Composition and Characteristics of Organo-Mineral Complexes of Red Soils in South China

The objective of the present study is to reveal the composition and characteristics of organo-mineral complexes in red soils (red soil, lateritic red soil and latosol) of south China in terms of chemical dissolution and fractional peptization methods. In the combined humus, most of the extractable humus could dissolve in 0.1 M NaOH extractant and belonged to active humus (H1), and there was only a small amount of humus which could be further dissolved in 0.1 M Na4P2O7 extractant at pH 13 and was stably combined humus (H2). The H1/ H2 ratio ranged from 3.3 to 33.8 in red soils, and the proportions of both H, and total extractable organic carbon (H1+H2) in total soil organic carbon and the ratios of H1 to H2 and H1 to (H1 +H2) were all higher in lateritic red soil and latosol than in red soil. The. differences of combined humus composition in various red soils were directly related to the content of Fe and Al oxides. In organo-mineral complexes, the ratio of Na-dispersed fraction (G1) to Na-ground-dispersed fraction (G2) was generally smaller than 1 for red soils, but there was a higher G1 / G2 ratio in red soil than in lateritic red soil and latosol. G1 fraction had a higher content of fulvic acid (FA), but G2 fraction had a higher content of humic acid (HA). The ratios of H1 to H2 and HA to FA were higher in G2 than in G1. The differences in the composition and activity of humus between G1 and G2 fractions were related to the content of free Fe and Al oxides. The quantities of complex Fe and Al, the Fe/ C and Al/ C atomic ratios were higher in G2 than in G1, and the ratio of Al/ C was much higher than that of Fe/ C. It may be deduced that aluminum plays a more important role than iron in the formation process of organo-mineral complexes in red soils.

Studies on Oxidation States of Cobalt Extracted from Soils with EDTA·HO Ac·NH_4OAc

A method determining di-and tri-valeht cobalt extracted from soils with EDTA·2HOAc·NH4OAc solution (pH 4.65) was developed based on the difference of the stability constants of Co(II)EDTA and Co(III)EDTA. Analytical results indicated that soil cobalt existed in both two oxidation states, i. e. , di-and tri-valent cobalt. Extractable di-valent cobalt in 60 soil samples collected from various soils in China ranged from 0.02 ppm to 3.54 ppm, with the mean of 0.62 ppm, and extractable tri-valent cobalt from 0.04 ppm to 27.65 ppm, with the mean of 2.93 ppm.

Diffusive transport of two charge equivalent and structurally similar ruthenium complex ions through graphene oxide membranes

Here, we report a study of ion transport across graphene oxide （GO） membranes of various thicknesses, made by vacuum filtration of GO aqueous solutions. The diffusive transport rates of two charge-equivalent ruthenium complex ions Ru（bpy）3^2＋ and Ru（phen）32% with a sub-angstrom size difference, are distinguishable through GO membranes and their ratio can be a unique tool for probing the transport-relevant pore structures. Pore and slit-dominant hindered diffusion models are presented and correlated to experimental results. Our analysis suggests that ion transport is mostly facilitated by large pores （larger than 1.75 nm in diameter） in the relatively thin GO membranes, while slits formed by GO stacking （less than 1.42 nm in width） become dominant only in thick membranes. By grafting PEG molecules to the lateral plane of GO sheets, membranes with enlarged interlayer spacing were engineered, which showed drastically increased ion transport rates and lower distinction among the two ruthenium complex ions, consistent with the prediction by the slit-dominant steric hindered diffusion model.

Complexation of radionuclide ^152＋154Eu(Ⅲ) with alumina-bound fulvic acid studied by batch and time-resolved laser fluorescence spectroscopy

To contribute to the understanding of Eu(Ⅲ)interaction properties on hydrous alumina particles in the absence and presence of fulvic acid(FA),the complexation properties of Eu(Ⅲ)with hydrous alumina,FA and FA-alumina hybrids are studied by batch and time-resolved laser fluorescence spectroscopy(TRLFS)techniques.The continuous increase in the fluorescence lifetime of Eu-alumina and Eu-FA with increasing pH indicates that the complexation is accompanied by decreasing number of hydration water in the first coordination sphere of Eu(Ⅲ).Eu(Ⅲ)is adsorbed onto alumina particles as outer-sphere surface complexes of≡(Al-O)-Eu·(OH)·7H_2O and≡(Al-O)-Eu·6H_2O at low pH values,and as inner-sphere surface complexes as≡(Al-O)_2-Eu^+·4H_2O at high pH.In FA solution,Eu(Ⅲ)forms complexes with FA as(COO)_2Eu^+(H_2O)_x and the hydration water number in the first coordination sphere decreases with pH increasing.The formation of≡COO-Eu-(O-Al≡)·4H_2O is observed on FA-alumina hybrids,suggesting the formation of strong inner-sphere surface complexes in the presence of FA.The surface complexes are also characterized by their emission spectra[the ratio of emission intensities of^5D_0→~7F_1(λ=594nm)and^5D_0→~7F_2(λ=619nm)transitions]and their fluorescence lifetime.The findings is important to understand the contribution of FA in the complexation properties of Eu(Ⅲ)on FA-alumina hybrids that the clarification of the environmental behavior of humic substances is necessary to understand fully the behavior of Eu(Ⅲ),or its analogue trivalent lanthanide and actinide ions in natural environment.