Characteristics of Rice Straw Ash

7/30/2019 Characteristics of Rice Straw Ash .

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CHARATERISTIC OF MASONY BLOCK

MANUFACTURED WITH RICE STRAW ASH

ABSTRACT

To prevent the burning rice straw in the field which affects the purity of air and

causes the formation of black clouds in Egypt. So that the aims of the present work was

to study the characterization of rice straw ash by using chemical analysis, mineralogical

composition as well as the effect of heat on ash in the temperature from 400 up to 1000 C.

Also, the application of the rice straw and its ashes in clay bricks at different clays were also

investigated.

The results indicated that the silica of rice straw is as amorphous at firing temperature400 up to 600C beside traces of calcite mineral. At 700C gave complete dissociation of

calcite. By increasing firing temperature from 800 to 900 C, the crystallinity increased as

well as cristobalite and tridymite were identified. The cristobalite was increased by

increasing firing temperature up to 1000C.By applying rice straw and its ash in clay bricks manufacture at different clays with

the same firing temperature at 900C for 2 hours soaking time. The results revealed that,

the crushing strength, bulk density and linear firing shrinkage were decreased by

increasing addition of straw and ash to clay bricks. At the same time, apparent porosity,

water absorption as well as loss in weight are increased. Also, the physico-mechanical

properties of clay to ash mixture were higher than clay with straw due to loss in weight

of ash was lower than straw and the reactivity of silica in the ash, which increases the

reactivity during firing process.


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INTRODUCTIO|N

Over one million acres of rice crops were grown in Egypt. One of acre of rice produces

two tones of straw, meaning that over two million tons of straw waste was left behind

after the harvest in October and November. Field burning of waste straw emits CO and

particulates, by products found to a significant effect on the quality of air and people's

health. Rice burning has been linked to the formation of similar black clouds around the

world.

Many attempts have been carried out to utilize the rice husk for the production of

building units. This method is concerned with the use of the husk, in their natural state, as

aggregate mixed with ordinary Portland cement to produce various constructional units

[1]. However, such products are a very limited use. In the second method, the ash residue

of the husk is mixed with Portland cement and lime and pressed bricks which are then

treated with special materials develop strength.


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The constituents of rice husks are both organic and inorganic compounds

Analysis reported in the literature showed that, the organic matter present in the husks are

generally, lygnin and cutin, carbohydrates and nitrogen compounds are also reported

such as lipids, organic acids and traces of vitamins. The inorganic constituents have

generally been determined in the ash which comprise about 13-29% of the husk [2]. The

predominant compound of ash is silica. Other elements are also present such as Na, K, Ca,Mg, Fe, Al, Mn, P and Cu. The silica values present about 94-96% by weight of the ash. In

general, the ash may well be considered as impure silica. The nature of white rice husk

as silica is still under investigation ]3]. The results showed that nuclei disordered

cristabalite is present and its growth is governed by two factors, namely nucleation and

temperature. The nucleation process manifests itself in the low temperature range 800-900C,

while growth is more pronounced in the temperature range 1000-1100C. Due to light silica

content and the porous texture of the ash produced by the incineration of rice husk, it is

recommended, the silica in rice husk ash is present in an amorphous state, which increases

its reactivity during the firing process.

Light weight clay bricks and blocks can be produced by adding any of the

following combustible material, which are the by product or waste products of different

industries: foamed polystyrene, perlite, saw dust shavings, paper making sludge, coal dust

and chopped straw [4-5]. The use of these combustible materials as pore forming agents in

the production of light weight, thermally insulating bricks has two additional advantages:

firstly, energy consumption in the early part of the firing process is reduced, due to the

large amount of energy generated by the combustion of the pore forming, resulting in

considerable savings in fuel. At the same time large quantities of waste products can be

consumed usefully instead of having to dispose of them as landfill.

