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Study of Rare Earths Leaching After Hydrothermal Conversion of Phosphogypsum

  • Amani Masmoudi-SoussiEmail author
  • Ines Hammas-Nasri
  • Karima Horchani-Naifer
  • Mokhtar Férid
Original Article
  • 26 Downloads

Abstract

Phosphogypsum (PG) is classified as the main hazardous waste present in large quantities in Tunisia. It is a by-product of the fertilizer industry produced by a sulfuric acid attack on calcium phosphate. Storage and management of this toxic waste are environmental problems that concern many countries producing phosphate fertilizer, especially since waste is, in principle, prohibited by international law. Therefore, finding out a solution for the valorization or the removal of phosphogypsum has become a universal preoccupation and a topical research field. In this work, a fresh produced PG sample was firstly characterized by various analytical methods to determine its chemical composition as well as its rare earth elements (REEs) amount. Then, a hydrothermal conversion of the PG allowed obtaining an insoluble residue of calcium carbonate richer in REEs than the starting sample such that the enrichment rate was 66%. The obtained residue, considered after that as an interesting source of rare earths, was leached with a hydrochloric solution (5–6%) in the presence of ascorbic acid as reducing agent. The leaching method favored the migration of 89% of REEs to the leach liquor.

Keywords

Phosphogypsum Conversion Calcium carbonate Leaching Rare earth elements 

1 Introduction

Phosphogypsum (PG) is the main waste of the fertilizer industry produced by the chemical attack on natural calcium phosphate by sulfuric acid according to the following simplified reaction:
$${\text{Ca}}_{ 10} \left( {{\text{PO}}_{ 4} } \right)_{ 6} {\text{F}}_{ 2} + { 1}0{\text{H}}_{ 2} {\text{SO}}_{ 4} + { 2}0{\text{H}}_{ 2} {\text{O }} \Rightarrow 10{\text{CaSO}}_{ 4} . 2 {\text{H}}_{ 2} {\text{O }} + {\text{ 6H}}_{ 3} {\text{PO}}_{ 4} + {\text{ 2HF}} .$$
(1)

Storage and management of this toxic waste are problems that concern many phosphate fertilizer producing countries. The production of a ton of phosphoric acid produces 5 tons of phosphogypsum [1].

The annual world production of phosphogypsum has been estimated to be around 200–300 million tons per year [2]. Most of this by-product (85%) is disposed without any treatment, usually by dumping in large stockpiles, while a small part (15%) is devoted to industrial or commercial use such as building materials, soil amendment for soil remediation, agricultural fertilizers or as a set controller as in the Portland cement manufacture [3, 4].

In Tunisia, according to the Tunisian Chemical Group official website, the phosphoric acid industry has been developed since the early 1950s [5]. The annual Tunisian phosphogypsum production is about 10 million tons which are stocked in sites near the SIAPE (Société Industrielle d’Acide Phosphorique et d’Engrais) in Sfax [6].

Various studies have been carried out to identify and quantify the impurities contained in the phosphogypsum. The latter may contain P2O5, fluoride, heavy metals and some radioactive elements [7, 8, 9, 10]. Concentrations of these hazardous elements depend on the origin of phosphate rock source, the type and efficiency of the wet process used and the storage time of phosphogypsum [7].

One of the approaches that can be explored for the valorization of this waste is its conversion into calcium carbonate [11, 12, 13]. Pure calcium carbonate has many uses in a wide variety of industrial and commercial applications. It is used in the manufacture of concrete or Portland cement, for producing lime to be used in soil stabilization and acid neutralization, for water treatment and flue gas desulfurization [14]. As it can also be used as a filler and coating pigment in paper, plastics, paints, rubbers and adhesives [15, 16].

However, Kolokolnikov and Kovalev [12] have shown that the calcium carbonate resulting from phosphogypsum conversion contains the majority of impurities initially present in the PG waste.

Rare earth elements are an example of such impurities which pass from phosphogypsum to calcium carbonate during the conversion step [12]. Recent study showed that, between the years 2020 and 2025, the growth in global demand for the rare earth elements will accelerate, which will lead to the opening of new mines or the search for an alternative source [17]. Therefore, the phophogypsum-derived calcium carbonate can be considered as an interesting source for rare earths recovery. Rare earths, associated with CaCO3, can be recovered by dissolution of the carbonate in mineral acid followed by extraction with tri-butyl phosphate or by thermal decomposition of the carbonate to the corresponding oxide which was then leached with a saturated solution of ammonium chloride to selectively dissolve the CaO [12, 18] and leave the elements in question in the residue. Extraction of these elements is then carried out from the obtained residue. Results indicated that up to 97% of the rare earths contained in the calcium carbonate are dissolved in solution by leaching preferentially with an HCl solution (5–6%) in the presence of reducing agent [19].

