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EFFECTS OF INCINERATION VARIABLES ON THE QUALITY

OF SILICA FROM RICE HUSK

Thesis Proposal

Presented to Prof. Lourdes Filoteo

Chemistry Department, College of Science and Mathematics

Western Mindanao State University

Normal Road, Zamboanga City

Prepared by:

Janine Bernadette A. Pontanar

BS Chemistry III

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Chapter 1

Introduction

1.1 Background of the Study

The rice husks or rice hulls (RH) are the hard coat of grains of rice.(1) Rice husks are by-

products of the milling industry and are rich in cellulose (28-36 %), crude fiber (34.5-45.9 %)

and ash (13.2 –21.0 %). (2) The variety of the rice affects the constituents of the rice husks.

This agro-industrial waste (rice husk) is abundant in Zamboanga Sibugay. Such huge amounts

are utilized inappropriately and the common exercise is to burn them. Burning rice husks causes

pollution hazards to the surrounding population. (3) These ashes are also disposed as landfill

which causes environmental problems. In the last decade, numbers of possible uses for rice

husks ash are being investigated and their applications have little value beyond the removal of

the waste.

Rice husk ash is the product of the carbonization of the rice husk. It is composed of 80-

90% silica depending on some factors such as type of the soil growing the rice, the fertilizing

practices and as well as the environment (4). Rice husk ash has been used in cement

manufacturing (5). The ash has also been used as an antiskidding agent and in rubber

compounding (6), an insulating material (7; 8; 2; 6) and soil conditioning agent (7; 8; 9). In

recent years, rice husk ash has also been used as an adsorbent for wastewater components (7; 10;

11; 12; 13) and for oil components like free fatty acids, lutein, phospholipids and carotene (14).

The silica in rice husk ash has only been explored by few research groups. The high

content of silica in rice husk ash has been studied as an alternative approach to the high cost

synthesis of silica. Silica from rice husk ash is also of low cost but has high purity. On the

second account, silica from rice husk ash is very abundant and for this reasons, it provides a

good motivation to conduct further research into the feasibility of this approach.

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1.2 Statement of the problem

The study aims to assess the effects of incineration factors on the quality of silica

from rice husk ash, and determine the optimum time and temperature in the production of good

quality silica from rice husk ash. Specifically, the study seeks to answer the following:

1. what is the percent silica composition of rice husk ash?

2. is there a significant difference in the quality of silica produced from rice husk ash under the

different incineration variables such as temperature and time variations?

1.3 Significance of the study

The study will be conducted mainly due to the commercial significance of silica.

Rice husk is also viable since there are rice mills abound in Zamboanga Sibugay that it became a

pollutant in the environment. It is on the other hand beneficial in terms of the reduction of the

environmental pollutant. The product-to be is on the other hand of cheap cost.

Ha: There is significance difference between the qualities of the silica synthesized under

different temperatures and time variations.

Ho: There is no significance difference between the qualities of the silica synthesized under

different temperatures and time variations.

1.4 Scope and delimitations

This study will collect rice husk from Brgy. JS Perfecto, RT Lim, Zamboanga

Sibugay. The study will be delimited in the synthesis of silica from rice husk using different

incineration variables that is, temperature and time. The silica will be synthesized from the rice

husk ash by treating the rice husk ash with different concentrations and volumes of prepared

NaOH.

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Chapter 2

Review of Literature and Related Study

2.1 Rice Husk and its Uses

Rice husks or rice hulls are the coating of the rice plant and are made of hard materials,

including opaline silica and lignin. During the milling process, it is removed mainly because it is

indigestible to humans. Rice husks are known to have relatively high content of inorganic

compounds representing approximately more than 94% of silica and the remaining wt% is

consists of K2O, CaO, MgO, Al2O3, P2O5 and is herein after referred to as trace impurities. (15)

Some of the current and potential applications of rice husks are Chemistry

(mesoporous molecular sieves and as adsorbent in waste water treatment), pet food fiber,

building material, pillow stuffing , fertilizer, silicon carbide production ‘’whiskers’’, as fuel,

brewing, and is also used in juice extraction. (1)

2.2 Rice husk ash

Rice husk ash is abbreviated as rice husk ash and is a general term describing the ash

produced from burning rice husks. Rice husk ash represents approximately 16-22 % by weight

of husk. Rice husk ash is very rich in silica and according to some studies; the silica content of

rice husk ash reaches up to 90% and to some are greater than this. The properties of the ash vary

considerably according to the burning technique. The silica in the ash undergoes structural

transformations depending on the conditions of combustion, and at 550°C – 800°C amorphous

ash is formed and at temperatures greater than the latter, crystalline ash is formed (17). Silica

from rice husk ash could be economical if the extracted silica was of sufficiently high quality and

quality depends on surface properties, particle size, size distribution and purity. The entire rice

husk ash product is used in an efficient and environmentally friendly approach.

