Can carboxymethyl cellulose molecules bind swelling montmorillonite layers in Water?

Accepted Manuscript Title: Can Carboxymethyl Cellulose Molecules Bind Swelling Montmorillonite Layers in Water? Authors: Yiming Yang, Tianxing Chen, Hongliang Li, Hao Yi, Shaoxian Song PII: DOI: Reference:

S0927-7757(18)30486-2 https://doi.org/10.1016/j.colsurfa.2018.06.006 COLSUA 22575

To appear in:

Colloids and Surfaces A: Physicochem. Eng. Aspects

Received date: Revised date: Accepted date:

19-4-2018 31-5-2018 2-6-2018

Please cite this article as: Yang Y, Chen T, Li H, Yi H, Song S, Can Carboxymethyl Cellulose Molecules Bind Swelling Montmorillonite Layers in Water?, Colloids and Surfaces A: Physicochemical and Engineering Aspects (2018), https://doi.org/10.1016/j.colsurfa.2018.06.006 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Can Carboxymethyl Cellulose Molecules Bind Swelling Montmorillonite Layers in Water?

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Yiming Yang a, Tianxing Chen a,*, Hongliang Li b, Hao Yi a, Shaoxian Song c, *

School of Resources and Environmental Engineering, Wuhan University of

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Technology, Luoshi Road 122, Wuhan, Hubei, 430070, China

School of Mining Engineering, Taiyuan University of Technology, Taiyuan, Shanxi,

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China c

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Hubei Key Laboratory of Mineral Resources Processing and Environment, Wuhan

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Corresponding

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University of Technology, Luoshi Road 122, Wuhan, Hubei, 430070, China

authors.

E-mail:

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[email protected] (S. Song).

[email protected]

(T.

Chen),

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Graphical Abstract:

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Abstract

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Sodium carboxymethyl cellulose (CMC) molecule binding montmorillonite (MMT) layers in aqueous suspension has been studied in this work. This study was performed through the

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measurements of adsorption capacity, swelling capacity and Fourier transform infrared spectroscopy, as well as molecular dynamics simulations. The results have shown that CMC

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molecules adsorbed on MMT edges through the formation of hydrogen bond with the Si-OH. However, the swelling capacity of MMT in water was almost the same in the presence and absence of CMC, meaning that CMC could not bind swelling montmorillonite layers in water. The molecular dynamics simulation with the CLAYFF force field indicated that the adsorption energy

of CMC onto MMT edges was much less than that of MMT hydration swelling, which might be attributed to that CMC molecules could not bind swelling montmorillonite layers in water.

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Keywords: montmorillonite; sodium carboxymethyl cellulose; swelling

1. Introduction

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In recent years, owing to its unique cation exchange, and low hydraulic conductivity and swelling properties, clay minerals are drawing great attention as buffer and backfill materials in

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spent nuclear fuel disposal. Montmorillonite (MMT), as the major component of clay minerals, mainly accounts for these properties[1-3]. MMT is a typical layered mineral in which each

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individual layer consists of a pair of tetrahedral sheets sandwiching an octahedral sheet.

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Silicon-oxygen tetrahedron and aluminum-oxide octahedron are combined by a common oxygen

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atom[4-6]. Owing to isomorphic substitutions of Al3+ for Si4+ in tetrahedral sites and Mg2+ for Al3+

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in octahedral sites, MMT particles have permanent negative charges on their faces [7, 8]. Depending

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on pH value, the broken bonds located at the edges of the platelet (alumina sheet) have a capacity to adsorb H+ or OH-[9]. As a result, the charges are balanced through cations held between individual

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layers in the interlayer space[10-12]. When water and polar organic molecules are attracted by the exchangeable cations and are intercalated in the layers, the structure expands in a direction

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perpendicular to the layers.

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MMT swelling as a key factor in its performance, has acquired extensive experimental and

theoretical investigations[13, 14]. Also, the swelling of MMT can give rise to production of a large number of colloidal particles and cause a wide range of different problems in mineral beneficiation circuits[15-18]. The investigations have demonstrated that the swelling behavior is influenced by multiple factors, including the hydration energy of the counterions and the basal

planes of the crystalline layers as the driving force, and the Van der Waals force and the electrostatic attraction caused by the counterions as the binding force[19]. The swelling of MMT in aqueous suspensions can be considered as two stages: (1)lattice expansion, caused by the adsorbed water molecules in the interlayer under the effect of electric field of negatively charged

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surface of MMT; (2) osmotic expansion, caused by the concentration of counterions difference between the interlayer and bulk solution, which would result in the fact that the water molecules

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are adsorbed into the crystalline layers under the effect of osmotic pressure[20-22].

