Study On Material Properties And Environmental Safety Of Red Mud In Sintered Products

The main factors limiting the comprehensive utilization of red mud are alkalinity,heavy metal toxicity and radioactivity.High temperature heat treatment is one of the important methods to effectively control these three factors.In this paper,the raw materials and sintered products of red mud are studied,and the appropriate ratio and sintering temperature are explored to optimize the control of alkalinity,heavy metal toxicity and radioactivity.On the one hand,the effect of sintering temperature on the properties of red mud materials is studied.On the other hand,the environmental safety of alkaline,heavy metal toxicity and radioactivity in the practical application environment is explored.The phase composition,micro morphology and chemical composition of the red mud after high temperature treatment were analyzed in order to analyze the feasibility of red mud application in the sintering products field.The results show that the mineral phase composition of the two red mud is complex,and calcium aluminum feldspar,tricalcium silicate,dicalcium silicate and nepheline will be formed during the heat treatment,which is the main source of strength after sintering.The main loss of burning in the heating process of Bayer and sintering red mud comes from the evaporation of water and the decomposition of calcium carbonate.At the same time,the volatile matter content of both is low at high temperature,and the secondary pollution will not be caused in the heat treatment process.The content of alkaline substance in Bayer red mud is higher,and it has lower melting temperature.The sintering process can produce liquid phase at lower temperature,which is more suitable for sintering products than sintering red mud.The alkaline dissolution experiment of Bayer red mud with deionized water shows that nepheline and albite are the main insoluble alkali in the original red mud,and the soluble alkali is mainly sodium hydroxide hydrate and some sodium hydrate zeolite,and the soluble alkali accounts for 25% of the total alkali of the original red mud.The vitrification reaction at high temperature plays a major role in the stability of alkali in red mud.The soluble alkali content in red mud sintered at 1150 ℃ can be reduced to 0.39%.Compared with the sample without additives,proper amount of additives can improve the alkali curing rate by 45%.The p H value of the extract solution at 180 d can be controlled below 8,which meets the requirements of class I water in the national surface water quality standard,high temperature heat treatment and auxiliary agent The addition of the new technology can realize the utilization of the red mud without alkali removal.The vitrification reaction of red mud at high temperature can not only stabilize alkali substances,but also effectively control the content of heavy metals.The samples are continuously and statically dissolved.ICP detection of the leaching solution shows that the red mud samples with 30% additive at 1150 ℃ have the best solid effect on heavy metals and the lowest content of heavy metals.Due to the diffusion and surface erosion during physical transmission,heavy metals in red mud were released in the early stage of soaking.After 270 days of soaking,the accumulated dissolution content of all elements of red mud sintered products meets the standard of class III water in the national surface water quality standard.Bayer red mud is a kind of cementitious aggregate composed of very small primary particles.High temperature will destroy the agglomeration structure of the original red mud,and cause partial radioactive nuclides to be released.Meanwhile,the high temperature makes the radionuclides concentrate and enrich,which leads to the improvement of the radioactivity level,which leads to the significant improvement of the radioactivity of the pre burned red mud compared with the original red mud.When the temperature continues to rise,the glass produced at high temperature is wrapped and solidified relative to radionuclide,and the radioactivity will not change significantly.After adding additive to make sintered brick,the radioactivity shielding rate of sintered brick can reach 15% compared with that of pre burnt red mud;after adding 5% barium sulfate,the shielding rate of barium element and hematite to the internal exposure index can reach 33.9%,and the shielding rate of external exposure index can reach 21.7%;when adding barium sulfate,barium ferroate will reduce the glass phase and the matrix will reduce the radioactive core The solidification effect of the element is weakened,and the radiation shielding effect is reduced.The 5% barium sulfate addition can maximize the efficiency of the radioactive shielding.The red mud sintered brick radioactivity can meet the class B decoration material standard in the national standards for the limit of radionuclides of building materials.