Partitioning of Cs-137 Between Sediment and Water From the Black Sea

Abstract

As part of a joint USA/USSR Environmental Agreement to determine the distribution and concentration of Chernobyl radioactivity in the northwest Black Sea area, the sediment from eight stations was collected and analyzed to assess the ability of this material to adsorb radiocaesium. Batch tests were conducted in which Cs-137 tracer was added to mixtures of sediment and bottom water, with contact solutions ranging from 85 Bq ml^?1 to 1,760 Bq ml^?1. This work was done in an argon atmosphere at 9.5°C, which is the average temperature of the sediment. Isotherms were linear for all cores and distribution ratios (R_D) calculated from the slopes of the isotherms ranged from 660 to 1,660 ml g^?1. These isotherms fit a simplified Freundlich isotherm. Correlations of R_D to a number of sediment parameters describing texture and mineralogy were determined. A close relationship was observed between R_D for caesium and the percentage of illite contained in the samples.     

Vertical Distribution and Inventories of 239,240Pu in Deep Sea Sediments of the Mediterranean Sea (Algerian Basin, Ionian Sea)

Deep-sea sediments collected in two areas of the Mediterranean Sea having different sedimentological characteristics have been analyzed to determine present concentrations and inventories of ^239,240Pu and to study the main mechanisms controlling them. Plutonium distribution in the deepest part of a submarine canyon (Taranto Valley, Ionian Sea) is compared to that obtained in an abyssal plain (north Algerian Plain). in the latter case, sedimentation is mainly due to the sinking of biogenic particles, while in the former lateral transport of terrigenous material along the slope of the canyon can significantly contribute to sediment accumulation on the bottom.

^239,240Pu surface concentration in the canyon ranged from 0.2 to 1 Bq kg^-1 (dry weight) and this was lower in the abyssal plain. in this area, plutonium was detectable only in the first 4 cm, while in the canyon it was present down to 11-15 cm. ^239,240Pu inventories are 3 Bq m^-2 in the plain and 45-60 Bq m^-2 in the canyon, indicating considerable input of terrigenous material towards the final part of the Taranto Valley.     

The Freshwater Mussel Parreysia Favidens (Benson) As A Biological Indicator of Polonium - 210 in A Riverine System

The concentration of ²¹⁰Po, an alpha emitter from the natural uranium series was measured in the soft tissues (total), shell, and different organs - digestive glands, gills, mantle and foot - of the freshwater mussel, Parreysia favidens (Benson), collected from the river Kaveri, at Tiruchirapalli in South India. the analyses were made in three size groups based on shell length (Group 1: 2-4 cm; Group 2: 4-5 cm; Group 3: 5-6 cm). the soft tissues of the mussel accumulated higher concentrations of ²¹⁰Po (74.0-125.5 Bq kg^-1 fresh) than the shell (2.9-3.9 Bq kg^-1 fresh). Further, younger mussels (1 group) showed higher concentrations (125.5+2.0 Bq kg^-1 fresh) in total soft tissues than older ones (III Group) (74.0+1.6 Bq kg^-1 fresh); concentration factors were 1.59x 10⁵ in I group and 9.37 × 10⁴ in III group. the ²¹⁰Po was observed to be non-uniformly distributed among the internal organs, which maintained the following descending order with reference to ²¹⁰Po accumulation: digestive glands, ranging from 286.2+3.5 Bq kg^-1 fresh to 43+1.3 Bq kg^-1 fresh. the concentration of ²¹⁰Po in the mussels was distinctly higher than that in the grass, Echinochloa colonum (J. Koenig), and carp, Cirrhinus cirrhosa (Bloch), from the same river. These data indicate that younger mussels could be used as an excellent biological indicator of ²¹⁰Po and among soft tissues, digestive glands are preferable to other tissues to monitor the distribution of ²¹⁰Po in the riverine system.     

