Inorganic polymers synthesized using biomass ashes-red mud as precursors based on clay-kaolinite system

Accepted Manuscript Inorganic polymers synthesized using biomass ashes-red mud as precursors based on clay-kaolinite system E. Bonet-Martínez, L. Pérez-Villarejo, D. Eliche-Quesada, B. CarrascoHurtado, S. Bueno-Rodríguez, E. Castro-Galiano PII: DOI: Reference:

S0167-577X(18)30753-5 https://doi.org/10.1016/j.matlet.2018.05.012 MLBLUE 24312

To appear in:

Materials Letters

Received Date: Revised Date: Accepted Date:

1 February 2018 17 April 2018 1 May 2018

Please cite this article as: E. Bonet-Martínez, L. Pérez-Villarejo, D. Eliche-Quesada, B. Carrasco-Hurtado, S. BuenoRodríguez, E. Castro-Galiano, Inorganic polymers synthesized using biomass ashes-red mud as precursors based on clay-kaolinite system, Materials Letters (2018), doi: https://doi.org/10.1016/j.matlet.2018.05.012

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Inorganic polymers synthesized using biomass ashes-red mud as precursors based on clay-kaolinite system E. Bonet-Martínez(1), L. Pérez-Villarejo(1*), D. Eliche-Quesada(1), B. CarrascoHurtado(2), S. Bueno-Rodríguez(3), E. Castro-Galiano(1) (1) Department of Chemical, Environmental, and Materials Engineering. University of Jaen, Campus Las Lagunillas, s/n, 23071 Jaén, Spain (2) Department of Graphic Engineering, Design and Projects, University of Jaen, Scientific and Technological Campus, 23700 Linares (Jaén), Spain (3) Fundación Innovarcilla. Pol. Ind. El Cruce. C. Los Alamillos, 25, 23710 Bailén. Spain. *

Corresponding author

ABSTRACT Geopolymers are a new class of non-Portland cements produced using an aluminosilicate material (natural minerals, waste and/or industrial by-products) and an alkaline activator to be subsequently cured at relatively low temperatures. The aim of this work is to produce a new type of geopolymer using metakaolin (MK), rice husk ash (RHA) and red mud (RM) by alkaline activation containing sodium silicate and sodium hydroxide (NaOH). Four different geopolymer compositions were prepared at various Si/Al molar ratios (3.85, 4.30, 4.45 and 5.30). A metakaolin based geopolymers were synthesized as a reference. Specimens were characterized by XRD, ATR-FTIR and SEM/EDS. The study revealed that geopolymerization products exhibit an amorphous homogeneous structure with acceptable mechanical properties. RMRHA1 geopolymers shows the best mechanical characteristics (30 MPa) after 60 curing days. MK-RHA-RM based geopolymers obtained seem to offer a feasible alternative to conventional Portland cement contributing to the valorization of the wastes. Keywords: Geopolymer; Red mud; Rice husk ash; Microstructure, sustainability

1. Introduction Inorganic polymers or geopolymers constitute a new class of materials synthesized from materials of aluminosilicate nature (clays and kaolin) and an alkaline activator to be used in multiple applications: cementitious material [1], catalytic support [2] and even as a reinforcing matrix for composite materials with fibers [3]. Geopolymers synthesis by chemical reaction between amorphous silica and alumina in combination with a highly alkaline environment at slightly elevated temperature produce a three-dimensional polymer gel of Si-O-Al-O-Si [4]. Wastes and by-products from various industrial fields, such as rice husk ash (rich in amorphous SiO 2) and red mud (rich in aluminum oxides and hydroxides) were used as precursors materials, as well as the dehydroxylated clay and metakaolin (calcined kaolin). Rice husk is an agricultural waste obtained from the outer covering of rice grains. Rice husk constitutes about 20 wt. % of rice. Rice husk ash (RHA) is an industrial by-product generated by burning rice husks. Rice husk ash is essentially amorphous silica, with gives it a great pozzolanic activity [5]. Red mud is the insoluble by-product generated during the production of alumina in the Bayer process. The large amount of wastes

