| Fly ash is the industrial solid waste produced by coal-fired thermal power plants.Because fly ash contains a large amount of oxides such as Si O2,Al2O3,Ca O and Fe2O3,it can be used as a raw material for ceramic production.Ceramic permeable bricks,as an emerging permeable material used in sponge cities,have great potential market demand.In this paper,fly ash based permeable ceramic bricks were prepared by pellet method and adding pore-former agent method,respectively,and the basic performance of prepared fly ash based permeable ceramic bricks is studied The main research contents are as follows:1.Preparation and properties of fly ash based ceramic permeable bricks by pellet methodThe fly ash and gold tailings were used as raw materials to prepare permeable ceramic bricks by pellet method and focused on its strength and water permeability.Under the optimized conditions（pellet size of 2-4 mm,water content of pellet of 16 wt%,molding pressure of 1 MPa,sintering temperature of 1200 oC）,permeable bricks with compressive strength of 48.6 MPa,bending strength of 6.1 MPa,permeability of 2.83×10-2 cm/s,and apparent porosity of 21.3%was prepared.Which could meet the requirements of class A permeable brick in Chinese national standard GB/T 25993-2010.The main crystalline phase of fly ash based ceramic permeable brick is anorthite,and the dense structure of anorthite interspersed with amorphous substance contributed the excellent mechanical strength of permeable bricks.When the sintering temperature increased from 1120 oC to 1200 oC,the apparent porosity was decreased,sintering densification and linear shrinkage of pellets were increased,leading to the increased average diameter of pores between pellets,reached 123.9μm,which ensures the good permeability of the permeable bricks.The porous medium model of permeable bricks at high sintering temperature was established by Comsol software.The calculation results show that even if the apparent porosity of the permeable bricks decreased,the permeability still has the possibility of increasing when the average pore size increased.The calculation results well verified the above conclusions.2.Preparation and properties of fly ash based ceramic permeable bricks by adding pore-former agent methodFly ash and gold tailings were mixed with water to get wet mixture,and then pore-forming agent was added to prepare permeable brick.The effects of the type,adding ratios and adding ways of pore-forming agent were studied.The results showed that dry sludge contains humus,inorganic components,with a certain degree of bonding,it could be well combined with sludge.Optimization showed that the optimal dosage of sludge was 20 wt%.The proposed way that adding pore-making agent in the wrapping method can make the pore-making agent fully contacted with each other and form larger connected pores in the permeable bricks,the permeability could be improved with mechanical strength could be guaranteed at the same time.Under the optimized conditions that the sintering temperature was 1175 oC and the sintering time was 3 h,the permeable bricks could meet the requirements of class A permeable brick.The mian phase of permeable brick was still anorthite.Compared with the pellet method,the pore-forming agent method can utilize more solid wastes,and the equipment cost is lower.The addition of sludge reduces the sintering temperature,but the sintering time is longer.3.Study on leaching toxicity and chemical stability of fly ash based permeable ceramic bricksThe contents of heavy metals Cr and Cu in fly ash,As in gold tailings and As,Ni and Cu in sludge exceed the requirements of heavy metal content in Class III soil standards in GB 15618-1995.Direct stacking will cause heavy metal pollution to soil.The leaching concentration of heavy metals in the fly ash based ceramic permeable bricks can meet the requirements of Class III surface water in GB 3838-2002,and both of them show a low leaching rate of heavy metals（<5%）.The fly ash based permeable ceramic bricks prepared by the two methods show excellent alkali corrosion resistance（Quality retention>95%）and relatively weak acid corrosion resistance（Quality retention>78%）. |
