Solidification and stabilization of cadmium ions in sand-cement-clay mixture

This study was carried out to test the ability of a mixture of sand, cement and clay for immobilizing cadmium ions from leaching out into water resources. Various samples with different mass ratios for this mixture were tested to determine their efficiency for adsorbing cadmium. The compressive test, cation exchange capacity (CEC), adsorption equilibrium and leaching test were applied to each sample. The sample that showed the highest cation exchange capacity with 53.1 meq/100 g and compressive strength with 11.05 N/mm2 consists of 25% sand, 50% cement and 25% clay. The equilibrium data for Cd2+ removal using this sample showed a multilayer adsorption, which could be fitted using Brunauer-Emmett-Teller adsorption isotherm model with a regression coefficient of 0.999. The maximum cadmium uptake obtained from this model was 82.618 mg/g solid. The mobility of Cd2+ in acidic solution drawn-off after 18 h of initial mixing was 66.06 mg when the solid sample initially contains 6.0 g Cd2+. This value decreased to 14.33 mg when only 1.0 g Cd2+ was initially spiked in the sample. Introducing clay into this sample enhanced its sorption capacity while the presence of sand and cement enhanced its compressive strength.     

Effect of ambient conditions on simultaneous growth and bioaccumulation of mercuric ion by genetically engineered E. coli JM109

Genetically engineered E. coli JM109, namely M1, which expressed both Hg(2+) transport system and metallothionein, was tested for its capability of simultaneous growth and bioaccumulation of Hg(2+) under low nutritional circumstances. The influential factors of ambient conditions, e.g. initial concentrations of mercuric ion, ionic strength, the presence of metal chelators and other coexisting metal ions were investigated. Hg(2+) bioaccumulation behavior of M1 proved to be well coupled with its growth. NaCl was essential to the growth of M1. Of all tested NaCl concentrations, 0.04 mol/L was optimal. The presence of 0.1 mol/L CaCl(2) or MgCl(2) could promote the growth of M1 and keep the Hg(2+) removal ratio high, but the growth of M1 was inhibited seriously as the concentration of CaCl(2) or MgCl(2) reached 0.3 mol/L. Chelator EDTA had a significant influence on M1 growth and Hg(2+) bioaccumulation, while the effect of citration was little. The presence of other coexisting metal ions inhibited the growth of M1. The influential order was as follows: Cd(2+)>Zn(2+)> or =Cu(2+)>Pb(2+)>Ni(2+). However, only Cd(2+) and Cu(2+) posed obviously adverse effects on Hg(2+) bioaccumulation during the SG&B process.     

Biosorption of lead(II) and cadmium(II) by protonated Sargassum glaucescens biomass in a continuous packed bed column

Biosorption of lead(II) and cadmium(II) from aqueous solutions by protonated Sargassum glaucescens biomass was studied in a continuous packed bed column. The selective uptake of Pb2+ and Cd2+ was investigated in a binary system with initial concentration of 1 mM for each metal ion. The selective uptake capacities of Pb2+ and Cd2+ at complete exhaustion point were obtained 1.18 and 0.22 mmol/g, respectively; therefore, the biosorbent showed much higher relative affinity for Pb2+ than for Cd2+. The optimum range of empty bed contact time (EBCT) was identified as 5-10 min in the packed bed column. The efficiency of biosorbent regeneration by 0.1 M HCl was achieved about 60%, so that the maximum uptake capacity of Pb2+ by the regenerated biomass was determined to be 0.75 mmol/g while the same value for the original biomass was 1.24 mmol/g. The Thomas model was found in a suitable fitness with the experimental data (R2 > 0.90 and % < 50%) at all different operation stages. Monitoring of pH in the effluent of the column presented the simultaneous release of H+ with the uptake of heavy metals; hence, ion exchange was confirmed to be one of the main biosorption mechanisms.     

