How to Make Hollow Blocks from Waste Materials A new type of hollow blocks can be fabricated out of wood wastes, agricultural wastes and soil mixed with minimum amount of cement. As far as strength and durability are concerned, results of test showed that this type of blocks is comparable to some of the commercial or traditional concrete hollow blocks. However, they are considered as strictly non-loading bearing.
Materials: 1 part cement
3 parts sawdust
ordinary soil
rice hulls
abaca waste
sugarcane bagasse
coconut coir dust
coconut trunk
Procedure:
1. Pulverized soil is passed through a wire screen, 1/4 inch wire mesh to separate larger pieces. A mixture of 1 part cement to 3 parts agri-waste is formulated. 2. Mix all materials together, add water and pour into molds. 3. Let stand for several hours until dry. 4. After drying, remove from molds and let stand along one side for 10 days while sprinkling water at regular intervals to avoid cracking
METHOD #1
Rural folks can beat the high prices of housing materials. Out of farm waster and ordinary soil, one can make durable hallow blocks comparable in strength to commercial ones. The hallow blocks can be made right on the b uilding site and fashioned similar to commercial hallow blocks. Although considered strictly non-load bearing, it is very satisfactory for low cost housing. Its compressive strength ranges from 197 to 386 pounds per square inch (psi).
This simple technology, developed by the Forest Product Research and Industries development Commission, makes use of a minimum amount of cement to make a stronger hallow block. One bag is enough to make 20 four-inch blocks or 12 six-inch blocks. The first step is to gather agri-wood waste such as sawdust, coconut trunk particles, sugar cane bagasse or ordinary soil. The latter has to be pulverized and sifted using a 1 /4 inch wire mesh. Abaca waste, left after extracting fiber from the stalk, as well as coconut coir dust, the residue from processing coconut husk in coirflex plants, can also be used. Rice hull works too, but additional soil is needed when mixing this with the cement. Improvise hand mold to shape the hallow block. This can be made out of steel or wood of relatively high density such as apitong, guijo or yakal. The mold should have three removable core blocks, and the sides should easily be opened and secured. Place hinges and lockpins as illustrated. Using the cubic foot measuring box, mix together one box of cement and three boxes of agriwaste, or the equivalent proportions. With the materials form a hill with a crater on the top. Pour water slowly, then, thoroughly mix them with shovel until the paste is formed. The mixture must be neither too dry or too wet such that they would stay packed when molded and when not spread out when removed from the mold. Place the flatboard at the bottom of the hand mold, then fill it with the mixture. Tamp and level off extra paste, then place another flatboard on the top. Turn the mold upside down, and tamp and level off as before. After a while, remove the three core blocks and the pin to let the sides open. Gently push the molded hallow block from the mold, leaving it in place on the flatboard. Place the hallow blocks in a shade for a few hours to dry. after one side has dried, turn the block upside down to dry the other side. Store these lock standing on their na rrow edges. For about ten days, cure them by occasional sprinkling water over the blocks. Afterwards, they are ready for use.
METHOD #2 – RICE HULLS Procedure: 1. Carbonize the rice hulls. 2. Pulverize the ash. 3. Mix the following: 60 parts cement, 40 parts carbonized ashwater 4. Pour the mixture into wooden molds 5. Allow to dry.
METHOD #3 – WASTE MATERIALS A new type of hollow blocks can be fabricated out of wood wastes, agricultural wastes and soil mixed with minimum amount of cement. As far as strength and durability are concerned, results of test showed that this type of blocks is comparable to some of the commercial or traditional concrete hollow blocks. However, they are considered as strictly non-loading bearing. Materials: 1 part cement + 3 parts sawdust, ordinary soil, rice hulls, abaca waste, sugarcane bagasse, coconut coir dust and coconut trunk. Procedure: 1.
