The Carbonation Reaction Characteristics And Mechanism Of Red Mud

Red mud is an industrial waste residue from aluminum industry,which could react with CO₂.The carbonation characteristic,kinetics,reaction process and mechanism between red mud and CO₂ using accelerated carbonation were researched in the present work.Judging from evidence achieved,a novel process for comprehensive consumption of red mud was proposed.The detail results were as follows:1.The type of red mud,water to solid ratio,CO₂ partial pressure and carbonation time had a great impact on the red mud carbonation.Compared to the Bayer red mud,Sintering red mud contained a lot of calcareous minerals such as di-calcium silicate minerals,which had higher CO₂ uptakes.With the increasing of water to solid ratio,the CO₂ uptakes first increased then decreased.The maximal CO₂ uptakes were 12.45% at the water to solid ratio of 0.1.The CO₂ partial pressure had a positive effect on the red mud carbonation.With the increasing of CO₂ partial pressure,the CO₂ uptakes increased.However the increasing extent decreased gradually.From 0 to 0.3MPa of CO₂ partial pressure,the increasing extent was significant,while from 0.3MPa to 1MPa of CO₂ partial pressure,the increasing extent was small.As carbonation time goes on,the CO₂ uptakes increased.However the increasing extent decreased gradually.From 0 to 8 hours,the increasing extent was significant,while from 8 to 24 hours,the increasing extent was small.2.The red mud carbonation process was an exothermic process.The rate of heat release was high in the first 30 minutes.After,the heat release rate slowed gradually.Besides,the red mud carbonation process was a diffusion controlled process.Test results were consistent with Jander kinetic model.The correlation coefficient was 0.984.3.The carbonation products of red mud were calcite and amorphous silica gels with highly polymerized three dimension network structure.The distribution condition of carbonation products were described as follows: calcite filled in the pore space within the particles,and the silica gels covered the non-carbonated red mud particles.After carbonation,the surface area increased,pore volume increased,and the pore diameter reduced.The pH values of red mud after carbonation leaching solution were decreased from 12 to 8.7.The red mud carbonation process was mainly a process of calcium leaching and silicate structure restructuring.4.The non-sinter and non-steam imitation rock bricks were produced by extrusion forming and accelerated carbonation,which were accord with the non-sinter tailings bricks standard in building material industry.