 22. For data close to and at equilibrium, the mathematical expression of the pseudo-second

166

order gives aligned points when the accuracy of fit with the pseudo-first order decreases. Another

167

criticism of the linear regressions involves the comparison of the correlation coefficient R2 of two

168

different functions on a transformed scale, which becomes irrelevant in the present context.

169

Therefore, kinetics data should be processed with more caution and non-linear fits should be

170

preferred over the linear fits 22.

171 172

Kinetics data of sorption of Ni2+, Co2+ and Cu2+ ions on TiP1 have been recently published also

173

following the linear regression analyses. Four kinetics models (pseudo-first order, pseudo-second

174

order, liquid film diffusion and intraparticle diffusion) were tested and it was found that the

175

experimental data could be best described by the pseudo-second order kinetics 12. In this article,

176

these data have been re-analyzed according to the non-linear approach for the pseudo-first and

177

pseudo-second order, described by Simonin 22, using the fit() function from MATLAB.

178

In brief, the equation for the pseudo-first order can be expressed as 23:

179

𝑞(𝑡) = 𝑞𝑒 [1 − exp(−𝑘1 𝑡)]

(1)

8


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180

Where q(t) is the amount of adsorbed solute at time t (mmol.g-1), qe is the value at equilibrium

181

(mmol.g-1), k1 is the pseudo-first order rate constant (min-1) and t is the time (min).

182 183

If the fractional uptake F(t) is defined as 𝐹(𝑡) = 𝑞(𝑡)/𝑞𝑒 , the constant k1 can be determined from

184

the non-linear regression of the plot F(t) versus [1 − exp(−𝑘1 𝑡)].

185

The reasoning for the pseudo-second order follows the one for the pseudo-first order. It can be

186

expressed as 24:

187

𝑞(𝑡) = 𝑞𝑒 1+𝑘2 ∗

188

Where k2 is the pseudo-second order rate constant (g.mmol-1.min-1).

𝑘∗ 𝑡 2

𝑡

with 𝑘2∗ = 𝑘2 𝑞𝑒

(2)

189 190

If the fractional uptake F(t) is defined as 𝐹(𝑡) = 𝑞(𝑡)/𝑞𝑒 , the constant k2 can be determined from

191

2 the non-linear regression of the plot F(t) versus 1+𝑘 ∗𝑡 .

𝑘∗ 𝑡 2

192 193

In both cases, the data were plotted for F(t) < 0.85 and the resulting constants were compared to

194

the ones previously published by Trublet et al.12 (determined from linear plots). The re-studied

195

kinetics involves sorption of Ni2+, Co2+ and Cu2+ ions (with an initial concentration of 2.5 mmol.L-

196

1

) on TiP1.

197 198

COLUMN DATA ANALYSIS

199 200

The adsorption data collected for the column experiments at different Ni2+ ions concentrations and

201

at different flow rates were analyzed as described below.

9



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202

The column capacity qsorbed (mmol) represents the number of moles of nickel(II) ions that are

203

retained by the column. It is calculated using the equation below:

204 205

𝑡=𝑡

𝑞𝑠𝑜𝑟𝑏𝑒𝑑 = 𝑄 ∫𝑡=0 𝑒𝑥ℎ (𝐶0 − 𝐶𝑡 ) 𝑑𝑡

(3)

206

With Q the flow rate (L.h-1), C0 the initial concentration (mmol.L-1) of Ni2+ ions at the feed, Ct the

207

concentration of Ni2+ ions at the outlet of the column at time t (mmol.L-1) and texh the time at the

208

exhaustion point.

209

The integral is calculated until the exhaustion point (texh) which corresponds to the time where the

210

concentration of Ni2+ ions at the outlet exceeds 95% of C0.

211 212

The experimental ion-exchange capacity (IECexp) in meq.g-1 of TiP systems represents the amount

213

Ni2+ ions uptaken by gram of sorbent. It is calculated using the following equation:

214 215 216

𝐼𝐸𝐶𝑒𝑥𝑝 =

𝑞𝑠𝑜𝑟𝑏𝑒𝑑 ∗2 𝑚𝐿𝑇𝑃

(4)

Where mLTP is the mass (g) of the sorbent in the column.

217 218

It has been reported that the ion-exchange capacity of TiP systems could also be estimated from

219

the Na+ uptake 19. In most of the cases, the ion-exchange capacity represented about 60 % of the

220

sodium uptaken by the TiP sorbent. Therefore, for the studied system of LTP, the calculated ion-

221

exchange capacity (IECcalc) was estimated to be 60% of the Na+ uptake.

