| Geopolymer is a kind of silicate inorganic polymer with cage structure,which has been paid attention to in the field of material and environment.The main structure of geopolymer is porous structure.In this paper,geopolymer was used as the adsorbent of heavy metal,and the adsorption of heavy metal on the surface of geopolymer was cured.Metakaolin is a product of kaolin dehydration at high temperature.The structure of geopolymer prepared by metakaolin is unified.Using metakaolin as raw material,sodium silicate,sodium hydroxide and sodium aluminate as activator,the raw materials react with the activator,then the formation of geopolymer.The concentration of activator,the ratio of activator,activation time,activation temperature and solid-liquid ratio were optimized.The excellent properties of geopolymer were prepared.The influencing factors of the adsorption process were studied,including the dosage,pH,coexisting ions,adsorption isotherms,adsorption kinetics and adsorption thermodynamics.With the help of modern analytical methods,the samples of metakaolin and the samples before and after adsorption of geopolymer were compared.Finally,the curing effect of geopolymer was studied.The main conclusions are as follows.（1）Using metakaolin as raw material,the polymer was prepared by hydrothermal reaction.The activation of sodium silicate,sodium hydroxide and sodium metaaluminate the best activator concentration were 0.5mol/L,0.8mol/L and 0.8mol/L.The optimal ratio ofactivator was n（Na2SiO3）: n（NaAlO2）: n（NaOH）was 6:4:6.The optimal reaction time was120 min.The optimum reaction temperature was 160 DEG C.The best solid-liquid ratio was1g（metakaolin）: 20 m L（activator）.The adsorption capacity of the polymer to the copper ion was 97.67mg/g.Sodium hydroxide and sodium aluminate have great influence on the adsorption capacity.The structure of the polymer was formed rapidly after the temperature is greater than 100 DEG C.The reaction time needed more than 120 min,and the solid-liquid ratio was less than 1G（metakaolin）: 8mL（activator）preferred.（2）The amount of geopolymer adsorption was 1g/L,pH was better in 4-5.The adsorption process satisfied the Freundlich adsorption isotherm.The reaction process satisfied the Ho equation,whichwas an apparent two order kinetics process.The enthalpy of adsorption reaction was positive,the Gibbs free energy was negative,and the reaction was a spontaneous endothermic process.Metakaolin was mainly composed of crystalline phases,including mullite,sillimanite,ferrocordierite and calcium aluminosilicate.After hydrothermal reaction,metakaolin formed geopolymer（Na-PS）.There was no significant change in the crystalline state before and after adsorption.The surface area of the geopolymer was three times that of the metakaoli surface area,and there were more mesoporous materials in the geopolymer.The coexistence of both metals and anions in solution could affect the removal of copper ions.（3）After the activation of the hydrothermal reaction,the geopolymer could recover the adsorption capacity of copper ions.After 5 times of regeneration,the removal rate of copperions was about 95%,and the cure rate of copper ions was more than 99%.Under the action of activating agent,the content of the unreacted aluminosilicate in the metakaolin was gradually transformed into a geopolymer,but the crystalline state of the polymer was not changed obviously,and the Na-PS was the main one.After 5 times regeneration,the pore size,pore volume and specific surface area of geopolymer decreased. |
