Biosorption mechanism of Cr （Ⅳ） onto cells of Synechococcus sp.

The biosorption mechanism of Cr （Ⅳ） ions on Synechococcus sp. biosorbent was studied by analyzing the biosorption kinetics as well as speciation change and bond formation during the biosorption process. The kinetics study shows that the adsorption process of Cr （Ⅳ） consists of a very fast stage in the first several minutes, in which more than half of the saturation adsorption is attained, and a slower stage that approximately follows the first order kinetic model, basically Freundlich isotherm models were observed. Comparative studies of FT-LR spectra of K2Cr2O7, free cells of Synechococcus sp., and Cr-bound cells of Synechococcus sp show that the speciation of chromium that binds to the cells ofSynechococcus sp. is Cr （Ⅲ）, instead of Cr （Ⅳ）, and the carboxylic, alcoholic, amido and amino groups may be involved in the binding of Cr （Ⅲ）. Integrative analyses of the surface electric potential, the effect of pH value on adsorption behavior of Cr （Ⅵ）, and the results of FT-IR show that the biosorption of Cr （Ⅵ） follows two subsequent steps, biosorption of Cr2O7 ^2- by electrostatical force at the protonated active sites and reduction of Cr2O7^2- to Cr^3＋ by the reductive groups on the surface of the biosorbents.     

Rapid biosorption and reduction removal of Cr（Ⅵ） from aqueous solution by dried seaweeds

Four types of common seaweeds（Laminaria japonica,Undaria pinnatifida,Porphyra haitanensis,and Gracilaria lemaneiformis） were examined to remove Cr（Ⅵ） ions from aqueous solution.The experimental parameters that affected the biosorption process including pH,biomass dosage,contact time and temperature were investigated via batch experiments.The surface characteristics of seaweeds before and after Cr（Ⅵ） adsorption were studied with scanning electron microscopy and Fourier transform infrared spectroscopy.The results show that an initial solution with the pH of 1.0 is most favorable for Cr（Ⅵ） adsorption.Rapid adsorption is observed in the initial stage and adsorption equilibrium state is reached within 1 h.The adsorption efficiency by Porphyra haitanensis is the maximum among four types of seaweed powders,followed by Laminaria japonica and Undaria pinnatifida with biosorption efficiency up to 90%.The removal rate of Gracilaria lemaneiformis is less than 60%.The kinetic data obtained using the seaweeds are found to follow pseudo-second order kinetic model.Experimental sorption data adequately correlate with the Langmuir model.FTIR indicates that amino and carboxyl groups play an important role in the process of Cr（Ⅵ） adsorption and a large percentage of Cr（Ⅵ） ions are reduced by reductive groups on the surface of seaweeds.     

Single-step synthesis of magnetic chitosan composites and application for chromate(Cr(Ⅵ)) removal

Magnetic chitosan composites(Fe3O4@chitosan) were synthesized in one single-step, characterized and applied in Cr(VI) removal from water. With the increase of loading proportion of chitosan, Cr(Ⅵ) adsorption capacity of Fe3O4@chitosan composites increased from 10.771 to 21.040 mg/g. The optimum adsorption capacities of Cr(VI) on Fe3O4@chitosan-3 were found in a pH range of 3.0-5.0. Kinetic study results show that the adsorption process follows pseudo-second-order model, indicating that the rate-limiting step in the adsorption of Cr(Ⅵ) involves chemisorptions. Moreover, FT-IR spectra analysis confirms that the amine and hydroxyl groups of chitosan are predominantly responsible for binding. Results from this work demonstrate that the prepared Fe3O4@chitosan composites possess great potential in Cr(Ⅵ) removal from contaminated water.     

