Effect of Acid Treatment on the Physicochemical and Mineralogical Properties of Smectite Clays from Cameroon.

Effect of Acid Treatment on the Physicochemical and Mineralogical Properties

of Smectite Clays from Cameroon.

University of Liege, ( jamache@yahoo.fr)

INTRODUCTION

ANALYTICAL METHODS

Samples of 10 g were dispersed in 100 ml of 0.0, 0.5, 0.7, 1.0 and 4.0 N H₂SO₄

(prepared from H₂SO₄ 96% p.a, Fischer), the slurry was stirred for 2H at 80°C. At the

end of each run, suspensions were filtered and the remaining solid phases were washed several times with pure water (MilliQ ultra filtration) to remove any unspent acid until the

filtrates were neutral (test of 5% BaCl₂). The obtained activated clays were then dried at

110°C, gently ground in an agate mortar. The clay samples thus prepared are designed as BN-0.0, BN-0.5, BN-0.7, BN-1.0 and BN-4.0; S-0.0, S-0.5, S-0.7, S-1.0 and S-4.0 with

the suffix indicating the concentration of H₂SO₄ used during the treatment. The acid

treated samples were stored in the plastic bottles closed tightly for uses to the analytical methods.

LPM

RESULTS

.

Acid activation is a useful method to modify the catalytic behavior, enhance clay properties, mainly their sorptive properties of clay minerals. Thus, acid treatment is commonly required when clays are used in industry, for example, as catalysts or catalyst supports in alkylation, dimerisation and polymerisation reactions and as a component in carbonless copying papers (Fahn and Fenderl, 1983). Probably the most widely used acid-activated clays are the bleaching earths (Anderson and Williams, 1962; Gates et al., 2002), which are capable of removing colour, odour and other impurities from cooking oils of vegetable and animal origin.

The focus of this study was to prepare clay materials by acid attack and determine the effect of acid treatment on the physicochemical and mineralogical properties of the new products obtained.

CONCLUSION

The results of this investigation show that the acid activation has caused remarkable change on the structure of smectite phase, the non-clay minerals like cristobalite, quartz and anatase remain unchanged during acid treatment. The specific surface area of activated clays increase, however the cation exchange capacity of clays decreases with increasing acid concentration.

References:

1. Anderson, A.J.C., Williams, P.N., 1962. Refining of Oils and Fats for Edible Purposes. Pergamon, New York.

2. Fahn, R., Fenderl, K., 1983. Reaction products of organic dye molecules with acid-treated montmorillonites. Clay Minerals. 18, 447– 458.

3. Gates, W.P., Anderson, J.S., Raven, M.D., Churchman G.J., 2002. Mineralogy of a bentonite from Miles, Queensland, Australia and characterization of its acid activation products, Applied Clay Science. 20 189–197.

ACID ACTIVATION

Structural modification

-

- Fourier transform infrared spectroscopy (FTIR) - Thermal analyses (DTA/TGA)

- Scanning electron microscopy (SEM)

Physicochemical properties

- Nitrogen adsorption – desorption isotherm (BET): for specific surface determination - Cation exchange capacity (CEC)

- Cations dissolution

- Particle size distribution

.

The main clay minerals are smectites associated with kaolinite; the non clay minerals are cristobalite (Crs), feldspars (Fps), antase (Ant) and quartz (Qtz).

Smectite : montmorillonite

Fig.1. XRD patterns of the natural samples

0 2 4 6 8 10 12 14 16 3 8 13 18 23 28 33 38 43 48 53 58 63 Int ens it y (u.a .) 2θ (CoKα1) K ln Sm Sm Sm Q tz Crs A n t Fs Q tz C r s C r s Sabga (S) Bana (BN) Fs 0 5 10 15 20 25 30 3 8 13 18 23 28 33 38 43 48 53 58 63 Int e ns it y (u.a.) 2θ (CoKα1) (a) Q tz Fs A n t Q tz Fs Kln A n t K ln S m + K ln Q tz Sm Sm: Smectite Kln: Kaolinite Qtz: Quartz Fs: Feldspars Ant: Anatase Hem: Hematite H e m BN-1.0 BN-0.7 BN-0.5 BN-0.0 BN BN-4.0 0 5 10 15 20 25 3 8 13 18 23 28 33 38 43 48 53 58 63 Int ens it y (u.a .) 2θ (CoKα1) (b) Sg C rs Fs Q tz C rs Q tz Sm Fs Sm Il m S-4.0 S-1.0 S-0.7 S-0.5 S-0.0 Sm: Smectite Qtz: Qua rtz Fs: Feldspa rs Ilm: Ilmenite Crs: Cristoba lite

