A new analytical approach for humin determination in sediments and soils

In this work a new analytical approach is proposed for the recovery of humin present in soil and sediments. The procedure is based on microwave oven treatment for humin deashing. In this way both the treatment time and the concentration of the HCl/HF mixture are significantly reduced (minutes rather than hours, 10% rather than concentrated). By means of the proposed scheme organic matter present in sediment and soil samples can be subdivided into the different fractions (hydrophobic and hydrophilic compounds, fulvic and humic acids, humin) making up the balance of organic carbon. Results obtained for samples characterised by different organic carbon content showed a loss of carbon ranging between 20% and 30%, consistent with previous reports about humin deashing.     

Derivatization of Humic Compounds: An Analytical Approach for Bound Organic Residues

Abstract

Bound residues of pesticides and their metabolites are defined as being nonextractable with organic solvents, but partly extractable together with the humic matrix by NaOH or other solvents suitable to extract humic compounds. Recently, an improvement in humus extraction from soils was achieved upon derivatization of the organic matter with silylating reagents at room temperature. By this method 70–90% of the organic carbon or nitrogen either from soil or from humin became soluble in organic solvents. The extracts were analyzed by means of ¹³C NMR-spectroscopy. The spectra were well resolved with signal-separation of less than 1 ppm. The extracted humic compounds were of rather low molecular weight, ranging from 300 to 4000 to 6000 d or more.

¹⁴C-labeled residues of pesticides or other xenobiotics found to be nonextractable after exhaustive organic solvent extraction became readily dissolved along with most of the humic matrix using this derivatization procedure. Between 60–80% of ¹⁴C anilazine residues or of ¹⁴C-labeled chlorinated phenols or anilines originating from both previously solvent extracted soil samples or from humin became solubilized in organic solvents.     

Sorption of cadmium in some arable and forest soils

The sorption of cadmium labeled with ¹⁰⁹Cd in nitrate form, from aqueous solutions in different horizons of some arable and forest soils was studied under static (batch) conditions. Before sorption, a method of sequential soil treatment was applied, which consist in the consecutive removal of individual soil components by the use of appropriate reagents and procedures. Three sorption isotherms were tested. Kinetic studies showed that the sorption of cadmium is rather rapid and it can be well described by a Freundlich or a linear isotherm, whereas the closeness of Langmuir isotherm to the experimental results is lower. From the different sorption isotherms, it would also be possible to estimate the effect of individual components on the sorption of cadmium in soils. It was found that the untreated soils exhibit the highest sorption and the sorption decreases in the order of untreated > acetate treated > water treated > peroxide treated > dithionite treated soil. Sorption of cadmium increases with the depth of the studied soils disregarding their chemical treatment.This revised version was published online in November 2005 with corrections to the Cover Date.     

Sorption study of 25 volatile organic compounds in several Mediterranean soils using headspace-gas chromatography-mass spectrometry

A sorption study of 25 volatile organic compounds (VOCs) in different agricultural soils was carried out by using headspace-gas chromatography-mass spectrometry. The extraction of the VOCs from soil samples was carried out following the EPA method with some differences such as addition of potassium chloride and different instrumental conditions which provide higher sample throughput. In addition, a complementary study on several procedures for soil fortification with VOCs was also assayed, fortification with minimal sample handling was selected in order to minimise evaporation losses of the VOCs. The effect of clay minerals (7.0-69.7%) and organic carbon (0.2-3.5%) contents on acid and alkaline (pH 5.3-8.8) soils were evaluated. Based on the results, all compounds assayed were more sorbed in alkaline soils than acid ones; chlorobenzenes interact more strongly with agricultural soils than do alkylbenzenes. The organic carbon content affects the sorption of 25 VOCs in alkaline soils (the highest sorption was found for the most organic soil), while in acid soils VOC sorption increases as the organic carbon content decreases. The clay mineral fraction plays an important role in the sorption of VOCs in acid soil owing to pi-/n-electron interactions, this effect being more marked for chlorobenzenes.     

