Remediation of cadmium- and lead-contaminated agricultural soil by composite washing with chlorides and citric acid.

Composite washing of cadmium (Cd)- and lead (Pb)-contaminated agricultural soil from Hunan province in China using mixtures of chlorides (FeCl3, CaCl2) and citric acid (CA) was investigated. The concentrations of composite washing agents for metal removal were optimized. Sequential extraction was conducted to study the changes in metal fractions after soil washing. The removal of two metals at optimum concentration was reached. Using FeCl3 mixed with CA, 44% of Cd and 23% of Pb were removed, and 49 and 32% by CaCl2 mixed with CA, respectively. The mechanism of composite washing was postulated. A mixture of chlorides and CA enhanced metal extraction from soil through the formation of metal-chloride and metal-citrate complexes. CA in extract solutions promoted the formation of metal-chloride complexes and reduced the solution pH. Composite washing reduced Cd and Pb in Fe-Mn oxide forms significantly. Chlorides and CA exerted a synergistic effect on metal extraction during composite washing.

[Aluminum dissolution and changes of pH in soil solution during sorption of copper by aggregates of paddy soil].

Size fractions of soil aggregates in Lake Tai region were collected by the low-energy ultrasonic dispersion and the freeze-desiccation methods. The dissolution of aluminum and changes of pH in soil solution during sorption of Cu2+ and changes of the dissolution of aluminum at different pH in the solution of Cu2+ by aggregates were studied by the equilibrium sorption method. The results showed that in the process of Cu2+ sorption by aggregates, the aluminum was dissoluted and the pH decreased. The elution amount of aluminum and the decrease of pH changed with the sorption of Cu2+, both increasing with the increase of Cu2+ sorption. Under the same conditions, the dissolution of aluminum and the decrease of pH were in the order of coarse silt fraction > silt fraction > sand fraction > clay fraction, which was negatively correlated with the amount of iron oxide, aluminum and organic matter. It suggested that iron oxide, aluminum and organic matters had inhibitory and buffering effect on the aluminum dissolution and the decrease of pH during the sorption of Cu2+.

Enhanced degradation of ortho-nitrochlorobenzene by the combined system of zero-valent iron reduction and persulfate oxidation in soils.

ortho-Nitrochlorobenzene (o-NCB) in soil poses significant health risks to human because of its persistence and high toxicity. The removal of o-NCB by both zero-valent iron (ZVI) and chemical oxidation (persulfate) was investigated by batch experiments. The o-NCB removal rate increases significantly from 15.1 to 97.3 % with an increase of iron dosage from 0.1 to 1.0 mmol g(-1). The o-NCB removal rate increases with the decrease of the initial solution pH, and a removal efficiency of 90.3 % is obtained at an initial pH value of 6.8 in this combined system. It is found that temperature and soil moisture could also increase the o-NCB removal rate. The o-NCB degradation rate increases from 83.9 to 96.2 % and from 41.5 to 82.4 % with an increase of temperature (15 to 35 °C) and soil moisture (0.25 to 1.50 mL g(-1)), respectively. Compared to the persulfate oxidation system and ZVI system, the persulfate-iron system shows high o-NCB removal capacity. o-NCB removal rates of 41.5 and 62.4 % are obtained in both the persulfate oxidation system and the ZVI system, while the removal rate of o-NCB is 90.3 % in the persulfate-iron system.

A novel three-dimensional AgI coordination polymer based on mixed naphthalene-1,5-disulfonate and aminoacetate ligands.

