Selective Sorption Of Thorium(?) From Aqueous Solutions By Biosorbents

Highly radioactive liquid waste generated in the reprocessing of spent nuclear fuel and hydrometallurgical processes contains highly radioactive and highly toxic lanthanide actinium ions that pose a significant potential hazard to humans and the environment.How to deal with high-level liquid waste safely,effectively and economically has become one of the major issues in the nuclear industry,especially in the sustainable development of nuclear energy.There exists an increasing interest in the efficient recycling of radioactive ions in radioactive wastewaters produced in the process of hydrometallurgy and nuclear industries.In recent years,agricultural and forestry wastes as a kind of very important biosorbent material,riched in lignin,cellulose and hemicellulose,are widely used in the treatment of heavy metal wastewater and dye wastewater.The use of biomass as an adsorbent to treat radioactive wastewater has been gradually studied.In view of this,the paper useed seven common biomass materials?ginkgo leaves,osmanthus leaves,banyan leaves,magnolia leaves,holly leaves,grapefruit peels and walnut shells?preparation of biosorbent for the treatment of radioactive wastewater.Studied their adsorption properties of lanthanide actinide ions,including the following parts:?1?Low-cost biosorbents?ginkgo leaves,osmanthus leaves,banyan leaves,magnolia leaves,holly leaves,grapefruit peels and walnut shells?were evaluated in the simultaneous removal of La³⁺,Ce³⁺,Pr³⁺,Nd³⁺,Sm³⁺,Eu³⁺,Gd³⁺,Yb³⁺,Lu³⁺,UO₂²⁺,Th⁴⁺,Y³⁺,Co²⁺,Zn²⁺,Ni²⁺,and Sr²⁺from aqueous solutions.Adsorption results show that under the experimental conditions,all of the seven bioorbents can have a certain adsorption efficiency for each nuclide,but all of the biosorbents show good adsorption effects on the lanthanide and lanthanide ions.In particular,the adsorption rate of Th⁴⁺is higher than that of other lanthanide ions.?2?By using the seven kinds of biosorbents in a mixed system of 16 nuclides,the adsorption efficiency of all the cations in the mixed solution is lower than that of the single nuclide system under the experimental conditions.However,the adsorption efficiency of Th⁴⁺is still higher than that of other metal cations.This may be due to the fact that Th⁴⁺is tetravalent,rendering the electrostatic attraction with carbonyls in biosorbents stronger than with trivalent or divalent cations.At the same time,the adsorption capacity of ginkgo leaves biosorbent is far higher than that of the other six biosorbents,probably because flavonoids and flavonoids are rich in ginkgo leaves,and the molecular formula of flavonoids and flavonoids is found.There is also a large amount of carbonyl oxygen?-C=O?,Ginkgo leaves with a large number of carbonyl,the use of ginkgo leaf as a biosorbent which will greatly increase its coordination sites with metal ions,increased as an adsorbent the amount of adsorption.The experimental results of increasing the dosage of ginkgo leaves indicate that ginkgo leaves have high selectivity for Th⁴⁺in the presence of competitive ions and therefore have potential for practical application.?3?Thorium?Th?is a natural radioactive actinide which is considered as a potential nuclear fuel.It not only possesses radiotoxicity,but also has strong physiological toxicity.Selective sorption and separation of Th⁴⁺in the nuclear industry and environmental testing is of great significance.According to the results of the competitive adsorption experiments,the adsorption of Th⁴⁺by ginkgo leaves was selected to make a more in-depth study.In this study,the single factor conditions of adsorbent treatment of Th⁴⁺and the isotherms of adsorption,kinetics and thermodynamics were analyzed in detail.The results showed that the optimum adsorption conditions of Th⁴⁺for ginkgo leaves were pH 4,adsorption time 120 min,The optimum adsorption efficiency was obtained under the condition of the dosage of 2g L^-1,the particle size of 150-200 mesh and the initial concentration of Th⁴⁺of 100 mg L^-1.The adsorption process followed the Langmuir model through the isotherm model fitting and the adsorption was in the monolayer adsorption,the maximum monolayer adsorption of thorium on the surface of ginkgo leaves was 103.8 mg g^-11 at 25?.Through kinetic analysis,the adsorption of Th⁴⁺by ginkgo leaves accords with the pseudo–second–order kinetic model.During the adsorption of thorium ions,the physical diffusion and chemisorption coexist,and the chemisorption is the main factor.Through thermodynamic analysis,the process of adsorption of Th⁴⁺by ginkgo leaves is an orderly spontaneous process.Through the regeneration experiment of adsorbent,ginkgo biosorbent does not have good reusability.At the same time,SEM,surface area and pore size analysis and FTIR analysis of Ginkgo leaves before and after the adsorption of Th⁴⁺were carried out.The adsorption mechanism was explored as the functional groups on the surface of ginkgo leaf,especially the carboxyl groups,and complexed with Th⁴⁺effect.?4?In order to explore the treatment effect of biomass adsorbent on actual radioactive waste water,the acid leaching solution of monazite was treated with ginkgo leaf,walnut shell and grapefruit peel.According to the results of experiment,it can be concluded that these three biosorbents have certain removal efficiency for each metal ion in the leachate,but all of the three biosorbents exhibit higher adsorption efficiency for Th⁴⁺,and the three biosorbents in the multinuclear mixed system have higher selectivity for Th⁴⁺adsorption.At the same time,the concentration of each nuclide in the monazite leachate solution can be obtained by a multi-nuclide mixture system composed of a plurality of different concentrations of metal ions,wherein the concentration of thorium ions is close to the concentration of 100 mg L^-1,the application of ginkgo leaf biosorbent to monazite mineral leachate treatment is of great importance for the recovery and utilization of radioactive contaminants containing Th⁴⁺to protect the environment from its radioactivity and toxicity.