The objective of the present work is to study the nature of rice straw ash formed at

different firing temperature from 400 up to 1000

C. Also the effect of rice straw and its ashon physico-mechanical properties of clay brick samples at different clays.


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Experimental Work

10 kg of rice straw was cut by scissor to obtain small pieces and ground in a ball mill

then sieved through 1mm. The thermal behavior as well as the ash content of the rice straw

was studied by diffraction thermal analyses and thermal gravimetry. Chemical analysis of

the rice straw ash is as follows: Si02 = 77.80%, A1203 = 9.79%, Fe203 = 0.76%, Ti02 =0.65%, CaO = 6.58%, MgO = 1.86%, K20 = 0.64, Na2O = 1.18, P205 =

0.65.Rice straw was heated in a muffle furnace in an atmosphere of air at a constant rate

of 20C/min up to required temperature. Heating was initiated at 400, 500, 600, 700, 800,

900 up to 1000C for 2 hrs, then cooled slowly in the furnace. The nature of the silica in the

rice straw ash was studied by X-ray diffraction analysis.

The rice straw was divided into two parts. One part was grinded to pass particles

of a diameter less than 1 mm. The second parts was fired at 400 C firing temperature for 2 hrs

soaking time and screen by sieving 1 mm to obtain ash which contains carbon content 17%.

Each mixture was prepared from clay [Wadi El-Hai or Aswan] and reducing agent such as

rice straw and its ash. The prepared batches were then mixed together with different ratio

for one hour in ball mill to obtain batches of complete homogeneity as shown in Table (1).


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Table 1 Mix composition of the prepared mixes, wt.

ix Aswan Clay Wadi El-Hai Rice Straw A

1

2

3

4

5

6

7

8

9

1

0

1

1

1

21

3

1

4

151

1

0

0

9

9

9

8

9

7

9

6

9

5

9

9

9

8

9

7

96

9

-

-

-

-

-

-

-

-

-

-

-

1

0

0

9

9

9

8

9

796

-

1

2

3

4

-

-

-

-

-

-

1

2

34

5

--

--

-

-

-

-

-

-

-

1

2

3

4

5

-

-

-

--

-

12

34

5

Ash* from firing rice straw at 400C, for 2 hrs soaking time.


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Table (2) Chemical analysis of the raw materials,

Oxides Aswan ClayWadiEl-

HaiRice Straw

Rice Straw

Ash at 4000C

Si02

A1203Fe203Ti02

CaO

MgO

Na20K

2

0

MnOP20

5L.O.I

T.I.O

54.

9523.17

7.

761.

85

0.

33

0.

84

59.

5212.30

7.

271.

55

3.

06

2.

29

10.

690.00

0.

000.

00

0.

00

0.

00

65.

577.10

0.

510.

85

4.

70

2.

42

L.O.I.- loss of ignition, T.I.O.- Total Impurity Oxides.

The mineralogical composition of the Aswan and Wadi El-Hai clays were

studied by x-ray diffactometer and DTA, TG techniques, finally grain size distribution

are seen in Table 3.


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Table 3. Grain size distribution of Aswan and Wadi El-Hai Clays

Particle sizepm Aswan, % Wadi EI-Hai,

1000-500500-250

250-125125-63

63-20

20-88-2


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higher temperature (900C) than in the present study. This result may be attributed to the

firing condition and the presence of lime (6.58%) can catalyse the conversion of quartz to

cristobalite, whilst iron (0.76%) favour the formation of tridymite [15]. The rate of

conversion of one form to another is also increased by increasing the fineness of the ash.

Organosilicon compounds are assimilated into the rice plant and form part of the

plant tissure. Silicon atoms are first transformed by the combustion process into amorphous

silica. Silicon atoms are first transformed by the combustion process into amorphous silica.

Silicon atoms in amorphous silica are bonded to oxygen atoms in two ways; either to two

oxygen atoms, thereby forming a siloane group (Si-O) or to a hydroxyl group, thereby

forming a silanol group (Si-O-H). Both groups exist at temperature up to 700C but

in varying properties depending on the firing temperature. The siloane groups unit by the

corners to produce low form cristobalite. Any impurities that are present enter the crystal

lattice, thereby forming a kind of solid solution.