In the present investigation, a complete analysis using different techniques of a phosphogypsum sample, taken from Sfaxian dumps, was firstly presented and discussed. Then, after hydrothermal conversion of the sample into calcium carbonate, rare earths leaching from the latter using a hydrochloric acid solution (5–6%), in the presence of ascorbic acid as a reducing agent, was studied. To make a detailed study, several analytical techniques were used for solids identification and rare earths content’s monitoring during the process.

2 Materials and Methods

2.1 Materials

The phosphogypsum sample was taken from storage stacks located at the Sfax industrial platform in eastern of Tunisia. The studied sample of fresh production was crushed manually and ground with an automatic mortar grinder to mix and homogenize the powders then was sieved using a sieve of 3 mm mesh size.

For economic reasons, a solution of dietary NaCl (25 g/L) was used for washing the phosphogypsum sample. On the other hand, the used sodium carbonate is of high purity (99.5%) produced by “Oxford Lab Chem”. A commercial concentrated solution of hydrochloric acid (37%) produced by “Merck” was used to prepare a diluted solution (5–6%) for the leaching process.

2.2 Methods

2.2.1 Infrared Spectroscopy

Infrared spectra were performed on a FT-IR System Perkin Elmer spectrometer using KBr pellets in the region of 4000–400 cm−1.

2.2.2 X-ray Diffraction Analysis

The X-ray powder diffraction patterns of all samples were recorded on an automatic X’PERT Pro PAN Analytical diffractometer at room temperature with Cu Kα radiation (λ = 0.15418 nm). This analysis was systematically carried out for all products previously crushed. After data acquisition, we obtained diffractograms with all peaks indexed using the X’Pert High Score Plus software. The phases were identified by comparison with the references in the ICDD (International Centre for Diffraction Data) database.

2.2.3 Differential Scanning Calorimetry

A Differential Scanning Calorimetry Mettler Toledo Model 823 was used to register for the thermographic curves for samples; a weighed sample portion being equal to 0.5 g, the heating rate amounting to 20 °C/min.

The method consists of simultaneously heating a reference (an empty aluminum sample capsule) in a first furnace and an aluminum capsule containing the sample to be studied in a second furnace. The principle of this method is power compensation, which consists in directly and continuously measuring the difference in electrical power to be supplied to the reference and the sample when an endothermic or exothermic reaction occurs in the latter so as to reduce and cancel the temperature difference between the sample and the reference by means of a previously established heating program. It is in fact the current intensity, provided by a power generator, necessary for the thermal balance between the two measuring heads that is recorded as a function of time and expressed in mcal/s, the recorded signal is therefore proportional to the difference in heat provided to the sample and the reference, and the result is given as a function of the average temperature of the two samples.

2.2.4 X-ray Fluorescence Spectrometry (XRF)

The X-ray fluorescence spectrometry (XRF) analyzes was performed at the SPECTRO research laboratory (France). The sample was analyzed by XRF spectrometry to determine its chemical composition of major and trace elements.

The powdered sample material was filled up to a height of approx. 10 mm into a disposable XRF sample cup with an outer diameter of 32 mm. The cup was closed on the analytical side with a 4 μm thin polypropylene film. The analysis results were calculated using a screening method which mathematically consists of a combination of a Compton correction model with a fundamental parameters program for fluorescence and scattering. The listed “Abs. Error” in the results is the statistical error for a confidence interval of one sigma (1 σ).

2.2.5 ICP/MS Analysis

ICP-MS analysis were performed at the Department of Biology, Ecology and Earth Sciences, University of Calabria. The PG sample was analyzed by a Perkin Elmer ICP-MS apparatus to determine its content of thorium and rare earth elements. For solid’s analysis, the dissolution step was carried out using a Mars5 microwave digester (CEM technologies). On the other hand, solution analysis was performed after dilutions with Millipore water.

