Fluoride Exposure Compromises Gas Exchange of Plants

Fluorine (F-) stands out for its phytotoxic potential, because it accumulates in plants, changes enzymes activity, reduces chlorophyll content and, consequently, affects growth and yield of crop plants. An experiment was conducted to evaluate the effects of F- on leaf gas exchange in coffee and sweet orange plants, compared to sensitive (gladiolus) and tolerant (ryegrass) reference species. Plants grown in pots were exposed to F- in a semi-open mist chamber. The experimental design was completely randomized with treatments defined by the combination of plant species and two intensities of exposure to atmospheric F, with nebulization of HF solutions (low = 0.065 mmol·m-3 and high = 0.260 mmol·m-3) in a mist chamber, as well as with non-exposed control samples. CO2 assimilation (A), transpiration (E), stomatal conductance (gs) and chlorophyll fluorescence rates were measured after 27 days of treatment application. The leaf gas exchange variables in ryegrass and orange plants did not vary in response to the increase in atmospheric F, while an increase in gs and E values was observed in gladiolus and coffee plants. A decrease in A and potential quantum efficiency of photosystem II (Fv/Fm) was found for gladiolus plants. On the contrary, an increase of A for coffee plants was associated with the apparent effect previously reported about the loss of leaf stomatal regulation related to the short assessment period of plants in this experiment. Damages caused to the photosynthetic system were reflected in the susceptibility of the evaluated species to the contamination by the element.

Electroanalytical Study of Electrode Processes on Carbon Anode in Lithium Fluoride and Neodymium Fluoride Melt

The anode processes of carbon electrode in LiF-70%NdF3 melt were studied by electroanalytical techniques, including cyclic voltammetry(CV) and chronoamperometry(CA). Anode gases were analyzed by gas chromatography(GC) on-line during controlled-potential electrolysis. Two anode peaks were observed. The first process starting at 2.0 V vs Li+/Li was corresponded to the discharge of residual oxide ions, with the generation of CO and CO2. The discharge of fluoride ions occurred at the potentials higher than 4.3 V vs Li+/Li, with the generation of a small amount of CF4 and C2F6, accompanied by a sudden drop in current, marking the onset of the anode effect. The second process occurred when the potential exceeded 5.5 V vs Li+/Li, with the generation of a large amount of CF4 and C2F6. When the temperature was changed from 1173 to 1273 K, the current of the second process decreased, leading to a stable anode effect.

Fluoride Ion Adsorption Effect and Adsorption Mechanism of Self-Supported Adsorbent Materials Based on Desulfurization Gypsum-Aluminate Cement

The adsorption method has the advantages of low cost,high efficiency,and environmental friendliness in treating fluorinated wastewater,and the adsorbent material is the key.This study combines the inherent anion-exchange adsorption properties of layered double hydroxides(LDHs).Self-supported porous adsorbent materials loaded with AFm and AFt were prepared from a composite cementitious system consisting of calcium aluminate cement(CAC)and flue gas desulfurization gypsum(FGDG)by chemical foaming technique.The mineral composition of the adsorbent material was characterized by X-ray diffraction(XRD)and Scanning electron microscopy(SEM).Through the static adsorption experiment,the adsorption effect of the mineral composition of the adsorbent on fluoride ions was deeply analyzed,and the adsorption mechanism was revealed.XRD and SEM showed that the main hydration phases of the composite cementitious system consisting of CAC and FGDG are AFm,AFt,AH_(3),and CaSO_(4)·2H_(2)O.FGDG accelerates the hydration process of CAC and inhibits the transformation of AFt to AFm.The AFt content increased,and the AFm content decreased or even disappeared as the amount of FGDG increased.Static adsorption experiment results showed that AFm and AFt in adsorbent materials could significantly enhance the adsorption of fluoride ions.The adsorption of F^(−)in aqueous solution by PAG tends more towards monolayer adsorption with a theoretical maximum capacity of 108.70 mg/g and is similar to the measured value of 112.77 mg/g.

An efficient approach for the treatment of radioactive waste perfluoropolyether lubricants via a synergistic effect of thermal catalysis and immobilization

Perfluoropolyether(PFPE)lubricants are a kind of high-molecular polymer with many excellent properties.However,the use of PFPEs in the nuclear industry can lead to partial decomposition and carrying radionuclides,resulting in a large amount of radioactive waste PFPE lubricants annually.Moreover,radioactive waste PFPE lubricants are difficult to be effectively treated due to their high stability,the risk of possible leakage of radionuclides,and hypertoxic fluorine-containing by-products.In this study,without any precedent,a strategy of Mn O_(2)-catalyzed decomposition and Na_(2)CO_(3)-immobilized conversion was proposed for PFPE lubricant decomposition and fluorine immobilization simultaneously based on the Lewis acid-base and oxygen vacancies concept.A high fluorine conversion efficiency of 95.4%was achieved.Meanwhile,the mechanism of decomposition suggested that Mn O_(2)mainly provided Lewis acid sites and attacked the(basic)fluorine or oxygen atoms in PFPE molecules.The decomposition of PFPE chains was proceed down and volatile fluorine-containing gas was released by partial electron transfer,intramolecular disproportionation reaction,and unzipping fashion.Subsequently,gas by-products could be further oxidized and then immobilized into fluoride salts by carbonate solid absorbents.Overall,this study provides a simple,safe,and potentially practical strategy for the harmless conversion of refractory fluorinated organic wastes,especially perfluoropolymers.