Phenanthrene sorption to environmental black carbon in sediments from the Song-Liao watershed (China)

Black carbon (BC) in ten contaminated sediments from the Song-Liao watershed, NE China, was isolated upon treatments using a combustion method at 375°C, and the isolates’ sorption isotherms for phenanthrene (Phen) were determined. All sorption isotherms were nonlinear and fitted well by the Freundlich model. A negative relation was found between Freundlich sorption nonlinearity parameter (n values) and BC/total organic carbon (TOC) content of the original sediments (r²=0.687, p<0.01), indicating the dominance of BC in Phen sorption nonlinearity. The BC isolates from this industrialized region had n values of 0.342 to 0.505 and logK_FOC values of 6.02 to 6.42(μg·kg⁻¹·OC⁻¹)/(μg·L⁻¹) ⁿ for Phen. At a given C_e, the BC had higher K_oc value than the original sediments, revealing a higher sorption capacity for BC. BC was responsible for 50.0% to 87.3% of the total sorption at C_e=0.05 S_w, clearly indicating the dominance of BC particles in overall sorption of Phen by sediments.     

Modified pretreatment method for total microbial DNA extraction from contaminated river sediment

Extraction of high-quality microbial DNA from contaminated environmental samples is an essential step in microbial ecological study. Based on previously published methods for soil and sediment samples, a modified pretreatment method was developed for extracting microbial DNA from heavily contaminated river sediment samples via selection of optimal pretreatment parameters (i.e., reagent solution, reaction duration, and temperature). The pretreatment procedure involves washing the river sediment sample for three times with a solution containing 0.1 mol·L^-1 ethylene diamine tetraacetic acid (EDTA), 0.1 mol·L^-1 Tris (pH 8.0), 1.5 mol·L^-1 NaCl, 0.1 mol·L^-1 NaH₂PO₄, and Na₂HPO₄ at 65°C with 180 r·min^-1 for 15 min to remove humic materials and heavy metals prior to the employment of standard DNA extraction procedures. We compared the results of standard procedure DNA extraction following pretreatment, without pretreatment, and with using a commercial PowerSoil^TM DNA Isolation Kit. The results indicated that the pretreatment significantly improved the DNA quality based on DNA yield, DNA fragment length, and determination of prokaryotic diversity. Prokaryotic diversity exhibited in the DNA with the pretreatment was also considerably higher than that extracted with the PowerSoil^TM DNA Isolation Kit only. The pretreatment method worked well even with a small amount of sediment sample (0.25 g or even lower). The method provides a novel, simple, cost-effective tool for DNA extraction for microbial community analysis in environmental monitoring and remediation processes.     

Species distribution of arsenic in sediments after an unexpected emergent discharge of high-arsenic wastewater into a river

The unexpected emergent discharge of high-arsenic wastewater into water environments results in significantly increased levels of arsenic in water; however, the species distribution of arsenic in sediments has never been reported before for such cases. This study focuses on an As pollution accident in the Dasha River, and uses sequential extraction procedures with deionized water, 1?mol·L^-1 MgCl₂ at pH= 8, 1?mol·L^-1 NaH₂PO₄ at pH= 5, and 1?mol·L^-1 HCl to investigate four binding phases of arsenic (i.e., water soluble, ion-exchangeable, strongly-bound, and precipitates) in sediments at different layers in different cross-sections along the river. The average ratio of arsenite (As(III)) to arsenate (As(V)) was found to decrease from 0.74:1 in river water to 0.48:1 in sediment, owing to its higher affinity toward As(V) than As(III). The content of arsenic in the sediments was relatively low and the maximum content was observed to be 36.3?mg·kg^-1 for As(III) and 97.5?mg·kg^-1 for As(V). As(III) and As(V) showed different binding phases in sediments, and the average fractions of these four species were determined to be 0.09, 0.11, 0.17, and 0.63 for As(III) and 0.03, 0.14, 0.63, and 0.20 for As(V), respectively. For all the sediment samples, the content of arsenic showed no relationship with the characteristics of the sediments such as the particle diameter, the content of organic carbon, Fe, and Mn, although a negative correlation with particle diameter was observed for the sediments in the uppermost 2-cm layer. The unexpected emergent As incident results in the high content of total arsenic in the surface sediment, which may be potential secondary source to the elevated As levels in surface water.     