About 100 mg (± 0.01 mg) of the powdered phosphogypsum sample was placed in a microwave vessel with a triacid mixture: 6 ml of Merck “suprapur” hydrofluoric acid, 5 ml of nitric acid and 3 ml of Perchloric acid. The microwave vessel containing the acids and the phosphogypsum, covered and sealed with a cap, subjected to an oven method consisting of a 15 min ramp to 200 °C and a pressure of 600 PSI and then kept at the temperature for 15 min and then cooling of 15 min. An unclear solution containing some residue was obtained. The contents of the vessel were allowed to heat up to 200 °C. 3 ml of pure HClO4 was added before the complete acid evaporation and the mixture was heated up to 200 °C. Before the complete evaporation, 5 ml of HNO3 (5%) was then added. A clear, colorless solution was finally obtained. This latter was left to cool down gently and made up to a standard volume in a 100 ml volumetric flask with Millipore water to prepare the mother solution. External calibration curves were prepared using Perkin Elmer “multi-element Calibration Standard 2 solution” to analyze rare earth elements. Standard reference materials Micaschist (SDC1) were prepared in the same way and were used as unknown samples during the analytical sequence. The elements concentrations were compared with certified values to evaluate accuracy and precision of analytical data.

2.2.6 Hydrothermal Conversion Method

The phosphogypsum sample was firstly washed with salt water ([NaCl] = 25 g/l) in order to remove water-soluble impurities [20].

The PG conversion to calcium carbonate was realized after that in a high-pressure and high-temperature Parr-reactor which is equipped with a suspended agitator and a turbine coupled to a controller. This tool served to adjust and control temperature, pressure and agitation’s speed.

The PG conversion was carried out by mixing 15 g of the washed sample with a pre-calculated quantity of water such that the concentration of the phosphogypsum suspension was 5% in weight. Then, the suspension was mixed for 20 min at ambient temperature.

An amount of sodium carbonate corresponding to a molar ratio Na2CO3/PG = 2 was added to the suspension of phosphogypsum. The mixture was introduced into the reactor for 2 h at a temperature set at 80–100 °C and with continuous stirring at a speed of 500 rpm. The residue of calcium carbonate was recovered finally by simple filtration of the mixture.

2.2.7 Leaching Experiment

The leaching of the calcium carbonate residue was carried out with an HCl solution (5–6% in weight) such that the molar ratio HCl/Ca was equal to 3. After stirring the mixture at room temperature, a mass of ascorbic acid satisfying the mass ratio between the liquid and solid (L/S) = 10 was added to the mixture.

The choice of use of ascorbic acid as a reducing agent was based on the Kolokolnikov and Kovalev study [19]. The reducing agent has the role of increasing the solubility of the rare earth elements to improve the extraction yield of the latter in the acidic liquor. It is preferable to use ascorbic acid as a reducing agent since the oxidation of this substance occurs with gaseous carbon dioxide evolution thus the leaching solution could not be contaminated with the products of its. Indeed, according to the CHON principle [21], it can be incinerated, releasing only CO2 and H2O.

Regarding its acidity, ascorbic acid is a diacid (pka1 = 4.1, pka2 = 11.7) [22]. It is much more acidic than would be expected, thanks to its double bond that allows for stabilization by delocalization. This could then beneficially improve the efficiency in the leaching [22].

The leaching was then carried out at a temperature between 80 and 90 °C for 1 h. The solid–liquid separation by centrifugation allowed recovering the acidic liquor and the residue.

3 Results and Discussion

3.1 Physico-chemical Study of the Phosphogypsum Sample

3.1.1 Infrared Spectroscopy Analysis

In the infrared spectrum of the studied phosphogypsum sample, depicted in Fig. 1, the characteristic bands of the dehydrate calcium sulfate were observed. The vibration modes for the 2248–2118 cm−1 are assigned to νO–S–O stretching modes [7]. The vibrations located at the 1150–1116 cm−1 range are attributed to the stretching modes ν3 and ν1 of sulfate groups [7]. Bands of varying intensity at 670 and 603 cm−1 can be attributed to the bending modes δO–S–O.
Fig. 1

Infrared spectrum of a fresh produced phosphogypsum sample (a 4000–2000 cm−1, b 2000–400 cm−1)

The bands at 1686–1622 cm−1 correspond to the bending modes of water vibrations, and broadband between 3600 and 3400 cm−1are characteristic of the H2O stretching modes.