222 223

The performance/yield of the column (Y in %) through the different cycles was calculated using

224

eq. (5): 10


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𝐼𝐸𝐶𝑒𝑥𝑝

225

𝑌 (%) =

226

The value of Y (in %) shows how well the theoretical sorption capacity is reached during the

227

sorption cycles.

228

The total amount of Ni2+ ions (in moles) loaded into the column until the exhaustion point, 𝑞𝑁𝑖2+,𝑡𝑜𝑡

229

was calculated as:

230

𝐼𝐸𝐶𝑐𝑎𝑙𝑐

∗ 100

(5)

𝑞𝑁𝑖 2+,𝑡𝑜𝑡 = 𝐶0 . 𝑄 . 𝑡𝑒𝑥ℎ

(6)

231 232

Finally, the total removal percent of Ni2+ ions from the feed solution was determined using the

233

equation below 25:

234

𝑞

𝐸(%) = 𝑞 𝑠𝑜𝑟𝑏𝑒𝑑 * 100

(7)

𝑁𝑖2+,𝑡𝑜𝑡

235

where E (%) can be considered as a measure of how efficient in time is the nickel(II) removal when

236

the sorbent capacity is reached.

237

COLUMN SORPTION MODELING

238 239

The Thomas model was used to obtain the breakthrough profile of packed bed sorption column

240

using LTP 26. It is derived from the equation of mass conservation in a flowing system. The axial

241

and radial dispersion in the column are considered to be negligible and the rate driving force

242

follows the second order reversible kinetics.

243

The linearized equation of the Thomas model can be expressed using the following equation:

244 245

𝐶

ln (𝐶0 − 1) = 𝑡

𝑘𝑇ℎ .𝑞𝑇ℎ .𝑚 𝑄

− 𝑘𝑇ℎ . 𝐶0 . 𝑡

(8)

246

11



247

Where kTh is the Thomas rate constant in L.mmol-1.h-1 and qTh the ion-exchange capacity of the

248

sorbent in mmol.g-1.

249

The Thomas model was applied to the experimental data located in the range 0.10 < C/C0 < 0.85.

250 251

RESULTS AND DISCUSSION

252

XRD

253

(c) Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 34

(b)

(a) 5 254

15

25

35

2θ, degrees

45

55

65

255

Figure 1. XRD diffractrograms of (a) referenced α-TiP 27, (b) LTP and (c) TiP111.

256

The XRD diffractograms of LTP is displayed in Figure 1b and reported patterns for α-TiP

257

(Ti(HPO4)2•H2O) and TiP1 (TiO(OH)(H2PO4•H2O) are shown for comparison in Figure 1a and

258

Figure 1c, respectively. The LTP displays a crystalline-like phase with a pattern that resembles a

259

mixture of two phases: TiP1 and α-TiP. One broad peak is observed at 2θ = 8.8 ° which corresponds

260

to an interlayer distance of 10.02 Å. It has been reported that such a peak was an indication of a

261

layered structure with low crystallinity phase in TiP1 systems

262

11.7 °, corresponding to an interlayer distance of 7.54 Å, is the main characteristic of α-TiP

11

. A second narrow peak at 2θ =

12


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27,28

. This confirms that the TiP1 and α-TiP systems are both present in the XRD

263

materials

264

diffractogram of LTP, suggesting that the new material is composed of two interconnected units

265

with different crystallinity.

266 267

31

P MAS NMR -14.9

(d) -14.8

(c)

5.4 2.6 -18.7 -7.0

(b) -18.8

(a)

-15.6

-30.4

30 20 10 0 -10 -20 -30 -40 -50 268 269 270

ppm

Figure 2. 31P MAS NMR of (a) LTP before washing with HCl (H-form) (b) LTP final compound (H-form), (c) Na-LTP and (d) LTP after the sixth desorption cycles (H-Na-form).

271

Figure 2 shows the 31P MAS NMR spectra of LTP at various stages from the synthesis to the end

272

of the column experiments. It has been reported that different phosphate groups in TiP systems

273

were characterized with different chemical shifts. For H-TiP materials (in proton form), the

274

resonance lines of –H2PO4 ion-exchange units are observed in the range of -5 to -11 ppm, while

275

the lines corresponding to −HPO4 groups are expected to be up to -25 ppm. The resonance line of

276

–PO4 groups would appear between -25 to -35 ppm and finally, poly/pyrophosphate groups would

31

P

13



29–33

Page 14 of 34

277

be observed from -35 to -55 ppm

. Regarding the Na form of TiP, the chemical shifts for

278

−PO4/−HPO4/−H2PO4 are expected to shift towards lower frequencies due to the presence of Na+

279

ions 34.

