Adsorption Study Of Ge(Ⅳ) On Persimmon Tannin Composites And Functionalized Titanium Dioxide

In this paper,the persimmon tannin composites and titanium dioxide adsorbents modified by hydroxyl groups were prepared,and their adsorption properties for germanium were compared,the specific research could be divided into three points.The persimmon tannin/chitosan bio-composite synthesized by one-step crosslinking method and post-crosslinking method using persimmon tannin as raw materialandglutaraldehydeascrosslinkingreagentwerenamedas CS-Glu60-PT@15 and CS-Glu-PT（P）,respectively.The results showed that CS-Glu60-PT@15 not only effectively resolve the problem of solidification of persimmon tannin,but also have a much higher adsorption capacity for germanium than CS-Glu-PT（P）.The adsorption capacities were 64.12 and 5.67 mg·g^-11 at pH 10,respectively.The best synthesis conditions for CS-Glu60-PT@15 by one-step crosslinking method were 15²0℃of the room temperature and the 2 g:60 mL ratio of persimmon tannin and glutaraldehyde,which is mainly related to the content of phenolic hydroxyl.In Ge-As binary system,CS-Glu60-PT@15 still had higher selectivity for germanium when the ratio of arsenic and germanium gradually increased.After five adsorption-desorption experiments,CS-Glu60-PT@15 still had a recovery rate more than 80%,indicating that CS-Glu60-PT@15 has good reproducibility.In order to improve the adsorption performance of the persimmon tannincomposite.Graphene oxide is used to replace chitosan as the matrix and compounded with persimmon tannin to synthesis GO-PT-6mLGlu by means of increasing the specific surface area of the matrix.Compared with CS-Glu60-PT@15,the adsorption capacity of GO-PT-6mLGlu(90.12 mg·g^-1)increased by 26 mg·g^-1.Thetitrationexperimentsofsurfacefunctionalgroupsrevealedthat GO-PT-6mLGlu(5.23 mmol·g^-1)had higher content of phenolic hydroxyl than CS-Glu60-PT@15(5.13 mmol·g^-1),respectively.SEM analysis showed that the surface morphology of GO and PT could be observed in GO-PT-6mLGlu,indicating that PT and GO were successfully compounded.By FTIR and XPS characterization,it was found that O-Ge bond was formed between the phenolic hydroxyl group of GO-PT-6mLGlu and GeO（OH）₃^-under alkaline conditions.The O atom also chelated with GeO（OH）₃^-to form chelates.GO-PT-6mLGlu had better selectivity for Ge in Ge-As binary systems.After five adsorption-desorption experiments,the recovery rate of GO-PT-6mLGlu for germanium could still reached about 80%,indicating that the stability of GO-PT-6mLGlu is better.In order to further find the adsorbent which has better adsorption capacity for germanium,the titanium dioxide adsorbents rich in hydroxyl groups modified by tartaric acid,malic acid and succinic acid were prepared,which was named TA-TiO₂-OH,MA-TiO₂-OH and SU-TiO₂-OH,respectively.The results showed that the adsorption rates of Ge in whole acidity range were all high,and the maximum adsorption capacity was 116.35,72.13 and 43.26 mg·g^-11 under the condition of pH 3,respectively.It can be seen that tartaric acid modified titanium dioxide adsorbent TA-TiO₂-OH has the greatest adsorption capacity for germanium,and has a wide acidity and higher adsorption capacity compared with the persimmon tannin composite containing phenolic hydroxyl.The titration results of surface functional groups showed that the content of TA-TiO₂-OH was 4.38 mmol·g^-1.Although the hydroxyl content of the TA-TiO₂-OH was lower than that of the phenolic hydroxyl content of persimmon tannin composite,the adsorption amount was different because of the different surface charge.Under the coexistence of Cu,Al,Zn,Si and Ge,TA-TiO₂-OH showed better selectivity for germanium.After five cycles of experiments,the recovery rate of TA-TiO₂-OH for Ge could still reached more than80%,indicating TA-TiO₂-OH has good regeneration ability.