Preparation Of High Strength And Self-Supporting Zeolites Synthesized From Alkali-Activated Cementitious Materials

With the rapid development of various zeolite materials in water treatment,soil improvement,industrial refining and other fields,people’s requirements for zeolite performance gradually improved,including zeolite itself unique adsorption,filtration,catalytic performance and mechanical properties,durability of zeolite products.There are some opposites to these performance,which means one performance improves while the other gets worse.Therefore,how to balance the functionality and practicality of zeolite,and fabricate zeolite products with high strength,high stability and good adsorption capacity is particularly important.In this paper,slag was introduced into metakaolin.Self-supporting zeolite A,(Na)and zeolite P,(Na)were insitu prepared by hydrothermal method using slag/metakaolin-based alkali-activated material as precursors.We studied the influence of different mix proportion and hydrothermal synthesis conditions.The effects of curing regime and mix proportion of raw material on precursors strength and zeolite conversion were investigated.Too high curing temperature will lead to crack and insufficient curing time will cause the residual metakaolin particles in the sample,resulting in the phenomenon of water collapse of the sample.The optimal curing regime was 60 ℃ curing for 1 d followed by standard curing for 2 d.The suitable mix proportion of precursors for fabrication of zeolites were as follows: water cement ratio 0.7,sodium silicate modulus 1.1,silicon aluminum ratio 1.5.In the process of metakaolin precursors converting zeolite,it was found that the strength loss was serious and the interface stratification occurred.The method of introducing slag was proposed to make use of the alkali-activated reaction activity of slag and the function of its hydration product,C-A-S-H gel,improve the strength of samples and weaken the stratification phenomenon.The slag/metakaolin-based precursor was prepared to explore the influence of hydrothermal synthesis conditions,while the metakaolin-based precursor was set as a control.The results show that the hydrothermal temperature affects the type of zeolite crystal and the percent conversion of zeolite,the hydrothermal time affects the completion of the hydrothermal reaction,and the concentration of alkali affects the content of sodalite and the type of zeolites.The suitable hydrothermal conditions for slag/metakaolin-based precursors to fabricate zeolites are 110 ℃,20 h,2mol/L NaOH.The effects and mechanism of slag on the conversion of zeolite from slag/metakaolin-based precursor were analyzed.The addition of slag reduces the conditions for hydrothermal reaction,improves the strength of samples,and weakens the stratification phenomenon.The influence of slag content on zeolite sample strength,phase and content,pore structure and erosion resistance was investigated.The experimental results show that the strength and zeolite percent conversion of samples are significantly improved by adding 10% slag.When slag content exceeds 10%,with the increase of slag content,the content of amorphous phase and the proportion of Na P zeolite in zeolite increases,while the content of sodalite,the percent conversion of zeolite and the strength of samples decreases.For pore structures,with the increase of slag content,the BET surface area and pore volume of samples decreased,while the concentrated pore size and average pore size increased.The erosion resistance of the sample was improved by adding proper amount of slag.Considering the mechanical properties,erosion resistance,pore structure,percent conversion,the suitable slag content is 20%.