The three-dimensional coordination polymer poly[[bis(µ3-2-aminoacetato)di-µ-aqua-µ3-(naphthalene-1,5-disulfonato)-hexasilver(I)] dihydrate], {[Ag6(C10H6O6S2)(C2H4NO2)4(H2O)2]·2H2O}n, based on mixed naphthalene-1,5-disulfonate (L1) and 2-aminoacetate (L2) ligands, contains two Ag(I) centres (Ag1 and Ag4) in general positions, and another two (Ag2 and Ag3) on inversion centres. Ag1 is five-coordinated by three O atoms from one L1 anion, one L2 anion and one water molecule, one N atom from one L2 anion and one AgI cation in a distorted trigonal-bipyramidal coordination geometry. Ag2 is surrounded by four O atoms from two L2 anions and two water molecules, and two AgI cations in a slightly octahedral coordination geometry. Ag3 is four-coordinated by two O atoms from two L2 anions and two AgI cations in a slightly distorted square geometry, while Ag4 is also four-coordinated by two O atoms from one L1 and one L2 ligand, one N atom from another L2 anion, and one AgI cation, exhibiting a distorted tetrahedral coordination geometry. In the crystal structure, there are two one-dimensional chains nearly perpendicular to one another (interchain angle = 87.0°). The chains are connected by water molecules to give a two-dimensional layer, and the layers are further bridged by L1 anions to generate a novel three-dimensional framework. Moreover, hydrogen-bonding interactions consolidate the network.

[Estrogens determination of livestock dung based on UE-SPE-HPLC/FLD].

A method for detecting the estrogens estriol, 17beta-estradiol, ethinyl estradiol, and bisphenol A in livestock dung was established by the combination of ultrasonic extraction (UE), solid phase extraction (SPE) purification, and high performance liquid chromatography (HPLC) with fluorescence detector (FLD). The dung samples were extracted with ethyl acetate ultrasonication for 30 min, and purified with C18 solid phase extraction column and related solvents. The test four estrogens in the dung samples were isolated with Inertsil ODS-SP-C18 reversed-phase columns (150 mm x 4.6 mm, 5 microm), and the isolated estrogens were detected with HPLC/FLD. The mobile phase of HPLC for the detection was methanol/acetonitrile/water (volume ratio of 20:30:50), with a flow rate of 0.8 mL x min(-1). The excitation and emission wavelengths of FLD were 280 and 310 nm, respectively, the HPLC column temperature was 40 degrees C, and the injection volume was 20 microL. Good linearity (correlation coefficient greater than 0.9995) was observed by the HPLC/FLD detection when the test four estrogens concentrations were in the range of 1.00-1000.00 microg x L(-1). The detection limit of estriol, bisphenol A, 17beta-estradiol, and ethinyl estradiol was 3.35, 5.01, 2.13, and 1.12 microg x kg(-1), respectively. When the added estrogens concentrations of pig, cow, and chicken dung samples were 0.05, 0.40, and, 1.00 microg x kg(-1), the average recovery of the four estrogens was 75.1%-91.1%, 78.4%-117.0%, and 78.6%-97.8%, respectively, with the relatively standard deviations (RSD, n = 6) all less than 6%. By adopting the established SPE-HPLC/FLD method to detect the estrogens in real pig, cow, and chicken dung samples from parts of the large-scale livestock raising farms in Nanjing of East China, the detection reproducibility was high, and the detection limit was low, being available and effective for the detection of the estrogens in livestock dung.

[Kinetic characteristics of Cr(III) oxidation by delta-MnO2].

The kinetics of Cr(III) oxidation by synthesized vernadite(delta-MnO2) was investigated through magnetic stirring and fractional centrifugation. The oxidation procedure of Cr(III) by delta-MnO2 could be divided into two first-order reactions, a fast reaction followed by a slow one. In high Cr(III) concentration solution, the reaction was also well sub-simulated with diffusion equation and Elovich equation according to the reaction phases. The rate constants markedly increased with temperature rising. The ratio of Cr(VI)/Mn(II) gradually decreased and eventually reached the theoretical value (0.667) with the reaction. Cr(VI), Cr(III) and Mn(II) adsorbed on delta-MnO2 only accounted 0.1 to 3% of the total amounts. The Cr(VI)/Mn(II) ratio on the surface of MnO2 was much smaller than the theoretical value due to the release of Mn(II) to the solution lagged behind Cr(VI). When Cr(III) was in low concentration, Cr(III) oxidation was controlled by the diffusion and adsorption of Cr(III). While in high Cr(III) concentration, the key step was the diffusion of Mn(II) to solution.