In densely populated industrial countries, regulations to protect the environment and the potential risk to ground water quality have led in recent years to a drastic reduction in the amount of available landfill space and a huge rise in the cost of land disposal of waste. Prevention and recycling o...
In densely populated industrial countries, regulations to protect the environment and the potential risk to ground water quality have led in recent years to a drastic reduction in the amount of available landfill space and a huge rise in the cost of land disposal of waste. Prevention and recycling of wastes is being encouraged by political authorities. Processing of waste paper generates fiber residues and sorting wastes (de-inking and waste water-treatment sludges). Until now, this paper residue was disposed of mainly by landfilling, discharge for agricultural purposes, composting, and utilization in the brick-making industry. In recent years, the paper industry has also been trying to dispose of the paper residue by thermal means in its own, very expensive, incinerators. Here, the biggest problem is disposal of the resulting ash, which often makes up 25% of the volume of the paper residue. The Wopfing Cement Works in Austria developed a new technology for 50,000 tons/year fiber residue processing in a cement kiln. This technology utilizes the calorific value of the dried paper fibers and the fiber residue ash, which contains limestone, and clay is used as raw material for the production of cement clinker.
In this study, an original method of utilization is proposed: the production of a very reactive pozzolan by a controlled-calcination process. The composition of the mineral fraction of the paper sludge is suitable for such production; it is composed mainly of highly pure kaolin and natural limestone. The temperature of calcination is chosen in the range of 700°C to 800°C to destroy the combustible cellulose fibers present in the waste and prevent the decarbonation of limestone. The pozzolanic activity of the calcined sludge is studied through the calcium hydroxide consumption in calcium hydroxide-sludge mixtures and compared to that of commercial metakaolin issued from the calcination of natural clays. The results show that it is possible to transform paper sludge to a highly reactive metakaolin that can be used in the concrete industry.
The results are as follows:
1) Highly reactive metakaolin can be produced from paper sludge by calcining this waste at 700°C or 750°C for 2 or 5 hours.
2) Superficial defects occur during calcination and increase the reactivity of the burnt product, especially at early ages.
3) The calcination has to be controlled to entirely destroy the organics present in the sludge and prevent the decarbonation of calcite. Under such conditions, calcite reacts with lime and metakaolin to produce monocar-boaluminate and C-S-H.
4) The proposed process seems to provide an application for paper sludges, avoiding landfilling that has become a very expensive operation in Korea.
5) Pilot scale and industrial tests of calcination are being performed, and the production of low cost metakaolin can be expected within a few years.
6) An investigation also has been undertaken to examine the influence of variations in the composition of sludges on their pozzolanic activity. The effect of the material in cement based systems will be presented in a future paper.
7) The paper industry that uses 100% recycled paper as a primary material generates waste paper sludge which, by its nature, constitutes an inestimable source of kaolin, with the subsequent environmental benefits. Controlled calcination of waste (500-800℃) supplies an alternative approach to obtain recycled metakaolin, a highly pozzolanic material for the manufacture of commercial cements.
8) The products obtained in this way present a high pozzolanic behavior, comparable to a natural metakaolin, which is very close to silica fume; temperatures of between 650-700℃ and 2 hours of retention time in the furnace are established as the most efficient laboratory conditions to obtain these pozzolans.
9) It is likewise worth highlighting their high pozzolanic compatibility with fly ash. The cement pastes prepared with 10% sludge calcined at 700℃/2h generate LDH compounds and CSH gels as stable products.
10) The incorporation of a second pozzolan (fly ash) into the blended cement system does not modify the reaction kinetics, for which reason it is worth highlighting the compatibility between both pozzolans.
11) In the manufacture of binary cements, and in a similar way to the regulations for silica fume, it is recommended that the percentage should be limited to around 10% clinker for paper sludge calcined at 700℃.
12) A compromise has to be reached between the positive effect on the mechanical properties and the determining factors associated with the reduction in setting times, loss of workability and excessive total drying shrinkage.
13) In the manufacture of ternary cements that contain sludge calcined at 700℃ and fly ash, the percentage of clinker replaced by the addition of these minerals should not exceed 21%, in order to guarantee the maximum pozzolanic effect (synergy between the two industrial by-products), while ensuring that the workability of the mixture is not adversely affected.
14) The results of this research have clearly shown the scientific and technical viability of including thermally activated waste.
