06-08-2013, 12:54 PM
Solid waste management
Solid waste .docx (Size: 375.38 KB / Downloads: 119)
ABSTRACT
Solid waste management is one among the basic essential services provided by municipal authorities in the country to keep urban centres clean. Due to rapid urbanization and industrialization the production of various types of solid wastes which pose serious problem to the environment have been generated. So the disposal and reuse of solid industrial wastes like phosphogypsum, flurogypsum, fly ash, slag and lime sludge, etc. is significant in view of their availability and potential application. It is estimated that about 300 million tonnes of inorganic waste from industrial and mining sectors are generated every year in India. Advances in solid waste management resulted in alternative construction materials as a substitute to traditional building materials like bricks, blocks, tiles etc. The efforts are being made for recycling different wastes and utilize them in value added applications. Since almost every natural resources are over exploited and are at the verge of extinction it is the high time for all of us to live aside our traditional conservative approaches and to move forward with new alternatives which are eco friendly and techniques that leads towards a sustainable development. The setting and hardening occurred due to formation of cementitious A-S-H and C-S-H gel (A =Al2O3 , S =SiO2 , C =CaO, H = H2O ). The technologies have been developed at bench scale and efforts are underway for scaling up to pilot plant level. This report aims at studying the recycling and utilisation of industrial wastes in making value added building materials.
INTRODUCTION
The concept of industrial ecology is based on integration of by-product and waste steams across industries leading to production of useful products with near zero flow of material to the environment. Building industry is one of the most dynamic sectors with enormous potential of industrial symbiosis and synergistic utilisation of industrial wastes. With increasing environmental wariness, there is growing concern worldwide for updating production processes, as well as development of green building materials. The green material can be defined as products made from waste, recycled or by-productsto conserve natural resources, circumvent toxic and other emissions, saves energy, and contribute towards a safe and healthy environment. Geopolymers, silico-aluminate materials formed through mimicking natural rock forming process, are fast emerging as new class of green building construction materials. In the process of geo-synthesis, silicon (Si) and aluminium (Al) atoms react to form molecules that are chemically and structurally comparable to those binding natural rock and allows for novel products synthesis that exhibit the most ideal properties of rock-forming elements, i.e., hardness, chemical stability and longevity. Fly ash, blast furnace slag and red mud are the three major industrial wastes in India.
GEOPOLYMERISATION OF WASTE
Most proposed mechanisms of geopolymerisation consist of dissolution of aluminosilicate phase, polymerisation and re-precipitation of gel phase, and transformation of the gel phase into geopolymer of varying crystallinity and structure. Depending upon experimental conditions, the different stages of geopolymer formation may overlap and even merge with each other. Isothermal conduction calorimetry was used to study the geopolymerisation of fly ash, mixture of (GBFS+fly ash), and the mixture containing (fly ash+GBFS+red mud).
DEVELOPMENT OF NOVEL BUILDING MATERIALS
GEOPOLYMER CEMENT
Low reactivity of fly ash has often restricted the use of fly ash for geopolymer cements due to slow strength development. The reactivity of fly ash depends on its vitreous phase content, which participates in geopolymerisation reaction. The remaining constituents takes longer time for reaction due to poor reactivity and leads to slow setting and strength development in geopolymers. Various methods such as chemical activation, mechanical activation and size classification of fly ash has been suggested as a means to improve the reactivity. Recently observations were made by the present authors that use of mechanically activated fly ash leads to high compressive strength in geopolymers. Two different approach were adopted to enhance reactivity of fly ash: (a) air classification to separate finer fractions, and (b) mechanical activation in attrition and vibratory mills. Small size cenosphere cools faster during their formation in coal combustion process and separation of finer fraction by air classification results in increase in the glass contents vis-à-vis raw fly ash. Mechanical activation results due to combined effect of particle breakage (surface area) and other bulk and surface physicochemical changes induced by the process of milling.
SELF GLAZED TILE
Conventionally ceramic tiles are produced by high temperature sintering/ vitrification of aluminosilicate and silicate minerals such as clay, quartz, feldspar, etc. The strength and other properties of tiles are developed due to formation of ceramic bonds. Development of stoneware tiles at 250-400°C by geopolymerisation of alumino-silicate minerals has been reported. The processing involved reaction between aluminosilicate mineral kaolinite and NaOH at 100°C-150°C resulting into the formation of hydro-sodaliteSi2O5 , Al2(OH)4 + NaOH⇒Na(-Si-O-Al-O)n kaolinitehydro sodalite. In the alkali activation of fly ash and slag mixture at ambient temperature, fly ash/slag ratio is the most relevant factor on the strength development. The main reaction product is a hydrated calcium silicate with high amount of tetra-coordinated Al in its structure. The additions of calcium content increase the degree of geopolymerisation at elevated temperature and results into higher strength. Beneficial effect of slag on fly ash geopolymerisation was exploited in the development of self glazed wall tiles.
The glazed surface and the body of tiles showed distinctly different microstructure as revealed by SEM micrographs shown in Fig 4.5a and Fig 4.5b, respectively.
PAVEMENT TILES
Pavement tiles are small cement structures in geometrical shapes that are usually laid on pathways or on any open ground as a solid platform. As these tiles are not cemented and only laid closely over a bed of loose sand, they can be easily removed, stored and reused as many times as possible. In India, the pavement tiles are mostly vibro-cast and/or pressed cement mortar or concrete hydrated for 28 days. The strength is obtained due to hardening of cement. Earlier research on alkali-slag-red mud-cement (ASRC) has indicated high early and ultimate strength together with excellent resistance against chemical attacks. This was achieved by introduction of solid composite alkali activator into slag–red mud mixture system instead of liquid water glass. The hydration products of ASRC cement were mostly C-S-H gel with low Ca/Si ratio in the range of 0.8 to 1.2.
SYNERGETIC USE OF INDUSTRIAL WASTE
Synergistic use of industrial waste is an emerging concept whereby combination of two or more wastes is used to develop a useful product. The main advantage of the synergy is the deficiency of constituents from one waste is compensated by using second or third waste, which is rich in deficient constituent. Synergistic use also includes industrial symbiosis where physical exchange of waste/by-products between geographically close industries is exploited. In the present work, waste from three industries, fly ash from thermal power plants, fly ash and granulated blast furnace slag from Steel Plants, and fly ash and red mud from Aluminium plants, has been used.
Fly ash was used for the development of geopolymers cement, combination of fly ash and blast furnace slag was used for self-glazed tiles and all three wastes fly ash, GBFS and red mud was used for pavement tiles. From the point of view of zero or minimum flow into environment, geopolymer cement is best suited for thermal power plant, where fly ash is the main by-product. Self-glazed tiles and pavement tiles are more suitable for iron & steel and aluminium industry respectively. Fig.5.1 shows the synergy map of these wastes.
CONCLUSION
Due to their ability to polycondense Silicon and Aluminium into solid monolithic ceramic like structure during alkali activation, geopolymers have the potential of utilization of industrial wastes rich in silico-aluminates such as fly ash, GBFS, red mud, etc. Novel building materials such as high strength geopolymers cement can be developed by additional processing such as mechanical activation, and self-glazed tile and pavement tiles can be developed by synergistic use of industrial waste namely fly ash, GBFS and red mud. The developed geopolymer products qualify as new members in the spectrum of eco-friendly construction materials due to easy and simple processing, low energy requirement and no CO2 emission. The products have good commercialisation potential with significant returns.
Solid waste .docx (Size: 375.38 KB / Downloads: 119)
ABSTRACT
Solid waste management is one among the basic essential services provided by municipal authorities in the country to keep urban centres clean. Due to rapid urbanization and industrialization the production of various types of solid wastes which pose serious problem to the environment have been generated. So the disposal and reuse of solid industrial wastes like phosphogypsum, flurogypsum, fly ash, slag and lime sludge, etc. is significant in view of their availability and potential application. It is estimated that about 300 million tonnes of inorganic waste from industrial and mining sectors are generated every year in India. Advances in solid waste management resulted in alternative construction materials as a substitute to traditional building materials like bricks, blocks, tiles etc. The efforts are being made for recycling different wastes and utilize them in value added applications. Since almost every natural resources are over exploited and are at the verge of extinction it is the high time for all of us to live aside our traditional conservative approaches and to move forward with new alternatives which are eco friendly and techniques that leads towards a sustainable development. The setting and hardening occurred due to formation of cementitious A-S-H and C-S-H gel (A =Al2O3 , S =SiO2 , C =CaO, H = H2O ). The technologies have been developed at bench scale and efforts are underway for scaling up to pilot plant level. This report aims at studying the recycling and utilisation of industrial wastes in making value added building materials.
INTRODUCTION
The concept of industrial ecology is based on integration of by-product and waste steams across industries leading to production of useful products with near zero flow of material to the environment. Building industry is one of the most dynamic sectors with enormous potential of industrial symbiosis and synergistic utilisation of industrial wastes. With increasing environmental wariness, there is growing concern worldwide for updating production processes, as well as development of green building materials. The green material can be defined as products made from waste, recycled or by-productsto conserve natural resources, circumvent toxic and other emissions, saves energy, and contribute towards a safe and healthy environment. Geopolymers, silico-aluminate materials formed through mimicking natural rock forming process, are fast emerging as new class of green building construction materials. In the process of geo-synthesis, silicon (Si) and aluminium (Al) atoms react to form molecules that are chemically and structurally comparable to those binding natural rock and allows for novel products synthesis that exhibit the most ideal properties of rock-forming elements, i.e., hardness, chemical stability and longevity. Fly ash, blast furnace slag and red mud are the three major industrial wastes in India.