Radioactive Isotopes of Strontium, Caesium and Plutonium in Sediments of the Northern Adriatic Sea

Sediment samples of different strata (0-3 and 12-15 cm) were collected between 1990 and 1992 during seasonal cruises in the Northern Adriatic Sea. A complete mapping of the Sr-90, Cs-137, Pu-238 and Pu-239(240) concentrations was obtained for samples covering a wide area, stretching from the Gulf of Trieste towards the Ancona shoreline. Sr-90 concentrations varied between 1.5 and 6.5 Bq kg^-1 dw, Cs-137 was in the range 0.9-38.9 Bq kg^-1 dw, Pu-239(240) in the range 0.08-1.5 Bq kg^-1 dw and Pu-238 around 0.03 Bq kg^-1 dw. Special reference was also put on the comparison between the off-shore environment and data obtained from samples collected inside the Po river delta. in spite of the major accumulation of Cs-137 inside the estuarine environment, higher concentrations of strontium and plutonium isotopes were detected in the offshore environment.     

Contributions of adsorption,bioreduction and desorption to uranium immobilization by extracellular polymeric substances

● EPS immobilizes U(VI) via adsorption, bioreduction and desorption. ● This work provides a framework to quantify the three immobilization processes. ● The non-equilibrium adsorption of U follows pseudo-second-order kinetics. ● The equilibrium adsorption of U followed Langmuir and Freundlich isotherms. Hexavalent uranium (U(VI)) can be immobilized by various microbes. The role of extracellular polymeric substances (EPS) in U(VI) immobilization has not been quantified. This work provides a model framework to quantify the contributions of three processes involved in EPS-mediated U(VI) immobilization: adsorption, bioreduction and desorption. Loosely associated EPS was extracted from a pure bacterial strain, Klebsiella sp. J1, and then exposed to H₂ and O₂ (no bioreduction control) to immobilize U(VI) in batch experiments. U(VI) immobilization was faster when exposed to H₂ than O₂ and stabilized at 94% for H₂ and 85% for O₂, respectively. The non-equilibrium data from the H₂ experiments were best simulated by a kinetic model consisting of pseudo-second-order adsorption (k_a = 2.87 × 10⁻³ g EPS·(mg U)⁻¹·min⁻¹), first-order bioreduction (k_b = 0.112 min⁻¹) and first-order desorption (k_d = 7.00 × 10⁻³ min⁻¹) and fitted the experimental data with R² of 0.999. While adsorption was dominant in the first minute of the experiments with H₂, bioreduction was dominant from the second minute to the 50^th min. After 50 min, adsorption was negligible, and bioreduction was balanced by desorption. This work also provides the first set of equilibrium data for U(VI) adsorption by EPS alone. The equilibrium experiments with O₂ were well simulated by both the Langmuir isotherm and the Freundlich isotherm, suggesting multiple mechanisms involved in the interactions between U(VI) and EPS. The thermodynamic study indicated that the adsorption of U(VI) onto EPS was endothermic, spontaneous and favorable at higher temperatures.     

Sorption and desorption of pymetrozine on six Chinese soils

Pymetrozine is a selective insecticide with a unique chemical structure and mode to control hemipteran and homopteran. While pymetrozine has brought great benefits to crop production by killing insects, its residues in soil may have a detrimental effect on environment. Therefore, it is of great importance to investigate its behaviors in soil. In this study, the sorption and desorption of pymetrozine on six Chinese soils were investigated using a batch equilibrium approach to understand its mobile behavior in the soils. Both sorption and desorption isotherms of pymetrozine were in good agreement with the Freundlich model. The sorption coefficient K_F varied between 3.37 and 58.32 mL∙g⁻¹ and the sorption isotherms were nonlinear, with 1/n ranging from 0.57 to 0.91. A regression equation was proposed to predict the sorption of pymetrozine on six different soil samples: log K_F = 4.3708 − 4.5709 × log (pH in 0.01mol·L⁻¹ CaCl₂) + 0.4700 × log OC% + 0.0057 × sand (%) + 0.0022 × CEC(clay), with R² = 0.9982. The organic carbon content of soil positively affected the sorption of pymetrozine, but soil pH had a negative effect on the sorption. Additionally, effects of CaCl₂ concentration, soil to solution ratio and pesticide form were investigated. The sorption was promoted with an increase in soil to solution ratio and a decrease in CaCl₂ concentration. The possible variation of the five formulated products of pymetrozine was also investigated.     

