Adsorption-desorption behavior of copper at contaminated levels in red soils from China

Adsorption-desorption of copper (Cu2+) at contaminated levels in two red soils was investigated. The red soil derived from the Quaternary red earths (clayey, kaolinitic thermic plinthite Aquult) (REQ) adsorbed more Cu2+ than the red soil developed on the Arenaceous rock (clayey, mixed siliceous thermic typic Dystrochrept) (RAR). The maximum adsorption values (M(A)) that are obtained from the simple Langmuir model were 25.90 and 20.17 mmol Cu2+ kg(-1) soil, respectively, for REQ and RAR. Adsorption of Cu2+ decreased soil pH, by 0.8 unit for the REQ soil and 0.6 unit for the RAR soil at the highest loadings. The number of protons released per Cu2+ adsorbed increased sigmoidally with increasing initial Cu2+ concentration for the RAR soil, but the relationship was almost linear for the REQ soil. The RAR soil released about 2.57 moles of proton per mole of Cu2+ adsorbed at the highest Cu2+ loading and the corresponding value for the REQ soil was 1.12. The distribution coefficient (Kd) decreased exponentially with increasing Cu2+ loading. Most of the adsorbed Cu2+ in the soils was readily desorbed in the NH4Ac. After five successive extractions with 1 mol L(-1) NH4Ac (p 5.0), 61 to 95% of the total adsorbed Cu2+ in the RAR soil was desorbed and the corresponding value for the REQ soil was 85 to 92%, indicating that the RAR soil had a greater affinity for Cu2+ than the REQ soil at low levels of adsorbed Cu2+.     

Adsorption characteristics of Cu and Ni on Irish peat moss

Peat has been widely used as a low cost adsorbent to remove a variety of materials including organic compounds and heavy metals from water. Various functional groups in lignin allow such compounds to bind on active sites of peat. The adsorption of Cu(2+) and Ni(2+) from aqueous solutions on Irish peat moss was studied both as a pure ion and from their binary mixtures under both equilibrium and dynamic conditions in the concentration range of 5-100mg/L. The pH of the solutions containing either Cu(2+) or Ni(2+) was varied over a range of 2-8. The adsorption of Cu(2+) and Ni(+2) on peat was found to be pH dependent. The adsorption data could be fitted to a two-site Langmuir adsorption isotherm and the maximum adsorption capacity of peat was determined to be 17.6 mg/g for Cu(2+) and 14.5mg/g for Ni(2+) at 298 K when the initial concentration for both Cu(2+) and Ni(2+) was 100mg/L, and the pH of the solution was 4.0 and 4.5, respectively. Column studies were conducted to generate breakthrough data for both pure component and binary mixtures of copper and nickel. Desorption experiments showed that 2mM EDTA solution could be used to remove all of the adsorbed copper and nickel from the bed.     

黄孢原毛平革菌吸附Cd2+和Zn2+的研究

利用黑曲霉常用液体培养基对黄孢原毛平革菌进行扩大培养，得到的菌丝球用于吸附废水中的Cd^2＋和Zn^2＋。本研究考察了初始pH、吸附时间以及共存离子对P．chrysosporium菌丝球吸附Cd^2＋和Zn^2＋的影响。在相同的实验条件下，研究重金属溶液初始浓度对吸附的影响发现其吸附曲线呈L2型，对重金属终浓度以及吸附量进行线性转换，发现Langmuir和Freundlich吸附模型能较好的描述P．chrysosporium菌丝球对Cd^2＋和Zn^2＋的吸附。将P．chrysosporium吸附Zn^2＋和Cd^2＋前后的红外光谱图作比较，发现P．chrysosporium吸附Zn^2＋和Cd^2＋后的主要成分和结构保持完整，3302cm^-1叫峰位分别移动61cm^-1和94cm^-1。     

