Study On Preparation And Properties Of Red Mud-Based Non-Sintered Ceramsite

With the acceleration of industrialization construction in China,large quantities of industrial wastes are generated.Solid industrial waste such as red mud,which contains heavy metals and high alkalinity,is inadequately recycled and improperly disposed of,resulting in serious environmental pollution and becoming a major factor hindering the sustainable development of green and low-carbon industry.In this study,following the principles of"reduction,harmless and resource recovery"of solid waste disposal,using bayer red mud,blast furnace slag and silica fume as raw materials,the red mud-based non-sintered ceramsite with excellent properties were prepared,and their properties were systematically studied.First of all,the preparation process of non-sintered ceramsite was studied,and various technical processes of granulation and pelletizing were determined through practical operation.In order to maximize the utilization of waste,the amount of red mud was set at 50%.The final matrix raw material ratio is red mud:slag:silica fume 5:4:1,cement content 10%,Na₂SiO₃ aqueous solution 2%.Through single factor and multi-level analysis,the mixing mode and dosage range of different activators were selected,and NaOH alone was selected as the activator,with the addition of 7%.Under the optimum mix ratio,after 28 days of natural curing,the compressive strength of non-sintered ceramsite is 4.14 MPa,the water absorption in 1 hour is 12.12%,and the bulk density is 870.15 kg/m³.Secondly,three variables,namely,constant temperature steam curing duration,steam curing temperature,and pre-curing duration,were set to explore the impact of steam curing on non-sintered ceramsite.The results showed that the best results were obtained at 3 h of pre-curing,80℃of constant temperature curing and 9 h of pre-curing.Comparing the performance of ceramsite under natural curing and steam curing,steam curing ceramsite exhibits extremely high early strength,with a strength of 3.94 MPa after 1 day,which is 95.17%of the strength after 28 days of natural curing.However,there is a loss in subsequent strength,and the water absorption is always 20%,which cannot meet the requirements.However,the late performance of ceramsite under natural conservation has developed well.In order to explore the influence and mechanism of different curing systems on the mineral phase composition and micro morphology of non-sintered ceramsite,XRD and SEM analysis were conducted on non-sintered ceramsite at different ages under two curing systems.The XRD spectrum shows that the curing method basically does not change the type of hydration products,and the main hydration products are ettringite,C-H-S and C-A-S-H gel;Observing SEM images,it was found that steam curing destroyed the continuity and uniformity of initial hydration products,resulting in multiple pores and cracks that affected subsequent performance development;The natural maintenance hydration products grow and develop steadily,interlace and overlap with each other,and connect the remaining adhesive particles to form a stable grid system.Finally,in order to carry out environmental and economic feasibility analysis of non-sintered ceramsite,the analysis and determination show that the leaching toxicity of Cr,Mn,Ni,Cu,Zn and As in non-sintered ceramsite is far lower than the standard limit,and there is no toxic pollution risk to the environment,belonging to the environmentally friendly ceramsite.The total cost of producing 1m³ ceramsite is about 160～180 yuan,which is low cost.The red clay based non-sintered ceramsite has remarkable economic,social and environmental benefits,conforms to the concept of green and sustainable development,and has a bright future.