Removal of fluoride from water using titanium-based adsorbents

Three adsorbents including TiO₂, Ti-Ce, and Ti-La hybrid oxides were prepared to remove fluoride from aqueous solution. The Ti-Ce and Ti-La hybrid adsorbents obtained by the hydrolysis-precipitation method had much higher sorption capacity for fluoride than the TiO₂ adsorbent prepared through hydrolysis. Rare earth (Ce and La) oxides and TiO₂ exhibited a synergistic effect in the hybrid adsorbents for fluoride sorption. The sorption equilibrium of fluoride on the three adsorbents was achieved within 4 h, and the pseudo-second-order model described the sorption kinetics well. The sorption isotherms fitted the Langmuir model well, and the adsorption capacities of fluoride on the Ti-Ce and Ti-La adsorbents were about 9.6 and 15.1 mg·g^-1, respectively, at the equilibrium fluoride concentration of 1.0 mg·L^-1, much higher than the 1.7 mg·g^-1 on the TiO₂. The sorption capacities of fluoride on the three adsorbents decreased significantly when the solution pH increased from 3 to 9.5. The electrostatic interaction played an important role in fluoride removal by the three adsorbents, and Fourier transform infrared (FTIR) analysis indicated that the hydroxyl groups on the adsorbent surface were involved in fluoride adsorption.     

Removing phosphorus from aqueous solutions by using iron-modified corn straw biochar

Iron-modified corn straw biochar was used as an adsorbent to remove phosphorus from agricultural runoff. When agricultural runoffs with a total phosphorus (TP) concentration of 1.86 mg·L⁻¹ to 2.47 mg·L⁻¹ were filtered at a hydraulic retention time of 2 h through a filtration column packed with the modified biochar, a TP removal efficiency of over 99% and an effluent TP concentration of less than 0.02 mg·L⁻¹ were achieved. The isotherms of the phosphorus adsorption by the modified biochar fitted the Freundlich equation better than the Langmuir equation. The mechanism of the phosphorus adsorbed by the modified biochar was analyzed by using various technologies, i.e. scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The results indicated that the surface of the modified biochar was covered by small iron granules, which were identified as Fe₃O₄. The results also showed that new iron oxides were formed on the surface of the modified biochar after the adsorption of phosphorus. Moreover, new bonds of Fe-O-P and P-C were found, which suggested that the new iron oxides tend to be Fe₅(PO₄)₄(OH)₃. Aside from removing phosphorus, adding the modified biochar into soil also improved soil productivity. When the modified biochar-to-soil rate was 5%, the stem, root, and bean of broad bean plants demonstrated increased growth rates of 91%, 64%, and 165%, respectively.     

Biotransformations of Chlorophenols in River Sediments

The accumulation of chlorophenols, including 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP), from river sediments from southern Taiwan were studied. Through simple or more exhaustive extractions, the results showed that 99% of the samples containing 2,4,6-TCP and PCP could be removed by simple extraction. the concentrations were found to range from non-detectable to 16.60 ngg¹ for 2,4,6-TCP and to 25.02 ngg¹ for PCP. Partition coefficients (K_p) were 0.71, 0.74 mlg¹ for 2,4,6-TCP, 1.35 and 1.41 mlg¹ for PCP. Biodegradation by DCP-adapted or unadapted anaerobes in sediment was carried out. During 21 days' incubation, the complete degradation time for 2,4,6-TCP in DCP-adapted anaerobic, unadapted anaerobic, and unadapted aerobic conditions were found to be 9, 10, 12 days for N3 sediment, and 8, 10, 11 days for N6 sediment, respectively; for PCP it was 19 days, without degradation, 14 days for N3 sediment, and 13, 17, 10 days for N6 sediment, respectively. the biodegradable products were identified as 2,3,4,5-tetrachlorophenol (2,3,4,5-TeCP), 3,4,5-TCP, 3,5-DCP, 3-MCP, phenol, methylphenol, and benzoate for PCP, and 2,4-DCP, 4-MCP, phenol, methylphenol, and benzoate for 2,4,6-TCP.     