Removal of anionic ions from single material solution by bauxite tailings modified with FeCl3·6H2O

The adsorbabilities of the unmodified and modified bauxite tailings for Cr(Ⅵ), As(Ⅴ) and F(Ⅰ) ions were investigated. Batch experiments were carried out to determine the removal rate as a function of adsorbent dosage, solution pH value and shaking time. The results show that the maximum removal rates of Cr(Ⅵ), As(Ⅴ) and F(Ⅰ) are respectively 99%, 99% and 90% by using the modified bauxite tailings. The isoelectric point of the unmodified bauxite railings is 3.6, and that of the modified bauxite tailings is 5.0, which shifts to lower pH values in Cr(Ⅵ) solution. This indicates a specific adsorption of the anionic species on the modified bauxite tailings. A new band of Cr2O72- appears in the FTIR, showing that Cr(Ⅵ) is adsorbed on the modified bauxite tailings in the form of chemistry adsorption. The adsorption data of Cr(Ⅵ) on the modified bauxite tailings are well described by Freundlich model. The investigations of kinetic models show that pseudo-second-order kinetic model provides the best correlation for the experimental data.     

Removal of anionic ions from single material solution by bauxite tailings modified with FeCl3·6H2O

The adsorbabilities of the unmodified and modified bauxite tailings for Cr（Ⅵ）, As（Ⅴ） and F（Ⅰ） ions were investigated. Batch experiments were carried out to determine the removal rate as a function of adsorbent dosage, solution pH value and shaking time. The results show that the maximum removal rates of Cr（Ⅵ）, As（Ⅴ） and F（Ⅰ ） are respectively 99%, 99% and 90% by using the modified bauxite tailings. The isoelectric point of the unmodified bauxite tailings is 3.6, and that of the modified bauxite tailings is 5.0, which shifts to lower pH values in Cr（Ⅵ） solution. This indicates a specific adsorption of the anionic species on the modified bauxite railings. A new band of Cr2O72 appears in the FTIR, showing that Cr（Ⅵ） is adsorbed on the modified bauxite railings in the form of chemistry adsorption. The adsorption data of Cr（Ⅵ） on the modified bauxite tailings are well described by Freundlich model. The investigations of kinetic models show that pseudo-second-order kinetic model provides the best correlation for the experimental data.     

Removal of lead in wastewater by immobilized inactivated cells of Rhizopus oligosporus

A novel technology for lead removal with nonliving Rhizopus oligosporus immobilized in calcium alginate was studied. The results show that the main influencing factors include pH value and interfering cations. pH value has different effects on biosorption of various heavy metals and lead adsorption can be proceeded by controlling pH value in a range of 2-5; interfering cations especially Cu( Ⅱ ) can make the adsorption amount of Pb( Ⅱ ) decrease by immobilized Rhizopus oligosporus. Desorption efficiency of different eluants and kinetics were investigated. Citrate the reaction equilibrium reaches 3 h. Immobilized biomass keeps high lead biosorption capacity after five cycles of regeneration.     

Adsorbability of Mycobacterium phlei on hematite surface

The adsorption of microorganisms on the mineral surface is the base of microorganisms that are considered as mineral processing reagents. The principles of the use of a highly hydrophobic and negatively charged bacterium, Mycobacterium phlei, as a flocculating-flotating agent for finely divided hematite were investigated. The flocculating-floating recovery is strongly dependent on the pH and the dosage of the bacterium. Generally the pH should be controlled over the range of 5.5-7, and the dosage should be controlled about 16 mg/L. The infrared spectrometry analysis indicates that the six functional groups of M. phlei, substituted aromatic compound groups, -（CH2） n-groups, -CH2（-CH3） groups, carbonyl groups, aromatic hydrocarbon groups, and carboxyl groups, are on the hematite surface, among which the first five ones contribute physical adsorption and only the carboxyl groups provide chemisorption. Microscopic analysis reveals that the dimensions and tight aggregation degree of the flocs of hematite particles formed by M. phlei are also impacted by the pH and the content of M. phlei in flotation.     