280

Figure 2a displays the 31P NMR spectrum of LTP before the post synthetic treatment with HCl. A

281

sharp resonance line is observed at -18.8 ppm which is characteristic of –HPO4 ion-exchange units

282

in α-TiP. The two weaker and broader lines at -15.6 ppm and -30.4 ppm are assigned to –HPO4 and

283

–PO4 groups, respectively. The spectrum of LTP after the washing process with HCl (in Figure 2b)

284

shows two resonance lines: one broad line centered at -7.0 ppm and one narrow line at -18.7 ppm,

285

attributed to –H2PO4 and –HPO4 groups, respectively

286

corresponds to the more crystalline α-TiP phase in the material and it can be seen that this phase is

287

not affected by the successive HCl rinses, as expected. On the other hand, protonation of the

288

phosphate groups from the more amorphous phase is observed during the post synthetic treatment;

289

where the two broad lines of hydrophosphate and phosphates groups (Figure 2a) are replaced by

290

one broad line corresponding to the presence of dihydrophospate groups. This resonance line (at -

291

7.0 ppm) corresponds to the –H2PO4 groups present in the TiP1 unit of the material. The

292

deconvolution data of the 31P NMR spectra of LTP reveals equality of the two P-exchange units.

293

Therefore, it can be confirmed that there is a 1:1 ratio of the two phases (α-TiP and TiP1) present

294

in the new sorbent (LTP).

295

The 31P NMR spectrum of the sodium form of LTP (Na-LTP) in Figure 2c displays one intensive

296

isotropic line at -14.8 ppm and one broader line with two narrow vertices at 5.6 and 2.6 ppm. The

297

sharp line at -14.8 ppm corresponds to the presence of –HPO4 groups and originates from the α-

298

TiP units. The chemical shift difference with the H-LTP spectrum comes from the difference in the

299

31

300

As for the TiP1 units, the broader line can be related to three phases that are coexisting during the

17

. The sharp resonance line at -18.8

P local environment of the –HPO4 groups, due to different Ti−O−P angles and/or bond distances.

14


Page 15 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


being

TiO(OH)(NaHPO4)•H2O

sodium

302

TiO(OH)(Na2PO4)•H2O11–13. Due to the quadrupolar nature of Na nuclei and their closeness to the

303

P-units as well as the overlapping signals of the different sodium dihydro and hydro-phosphate

304

units, the 31P MAS NMR data for the amorphous Na-TiP1 phase is relatively broad and complex.

305

After the sixth column regeneration with HCl (Figure 2d), the 31P signal belonging to α-TiP units

306

remains almost unchanged indicating that –HPO4 groups are not involved in the ion-exchange

307

process. The broad

308

units is observed from 10 to -12.5 ppm. This indicates that TiP1 units can be regenerated to H-form

309

and can be used for further sorption cycles. The sodium dihydro and hydro-phosphate groups are

310

still present in the material as about 60 % of the Na+ uptake is exchanged. The signal to noise in

311

this 31P NMR spectra is considerably higher, most likely due to minimal amount of paramagnetic

312

nickel(II) ions left in the sorbent and that could not be entirely desorbed.

313

uptake,

TiO(OH)(H2PO4)•H2O,

301

31

and

P resonance line covering the area of Na2PO4//NaHPO4//H2PO4-exchange

TGA data

314 315 316

Figure 3. TGA and DTG (derivative of the TG curve) data for LTP (solid lines, right) and for a mixed sample A (α-TiP : TiP1 = 1:1) (dotted line, left).

15



Page 16 of 34

317

The thermogravimetric data of LTP are shown in Figure 3. For comparison, the thermogravimetric

318

data of a mixed sample corresponding to a 1: 1 molar ratio of α-TiP and TiP1 (sample A) are also

319

displayed in Figure 3. The total weight loss for LTP and for sample A was recorded to be 17.8 and

320

17.5 %, respectively, supporting the fact that LTP consists of two phases (TiP1 and α-TiP) present

321

in equimolar amount. In the thermogram of sample A (Figure 3, left), the first weight loss of 5.9

322

%, observed at 58 °C, is attributed to the release of lattice water in the sample. The number of these

323

water molecules is estimated to be about 0.75 molecules of water per mole of sample A. The second

324

weight loss of 6.9 % is observed at 174 °C. This value is in good agreement with the theoretical

325

value of 6.5 % calculated if the polycondensation of hydroxo and dihydro-phosphates groups in

326

the TiP1 unit is considered as the next thermal step 11. Finally, the last weight loss of 4.7 % observed

327

at 415 °C could correspond to the theoretical value of 4.6% for the condensation of the hydro-

328

phosphates groups in the α-TiP phase. Previously reported thermograms of α-TiP revealed a similar

329

pyrolytic process weight loss in the range of 250-700 °C

330

inclined to condensate first due to the presence of accessible OH- groups while the pyrolytic process

331

of the rigid α-TiP structure would initiate at higher temperatures.