generated, and its high alkalinity make it a high environmental problem due to the cost management and control. Al2O3 and SiO2 are the main components of geopolymer cement. The molar ratio of Si to Al determines the molecular configuration types of the products [6]. RHA contains high silica content and RM is rich in alumina. Both wastes are viable as raw materials to form geopolymer-based materials. In this study, new formulations of geopolymers obtained from the mixture of metakaolin, rice husk ash as source of silica and red mud as source of alumina to adjust the Si/Al molar ratio were investigated. MK was partially replaced by RHA and RM wastes in inorganic polymers. These sustainable materials were characterized using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Scanning Electron Microscopy (SEM/EDS). The influence of interactions between different precursor materials and geopolymeric gel still require research on the micro-structures of geopolymers synthesized [7].

2. Materials and Methods 2.1. Materials Geopolymers were designed by using metakaolin (MK), red mud (RM) provided by Alcoa Company, an aluminium industry, located in San Ciprián (Lugo, Spain) and rice husk ash supplied by Herba Ricemills S.L., a rice-producing industry in San Juan de Aznalfarache (Seville, Spain). Precursors materials were pre-treated and subjected to drying and ground to a particle size of 0.1-0.2 mm. For alkaline activation, a mixture of hydrated sodium silicate (Panreac S.A.; 8.9 wt.% Na2O, 29.2 wt.% SiO2 and 61.9 wt.% H2O) and NaOH (Panreac S.A.; reactive grade, 98 wt.%) was used. The NaOH solution was prepared in distilled water (5 M). The weight ratio between alkali solution and sodium silicate was 0.25. All geopolymeric mixtures were prepared with liquid to solid ratio of 0.97. 2.2. Preparation of geopolymers The geopolymers were prepared with five different compositions: pure MK, RMRHA1 (50 wt.% MK, 25 wt.% RM, 25 wt.% RHA with a molar ratio Si/Al = 4.45), RMRHA2 (50 wt.% MK, 33 wt.% RM, 17 wt.% RHA, Si/Al = 3.85), RMRHA3 (40 wt.% MK, 35 wt.% RM, 25 wt.% RHA, Si/Al = 4.30) and RMRHA4 (40 wt.% MK, 25 wt.% RM, 35 wt.% RHA, Si/Al = 5.30). The synthesis was carried out by mixing the raw materials for 10 minutes. Subsequently the activating solution was added and stirred for 15 minutes and then the generated slurry was transferred to plastic molds. The samples were cured under controlled conditions (70 ºC) for 24 h. The specimens were removed from the moulds and kept at ambient conditions for 60 days of curing. 2.3. Characterization of materials The microstructural characterization was carried out by SEM (JEOL SM 840 equipped with energy dispersive spectroscopy, EDS). Crystalline phases of RHA, MK and RM and geopolymers were evaluated using X-ray diffractometry with an X’Pert Pro MPD automated diffractometer (PANanalytical), equipped with a Ge (111) primary monochromator, using monochromatic Cu Kα radiation and an X’Celerator detector. The quantitative phase analysis was performed using Maud software (Material Analysis Using Diffraction), a general diffraction/reflectivity analysis program based on the Rietveld method. Chemical composition was determined by X-ray fluorescence (XRF) using a Philips Magix Pro (PW-2440). Compressive strength was measured according to UNE-EN 772-1:2011a on a MTS 810 Material Testing Systems laboratory press. An ATR-FTIR Vertex 70 instrument from Bruker was used for the characterization of

geopolymers. To evaluate the concentration of metals an Agilent model 7500th ICP-MS spectrometer was used after a leaching stage in which the TCLP method was used [8]. The TCLP uses a 20:1 liquid-to-solid (L/S) ratio (by mass), and the samples were continuously rotated to ensure mixing for 18±2 hr. at 30 rpm. The mixtures were then filtered and the liquid portion retained for analysis.