Ecotoxicological studies of CdS nanoparticles on photosynthetic microorganisms

The potential ecotoxicity of nanosized cadmium sulfide (CdS), synthesized by the polyol process, was investigated using common Anabaena flos-aquae cyanobacteria and Euglena gracilis euglenoid microalgae. The photosynthetic activities of these microorganisms, after addition of free Cd2+ ions and CdS nanoparticles, varied with the presence of tri-n-octylphosphine oxide (TOPO) used to protect surface particle to avoid toxicity and also to control particle size and shape during the synthesis. The nanoparticle concentration was varied from 10(-3) to 5 x 10(-4) M. It was observed that the cadmium concentration, the addition of TOPO protective agent and the particle dissolution process in the culture medium play an important role during the ecotoxicological tests. Viability tests were followed by PAM fluorimetry. Cd2+ ions were very toxic for Anabaena flos aquae. The same behavior was observed after contact with CdS and CdS-TOPO nanoparticles. However, for Euglena gracilis, the photosynthetic activity was stable for more than 1 month in the presence of Cd2+ ions. Moreover, it was observed that the toxicity varies with the concentration of CdS and CdS-TOPO nanoparticles, both kind of nanoparticles are toxic for this microorganism. Transmission electron microscopy (TEM) analyses of microorganisms ultrathin sections showed that polysaccharides produced by Anabaena flos-aquae, after contact with CdS and CdS-TOPO nanoparticles, protect the microalgae against particle internalization. Only some particles were observed inside the cells. Moreover, the nanoparticle internalization was observed after contact with all nanoparticles in the presence of Euglena gracilis by endocytosis. All nanoparticles are inside vesicles formed by the cells.     

Cadmium-induced physiological response and antioxidant enzyme changes in the novel cadmium accumulator, Tagetes patula

The accumulation and effect of cadmium (Cd) on the growth and enzymatic activities changes of antioxidants in Tagetes patula, French marigold, were investigated to reveal the physiological mechanisms corresponding to its Cd tolerance and accumulation. Hydroponically grown T. patula plants were treated with different concentrations of Cd (0, 10, 25, 50 μM Cd Cl(2)) at various regime of times. T. patula accumulated Cd to a maximum of 450 mg Cd kg(-1) dry weight (DW) in shoot and 3500 mg Cd kg(-1) DW in root after 14 days' exposure at 10 and 50 μM Cd Cl(2), respectively. The translocation factors of Cd were greater than 1 in plants exposed to 10 μM Cd Cl(2). Toxic effects were gradually observed with increasing Cd concentration (25 and 50 μM) accompanied with the reduction of biomass, chlorophyll content, decrease of cell viability and the increase level of lipid peroxidation. In leaves of T. patula, the activities of ascorbate peroxidase (APX), glutathione reductase (GR) and superoxide dismutase (SOD) were induced by Cd. However, in roots, activities of APX, GR, SOD and catalase (CAT) were significantly reduced by 25 and 50 μM Cd treatment but not 10 μM Cd. In-gel zymography analysis revealed that Cd induced the enzymatic activities of APX, MnSOD, CuZnSOD and different isozymes of GR in leaves. These results indicate that T. patula is a novel Cd accumulator and able to tolerate with Cd-induced toxicity by activation of its antioxidative defense system.     

Recovery of Cu(II) and Cd(II) by a chelating resin containing aspartate groups

A chelating resin, crosslinked poly(glycidyl methacrylate-aspartic acid) (PASP), was synthesized by anchoring sodium aspartate to crosslinked poly(glycidyl methacrylate) for the recovery of Cu2+ and Cd2+ from aqueous solutions. The resin was characterized by Fourier transform infrared spectroscopy, scanning electron microscope and mass balance. In non-competitive conditions, the adsorptions tended toward equilibrium at 60 min and the equilibrium adsorption capacities were 1.40 and 1.28 mmol/gPASP for Cu2+ and Cd2+, respectively. The adsorption isothermals of the metal ions by PASP followed the Freundlich isotherm. Adsorption of Cu2+ was affected slightly in the presence of NaNO3 (0-0.3M) but the uptake of Cd2+ decreased significantly in the same condition. Except pH> or =4.0, the adsorption capacity of each metal ion decreased with lowering of solution pH. The reusability of PASP in adsorptions was investigated for five successive adsorption-desorption operations. When the pH of Cu2+/Cd2+ mixture was 2 or 2.5, the competitive adsorption tests confirmed this resin had good adsorption selectivity for Cu2+ with the coexistence of Cd2+.     