Pulverized soil is passed through a wire screen, 1/4 inch wire mesh to separate larger pieces. A mixture of 1 part cement to 3 parts agri-waste is formulated. 2. Mix all materials together, add water and pour into molds. 3. Let stand for several hours until dry. 4. After drying, remove from molds and let stand along one side for 10 days while sprinkling water at regular intervals to avoid cracking. The three basic needs of man are food, clothing and shelter. The need for shelter is critical. There are three needs we have with regard to shelter which are: protection, comfort and convenience. Man needs protection from storm, cold, heat and bad elements. He needs a house to provide him and his family a place to rest, comfort and privacy. It is an important requirement in building a home. Shelter basically involves construction, hence its importance in the development of man.
In the Philippines, some houses are designed with adequate space and furnishings for convenient households operation, comfort, provisions for childcare, and creation. Unfortunately, however, inadequacy of dwellings is prevalent because of poverty. Housing conditions are still below standard condition especially in the depressed barrios and areas. A house is a structure where man lives. It includes the buildings, the furnishings and the neighborhood. It may be made of materials like nipa, bamboo, wood, cement and galvanized iron. As observed, there are thousands of families housed in shanties and other forms of temporary shelter outside their homes. One principal reason for this is the affordability of the cost of materials used in construction. The situation therefore, prompted the Mabini Limers and Farmers Multipurpose Cooperative, Brgy. Mabini, Buenavista, Guimaras to conceptualize a new product that could be used as a construction material in building a house that is strong and permanent in structure and is a ffordable for the poor. This product can be an effective substitute for sand-made hollow blocks, the basic construction materials used in building a house today. The increased cost of construction materials has posed a problem to the growing needs of some builders in the country today. To alleviate the situation and to accelerate rural development programs being undertaken by the government, a concerted effort to evolve a common program of developing low-cost indigenous materials was exerted. Due to the price increase of building materials today like cement which is used as a primary binder in making of hollow blocks and with the scarcity of sources of cement being sold to far-flung areas, this made the cement more expensive and could hamper the construction of low-cost housing in the area. Lime is an important ingredient for the manufacture of cement. As building material, lime is usually used as mortar, plastering, and white washing. With these characteristics of lime, the Mabini Limers and Farmers Multipurpose Cooperative find-out the potentials of lime waste materials as aggregates and cement as binder in hollow block making. Compared to other construction materials, hollow block can be manufactured anywhere provided that lime waste materials are available. Since large production of lime is produced daily, productions of manually-
made hollow blocks can be relatively cheaper and without expense. Imported aggregates like sand and gravel may cost relatively higher than the existing price of construction materials. Traditional concrete hollow block can be manufactured with sand-cement as materials. But there are indigenous raw materials which are used as additive in making of another locally-made concrete hollow block. In this juncture, hydrated lime can be used as additive while lime-waste materials can also be used as aggregates in making of hollow blocks. They can be useful as alternative construction materials which can be produced in the locality. The abundance of limestones in the Province of Guimaras has challenged the Mabini Limers and Farmers Multipurpose Cooperative initiative to utilize them into useful construction materials
A new type of hollow blocks can be fabricated out of wood wastes, agricultural wastes and soil mixed with minimum amount of cement. As far as strength and durability are concerned, results of test showed that this type of blocks is comparable to some of the commercial or traditional concrete hollow blocks. However, they are considered as strictly non-loading bearing. In view of the rising cost of cement, the Forest Products Research and Development Institute made an attempt to form building blocks out of soil and water alone or in combination with one or two other agriforestry waste materials, such as rice hull, coconut coir dust and wood ash. Lime is used as a binder. Lime is found in large quantities in Rizal, Negros Occidental and Davao Oriental. Coconut coir and other materials are available almost nationwide