Adsorption of cadmium on biosolids-amended soils

Debate exists over the biosolid phase (organic or inorganic) responsible for the reduction in phytoavailable Cd in soils amended with biosolids as compared with soils amended with inorganic salts. To test the importance of these two phases, adsorption isotherms were developed for soil samples (nine biosolids-amended soils and their five companion controls) and two biosolids samples from five experimental sites with documented histories of biosolids application. Subsamples were treated with 0.7 M NaClO to remove organic carbon. Cadmium nitrate was added to both moist soil samples and their soil inorganic fractions (SIF) in a 0.01 M Ca(NO3)2 solution at three pH levels (6.5, 5.5, and 4.5), and equilibrated at 22 +/- 1 degrees C for at least 48 h. Isotherms of Cd adsorption for biosolids-amended soil were intermediate to the control soil and biosolids. Decreasing pH did not remove the difference between these isotherms, although adsorption of Cd decreased with decreasing pH level. Organic matter removal reduced Cd adsorption on all soils but had little influence on the observed difference between biosolids-amended and control soils. Thus, increased adsorption associated with biosolids application was not limited to the organic matter addition from biosolids; rather, the biosolids application also altered the adsorptive properties of the SIF. The greater affinity of the inorganic fraction of biosolids-amended soils to adsorb Cd suggests that the increased retention of Cd on biosolids-amended soils is independent of the added organic matter and of a persistent nature.     

Use of magnesia for boron removal from irrigation water

The risk of B phytotoxicity due to high levels of B in irrigation water can be avoided by removing B from the water, before its use, through adsorption on certain adsorbents, such as magnesia (industrial MgO), if the latter can be proven to be an effective and easy to handle means for B removal. In addition, if such a material is applied as a fertilizer after its use and the adsorbed B is easily released into the soil solution, B phytotoxicity could constitute a potential hazard. The objectives of this work were to: (a) establish the optimum working conditions (equilibration time, solution to adsorbent ratio, and particle size of the adsorbent) for B adsorption, (b) assess the magnitude of B adsorption by magnesia, both in capacity and intensity terms, as well as the influence of temperature, (c) study B desorbability from magnesia, spiked with B at two rates, 5 and 0.5 mg g(-1), and (d) compare the results from b and c to those obtained using reagent grade MgO. The results showed that the time to achieve equilibrium depended on the B concentration of the external solution and ranged from 6 h (for B /= 50 mg L(-1)). The percentage of B adsorbed decreased as the volume of external solution to adsorbent increased and a working ratio of 50:1 was selected. For magnesia, B adsorption was particle size dependent with the smallest fraction (<0.1 mm) sorbing more B than the other three fractions studied (0.1-1.0, 1.1-2.0, 2.1-4.0 mm). Boron adsorption was conducted under strongly alkaline pH (10.3 +/- 0.2 and 10.4 +/- 0.1 for the reagent and magnesia, respectively) and increased with temperature. Both adsorbents exhibited a high B adsorption capacity (Langmuir maximum values were 5.85 +/- 0.39 and 4.45 +/- 1.31 mg B g(-1) for the reagent and magnesia, respectively) comparable to other metal oxides. However, the reagent grade MgO seemed to be superior to magnesia in terms of capacity and strength of B retention. This superiority of the reagent was attributed to its greater surface area (34.7 compared with 5.8 m(2) g(-1) for magnesia) and to its conversion to Mg(OH)(2) during the adsorption process, whereas magnesia remained unaltered, as was evident from X-ray diffractograms. Based on this data, magnesia seems to be an effective means for removing excess B from irrigation water, particularly if a material of fine particle size is used. Boron desorbability after 240 h of desorption time was more pronounced for magnesia reaching up to 55 and 60% of the amount of B added, at the spiked rates of 5 and 0.5 mg g(-1), respectively. Although these figures indicate that approximately half of the amount of B added remained adsorbed, they cannot be easily extrapolated to field conditions, and if B-laden magnesia is applied to soils, the possibility of B phytotoxicity cannot be excluded.     

