ASSESSMENT OF THE SUITABILITY OF SAW DUST ASH AS FLUXING RAW MATERIAL IN SODA LIME SILICA GLASS PRODUCTION

ABSTRACT

 

This research was conducted to study the suitabilty of saw dust ash in glass preparations. Saw dust from Isoberlinea doka (doka), Terminalia superba (Afara), Anogeissus leiocarpus (marke) and the mix saw dust (without taking note of the wood type) were used. They were collected from local market Sabon Gari, Zaria. The saw dusts were ashed using muffle furnace at 550⁰C and analysed using affluent absorption spectrophotometer and percentage oxides were calculated. The following results were obtained: Terminalia superba (Afara) 7.85% SiO₂, 1.89% Al₂O₃, 18.00% K₂O, 24.80% CaO, 5.40% Na₂O, 5.07% MgO, 1.97% Fe₂O₃. Anogeissus leiocarpus (marke) 7.31% SiO₂, 2.27% Al₂O₃, 22.80% K₂O, 19.05% CaO, 9.17% Na₂O, 9.04% MgO, 1.37% Fe₂O₃. Isoberlinea doka (doka) 7.10% SiO₂, 6.42% Al₂O₃, 21.50% K₂O, 8.42% CaO, 7.55% Na₂O, 24.21% MgO, 1.92% Fe₂O₃. Mixed saw dust 7.27% SiO₂, 7.56% Al₂O₃, 29.90% K₂O, 24.47% CaO, 5.40% Na₂O, 15.61% MgO, 4.57% Fe₂O₃. Four glass batches containing these ashes were prepared and melted in refractory crucibles at 1300⁰C for five hours where two batches 1 and 4 melted and formed glasses while 2 and 3 sintered. Some properties of the two glasses obtained was determined, the density was determined by measurement and by calculation. The result from measurement was found to be 2.46gdm^-3 while by calculations, the result was 2.42gdm^-3. The variation in densities might be as a result of foreign inclutions from refractory crucibles or the introduction of excess K₂O into the glass batches. Chemical durability test of the glasses was found to be in compliance with standard soda lime silica glass. The Xray diffraction of the melt showed the formation of amorphous phase in sample 1 and 4, which indicated the formation of glass while that of 2 and 3 indicated the formation of crystalline phase which confirmed the formation of sintered bodies. The electron dispersive spectroscopy from scanning electron microscopy (SEM) of glasses from batch 1 and 4 showed the consistency of major elements forming the glass compositions, Si, Na and O, indicating the homogeinity of the melts and accuracy of the temperature range. While the external morphology of the glasses showed rough surfaces as a result of not subjecting the glasses into mechanical stirring or any of the forming processes, and also presence of pores but not large enough to cause any form of deformity to the glasses. Based on the results obtained, saw dust ash can best be used as sources stabilizers in glass making due to high percentage of CaO and K₂O.

CHAPTER ONE

INTRODUCTION

1.1         Background of the Study

The unavailability of raw materials for industrial production of any product including glass can cause some difficulties, or problems to mass production or research within that particular area. This problem is among observations raised at the seminar organized by Raw Materials Research and Development Council on the Prospects and Challenges of Sourcing Raw Materials for the Chemicals and Pharmaceutical Industries in Lagos, Nigeria in the year 2001. It was highlighted that over 90% of raw materials used in chemical and pharmaceutical industries are imported and the cost of importation of such chemical raw materials is enormous. Some locally available raw material such as kaolin, carbon black etc, are of very poor quality and do not meet the specifications of the industries. The report also stated that there is lack of intermediate industries to produce the required raw material. Because of these and similar problems affecting glass production, there is need to have easier and cheaper means of obtaining these required oxides in glass preparation at the local, national or universal level. So, ash is something that can be obtained any where worldwide. Ash utilization in glass production will immensely reduce environmental pollution and at the same time provide extra income to some individuals that will be involve in sourcing or marketing of the ash or materials that when burnt will provide the required ash at the required quality and quantity. The practice of recycling solid waste into something useful is an ancient one. Metal implements were melted down and recast in prehistoric times. Today, according to Huang (2008), recyclable materials are recovered from municipals refuse by a number of methods, including shredding, magnetic separation of metals, air classification that separates light and heavy fractions, screening, and washing. Another method of recovery is the wet pulping process: Incoming refuse is mixed with water and ground into slurry in the wet pulper, which resembles a large kitchen disposal unit. Large pieces of metal and other non pulpable materials are pulled out by a magnetic device before the slurry from the pulper is loaded into a centrifuge called a liquid cyclone. Here the heavier non combustibles, such as glass, metals, and ceramics, are separated out and sent on to a glass-and metal-recovery system; other, lighter materials go to a paper-fiber-recovery system. The final residue is either incinerated or is used as landfill. Waste materials residues of incineration generated from combustion of coal from thermal power station such as coal ash and fly ash, as well as bottom ash from grate of incinerators, sewage sludge ash, sludge from pulp paper waste, slag from metallurgical process and sugar cane bagasse are common waste residues that are useful in glass ceramic production. (Isa and Abdulmumini, 2015).