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2.3 Silica and its Properties

Silica or silicon dioxide is an oxide of silicon which has a formula of SiO2. It is known by

its hardness since antiquity and is commonly found in nature as sandstone, silica sand or

quartzite, and as well as in the cell walls of diatoms.(1) It is found in nature in many different

forms: i) quartz or rock crystal, ii) sand, iii) artificial silica. (18) It is the primary source of

silicon which is economically useful for the synthesis of low cost silicon for photovoltaic

applications. (1)

Silica is one of the most abundant oxide materials in the earth's crust. It can exist in an

amorphous form (vitreous silica) or in a variety of crystalline forms. Often it will occur as a

non-crystalline oxidation product on the surface of silicon or silicon compounds. Silica is a

group IV metal oxide, which has good abrasion resistance, electrical insulation and high thermal

stability. It is insoluble in all acids with the exception of hydrofluoric acid (HF). (19)

Table 2.1 Physical, mechanical, thermal and electrical properties of quartz and fused silica. (19)

Material

Density

(g/cm3)

Thermal

conductivity

(Wm-1 K)

Thermal

expansion

coeff.

(10-6 K-

1)

Compressive

strength

(MPa)

Poisson's

ratio

Dielectric

field

strength

(kV/mm)

*

Melting

point

(°C)

Resistivity

(Wm) *

Quartz

2.65

1.3

12.3

2070

0.17

15.0-25.0

1830 1012-

1016

Fused

silica

2.2

1.4

0.4

690-1380

0.165

15.0-40.0

1830 >1018

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2.4 Silica and its Uses

One of the important uses of silica is in fiber optics - a branch of optics dealing with the

transmission of light through hair-thin, transparent fibers and these optical fibers are made up of

silica. The most widespread use of fiber optics is in communications. Companies such as

AT&T, MCI WorldCom, and Sprint have virtually replaced their long-distance copper lines with

optical-fiber cables. Local telephone service providers use fiber-optic cables between central

office switches and sometimes extend it into neighbourhoods and even individual homes. Cable

television companies transmit high-bandwidth TV signals to subscribers via fiber-optic cable.

Local area networks (LANs) are another growing application for fiber optics. Unlike long-

distance communications, LANs connect many local computers to shared equipment such as

printers and servers. LANs readily expand to accommodate additional equipment and users.

Private companies also use fiber optics and its inherent security to send and receive data. Such

firms and institutions as IBM, Wall Street brokerages, banks, and universities transfer computer

and monetary information between buildings and around the world via optical fibers.

One simple application of silica in fiber optics is a dentists’ drills, for example, often

incorporate a fiber-optic cable that lights up the insides of patients’ mouths. Silica is also used in

the manufacture of glass, glazes, enamels, cement, and porcelain, and has important individual

applications. Silica could also be a synthetic lubricant that is a special product that can operate at

very high temperatures, as in advanced automobile diesel engines. Lubricants are substances

applied to the bearing, guiding, or contact surfaces of machinery to reduce friction between

moving parts.

Silica is the primary source of silicon. Silicon chips are the hearts of modern computers.

Microscopically thin layers of silicon are etched away to produce the millions of tiny circuits that

make up a computer chip. The silicon layers can be shaped into levers, gears, and other tiny

mechanical devices. (20) There are other innumerable uses of silica.

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Chapter 3

Methodology

3.1 Research Design

To be able to differentiate the effects of the incineration variable to the purity of silica

from rice husk ash, a design of the experiment will be established. The rice husk will be burned

in different temperatures and in different time variations. The derived silica from rice husk ash

of the different variations that will be made will then be compared as to their quality. The

quality of the silica will depend on the purity of the product.

