腐殖质与铀和超铀元素相互作用的研究进展

腐殖质是一类广泛存在于自然界中的高分子有机化合物,能与放射性核素相互作用,从而影响其在自然环境中的化学形态、迁移沉降、氧化还原行为等。本文介绍了目前国内外关于腐殖质与铀和超铀元素相互作用的研究现状和进展,并对存在的问题及今后的发展方向进行了初步讨论。     

Determination of Organic Compounds,Fulvic Acid,Humic Acid,and Humin in Peat and Sapropel Alkaline Extracts

Black, brown, and light peat and sapropel were analyzed as natural sources of organic and humic substances. These specific substances are applicable in industry, agriculture, the environment, and biomedicine with well-known and novel approaches. Analysis of the organic compounds fulvic acid, humic acid, and humin in different peat and sapropel extracts from Lithuania was performed in this study. The dominant organic compound was bis(tert-butyldimethylsilyl) carbonate, which varied from 6.90% to 25.68% in peat extracts. The highest mass fraction of malonic acid amide was in the sapropel extract; it varied from 12.44% to 26.84%. Significant amounts of acetohydroxamic, lactic, and glycolic acid derivatives were identified in peat and sapropel extracts. Comparing the two extraction methods, it was concluded that active maceration was more efficient than ultrasound extraction in yielding higher amounts of organic compounds. The highest amounts of fulvic acid (1%) and humic acid and humin (15.3%) were determined in pure brown peat samples. This research on humic substances is useful to characterize the peat of different origins, to develop possible aspects of standardization, and to describe potential of the chemical constituents.     

Development of sample preparation technique to characterize chemical structure of humin by synchrotron-radiation–based X-ray photoelectron spectroscopy

Carbon-binding state of humin (HM, a non-conductive insoluble organo-mineral humic substance) was successfully characterized for the first time by synchrotron-radiation–based X-ray photoelectron spectroscopy (XPS). Four sample preparation techniques—HM on double-sided carbon tape, indium sheet, copper mesh, and in pellet formed from the mixture of HM and copper powder (Cu) at different mixing ratios (1:1, 1:2, and 1:6 v/v)—were compared. The results show that HM samples prepared using the first three methods had significant charge buildup, which made the interpretation of the XPS spectra impossible because of the shifts in the binding energy of C 1s XPS spectra. Pellets of HM:Cu mixture enhanced the electrical conductivity and reduced charge buildup on the sample surface. Pellets prepared with HM:Cu ratio of 1:1 (v/v) provided the minimum charge buildup and high sensitivity with difference in C 1s spectra regardless of the observing position. The C 1s spectra, estimated by the subtraction of the carbon contamination in Cu, showed the resolution of CC (284.0 eV), C C/C H (285.1 eV), C O (286.3 eV), CO (287.3 eV), and OC O (288.3 eV) and three additional peaks of CF (289.3 eV), CF₂ (290.2 eV), and CF₃ (291.4 eV). Soft X-ray absorption spectroscopic (XAS) analysis further proved the existence of fluoride (F 1s) in HM structure. The detection of fluorinated carbon in HM showed a great advancement of XPS compared with other conventional analyses. X-ray with the incident angle of 0° provided the smallest (nearly negligible) energy shift in the C 1s spectra of HM and did not damage the surface of the sample.     

堆肥过程中胡敏素的变化及其对五氯苯酚(PCP)吸附能力的影响

以城市污泥为堆肥原料,分别以药渣和木屑为辅料,探讨了为期120d堆肥过程中胡敏素的变化及其对五氯苯酚(PCP)吸附的影响.结果表明,随着堆肥时间的延长,堆料的总有机碳和胡敏素含量降低;堆料比表面积和孔容变小,而从堆料中提取的胡敏素的比表面积和孔容随堆肥时间的延长逐渐增大,堆料有机组分随时间的延长芳构化程度增加.吸附试验表明,堆置不同时间的堆料和其中的胡敏素对PCP的吸附均符合Freundlich模型,胡敏素的吸附能力占堆料总吸附能力的比例随堆肥时间的延长逐渐增加.但是由于堆肥的总有机碳含量下降,比表面积和孔容减小,以及胡敏酸含量的升高造成了竞争吸附作用增强,使得2种堆料对PCP的吸附能力随着堆肥时间的延长逐渐降低.