1.2         Glass

Glass is defined as an amorphous solid completely lacking in long range, periodic atomic structure, and exhibiting a region of glass transformation behavior. Any material whether it is inorganic, organic, or metallic, formed by any technique, which exhibits glass transformation behavior is a glass. (Shelby, 2005). He adopted this definition due to the fact that there are numbers of discoveries in the field of glass science and technology that earlier definitions had to be looked in and therefore, had to be reviewed. Some of the advancements according to him are that silica is not the required component of a glass as other inorganic materials which do not contain silica can be used to produce glass, example P₂O₅ and GeO are glass network forming oxides after cooling from melt. Also cooling from the melt is not requirement for glass formation. Glass can be produce by other methods like sol gel process of solutions, vapour deposition and neutron irradiation of crystalline materials. Varshneya (2005) stated that As₂O₅, Sb₂O₃ and V₂O₅ are able to produce glass by vapour phase condensation.

Apart from the above mentioned advancements, Shelby (2005), also described that glasses inorganic or non metallic nature of glasses can not be used to define glass because, currently there are organic glasses and metallic glasses. Varshneya (1999) cited some examples of glass formation in metallic systems which include, Transition metals metalloid (T-M) system, example Pb₈₀Si₂₀, Ni₈₀P₂₀ and FeNi₄₀P₁₄. Early and late transition metals (TE, TL); examples are Nb₆₀Ni₄₀, W₄₅Fe₅₅, Zr₇₆Fe₂₄, Co₃₃Gd₆₇ and Ni₃₀Gd₇₀. The alkaline earth (AE) with rare earth (RE) and simple metals (S), examples Ca₆₇Mg₃₃, Mg₇₀Zn₃₀, Ca₆₇Pb₃₅ and Al₃₀La₇₀. The transition metals actinides (T-AC) system, example U₇₀Cr₃₀. Shelby (2005) therefore, stated two common characteristics of all glasses, firstly, no glass has a long range, periodic atomic arrangement and secondly, time dependent glass transformation behavior. Therefore, any material inorganic, organic, metallic or non metallic formed by any technique which exhibits glass transformation behavior is glass.

1.3         Glass Making Raw Materials

Before any type of glass is produced, good selection of raw materials is put into consideration. The raw materials should be abundant, cheap and free from impurities. Physical nature such as grain size is also an important factor that plays some roles in success of obtaining the type of glass intended to be produced. Glass making oxides are categorized into various groups, Samuel (1974) classified glass raw materials into Glass forming oxides, flux, oxidizing agents, reducing agents, fining agents and colouring agents. Shelby (2005), categorized glass making oxides into Glass Former, Flux, Property Modifier, Colourant, and Fining Agent.

1.3.1     Glass Forming Oxides

The primary glass formers in commercial oxide glasses are silica (SiO,), boric oxide (B₂O₃), and phosphoric oxide (P₂O₅), which all readily form single component glasses. A large number of other compounds may act as glass formers under certain circumstances, including GeO, As₂O₃, Sb₂O₃, TeO,, A1₂O₃, GaO₃, and VO. With the exception of GeO, these oxides do not readily form glasses by themselves unless very rapidly quenched or vapor deposited, but can serve as glass formers when mixed with other oxides. The elements S, Se, and Te act as glass formers in chalcogenide glasses. Although halide glasses can be made in many systems, with many different compounds acting as glass formers, the two most common halide glassformers are BeF, and ZrF (Shelby, 2005)

1.3.2     Flux

This is a group of oxides which when impact into glass; modify the glass structure resulting in the decrease in the temperature of fusion. Shelby (2005), mentioned that the most common fluxes are the alkali oxides, especially Na,O (soda) and PbO. Most commercial glasses contain soda, including those used for containers and window glasses. Potassium oxide is also used extensively in commercial glasses, while lithium oxide is used in a number of commercial glass-ceramics. Addition of large amounts of alkali oxides results in serious degradation in many properties.