Sorption, desorption and extraction of cadmium from some arable and forest soils

Summary The behavior of cadmium labeled with ¹⁰⁹Cd in different depth horizons of arable and forest soils were studied under static (batch) conditions in three interconnected processes, which consist of sorption, desorption and extraction. In the sorption, Cd²⁺ was applied in the aqueous calcium nitrate solution. Both untreated soils and peroxide treated soils were used in order to remove organic matter from some of the soil samples used in parallel. The influence of the V/m ratio on the sorption coefficients was investigated in preliminary experiments with untreated soils. Contrary to the usually short-term sorption, a long-term sorption of cadmium was investigated in untreated and treated soil horizons, which lasted more than fortnight. Kinetic studies of sorption were carried out and cadmium concentration dependence in aqueous phase of the second order kinetic constants was observed. For evaluation of sorption and desorption processes Freundlich isotherms were used. It was found that the Freundlich adsorption intensity coefficient is more time dependent than the absorption capacity coefficient, and the sorption itself consists of rapid and slow processes according to the soil constituents. Desorption and extraction processes revealed the possibility of cadmium recovery from various soil horizons. Based on the obtained results two- or three-stage theory of cadmium retention in soils was proposed. Some new insight into the role of organic matter in the sorption/desorption process of cadmium is also presented.     

Effect of some environmental ligands on the sorption of radionuclidesby peat humin

Summary In a previous paper we studied the interaction of the radionuclides ^110mAg, ⁶⁰Co and ⁶⁵Zn with peat humin. These nuclides are among the fission or corrosion products in nuclear reactors. The aim of this paper is to study the effect of certain ligands, which are present in the environment, such as humic acid, fulvic acid, EDTA and urea, on the sorption of these radionuclides by humin. The obtained results indicated that urea has no effect on the sorption of Co and Zn by humin, and only a little in case of Ag. However, the presence of the other ligands (humic acid, fulvic acid or EDTA) leads to different decreases in the sorption of the three nuclides by humin. The results are interpreted in the light of the complex formation between ligands and the metal cations and of the strength of binding of these cations to the humin sorbent. The release of Ag⁺in the presence of different ligands was found to follow the order: humic acid>EDTA>fulvic acid>urea. In the case of both Co²⁺and Zn²⁺, the sequence is changed to be: EDTA>humic acid>fulvic acid>urea, with a higher release in the case of Zn²⁺. The results showed that cobalt is bound more strongly to humin than silver and zinc. The sulphur content of the humic fractions plays a significant role in the competition for silver and zinc.     

Interaction and fractionation of added cadmium in some typical soils of the Danubian Lowland

This study was conducted to investigate the effect of time on cadmium (¹⁰⁹Cd) availability in four typical soils of the Danubian Lowland through the modified Tessier’s sequential extraction procedure as well as its short-term sorption in the bulk soils and their two grain-size fractions. Results of the fractionation study showed that there were significant changes in the proportional distribution of cadmium in all studied soils during 180 days of incubation with spiked cadmium. Generally, the proportions of cadmium associated with the most weakly bound fractions (water soluble and exchangeable) tended to decrease with corresponding increases in the residual fraction during the incubation. The extent of cadmium sorption in all studied soils was high, exceeding 95% of the spiked amount after 60 min of incubation, likely due to slightly alkaline character of the soils. The finding that soil particles less than 10 μm sorbed up to 51% of the spiked cadmium in soils is of great importance since they could play a role in colloid-facilitated transport of cadmium through preferential pathways, as previously observed in the region. Addition of 1 M ammonium nitrate into the soil solution generally decreased cadmium sorption in all four soils. The lowest extractabilities of Cd were obtained using 1 M ammonium nitrate as a single extractant, whereas 0.025 M ammonium ethylenediaminetetraacetate solution extracted the highest proportions of cadmium from the studied soils.     

Fluorine sorption by soils developed from various parent materials in Galicia (NW Spain)