Increasing garbage and its proper disposal management are among the major headaches of municipalities today. Most view garbage as a cause of the floods that wreak havoc during typhoons, such as the Ondoy typhoon, which happened September 2010. Even before Ondoy and Pepeng hit the Philippines, the country had been plagued by floods. However, what set apart the two recent catastrophes is their gravity. In six hours, Metro Manila received a month's worth of rainfall, according to thePhilippine Atmospheric, Geophysical, and Astronomical Services, Administration (PAGASA), the worst ever recorded in history. Although many argue the cause of Ondoy's disaster as a confluence of various factors, many people also concluded that the increasing garbage in the Metro was a major contributor to the heavy flood. This is one of the reasons why a growing number of municipalities are attracted to technologies that would introduce innovative ways of reducing garbage and disposing of it properly. Currently being used by municipalities is the waste-conversion technology, among the most
popular by-products of which are the concrete blocks, better known as “hollow blocks.” The technology is popular because it does not only reduce garbage but it also helps in combating climate change. Moreover through this initiative, municipalities are also attempting to challenge the quarrying activities done within their respective area. The production of commercially-available concrete is estimated to produce more than six billion pounds of carbon dioxide (CO2) annually. If less concrete is manufactured, then CO2 emissions will also be lessened. The energy-intensive process of manufacturing conventional concrete makes the technology dirty because of the CO2 emissions, thus contributing to climate change. To briefly explain the technology, plastic wastes and styrofoam containers are segregated from the garbage to be fed into a diesel-powered pulverizing machine, which pulverizes the plastics into tiny bits and pieces. These are then mixed into a wet mound of cement and sand. The mixture will then be poured into the molder up to its brim. The molder is then lifted upside down to eject the freshly made hollow block. One of the municipalities producing these alternative bricks is Teresa, Rizal. According to Teresa's solid waste management program chief Marlon Pielago, the blocks they produce are not as strong as the ones available commercially, and are not intended to replace the commercially produced ones. Other cities and municipalities using the same and other related concrete-producing technology are Bantayan in Cebu; Sto. Tomas, Davao del Norte; Laoag City, Ilocos Norte; and Mandurriao district in Iloilo City.
Rapid construction activities and growing demand of houses have led to the short fall of traditional building materials. Bricks, sand, and wood are now becoming scarce, if not expensive. The demand of good quality building materials to replace the traditional ones and the need for cost efficient materials for low-cost housing have necessitated researchers to develop variety of new and innovative building materials which are environmentfriendly as well. Conventional hollow concrete masonry unit (CMU) aggregates consists of sand. However, there is a growing interest in substituting alternative aggregate materials, largely as a potential use for recycled materials. There is significant research on many different materials for aggregate substitutes (such as granulated coal ash, blast furnace slag or various solid wastes including fiberglass waste materials, granulated plastics, paper and wood products / wastes, sintered sludge pellets and others). In the Philippines, there are 39 sugar mills in operation, each with an average daily capacity of 4,600 tonnes of sugarcane. Bagasse, the fibrous residue generated when the juice has been extracted from sugarcane, amounts to about 7 million tonnes per annum (PRESA 2005). Large quantities of this waste are left unused or burnt. Bagasse has been used in applications such as boards for construction. However, research is not yet Symposium on Infrastructure Development and the Environment 20067-8 December 2006, SEAMEO-INNOTECH University of the Philippines, Diliman, Quezon City, PHILIPPINESconclusive to recommend its use in structural concrete applications. The use of fibers as additives in concrete is useful in crack control and helps increase the strength of concrete flatwork (Merrit and Ricketts 2002). This paper explores the possibility of utilizing bagasse as an alternative aggregate in hollow CMU.
