Study On Self-gelling Characteristics And Uranium Adsorption Properties Of Premna Microphylla Turcz Leaves

The radioactive waste water produced in the development and application of nuclear energy not only causes environmental pollution,but also poses a serious threat to human health and even life.Therefore,the treatment of radioactive waste water pollution has always been the concern of scientists from all over the world.Traditional radioactive wastewater treatment methods include chemical reduction,ion exchange,adsorption,etc.Among them,the adsorption method is widely used in low-concentration wastewater treatment due to its simplicity and high efficiency.The core of the adsorption method lies in the excellent adsorption performance of the adsorbent.Different adsorbents have different advantages and disadvantages.Premna microphylla turcz is a wild plant that has both medicinal and edible values.Because its leaves contain a lot of rich pectin,the plant is often made into foods such as"Guanyin Tofu".It has a wide range of sources,abundant output,low price,degradable,renewable,environmental friendly and other advantages,which greatly enhance its application value as an environmentally friendly functional material.The main components of Premna microphylla turcz leaves,such as pectin,cellulose,and other natural polymers,are rich in active groups such as hydroxyl and carboxyl groups,which making them have the potential to be used as heavy metal ion adsorption materials.In this paper,Premna microphylla turcz leaves were used as raw materials,combined with its self-gelling properties,and its structure wass adjusted through different preparation methods and preparation conditions,structure-controllable self-gelling adsorption materials of Premna microphylla turcz leaves were prepared,and their effect on uranium were studied.The self-gelling characteristics,mechanism of Premna microphylla turcz leaves and uranium adsorption mechanism of Premna microphylla turcz leaves self-gelling materials were explored.The main contents include the following aspects:（1）The effects of mass fraction,solution pH,solution temperature,solution type and metal ions on the self-gelling characteristics of Premna microphylla turcz leaves were studied.The results showed that temperature and pH had little effect on the self-gelling properties of Premna microphylla turcz chai leaves,while the mass fraction and the type of solution had greater effects on its self-gelling properties.Ca²⁺,Mg²⁺,Cu²⁺,Al³⁺could promote the self-gelling of Premna microphylla turcz leaves.When the pH of the solution was in the range of 2～12 and the temperature was in the range of 25～100℃,Premna microphylla turcz leaves could form a massive gel.When the mass fraction was less than 1%,and the solution type was 1%ammonium oxalate solution and 1%ammonium alginate solution,the Premna microphylla turcz leaves could not self-gelatinize to form a massive gel,and no longer have the self-gelling ability.The self-gelling mechanism of Premna microphylla turcz leaves was explored.It was speculated that the self-gelling mechanism may be due to the cross-linking of-COO^-on the molecular chain of low-ester pectin contained in the leaves with the metal ions such as Ca²⁺contained in the leaves to form"eggs Box"type structure to form a gel.（2）The Premna microphylla turcz leaves self-gelling block material was prepared by the direct centrifugation-gel method,and its adsorption properties for uranium were explored.The results showed that the optimal conditions for the preparation of the self-gelling block material were as follows:the solid-liquid ratio was 3:50（w/v）,and the centrifugal speed was5000 rpm.The optimized conditions for the adsorption of uranium ions were as follows:pH value was 5,adsorbent dosage was 0.01 g,and adsorption temperature was 25°C.The adsorption process can be described by the Langmuir isotherm adsorption model and the pseudo-second-order kinetic model.and its maximum adsorption capacity was 547.81 mg·g.When Cu²⁺,Zn²⁺,Cd²⁺,Co²+,Mn²⁺existed in the solution,it had no effect on the adsorption of uranium by Premna microphylla turcz leaves self-gelling block material.The removal rate would not decrease after five desorption/adsorption cycles.Combining with scanning electron microscope（SEM）,Fourier infrared spectrometer（FTIR）,X-ray photoelectron spectrometer（XPS）,inductively coupled plasma emission spectrometer（ICP）and other characterization techniques and adsorption models,it was speculated that the adsorption mechanism was mainly the complexation between the active groups（hydroxyl and carboxyl）in the structure and the uranium ion and the ion exchange between uranium ions and the metal ions contained in itself(mainly Ca²⁺,Mg²⁺).（3）The Premna microphylla turcz leaves self-gelling microspheres was prepared by the inverse suspension method,and its static adsorption characteristics for uranium were explored.The results showed that the optimal conditions for the preparation of self-gelling microspheres were:no metal ions,solid-to-liquid ratio of 1:15（w/v）,stirring speed of 1200rpm,and water-oil ratio of 1:5;The optimal conditions for adsorption of uranium were:pH was 5,adsorbent dosage was 0.03 g,and adsorption temperature was 25°C.The adsorption process could be described by the Freundlich isotherm adsorption model and the pseudo-second-order kinetic model.The maximum adsorption capacity was 345.46 mg·g.When Cu²⁺,Zn²⁺,Cd²⁺,Co²⁺,Mn²⁺existed in the solution,it had no effect on the adsorption of uranium.by Premna microphylla turcz leaves self-gelling micropheres The removal rate could reach more than 90%after five desorption/adsorption cycles.Combined with SEM,FTIR,XPS,ICP and other characterization techniques and adsorption models,it was speculated that the adsorption mechanism was mainly the complexation between the active groups（hydroxyl and carboxyl）in the structure of Premna microphylla turcz leaves and uranium ions,and ion exchange between the metal ions contained in itself and uranium.（4）Through the column adsorption experiment,the dynamic adsorption performance of the Premna microphylla turcz leaves self-gelling microspheres material on uranium was explored under different filler heights,different solution flow rates and different initial concentrations of uranium solution.The results showed that the higher the filler height,the later the depletion point and the penetration point.The faster the flow rate of the solution,the greater the initial concentration,the earlier the breakthrough point and the depletion point.In summary,this subject had studied the self-gelling characteristics and self-gelling mechanism of Premna microphylla turcz leaves.The self-gelling adsorption materials of Premna microphylla turcz leaves with different structures were prepared by adjusting the gel characteristics,and the uranium adsorption characteristics of the self-gelling materials with different were studied;the adsorption kinetics and adsorption mechanism were analyzed.It could provide a theoretical basis for the further application of the self-gelling adsorption material of Premna microphylla turcz leaves.The research results would provide a new way for the utilization of Sichuan’s characteristic resources of Premna microphylla turcz leaves,and provide new materials and new methods for the treatment of uranium-containing wastewater.