3. Results and Discussion 3.1 Raw materials characterization The chemical composition of the raw materials (in wt.%) used yielded the following results: MK is comprised for SiO2 (66.7 wt.%), Al2O3 (25.7 wt.%), K2O (3.1 wt.%), Fe2O3 (0.54 wt.%), MgO (0.12 wt.%), CaO (0.14 wt.%), Na2O (0.07 wt.%), TiO2 (0.26 wt.%), and a loss of ignition (LOI) value of 2.28 wt.%. The most important component of RHA is SiO2 (76.7 wt.%) but also low amounts of K2O (0.90 wt.%), Al2O3 (0.8 wt.%), Fe2O3 (2.7 wt.%), MgO (0.46 wt.%), CaO (0.34 wt.%), SO3 (0.12 wt.%) and P2O5 (0.36 wt.%), with a percentage of LOI of 16.37 wt.%. The RM is composed of Al2O3 (19.80 wt.%), Fe2O3 (39.23 wt.%), SiO2 (8.77 wt.%), CaO (4.54 wt.%), Na2O (5.02 wt.%), K2O (0.14 wt.%), P2O5 (0.44 wt.%), TiO2 (10.09 wt.%) and a loss of ignition (LOI) of 11.16 wt.%. The XRD patterns of metakaolin (MK), red mud and rice husk ash (RHA) are reported in Fig. 1. The analysis of the XRD pattern shows that RM consisted of mainly hematite, goethite and sodalite. The only crystalline phase present in RHA is cristobalite. The content of amorphous SiO2 in RHA was 88.45%, which explains its high chemical reactivity. XRD patterns of MK shows a large number of diffraction peaks matched with Quartz. The content of amorphous SiO2 in MK was 85.79%. 3.2 Geopolymers characterization Table 1 shows the results obtained for TCLP leaching tests for the four designed geopolymers and MK-based geopolymers used as reference. The composition of elements (in ppb) obtained for alkaline activated control MK-geopolymers are significantly lower than those of the four mixtures prepared with, RHA and RM. The total data show that heavy metals content were below the regulatory limit for hazardous waste classification according to TCLP. The heavy metals presents in geopolymers are trapped inside the matrix and not released into the environment. The environmental study thus shows that no serious environmental problems are anticipated for geopolymers synthesized. The mechanical strength of the MK-RHA-RM geopolymers materials was studied analyzing the evolution of the compressive strength with curing time (Figure 2a). Pure MK presents a compressive strength of 61 MPa at 60 curing days. Geopolymers containing waste have a lower compressive strength than the reference sample. The higher compressive strength (27 MPa) was obtained for RMRHA1 geopolymers after 60 curing days. MK and RMRHA1 geopolymer series showed a semi-logarithmic increase with curing time, producing a more pronounced increase at shorter curing time (until 28 days). The compressive strength of RMRHA2 (7.8 MPa) and RMRHA3 (13.9 MPa) geopolymer series increase linearly with curing time. SEM micrographs of RMRHA4 and RMRHA1 geopolymers after 28 curing days are shown in Figure 2b and 2c respectively. In the EDS analyzes carried out, differences can be observed between the two samples in terms of Si Al ratios. When the Si/Al ratio is close to 1, as in the case of the RMRHA4 sample (Fig. 2b), the compressive strength

values decrease. However, as the amount of Si increases with respect to Al, as in the case of the sample RMRHA1 (Fig. 2c), the mechanical resistance values increase. The RMRHA4 geopolymers (Figure 2b) a lower Si/Al molar ratio and showed worse mechanical performance. The increase in the Si/Al molar ratio is related to the formation of the geopolymeric network according to IR spectra data (Figure 3). An increase in the geopolymeric network improves the mechanical strength. It also indicates the lower appearance of cracks in the surface of the sample. According to Fernández-Jiménez and Palomo [9], the interpretation of infrared absorption bands for geopolymeric materials is complicated. In the vibration spectra of geopolymers appear vitreous and amorphous materials have broad and diffuse bands. For MK (Fig. 3b) the band centered around 965 cm-1 is characteristic of the geopolymerization reaction and corresponds to the stretching or asymmetric vibration bands of Si-O-Al and Si-O-Si which is typical of the polymerization of the silicate group with the formation of CSH [10,11]. In addition, this band moves towards larger wave numbers as a consequence of the geopolymerization reaction. Normally this fact is indicative of the increase of Si content in the gel. The position of this band depends on the Al/Si ratio of the reaction product. The increase of Si shifts the Al which involves a reduction of the M-O-M angle (M = Al or Si) that causes the displacement of the band, because the strength of the AlO bond is greater than Si-O [9]. The large band that appears at 1394 cm-1 is attributed to the stretching vibrations of CO32- ions. It is a confirmation of the existence of carbonate species [9]. Future research will be in connection of a deep study of these geopolymers.

