| Based on the background that chloride ions induced the erosion of steel bar resulting in the lack of durability of the reinforced concrete structure,a series of related studies were conducted to improve the corrosion resistance of concrete structures by adding materials with chloride ion adsorption properties in this study.Traditional hydrothermal method and alkali fusion-assisted hydrothermal method were evaluated for the preparation of zeolites from waste basalt powder.The effects of acid treatment,alkali/basalt ratio,calcination temperature and crystallization temperature on the zeolite formation were studied.The synthesized products were characterized by XRF,XRD,SEM,FTIR and BET in order to analyze the synthesis mechanism.Then the synthesized zeolite was used to absorb chlorine ions in aqueous solution.The effects of adsorption temperature,pH value,initial concentration,contact time,and adsorbent dosage on the adsorption process,and the adsorption kinetics and isotherms and the adsorption mechanism were investigated.Last,dispersed the synthesized zeolite into the cement slurry to explore its chloride ions adsorption capacity and the effects of different mixing proportions and aging time were investigated.The experiments result shows that:1.Zeolite X with high crystallinity and purity was synthesized from basalt powder by alkali fusion-assisted hydrothermal method,with a specific surface area of 486.46m2·g-1.Acid treatment,alkali/basalt ratio,calcination temperature and crystallization temperature played a significant role in the conversion from basalt to zeolites.The acid treatment enhanced the yield and quality of synthetic zeolites;calcination temperature?550–750°C?affected the degree of crystallinity,but not the synthesized zeolite types.NaOH/basalt ratio and crystallization temperature affected not only the degree of zeolite crystallinity but also the synthesized zeolite types.The optimum synthesis condition of zeolite X was acid treatment of 5wt%HCl solution,NaOH/basalt ratio of 1:1,calcination temperature of 650°C and crystallization temperature of120°C.2.The synthesized basalt based zeolite showed a good performance in adsorption of chloride ions with the experimental uptake capacity of11.29 mg·g-1.Langmuir model fitted the experimental data well and the calculated maximum adsorption capacity was 14.835mg·g-1.The adsorption kinetics was well described by Pseudo-first-order model.The optimum condition for removal of chloride was:pH value of 7,temperature of 35?,adsorbent dosage of 16.7 g·L-1,time of 3 h,initial concentration of 354.5 mg·L-1.3.The synthesized zeolite could effectively immobilize the chloride ions in cement paste.The increase of zeolite/cement ratio could significantly increase the amount of immobilized chloride ions.In a certain range of zeolite/cement ratio,the higher the ratio,the better adsorption capacity.However,beyond the value,the adsorption capacity decreased as the quantity of the immobilized chloride ions increased.Aging time affected the adsorption process dramatically.The immobilization of chloride ions progressed rapidly in the early stage,and slowed down later until the adsorption dynamic stability was achieved. |
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