Rural folks can beat the high prices of housing materials. Out of farm waste and o rdinary soil, one can make durable hallow blocks comparable in strength to commercial ones. The hallow blocks can be made right on the building site fashioned similar to commercial hallow b locks. Although considered strictly non-load bearing, it is very satisfactory for low-cost housing. Its compressive strength ranges from i97 to 386 pou nds per square inch (psi). This simple technology, developed by the Forest Product Research and Industries Development Commission, makes use of a minimum amount of cement to make a stronger hallow block. One bag is enough to make 20 four-inch blocks or 12 six-inch blocks. The first step is to gather agri-wood wastes such as sawdust, coconut trunk particles, sugar cane bagasse or ordinary soil. The latter has to be pulverized and sifted using a 1/4 inch wire mesh. Abaca waste, left after extracting fiber from the stalk, as well as coconut coir dust, the residue from processing coconut husk in coirflex plants, can also be used. Rice hull works too, but additional soil is needed when mixing this with cement. Improvise a hand mold (see illustration) to shape the hallow block. This can be made out of steel or wood of relatively high density such as apitong, guijo or yakal. The mold should have three movable core blocks, and the sides should easily be opened and secured. Place hinges and lockpins as illustrated. Using a cubic foot measuring box, mix together one box of cement and three boxes of agriwaste, or the equivalent proportion. With the materials, form a hill with a crater on top. Pour water slowly, then thoroughly mix them with a shovel un til a paste is formed. The mixture must be neither too dry-nor too wet such that they would stay packed when molded and would not spread out when removed from the mold. Place a flatboard at the bottom of the hand mold, and then fill it with the mixture. Tamp and level off extra paste, then place another flatboard on top. Turn the mold upside down, and tamp and level off as before. After a while, remove the three core’ blocks and then lock the pin to let the sides open. Gently push the molded hallow blocks from the mold, leaving it in place in the flatboard. Place the hallow blocks in a shade for a few hours to dry. After one side has dried, turn the block upside down to dry the other side. Store these blocks standing on their narrow edges. For about 10 days, cure them by occasionally sprinkling water over the blocks. Afterwards, they are ready for use.
Essential equipment • Shovel • Wire mesh • Measuring container/box (preferably the 12′ x 12′ type commonly used in construction work to facilitate proportioning since a bag of cement is about 1 cubic foot volume) Wooden hand mold (If manufacture is to be undertaken on a self-help basis, the use of an easily devised hand mold is recommended. This tool can be made out of steel or wood of medium to high densities preferably apitong, guijo, yakal). Popularity: 5%
Popularity: 5%
New wall materials small hollow blocks the market development analysis (a) small hollow blocks market forming background In our country is a person much less, the energy shortage of countries, per capita covers only the world average per quarter, but a population in constant rapid growth, And another scenario is: every year because of traditional wall clay ShiXinZhuan destroyed tian 66 million mu, swallow 70 million tons of BiaoZhunMei and discharge atmospheric lots of harmful gas, severe environmental pollution, The third kind of scene: a year for power generation, steelmaking industry etc with coal gangue, coal ash emissions plenty of other industrial wastes, these slag stacking area occupied large except, serious damage soil geology. Judging from these three stern question, such as not adopt corresponding measures the survival of mankind will be threatened. For protecting human survival environment and sustainable development. In continuous control population growth premise, proposed innovation to traditional wall materials - - new concrete block basically solve traditional produced, not only ShiXinZhuan and industrial waste residue brought by environmental problems, but also change the traditional building cost is high, wall, varied and new walling blocks varieties and complete equipments, such as: weight-bearing and blame bearing block, decoration &fitment block etc; Using industrial waste residue as raw materials, without sintering, accomplish truly energysaving, section soil, recycling and light weight, high strength and multifunctional building materials of new products. (2) small hollow blocks development prospects
Look from economic Angle: according to the average annual growth of GDP per year on average 7% plan, to social fixed assets investment 4 trillion yuan. In the national economy rapid and healthy development and social progress will continuously for new walling building materials product demand maintains steady growth trend. At present, new building materials market share