3.2 Sampling

The rice husk will be collected in a local rice mill factory at JS Perfecto, RT Lim,

Zamboanga Sibugay. The rice husk will then be burned to produce rice husk ash and silica will

be extracted from rice husk ash. The rice husk ash must be dried to be able to remove the

moisture content.

3.3 Data Gathering Procedure

3.3.1 Reagents and Materials

Sodium hydroxide (99%) and sulfuric acid will be used. Magnetic stirrer, Dewar flask,

stop watch, analytical balance, spatula, thermometer, mortar and pestle and microwave oven will

be utilized and as well as filter paper. (20)

3.3.2 Production of Rice husk ash

Rice husk will be burnt at different temperatures (between 400-700oC) e.g at 400

oC, at

500oC, at 600

oC separately, and time of incinerations will also be varied. The burning of the rice

husk will produce rice husk ash which is very rich in silica. Silica will then be extracted with few

methods.

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3.3.3 Extraction of Silica gel

Ten grams of rice husk ash will be added to various volumes and concentrations of

sodium hydroxide solution (most solutions were 2.0 M = 165 ml, 1.0 M = 330 ml, 0.5 M = 660

ml, because the above solutions provide a minimum amount of NaOH to produce sodium silicate

with SiO2/Na2O ratio = 1) in an adiabatic container. The mixture will then be heated in an oven

at 100oC for 5 min or 10 min.

The solution will then be filtered through filter paper (10 μm) and the carbon residue will

be washed with 100 ml of de-ionized water. The filtrate and washings will then be allowed to

cool at room temperature. Concentrated sulfuric acid will then be added to the obtained solution

until pH 7.0 and will be incubated for 48 hours to promote silica gel formation. The silica gel

produced will be separated from soluble salt solution by filtration and then washed with de-

ionized water. Then silica gel will again be dried at 150oC for 48 hours and be ground into

powder. The obtained silica gel will be white rough powder. The extraction will be repeated but

instead of heating the mixture of rice husk ash and NaOH at 100oC for 5 min or 10 min, 200

oC

will be done and several variations will be made such changing the time of incineration. (17)

3.3.4 Analysis of Silica Content

The product will be analyzed by spectrophotometric method to be able to determine its

silica content. Three grams of the silica will be diluted to one litter of distilled water to produce

3ppt. The product of the synthesis will be diluted with water to several volumes to make at least

6 standards (1 ppt, 2 ppt, 3 ppt, 4 ppt, 5 ppt, and 6 ppt). The blank that will be used is distilled

water.

3.4 Data Analysis

The analyses of the data that will be gathered for the variations made will be carried out

by examining the percent silica synthesized from rice husk for different conditions. The

different silica content in every variation will be analyzed and then be compared to assess the

effects of incineration variables. Analysis of variance (ANOVA) could also be used in

comparing the silica content in each of the variations made.

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References

1. Wikipedia encyclopedia, http://en.wikipedia.org, accessed on August 2, 2011 and

October 2, 2011

2. Juliano,1985

3. R. N Swammy (edi.), New Concrete Materials, 1986, p. 171

4. A R Khane, Ref 10, p. 33

5. Mehta and Pitt,1976; Cook and Suwanvitaya, 1981; Hamad and Khattab 1981;

UNIDO,1984

6. Luh, 1980, 1991

7. Beagle,1978

8. Govind Rao,1980

9. Sistani et al., 1997

10. Mamipitiyarachchi, 1981

11. Pandya et. al., 1985

12. Ahmed and Ram 1992

13. Tiwari et al., 1995

14. Brown and Snyder, 1985; Proctor and Snyder, 1987;

15. de Souza, M.F.M., W. L. E. Presegil, M. C., Silica Derived from Burned Rice Hulls.

Materials Research, 2002. 5(4): p. 467-474.

16. Synthesis of High Purity Silicon from RiceHusks; researcher’s title is derived from the

recommendation of Kingsley Kweku Larbi thesis

17. Journal of Metals, Materials and Minerals, Vol.19 No.2 pp.45-50, 2009; Supitcha

RUNGRODNIMITCHAI*, Wachira PHOKHANUSAI and Natthapong SUNGKHAHO

18. Tutor Vista, http://www.tutorvista.com/content/chemistry/chemistry-iv/p-block-

elements/silica-forms.php , accessed on September 30, 2011

19. http://www.azom.com/article.aspx?ArticleID=1114, accessed on September 30, 2011

20. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation.