Dynamic Hydrothermal Synthesis Of Tobermorite From ?-dicalcium Silicate

The soda-lime sintering process is 80%of the composition of red mud,which is the calcium carbonate,20%of the ingredients are calcium carbonate,The red mud in soda-lime sintering process is not well handled in China at present.It can only be piled up in large quantities or produced in low cost industrial cement.This will not only adversely affect the ecological environment,but also reduce the production efficiency of the aluminum oxide factory.This paper mainly studied the use of ?-calcium silicate as calcium raw materials,and the use of alkali and direct method to make use of the high added value of tobermorite powder.The effects of the orthogonal test on the composition and lattice structure,micromorphology,particle size and other physicochemical properties of the synthetic tobermorite powders were studied systematically.The main results of this paper are as follows:?-calcium silicate was prepared from analytical pure reagent CaCO3 and SiO2.Reaction conditions:temperature 1440? heat preservation 2h,add 0.5%B2O3 as stabilizer,cooled to 1050? when take out air cooling,can get high purity of ?-calcium silicate powders.Its microscopic appearance presents irregular blocks with different shapes,and large chunks of small clumps are clustered around the larger blocks,with a small amount of whiskers on the surface.The synthesis of tobermorite powder was made by the hydrothermal synthesis of ?-calcium silicate and sodium silicate solution.XRD semi-quantitative analysis was adopted for the conversion rate of the synthetic tobermorite powder.Through orthogonal test to investigate the reaction temperature,reaction time and solid-liquid ratio on tobermorite conversion rate and degree of the influence of physical properties,it is concluded that the synthetic tobermorite conversion and bulk density is the biggest factor influence temperature,followed by the L/S,the last is the reaction time;The effects of L/S on the oil absorption value of the synthetic products were the most,and the reaction temperature and time were similar to that of the oil absorption value of the synthetic products.Alkaline or synthetic tobermorite powder is flake fiber will overlap and become more spherical particles,its internal fluffy approximate honeycomb,its granularity are mainly distributed in about 50 microns,with the extension of reaction time,the powder particle size increases gradually.Based on the calcium and silica ratio,the particle size of ?-calcium silicate and the mixing speed of the water thermal synthesis of the tobermorite single factor test,The following conclusions are obtained:Alkaline hydrothermal synthetic tobermorite optimum reaction conditions for reaction temperature 180?,reaction time L/S=20h,C/S=0.83,stirring speed of 300 r/min,?-calcium silicate 500 mesh particle size,and in this condition can achieve the complete transformation of tobermorite,no other phase generated in the process of reaction,synthetic tobermorite bulk density of 0.191g/cm3,oil absorption value of 4.33g/g,the average particle size of 54.96?m.In single factor experiment,with the improvement of calcium silicon ratio and stirring speed,the formation of spherical hollow secondary particles,significantly accelerated the formation of tobermorite,tobermorite powder crystal,fine granularity,specific surface area is big,the smaller the powder bulk density and true density,oil absorption value and water absorption.The hydrothermal direct method was used to synthesize the tobermorite powder,and the reaction temperature was greater than the liquid solid ratio of calcium silicate.The best reaction conditions are:Reaction temperature is 200?,reaction time is 16h,liquid-solid ratio 15:1.?-calcium silicate in direct response to generate tobermorite of orthogonal experiment,with the increase of reaction temperature,reaction time,tobermorite conversion rate increase gradually,at the same time will be accompanied by the generation of xonotlite,doping in the generation of tobermorite.Due to the formation of hard silica calcic,the resulting product density becomes smaller and the powder is more fluffy.With the increase of temperature,the accumulation density value shows the decrease trend,and the oil absorption value shows the uptrend.