in 2000 was 28%, market space share investment prospect; large, Meanwhile, urbanization, middle and small town construction investment scale will have greatly increased, housing industrialization and improvement of people's living standard, farmers housing improvement factors of new wall blocks demand is a very big driving force. Secondly politically see: our country government departments have enacted laws, rules ban traditional ShiXinZhuan in national 170 in big cities in 2005, and used in the national capital cities all ShiXinZhuan, another country to disable the clay for production of new wall brick enterprises adopt relevant policy support (see section the second part) xiangfei enterprise investment and development, to provide a good platform. Proceedings: Tenth International Ferro alloys Congress; 1 – 4 February 2004 INFACON X: ‘Transformation through Technology’ Cape Town, South Africa ISBN: 0-9584663-5-1 Produced by: Document Transformation Technologies
A PRACTICE OF FERROALLOY PRODUCTION IN AN “ENVIRONMENT-FRIENDLY AND RECYCLING” WAY J. Song and G. Kang Shanxi Jiaocheng Yiwang Ferroalloys Works, China. E-mail:
[email protected]
ABSTRACT The ferroalloys industry has generated historically substantial solid waste. The accumulated waste causes serious problems to the environment. However, it is possible to transform the solid waste into an environment-friendly resource to serve the human being. Consequently, the construction of plants that are “environment-friendly” and that accommodate “recycling” has become a target of most ferroalloy producers in the world to ensure sustainable development. This paper introduces the practice of Shanxi Jiaocheng Yiwang Ferroalloys Works, the biggest manganese metal producer in China, in the development of an “environment-friendly and recycling” process. The process includes power generation using coal gangue, waste from local coal mines; hollow bricks manufacture using slag and fly ash from the power station; cement production using slag from ferroalloy smelting; recovery of ferrous and non-ferrous elements in the dust from the furnace gas cleaning system; application of silica dust in construction and so on. The final objective of the plant is to realize zero discharge of solid waste. The profit of the “environment-friendly and recycling” process compensates in part for the operational expense of the environment facilities.
1. INTRODUCTION Great amount of wasted material is generated by industries and has caused tremendous harm to both the environment and ecology. The development of science and technology has made it possible to transform the waste into new resources to benefit human beings. In fact, zero discharge of waste materials in many industries becomes true. The construction of pollution free and recycling plants is the target of sustainable development of ferroalloy industry in all countries of the world. Excessive ferroalloy production has been a problem for many years in the international market. The industry has to reduce its production cost in order to survive in the competitive market. Currently fe rroalloy production capacity in China is more than 7 million t/a. The production capacity of manganese metal is over
300 000 t/a, of which 90% is in the form of manganese flake. The production of electrolytic manganese flake in China relies on the abundant lean ore reserves and local hydroelectricity supply. The production of smelted manganese metal, however, requires high quality manganese ore a nd consistent power supply. More and more ferroalloy producers in the world realize that the ferroalloy industry would not survive unless it consolidates with the upstream industry, like the mining and the power industries. Shanxi Jiaocheng Yiwang Ferroalloy Works is the largest manganese metal producer in China. It consists of a power plant, smelting plants and a hollow block plant. Yiwang Ferroalloys Works has gained extensive experiences in the practices of environment protection and material recycling. The whole production process becomes pollution-free, with the emphasis on recycling. These initiatives include: • Power generation from coal gangue, which supply power for ferroalloy production; • Preheating of manganese ore in a rotary kiln and hot charging; • Ferroalloy production in submerged arc furnaces, as well as in refining furnaces; • Hot metal treatment to recover manganese from the molten slag; • Briquetting and recycling of manganese dust fines; • Lead recovery from manganese ore; • Hollow block manufacturing using fly ash and slag. The application of the novel processes and the recycling process have not only reduced the production cost, but have also saved energy and optimized the utilization of resources. Zero discharge of waste materials has become a reality in the production process.