332

In Figure 3, the thermogram of LTP displays four steps of weight losses with three of them being

333

somewhat similar to the steps observed for sample A. The first weight loss of 5.3 % ranges from

334

30 to 120 °C and can be attributed to the lattice water in LTP. The second weight loss (6.6 %)

335

consists of two small shoulders at 169 °C and 218 °C, while the third weight loss (4.9 %) is

336

observed at 436 °C. The last weight loss consists of a smaller step of 1 % and can be seen at 732

337

°C. By looking at the weight losses, it seems that some of the lattice water is condensed above 120

338

°C and that the polycondensation of the dihydro and hydro-phosphate groups in the two phases is

339

occurring simultaneously. The DTG curve of LTP displays broader and more complex peaks than

16,17

. It seems that TiP1 units are more

16


Page 17 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


340

for sample A and the increase in the temperature for the polycondensation of the phosphates

341

indicates a linkage between the two different units in the LTP ion-exchanger. This can be related

342

to the possibilities of the two phases being connecting via either oxo/hydroxo bridge(s) or inner-

343

sphere H2O complexation through the common TiO6 edges.

344

Batch experiments: sodium uptake and revisited kinetics

345

The ion-exchange capacity is one of the most important parameters of a sorbent. For TiP systems,

346

the maximum exchange capacity is often evaluated as alkaline ions uptake such as sodium ions 19.

347

The sodium ions (Na+) uptake by LTP was found to be 2.85 meq.g-1. This value is in good agreement

348

with the previously published data of TiP1 where the sodium uptake of LTP would correspond to

349

3.1 meq.g-1, if the ratio 1:1 is considered 11,12. Bearing in mind the fact that 60 % of Na+ is expected

350

to be exchanged, one could calculate the actual ion-exchange capacity of Na- LTP, as an IECcalc of

351

1.71 meq.g-1.

352 353 354

Figure 4. Non-linear fits of experimental kinetics data (o) for the sorption of Ni2+ ions on TiP1 using the pseudo-first order (···) and pseudo-second order (---).

355 356

All kinetics data of TiP1 were re-analyzed according to the non-linear approach of the pseudo

357

first and pseudo second order laws described by Simonin (Simonin, 2016). The experimental data 17



Page 18 of 34

358

points close to the equilibrium were not taken into consideration. It has been demonstrated that

359

linear kinetics approaches tend to favor the pseudo-second order due to the mathematical

360

expression and therefore kinetics data should be preferably processed using the non-linear fits as

361

described in the section “Batch experiments: Revisited kinetics”.

362

The results of the modeling of the experimental data can be found in Figure 4. All parameters

363

(kinetic rate constants and coefficients of determination) obtained from the non-linear and the

364

linear approaches can be found in Table S2. The simulation using the pseudo-first order gives a

365

constant k1 of 0.209 min-1 and a coefficient of determination (R2) of 0.9783; while the pseudo-

366

second order fit gives a constant k2* of 0.400 min-1 (which is equivalent to k2 = 0.013 g.mg-1.min-

367

1

368

which would indicate that both models could well describe the experimental data. The constant k1

369

found for the pseudo-first order data is close to the one published by Trublet et al. obtained with

370

the linear fits (0.225 min-1). Similar observations are made for the constant k2 calculated where the

371

non-linear fit gave similar value to the previously published data obtained with the linear fits

372

(0.0132 g.mg-1.min-1). Taking a closer look at Figure 4, the pseudo-second order appears to better

373

describe the sorption kinetics data of Ni2+ ions on TiP1, despite a coefficient of determination close

374

to 1 for both models. Similar observations were made for sorption of Co2+ and Cu2+ ions on TiP1

375

using the non-linear regression analyses (Figure S1).

376

This is a stronger proof that the pseudo-second order governs the kinetics in the sorption process

377

of these transition metal ions on TiP1 and that chemisorption is the rate limiting step.

