Adsorption Of Fluoride And Lead By Bayberry Tannin Foam Loaded Zirconium And Its Application In Tea Garden Soil

Tea is rich in flavonoids such as catechins which can reduce cardiovascular diseases,prevent cancer and lower lipids.Drinking tea is beneficial to human health,known as the green drink in the 21st century.However,tea tree is a kind of fluoride accumulating plant.In recent years,excessive intake of fluoride caused human health problems through tea drinking.Especially in Sichuan,Xinjiang,Tibet,Inner Mongolia and other minority areas,people are used to drinking brick tea for a long time,endemic fluorosis of tea drinking has been found one after another.Meanwhile,it is reported that the average pH of the soil is 4.73 in Chinese tea garden.And the acidification of the tea garden soil is serious.In acidic environmental conditions,the mobility and bioavailability of heavy metal ions increases,which increased the possibility of heavy metal entering tea.Ya’an is the main producing area of Sichuan tea and the lead content is about 40.00 mg/kg in the soil.The lead content in the tea can reach 5.705 mg/kg through testing,which exceeds the limit standard specified in"Non-polluted Food-Tea"（NY 5244-2004）（5 mg/kg）.Therefore,natural products bayberry tannin was used as raw material,and immobilized into foam.The functional material was prepared for simultaneous adsorption of F^-and Pb²⁺based on the reactivity between tannin and metal and the affinity between zirconium and fluoride.The adsorption properties of the materials for F^-and Pb²⁺were investigated.Then the functional material was applied to the tea garden soil.The effects of the materials on the form change of fluoride and lead in tea garden soil were explored through simulation experiments.The results provide a theoretical basis for effectively preventing and controlling the migration of fluoride and lead from the tea garden soil to tea plants.It realizes the simultaneous control of fluoride and lead in the tea garden soil,and provides a new idea for the treatment of compound pollution of fluoride and heavy metals in water and soil.The research contents and results are as follows:（1）The bayberry tannin foam impregnated zirconium（TF-Zr）was prepared by using the reactivity of the ortho-position phenolic hydroxyl group of bayberry tannin with metal and the affinity between zirconium ion and fluoride through in-situ curing and chelation.SEM-Mapping,EDS,FTIR,XPS,XRD,BET,etc.characterize the physical and chemical properties of the material.The results show that the TF-Zr material maintains the porous structure of bayberry tannin foam（TF）and a large number of phenolic hydroxyl groups.The stable five-membered ring was formed by Zr⁴⁺and tannin o-phenolic hydroxyl groups.At the same time,no crystal structure of ZrO2 appeared.These are beneficial to the adsorption of fluoride and lead by TF-Zr under a wide pH.（2）Through static adsorption and dynamic adsorption experiments,the adsorption of fluoride and lead in water by TF-Zr was studied,and the influence of factors such as pH value,amount of adsorption material,temperature and time on adsorption performance were explored.The results show that TF-Zr has a good adsorption performance for F^-in a wide range of pH（3-8）,and the adsorption of F^-is suitable for Langmuir adsorption and pseudo second-order kinetic adsorption model.The adsorption is controlled by chemical adsorption.The results of TF-Zr adsorption for Pb²⁺show that its optimal pH is 4.5～5.5.The adsorption process for Pb²⁺is also applicable to Langmuir adsorption and pseudo second-order kinetic adsorption models.The simultaneous adsorption of two components of F^-and Pb²⁺by TF-Zr is similar to that of single component of F^-and Pb²⁺.The adsorption capacity by TF-Zr for F^-and Pb²⁺is 4.89 mg/g and 3.61 mg/g respectively,and the optimum adsorption pH is 4.5～5.5.After adsorption,SEM-Mapping,EDS and XPS showed that TF-Zr maintained the porous structure of tannin foam in acid environment（pH>3）,and TF-Zr can adsorb F^-and Pb²⁺simultaneously under acidic conditions.TF-Zr is expected to be used for the inhibition and control of fluoride and lead in acidic tea garden soil.（3）The soil of Ya’an tea garden was collected,and the lead source（1250 mg/kg）was added to the soil to obtain the experimental soil.The effects of TF-Zr on various forms of lead and fluoride in tea garden soil were investigated by applying the materials into the experimental soil to simulate the humid environment of Ya’an soil.The results show that after 60 days of experiment,the soil pH with the addition of TF-Zr of 0.8g/100g soil increased.Based on the presence of H⁺in bayberry tannin,the soil pH decreased slightly with the increase of the material addition.With the increase of the amount of TF-Zr material,the various forms of fluoride in soil,such as water-soluble,ion-exchange,organic bound,all showed a downward trend,in which the content of water-soluble fluoride decreased from 2.04 mg/kg to 0.284 mg/kg.While iron-manganese oxidation fluoride has little change,and the residual fluoride has increased.The exchangeable form of lead in soil decreased from 400 mg/kg to240 mg/kg.The contents lead of iron-manganese,and organic-bound decreased,and the lead of carbonate bound form and residual form showed an increasing trend.The results show that TF-Zr has a fixed effect on water-soluble and exchangeable F^-and Pb²⁺.As-prepared material can be used to control fluoride and lead in acidic tea garden soil.