Effect of liquid cow manure on andisol properties and atrazine adsorption

Application of animal manure amendments to agricultural soils is a common practice to improve soil fertility through the addition of essential plant nutrients. This practice may increase the potential for atrazine (2-chloro-4-ethylamino-6-isopropylamino-1, 3, 5-triazine) leaching due to competition for adsorption sites between the pesticide and dissolved organic carbon (DOC) added through manure. We evaluated the influence of liquid cow manure (LCM) application on soil properties, atrazine adsorption, and the physicochemical controlling mechanisms in an Andisol. The LCM was applied at rates equivalent to 0, 100,000, 200,000, and 300,000 L ha(-1), resulting in treatments S-0, S-100, S-200, and S-300, respectively. The LCM application increased DOC and pH of the soils immediately on addition, but pH returned to S-0 values 30 d after application. The LCM application did not modify atrazine adsorption with the two lowest application rates (S-100 and S-200), but atrazine adsorption was decreased in S-300 (K(f) = 0.96) compared with the control (S-0) (K(f) = 1.19), possibly due to the competitive adsorption of DOC with the pesticide. The Fourier-transformed infrared analysis showed that LCM increased aliphaticity and presence of N-containing groups and polysaccharide-like groups in amended soils; however, these properties did not modify the atrazine interaction in the studied amended soils. Interestingly the addition of DOC to soil at the high application rate (S-300) reduced atrazine adsorption in this rich OM Andisol despite the LCM not raising the concentration of stable organic matter. The application of high rates of liquid manure containing DOC incurs an increased risk of pesticide leaching.     

Adsorption and degradation of the weak acid mesotrione in soil and environmental fate implications

The ability of soils to adsorb and degrade pesticides strongly influences their environmental fate. This paper examines the adsorption and degradation of a weak acid, a new herbicide mesotrione 12-[4-(methylsulfonyl)-2-nitrobenzoyl]-1,3-cyclohexanedione], in 15 different soils from Europe and the USA. Experiments were conducted to understand the influence of soil properties, covering a wide range of soil textures, soil pH values (4.4 to 7.5), and organic carbon contents (0.6 to 3.35%). Mesotrione adsorption (Kd values ranged from 0.13 to 5.0 L/kg) was primarily related to soil pH, and to a lesser extent by percent organic carbon (%OC). As soil pH rose. mesotrione Kd values got smaller as mesotrione dissociated from the molecular to anionic form. Mesotrione degradation (half-lives ranged from 4.5 to 32 d) was also related to soil pH, getting shorter as soil pH rose. Simple regression of mesotrione adsorption against soil pH and %OC and against degradation provided a close fit to the data. The correlation between mesotrione adsorption and degradation means that Kd and half-life values are only relevant for use in environmental fate assessment if these values are "paired" for the same soil pH and %OC. The implications were as illustrated for leaching, raising important issues about combining pesticide adsorption and degradation behavior in environmental fate assessments.     

Phosphate adsorption by ferrihydrite-amended soils

New technology and approaches for reducing P in runoff from high sediment yield areas are essential due to implementation of increasingly rigorous water quality standards. The objectives of this research were to characterize ferrihydrite (Fe(5)HO(8).4H(2)O) in terms of its ability to adsorb P from soil solutions and relate its P adsorptive capacity to several soil properties that influence P mobility. A naturally occurring ferrihydrite, collected as an Fe oxide sludge by-product from a water treatment facility, was equilibrated with soil samples at equivalent rates of 0, 0.34, 3.36, 16.80, and 33.60 Mg ha(-1) for a 60-d period. Individual 2-g subsamples of each soil were then equilibrated with 0, 5, 10, 20, and 40 mg kg(-1) P in 20 mL of 0.01 M CaCl(2) on a reciprocating shaker for 24 h. After 24 h, P in solution was measured by colorimetric methods, and designated as final P concentrations. The data indicated that the unamended soils with a pH of <6.0 adsorbed, in some cases, 50 times more P than soils with a pH of >7.0. The final P concentrations, averaged for all initial P concentrations and ferrihydrite rates, ranged from 0.09 to 4.63 mg kg(-1), and were most highly correlated with pH (r = 0.844; P < or = 0.01), oxalate-extractable Fe (r = -0.699; P < or = 0.10), and dithionite-extractable Fe (r = -0.639; P < or = 0.10) contents of the unamended soils. In terms of individual soils, correlation coefficients (r) for final P concentrations versus ferrihydrite amendment rates indicated a statistically significant (P < or = 0.001) negative relationship at all initial P concentrations for most A horizons. The r values for the high Fe oxide content B horizon soils did not show a statistically significant response to ferrihydrite additions. The results indicate that P adsorption, in soils amended with ferrihydrite, will be greatest under acid pH conditions below the ferrihydrite zero point of charge (pH 5.77), and low incipient Fe oxide contents.     