The bands at 796 cm−1, 875 cm−1 and 1004 cm−1 confirm the presence of HPO42− impurities in the sulfate matrix of the sample (fresh produced).In fact, such ions (HPO42−) correspond to impurities of residual acids (having as origin the phosphate ore attack).

3.1.2 X-ray Diffraction Analysis

The PG sample was analyzed through X-ray diffraction (XRD) to determine its crystalline composition.

It was mainly identified to the gypsum phase CaSO4·2H2O (file PDF No. 01-074-1433) (which crystallizes in the monoclinic system with I2/c as space group); with the coexistence of other impurity phases which correspond mainly to calcium sulfate hydrate CaSO4·H2O and Quartz SiO2 (see Fig. 2.).
Fig. 2

X-ray diffraction pattern of the studied phosphogypsum sample

3.1.3 Thermal Analysis (DSC)

The thermal behavior of the PG sample was studied using a differential scanning calorimetry (DSC) (with a heating rate of 20 °C/min up to 600 °C).

The obtained thermogram (see Fig. 3) showed that the decomposition of the initial material into hemihydrate (CaSO4·1/2H2O) occurred at 147 °C. The temperature of the phase transition from hemihydrate to anhydrite III (CaSO4 hexagonal) was observed at 160 °C. The exothermic peak, located at 445 °C, is related to the transformation from anhydrite III (CaSO4 hexagonal) to anhydrite II (CaSO4 orthorhombic) [23].
Fig. 3

Thermogram of the PG sample

3.1.4 Elemental Analysis by X-ray Fluorescence Spectrometry (XRF)

The PG sample was analyzed also by XRF spectrometry to determine its chemical composition of major and trace elements. The results are summarized in Tables 1 and 2, respectively.
Table 1

The major elements composition of the PG sample (expressed as %)

Element (%)

Content (%)

Abs. error

Na2O

0.09

0.005

MgO

0.10

0.0058

Al2O3

0.15

0.0012

SiO2

0.77

0.002

P2O5

4.1

0.004

K2O

0.02

0.00038

CaO

21.06

0.01

SO3

42.42

0.02

Fe2O3

0.13

0.0005

S

9.78

0.003

H2O tot

19.83

Table 2

The trace element composition in the PG sample (expressed as mg/kg)

Element

Cl

Sc

Ti

V

Cr

Mn

Co

Ni

Cu

Content (mg/kg)

82.5

67.6

83.8

12.1

47.2

3.3

< 1.3

6.5

4.4

Abs. error

0.9

2

1.3

0.7

0.6

1.1

0.5

0.3

Element

Zn

Ga

Ge

As

Se

Rb

Sr

Zr

Nb

Content (mg/kg)

65.9

0.6

<0.1

0.5

4.1

1.6

883.9

26.9

2.3

Abs. error

0.5

0.1

0.1

0.1

0.1

0.8

0.4

0.2

Element

Mo

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Content (mg/kg)

4.1

< 0.3

< 0.1

< 0.6

1.5

17.2

< 0.7

< 1.2

< 1.6

Abs. error

0.3

0.2

0.6

Element

Cs

BaO

Ba

Hf

Ta

W

Pt

Au

Hg

Content (mg/kg)

< 7.4

< 11

< 10

< 1.1

< 1.3

0.8

< 0.5

< 0.7

< 0.4

Abs. error

0.4

Element

Tl

Te

I

Pb

Bi

U

Content (mg/kg)

< 0.2

< 2.9

< 3.3

3.1

< 0.3

6.1

Abs. error

0.2

0.2

The main elemental composition of phosphogypsum was dominated by Ca (CaO) and S (SO3) because it is mainly composed of gypsum. P2O5 and silica (SiO) were the most abundant species of phosphogypsum just after CaO and SO3, with values rising to 4.1 and 0.77%, respectively. The concentration of phosphorus was higher than the average (0.05–1.42), which may be due to residual acid phosphoric effects and unaffected phosphates [24]. Phosphate can also be substituted for the crystalline structure of gypsum crystals [25].

Of the 42 trace elements presented in Table 2, the most abundant were Sr (up to 883.9 mg kg−1), Ti (up to 83.8 mg kg−1), Cl (up to 82.5 mg kg−1), Sc (up to 67.6 mg kg−1), Zn (up to 65.9 mg kg−1), Cr (up to 47.2 mg kg−1), Zr (up to 26.9 mg kg−1), Cd (up to 17.2 mg kg−1), V (up to 12.1 mg kg−1) and Ni (up to 6.5 mg kg−1).