Oxidation and biotoxicity assessment of microcystin-LR using different AOPs based on UV,O3 and H2O2

MC-LR removal performances under different AOPs were compared systematically. Higher removal efficiency and synergistic effects were obtained by combined process. The acute biotoxicity raised in different degrees after oxidation. Microcystin-LR attracts attention due to its high toxicity, high concentration and high frequency. The removal characteristics of UV/H₂O₂ and O₃/H₂O₂ advanced oxidation processes and their individual process for MC-LR were investigated and compared in this study. Both the removal efficiencies and rates of MC-LR as well as the biotoxicity of degradation products was analyzed. Results showed that the UV/H₂O₂ process and O₃/H₂O₂ were effective methods to remove MC-LR from water, and they two performed better than UV-, O₃-, H₂O₂-alone processes under the same conditions. The effects of UV intensity, H₂O₂ concentration and O₃ concentration on the removal performance were explored. The synergistic effects between UV and H₂O₂, O₃ and H₂O₂ were observed. UV dosage of 1800 mJ·cm⁻² was required to remove 90% of 100 mg·L⁻¹ MC-LR, which amount significantly decreased to 500 mJ·cm⁻² when 1.7 mg·L⁻¹ H₂O₂ was added. 0.25 mg·L⁻¹ O₃, or 0.125 mg·L⁻¹ O₃ with 1.7 mg·L⁻¹ H₂O₂ was needed to reach 90% removal efficiency. Furthermore, the biotoxicity results about these UV/H₂O₂, O₃/H₂O₂ and O₃-alone processes all present rising trends with oxidation degree of MC-LR. Biotoxicity of solution, equivalent to 0.01 mg·L⁻¹ Zn²⁺, raised to 0.05 mg·L⁻¹ Zn²⁺ after UV/H₂O₂ or O₃/H₂O₂ reaction. This phenomenon may be attributed to the aldehydes and ketones with small molecular weight generated during reaction. Advice about the selection of MC-LR removal methods in real cases was provided.     

Retention of 137cesium in acid sulphate soils of South Central Thailand

Adsorption and desorption of ¹³⁷Cs by acid sulphate soils from the Nakhon Nayok province, South Central Plain of Thailand located near the Ongkarak Nuclear Research Center (ONRC) were investigated using a batch equilibration technique. The influence of added limestone (12 and 18 tons ha^-1) on ¹³⁷Cs adsorption-desorption was studied. Based on Freundlich isotherms, both adsorption and desorption of ¹³⁷Cs were nonlinear. A large portion (98.26-99.97%) of added ¹³⁷Cs (3.7 × 10³-7.03 × 10⁵ Bq l^-1) was sorbed by the soils with or without added lime. The higher lime treatments, however, favoured stronger adsorption of ¹³⁷Cs as compared with soil with no lime, which was supported by higher K_ads values. The addition of lime, the cation exchange capacity and pH of the soil increased and hence favoured the stronger adsorption of ¹³⁷Cs. Acid sulphate soils with a high clay content, medium to high organic matter, high CEC, and predominant clay types consisting of a mixture of illite, kaolinite, and montmorillonite were the main soil factors contributing to the high ¹³⁷Cs adsorption capacity. Competing cations such as NH₄⁺, K⁺, Na⁺, Ca²⁺, and Mg²⁺ had little influence on ¹³⁷Cs adsorption as compared with liming, where a significant positive correlation between K_ads and soil pH was observed. The ¹³⁷Cs adsorption-desorption characteristics of the acid sulphate soils studied exhibited a very strong irreversible sorption pattern. Only a small portion (0.09-0.58%) of ¹³⁷Cs adsorbed at the highest added initial ¹³⁷Cs concentration was desorbed by four successive soil extractions. Results clearly demonstrated that Nakhon Nayok province acid sulphate soils have a high ¹³⁷Cs adsorption capacity, which limits the ¹³⁷Cs bioavailability.     