1.3.3     Property Modifier

Addition of fluxes to silica lead to decrease in cost of glass formation, the addition of large amounts of alkali oxides results in serious degradation in many properties. The degradation in properties is usually countered by addition of property modifiers, which include the alkaline earth and transition metal oxides, and, most importantly, aluminum oxide. They also improve many of the properties of the resulting glasses. The properties are thus modified, or adjusted, by careful control of the amount and concentration of these oxides to obtain precisely the desired results (Shelby, 2005).

1.3.4     Oxidizing Agents

These are oxides that liberate oxygen during glass melting by decomposing organic matter present in the batch, change ferrous to ferric state (FeO to Fe₂O₃) by this, it also prevent discolouration of glass in the manufacture of colourless glass. Oxidizing agents hinder chemical reduction to obtain specific colour in the manufacture of coloured glass. It also help in fining by evolving oxygen bubbles. Examples are KNO₃, NaNO₃, Ba₂O₂ and MnO (Samuel, 1974)

1.3.5     Reducing Agents

These are oxides that extract oxygen from some constituents of the batch. They reduced ferric to ferrous (Fe₂O₃ to FeO) in specific case of ultra violet light transmitting glasses. These oxides are also introduced to promote incorporation of some batch forming oxides into a glass by reducing sodium sulphate to sodium sulphite (Na₂SO₄ to Na₂SO₃) which reacts quicker with SiO₂. Example is carbon as coal or coke. And it hinders oxidizing atmosphere in the development of certain coloured glass. Examples of reducing agents are coal, anthracite, K₂NO₂ and tartaric acid,

1.3.6     Fining Agents

Fining agents are added to glass forming batches to promote the removal of bubbles from the melt. Fining agents include the arsenic and antimony oxides, potassium and sodium nitrates, NaCl, fluorides such as CaF,, NaF, and Na,AlF,, and a number of sulfates. These materials are usually present in very small quantities usually less than 1 wt%, and are usually treated as if they have only minor effects on the properties of the final glasses. Their presence, however, is essential in many commercial glasses, which would be prohibitively expensive to produce without the aid of fining agents in reducing the content of unwanted bubbles in the final product. (Shelby, 2005)

1.3.7     Colouring Agents

These are substances that impacts colour to glass, and in most cases according to Shelby (2005), are oxides of either the 3d transition metals or the 4f rare earths. For example Cr₂O₃ introduces green colour, CrO₃ gives orange – red colour, while V₂O₃ impact yellow to glass. Iron oxides, which are common impurities in the sands used to produce commercial silicate glasses, act as unintentional colorants in many products.

1.4         Glass Making Raw Materials Sources

Isa (2009) described that all glass making raw materials are being sourced from Mined or quarried raw material, Synthetic raw materials or by product materials.

1.4.1     Mined or Quarried Raw Material

These are mined materials and beneficiated in some ways after extraction from their various ores to meet the requirements for glass production and market demands. Such raw materials are sand, quarts, limestone, dolomite and feldspar (Isa, 2009)

Sand which is near the surface is explored by open cast method in which the upper top soil is removed and then the sand dug up. Generally, machines are used to dig up minerals by this method. While feldspar, limestone and dolomite are explored by bulk extraction in which explosives devices are used to break it into smaller fragments for easy handling and transportation from one place to another. (RMRDC, 2009)

1.4.2     Synthetic Raw Materials

These are manufactured chemical substances which include the soda ash, boric acid, aluminium hydrate, potash, borax etc. Fwotmwol and Garkida (2005) stated that these oxides are supplied in Nigeria by vendors from importation or by locally based chemical processing plants. Example of such plant is the soda ash processing plant in Borno state.

1.4.3     By Product Materials

These are materials produced as a result of the manufacture or production of something else, often useful or commercially valuable. These include the cullet from within the factory as a result of defects along the production line and from external sources. Also, blast furnace slag and phosphate slag are chemical by products.

1.5         The Ash

Ash as defined by Redmond (2009), as simply a solid product of combustion. If combustion is complete, the ash is wholy inorganic. The ash from wood or similar plant material generally consists principally of sodium carbonate and potassium carbonate. Ash from animal bones also contains oxides similar to that from plants and some others not obtainable from plants. Alemaka (2002) found out that bones and bone ashes contain calcium phosphate (v) in addition to calcium carbonate, fat and organic matter containing nitrogen.