378

Based on the 31P MAS NMR and the sodium uptake, LTP is expected to behave similarly to TiP1

379

and therefore, the column experiments were designed following the batch kinetics data of TiP1.

) and a R2 of 0.9978. The coefficients of determination are in the same range and very close to 1

18


Page 19 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Column experiments

380

381

In batch experiments, it was found that for an initial concentration of 2.5 mM in nickel(II) ions, the

382

sorption equilibrium was reached within 10 min. This corresponds to a flow rate of 54 mL/hour in

383

the described fixed bed column of this study. The effects of the initial concentration and of the flow

384

rate on the sorption equilibrium were investigated as discussed below. Effect of the flow rate

385

C/C0 1.0

1.0

0.9

0.9

0.8

0.8

0.7

0.7

0.6

C/C0

0.6 54 mL/hour

0.5

78 mL/hour

0.4

54 mL/hour

0.4

0.3

0.3

0.2

0.2

0.1

96 mL/hour

0.5

(a)

(b)

0.1

0.0

0.0 0.0

20.0

40.0

60.0 80.0 Time, hours

0.0

10.0


386

Figure 5. Breakthrough curves for Ni2+ ions sorption on LTP at various flow rates; (a) C0 = 2.5

387

mM and (b) C0 = 5.0 mM. For all cases, the solid line (−) represents the calculations

388

using Thomas model.

389

Figure 5 shows the sorption breakthrough curves of Ni2+ ions on TiP1 at different flow rates for an

390

initial Ni2+ ions concentration of C0= 2.5 mmol/L (Figure 5a) and C0= 5.0 mmol/L (Figure 5b). The

391

solid lines represent the data calculated from the Thomas model.

19



Page 20 of 34

392

At the beginning of the experiments, the concentrations in Ni2+ ions in the effluent is very low since

393

the ions are sorbed onto the LTP column. At a certain point (breakthrough point), the concentration

394

of Ni2+ ions starts increasing as the sorbent becomes less effective; the process continues until the

395

column exhaustion point is reached (point where the sorbent is considered to be practically

396

saturated) and where the concentration of Ni2+ ions at the inlet and outlet of the column are nearly

397

identical (C/C0 ≈ 1). With a high flow rate, the breakthrough point occurs sooner and the amount

398

of exchanged Ni2+ ions could decrease (if the solute residence time is not long enough for the

399

sorption equilibrium to take place) resulting in nickel ions passing by the column beds before

400

equilibrium occurs

401

breakthrough curve as sharp as possible and to maintain the sorption capacity of LTP high.

402

Mathematically, in BV-units, this means a big BV-number before the breakthrough point and as

403

small as possible after it.

404

The European regulations for the maximum allowance of Ni2+ ions in drinking water is about 0.02

405

mg/L (i.e. 0.34 .10-5 mmol/L)

406

experimental data at which the effluent concentrations at the outlet of the column reach 0.34 .10-5

407

mmol/L. It can be seen that for the same concentration, the breakthrough volume (corresponding

408

to the breakthrough point) decreases with increase of the flow rate, as higher amount of effluent

409

passes through the sorbent in a shorter time, resulting in a faster saturation of the beds.

410

In Figure 5a (C0 = 2.5 mM), the breakthrough volume is estimated to be ca. 450 mL (i.e 56 BV)

411

for both flow rates, Q = 78 and 54 mL/hour. The breakthrough curve at a flow rate of 78 mL/h is

412

considerably sharper with an exhaustion point of 12 h versus 48 h for the flow rate of 54 mL/h.

413

The solute volume between the breakthrough and the exhaustion points is much larger (ca. 268

414

BV) for the lowest flow rate (Q = 54 mL/h) than for the Q = 78 mL/h (ca. 61 BV). For these

415

conditions the IEC (in Table 1) are calculated from the column data to be 1.7 meq.g-1 and 0.8 meq.g-

35,36

. To achieve the best column efficiency, it is desirable to have the

37

. In Figure 5, the breakthrough points correspond to the

20


Page 21 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


416

1

417

of 2.5 mmol/L, the flow rate of 78 mL/h is too high for the sorption process to reach equilibrium.

418

This is in good agreement with the kinetics data in batch experiments, where a contact time of 10

419

min for C0= 2.5 mmol/L was found for Ni2+ ions, which corresponded to a flow rate of 54 mL/h in

420

the present column design.

421

Similar observations can be seen in Figure 5b for the initial concentration C0 = 5.0 mM. The

422

breakthrough curve for the highest flow rate (Q = 96 mL/h) is sharper than for the lowest (Q = 54

423

mL/h). The breakthrough volume calculated is around 580 mL (i.e 73 BV) in both cases. In other

424

words, this means that a higher flow rate would ensure faster running time and similar amount of

425

Ni2+ ions uptaken below 0.34 .10-5 mmol/L (EU recommendations). The IEC for both cases is

426

calculated to be 1.6 meq.g-1 which shows that in the case of C0 = 5.0 mmol/L, a high flow rate (96

427

mL/h) is preferable for the sorption of Ni2+ ions onto LTP.

for Q = 54 mL/h and Q = 78 mL/h, respectively. This shows that for an initial nickel concentration

428 429

21



Page 22 of 34

Effect of the Ni2+ concentration in the feed solution

430

C/C0

1.0 0.9 0.8 0.7 0.6 0.5 0.4

2.5 mmol/L

0.3

5 mmol/L

0.2 0.1 0.0 0.0 431

20.0

40.0


432

Figure 6. Breakthrough curves for Ni2+ ions sorption on LTP at various concentrations with a flow

433

rate Q = 54 mL/h. For all cases, the solid line (−) represents the calculations using

434

Thomas model.

435

The influence of the concentration of Ni2+ ions is also studied and data are shown in Figure 6. The

436

breakthrough curve at higher concentration (C0 =5.0 mM) is sharper than at lower concentration

437

(C0 = 2.5 mM), as expected. The breakthrough volumes is estimated to 580 mL (i.e 73 BV) and

438

450 mL (i.e 56 BV), respectively. This indicates that more Ni2+ ions are being exchanged below

439

the EU regulations in the case of C0 =5.0 mM, despite a similar IEC observed on the overall

440

sorption process for both concentrations. This can be explained by the sharper breakthrough curve

441

observed for the highest concentrations (C0 =5.0 mM) and therefore a faster sorption process.

442

The Thomas approach was used to model the experimental points and the fittings can be seen in

443

Figure 5 and Figure 6. The Thomas model is a mathematical description of performances in cation 22


Page 23 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


444

exchange column in which the rate of the exchange is determined by a second order law. The

445

intraparticle diffusion and the external resistance during the mass transfer processes are considered

446

to be negligible by the model 26. It can be seen that the Thomas model fits well the experimental

447

data which is in good agreement with previously kinetics data on TiP1 sorbent where the pseudo

448

second order kinetics was found to be the best model to describe the sorption process. The ion-

449

exchange capacities found from the Thomas model (qTh in Table 1) are in good agreement with the

450

ion-exchange capacities determined experimentally (IEC in Table 1) with less than 1.5 % deviation.

451

452

Table 1. Sorption performances of LTP (C0:initial concentration, Q:flow rate, IECexp:

453

Experimental ion-exchange capacity, Y:column performance, qTh: IEC calculated with

454

the Thomas model, E: efficiency of the column) (n.a. not applicable). Cycles

1

2

3

4

5

6

C0, mmol/L

2.5 5.0 2.5 5.0 5.0 5.0

Q, mL/h

54

96

78

54

54

54

Y, %

99

94

47

94

64

70

IECexp, meq.g-1 1.7 1.6 0.8 1.6 1.1 1.2 qTh, meq.g-1

1.7 1.4 0.7 1.5 n.a n.a

E, %

63

66

78

80

62

75

455

456

Table 1 summarizes the sorption performances of the LTP sorbent through the six sorption cycles.

457

The yield of the column (Y %) is calculated with respect to the theoretical ion-exchange capacity

458

calculated from the Na+ uptake of LTP (IECcalc) which is estimated to be ca. 1.71 meq.g-1 (see 23



Page 24 of 34

459

section sodium uptake). A low yield signifies that not all sorption sites are saturated. The first

460

cycle was designed according to previously published batch kinetics data of TiP1 12. The flow rate

461

was chosen so that the contact time in the column was optimized to 10 min for an initial

462

concentration of 2.5 mmol/L. Under these conditions, the experimental ion-exchange capacity of

463

1.7 meq.g-1 reaches 99 % (Y) of the theoretical ion-exchange capacity (1.71 meq.g-1). The total

464

removal percent of Ni2+ ions from the feed solution that has passed through the column (E) is

465

estimated to be around 63 % due to larger 𝑞𝑁𝑖 2+ ,𝑡𝑜𝑡 (resulting in more tilted breakthrough curve).

466

Cycle 3 represents the effect of an increased flow rate under the same concentration conditions. In

467

this case, the efficiency (E) was calculated to be 78 % although the yield (Y) of the column dropped

468

down to 47 %, as a result of a shorter contact time between the nickel(II) ions and the LTP beds

469

(inability to reach sorption equilibrium). In order to get a higher E, multiple cycles and/or multiple

470

columns would be required providing that the flow rate and the concentration are optimized. For

471

example, in cycle 4, the concentration is raised to 5.0 mmol/L compared to cycle 1 and the

472

percentage of Ni2+ ions retained from the feed solution is 80 % (E), which is the highest recorded

473

for all cycles. The ion-exchange capacity recorded is 1.6 meq.g-1, which corresponds to a high

474

column yield of 94 % (Y). Furthermore, the second cycle involves the highest flow rate and

475

concentration used in this study. In this case, the yield (Y) is also determined to be 94 % which is

476

similar to cycle 4 but the removal percentage of Ni2+ from the feed solution (E) decreased down to

477

66 %, which discloses the importance of optimizing both the flow rates and the concentrations

478

when designing a column. Consequently, the optimal conditions for the sorption of Ni2+ ions on

479

LTP in a continuous mode and the current column design are revealed in cycle 4 (high E and high

480

Y). Two more cycles at these optimal conditions were run and a decrease in the yield is observed

481

down to 64 and 70 % for cycle 5 and 6, respectively. This is most likely due to some residual nickel

24


Page 25 of 34

482

left in the sorbent that could not be totally desorbed (as indicated by the NMR data; refer to 31P

483

MAS NMR section) and with time could limit the access to the sorbent-exchange sites. It can be

484

concluded that the LTP ion-exchanger could be sufficiently regenerated for at least four times

485

(where the IEC is kept high) and if required additionally two more times with a decreased IEC. Desorption studies

486

5.0

50.0 [HCl] = 0.05 M

40.0

C, mmol/L

C, mmol/L

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


96 mL/h

30.0 20.0 10.0 0.0

488

3.0

96 mL/h

2.0

54 mL/h

1.0 0.0

0

487

[HCl] = 0.01 M

4.0

200 400 Volume, mL

600

0

500 1000 Volume, mL

1500

Figure 7. Desorption profiles of Ni2+ ions during LTP regeneration using HCl at different concentrations and flow rates.

489

Desorption experiments with HCl were performed and the curves are shown in Figure 7. The first

490

desorption experiment with 0.05 M HCl at a flow rate of 96 mL/h was performed after the second

491

cycle while the desorption studies with 0.01 M HCl at 96 mL/h and 54 mL/h were performed after

492

the third and fourth cycles, respectively. The first desorption of LTP with 0.05 M HCl (Figure 7,

493

left) occurs in a volume range of about 250 mL which is equivalent to a bed volume of 31 BV. The

494

amount of Ni2+ ions desorbed decreases almost linearly with time during the first 200 mL used and

495

the resulting Ni2+ ions concentration in the desorption batch is estimated to be about 16 mmol/L,

496

which is about 3 to 6 times more concentrated than the initial amounts used for the sorption studies

497

(2.5 and 5.0 mmol/L).

25



Page 26 of 34

498

The desorption experiments with 0.01 M HCl display different profiles. The amount of Ni2+ ions

499

desorbed is at first constant forming a plateau (about 4.4 mmol/L) and then decreases nearly

500

exponentially. The desorption volumes for the flow rates of 96 mL/h and 54 mL/h are about 600

501

mL (i.e 75 BV) and 1050 mL (i.e 131 BV), respectively. The smaller volume collected is related

502

to the experimental conditions of the third sorption cycle (Y ca. 47 %). Only half of the nickel(II)

503

ions have been uptaken and thus much less volume is required to desorb the ions completely. The

504

flow rate does not seem to play a major role in the shape of the desorption curves as similar

505

sharpness and behavior are observed. On the other hand, when diluted acid is used (Q = 54 or 96

506

mL/h), about four times more volume is needed to completely convert the sorbent into the H-form.

507

This also corresponds to a desorbed nickel(II) amount of 3.5 mmol/L. Such a difference between

508

the starting Ni2+ concentration (of 2.5 or 5.0 mmol/L) and the final one could not justify the process

509

costs and would result in a secondary pollution. Therefore, the highest acid concentration (0.05 M

510

HCl) is preferable for LTP regeneration by HCL.

511

The sorbent was then converted to its sodium form using 0.5 M Na2CO3 before starting a new

512

cycle.

513

Chelating ion-exchange resins (such as Lewatit TP 207) have shown to be effective in removing

514

nickel ions from groundwaters. The IEC exchange capacity for such resins ranges from 0.65 to 1.9

515

meq.g-1 depending on the operating conditions: batch or column, ionic form (Na, Ca or H-forms),

516

flow rate and Ni2+ ions concentrations in the feed solution. They are often regenerated using 2-4 M

517

HCl and HNO3 is added when lead is present in the water 1,38. The LTP sorbent described in this

518

study displays similar or higher sorption capacities and can be regenerated using lower acid

519

concentrations.

520

26


Page 27 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


521

Very few research papers describe a complete study on the sorption performances of any sorbents

522

when it comes to continuous experiments. Data about regeneration cycles or sorption capacity (per

523

gram of sorbent) are often insufficient in order to enable comparison of sorption performances. In

524

this work, the sorption performances of a mixed type TiP ion-exchanger (LTP) in continuous

525

systems were thoroughly studied towards Ni2+ ions. The LTP ion-exchanger displayed excellent

526

continuous sorption properties that are in good agreement with the behavior in batch experiments,

527

which facilitate the prediction and the design of fixed bed columns (using batch sorption data).

528

This is a big advantage as the sorption features of LTP towards a specific ions could be first tested

529

in batch conditions (easier to implement) before planning continuous experiments. More work

530

focusing on the continuous sorption tests on amorphous TiP1 and mixture of divalent metal ions is

531

in progress and will be published elsewhere.

532 533

SUPPORTING INFORMATION

534

Kinetics data of the sorption of Co2+ and Cu2+ ions on TiP1 modeled with the non-linear approach

535

(Figure S1), Schematic representation of the column design used for the sorption of Ni2+ ions on

536

LTP (Figure S2), Fixed and variable parameters used during the whole column experiment (Table

537

S1) and comparison of the rate constant parameters together with the coefficients of determination

538

of the non-linear approach data for the pseudo-first and pseudo-second orders (Table S2).

539 540

ACKNOWLEDGMENT

541

The authors thank the Swedish Research Council Formas and Boliden Mineral AB for financial

542

support of this work. The authors acknowledge the LTU-based Centre of Advanced Mining and

27



Page 28 of 34

543

Metallurgy (CAMM2) for their part in financial support. We would also like to thank Prof. Jean-

544

Pierre Simonin for his valuable advice in re-analyzing the kinetics data. The foundation in memory

545

of J.C. Kempe and S.M. Kempe and LTU funds are acknowledged for grants used to upgrade the

546

NMR spectrometer to a Bruker Ascend Aeon WB 400 spectrometer.

547

548

REFERENCES

549

(1)

Quality; 2005.

550

551

(2)

(3)

(4)

Fu, F.; Wang, Q. Removal of Heavy Metal Ions from Wastewaters: A Review. J. Environ. Manage. 2011, 92 (3), 407–418, DOI 10.1016/j.jenvman.2010.11.011.

556

557

IARC. Nickel and nickel compounds. In Chromium, nickel and welding; Lyon, 1990; pp 257–445.

554

555

Macomber, L.; Hausinger, R. P. Mechanisms of nickel toxicity in microorganisms. Metallomics 2011, 3 (11), 1153–1162, DOI 10.1039/C1MT00063B.

552

553

World Health Organization. Nickel in Drinking-water. In Guidelines for Drinking-water

(5)

Arshadi, M.; Amiri, M. J.; Mousavi, S. Kinetic, Equilibrium and Thermodynamic

558

Investigations of Ni(II), Cd(II), Cu(II) and Co(II) Adsorption on Barley Straw Ash. Water

559

Resour. Ind. 2014, 6, 1–17, DOI 10.1016/j.wri.2014.06.001.

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(6)

Rathor, G.; Adhikari, T.; Chopra, N. Management of Nickel Contaminated Soil and Water

561

Through the use of Carbon Nano Particles. J. Chem. Biol. Phys. Sci. Sect. A 2013, 3 (2),

562

901–905.

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(7)

Vengris, T.; Binkiene, R.; Sveikauskaite, A. Nickel, copper and zinc removal from waste 28


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water by a modified clay sorbent. Appl. Clay Sci. 2001, 18 (3), 183–190, DOI

565

10.1016/S0169-1317(00)00036-3.

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(8)

Álvarez-Ayuso, E.; Garcı́a-Sánchez, A.; Querol, X. Purification of metal electroplating

567

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662 663 664 665 666 667 668

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TABLE OF CONTENTS For Table of contents use only Good correlation between column experiments and batch sorption data with the same ionexchange capacity over at least four cycles.

669 670 671

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Complete Column Trials for Water Refinement Using Titanium(IV

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