3.1.5 ICP-MS Analysis

The amounts of rare earth elements and thorium present in the PG sample were determined by ICP/MS analysis. The results, grouped in the Table 3, showed a total REEs content of about 383 ppm.
Table 3

Thorium and rare earth elements content in the PG sample (expressed as mg/kg)

Element

Y

La

Ce

Pr

Nd

Sm

Eu

Gd

Content (mg/kg)

73.57

67.94

114.18

16.65

59.65

12.10

2.70

13.09

Element

Tb

Dy

Ho

Er

Tm

Yb

Lu

Th

Total REEs

Content (mg/kg)

1.89

9.38

2.13

5.34

0.72

3.30

0.49

1.89

383.13

3.2 Hydrothermal Conversion of the PG

3.2.1 Residue’s Characterization

The infrared spectrum of the residue (see Fig. 4) showed the presence of the characteristic vibrations of the O–C–O bonds. Indeed, the bands observed around 1440 cm−1 and 1054 cm−1 correspond, respectively to ν3 stretching vibrations (as) (CO) and ν1 (s) (CO). The bands observed at 872 cm−1 and 713 cm−1are attributed to CO3 out-of-plane deformation (ν2) and O–C–O bending in-plane deformation (ν4), respectively [26]. To conclude, the bands at 1440, 872 and 713 cm−1 are the characteristic absorption bands of calcium carbonate [27].
Fig. 4

The infrared spectrum of the obtained residue

Also, the results of X-ray diffraction on the obtained residue are in good agreement with those of infrared spectroscopy. The X-ray pattern depicted on Fig. 5 showed that the major phase corresponds to the calcium carbonate of the Rhomboedric structure with space group R-3c (file PDF No. 01-072-1937). It also contains impurities of quartz and calcium carbonate phosphate hydroxide. The presence of the latter can be explained by the use of a fresh produced phosphogypsum characterized by a relatively high amount of P2O5.
Fig. 5

X-ray diffraction pattern of the obtained residue

3.2.2 REEs Content in the Residue

As shown in previous studies, rare earths pass from phosphogypsum to calcium carbonate during the conversion step [19]. Therefore, the content of some REEs in the obtained calcium carbonate were measured by ICP-MS analysis (see Table 4).
Table 4

Comparison of thorium and rare earth elements contents in the obtained calcium carbonate with those in the starting PG (expressed as mg/kg)

Element

Content in PG (ppm)

Content in CaCO3 (ppm)

Enrichment (%)

Y

73.57

148.7

50.52

La

67.94

200.6

66.13

Ce

114.18

492.13

76.80

Pr

16.65

52.13

68.06

Nd

59.65

166.48

64.17

Sm

12.10

27.1

55.35

Eu

2.7

12.33

78.1

Gd

13.09

47.2

72.27

Tb

1.89

4.22

55.21

Dy

9.38

19.6

52.14

Ho

2.13

4.5

52.67

Er

5.34

12.3

56.58

Tm

0.72

1.84

60.87

Yb

3.30

11.6

71.55

Lu

0.49

13.3

96.31

Th

1.89

11.6

83.71

Total

  

66.28%

Results showed that the hydrothermal conversion method has transformed the PG into calcium carbonate richer in rare earths and thorium than the starting solid, such that the enrichment rate, calculated as follows, was equal to 66.28%:
$$REE\,enrichment \left( \% \right)\frac{{REE_{{CaCO_{3} }} - REE_{PG} }}{{REE_{{CaCO_{3} }} }} \times 100.$$

Rare earths migration to the carbonated matrix may be explained by two facts: the first may be linked to the insertion of REEs into the gypsum matrix by replacement of calcium ions (in phosphogypsum) [7, 28, 29] so while forming the calcium carbonate (which is more stable than the calcium sulphate due to its lesser solubility product) REEs migrate to the carbonated matrix by following the calcium ions, the second may be relied to the known affinity of REEs towards carbonates in an alkaline pH [30, 31] so we can suggest the establishment of chemical bonds between REEs and carbonates. To prove such explanation further studies must be done.

Table 4 shows that the enrichment rate of most rare earths is approximately close to each other (in the range 50–70%), with the exception of the Lu element (96%). No explanation for this can be given without resorting to further studies.