Competitive adsorption of heavy metal ions on peat

The uptake capacities, and the adsorption kinetics, of copper, Cu(Ⅱ), nickel, Ni(Ⅱ), and cadmium, Cd(Ⅱ), on peat have been studied under static conditions. The results show that the adsorption rates are rapid: equilibrium is reached in twenty minutes. The adsorption of copper, nickel and cadmium is pH dependent over the pH range from 2 to 6. The adsorption kinetics can be excellently described by the Elovich kinetic equation. The adsorption isotherm fits a Langmuir model very well. The adsorption capacifies follow the order Cu2 ＞Ni2 ＞Cd2 in single-component systems and the competitive adsorption capacities fall in the decreasing order Cu2 ＞ Ni2 ＞Cd2 in multi-component systems. The adsorption capacities of these three heavy metal ions on peat are consistent with their observed competitive adsorption capacities.     

Adsorption of copper（ Ⅱ ） and chromium（Ⅵ） on diaspore

The adsorption of Cu（ Ⅱ ） and Cr（Ⅵ） on diaspore was studied with the help of X-ray diffraction analysis, BET measurement, zeta potential measurement and atomic adsorption spectrometry. The adsorption equilibrium almost reaches within 60 min. The adsorption isotherms of Cu（ Ⅱ ） and Cr（Ⅵ） could be well described by the Langmuir equation. The adsorption capacities of Cu（Ⅱ） and Cr（Ⅵ） are 1.944 and 1.292 mg/g, respectively. The adsorption percentage of Cr（Ⅱ ） increases with the increment of solution pH, but the adsorption percentage of Cr（Ⅵ） decreases. This could be explained by zeta potential theoretical and electrostatic attraction between metal ions and diaspore surface.     

Removal of Pb(Ⅱ) from aqueous solution by magnetic humic acid/chitosan composites

A novel adsorbent named magnetic humic acid/chitosan composite(M-HA/Cs) was synthesized by decorating humic acid/chitosan composites with Fe_3O_4 nanoparticles. The adsorption capacity of M-HA/Cs was 1.5 times that of MCs. The effects of solution p H, initial concentration of Pb(Ⅱ) ions and adsorption temperature on Pb(Ⅱ) removal were examined in a batch system and further optimized using Box-Behnken analysis. The recommended optimum conditions are initial Pb(Ⅱ) concentration of 139.90 mg/L, initial pH of 4.98, and temperature of 43.97 oC. The adsorption processes could be well described by pseudo-second-order and Elovich models. Isotherm studies reveal that the adsorption process follows Sips and Temkin models. The thermodynamic study indicats that the adsorption process is spontaneous and exothermic. The potential mechanism of Pb(Ⅱ) on M-HA/Cs at pH 5 may be surface electrostatic attraction, coordination and hydrogen bonding.     

Isothermal Adsorption Characteristics and Kinetics of Cr Ions onto Ettringite

The isothermal absorption properties and kinetic model of Cr(VI) and Cr(III) onto ettringite were investigated using the batch adsorption method. IR analysis was used to study the difference and mechanism of the adsorption of chromium ions with different valence states. The results show that the adsorption of Cr(III) onto ettringite at 20 ℃ agrees with Langmuir's isothermal model. The ion binding stability was significantly greater than that of Cr(VI). While the adsorption of Cr(VI) onto ettringite agrees with Freundlich's isothermal model, the D-R model fits the adsorption isotherms of two types of valence Cr(R20.994). It can be concluded that the adsorption of Cr(III) onto ettringite is mainly by chemical adsorption and that the adsorption of Cr(VI) onto ettringite is mainly by physical adsorption. Dynamic model fitting and model parameter analyses show that the adsorption of Cr(III) onto ettringite agrees with the pseudo second order kinetics model given by Lagergren. The formation of chemical bonds is the main factor causing the fast adsorption. Cr(VI) adsorption is mainly dominated by liquid film diffusion, and the adsorption rate is much slower than that of Cr(III) adsorption.     