1.5.1     Uses of Ash

Ash can serve as both waste and item of economic importance depending on individual need, trade or culture. It is waste to a person that run a restaurant and to those that use woods as source of domestic energy in cooking, room warming or trades like blacksmithing. It is at the same time a good source of manure to gardeners and crop farmers. Ewule, (2002) stated that wood ash is used by farmers as a source of manure because of its high content of potash and potassium. In some parts of Nigeria, wood ash is also applied as insect repellants to farm crops due to its toxicity, and as traditional source of easy and quick method of fruit ripening. Because of its high alkaline content, Serafimova, Mladenov and Pelovski, (2011) recommended the use of wood ash for soil acid neutralization.

Ash is also a good source of locally obtainable glazes to ceramics as stated by Ojie and Egede (2002). “In a majority of cases, wood ash contains considerable soluble alkalis such as potash and soda in addition to silica and alumina. Combination of these alkali and the glass formers gives very good glazes. Ash does not only serve as raw material in production but also serve as food additives in some areas of Northern Nigeria”. Serafimova et al (2011) stated that in most cases, ash from combustion of plants waste does not contain heavy metals and other toxic elements in concentration that could lead to environmental contamination. Also, such type of ashes could be used as a secondary raw material contributing to the reduction of the quantity of generated wastes and achieving greater sustainability. Analyses confirmed that the basic components of wood ash are CaCO₃, SiO₂ and K₂Ca(CO₃)₂. Therefore, this determined the nature of alkaline extracts in wood ash is attractive material for use in glass production.

1.6 Statement of the Problem

The problem of this research is to find a way of recycling waste saw dust ash to curb environmental pollution. The general way of waste disposal in Nigeria is dumping in an open land, land filling and in few cases by incineration. Isa and Abdulmumini (2015) pointed out that these methods have adverse effects such as emission of green house gases and making environments so irritating to its inhabitant. Therefore, recycling and utilization of wastes is an important aspect of environmental sanitation and minimizes the exploitation of virgin raw materials for any form of production.

1.7         Aim and Objectives of the Study

The aim of this research was to use saw dust ash as cheaper source of flux in the production of soda lime silica glass. This aim was achieved through the following objectives which were to;

1. Source for saw dust from saw mills.
2. Burn the saw dust obtained from the saw mill into ash.
3. Carry out chemical analysis of the saw dust ash to determine its chemical composition.
4. Prepare a glass batch based on soda lime silica glass with the ash as an additive.
5. Test melt the glass at temperature range of 1250^oC to 1300^oC
6. Carry out some properties tests on the glass prepared; chemical durability test, density test, x ray diffraction (XRD) and scanning electron microscopy (SEM).

1.8         Research Questions

1. What are the sources of saw dust?
2. What is the best method of obtaining ash from saw dust?
3. What is the chemical composition of saw dust ash?
4. Can soda lime silica glass be prepared from saw dust ash?
5. What is the temperature range for melting soda lime silica glass containing saw dust ash?
6. What are the properties of glass containing saw dust ash?

1.9       Significance of the Study

Considering the unavailability and cost of importation of glass making ingredients like soda ash, borax etc, there is need to find cheaper ways obtaining soda ash, borax etc. or its supplements locally to discourage importation of glass making raw materials. The utilization of saw dust ash in glass production especially soda lime silica glass, which is produced in mass will make saw dust to be utilized in large quantity thereby converting waste to wealth and reduce environmental pollution caused by saw mills

The research will contribute not only to the field of glass technology but also to areas like agriculture in synthesizing organic fertilizer from plant wastes and ash. The success of the research will also help in increasing earning of saw mill owners as saw dust will no more be discarded as waste. Different individuals may be engaged in collection and sale of saw dust if it becomes an industrial raw material.

1.10      Scope of the Research

The research was delimited to the use of saw dust ash as fluxing raw material in the preparation of soda lime silica glass. The saw dust was obtained from saw mills in Sabon Gari market, because of its ready availability and effects to the environment, particularly the saw mills and their neighborhood.

1.11      Justification of the Research

Saw dust is selected instead of wood ash for environmental reason, as anything that has to do with cutting down wood from trees; goes hand in hand with deforestation, which is a major cause of desert encroachment, soil erosion and global warming. NEEDS (2005), stated that Nigeria used to have some 92000 hectares of forest but only half of that forest remained today. It further described that apart from deforestation and erosion, desertification in some areas is another environmental problem facing Nigeria.

 

 

 

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