Removal of lead(II) and cadmium(II) from aqueous solutions using grape stalk waste

The sorption of lead and cadmium from aqueous solutions by grape stalk waste (a by-product of wine production) was investigated. The effects of the contact time, pH of the solution, ionic medium, initial metal concentration, other metal ions present and ligands were studied in batch experiments at 20 degrees C. Maximum sorption for both metals was found to occur at an initial pH of around 5.5. The equilibrium process was described well by the Langmuir isotherm model, with maximum grape stalk sorption capacities of 0.241 and 0.248 mmol g(-1) for Pb(II) and Cd(II), respectively, at pH around 5.5. Kinetic studies showed good correlation coefficients for a pseudo-second-order kinetic model. The presence of NaCl and NaClO(4) in the solution caused a reduction in Pb and Cd sorption, the latter being more strongly suppressed. The presence of other metals in the uptake process did not affect the removal of Pb, while the Cd uptake was much reduced. HCl or EDTA solutions were able to desorb lead from the grape stalks completely, while an approximately 65% desorption yield was obtained for cadmium. From the results obtained it seems that other mechanisms, such as surface complexation and electrostatic interactions, must be involved in the metal sorption in addition to ion exchange.     

Cadmium fixation by synthetic hydroxyapatite in aqueous solution--thermal behaviour

This study deals with the mechanism of the cadmium uptake by synthetic hydroxyapatite (HA: Ca10(PO4)6(OH)2) in aqueous solution. The rate of cadmium fixation by hydroxyapatite was investigated at 10 and 50 degrees C using batch experiments. Inductively coupled plasma atomic emission spectrometry, X-ray diffraction, FT-IR spectroscopy and electron microscopy were used to characterize the starting HA and the samples. The thermal behaviour of the powders was determined with the help of three thermoanalytical techniques (TGA, DTA, and MS) and temperature programmed X-ray diffraction. Cadmium immobilization kinetics can be divided into two steps: substitution of Ca2+ ions by Cd2+ in the HA lattice at the particle's surface, followed by their incorporation into the hydroxyapatite bulk. This results in the formation of an apatite solid solution, which is very important because in this way decontamination and storage can be performed with the same material.     

Suppressive effects of magnesium oxide materials on cadmium uptake and accumulation into rice grains I: Characteristics of magnesium oxide materials for cadmium sorption

The objective of this study is to assess the applicability of a commercial magnesium oxide (MgO) and a composite material containing MgO and natural minerals ('MgO-SH-A') as the soil amendments for suppression of cadmium (Cd) uptake and accumulation into rice grains. Firstly, the mineralogical and physicochemical properties, soil neutralizing capacities and Cd sorption characteristics of these materials were investigated. Both materials were strongly alkaline and possessed large surface areas. The X-ray diffraction pattern of MgO-SH-A indicated the presence of MgO and a magnesium-silicate mineral (antigorite) as the main components. MgO-SH-A showed a milder soil neutralizing capacity as compared to commercial MgO. The sorptions of Cd on commercial MgO and MgO-SH-A both fitted Langmuir isotherm. The maximum Cd sorption capacity of commercial MgO (46.8 mmol g(-1) DW) was higher than that of MgO-SH-A (5.87 mmol g(-1) DW), although the latter material showed higher affinity to Cd as compared to the former one. The dominant reaction involved in the Cd sorptions was suggested to be precipitation of Cd(OH)2 on the material surface. About 40% of Cd sorbed on MgO-SH-A was resistant to desorption by 0.1 M HCl, implying that this portion was strongly retained on the material surface.     

Cadmium tolerance and accumulation characteristics of Bidens pilosa L. as a potential Cd-hyperaccumulator

Recently, researchers are becoming interested in using hyperaccumulators for decontamination of heavy metal polluted soils, whereas few species that hyperaccumulate cadmium (Cd) has been identified in the plant kingdom. In this study, the physiological mechanisms at the seedling stage and growth responses and Cd uptake and accumulation at flowering and mature stages of Bidens pilosa L. under Cd treatments were investigated. At the seedling stage, when soil Cd was lower than 16mgkg(-1), the plant did not show obvious symptom of phytoxicity, and the alterations of chlorophyll (CHL), superoxide dismutase (SOD), peroxidase (POD), malondialdehyde (MDA), and soluble protein (SP) did not have significant differences when compared with the control. At the flowering and mature stages, under low Cd treatments (相似文献   