2. EXPLOITATION OF ENERGY RESOURCES Power supply exerts influences on the ferroalloy market to a considerable extent. With the development of the national economy the Chinese power industry has been growing very rapidly. However, the power supply in many places in China is still tight. The power generation in South China varies with seasons, where hydropower is dominant. The ferroalloy production there has been conditioned in dry season. On the other hand, the economy in East China has become more developed than the economy in West China. The power supply in the West China is relatively abundant. Consequently, a tremendous amount of electric power is transmitted from West to East China. The power supply to many ferroalloy plants in China is restricted in peak hours and in the dry season. The government restricts the installation of the power generators less than 50,000 kW in order to keep the utilization of energy efficient. However, the installations of power stations that utilize waste materials and secondary energy, such as coal gangue power stations, has been encouraged. Several incentives including exemption of income tax and value adding tax are given to this kind of projects. Coal gangue is a waste material in the coal production process, with 200 m illion tons of gangue is discharged from coal mines each year in China. This waste overlays 1,400 hectares of land that causes numerous problems to the environment and the ecology. The government has encouraged the protection of farmland and the utilization of gangue in industry. However, so far only 15% of the accumulated gangue is consumed in industry due to various technical problems.
The area where Yiwang Ferroalloys Works is located is rich in gangue disposal. There are more than 20 coal washing plants in the surrounding area, with 500,000 t of coal gangue that is produced each year. It overlays a great deal of land and causes significant pollution. The gangue is a potential resource of energy with a heat value that ranges from 7,000 to 13,000 kJ/kg. During 2000 a gangue power station of two 6, 000 kW power generators was completed in Yiwang Ferroalloy Works. This power station consumes 200,000 t/a of coal gangue, resulting in a power generation of 100,000 MWh/a. In addition it supplies 40 t/h of steam to local heating system. Generally, the cost of the power generated in the Gangue Power Station compares to one third of the power tariff of the national power network only. The overall power consumption of LC FeMn and manganese metal is around 7,000 kWh/t. The cost of power consumption contributes to nearly 30% of the production cost. The installation of the power station has considerably enhanced the competitive nature of our product in the market. Besides, since the installation of the gangue power station the supply of our products to the market has no longer been dictated by power supply.
3. IMPROVEMENT OF HEAT EFFICIENCY IN THE SMELTING PROCESS 3.1 Potential of heat efficiency improvement in the ferroalloy industry Ferroalloy production is a high energy consuming industry. Ferroalloy smelting not only consumes great amounts of electric energy but also consumes a great deal of chemical energy in the form of coal and coke. The metal, slag and furnace gas generated in the process, leave the furnace carrying a lot of sensible heat energy. It is considerably advantageous to be able to use the latent energy of the materials in the process.
3.2 Preheating of manganese ore Preheating of manganese ore in a rotary kiln is applied in the process of HC FeMn production at YiWang Ferroalloys Works. Manganese ores contain a certain amount of combined moisture and adhesive water. The moisture in manganese ores ranges from 2% to 10% or even higher in the rainy season. At elevated temperatures a great amount of CO 2 and H2O gas is released from manganese ore, descending to the hearth in the smelting process. It is troublesome when an ore with high moisture is charged to the furnace. Not only does it consume a great deal of coke but it also causes slagging and “blowing” problems. Serious “blowing” incidents may damage equipment and cause injury to operators around furnaces, resulting in hot stoppages of the furnaces. The benefits of ore preheating and hot charging are as follows: • Utilizing cheaper energy to heat charge materials in order to reduce the power consumption; • Reducing the risk of furnace “blowing”; • Improving the furnace efficiency. As a result the specific power consumption is reduced by 10%. Consequently, the output of the furnace is increased by 10%.
3.3 Ladle treatment and hot charging The Chinese ferroalloy industry has developed a variety of techniques to improve the heat efficiency of smelting processes, especially in the refining process. The basic principle of the process is based on the
utilization of the latent heats of hot metal and slag, as well as the chemical potentials of the materials. The process consists of two stages. The first stage is the ladle treatment of hot metal and slag. The second stage is hot charging. Yiwang Ferroalloys Works applies this process in LC FeMn and manganese metal smelting. Figure 1. Energy structure system in Yiwang Ferroalloys Works. The process innovation has substantially improved the heat efficiency and the power consumption. The production results indicated that around 30% of the power consumption in the refining process was reduced. Figure 1 shows the integral energy structure of Yiwang Ferroalloys.