Imazaquin adsorbed on pillared clay and crystal violet-montmorillonite complexes for reduced leaching in soil

Ground water pollution due to herbicide leaching has become a serious environmental problem. Imazaquin [2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)quinoline-3-carboxylic acid] is an herbicide used to control broadleaf weeds in legume crops. Imazaquin is negatively charged at the basic pH of calcareous soils and exhibits high leaching potential in soils. Our aim was to design formulation of imazaquin to reduce herbicide leaching. Imazaquin sorption on pillared clay (PC) and crystal violet (CV)-montmorillonite complexes was studied. The CV-montmorillonite complexes become positively charged with adsorption of CV above the cation exchange capacity (CEC) of montmorillonite, and thus can sorb imazaquin. The Langmuir equation provides a good fit to isotherms of imazaquin sorption on PC and CV-montmorillonite complexes, but for charged complexes an equation that combines electrostatics with specific binding was preferred. Maximal imazaquin sorption was 17.3 mmol kg-1 for PC and 22.2 mmol kg-1 for CV-montmorillonite complexes. The extents of imazaquin desorption into water were 21% for PC and 5% for CV-clay complexes. The presence of anions decreased imazaquin sorption on both sorbents in the sequence phosphate > acetate > sulfate. Reduction of imazaquin sorption by the anions and the extent of its desorption in electrolyte solutions were higher for PC than for CV-clay complexes. Leaching of imazaquin from CV-montmorillonite formulations through soil (Rhodoxeralf) columns was two times less than from PC formulations and four times less than that of technical imazaquin. The CV-montmorillonite complexes at a loading above the CEC appear to be suitable for preparation of organo-clay-imazaquin formulations that may reduce herbicide leaching significantly.     

Environmental index for estimating the risk of phosphorus loss in calcareous soils of Manitoba

The degree of phosphorus saturation (DPS) has been used in evaluating the risk of P loss from soil to runoff. While techniques are available for calculating DPS for acid soils, no widely used technique exists for neutral to calcareous soils that are typical of the Northern Great Plains, including Manitoba (Canada) soils. This study aimed to develop techniques of calculating the DPS of neutral to alkaline soils. Four measures of soil labile P and ten indices of P sorption capacity were used to calculate the DPS of 115 Manitoba soils. The various DPS calculated were evaluated using water-extractable ((H2O)) P as an index of P susceptibility to runoff loss. The DPS obtained using Olsen-extractable ((Ols)) P and the Langmuir adsorption maximum (ES(max)) ranged from 0.5 to 31.9% while those obtained from P(Ols) and the single-point adsorption index (P(150)) ranged from 0.9 to 73.9%. Of all the DPS evaluated, those that included P(Ols) and Mehlich 3-extractable ((M3)) P as the numerator with either P(150) or ES(max) as the denominator were fairly well correlated with P(H2O) (r values ranged between 0.45 and 0.63). Along with ES(max) and P(150), a new method of calculating DPS was formulated as the ratio of P(Ols) or P(M3) to Ca(M3) or (Ca + Mg)(M3). We found that the ratio of ammonium oxalate-extractable ((ox)) P to (Al + Fe)(ox), which has been widely used to calculate DPS in acid soils, was not suitable for neutral to alkaline soils of Manitoba. In these neutral to alkaline soils, Ca(M3) or (Ca + Mg)(M3) were better indices of P sorption capacity while P(Ols) and P(M3) provided better estimates of labile soil P. The DPS calculated using Ca(M3) or (Ca + Mg)(M3) were well correlated with P(H2O); however, they were numerically smaller than those obtained from the Langmuir adsorption maximum. As such, a saturation coefficient (alpha) with a value of 0.2 was generated to improve the numerical values of the newly estimated DPS. This new approach can be used to estimate the DPS in neutral and calcareous soils without the need to generate a P adsorption maximum.     

Cellulose-based anion exchanger with tertiary amine functionality for the extraction of arsenic(V) from aqueous media