Fluorine is a phytotoxic element that can reach the soil from various industrial activities. Fluorine sorption by soil is crucial to protect water and food chain from fluorine pollution. In Galicia (NW Spain), various activities emit fluorine into the atmosphere, mainly ceramic industries and an aluminium smelter. This study, aiming to investigate fluorine sorption by Galician soils, was conducted on natural soil horizons representative of the area. Most soils were acid and rich in organic matter and showed strong fluorine sorption. The lowest sorptions were exhibited by a near-neutral serpentinite-derived soil (1001 mg kg(-1)) and the B horizons of soils developed from quartz schist (989 mg kg(-1)), and the highest by the A horizons of amphibolite-derived soils (1783 mg kg(-1)). In soils developed from quartz schist, biotitic schist and amphibolite, A horizons sorbed more fluoride than the corresponding B horizons (average 1621 and 1324 mg kg(-1), respectively), while the opposite is true in granite-derived soils (average 1644 and 1324 mg kg(-1), respectively). In the A horizons, the F sorption significantly correlated to soil pH (r=-0.79), pH in NaF (r=0.83) and oxalate Al (r=0.81). In the B horizons, sorption correlated to soil pH (r=-0.78), oxalate Fe (r=0.71) and organic C (r=0.66). F sorption can be described by both the Langmuir and Freundlich equations. The concentration of free fluoride in the equilibrium solutions increased above pH 6.     

Sorption and desorption of radiostrontium on calcareous soil and its solid components

The effect of different solid components of calcareous soil on the retention of Sr was investigated by using batch technique and selective extraction method. The sorption and desorption isotherms of Sr on the untreated calcareous soil and the three treated soils were determined at 20°C, pH 7.8±0.2 and in the presence of 0.001 M CaCl₂. It was found that all isotherms are linear and that the sorption of Sr on the calcareous soil can be described by a reversible sorption process and the sorption mechanism is mainly ion exchange.     

Interaction of Cs+, Sr2+ and Gd3+ with humin

Humin is separated from a soil sample and characterized by elemental analysis, IR and potentiometric titration. These investigations indicated that humin displayed similar characteristics as humic acid. The sorption behavior of¹³⁷Cs,⁹⁰Sr and¹⁵³Gd with humin was investigated from aqueous solution. The results indicated that the sorption process follows the order: Gd³⁺≫Sr²⁺>Cs⁺. It was time dependent and increased with pH. The sorption in the presence of humic acid or EDTA showed that both form a metal-ligand complex and consequently decrease the % uptake.     

Effect of phosphate on phenanthrene sorption in soils

Phosphate is ubiquitous in the environment. However, its impact on sorption of hydrophobic organic compounds in soils has received little attention. Some effects of phosphate on phenanthrene sorption were investigated in this study using two Chinese soils with contrasting properties. The presence of phosphate significantly decreased the capacity and increased the nonlinearity of phenanthrene sorption in the soils, and this sorption-inhibiting effect was more significant at high phosphate concentration. The influence of phosphate on phenanthrene sorption in the soils was governed by the release of dissolved organic carbon (DOC), particularly higher-molecular-weight and highly aromatic DOC, which tended to be enhanced in the presence of phosphate (p<0.01) as evidenced by size exclusion chromatography and specific UV absorbance analysis. Atomic force microscopy and ζ potential analysis reveal that the ringed microaggregates of DOC were disrupted into larger condensed microaggregates and the solid interfaces tended to be more hydrophilic in the presence of phosphate which also inhibited the accumulation of phenanthrene in the soils. This study for the first time points to an important role of phosphate in the sorption of phenanthrene in soils and provides substantial evidence for the mechanisms involved using a combination of microscopic and chromatographic techniques.     

改性土壤对水中苄黄隆的吸附行为研究

研究了季铵盐阳离子表面活性荆四甲基铵离子(TMA)和十六烷基三甲基铵离子(HDTMA)改性的黄土l,黄土2，沉积物对水中苄黄隆的吸附作用．结果表明：改性后土壤对苄黄隆的吸附能力提高．同时考察了改性土壤对苄黄隆吸附的热力学行为．结果表明：HDTMA改性的土壤对苄黄隆的吸附等温线为线性，吸附类型以分配为主．HDTMA改性黄土1吸附热为-6．12kJ/mol，HDTMA改性黄土2的吸附热为-8．44kJ/mol。HDTMA改性沉积物的吸附热为-4．04kJ／mol．结合力以疏水作用力为主：TMA改性的土壤对苄黄隆的吸附等温线符合Freundlich方程．考察了溶液pH对吸附量的影响．结果表明在酸性条件下．改性土壤的吸附能力较大．     