Removal and recovery of heavy metals from aqueous solution using Ulmus carpinifolia and Fraxinus excelsior tree leaves

Ulmus carpinifolia and Fraxinus excelsior tree leaves, which are in great supply in Iran, were evaluated for removal of Pb(II), Cd(II) and Cu(II) from aqueous solution. Maximum biosorption capacities for U. carpinifolia and F. excelsior were measured as 201.1, 172.0 mg/g for Pb(II), 80.0, 67.2 mg/g for Cd(II) and 69.5, 33.1 mg/g for Cu(II), respectively. For both sorbents the most effective pH range was found to be 2-5 for Pb(II), 3-5 for Cd(II) and 4-5 for Cu(II). Metal ion biosorption increased as the ratio of metal solution to the biomass quantity decreased. Conversely, biosorption/g biosorbent decreased as the quantity of biomass increased. The biosorption of metal ions increased as the initial metal concentration increased. Biosorption capacities of metal ions were in the following order: Pb(II)>Cd(II)>Cu(II). The equilibrium data for Pb(II) and Cu(II) best fit the Langmuir adsorption isotherm model. Kinetic studies showed that the biosorption rates could be described by a second-order expression. Both the sorbents could be regenerated using 0.2 M HCl during repeated biosorption-desorption cycles with no loss in the efficiency of the Cu(II) removal observed. Biosorption of Pb(II), Cd(II) and Cu(II) was investigated in the presence of Na, K, Mg and Ca ions. The results from these studies show a novel way of using U. carpinifolia and F. excelsior tree leaves to remove Pb(II), Cd(II) and Cu(II) from metal-polluted waters.     

Adsorption of Cd(II) and Cu(II) from aqueous solution by carbonate hydroxylapatite derived from eggshell waste

Carbonate hydroxylapatite (CHAP) synthesized by using eggshell waste as raw material has been investigated as metal adsorption for Cd(II) and Cu(II) from aqueous solutions. The effect of various parameters on adsorption process such as contact time, solution pH, amount of CHAP and initial concentration of metal ions was studied at room temperature to optimize the conditions for maximum adsorption. The results showed that the removal efficiency of Cd(II) and Cu(II) by CHAP could reach 94 and 93.17%, respectively, when the initial Cd(II) concentration 80 mg/L and Cu(II) 60 mg/L and the liquid/solid ratio was 2.5 g/L. The equilibrium sorption data for single metal systems at room temperature could be described by the Langmuir and Freundlich isotherm models. The highest value of Langmuir maximum uptake, (b), was found for cadmium (111.1mg/g) and copper (142.86 mg/g). Similar Freundlich empirical constants, K, were obtained for cadmium (2.224) and copper (7.925). Ion exchange and surface adsorption might be involved in the adsorption process of cadmium and copper. Desorption experiments showed that CaCl2, NaCl, acetic acid and ultrasonic were not efficient enough to desorb substantial amount of metal ions from the CHAP. The results obtained show that CHAP has a high affinity to cadmium and copper.     

Conformational behavior of DNA-templated CdS inorganic nanowire

We describe the conformational behavior and morphological control of DNA-mineralized CdS nanowires in a bulk solution. The conformational behavior of individual double-stranded DNA in the presence of cadmium ions and stoichiometric mixtures of cadmium ions and sulfide ions was directly visualized by fluorescence microscopy. It was found that in the presence of mixtures of cadmium ions and sulfide ions, DNA molecules exhibit a conformational transition from an elongated coil to a compacted state. Mineralized DNA nanowires possess a significant conformational freedom at a microscale, and flexibility in the micro- and nanodimensions. The density of the inorganic material on the nanowire can be controlled by varying the concentrations and the molar ratio of Na(2)S to Cd(ClO(4))(2).     