A novel cellulose-based anion exchanger (Cell-AE) with tertiary amine functionality was synthesized by graft polymerization reaction of cellulose and glycidyl methacrylate using N,N′-methylene-bis-acrylamide as a crosslinker and benzoyl peroxide as an initiator, followed by dimethylamine (amination) and acid (HCl) treatment. The chemical modification was confirmed by infrared spectroscopy and CHN analysis. The anion exchanger was used in batch processes to study AS(V) adsorption in solutions. The operating variables studied were pH, contact time, initial As(V) concentration, sorbent mass, and ionic strength. The process was affected by solution pH with an optimum adsorption occurring at pH 6.0. Adsorption equilibrium was achieved within 1 h. Increasing ionic strength of solution negatively affected the arsenic uptake. The adsorption process performed more than 99.0% of As(V) removal from an initial concentration of 25.0 mg/L. The process of adsorption followed pseudo-second-order kinetics. The adsorption equilibrium isotherm data were analyzed using the Langmuir, Freundlich, Redlich–Peterson and Langmuir–Freundlich equations. The Langmuir–Freundlich isotherm described the adsorption data over the concentration range 25–400 mg/L. The adsorption mechanism appears to be a ligand-exchange process. A simulated groundwater sample was treated with Cell-AE to demonstrate its efficiency in removing As(V). The adsorbed As(V) ions were desorbed effectively by a 0.1 M NaOH solution.     

Speciation of phosphorus in phosphorus-enriched agricultural soils using X-ray absorption near-edge structure spectroscopy and chemical fractionation

Knowledge of phosphorus (P) species in P-rich soils is useful for assessing P mobility and potential transfer to ground water and surface waters. Soil P was studied using synchrotron X-ray absorption near-edge structure (XANES) spectroscopy (a nondestructive chemical-speciation technique) and sequential chemical fractionation. The objective was to determine the chemical speciation of P in long-term-fertilized, P-rich soils differing in pH, clay, and organic matter contents. Samples of three slightly acidic (pH 5.5-6.2) and two slightly alkaline (pH 7.4-7.6) soils were collected from A or B horizons in two distinct agrosystems in the province of Québec, Canada. The soils contained between 800 and 2100 mg total P kg(-1). Distinct XANES features for Ca-phosphate mineral standards and for standards of adsorbed phosphate made it possible to differentiate these forms of P in the soil samples. The XANES results indicated that phosphate adsorbed on Fe- or Al-oxide minerals was present in all soils, with a higher proportion in acidic than in slightly alkaline samples. Calcium phosphate also occurred in all soils, regardless of pH. In agreement with chemical fractionation results, XANES data showed that Ca-phosphates were the dominant P forms in one acidic (pH 5.5) and in the two slightly alkaline (pH 7.4-7.6) soil samples. X-ray absorption near-edge structure spectroscopy directly identified certain forms of soil P, while chemical fractionation provided indirect supporting data and gave insights on additional forms of P such as organic pools that were not accounted for by the XANES analyses.     

Removal of direct red 12B and methylene blue from water by adsorption onto Fe (III)/Cr (III) hydroxide, an industrial solid waste

Removal of direct red 12B and methylene blue by adsorption onto Fe (III)/Cr (III) hydroxide was studied using various parameters such as agitation time, dye concentration, adsorbent dose and pH. Equilibrium adsorption data followed both Langmuir and Freundlich isotherms. Adsorption followed second-order rate kinetics. The Langmuir adsorption capacity (Qo) was found to be 5.0 and 22.8 mg dye per g of the adsorbent for direct red 12B and methylene blue, respectively. Acidic pH was favorable for the adsorption of direct red 12B and basic pH for methylene blue. Desorption studies showed that chemisorption seems to be the major mode of adsorption.     

Adsorption of cadmium on carbonaceous adsorbents developed from used tire rubber

Carbonaceous adsorbents (CAs) are developed from used tire rubber (UTR) and tested as adsorbents of Cd(2+) in aqueous solution. In the preparation of the CAs, UTR was treated thermally at 400-900 °C for 2 h in N(2) and at 850 °C for 2 h in steam. Concentrated NaOH, HCl, H(2)SO(4), HNO(3) and H(2)O(2) solutions were also used. UTR and H900 (i.e. UTR pyrolyzed at 900 °C) were treated with O(3) at 25 °C for 1 h and with air at 250 °C for 1 and 24 h. CAs were characterized texturally by N(2) adsorption at -196 °C, mercury porosimetry, and density measurements. The surface groups were analyzed by FT-IR spectroscopy. Using the batch method, the adsorption process of Cd(2+) was studied mainly from the kinetic standpoint at various pH values of the adsorptive solution. Significant porosity developments are achieved only when UTR is heat-treated, in particular in steam. However, the variety and concentration of surface groups are low in CAs. This is so even for CAs prepared using oxidizing agents as strong as O(3) and H(2)O(2), which has been associated with a lack of available or accessible surface active sites for oxidation in UTR and H900, respectively. Thermal and thermal-chemical treatments are usually more effective than chemical treatments to increase the adsorption of Cd(2+) in aqueous solution. The adsorption process of Cd(2+) is first fast and then much slower. Adsorption-time data fit better to a pseudo-second order kinetic equation than to a pseudo-first order kinetic equation. The extent to which the adsorption process occurs is strongly dependent on the pH of the Cd(2+) solution, being larger at pH 4.6 or 7.0 according to the adsorbent.     

