Preparation Of Green Red Mud Based Sintering-free Ceramsites And Its Performance Research

With the acceleration of our country industrialization process and the improvement of people's quality of life,along with the generation of large amounts of industrial waste,the low efficiency resource utilization and improper safe disposal of industrial waste have caused serious environment pollution,especially those containing heavy metals and highly alkaline,such as red mud.At present,red mud mainly adopts the open-air storage method in China,which causes serious pollution to the ecological environment such as water,air,and soil etc.,even threatens the health of the people.Using red mud to prepare building materials is an effective way to realize the resource utilization of red mud.Among them,ceramsites prepared by using red mud has a broad market and application potential.Therefore,this article proposed a new preparation concept of green red mud-based ceramsites,which using red mud and sulphoaluminate cement as raw materials through sintering-free process.This process can not only reduce energy consumption,but also realize large-scale resource utilization of red mud.First,based on the study of our research team,four industrial solid wastes,including red mud,desulfurized gypsum,aluminum ash,and calcium carbide slag,were used to prepare solid waste-based sulfoaluminate cement with the performance of fast hardening,early strength and high strength.Then,using solid waste-based sulfoaluminate cement as the cementing agent,recombining red mud,and using a disc granulator to realize the preparation of red mud-based sintering-free ceramsites.Its physical properties,hydrated minerals,microstructure and heavy metal leaching characteristics have been studied.Finally,red mud-based sintering-free ceramsites is used as coarse aggregate to prepare dry-pressed pavement bricks,and its strength,water absorption,dry density,frost resistance and preparation cost were analyzed.This study provides a new idea for the engineering application of red mud-based sintering-free ceramsites,and form a total solid waste integration technology from solid waste to red mud-based sintering-free ceramsites to dry-pressed bricks route.Research indicates:(1)The main mineral phases of solid waste-based sulfoaluminate cement clinker prepared from four industrial solid wastes of red mud,aluminum ash,desulfurized gypsum and calcium carbide slag are C4A3S,AH3 and C2S,which is similar to the mineral composition of ordinary sulfoaluminate cement.It has the excellent properties of early strength,high strength and fast hardening.(2)The best preparation process parameters of the red mud-based green sintering-free ceramsites:the content of solid waste-based sulfoaluminate cement is 30%,the inclination angle of pelletizing disc is 45°,and the critical speed of pelletizing disc is 33 rpm.The pelletizing rate of the red mud-based sintering-free ceramsites prepared under the optimal process conditions is approximately 90%;the particle size is mainly distributed between 5-20 mm;the bulk density is 900-1000 kg/m3,which can meet the requirement of 1000 density grade in GB 174311-2010;apparent density between 1890-2014 kg/m3,lower than the apparent density of ordinary stone 2300-2600 kg/m3;the water absorption for 1 h is approximately 11.46%,slightly higher than GB 174311-2010,which the 1 h water absorption rate of artificial lightweight aggregates was less than 10%;the 28 d cylinder compressive strength of red mud-based green sintering-free ceramsites is 7.98 MPa,which exceed the standard that the cylinder compressive strength of the artificial high-strength lightweight coarse aggregate need to reach 6.5 MPa.(3)The main hydration products of the red mud-based sintering-free ceramsite are ettringite(AFt),dicalcium silicate(C2S)and alumina gel(AH3).The formation of ettringite is the fundamental reason for the high strength performance of the red mud-based green sintering-free ceramsites.From the microscopic morphology,AFt with higher crystallinity is in the shape of rods or columns,and the AH3 is distributed in the shape of pompoms.The ettringite overlaps each other to form a framework structure,red mud particles that are not involved in the hydration reaction and aluminum gel are cementitious and filled in the framework structure to form a microstructure of the red mud-based green sintering-free ceramsites hardened body.This is structural reasons for the red mud-based green sintering-free ceramsites to obtain high-strength performance.The leaching concentration of heavy metals from red mud-based green sintering-free ceramsites were far lower than the corresponding concentration limit of heavy metal leaching in GB/T 5085.3-2007,and the ettringite produced by the hydration of solid waste-based sulfoaluminate cement has a good solidification and stabilization effect on Cr.(4)The preparation of dry-pressed pavement bricks were performed by using all industrial solid waste.When the content of red mud-based green sintering-free ceramsites is 30%,the desulfurization gypsum is 5%,the water consumption is 12%,the brick press equipment load is 14 MPa,and the 28 d compressive strength of the prepared dry pressed pavement brick is 47.63 MPa,it can meet the strength standard of Cc40 in GB 28635-2012.The water absorption rate for 24 h is 5.87%.After 25 freeze-thaw cycles,the compressive strength loss rate of dry pressed brick is 19.08%,and the mass loss rate is 4.78%,which meets the requirements of GB 28635-2012 frost resistance performance index requirements.The total cost of preparing dry-pressed pavement bricks is about 16.1-20.3 yuan/m2,which is lower than the cost of about 24 yuan/m2 for the industrial production of ordinary dry-pressed pavement bricks.At the same time,about 788 kg refuse incineration residue and 525 kg red mud-based green sintering-free ceramsites can be used to prepare 1 m3 of dry-pressed pavement bricks.Therefore,using red mud-based green sintering-free ceramsites and refuse incineration residue to prepare dry-pressed pavement bricks has the advantages of low cost,high performance,good environmental benefits,and great application potential.