Figure (2) shows the DTA and TG curves of rice straw, initial endothermic peak atabout 100C followed small endothermic at 166C corresponding to the loss of

mechanical held water. This is accompanied by loss in weight represented by the TG

curve of about

9.25% of the initial weight sample. The thermal decomposition of the rice straw is

characterized by an exothermic peak at 283C. This peak is probably characteristics

of cellulose and hemicellulose which are the main major constituents of organic part of the

rice straw. Corresponding to these reactions, an abrupt loss in weight of about 53.78%. At

564-

630

C a small endothermic peak may be due to the low high quartz transformation.

At930C the presence of an exothermic peak indicates complete decomposition of Si02

in

the rice straw 16.97% is the weight loss of the remaining part of the rice straw was gradual

increased and completed at about 1000C.

Characterization of Clays in Investigated

Work

The grain size distribution of the clay affects the linear shrinkage, the

drying behaviour, apparent porosity, bulk density and also crushing strength of the fired

bricks [16]. Winkler [17-18] has described the possibility of producing different types of

bricks based on the grain size distribution of the investigated clays. The percentages ofthe fractions 20 m were determined and plotted on a triangle

diagramme Figure (3). It contains fo ur areas ea ch one is suitable for one type of

bricks 1-solid bricks; 2- perforated bodies; 3- roof tiles and hollow bricks and 4-

thin-walled, large ceiling and hollow bricks.

From the results of grain size distribution, it was evident that clay Wadi El-Hai was

suitable for perforated bodies while Aswan clay can be used for thin walled, large celling

and hollow bricks.

Figure (4) show the x-ray diffraction pattern of Wadi El-Hai clay sample which

contains quartz and feldspare as major mineral, in addition to montmorillonite,

goethite, halite as minor mineral and traces of calcite as well as gypsum. On other hand

Aswan clay contains kaolinite clay mineral is the predominant one, in addition to quartz,magnetite and feldspar.

Figures (5) show DTA and TG analyses pattern of Wadi El Hai, and Aswan clays.

Ramachanch [19] indicated the characterstic endothermic and exothermic effects of

different clay minerals. The thermograms of Wadi El-Hai Clay show a large endothermic

peak existing at temperature 118C and 150C. This large low temperature endothermic


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effect is characteristics to the three layer clay minerals namely montmerillonite. It is

mainly due


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to the loss of sorbed water, largely that existing in the inter layer spaces of

montmorillonite structure. The size shape and temperature of such peak depend on

the type of exchangeable cation held with water in the interlayer species [20,21]. The

dehydration of interlayer water of montmorillonite is accompanied with a total loss in

weight of about 4.95% up to 160C. A weak endothermic is observed at about277C, which is probably due to the dehydroxylation of small amount of goethite and or

gibbsite [22]. The dehydration is accompanied with a loss in weight of about 0.7%. At

507-574C there is large and broad enothermic peak doublet due to the

dehydroxylation of montmorillonite clay mineral which is accompanied with about 4.1%

loss in weight. Th i s eak includespartl y t he endothermi c effect occuring at 574 due

t o t he low high quartz

transformation. By rising the temperature up to 890C endothermi c pe ak i s observ

ed, and it is meanly due to the dissociation of calcium carbonate mineral. The loss in

weight at this temperature is about 1.3%. Finally an endothermic/ exothermic (S) shaped

reaction at890-930C due to a structural reorganization and formation of new crystalline phases e.g.

silica rich, - A12O

3having the spinel structure [20,21].

The DTA and TG of Aswan clay are shown in figure (5). As it is shown a broad

endothermic at 106C which is meanly due to the dehydration of the adsorped and

interlayer water of the Kaolinite that accompanied with about 0.9% loss in weight. At

338C there is exothermic peak due to the presence of magnetite mineral, with about 1.13%

loss in weight by dehydration. Followed by a large endothermic peak at 541 C due to the

dehydroxylation of kaolinite mineral which is accompanied with about 6.2% loss in weight.

Also, exothermic peak is detected at about 952C due to recrystallization of -A12O

3in

the spinel structure, with 1.15% loss of weight.