Up to date, there are several ways to inhibit MMT swelling based on the swelling stages of

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MMT: (1) Ion exchange with the low hydration energy counterions[23, 24]. Jia Liu et al. found

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that the swelling capacity of Ca-, Mg-, and Al-MMT decreased significantly than the Na-MMT,

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caused by the weak hydration capacity of Ca2+, Mg2+, Al3+[25]. (2) Reducing the counterions. Clay

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swelling inhibitor can combine strongly with the hydroxylated and negatively-charged clay surface,

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and neutralize its electricity for reducing the counterions, showing excellent anti-swelling ability[26]. (3) Reducing the hydration of the basal planes of the MMT layers. The main principle

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of this method is to change the hydrophobicity of MMT surface and reduce the hydration of the basal planes of the MMT layers, affecting the swelling ability of MMT[27, 28]. (4) Protecting the

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MMT from water. Sheu studied that the water soluble shale stabilizing polymers can effectively stabilize many shale formations through combination with the surface of the clay particles and

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preventing contact of the free water molecules[29]. Carboxymethyl cellulose (CMC), as the subject of this present study, is a water soluble polymer derived from cellulose. It is widely used as a thickener, binder, suspension, stabilizer and water retaining agent in pharmaceutical, food industry, paper, cosmetic and other industrial areas.

To our knowledge, there has been no report about inhibiting the hydration swelling of MMT using CMC as an inhibitor. In this study, an attempt has been made to investigate the effect of CMC on hydration swelling of MMT, which provides the theoretical basis and practical significance for

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further study of MMT hydration swelling.

2. Experimental

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2.1 Materials

The original Na-MMT sample used in this study is from Chifeng Ningcheng MMT Co. Ltd

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(Inner Mongolia, China). A common method to purify colloidal MMT is fractionation by

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sedimentation. The XRD pattern of MMT was shown in Fig. 1.

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As seen in Fig. 1, the montmorillonite was Na-MMT with very high grade. The particle size

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distribution of MMT was given in Fig. 2. It was shown that the size composition with the D90 (particle size at 90% of cumulative undersize) is 7.62 μm and the D50 (particle size at 50% of

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cumulative undersize) is 4.52 μm.

In this work, the hydrochloric acid(HCl) used was obtained from East Chemical Co. Ltd from

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Xinyang of China and other chemical reagents were from sinopharm Chemical Reagent Co. Ltd

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from Shanghai of China. The viscosity of the sodium carboxymethyl cellulose(CAS:9004-32-4) is 800-1200 mPa·s. The CMC was of chemical purity and other chemical reagents were of analytic

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purity. Milli-Q ultrapure water used in this work was produced by a water purification system with 18.2 MΩ.

2.2 Measurements 2.2.1

Characterization of Na-MMT

X-ray diffraction (XRD) analysis was performed by a Bruker D8 ADVANCE x-ray

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diffractometer at a voltage of 40 kV and a current of 40 mA with Cu K radiation. The particle size distribution was measured using a Malvern Mastersizer 2000. FTIR analysis of MMT/CMC was

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determined using a Nicolet6700 (Nicolet, U.S.A) with the wave number range 4000-400 cm-1 and the highest resolution 0.019 cm-1. The sample for FTIR analysis was collected after measurement

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of the swelling capacity of Na-MMT. Before FTIR analysis, the collected sample was centrifuged,

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Adsorption experiments

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washed and dried.

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Adsorption experiments of CMC on MMT was performed in the container at room temperature. In the adsorption studies, 0.1 g MMT was firstly added into CMC solution with a given concentration of 20 mg/L, followed by mechanical shaking at 450 rev/min for a

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predetermined time intervals. After that, the suspension was filtered with 0.22 µm filter membrane

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and the filtrate was collected for the Ultraviolet spectrophotometry of CMC concentration. 2 ml of the filtrate was added into 10 ml centrifuge tubes. Then 2.0 mL BR buffer solution (pH=8.0), 1.0

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mL acridine orange solution(8×10-4 mol/L) and 5mL deionized water was added in turn. Shake well and the solution was estimated by Origin Aquamate 8000 UV-Vis Spectrophotometer at 490 nm after setting for about 30min at room temperature.

