Adsorption Of Mgnial Layered Double Hydroxides For Chloride Ion In Cement-based Material

The problem of durability of reinforced concrete under chloride ion erosion has been widely concerned.In this study,a new type of hydrotalcite layered compound was prepared and studied to adsorb chloride ions,and was applied to cement based materials to improve its resistance to chloride ion erosion.In this study,hydrothermal method was used to prepare club-shaped MgNiAl-LDHs and MgAl-LDHs,and the structural morphology of MgNiAl-LDHs and MgAl-LDHs,the adsorption performance of MgNiAl-LDHs,MgAl-LDHs and roasted products MgNiAl-LDOs and MgAl-LDOs on chloride ions in aqueous solution were compared.The effects of MgNiAl-LDOs on adsorption of chloride ions under different pH values 、 calcination temperature、 adsorbent dosage、 adsorption temperature and concentration of chloride ion solution were discussed.The ability of MgNiAl-LDOs to solidify chloride ions in cement based materials was studied by chloride ion exosmosis method,and the performance of MgNiAl-LDOs to solidify chloride ions in cement based materials was analyzed.Experimental results show that:(1)Rod-shaped MgNiAl-LDHs and MgAl-LDHs can be prepared by hydrothermal method.(2)After the roasting of MgNiAl-LDHs,the interlayer water and anions were lost,and the layered structure was destroyed.After the reabsorption of anions in the aqueous solution,the layered structure could be restored after structural restructuring,but the structural integrity after reconstruction decreased.(3)After 500 ℃ calcination MgNiAl-LDHs in dosing quantity is 2.0 g/L,the pH value of 8,adsorption temperature 50 ℃ under the condition of optimal adsorption performance and the equilibrium adsorption from the biggest to 130.02 mg/g.(4)Adsorption kinetic model shows that MgNiAl-LDOs adsorption process of chloride ions conforms to the quasi-second-order kinetic equation;The adsorption isotherm model showed that the adsorption process of chloride ions was consistent with the Langmuir adsorption isotherm model,and the theoretical maximum adsorption capacity was 130.79mg/g.(5)Under the conditions of 1mol/L chloride ion concentration and 28 d chloride ions erosion,the amount of solidified chloride ion in the concrete mixed with 40% cement replaced by MgNiAl-LDOs was 54.1mg/g.The amount of chloride ion solidified in cement based materials of MgNiAl-LDOs is positively correlated with the erosion time,concentration of chloride ion and the substitution amount of MgNiAl-LDOs.(6)MgNiAl-LDOs mixed into cement based materials reconstructs the layered structure of hydrotalc and forms an irregular shape.Based on this research,the preparation of more and better new hydrotalcite compounds was promoted to improve the chloride penetration resistance of concrete.