Attenuation of divalent toxic metal ions using natural sericitic pyrophyllite

The present study investigated the effectiveness of an inexpensive and ecofriendly alumino silicate clay mineral, sericitic pyrophyllite, as an adsorbent for the possible application in the removal of some divalent toxic metal cations such as Pb(2+), Cu(2+)and Zn(2+) from aqueous systems. Batch scale equilibrium adsorption studies were carried out for a wide range of initial concentration from 24.1 to 2410mumolL(-1) for lead, 78.65 to 7865mumolL(-1) for copper and 76.45 to 7645mumolL(-1) for zinc solutions. The removal of Pb(2+) was almost complete at low concentration (maximum lead removal capacity, LRC, 32mg of lead/g of pyrophyllite) with 10gL(-1) of adsorbent in a 30min equilibration time. The effects of temperature on adsorption of heavy metal ions were studied. The applicability of the Langmuir, Freundlich and Dubinin-Radushkevich adsorption models in each case of lead, copper and zinc adsorption was examined separately at different temperatures. The adsorption process was found to be endothermic and the Freundlich adsorption model was found to represent the data at different temperatures more suitably.     

Experimental investigation of groundwater contamination by surface sources: Determination of adsorption capacity,diffusion, and sorption potential of selected anions in different soils

The present study investigated the fate and transport of two significant anions through soil to explore their potential as groundwater contaminants. The retention properties of chloride and sulfate in soils having several significantly different characteristics (soil‐1 and soil‐2) were determined using adsorption test and adsorption‐diffusion column experiments. The maximum adsorption capacity of chloride was 3.7 and 1.16 mg/g, respectively, in soil‐1 and soil‐2, with organic matter (OM) content of 3.92% and 4.69%, respectively. The sulfate adsorption obtained was 24.09% and 13.83%, respectively, in the two soils. The anions exhibited monolayer adsorption in the soils with replacement of hydroxyl ions from soils as the major mechanism of adsorption. On the other hand, the adsorption capacities obtained from the adsorption‐diffusion column experiment were about 100 times lower compared to that of the column tests of both of the soils. The maximum adsorption capacity of chloride was 0.03 mg/g and 0.01 mg/g, respectively, in soil‐1 and soil‐2, whereas that of sulfate was 0.04 mg/g and 0.03 mg/g. The empirical relation for depth of penetration (d) from a known spillage onto the soil surface was determined as a function of sorption capacity (S) and initial anion concentration (C) as d = 0.0073e^(?57S)C and d = 0.0038e^(?35S)C for chloride and sulfate, respectively.     

Removal of basic dye (Astrazon Blue FGRL) using macroalga Caulerpa lentillifera

The macroalga Caulerpa lentillifera was found to have adsorption capacity for a basic dye, Astrazon Blue FGRL. For the whole range of concentrations employed in this work (20-1280 mgl(-1)), the adsorption reached equilibrium within the first hour. The kinetic data corresponded well with the pseudo second-order kinetic model where the rate constants decreased as initial dye concentrations increased. At low dye concentrations (20-80 mgl(-1)), an increase in the adsorbent dosage resulted in a higher removal percentage of the dye, but a lower amount of dye adsorbed per unit mass (q). The adsorption isotherm followed both the Langmuir and Freundlich models within the temperature range employed in this work (18-70 degrees C). The highest maximum adsorption capacity (q(m)) was obtained at 50 degrees C. The enthalpy of adsorption was estimated at 14.87 kJmol(-1) suggesting a chemical adsorption mechanism.     