3.3 REEs Leaching from the Carbonate Residue

3.3.1 REEs Content in the Leach Liquor

The content of rare earth elements present in the obtained leach liquor was measured by ICP/MS. Based on the results grouped in Table 5, leaching the obtained calcium carbonate according to the method detailed in the Sect. 2.2.7 has favored a rare earths and thorium migration in the acidic liquor with a rate of 89.74%. This recovery rate was calculated as follows:
$$Recovery\,rate \left( \% \right) = \frac{{REE_{ac.liquor} }}{{REE_{{CaCO_{3} }} }} \times 100.$$
Table 5

Rate of thorium and rare earth elements migrations from calcium carbonate to the hydrochloric leach liquor (expressed as mg/kg)

Element

Content in acid liquor

Recovery (%)

Y

132.89

89.36

La

192.89

96.16

Ce

472.79

96.07

Pr

48.75

93.52

Nd

138.06

82.93

Sm

26.68

98.45

Eu

10.62

86.13

Gd

42.01

89

Tb

3.99

94.55

Dy

18.74

95.61

Ho

3.94

87.55

Er

10.83

88.05

Tm

1.64

89.13

Yb

7.91

68.2

Lu

11.95

89.85

Th

10.59

91.29

Total

 

89.74%

Such attractive rate of REEs and thorium migration was obtained thanks to the ease dissolution of calcium carbonate in acid medium (better than sulphate). For this reason, the method started with PG conversion to calcium carbonate. REEs recovery may be carried out after that by precipitation or by solid/liquid extraction methods.

4 Conclusions

A fresh produced Tunisian phosphogypsum was firstly characterized by different techniques in order to provide a complete overview on the sample used in this work. The PG is predominantly composed of gypsum CaSO4·2H2O with the coexistence of various impurities such that P2O5 and quartz (SiO2) were the most abundant. Since the work is interested in REEs, ICP/MS analysis of the starting PG showed a total amount of 383 ppm of such elements.

The hydrothermal conversion of the phosphogypsum to calcium carbonate was performed in a reactor at 80–100 °C for 2 h. The results showed the effectiveness of the hydrothermal method to ensure a complete conversion of the sulphated matrix to the corresponding carbonate. X-ray diffraction showed that the major phase of this insoluble residue corresponds to calcium carbonate with presence of, as secondary phases, silica and calcium carbonate hydroxide phosphate. Obtaining the latter phase was linked to the use of a fresh produced phosphogypsum characterized by the presence of residual phosphate acids (having as origin the phosphate ore attack). ICP/MS analysis proved the enrichment of the calcium carbonate with REEs and thorium such as the rate was 66%. This may be related to the insertion of REEs into the gypsum matrix by replacement of calcium ions (in phosphogypsum) and by the known affinity of REEs towards carbonates in an alkaline pH.

Leaching the obtained calcium carbonate with a hydrochloric solution (5–6%) at 80–90 °C for an hour, in the presence of ascorbic acid as reducing agent, allowed the migration of 89% of REEs and thorium to the acid liquor. The interest of converting PG into calcium carbonate (which is easily dissolved in an acidic medium) can be understood at this level, favoring thus the migration of rare earths into the liquor.

To conclude, the present work has shown the effectiveness of the proposed method for achieving such a rare earth migration rate in the acid solution. The method is simple since it was simply formed by two steps: hydrothermal conversion of PG and acid leaching of calcium carbonate.

The extraction of these elements from the leach liquor may be done after that by precipitation or by solid/liquid extraction.

Notes

Acknowledgements

Special thanks to the entire team of the Laboratory of Physico-Chemistry of Mineral Materials and their applications to the National Center for Research in Materials Science, Technopole Borj Cedria and all those who contributed directly or indirectly to the realization of this work. Project supported by the Ministry of Higher Education and Scientific Research of Tunisia.

Compliance with Ethical Standards

Conflict of interest

On behalf of all authors, the corresponding author states that there is no conflict of interest.

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Copyright information

© The Tunisian Chemical Society and Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Laboratory of Physical Chemistry of Mineral Materials and their ApplicationsNational Research Center in Materials Sciences, Technopole Borj CedriaSolimanTunisia
  2. 2.Faculty of Sciences of BizerteUniversity of CarthageJarzounaTunisia

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