Study On The Preparation Of Geopolymer From Bayer Red Mud And Mechanism Of Hydration

There is a problem of high energy consumption and high pollution in cement production,and it is urgent to find an alternative green cementitious material.Meanwhile,with the low utilization rate of industrial solid waste in China,it has become an important trend to develop alternative geopolymer materials by using industrial waste residue.As the industrial residue discharged from alumina production,bayer red mud contains more Al2O3 and Si O2,which has potential advantages in preparing in-situ polymer materials.Supported by the National Natural Science Foundation of China(51978353).This paper takes Chiping bayer red mud as the main raw material of production,and the powder is obtained by crushing,drying and grinding.To study the chemical components,mineral composition,selection of initiator,hydration products and excitation mechanism.Selecting bayer red mud as the main raw material,petroleum coke desulfuration residues(PCR),slag,sulphoaluminate cement and sodium silicate as activators,through single factor and multi-factor compound excitation,and according to its mechanical strength as the standard,selecting the best ratio of base polymer materials for preparing bayer process red mud without clinker.(1)Through X-ray diffraction analyzer,SEM,Simultaneous Thermal Analyzer and other methods to analyze the characteristics of bayer red mud powder,the test found that bayer process red mud powder particle size is small,has a large specific surface area,up to the nano level.The content of iron,aluminum and silicon in the raw material is relatively high,and the mineral composition is mainly composed of iron oxide,zeolite and amorphous aluminosilicate,which has the potential advantage of producing geopolymer.(2)The results show that the petroleum coke desulfuration residues can effectively activate bayer red mud.When the ratio of red mud and slag is 55:45,the excitation effect is the best,the compressive strength reaches 9.4 MPa in 28 d,forming the polymerization system of active Bayer red mud base.The hydration products and microscopic characteristics show that the petroleum coke desulfuration residues can supplement calcium and improve the basicity of the system.Meanwhile,the existence of SO42-provides conditions for the formation of ettringite and improves the strength of the system.The formation of ettringite reduces the concentration of aluminum in the system,and then promotes the hydrolysis of aluminosilicate minerals in red mud to produce particles with higher activity,which effectively stimulates the activity of bayer red mud.(3)To study the effect of sulphoaluminate cement or slag on active red mud base polymeric materials.The results show that the mechanical strength of red mud system excited by slag is higher than that of sulphoaluminate cement.The synergistic effect of slag and red mud is more advantageous.A highly active geopolymer system consisting of bayer red mud,petroleum coke desulfuration residues and slag is selected.The hydration products are mainly composed of zeolites,which are formed by the polymerization of silica and alumina monomers in the system.The addition of slag or sulphoaluminate cement increased the content of calcium and silicon oxygen,aluminum oxide in the system,and formed a lot of geopolymer and C-(A)-S-H gel,which formed a more dense structure and improved the strength of the system.(4)In order to further improve the performance of geopolymer system,sodium silicate was used as the activator.Through orthogonal test: Geopolymer materials with compressive strength of 33.5 MPa can be obtained in activated bayer red mud base polymerization system when the content of mineral powder is 25%,the modulus of sodium silicate is 1.8 and the content of Na2 O is 8%.The addition of sodium silicate can further improve the Si/Al ratio and basicity of the system.The dissolution of aluminosilicate in red mud and mineral powder is promoted by high alkaline environment,and Si(OH)4 and [Al(OH)4]-monomers are formed.The polymerization reaction is repeated to form geopolymer matrix.The results of SEM observation show that the RM-PCR system and RM-PCR-slag system have interlaced rodlike and amorphous gel interlacing,and the RM-PCR-slag system activator by sodium silicate has a denser geopolymer matrix structure,and the strength of the product is relatively higher.This research work provide a new way for the comprehensive utilization of bayer red mud,and have some reference value for the preparation of geopolymer materials from solid waste.