4. Conclusions Alternative geopolymers formulations were synthetized by alkaline activation of mixtures of metakaolin, rice husk ash and red mud. Geopolymers confirm the immobilization of most of the heavy metals present in the red mud as indicated TCLP leaching test results. FTIR spectrum and XRD diffractograms show, in all cases, that geopolymer structure was formed with an amorphous homogeneous structure with curing time. Compressive strength increases with the curing time. RMRHA1 and RMRHA2 geopolymers series reveal logarithm increase in the compressive strength while RMRHA3 and RMRHA4 geopolymers present linearly increase. Compressive strength of metakaolin based geopolymer was about 51 MPa. The best results were obtained by the RMRHA1 geopolymers series with compressive strength of 30 MPa after 60 curing days. MK-RHA–RM based geopolymers obtained seem to offer a feasible alternative to conventional Portland cement contributing to the valorization of rice husk ash and red mud wastes.

References [1] P. Sturm, G.J.G. Gluth, H.J.H. Brouwers, H.C. Kühne, Synthesizing one-part geopolymers from rice husk ash. Constr. Build. Mater. 124 (2016) 961-966. [2] M.I.M. Alzeer, K.J.D. Mackenzie, R.A. Keyzers, Porous aluminosilicate inorganic polymers (geopolymers): a newclass of environmentally benign heterogeneous solid acid catalysts. Appl. Catal. A: Gen. 524 (2016) 173-181.

[3] M. Alshaaer, S.A. Mallouh, J. Al-Kafawein, Y. Al-Faiyz, T. Fahmy, A. Kallel, F. Rocha, Fabrication, microstructural and mechanical characterization of Luffa Cylindrical Fibre-Reinforced geopolymer composite. Appl. Clay Sci. 143 (2017) 125133. [4] C.L. Hwang, T.P. Huynh, Effect of alkali-activator and rice husk ash content on strength development of fly ash and residual rice husk ash-based geopolymers. Constr. Build. Mater. 101 (2015) 1-9. [5] J. Hue, Y. Jie, J, Zhang, Y. Yu, G. Zhang. Synthesis and characterization of red mud and rice husk ash-based geopolymer composites. Cement Concrete Comp. 37 (2013) 108-118. [6] Z. Yunsheng, S. Wei, L. Zongjin. Composition design and microstructural characterization of calcined kaolin-based geopolymer cement. Appl. Clay Sci. 47 (2010) 271–27. [7] Q. Wan, F. Rao, S. Song, D. F. Cholico-Gonzalez, N. L. Ortiz. Combination formation in the reinforcement of metakaolin geopolymers with quartz sand. Cement Concrete Comp. 80 (2017) 115-122. [8] SW-846 Test Method 1311: Toxicity Characteristic Leaching Procedure. United States Environmental Protection Agency (1992). [9] A. Fernández-Jiménez, A. Palomo. Mid-infrared spectroscopic studies of alkali activated fly ash structure. Micropor. Mesopor. Mat. 86 (2005) 207-14. [10] I. García-Lodeiro, A. Fernández-Jiménez, M.T. Blanco, A. Palomo. FTIR study of sol-gel synthesis of cementitious gels: CSH and NASH. J. Sol-Gel Sci. Techn. 45 (2008) 63-72. [11] I. García-Lodeiro, D. Macphee, A. Palomo, A Fernández-Jiménez. Effect of alkalis on fresh CSH gels. FTIR analysis. Cement Concrete Res. 39 (2009) 147-153. List of captions Figure 1. Diffractograms of raw materials, a) MK, b) RM, and c) RHA. Q: Quartz, H: Hematite, G: Gibbsite, Gt: Goethite, S: Sodalite, A: Anatase, B: Boehmite, R: Rutile, C: Cristobalite. Figure 2. a) Compressive strength evolution of designed geopolymers and SEM micrographs and EDS analysis of: b) RMRHA4 and c) RMRHA1. Figure 3. FTIR spectroscopic profiles of designed geopolymers at several curing ages, a) RMRHA1 and b) MK.