Sorption and partitioning parameters of benzotriazole compounds

Benzotriazole compounds have major commercial applications as anticorrosive agents in automotive antifreeze and airplane deicer fluids. This study assesses the sorption of benzotriazole (BT), 5-methylbenzotriazole (MBT), and 5-chlorobenzotriazole (CBT) from aqueous solutions to four top soils. The concentration range of 10-500 mg l⁻¹ was used with soils differing in total organic carbon content from 0.27 to 1.72%. Batch systems facilitated the equilibrium sorption with analysis by HPLC. The sorption of these compounds was as much as 60% by mass to a soil with 0.33% Org. C. The log octanol-water partition coefficients (log K_ow) were determined to be 1.23 for BT, 1.89 for MBT, and 2.17 for CBT. The relationship between the log of the sorption partition coefficient, log K_oc and log K_ow differed from previous correlations because hydrophobicity was not the only factor affecting sorption. These compounds have substantial permanent dipole moments as well as being hydrophobic. At high pH where CBT molecules approach their pK_a, sorption was approximately 50% less (by mass) than that of relatively non-ionized CBT molecules.     

土壤腐殖质各组分红外光谱研究

土壤腐殖质是土壤中所特有的一类特殊的高分子化合物,具有重要的肥力和环境调节功能。其中胡敏素的提取和纯化很困难,从而限制了对其性质和结构的研究。为揭示胡敏素的结构性质,本研究按Pallo分组,将胡敏酸(HA)分为焦磷酸钠提取的胡敏酸(HAP)、氢氧化钠提取的胡敏酸(HAS);富里酸(FA)分为焦磷酸钠提取的富里酸(FAP)和氢氧化钠提取的富里酸(FAS);胡敏素(HM)分为铁结合胡敏素(HMi)、粘粒结合胡敏素(HMc)和不溶性胡敏素(HMr)三个组分,采用红外光谱法对黑土、草甸土以及黑土底土加入大量玉米秸秆培养后腐殖质各组分的结构特征进行研究。腐殖质各组分按Pallo法分组。结果表明:铁结合胡敏素(HMi)、粘粒结合胡敏素(HMc)与胡敏酸(HA)、富里酸(FA)具有相似的光谱特征,但存在明显差异。黑土、草甸土中HMi和HMc的脂族性强于HA和FA;HMi与HMc相比,HMi具有较高的脂族性。黑土中氢氧化钠提取的胡敏酸(HAS)的脂族性强于焦磷酸钠提取的胡敏酸(HAP);NaOH提取的富里酸(FAS)的脂族性强于Na4P2O7提取的富里酸(FAP)。草甸土中HAP的脂族结构较多,而HAS脂族结构相对较少。在培养土中,新形成的FA脂族性强于HA、HMi和HMc组分。新形成的HMc脂族性强于HMi和HMc的脂族性强于HAP,而弱于HAS。     

Sorption of two aromatic acids onto iron oxides: experimental study and modeling

The transport of aromatic carboxylate compounds in the environment can be strongly influenced by adsorption onto certain minerals, such as iron oxides and hydroxides, found in ground water and soils. Batch experiments with five iron oxides were conducted to quantify the contributions to adsorption from different iron mineral surfaces and compare adsorption characteristics of selected organic acids (gentisic acid (GA) and 1-hydroxy-2-naphthoic acid (HNA)). Because of their widespread abundance in soils and sediments, goethite, lepidocrocite, ferrihydrite, hematite, and magnetite were investigated. Sorption of two organic acids onto iron oxides was examined over a wide range of conditions (pH, ionic strength, and sorbate concentration). Specific surface area and mineral surface charge proved be important for the adsorption of these compounds. The sorption isotherm was described well by the Tempkin equation for both organic acids, with the adsorption constant higher for HNA than GA. For modeling the sorption edges of ferrihydrite and hematite, surface reactions involving the formation of mononuclear (1:1) surface species were proposed. These results indicate that the generalized two-layer model, with the assumption of homogeneous surface sites, could predict sorption on iron oxides over a range of pH conditions. The results of this study suggest that the mineralogy of the iron oxides and the pH value should be considered when predicting sorption of aromatic acids onto iron oxides and their fate in the soil and the environment.     