硝酸钙投加频次对污泥生物调理效果的影响

在接种了反硝化菌的剩余污泥中投加硝酸钙药剂,利用反硝化菌消耗NO3-进行反硝化作用去除污泥中易生物降解的有机物,利用Ca2＋的中和、架桥作用,改善污泥的脱水性能.固定NO;总投加浓度为100 mg?g-1 TS,在6d的时间内,按1次、2次、3次、6次的投加频次向污泥中投加硝酸钙.结果表明,1次投加对污泥脱水性能的提升...     

Wastewater-nitrogen removal using polylactic acid/starch as carbon source: Optimization of operating parameters using response surface methodology

The use of PLA/starch blends for nitrogen removal was achieved. The influence of different operating parameters on responses was verified using RSM. The conditions for desired responses were successfully optimized simultaneously. Blends material may have a promising application prospect in the future. Nitrogen removal from ammonium-containing wastewater was conducted using polylactic acid (PLA)/starch blends as carbon source and carrier for functional bacteria. The exclusive and interactive influences of operating parameters (i.e., temperature, pH, stirring rate, and PLA-to-starch ratio (PLA proportion)) on nitrification (Y₁), denitrification (Y₂), and COD release rates (Y₃) were investigated through response surface methodology. Experimental results indicated that nitrogen removal could be successfully achieved in the PLA/starch blends through simultaneous nitrification and denitrification. The carbon release rate of the blends was controllable. The sensitivity of Y₁, Y₂, and Y₃ to different operating parameters also differed. The sequence for each response was as follows: for Y₁, pH>stirring rate>PLA proportion>temperature; for Y₂, pH>PLA proportion>temperature>stirring rate; and for Y₃, stirring rate>pH>PLA proportion>temperature. In this study, the following optimum conditions were observed: temperature, 32.0°C; pH 7.7; stirring rate, 200.0 r·min^-1; and PLA proportion, 0.4. Under these conditions, Y₁, Y₂, and Y₃ were 134.0 μg-N·g-blend^-1·h^-1, 160.9 μg-N·g-blend^-1·h^-1, and 7.6 × 10³ μg-O·g-blend^-1·h^-1, respectively. These results suggested that the PLA/starch blends may be an ideal packing material for nitrogen removal.     

Effect of metal ion-doping on characteristics and photocatalytic activity of TiO2 nanotubes for removal of humic acid from water

The effect of ion-doping on TiO₂ nanotubes were investigated to obtain the optimal TiO₂ nanotubes for the effective decomposition of humic acids (HA) through O₃/UV/ion-doped TiO₂ process. The experimental results show that changing the calcination temperature, which changed the weight fractions of the anatase phase, the average crystallite sizes, the Brunauer-Emmett-Teller surface area, and the energy band gap of the catalyst, affected the photocatalytic activity of the catalyst. The ionic radius, valence state, and configuration of the dopant also affected the photocatalytic activity. The photocatalytic activities of the catalysts on HA removal increased when Ag⁺, Al³⁺, Cu²⁺, Fe³⁺, V⁵⁺, and Zn²⁺ were doped into the TiO₂ nanotubes, whereas such activities decreased as a result of Mn²⁺- and Ni²⁺-doping. In the presence of 1.0 at.% Fe³⁺-doped TiO₂ nanotubes calcined at 550°C, the removal efficiency of HA was 80% with a pseudo-first-order rate constant of 0.158 min⁻¹. Fe³⁺ in TiO₂ could increase the generation of ·OH, which could remove HA. However, Fe³⁺ in water cannot function as a shallow trapping site for electrons or holes.     