4. RESOURCE RECYCLING AND ENVIRONMENT PROTECTION 4.1 Improvement of manganese yield in production China is short in manganese reserve, especially in high grade manganese ore. The average Mn content in the local ore is only 30%. The annual manganese ore production in China is 5 - 6 million t/a. It is substantially less than the local demand for manganese consumption in iron and steel production. China imports more than 2 million tons of manganese ore each year. Yiwang Ferroalloys imports 40,000 t/a of manganese ore. The proportion of manganese ore in ferromanganese production cost is approximately 40%. Manganese has been considered as a valuable commodity in our plant and a great deal of attention is paid to the improvement of manganese yield in the production process. In order to reduce the pollution caused by the gaseous emissions, bag filters have been installed on all furnaces and inside raw material treatment facilities. Each year a significant tonnage of manganese dust fines are recovered via the environment protection system. Table 1 shows the dust recovery of the facilities. Table 1. Distribution of manganese dust recovery. Origin FeMn Furnaces Refining Furnace Rotary Kiln Output t/a 1,300 400 1,500 Manganese emission in smelting plants is detrimental to human health. The exposure to manganese is a risk for the development of neurological illnesses. On the other hand, manganese dust fines is a useful resource of manganese. Table 2 shows the chemistry of these fines. The particle size of the fines is too small to be used directly in the smelting process. Many plants dispose the dust as waste material. We have developed an agglomeration process for the dust fines. Currently, 100% of the fines is recovered and smelted in the process. As a result the overall yield of manganese in the process is enhanced by 3%. This increased recovery of the manganese units helps to compensate for the costs of the dust cleaning system. The installation of bag houses at all the furnaces greatly reduced manganese exposure at Yiwang Ferroalloys. Table 2. Chemistry of manganese dust, %. Chemistry Mn SiO 2 CaO Al2O3 MgO HC FeMn, % ~32 ~10 ~6 ~6 ~2 Refining, % ~18 ~5 ~43 ~3 ~1
The following innovations were introduced in our ferromanganese production process: • Ladle treatment technique where hot metal with a high silicon content and molten slag with a high manganese content is mixed outside of the furnace. As a result the residual content of the manganese in the waste slag is as low as 3 – 5%. • The hoods of the furnaces were modified as such to avoid the loss of dust and to reduce the amount of flue gas. • Metal particle recovery. A lot of scrap metal is generated by the finishing operations on the final ferroalloy products and by the metal separation from the slag. All the scrap is recycled in the process.
4.2 Utilization of waste solid materials The solid waste in Yiwang Ferroalloys consists of slag and fly ash. The particle size of fly ash is extremely small. In windy weather these fines are deposited all over the plant and its surroundings, causing serious pollution to the environment. The composition of fly ash is shown in Table 5. Another problem caused by the solid waste is that the disposal of fly ash and slag cover a significant portion of farmland. It is estimated that there is 14,000 hectares of land in China covered by 700 million tons of fly ash. The disposal of large quantities of waste material creates a lot of problems in the ecology and the environment. The annual disposal of slag and fly ash is shown in Table 3 . Table 3. Annual disposal of solid waste in Yiwang Fer roalloys. Solid waste Fly ash Boiler slag Ferroalloy slag Amount, t/a ~ 50,000 ~ 20,000 ~ 60,000 The government has paid attention to the pollution control of solid waste disposal. Preference has been given to the projects such as recycling of waste materials. Incentives by the government include the exemption of value-added tax, the exemption of income tax in the initial 5 years and the exemption of import tax on the technical facilities.