Chemieal Strueturcs and Adsorptive Behaviors of Superplastieizers on β-C2S

The chemical structures of four types of superplasticizers （SPs） and their adsorptive behaviors on β-C2S were investigated. The adsorption properties of SPs on β-C2S were measured and the relationship between the adsorption quantity and the specific surface of β-C2S was analyzed. The experimental results show that the adsorption quantity increases with the surface area increase of β-C2S, but the adsorption quantity per surface area is similar, which means that the main adsorbent is β-C2S itself. Polycarboxylic ester （PCE） showed the highest adsorption amount on β-C2S, followed by β-naphthalene sulfonates （NSF） and formaldehyde-acetone condensates sulfonates （FAS）, amino sulphonate （AS） showed the least adsorption amount on β-C2S. PCE affected the surface potential of β-C2S particles in water differently in comparison with other types of SPs. The adsorption capacity of SPs on β-C2S is determined by factors such as molecular structure, functional groups and molecular weight of SPs.     

Adsorption of copper(Ⅱ) and chromium(Ⅵ) on diaspore

The adsorption of Cu(Ⅱ) and Cr(Ⅵ) on diaspore was studied with the help of X-ray diffraction analysis, BET measurement, zeta potential measurement and atomic adsorption spectrometry. The adsorption equilibrium almost reaches within 60 min. The adsorption isotherms of Cu(Ⅱ) and Cr(Ⅵ) could be well described by the Langmuir equation. The adsorption capacities of Cu(Ⅱ) and Cr(Ⅵ) are 1.944 and 1.292 mg/g, respectively. The adsorption percentage of Cr(Ⅱ) increases with the increment of solution pH, but the adsorption percentage of Cr(Ⅵ) decreases. This could be explained by zeta potential theoretical and electrostatic attraction between metal ions and diaspore surface.     

Effect of Nb on the transformation kinetics of low carbon （manganese） steel during deformation of undercooled austenite

The hot compression tests using Gleeble 1500 were performed by varying the true strain up to 1.6 （80% reduction） in Nbfree and Nb-microalloyed steels. The effect of Nb addition on the transformation kinetics during deformation of undercooled austenite was investigated. It was found that as compared with Nb-free steel, the transformation incubation period of Nb-bearing steel was prolonged and the transformation kinetics curves parallelly moved to higher strain because of the solute Nb drag effect. Studies on kinetics also showed that the deformation-enhanced ferrite transformation （DEFT） of the two steels were composed of three stages, which can be expressed by the J-M-A equations individually. However, the parameter n related to the mode of nucleation and growth is somewhat different in the first and second stages of the two steels, and the same in the third stage for both the steels corresponding to the nucleation Of retained austenite.     

Adsorption of congo red onto lignocellulose/montmorillonite nanocomposite

Lignocellulose/montmorillonite (LNC/MMT) nanocomposites were prepared and characterized by FTIR and XRD. The adsorption of congo red (CR) on LNC/MMT nanocomposite was studied in detail. The effects of contact temperature, pH value of the dye solutions, contact time and concentration of dye solutions on the adsorption capacities of lignocellulose (LNC), montmorillonite (MMT) and the nanocomposite were investigated. The adsorption kinetics and isotherms and adsorption thermodynamics of the nanocomposite for CR were also studied. The results show that the adsorption capacity of LNC/MMT nanocomosite is higher than that of LNC and MMT. All the adsorption processes fit very well with the pseudo-second-order and the Langmuir equation. From thermodynamic studies, it is seen that the adsorption is spontaneous and endothermic.     