Q

a

Q Q Q Q Q Q 5

10

15

20

25

30

35 40 2 Theta (º)

45

Q

50

Q 55

60

65

H

b

Gt H

S G

G G

S

5

10

15

20

25

30

35 40 2 Theta (º)

45

50

55

60

65

C

c

C C

5

HH

A R B

10

15

20

25

30

C

35

2 Theta (º)

40

45

50

55

60

65

60

RMRHA 1 RMRHA 2 RMRHA 3 RMRHA 4 MK

a

Compressive strength (MPa)

50

y = 28.449ln(x) - 51.408 R² = 0.9768

40

30

y = 11.864ln(x) - 22.831 R² = 0.9757

20 y = 0.2656x - 2.5825 R² = 0.975 y = 0.1532x - 1.1264 R² = 0.9964 y = 0.1512x - 1.1094 R² = 0.9819

10

0 0

5

10

15

20

b

25 30 35 Cured age (days)

40

45

50

55

60

c

2 1

1

1

1

2

1 0.9

a

0.8 0.7

0.5 0.4 RMRHA1 1 Hour

0.3

RMRHA1 3 Hours RMRHA1 7 days

Intensity (a.u.)

0.6

0.2

RMRHA1 14 days RMRHA1 28 days

0.1

RMRHA1 60 days

0 4000

3500

3000

2500

2000

1500

1000

500

Wavenumber (cm-1) 1

0.9

b

0.8 0.7

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

MK 1 Hour MK 3 Hours MK 7 days MK 14 days MK 28 days MK 60 days

1300

1200

1100

1000

900

800

700

0.5 0.4 0.3 0.2 0.1

600

0 4000

3500

3000

2500

2000

1500

Wavenumber (cm-1)

1000

500

Intensity (a.u.)

0.6

Table 1. Chemical results for leachates for the MK sample and the four designed geopolymers and MK-based geopolymers synthesized in this work.

USEPA Component (ppb)

regulated MK

RMRHA1

RMRHA2 RMRHA3 RMRHA4

TCLP limits (ppb)

Li

51.64

42.31

35.91

37.40

28.35

N/A

Mg

30.24

1495.36

436.69

247.65

2162.49

N/A

Al

4618.83

7686.21

8499.82

7133.51

10022.86

N/A

K

13769.11

27799.44

24238.40

27346.49

31357.58

N/A

Ca

23.71

1441.64

418.74

553.26

2582.32

N/A

V

250.22

1798.92

2362.52

2601.43

1591.71

N/A

Cr

22.29

119.08

72.36

59.84

180.56

5000

Fe

33.88

455.11

290.93

170.34

1365.70

N/A

Co

0.35

0.27

0.18

0.22

0.66

N/A

Ni

0.68

2.50

1.01

0.81

3.45

250,000

Cu

14.43

4.08

6.02

12.82

6.26

5000

Zn

1.04

15.68

5.34

25.68

22.62

300,000

Ga

53.79

35.97

49.26

34.22

27.84

N/A

As

45.06

83.66

99.14

105.88

70.47

5000

Se

0.80

1.30

1.48

1.08

0.79

1000

Rb

11.26

30.56

33.56

32.90

36.94

N/A

Sr

1.47

38.07

11.20

22.77

59.95

N/A

Cd

0

0.07

0.04

0.07

0.06

1000

Cs

2.64

0.67

1.05

1.05

1.12

N/A

Ba

0.97

6.06

2.18

1.96

15.97

100,000

Hg

0.03

0.01

0.01

0.42

0.02

200

Pb

2.52

2.40

2.09

15.18

3.76

5000



Valorization of rice husk ash used as precursors for inorganic polymer synthesis.



Study of the evolution of the properties of inorganic polymers.



Microstructural, assessment.

mechanical,

spectroscopic

analysis

and

environmental