Fig.2. XRD patterns of the acid activated clays: (a) Bana; (b) Sabga

1. Structural modification

.

 SCANNING ELECTRON MICROSCOPY (SEM)

44 45 46 47 48 49 50 51 52 53 0 100 200 300 400 500 600 700 800 900 10001100 % we ig ht Temperature ( C) (a) TGA-BN-0.0 TGA-BN-4.0 -4,5 -4 -3,5 -3 -2,5 -2 -1,5 -1 -0,5 0 0 100 200 300 400 500 600 700 800 900 1000 1100 He at flow (uV ) Temperature ( C) (b) DTA-BN-0.0 DTA-BN-4.0 -4,5 -4 -3,5 -3 -2,5 -2 -1,5 -1 -0,5 0 34 35 36 37 38 39 40 41 42 0 100 200 300 400 500 600 700 800 900 10001100 He at flow (uV ) % we ig ht Temperature ( C) (c) TGA-S-0.0 TGA-S-4.0 DTA-S-0.0 DTA-S-4.0

Fig. 4. (a) TGA curves of untreated and treated BN sample, (b) DTA curves of untreated and treated BN sample, (c) DTA-TGA curves of untreated and treated S sample

N-BN A-BN N-S A-S Acid activation at 4 N, 80°C, 2H sample BN Acid activation at 4 N, 80°C, 2H sample S

Fig.5. SEM micrographs before and after acid activation: N (Natural); A (Activated); BN and S (samples) 600 700 800 900 1000 1100 1200 A bs or ba nc e (a .u. ) Wavenumbers (cm-1₎ (b) 1114 1022 915 895 ₇₉₈ 753 696 BN-4.0 BN-1.0 BN-0.7 BN-0.5 BN-0.0 3550 3600 3650 3700 3750 A bs or ba nc e (a .u.) Wavenumbers (cm-1₎ (a) 3698 3622 3659 BN-1.0 BN-4.0 BN-0.7 BN-0.5 BN-0.0 3550 3600 3650 3700 3750 A bs or ba nc e (a .u.) Wavenumbers (cm-1₎ (a) S-4.0 S-0.0 S-0.5 S-0.7 S-1.0 3636 600 700 800 900 1000 1100 1200 A bs or ba nc e (a .u.) Wavenumbers (cm-1₎ (b) S-4.0 S-1.0 S-0.7 S-0.0 S-0.5 794 887 936 1036 1120 617

Fig.3. FTIR spectra of natural and activated Bana clay: (a) OH stretching domain (b) Si-O stretching domain

Fig.3 bis. FTIR spectra of natural and activated Bana clay: (a) OH stretching domain (b) Si-O stretching domain

Particle size distribution:

Natural clay (1-10µm): 26.9%; Activated clay: 48.09% (sample BN) Natural clay (10-20µm): 19.65%; Activated clay: 26.06% (sample BN)

CEC: Cation exchange capacity decreases continously with acid concentration

(56 to 46 meq/100g for BN and 36 to 25 meq/100g for sample S)

Specific surface area (S_BET): Specific surface area of acid-activated samples increased

with the acid concentration, such that acid activation at 4 N gave rise to a specific surface area 134 m2_{/g and 84 m}2_{/g, respectively for BN and S clay samples, whereas in the}

untreated samples it was 65 m2_{/g and 74 m}2_{/. g}

Cations dissolution: Increase of H₂SO₄ concentration up to 4 N caused increase of cation dissolution (Ca, K, Mg, Na, Al, Fe and Si), and no amount of titanium is dissolved during acid treatment, indicating that anatase is not destroyed.