Effect of straw and its ash on Clay

Bricks

The strength of material is due to the cohesion of particles of which it iscomposed and the resistance to pressure of the individual grains. The crushingstrength of material is expressed in terms of its resistance to compression. It has a greatimportance for the utilization of most ceramic materials, especially those used forconstructional purposes. As the ceramic material acquires a high crushing strength, itmust comprise a good binding agent, the grains must interlock sufficiently and the

individual grains must be of considerable density, or lower porosity. The crushingstrength is therefore closely related to the texture of material.Tables (4) and (5) show the physico-mechanical properties of briquettes such as

dry and fired crushing strength, water absorption, apparent porosity, bulk density as

well as loss in weight and linear shrinkage made from wadi E1-Hai and Aswan clays with

variable amounts of rice straw as well as its ash fired at 900 C for 2 hours soaking time.

From the results, it was revealed that the dried strength increases with the

increases of rice straw and decreases with ashes in bricks Wadi El-Hai and Aswan clays

as the fibrous structure of rice straw has a favourable influence on the stability of

green bodies during drying and counteracts cracking. At the same time the

compressibility of rice straw is low; so that a relatively high shaping pressure can be

applied which increases the stability of the green body [23]. But ash, as a silica, (nonplastic material) decreases the binding clay so that the green crushing strength was

decreased.

The crushing strength of fired Wadi El Hai clay brick samples is lower than that of

Aswan brick samples. This is due to the large proportion of fluxes in Wadi El-Hai that

equals


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to 17% which affects the strength. The bond produced by the fluxes will be soft and

mobile therefore, unable to import the necessary rigidity of the fired bricks. Another

explanation is

the difference in composition and mineralogical constitution that occur when clays are

fired, accompanied by corresponding changes in physical properties.

From the results of the above tables, it is found that the bulk density and linear

firing shrinkage were decreased by increasing addition of straw and ash to clay

briquettes at the same time apparent porosity and water absorption as well as loss

on weight are increased. This is due to the great loss of rice straw and ash. It gives about

80% loss on ignition of rice straw and 17% in the case of ash.

Therefore, the loss in clay weight relate to the loss in weight rice straw or rice ash

increases with the increase of rice straw or ash content. In another words, the loss in weight

upon firing is proportional to the amount of the clay refacture also the amount rice

straw or ash.

Briquettes with high amounts of rice straw or as give high percentage of

apparent porosity, water absorption due to their contents of components which volatilise,

evaporate or decompose with gas liberation at particular temperature. The rice straw or

ash decomposes with the evolution of gases leaving nearly 17-80% of its volume as voids

which increases the apparent porosity and water absorption.

The water absorption and apparent porosity are inversely proportional to thecrushing strength and bulk density. The results illustrated that physical properties of clay:Ash mixture were higher than clay straw mixtures due to loss in weight content of ash waslower than straw and the activity of amorphous silica in the ash which increases thereactivity during firing process. The ash plays two roles as a pore forming agent andactivation role but straw gives another roles as a pore of forming material as well asretarding effect. This result is agreed with the x-ray diffraction pattern of (Wadi El-Hai and Aswan Clays) clays with straw and/or Ash bricks. The mix composition contains(100-95) % clay and (0-5)% straw or Ash fired at 900C for 2 hours soaking time as seen

in Figure (6). Albite, hematite and quartz are main minerals of fired pure Wadi el-Hai

clay. The same minerals were appeared by mixture composition contains 95% clay and

5% Ash but different in intensity of peaks albite and quartz due to amorphous silica in

ash which increase the reactivity indicated by intensity of the above minerals. In

the case of contains 95% clay with 5% Straw, beside main minerals, calcite wasappeared at the same condition, in spite of the calcite disappeared at 750C fired clay so

that, straw as retarding effect.

Also, the Aswan clay was indicated by the same direction when firing clay at900C Figure (7). The main minerals were albite, hematite and quartz. The mixture

contains

95% Aswan with 5% straw was indicated the presence of Kaolinite mineral

which approved that straw has retarding effect in clay bricks during firing process.


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CONCLUSIONS

From the above results obtained it was concluded that:

I . Rice straw and its ash can be used as a pore forming agent in clay bricks

at different clays.2. Rice straw has higher poring effect and usage in insulating products

than rice ash.


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3. Straw can be used in clay bricks to prevent burning in the fields which effects on

the quality of air.