4.2.1 Utilization of ferroalloy slag The manganese content in the slag is extremely low after the ladle treatment. Though this slag is a waste product for the ferroalloy industry, it is regarded as a resource for the construction material industry. Table 4 shows the chemistry of the waste slag discarded from ferromanganese/manganese metal production. Table 4. Chemistry of manganese slag disposal. Term Mn SiO2 CaO Al2O3 MgO % < 5 ~ 42 ~ 43 ~ 6 ~ 3 Water granulation is used during slag treatment. After the treatment all the granules are transported to the adjacent cement works. The cement production process has proved that slag is very useful as a blending material.
4.2.2 Manufacturing of hollow blocks Though China is an agricultural country, the average area of farmland relative to the population, is lower than that of the rest of the world. With the development of the national economy the area utilized for construction has increased. Among the utilized land, considerable area is used for the manufacturing of bricks. There are 120,000 brick manufacturing plants, occupying 420,000 hectare of land. These plants consume 1,430 million tons of clay each year. The extravagant consumption of resources has brought serious problems in the ecology and the environment. For this reason the central government restricts the use of clay bricks in the 170 major cities and encourages utilization of construction materials, produced from waste.
There is some residual carbon in the fly ash, which is available for the block sintering process. The chemistry of the fly ash is shown in Table 5. Table 5. Chemistry of fly ash. Ignitio n loss SiO 2 Fe2O3 Al2O3 CaO MgO SO3 TiO2 K 2O Na2O % 24.48 38.03 6.48 26.62 0.79 0.59 0.60 1.18 0.67 0.45 The construction of a hollow block manufacturing line started in 2002. Fly ash and slag are used as the raw materials for hollow block production. The flow chart of the process is shown in Figure 2. Figure 2. Flow chart of hollow block manufacture. The advantage of the hollow block lies in its low thermal conductivity of 0.454W/m 2K, that is 60% of the thermal conductivity of the clay bricks only. It is estimated that 30% of heat energy is saved by using fly ash and slag. This is beneficial in r educing the heat loss of houses in winter. Another advantage of the hollow blocks is the lower volume specific weight. The weight of a wall constructed with the hollow blocks may be reduced by 420 kg/m 2 (Weight per construction area). The production capacity of the plant is 60 million blocks per annum. The plant consumes 53,000 t/a of fly ash and 23,000 t/a of slag. The construction of the plant didn’t only substantially reduce the pollution of solid waste, but it has also changed the product structure, which is beneficial to the sustainable development of our company.
4.3 Pb Recovery in smelting The manganese ore from local mines contains a certain amount of lead. Some lead enters the metal during smelting and contaminates the product and occasionally results in the lead content being beyond the specification. Table 6 shows the chemistry of the local manganese ore. A technique of lead recovery was developed at plant scale and a novel device was installed in the smelting furnace. As a result, huge quantities of lead are recovered by smelting each year. Table 6. Composition of lead bearing manganese ore. Chemistry Mn Fe SiO2 CaO P Pb % 32 7 25 8 0.05 0.7 The quality of the product has been improved since the recovery technique was developed. It is also beneficial to resource conservation. Figure 3 shows the material flow c hart of Yiwang Ferroalloys Works. Figure 3. Materials flow chart in Yiwang Ferroalloys.
5. CONCLUSIONS The solid waste generated by the ferroalloy industry is a potential resource for the sustainable development of the national economy. The operation at Yiwang Ferroalloys Works indicated that the recycling of waste material is beneficial to the development of the ferroalloy industry. • The use of the latent heat of molten slag and hot metal improves the energy efficiency of the ferroalloy smelting process. • Manganese emissions in smelting plants is detrimental to human health. The installation of bag houses in furnaces greatly reduces manganese exposure. The recovery of Mn dust is helpful to improve Mn yield of the smelting process. • Utilization of fly ash and slag in the manufacturing of construction materials greatly reduces the disposal •
of solid waste from the power and the ferroalloy industries. • The profit of the “environment-friendly and recycling” process compensates in part for the operating expense of the environment facilities. The recycling of waste m aterials has considerably enhanced the competitive ability of our products in the market.