Structural and sorption characteristics of adsorbed humic acid on clay minerals

Clay-humic complexes are commonly distributed in natural environments. They play very important roles in regulating the transport and retention of hydrophobic organic contaminants in soils and sediments. This study examined the structural changes of humic acid (HA) after adsorption by clay minerals and determined phenanthrene sorption by clay-humic complexes. Solid- and liquid-state 13C nuclear magnetic resonance (NMR), for the first time, provided direct evidence for HA fractionation during adsorption on mineral surfaces, that is, aliphatic fractions were preferentially adsorbed by clay minerals while aromatic fractions were left in the solution. The ratio of UV absorbance of HA at 465 and 665 nm (E4 to E6 ratio), which is related to aromaticity, corroborated with the NMR results. For both montmorillonite and kaolinite, adsorbed HA fractions had higher sorption linearity (N) and affinity (K(oc)) than the source HA. The K(oc) of adsorbed HA for the clay-humic complexes could be up to several times higher than that of the source HA. This large increase may be contributed by the low polarity of the bound HA. Moreover, for each mineral, the N values of adsorbed HA increased with increasing HA loading. It is believed that HA may develop a more condensed structure on mineral surface at lower HA loading level due to the stronger interactions between HA and mineral surface as a result of close contacts.     

Mercury speciation in highly contaminated soils from chlor-alkali plants using chemical extractions

A four-step novel sequential extraction procedure (SEP) was developed to assess Hg fractionation and mobility in three highly contaminated soils from chlor-alkali plants (CAPs). The SEP was validated using a certified reference material (CRM) and pure Hg compounds. Total, volatile, and methyl Hg concentrations were also determined using single extractions. Mercury was separated into four fractions defined as water-soluble (F1), exchangeable (F2) (0.5 M NH4Ac-EDTA and 1 M CaCl2 were tested), organic (F3) (successive extractions with 0.2 M NaOH and CH3COOH 4% [v/v]), and residual (F4) (HNO3 + H2SO4 + HClO4). The soil characterization revealed extremely contaminated (295 +/- 18 to 11 500 +/- 500 mg Hg kg(-1)) coarse-grained sandy soils having an alkaline pH (7.9-9.1), high chloride concentrations (5-35 mg kg(-1)), and very low organic carbon content (0.00-18.2 g kg(-1)). Methyl Hg concentrations were low (0.2-19.3 microg kg(-1)) in all soils. Sequential extractions indicated that the majority of the Hg was associated with the residual fraction (F4). In Soils 1 and 3, however, high percentages (88-98%) of the total Hg were present as volatile Hg. Therefore, in these two soils, a high proportion of volatile Hg was present in the residual fraction. The nonresidual fraction (F1 + F2 + F3) was most abundant in Soil 1 (14-42%), suggesting a higher availability of Hg in this soil. The developed and validated SEP was reproducible and efficient for highly contaminated samples. Recovery ranged between 93 and 98% for the CRM and 70 and 130% for the CAP-contaminated soils.     

Adsorption of Pb and Cd on the natural surface coatings (NSCs) in the presence of organochlorine pesticides: a preliminary investigation

Adsorption of Pb and Cd in the presence and absence of organochlorine pesticides (OCPs) on natural surface coatings (NSCs), which were collected in the Nanhu Lake in Changchun, China, was measured in order to investigate the effect of the OCPs on the adsorption of heavy metals on the NSCs. Adsorption of Pb/Cd was carried out under controlled laboratory conditions (mineral salt solution with defined species, ionic strength 0.05 mol/l, 25 degrees C and pH 6.0) with initial Pb and Cd concentrations ranging from 0.2 to 2.5 mol/l. The classical Langmuir adsorption isotherm was applied to estimate the equilibrium coefficients of the adsorption of Pb and Cd on the NSCs. Adsorption interference between Pb/Cd and the OCPs on the NSCs indicated that the adsorption of Pb/Cd on the NSCs was influenced by the OCPs, and competitive adsorption between Pb and the OCPs was observed while adsorption of Cd was enhanced by addition of the OCPs. Adsorption data fit the Langmuir isotherm well for the NSCs treated with the OCPs at different equilibrium concentrations. The results showed that the amount of adsorbed Pb decreased by more than 40% while the amount of adsorbed Cd increased by over 60% with an increase in the initial concentrations of the OCPs ranging from 0 to 5.0 microg/l and that adsorption of Pb/Cd on the NSCs was strongly affected by the OCPs. This preliminary study highlights the importance of the OCPs on the NSCs in controlling the transport, fate, biogeochemistry, bioavailability and toxicity of trace metals in aquatic environments.