Insights into cadmium induced physiological and ultra-structural disorders in Juncus effusus L. and its remediation through exogenous citric acid

This study appraised cadmium (Cd) toxicity stress in wetland plant Juncus effusus, and explored its potential for Cd phytoextraction through chelators (citric acid and EDTA). Cadmium altered morphological and physiological attributes of J. effusus as reflected by growth retardation. Citric acid in the presence of 100 μM Cd significantly countered Cd toxicity by improving plant growth. Elevated Cd concentrations reduced translocation factor that was increased under application of both chelators. Citric acid enhanced Cd accumulation, while EDTA reduced its uptake. Cadmium induced oxidative stress modified the antioxidative enzyme activity. Both levels of citric acid (2.5 and 5.0 mM) and lower EDTA concentration (2.5 mM) helped plants to overcome oxidative stress by enhancing their antioxidative enzyme activities. Cadmium damaged the root cells through cytoplasmic shrinkage and metal deposition. Citric acid restored structure and shape of root cells and eliminated plasmolysis; whereas, EDTA exhibited no positive effect on it. Shoot cells remained unaffected under Cd treatment alone or with citric acid except for chloroplast swelling. Only EDTA promoted starch accumulation in chloroplast reflecting its negative impact on cellular structure. It concludes that Cd and EDTA induce structural and morphological damage in J. effusus; while, citric acid ameliorates Cd toxicity stress.     

Cadmium sorption by EPSs produced by anaerobic sludge under sulfate-reducing conditions

This study showed that EPS produced by anaerobic sludge under sulfate-reducing bacteria was effective in removing Cd(2+) from solution. The sorption data could be described by the Freundlich isotherm model. The q(m) derived from the Langmuir isotherm model was up to 2720 mg/g EPSs. The presence of copper and nickel ions had significantly reduced the cadmium sorption by EPS and the presence of zinc had little effect. Analysis of FTIR spectra demonstrated that C-O-C of polysaccharides at 1150-1030 cm(-1), group of the amide(I), CH(2) group of the lipids, carboxyl and -OH groups of proteins and polysaccharides were involved in cadmium binding, of which the -OH groups and the C-O-C group of polysaccharides played a major role in cadmium sorption by EPSs.     

Chitosan selectivity for removing cadmium (II), copper (II), and lead (II) from aqueous phase: pH and organic matter effect

The aim of this study was to investigate the selectivity of chitosan for cadmium, copper and lead in the presence and absence of natural organic matter (NOM) in different pH solutions. Adsorption isotherms of one and three adsorbates at initial concentration of 5-100mg/L were carried out in batch reactors at pH 4, 5, or 7 and 25 degrees C in reactive and clarified water. The chitosan employed had a MW of 107.8 x 10(3)g/mol and degree of acetylation (DA) of 33.7%. The chitosan adsorption capacity at pH 4 in reactive water was 0.036, 0.016, 0.010mmol/g for Pb(2+), Cd(2+), and Cu(2+), respectively, and it decreased for Pb(2+) and Cd(2+) in clarified water. Conversely, experiments carried out in clarified water showed that the cadmium adsorption capacity of chitosan was enhanced about three times by the presence of NOM at pH 7: an adsorption mechanism was proposed. Furthermore, it was found that the biosorbent selectivity, in both reactive and clarified water at pH 4, was as follows Cu(2+)>Cd(2+)>Pb(2+). Finally, the preliminary desorption experiments of Cd(2+) conducted at pH 2 and 3 reported 68 and 44.8% of metal desorbed, which indicated that the adsorption mechanism occurred by electrostatic interactions and covalent bonds.     

Immobilization of aqueous cadmium by addition of phosphates

In situ immobilization of heavy metals in polluted soils using phosphates leads to formation of products which are highly insoluble and thermodynamically stable over a broad pH and Eh range. In this research effectivity of Cd ions immobilization (initial [Cdaq]-4.800 mM) from aqueous solutions by different phosphorus compounds (K2HPO4, NH4H2PO4 and "Polifoska 15" fertilizer) was compared at pH in the range 4.00-9.00 and for reaction times 2-1440 h. The highest reduction of cadmium concentration (>99%), owing due to the formation of cadmium phosphates, was observed for all used phosphorus sources within pH range of 6.75-9.00. Uptake of cadmium for pH< or =5.00 did not exceed 80% and was lowest in the reaction with "Polifoska 15" fertilizer (28.25%). Identification of phases formed in the reactions using XRD, FTIR and SEM-EDS-EBSD was carried out. It was noticed that crystallinity of formed solid decreased with pH increase. Formation of Cd5H2(PO4)4.4H2O was observed in acidic conditions (pH< or =5.00), at pH approximately 7.00 mixture of following cadmium phosphates Cd(H2PO4)2, Cd3(PO4)2 and Cd5H2(PO4)4.4H2O was formed. Amorphic cadmium phosphates were noticed in alkaline conditions (pH>8.50).     