2.2.3

Measurement of the swelling capacity of Na-MMT

The measurement of the swelling capacity of MMT was performed according to the procedure described previously[25]. First, different concentrations of CMC solution and 1 M HCl

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solution were prepared. Then, 1 g montmorillonite was slowly added into the CMC solution. Deionized water was added up to 75 mL. The solution was stirred for 4 min at 450 rev/min with

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an IKA RW 20 oscillator. 25 mL of the previously prepared HCl solution was added into the

container, and the solution was continually stirred at 450 rev/min for 1 min. Finally, the solution was poured into a glass-strppered 100 mL graduated cylinder, which was placed on a horizontal

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countertop for 24 h. The value of the solid–liquid interface indicated the swelling capacity of

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Na-montmorillonite.

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2.2.4 Molecular dynamics simulation

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In this work, the molecular dynamics simulations were all carried out in Forcite module of Materials Studio 8.0. The clay force field (CLAYFF) was chosen for simulation running. The

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unit-cell formula of Na-MMT model was: Na0.75(Si7.75Al0.25)(Al3.5Mg0.5)O20(OH)4. Space group was C2/m, the fundamental cell parameter of MMT model was derived from empirical models

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introduced by Skipper[30-32]: a = 0.523 nm, b = 0.906 nm, the value of c was from 0.960 nm to

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1.850 nm, α = γ = 90°, β = 99°. Spatial coordinates of atoms and interlayer cations in montmorillonite unit cell were performed according to the data described previously[32]. Super-cell model utilized in this work included two clay layers where each layer contained 4 × 2 × 1 unit cell. One out of eight Al atoms in the octahedral sites and one out of 32 Si atoms in the tetrahedral sites was substituted by a Mg atom and an A1 atom, respectively. These substitutions were typical for a

Wyoming-type montmorillonite[33] and lead to an overall negative charge on the clay framework.

3. Results and Discussions Adsorption kinetics tests of CMC on MMT in aqueous solution are shown in Fig. 3. The

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kinetic parameters obtained by linear fitting using the pseudo-first-order and pseudo-second-order models were summarized in Table 1. Parameter qe and qe,exp are the calculated and experimental

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equilibrium adsorption capacity of CMC on MMT, respectively. The discrepancy between the R2 indicated that the adsorption followed the pseudo-first-order kinetics model, and qe of

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pseudo-first-order kinetics model was closer to qe,exp (1.34 mg/g). The adsorption reaction was

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about 1h to reach equilibrium and the equilibrium adsorption capacity was about 1.34 mg/g. It

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suggested that CMC can adsorb onto MMT surface quickly.

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FTIR spectroscopy was carried out for confirming the reaction mechanism between MMT and CMC. According to the FTIR spectrum in Fig. 4, the absorption peak at 3629 cm-1 corresponded to

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the absorption peaks of stretching bands of structural O-H. And the absorption peak appeared at 3439 cm-1 is assigned to the O-H stretching mode of the interlayer water. The flexural vibration

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frequency of the interlayer water was appeared at 1638 cm-1, which indicates that MMT plates

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contain crystalline water. The absorption peak at 1420 cm-1 is assigned to in-plane flexural vibration of non-aqueous hydroxyl group(Si-OH). Besides, the absorption peak at 1036 cm-1 corresponded to

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the absorption peak caused by the Si-O stretch vibration. In the FTIR spectrum of MMT adsorbed by CMC, it could be found that the Si-OH absorption peak almost totally disappeared. These results illustrated that adsorption of CMC affected the Si-OH in-plane flexural vibration of the clay framework. In other words, the CMC molecules adsorbed on the edges of MMT plates through hydrogen bond. CMC is a macromolecular reagent with many branched chains and can bind up the

surface of the clay particles. From this result, we reasonably believe that CMC as inhibitor can efficiently inhibit the swelling of MMT. The swelling capacity of Na-MMT as a function of mass ratio of CMC to MMT and solution volume firstly added were shown in Fig. 5 and 6. It was shown from Fig. 5 that the swelling

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capacity was 68 mL/g in the absence of CMC solution, which indicated that MMT had excellent swelling property and the MMT could be used for swelling test. With the increase of the mass

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ratio of CMC to MMT from 0 to 10, 100, 1000 μg/g, the swelling capacity of MMT was maintained around 68 mL/g. It could be seen that CMC cannot inhibit the swelling of MMT.

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Considering that there was too much water in the 50 ml solution added firstly, MMT may have

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expanded before adsorption with CMC, so the swelling capacity test was modified and the results

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were shown in Fig. 6.

