Adsorption of uranium(VI) by natural vermiculite: Isotherms, kinetic, thermodynamic and mechanism studies.

Human activities such as mining uranium resources, hydrometallurgy, and nuclear fuel preparation inevitably produce wastewater sludge containing radionuclides, posing a severe threat to the environment around the production site. Natural clay minerals have been widely used in groundwater pollution remediation because of their high cation exchange capacity. Through static batch experiments, the optimal pH range of vermiculite for U(VI) adsorption was 6-8,the maximum adsorption capacity was 1.62 × 10-5 mol g-1. The kinetic adsorption results indicated that the adsorption mode was mainly multilayer non-homogeneous chemisorption. In addition, the adsorption of vermiculite on U(VI) was found to be a heat absorption process according to the thermodynamic model fitting, and the spontaneous reactivity of U(VI) adsorption on vermiculite surface was positively correlated with temperature and negatively correlated with the initial concentration of U(VI). Combined with SEM-EDS and FT-IR results, the adsorption process of vermiculite on U(VI) is mainly an ion exchange and complexation reaction, and U(VI) is removed in the form of ≡ SUOU22+ or ≡ SOUO2OH, etc., by XPS means. The results of this study not only investigated the adsorption behavior and mechanism of natural vermiculite in groundwater contaminated with simulated uranium but also provided theoretical support for its feasibility in remediating uranium-polluted groundwater.

[Habitat suitability and quality division of Mentha haplocalyx].

In this study, ecological factors, occurrence records, the essential oil components content were used to predict the potential geographical distribution and quality division of Mentha haplocalyx in China based on the MaxEnt modeling and geographic information system(GIS). The AUC of ROC curve was above 0.950,indicating that the predictive results with the maximum model were highly precise. The results showed that the main environmental factors determining the potential distribution were annual average precipitation (the contribution rate, 45.87%), mean temperature of wettest quarter (11.92%), mean temperature of warmest quarter (7.84%), average monthly precipitation of May (6.80%), standard deviation of seasonal temperature variation (4.42%), mean temperature of the coldest quarter (3.47%) and altitude (2.92%). The environmental variables in the highly potential areas were determined as annual average precipitation around [530,1 465] mm, mean temperature of wettest quarter around [24.5,29] ℃, mean temperature of the warmest quarter around [25.5,29] ℃, average monthly precipitation of May around [67,133] mm, standard deviation of temperature seasonal change around [8 333,9 643], mean temperature of the coldest quarter around [1.7,8.3] ℃ and the altitude around [0,165] mm. The best quality distribution of M. haplocalyx was mainly located in Jiangsu, Anhui, Shandong, Zhejiang and Heilongjiang. The zoning results basically coincide with the actual situation. The quality division of M. haplocalyx can be used for providing a scientific basis for selection of artificial planting base and guidance of its production.