Characterization of Cd- and Pb-resistant fungal endophyte Mucor sp. CBRF59 isolated from rapes (Brassica chinensis) in a metal-contaminated soil

To better understand the characteristics of fungal endophytes in the development of effective phytoremediation of heavy metals, the objectives of this study were to isolate a fungal endophyte tolerant Cd and Pb from rape roots grown in a heavy metal-contaminated soil, to characterize the metal-resistant fungal endophyte, and to assess its potential applications in removal of Cd and Pb from contaminated solutions and experimental soil. The isolate CBRF59 was identified as Mucor sp. based on morphological characteristics and phylogenetic analysis. From a Cd solution of 2.0mM, the maximum biosorption capacity of Cd by dead biomass of Mucor sp. CBRF59 was 108 mg g(-1). Under the same conditions, the bioaccumulation capacity of Cd by active biomass of the strain was 173 mg g(-1). The bioaccumulation capacity of Pb by active biomass of the strain was significantly lower than that by dead biomass in the initial Pb concentrations from 1.0 to 2.0mM. The ratio of Pb to Cd and initial pH values in the mixed Cd+Pb solutions affected the bioaccumulation and biosorption capacities of the metals by CBRF59. The addition of the active mycelia of CBRF59 significantly increased the availability of soil Pb and Cd by 77% and 11.5-fold, respectively. The results showed that the endophytic fungus was potentially applicable for the decontamination of metal-polluted media.     

含镉羟基磷灰石的形成及其稳定性

采用液相共沉淀方法合成了不同镉摩尔含量X_Cd(即: Cd/(Ca+Cd))的镉羟基磷灰石. 通过XRD, FT-IR, FE-SEM, TG-DTG-DSC-MS和TCLP对产物的组成、形貌、热稳定性及化学稳定性进行了探讨. 结果表明, 随着X_Cd的增加, Cd²⁺进入到羟基磷灰石的晶格中依次形成Ca_3.9(Ca_4.7Cd_0.7)(PO₄)₆(OH)_1.8, Ca_3.8(Ca_4.1Cd_0.73)(PO₄_₆(OH)_1.8, Ca_3.6(Ca_4.5Cd_0.76)(PO₄)₆(OH)_1.6和Cd₅(PO₄)₃OH; 这些产物在500℃以下均可稳定存在, 且热稳定性随着X_Cd的增加明显提高; 毒性浸出结果显示, Cd²⁺能够进入到羟基磷灰石的晶格中, 但产物的化学稳定性不高.     

Experimental and thermodynamic investigation on transfer of cadmium influenced by sulfur and chlorine during municipal solid waste (MSW) incineration

We used two approaches to investigate the impact of sulfur and chlorine compounds on transfer of a semivolatile heavy metal, cadmium, during municipal solid waste (MSW) incineration: experiments using a tubular furnace reactor and thermodynamic equilibrium calculations. Artificial wastes representative of typical MSW in China with and without the presence of sulfur and chlorine compounds were combusted at 850 degrees C, and the partitioning of Cd among bottom ash, fly ash and flue gas was quantified. The results indicate that sulfur compounds in the elemental form and reduced state could stabilize Cd in the form of CdS due to local reducing environment, while sulfur in the oxidized forms slightly increased Cd volatilization during incineration. In contrast, the presence of chlorine compounds significantly increased the partitioning of Cd on fly ash. Chemical equilibrium calculations show that sulfur binds with Cd and alters Cd speciation at low temperatures (<700 degrees C), while chlorine significantly increases the volatilization of Cd through formation of volatile CdCl(2) and thus its partitioning on the fly ash between 400 and 1000 degrees C. The equilibrium calculation results also suggest that SiO(2)- and Al(2)O(3)-containing minerals could function as sorbents stabilizing Cd as condensed phase solids (CdSiO(3) and CdAl(2)O(4)). These findings provide useful information on understanding the partitioning behavior of Cd and can help development of strategies to control volatilization of Cd during MSW incineration.