In densely populated industrial countries, regulations to protect the environment and the potential risk to ground water quality have led in recent years to a drastic reduction in the amount of available landfill space and a huge rise in the cost of land disposal of waste. Prevention and recycling of wastes is being encouraged by political authorities. Processing of waste paper generates fiber residues and sorting wastes (de-inking and waste water-treatment sludges). Until now, this paper residue was disposed of mainly by landfilling, discharge for agricultural purposes, composting, and utilization in the brick-making industry. In recent years, the paper industry has also been trying to dispose of the paper residue by thermal means in its own, very expensive, incinerators. Here, the biggest problem is disposal of the resulting ash, which often makes up 25% of the volume of the paper residue. The Wopfing Cement Works in Austria developed a new technology for 50,000 tons/year fiber residue processing in a cement kiln. This technology utilizes the calorific value of the dried paper fibers and the fiber residue ash, which contains limestone, and clay is used as raw material for the production of cement clinker.
In this study, an original method of utilization is proposed: the production of a very reactive pozzolan by a controlled-calcination process. The composition of the mineral fraction of the paper sludge is suitable for such production; it is composed mainly of highly pure kaolin and natural limestone. The temperature of calcination is chosen in the range of 700°C to 800°C to destroy the combustible cellulose fibers present in the waste and prevent the decarbonation of limestone. The pozzolanic activity of the calcined sludge is studied through the calcium hydroxide consumption in calcium hydroxide-sludge mixtures and compared to that of commercial metakaolin issued from the calcination of natural clays. The results show that it is possible to transform paper sludge to a highly reactive metakaolin that can be used in the concrete industry.
The results are as follows:
1) Highly reactive metakaolin can be produced from paper sludge by calcining this waste at 700°C or 750°C for 2 or 5 hours.
2) Superficial defects occur during calcination and increase the reactivity of the burnt product, especially at early ages.
3) The calcination has to be controlled to entirely destroy the organics present in the sludge and prevent the decarbonation of calcite. Under such conditions, calcite reacts with lime and metakaolin to produce monocar-boaluminate and C-S-H.
4) The proposed process seems to provide an application for paper sludges, avoiding landfilling that has become a very expensive operation in Korea.
5) Pilot scale and industrial tests of calcination are being performed, and the production of low cost metakaolin can be expected within a few years.
6) An investigation also has been undertaken to examine the influence of variations in the composition of sludges on their pozzolanic activity. The effect of the material in cement based systems will be presented in a future paper.
7) The paper industry that uses 100% recycled paper as a primary material generates waste paper sludge which, by its nature, constitutes an inestimable source of kaolin, with the subsequent environmental benefits. Controlled calcination of waste (500-800℃) supplies an alternative approach to obtain recycled metakaolin, a highly pozzolanic material for the manufacture of commercial cements.
8) The products obtained in this way present a high pozzolanic behavior, comparable to a natural metakaolin, which is very close to silica fume; temperatures of between 650-700℃ and 2 hours of retention time in the furnace are established as the most efficient laboratory conditions to obtain these pozzolans.
9) It is likewise worth highlighting their high pozzolanic compatibility with fly ash. The cement pastes prepared with 10% sludge calcined at 700℃/2h generate LDH compounds and CSH gels as stable products.
10) The incorporation of a second pozzolan (fly ash) into the blended cement system does not modify the reaction kinetics, for which reason it is worth highlighting the compatibility between both pozzolans.
11) In the manufacture of binary cements, and in a similar way to the regulations for silica fume, it is recommended that the percentage should be limited to around 10% clinker for paper sludge calcined at 700℃.
12) A compromise has to be reached between the positive effect on the mechanical properties and the determining factors associated with the reduction in setting times, loss of workability and excessive total drying shrinkage.
13) In the manufacture of ternary cements that contain sludge calcined at 700℃ and fly ash, the percentage of clinker replaced by the addition of these minerals should not exceed 21%, in order to guarantee the maximum pozzolanic effect (synergy between the two industrial by-products), while ensuring that the workability of the mixture is not adversely affected.
14) The results of this research have clearly shown the scientific and technical viability of including thermally activated waste.
주제어
#Recycling Utilization Paper waste water sludge Calcined paper sludge Calcination conditions Pozzolanic activity Mortars
※ AI-Helper는 부적절한 답변을 할 수 있습니다.