GEOPOLYMERISATION OF WASTE
Most proposed mechanisms of geopolymerisation consist of dissolution of aluminosilicate phase, polymerisation and re-precipitation of gel phase, and transformation of the gel phase into geopolymer of varying crystallinity and structure. Depending upon experimental conditions, the different stages of geopolymer formation may overlap and even merge with each other. Isothermal conduction calorimetry was used to study the geopolymerisation of fly ash, mixture of (GBFS+fly ash), and the mixture containing (fly ash+GBFS+red mud).
DEVELOPMENT OF NOVEL BUILDING MATERIALS
GEOPOLYMER CEMENT
Low reactivity of fly ash has often restricted the use of fly ash for geopolymer cements due to slow strength development. The reactivity of fly ash depends on its vitreous phase content, which participates in geopolymerisation reaction. The remaining constituents takes longer time for reaction due to poor reactivity and leads to slow setting and strength development in geopolymers. Various methods such as chemical activation, mechanical activation and size classification of fly ash has been suggested as a means to improve the reactivity. Recently observations were made by the present authors that use of mechanically activated fly ash leads to high compressive strength in geopolymers. Two different approach were adopted to enhance reactivity of fly ash: (a) air classification to separate finer fractions, and (b) mechanical activation in attrition and vibratory mills. Small size cenosphere cools faster during their formation in coal combustion process and separation of finer fraction by air classification results in increase in the glass contents vis-à-vis raw fly ash. Mechanical activation results due to combined effect of particle breakage (surface area) and other bulk and surface physicochemical changes induced by the process of milling.
SELF GLAZED TILE
Conventionally ceramic tiles are produced by high temperature sintering/ vitrification of aluminosilicate and silicate minerals such as clay, quartz, feldspar, etc. The strength and other properties of tiles are developed due to formation of ceramic bonds. Development of stoneware tiles at 250-400°C by geopolymerisation of alumino-silicate minerals has been reported. The processing involved reaction between aluminosilicate mineral kaolinite and NaOH at 100°C-150°C resulting into the formation of hydro-sodaliteSi2O5 , Al2(OH)4 + NaOH⇒Na(-Si-O-Al-O)n kaolinitehydro sodalite. In the alkali activation of fly ash and slag mixture at ambient temperature, fly ash/slag ratio is the most relevant factor on the strength development. The main reaction product is a hydrated calcium silicate with high amount of tetra-coordinated Al in its structure. The additions of calcium content increase the degree of geopolymerisation at elevated temperature and results into higher strength. Beneficial effect of slag on fly ash geopolymerisation was exploited in the development of self glazed wall tiles.
The glazed surface and the body of tiles showed distinctly different microstructure as revealed by SEM micrographs shown in Fig 4.5a and Fig 4.5b, respectively.
PAVEMENT TILES
Pavement tiles are small cement structures in geometrical shapes that are usually laid on pathways or on any open ground as a solid platform. As these tiles are not cemented and only laid closely over a bed of loose sand, they can be easily removed, stored and reused as many times as possible. In India, the pavement tiles are mostly vibro-cast and/or pressed cement mortar or concrete hydrated for 28 days. The strength is obtained due to hardening of cement. Earlier research on alkali-slag-red mud-cement (ASRC) has indicated high early and ultimate strength together with excellent resistance against chemical attacks. This was achieved by introduction of solid composite alkali activator into slag–red mud mixture system instead of liquid water glass. The hydration products of ASRC cement were mostly C-S-H gel with low Ca/Si ratio in the range of 0.8 to 1.2.
SYNERGETIC USE OF INDUSTRIAL WASTE
Synergistic use of industrial waste is an emerging concept whereby combination of two or more wastes is used to develop a useful product. The main advantage of the synergy is the deficiency of constituents from one waste is compensated by using second or third waste, which is rich in deficient constituent. Synergistic use also includes industrial symbiosis where physical exchange of waste/by-products between geographically close industries is exploited. In the present work, waste from three industries, fly ash from thermal power plants, fly ash and granulated blast furnace slag from Steel Plants, and fly ash and red mud from Aluminium plants, has been used.
Fly ash was used for the development of geopolymers cement, combination of fly ash and blast furnace slag was used for self-glazed tiles and all three wastes fly ash, GBFS and red mud was used for pavement tiles. From the point of view of zero or minimum flow into environment, geopolymer cement is best suited for thermal power plant, where fly ash is the main by-product. Self-glazed tiles and pavement tiles are more suitable for iron & steel and aluminium industry respectively. Fig.5.1 shows the synergy map of these wastes.
CONCLUSION
Due to their ability to polycondense Silicon and Aluminium into solid monolithic ceramic like structure during alkali activation, geopolymers have the potential of utilization of industrial wastes rich in silico-aluminates such as fly ash, GBFS, red mud, etc. Novel building materials such as high strength geopolymers cement can be developed by additional processing such as mechanical activation, and self-glazed tile and pavement tiles can be developed by synergistic use of industrial waste namely fly ash, GBFS and red mud. The developed geopolymer products qualify as new members in the spectrum of eco-friendly construction materials due to easy and simple processing, low energy requirement and no CO2 emission. The products have good commercialisation potential with significant returns.