Continuous microwave-assisted extraction, solvent changeover and preconcentration of monophenols in agricultural soils

An automatic extraction, preconcentration and clean-up module for the extraction of phenolic compounds from soils was developed; the separation and quantitation of each phenol is accomplished by GC-MS. The sorption-desorption of thirteen phenols on soils containing variable amounts of organic carbon (0.05-3.4%) and clay minerals (2-43%) at pH 5.7-8.6 was investigated. For this purpose, uncontaminated soils were spiked with 5 or 20 microg of each phenol per g of soil; the soils were then stored at 4 degrees C for at least 3 months prior to analysis in order to simulate analyte-matrix interactions other than material losses and environmental degradation in actual contaminated soils. The organic carbon content in acid and alkaline soils affects the sorption of chlorophenols but not that of alkylphenols. On the other hand, alkylphenols are preferentially sorbed by neutral soils, the process being influenced by the clay mineral content. Based on the results, alkylphenols interact more strongly with agricultural soils than do chlorophenols; also, both types of compound are less strongly sorbed by loamy sand soils owing to their increased sand contents.     

Sorption and desorption of radiocesium on calcareous soil: Results from batch and column investigations

The sorption and desorption of radiocesium on a calcareous soil from Jiuqian County of Gansu Province (China) were studied by using batch and column experiments. The sorption-desorption isotherms and the breakthrough curves, displacement curves on the whole soil and two treated soils were determined. Based on these results, it was found that the sorption and retention of cesium are mainly determined by the clay minerals, that the sorption-desorption hysteresis of cesium on the calcareous soil is obvious and that the organic matter has a little positive contribution and the calcium carbonate has a little negative contribution to the sorption of cesium on the whole soil. The results from batch experiments were consistent with the results from column experiments.     

Effect of fulvic acid and ionic strength on the sorption of radiostrontium on Chinese calcareous soil and its solid components

Summary The sorption and desorption of radionuclide ⁹⁰Sr²⁺were investigated on untreated calcareous soil and two treated soils to remove organic matter and calcium carbonate using batch technique. The experiments were carried out at ambient condition, pH 7.8±0.1 and in the presence of 0.001M NaCl. Effects of fulvic acid and ionic strength on the sorption of ⁹⁰Sr²⁺on calcareous soil were also studied. It was found that the sorption isotherms are linear in the strontium concentration range used herein, and the sorption of ⁹⁰Sr²⁺on the calcareous soil can be described as a reversible sorption process and the sorption mechanism is mainly ion-exchange. The sorption is dependent on ionic strength, and fulvic acid enhances the sorption of ⁹⁰Sr²⁺on calcareous soil. Organic matter present in the calcareous soil is a significant trap of ⁹⁰Sr²⁺and is responsible for the sorption.     

Sorption and desorption of neptunium(V) on calcareous soil and its solid components: A comparative study

The sorption and desorption isotherms of untreated calcareous soil and three treated soils to remove CaCO₃, organic matter (OM) and both CaCO₃ and OM were determined and analyzed with the Freundlich equation at pH 7.8, moderate concentrations of NpO₂ ⁺ (~10^-5mol/l), in the presence of 0.01 mol/l CaCl₂ and under ambient aerobic conditions. The relative contribution of CaCO₃ and OM to the neptunium(V) sorption on calcareous soil and the sorption/desorption hysteresis is discussed. The effects of adding fulvic acid (FA) and carbonate in to the solution on the sorption of neptunium(V) on the soils were also studied. The sorption and desorption characteristics of NpO₂ ⁺, Zn²⁺, Sr²⁺ and Cs⁺ on the soils are compared.     

Sorption of cobalt(II) on soil: effects of birnessite and humic acid

To study the sorption behavior of Co(II) on soil and soil components such as birnessite, humic acid (HA) and their mixture, a series of experiment were conducted using the batch equilibrium technique on parameters such as equilibrium time, ionic strength, solution pH, and temperature. The soil samples collected from location near radioactive waste repository in Korea were used and birnessite was synthesized using a method by McKenzie for experiment. The experimental results indicate that Co sorption on soil, birnessite and soil with birnessite are strongly affected by the pH of solution. Typical for metal sorption to soils, the fraction of Co adsorbed increased as a function of pH at the experimental conditions. For sorption isotherm, the Freundlich equation provides a good fit for sorption on soil and soil with birnessite. Adsorption of HA on birnessite decreased with increase of pH, with a sharp decrease at pH 5?C6. From Co sorption experiment in a ternary system of Co, birnessite, and HA, the presence of HA enhanced Co adsorption at pH below 6.5 and reduced the Co sorption at the intermediate and high pH.