Study On Preparation Mechanism Of Low Radioactive Alumina Red Mud Geopolymer

With the rapid development of economy,a large amount of red mud solid waste is discharged from alumina industry every year.These red mud not only occupies land,but also pollutes water,air and soil.At present,the application of red mud in China is mainly in the fields of building materials production and valuable metal recovery.However,the application of red mud in these fields is low in utilization rate and low in economic benefit due to its different quality,high radioactivity and strong alkalinity.In this paper,red mud geopolymer with certain strength was prepared by studying different activation modes,activation effects of different activators and admixture composition of red mud.Then the micro-morphology and polymerization mechanism of red mud geopolymer are analyzed,and the physical properties of ordinary Portland cement are compared,and the performance indexes of red mud geopolymer cement are analyzed,which provides important data support for the industrial application of red mud geopolymer.Specific research contents are as follows:(1)Through the study of thermal activation and mechanical activation of red mud,it is concluded that thermal activation of red mud can improve its activity,the highest activity index is 0.81 after calcination for 3 hours at 700℃,which is 19% higher than that of unactivated red mud.After activation,the bond breakage occurs between Si-O and Al-O in red mud,the degree of polymerization decreases,and the depolymerization reaction occurs more easily.At 700℃,the structure is in a metastable state and the activity is higher.Mechanical activation further improves the activity of red mud.The particle size of red mud is the smallest when grinding for 15 minutes,and the average particle size is 3.64 um.At this time,the activity index is increased to 0.83.(2)By optimizing the alkali activation effect of sodium silicate,quicklime and gypsum and the composition of blast furnace slag powder and metakaolin admixture,red mud ground polymer cement with red mud content of 60%,mineral powder content of 40%,sodium silicate modulus of 1.5 and 20% was prepared,and its flexural strength and compressive strength reached 7.1 MPa and 42.0 MPa.(3)The mineral composition,micro-morphology and radiosolidification effect of red mud geopolymer were analyzed by XRD,scanning electron microscopy and multi-channel gamma-ray spectrometer.The results showed that there were a large number of Aluminosilicate polymer products such as feldspar,calc-alumina feldspar and nepheline in red mud geopolymer,as well as hydration products such as C-(A)S-H.The early stage(3d)of red mud geopolymer showed porous structure and partly returned.There are cotton flocculent substances;with the increase of time(7d),the structure is gradually compact and petal-shaped hydration products are formed locally;at 28 d,the red mud ground polymer reacts sufficiently and becomes a compact whole;the radioactivity of primary red mud is higher than the national radiation standard for building materials;after high temperature activation,the radioactivity of red mud will be increased,but after solidification,the internal irradiation index and external irradiation of red mud ground polymer will be increased.The index decreases significantly,which is in line with the category A construction materials of the country,and its production and marketing will be unrestricted.(4)The technical performance indexes of ordinary Portland cement and red mud geopolymer cement are compared and studied.The results show that the water consumption of standard consistency of red mud geopolymer cement is higher than that of ordinary Portland cement;the setting and hardening of red mud geopolymer cement is faster,the initial setting and final setting meet the requirements of national standards for ordinary Portland cement;and the stability of red mud geopolymer cement meets the requirements.