Controlled sintering for cadmium stabilization by beneficially using the dredged river sediment

● Dredged river sediment was proved as a ceramic precursor rather than a solid waste. ● Cd was stabilized in Cd-Al-Si-O phases at low temperatures via sediment addition. ● < 5% of Cd was leached out from sintered products even after a prolonged time. ● A strategy was proposed to simultaneously reuse wastes and stabilize heavy metals. Cd-bearing solid wastes are considered to be a serious threat to the environment, and effective strategies for their treatment are urgently needed. Ceramic sintering has been considered as a promising method for efficiently incorporating heavy metal-containing solid wastes into various ceramic products. Mineral-rich dredged river sediment, especially Al and Si-containing oxides, can be treated as alternative ceramic precursors rather than being disposed of as solid wastes. To examine the feasibility of using waste sediment for Cd stabilization and the phase transition mechanisms, this study conducted a sintering scheme for the mixtures of CdO and dredged river sediment with different (Al+Si):Cd mole ratios. Detailed investigations have been performed on phases transformation, Cd incorporation mechanisms, elemental distribution, and leaching behaviors of the sintered products. Results showed that Cd incorporation and transformation in the sintered products were influenced by the mole ratio of (Al+Si):Cd. Among the high-Cd series ((Al+Si):Cd = 6:1), CdSiO₃, Cd₂SiO₄, CdAl₂(SiO₄)₂ and Cd₂Al₂Si₂O₉ were predominant Cd-containing product phases, while Cd₂Al₂Si₂O₉ was replaced by CdAl₄O₇ when the mole ratio of (Al+Si):Cd was 12:1 (low-Cd series). Cd was efficiently stabilized in both reaction series after being sintered at ≥ 900 °C, with < 5% leached ratio even after a prolonged leaching time, indicating excellent long-term Cd stabilization. This study demonstrated that both Cd-containing phases and the amorphous Al-/Si-containing matrices all played critical roles in Cd stabilization. A promising strategy can be proposed to simultaneously reuse the solid waste as ceramic precursors and stabilize heavy metals in the ceramic products.     

Competitive adsorption and desorption of copper and lead in some soil of North China

The competitive adsorption and desorption of Pb(II) and Cu(II) ions in the soil of three sites in North China were investigated using single and binary metal solutions with 0.01 mol·L^-1 CaCl₂ as background electrolyte. The desorption isotherms of Pb(II) and Cu(II) were similar to the adsorption isotherms, which can be fitted well by Freundlich equation (R₂>0.96). The soil in the three sites had greater sorption capacities for Pb(II) than Cu(II), which was affected strongly by the soil characteristics. In the binary metal solution containing 1∶1 molar ratio of Pb(II) and Cu(II), the total amount of Pb(II) and Cu(II) adsorption was affected by the simultaneous presence of the two metal ions, indicating the existence of adsorption competition between the two metal ions. Fourier transform infrared (FT-IR) spectroscopy was used to investigate the interaction between soil and metal ions, and the results revealed that the carboxyl and hydroxyl groups in the soil were the main binding sites of metal ions.     

Comparing the adsorption behaviors of Cd,Cu and Pb from water onto Fe-Mn binary oxide,MnO2 and FeOOH

The adsorption potential of FMBO, FeOOH, MnO₂ for the removal of Cd²⁺, Cu²⁺ and Pb²⁺ in aqueous systems was investigated in this study. Comparing to FMBO and FeOOH, MnO₂ offered a much higher removal capacity towards the three metal ions. The maximal adsorption capacity of MnO₂ for Cd²⁺, Cu²⁺ and Pb²⁺ were 1.23, 2.25 and 2.60 mmol·g^-1, respectively. And that for FMBO were 0.37, 1.13, and 1.18 mmol·g^-1 and for FeOOH were 0.11, 0.86 and 0.48 mmol·g^-1, respectively. The adsorption behaviors of the three metal ions on the three adsorbents were all significantly affected by pH values and heavy metal removal efficiency increased with pH increased. The Langmuir and Freundlich adsorption models were used to describe the adsorption equilibrium of the three metal ions onto the three adsorbents. Results showed that the adsorption equilibrium data fitted well to Langmuir isotherm and this indicated that adsorption of metal ions occurred on the three metal oxides adsorbents limited to the formation of a monolayer. More negative charged of MnO₂ surface than that of FMBO and FeOOH could be ascribed by lower pH_iep of MnO₂ than that of FMBO and FeOOH and this could contribute to more binding sites on MnO₂ surface than that of FMBO and FeOOH. The higher metal ions uptake by MnO₂ than FMBO and FeOOH could be well explained by the surface charge mechanism.