4. Straw as retarder but Ash as accelerator during firing.

REFERECES

1. Chittenden, A.E. and Flams, I.J. "The use of rice hulls as aggregate in light-

weight concrete" Trop. Prod. Inst., Minstry of Overseas Development, London,

(1960).


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2. Gobel, R.L. and Burke, J.O. "Progress in Ceramic Science" VIII, Pergamon Press

(1963).

3. Ibrahim, D.M. and Helmy, M. "Crystalline growth of rice husk ash silica

"Thermochim. Acta, 45, P. 79 (1981).

4. Hauck, D. and Jung, E. "Improvement of the Coefficient of thermal conductivity

of Light Weight Clay Bricks and Blocks" In: ZI Annual for the Brick and Tile, Structural

Ceramic and Clay Pipe Industries (Ed. C. Kokot), Wiesbaden, P. 108 (1991).

5. Junge, K. and Spitzer, M. "Foamed clay Bricks insulation Material" In: ZI Annual for

the Brick and Tile, Structural Ceramic and Clay Pipe Industries (Ed. C.

Kokot), Wiesbaden, P.96 (1997).

6. Lanning, F.C., J. Agric. Food Chem., 11, P. 435 (1963).

7. Houston, D.F. "Rice Chemistry and Technology" American Association of CerealChemists, (1972).

8. Fenner C.N., Am. J. Sci., V. 4, P. 331 (1913).

9. Florke, O.W. Ber, Dtsch. Keram. Ges., V. 32, P. 359 (1955).

10. Coquerelle, M. Silic. Ind., V. 26, P. 505 (1961).

11. Dekeyser, W. and Cypres, R. Silic. Ind., V. 26, P. 237 (1961).

12. Wahl, F.M., Grim, R.E. and Graf, R.B. Am. Mineral., V. 46, P.196, (1961).

13. Eitel, W. Am. Ceram. Soc. Bull., V. 36, P. 142, (1957).

14. Ibrahim, D.M.; El-Helmaly, S.A. and Abdel-Kerim, F.M., Thermochim. Acta, V. 37, P.

307 (1980).

15. Ryan, W. "Properties of Ceramic raw Materials" 2nd Edition (1978).


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16. Balint, P., Und Mattyasovsky, T. "Anwendung des Winkler Schen Dreieck Diagramms

Zur Qualitatsbeurteilung Von Tonen Und Massen. Tonind-Ztg. V. 102, P. 588,

(1978).17. Winkler, H.G.F., Ber. Dt. Keram. Ges. V. 11, P. 337, (1954).

18. Winkler, H.G.F., Ziegel-Ind. V. 6, P. 281, (1953).

19. Ramachandran, V.L. " Application of differential thermal Analysis in Cement

Chemistry" Chemical Publishing Co. Inc., New York (1969).

20. Grim, R.E. and Bradley, W.F. "Investigation of Effect of Heat on Clay Mineral, Illite

and

Mentmorillonite" J.Am. Ceram. Soc., V. 23, P. 242, (1940).

21. Todor, D.N. "Thermal Analysis of Minerals" Abacus Press. Abacus House,

England, (1976).

22. Basta, E.Z., Philip, G. and Halaka, S.G. "Mineralogical Studies on the Clay Fraction

of Some Soil Sediments from El-Beheira Governorate, North and South Nubariya

Canal". Egypt. J. Soil. Sci., V. 22, 111, (1982).

23. Junge, K. "Porous Light Weight Clay Bricks and Blocks" A step Towards a better

Environment, ZI-Brick and Tile Industry International, V. 1, P.35 (1994).


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Figure 1. X-ray diffraction pattern of rice straw ash fired at 400, 500. 600, 700, 800,

900 and 1000C for 2 hours soaking time.


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Figure 2: DTA and TG of rice straw


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Figure 5: DTA and TG of Wadi El-Hai and Aswan Clays.


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Figure 6: X-ray diffraction pattern of Wadi EI-Hai Clay bricks without and/with straw

or ash fired at 900

C for 2 hours soaking time.


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Figure 7: X-ray diffraction pattern of Aswan clay bricks without and/ Withstraw or ash fired at 900C for 2 hours soaking time.

Documents

Characteristics of Rice Straw Ash