Extraction study of rare earth elements with N,N'-dibutyl–N,N'-di(1-methylheptyl)-diglycolamide from hydrochloric acid

A novel,unsymmetrical diglycolamide,N,N'-dibutyl-N,N'-di(1-methylheptyl)-diglycolamide(DBD1MHDGA),was synthesized.The extraction of rare earth elements(REEs) from a hydrochloric acid medium with DBD1 MHDGA was investigated.The results of the extraction experiments indicated that the distribution ratios of RE(Ⅲ) ions increase with an increase in HC1 concentration,atomic number,and extractant concentration.The calculated thermodynamic data show that the extraction process is an exothermic reaction.The organic phase loaded rare earth ions were characterized by infrared spectroscopy.The composition of the extracted complex was determined.

Extraction of lanthanide ions with N,N,N′,N′-tetrabutyl-3-oxadiglycolamide from nitric acid media

Extractability and extraction mechanism of lanthanide ions were investigated by using a new extractant,N,Nn,N′,N′-tetrabutyl-3-oxa-diglycolamide(TBDGA),in toluene from nitric acid media.The effects of HNO_3 and TBDGA concentrations,and temperature,on extraction of lanthanide ions were studied.Stoichiometrics of the main extracted species were HNO_3·TBDGA and M(NO_3)_3-3TBDGA(M = Er,Dy,Tb,Gd,La,Ce,Nd,Sm and Eu).The extracted species for metal ions were established to be ionic complex.In this complex,nitrate anion was not coordinated to the central ion.The extraction pattern increased gradually across the lanthanide ions series,showing enhanced affinity of TBDGA toward heavy lanthanide ions.Thermodynamic parameters were investigated for the exothermic extraction reaction.

Separation of hafnium from zirconium in hydrochloric acid solution with di(2-ethylhexyl)phosphoric acid by solvent extraction

The preparation of nuclear-grade zirconium and hafnium is very important for nuclear power. The separation of hafnium from zirconium in a hydrochloric acid solution by solvent extraction was investigated with di(2-ethylhexyl)phosphoric acid(D2 EHPA). The effects of hydrochloric acid concentration, extractant concentration,diluents, and temperature on the distribution coefficient of hafnium and zirconium were studied. The species extracted were ZrOA_2·2 HA and HfOA_2-2 HA. In this process, the separation factors varied with different diluents and followed the order octane > hexane > toluene > chloroform.A high separation factor value of 4.16 was obtained under the conditions of a solution containing 0.05 mol/L HCl and0.01 mol/L D2 EHPA for the separation of hafnium from zirconium. The extraction reaction was endothermic.

Solvent extraction of U(Ⅵ) by N,N-dimethyl-N',N'-dioctylsuccinylamide and N,N-dimethyl-N',N'-didecylsuccinylamide in cyclohexane

The extraction of uranyl nitrate by novel extractants of N,N-dimethyl-N',N'-dioctylsuccinylamide(DMDOSA)and N,N-dimethyl-N',N'-didecylsuccinylamide(DMDDSA) from aqueous nitric/nitrate solutions was investigated.It was found both the concentration of HNO_3 and extractants had an effect on the U(Ⅵ) extraction distribution.The extraction mechanism was established,and stoichiometry of the main extracted species was confirmed to be UO_2(NO_3)_2·2DMDOSA and UO_2(NO_3)_2·2DMDDSA,respectively.Both of the extraction reactions are exothermic.FTIR spectral study of the U(Ⅵ) extracted species was also made.

Evaluation of water management on arsenic methylation and volatilization in arsenic-contaminated soils strengthened by bioaugmentation and biostimulation

Arsenic(As) fate in paddy fields has been one of the most significant current issues due to the strong As accumulation potential of rice plants under fooded conditions. However,no attempt was done to explore As methylation and volatilization under non-fooded conditions. Herein, we investigated the effects of water management on As methylation and volatilization in three arsenic-contaminated soils enhanced by biostimulation with strawderived organic matter and bioaugmentation with genetic engineered Pseudomonas putida KT2440(GE P. putida). Under fooded conditions, the application of biochar(BC), rice straw(RS)and their combination(BC+RS) increased total As in porewater. However, these effects were greatly attenuated under non-fooded conditions. Compared with RS amendment alone, the combination of GE P. putida and RS further promoted the As methylation and volatilization,and the promotion percentage under non-fooded conditions were significantly higher than that under fooded conditions. The combined GE P. putida and RS showed the highest efficiency in As methylation(88 μg/L) and volatilization(415.4 μg/(kg·year)) in the non-fooded soil with moderate As contamination. Finally, stepwise multiple linear regression analysis presented that methylated As, DOC and p H in porewater were the most important factors contributing to As volatilization. Overall, our findings suggest that combination of bioaugmentation with GE P. putida and biostimulation with RS/BC+RS is a potential strategy for bioremediation of arsenic-contaminated soils by enhancing As methylation and volatilization under non-fooded conditions.

Rapid evaluation of arsenic contamination in paddy soils using field portable X-ray fluorescence spectrometry

Arsenic（As） in paddy fields is deteriorating food security and human health through rice ingestion. Rice is the dominant food source of arsenic exposure to half of the world’s population. Therefore, an in situ effective method for As risk evaluation in paddy soil is strongly needed to avoid As exposure through rice ingestion. Herein, we developed a rapid analytical methodology for determination of As in plant tissues using field portable X-ray fluorescence spectrometry（FP-XRF）. This method was applied to rice roots in order to evaluate the As contamination in paddy soils. The results showed that rice roots with iron plaques were superior to rhizosphere soils for generating FP-XRF signals, especially for field sites with As concentrations lower than the soil detection limit of FP-XRF（30.0 mg/kg）.Moreover, the strong linear relationships of As concentrations between the rice roots and corresponding leaves and grains proved that the rice root, rather than the soil, is a better predictor of As concentrations in rice grains. The research provides an efficient As monitoring method for As contaminated paddy fields by using wetland plant roots with iron plaques and XRF-based analytical techniques.

Responses of soil ammonia oxidizers to a short-term severe mercury stress

The responses of soil ammonia-oxidizing archaea（AOA） and ammonia-oxidizing bacteria（AOB） to mercury（Hg） stress were investigated through a short-term incubation experiment.Treated with four different concentrations of Hg（CK,Hg25,Hg50,and Hg100,denoting 0,25,50,and 100 mg Hg/kg dry soil,respectively）,samples were harvested after 3,7,and 28 day incubation.Results showed that the soil potential nitrification rate（PNR） was significantly inhibited by Hg stress during the incubation.However,lower abundances of AOA（the highest in CK： 9.20 × 10~7 copies/g dry soil; the lowest in Hg50： 2.68 × 10~7 copies/g dry soil） and AOB（the highest in CK： 2.68 × 10~7 copies/g dry soil; the lowest in Hg50：7.49 × 10~6 copies/g dry soil） were observed only at day 28 of incubation（P 〈 0.05）.Moreover,only the community structure of soil AOB obviously shifted under Hg stress as seen through DGGE profiles,which revealed that 2-3 distinct AOB bands emerged in the Hg treatments at day 28.In summary,soil PNR might be a very useful parameter to assess acute Hg stress on soil ecosystems,and the community structure of soil AOB might be a realistic biological indicator for the assessment of heavy metal stress on soil ecosystems in the future.