The Research Of Perchlorate Removal By Chitosan Beads

Perchlorate is a kind of pollution which is harmful to human,especially to infants.As the radius of perchlorate is similar to iodide ion,it can compete with iodide ion to interfere with the normal uptake of iodide ion by thyroid gland,reducing the amount of thyroid hormone synthesis,which leads to human development defects,and even affects the normal development of bone system and central nervous system.Due to its spatial tetrahedral configuration and high stability,perchlorate is uneasy to be reduced under natural conditions,and its high solubility leads to its rapid diffusion in the water environment and wide pollution range.At present,perchlorate pollution has become the environmental problem the countries in the world have to face.But due to varying attention on perchlorate pollution,the development of the research and regulations related to perchlorate is different in various counties.In our country,for the moment,no relevant laws and regulations of perchlorate have been enforced in wastewater discharge standards or regarding the safe concentration in drinking water,but the research of perchlorate removal method has attracted wide interest.Chitosan,as a cheap and readily available natural polymer material,has been proved to have good adsorption capacity for perchlorate.Therefore,the purpose of this paper is to prepare a kind of adsorbent with chitosan material as the base to adsorb and remove perchlorate in wastewater with high efficiency.By exploring its adsorption mechanism and applicable conditions,this study aims at making the perchlorate removal by chitosan practical and operable.In order to ensure that the adsorbent has good adsorption and mechanical properties,the chitosan material was fabricated to be in microsphere shape.By preparing chitosan microspheres under different conditions with different crosslinking agents（glutaraldehyde（GA）,epichlorohydrin（ECH）,1,2,7,8-diepoxyoctane（DEO））,the optimal preparation method of chitosan microspheres was determined by evaluating the adsorption capacity of perchlorate.It was found that the best preparation conditions of chitosan microspheres were as follows: the crosslinking agent as epichlorohydrin（ECH）,the ratio of crosslinking agent to chitosan powder（molar ratio）at 1:1,and the method of drying,and consequently the removal rate of perchlorate reached 78.4%.The adsorption performance of perchlorate on chitosan microspheres prepared under optimal conditions was studied in this paper,and it was found that when pH value changed,the adsorption capacity would be affected.When pH value was 4～6,the optimal adsorption was observed in the adsorption experiments.When co-existing ions were present,the adsorption capacity of chitosan microspheres on perchlorate decreased.The order of affinity strength of the adsorbent on different co-existing ions is SO₄^2-> H₂PO₄^->ClO₄^-.The adsorption behavior of chitosan microspheres to perchlorate can be fitted with the pseudo-second-order kinetic model and Langmuir thermodynamic equation model.Chitosan microspheres are adsorbents with high reuse and regeneration ability.In the 10 cycles of adsorption,desorption,regeneration and re-adsorption of perchlorate,the average adsorption removal rate can reach 81.6%.According to SEM image analysis,this adsorption process mainly depends on surface adsorption.The modification of chitosan microspheres by metal oxide（ZrO₂）can improve the electrostatic adsorption attraction,so as to increase the adsorption capacity of perchlorate.It was found that when the adsorption equilibrium was reached,the adsorption capacity of the modified chitosan microspheres increased by 48.9% compared with the saturated adsorption capacity before modification.The pH value,temperature and other conditions of the adsorption using modified chitosan microspheres were also investigated in this study.The adsorbent has a wide range of applicable pH,and the ideal adsorption can be achieved without pH adjustment.