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Under the condition where the mass ratio of CMC to MMT was 100 μg/g, with the increase

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of solution volume added firstly from 10 to 20, 50 mL, the swelling capacity of Na-MMT was maintained in 76 mL/g around. And in the presence and absence of CMC, the swelling capacity of

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MMT was almost the same. So CMC could not inhibit the swelling of MMT. This phenomenon cannot correspond well with the results of the FTIR spectroscopy test. It may be due to that the

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adsorption energy of CMC onto MMT edges was less than that of MMT hydration swelling,

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caused the effect of inhibiting disappearing. To verify the experimental observations, the molecular dynamics simulation was used to

simulate the swelling of Na-MMT minerals under the action of the water molecule. Fig. 7a showed a simulated diagram of the MMT minerals without water molecules in the interlayer, and the interlayer spacing of MMT minerals was 1.09 nm. Fig. 7b showed the effect of ion hydration

between MMT layers on layer spacing. When ions were hydrated by 12 water molecules, the layer spacing reached 2.06 nm. Fig. 7c showed a schematic diagram of the MMT interlayer hydration, and it was found that when the layers were filled with water molecules, the interval also was 2.06 nm. It was indicated that interlayer ionic hydration was the main influence factor of MMT mineral

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swelling. As seen in the result, it was shown that the swelling energy of MMT minerals was -71 kJ/mol when Na+ was hydrated with 12 water molecules.

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In Fig. 8, the COMPASS field was used to simulate the hydrogen bonding between the MMT edges and CMC. As shown in the Fig. 8, oxygen atoms in CMC carboxyl were hydrogen-bonded

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with the hydrogen atoms at MMT edges, and the energy of the edge hydrogen bond was -35 kJ/mol.

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In comprehensive, when MMT absorbed water completely, the swelling energy (-71 kJ/mol) of

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MMT mineral was greater than the adsorption energy (-35 kJ/mol) of hydrogen bond formed by

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MMT edges and CMC. So the hydrogen bond would break down during the swelling of the MMT,

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and CMC could not achieve the aim of preventing the water molecule from entering the layer by binding MMT. The calculation results demonstrated that CMC could not inhibit swelling of MMT

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in aqueous solution.

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4. Conclusions

The experimental results from this study have shown that CMC cannot bind swelling

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montmorillonite layers in water, even though the formation of hydrogen bond between CMC and the Si-OH of montmorillonite edges. The change of swelling capacity of MMT is negligible in the presence and absence of CMC, which means that CMC could not bind swelling montmorillonite layers in water. This phenomenon might be attributed to the energy of hydration swelling of montmorillonite (-71 kJ/mol) is high than the binding energy of CMC on montmorillonite (-35

kJ/mol). It is demonstrated that the CMC is useless for restraining the swelling of montmorillonite, which provides a fundamental theoretical guidance in industry.

Acknowledgements

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This work was financially supported by the Natural Science Foundation of Hubei Province (project 2015CFB221) and the National Natural Science Foundation of China under the project

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(projects Nos.51474167 and 51674183).

References

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Figures:

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Figure 1. XRD pattern of MMT.

Figure 2. Particle size distribution of MMT.

1.4 1.2

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Experimental data Pseudo-first-order kinetic model Pseudo-second-order kinetic model

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qe(mg/g）

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Time(min)

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Figure 3. Adsorption kinetics of CMC on MMT with an initial CMC concentration

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3629 3439

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Transmitance (%)

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1-MMT 2-MMT/CMC 4000

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of 20 mg/L.

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1000 -1

wavenumber (cm )

Figure 4. FTIR spectra of MMT and MMT/CMC complex.

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50 40 30

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Swelling capacity(mL/g)

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10 100 CMC/MMT ( μg/g)

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Figure 5. Swelling capacity of MMT as a function of mass ratio of CMC to MMT.

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H2O CMC

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Swelling capacity(mL/g)

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100

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20 Volume(mL)

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Figure 6. Swelling capacity of MMT as a function of solution volume added

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firstly.

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Figure 7. Simulation diagram of hydration of MMT (a: MMT; b: Hydration of

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interlayer ions; c: Hydration).

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Figure 8. Simulation of the hydrogen bonding between the MMT edges and CMC.

Table:

Table 1. Pseudo-first- and Pseudo-second-order kinetic model parameters for CMC adsorption on MMT.

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Pseudo-second-order kinetic model

qe

qe

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R (mg/g)

(mg/g)

(g·mg ·min )

1.34

1.35

0.064

0.99

-1

(mg/g)

(g·mg ·min )

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0.074

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Na-MMT

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Materials

Pseudo-first-order kinetic model

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