Research On The Preparation Process And Mechanism Of Anti-hygroscopic Calcined Dolomite

The problem of moisture absorption for calcined dolomite during the process of production and storage have affected the development of primary magnesium industry seriously.Declination of calcined dolomite’s activity will affect metal magnesium productivity.Hence,research how to effectively handle the calcined white make it in the process of kiln,fine grinding,press,storage and transportation the activity can be remained for a long time,is one of the most priority mission we should resolved and also is a very important and arduous task for our metallurgical workers.This article first preparation of qualified calcined dolomite,then calcined dolomite as raw material,silane coupling agent KH560 as modifier,the physical and chemical method is adopted to disposing calcined dolomite.Through orthogonal experiment to determine optimum process parameters of preparation anti-hygroscopic calcined dolomite,adopting physical adsorption instrument,the contact Angle tester,scanning electron microscope,infrared spectrum analyzer,X-ray photoelectron spectroscopy analysis instrument to analysis calcined dolomite of the before and after modification were characterized,and studying the moisture absorption and moisture absorption mechanism of the calcined dolomite,the results are as follows:（1）The experiment of preparation of calcined dolomite within 0～360min hygroscopic rate from 0.59%to 0.59%,increased by 1.16%,growth velocity 0.322%· min^-1;In 360～1920 min growth rate slows,moisture absorption rate from 1.75%to 2.87%,Increased by 1.120%,the growth velocity 0.072%.min^-1;1920 min later,the change in the moisture absorption rate gradually leveled off.（2）Calcined dolomite hygroscopic rate change with time,when calcined dolomite exposed to weather,at first due to Moisture absorption reaction of reactant concentration is higher,the reaction is rapid,moisture absorption rate rising sharply.As the reaction goes on,calcined dolomite surface is more and more thick carbonate,the hydration products package,to some extent,cut off the hydration,carbonate process,at the same time H2O and CO2 molecular diffusion through the reaction layer need higher activation energy,so the moisture absorption rate slows,leveled off after hygroscopic saturated.（3）Through the orthogonal experiment analysis:the most significant effect on the modification performance factor is the amount of modifier are added,followed by the modification temperature,finally,the modification time.（4）The modification effects of calcined dolomite with modifier（KH560）adding amount,modification temperature,modification time varies,with the increase of adding amount,modification temperature rise,the extension of modification time,the contact Angle is is growing.When the contact Angle increases to 101.21 ℃,and continue to change the three factors,the change of contact Angle is stable.Preparation anti-hygroscopic calcined dolomite the best process conditions for the modifier（KH560）amount of 0.03mL/g-calcined dolomite,modification temperature of 55 ℃,the time of 80 min.（5）After modification,the specific surface area of calcined dolomite from 23.1421 m2/g to 6.5343m2/g,decreased 79.67%;the total pore volume of calcined dolomite from 0.115112cm3/g to 0.011621cm3/g,decreased 89.90%;contact Angle of calcined dolomite from 37.04° to 100.05°,increased 62.98%and moisture absorption rate of calcined dolomite from 2.01%to 0.35%,decreased 82.5%.（6）The mechanism of prepare anti-hygroscopic calcined dolomite is that the surface of the calcined dolomite-OH was replaced by KH560 hydrophobic groups through condensation reaction.Then create a waterproof membrane on the surface of calcined dolomite,and yield prevent moisture absorption effect.（7）The reaction of prepare anti-hygroscopic calcined dolomite was done in two steps:（1）The alkoxyl radical of KH560 in acid condition will be hydrolyzed into oxhydryl;（2）The KH560 hydrolyzed into oxhydryl condensation reaction with oxhydry on the surface of the calcined dolomite,and the hydrophilic groups on the surface of the calcined dolomite is replaced by the hydrophobic groups in KH560,form modified calcined dolomite.