Biosorption of methylene blue by chemically modified cellulose waste

Citric acid modifi ed cellulose waste（CMCW） was prepared via esterifi cation and used as a low-cost biosorbent for the removal of methylene blue（MB） from aqueous solutions. The effects of biosorbent concentration, initial pH of MB solution, biosorption temperature, contact time, and initial MB concentration on the biosorption of MB were investigated using batch biosorption technique under static conditions. The experimental results showed that CMCW exhibited excellent biosorption characteristics for MB. The maximum biosorption capacity of MB was up to 214.5 mg/g at an adsorption temperature of 293 K. The removal rate of MB onto CMCW reached the maximum at pH〉4 and the biosorption reached an equilibrium at about 50 min. The kinetic data can be described well with the pseudo-second-order model and the isotherm data was found to fi t the Langmuir isotherm with a monolayer adsorption capacity of 211.42 mg/g. The biosorption appears to be controlled by chemisorption and may be involved in surface adsorption and pore diffusion during the whole biosorption process.     

Adsorption behavior of Pb^2＋ and Cd^2＋ ions on bauxite flotation tailings

The adsorption behavior of Pb^2＋ and Cd^2＋ ions on bauxite flotation tailings was investigated to demonstrate the adsorptivity of the bauxite flotation tailings. The adsorption percentage of Pb^2＋ and Cd^2＋ ions as a function of adsorbent dosage, solution pH value and shaking time were determined by batch experiments. The maximum adsorption percentage of 99.93% for Pb^2＋ ions and 99.75% for Cd^2＋ ions were obtained by using bauxite flotation tailings as adsorbent. The methods, such as zeta potentials, specific surface area measurements and the analysis of adsorption kinetics, were introduced to analyze the adsorption mechanisms of the Pb^2＋ ions on bauxite flotation tailings. The isoelectric point of bauxite flotation tailings shifts from 3.6 to 5.6 in the presence of Pb^2＋ ions. The specific surface area of bauxite flotation tailings changes from 12.57 to 20.63 m^2/g after the adsorption of Pb^2＋ ions. These results indicate that a specific adsorption of the cation species happens on the surface of bauxite flotation tailings. Adsorption data of Pb^2＋ ions on the surface of bauxite flotation tailings can be well described by Langmuir model, and the pseudo-second-order kinetic model provides the best correlation for the adsorption data of Pb^2＋ and Cd^2＋ ions on bauxite flotation tailings.     

Adsorption of Cu and Ni Ions from Aqueous Solutions by Commercial Activated Carbon and the Reutilization in Glass Coloration

Toxic Cu(Ⅱ) and Ni(Ⅱ) ions in aqueous solutions were adsorbed by microporous activated carbon(AC). The adsorption isotherm and kinetics correlation coefficients indicate that the adsorption of Cu(Ⅱ) and Ni(Ⅱ) ions on the AC fits the pseudo second-order rate model and Langmuir adsorption model. The used AC adsorbents containing the adsorbed Cu and Ni ions were used as colorant in glass preparation. The coloration effect of Cu ions was influenced by the carbon absorbent included in the glass batch due to the reduction phenomenon, while the coloration of Ni ions was not affected.     

Synthesis and adsorption properties for Au(Ⅲ) of alkoxycarbonyl thiourea resin

A novel alkoxycarbonyl thiourea resin(ATR) was synthesized by monomer polymerization of oxydiethane-2,1-diyl dicarbonisothiocyanatidate and polyethylene polyamine, and characterized by FT-IR. The adsorption properties of ATR were investigated by batch test. The adsorption capacities for Au(Ⅲ), Ag(Ⅰ), Cu(Ⅱ), Zn(Ⅱ), Fe(Ⅲ), Ca(Ⅱ) and Mg(Ⅱ) are 4.65, 4.40,0.40, 0.90, 0.86, 0.0080 and 0.016 mmol/g, respectively, when the adsorption condition is as follows: contact time 24 h, temperature 30 ℃, initial concentration of Au(Ⅲ) 5.08 mmol/L and that of other metals 0.10 mol/L, and concentration of acid 1.0 mol/L. The adsorption capacity for Au(Ⅲ) increases with the increase of contact time, temperature and initial concentration of Au(Ⅲ). The capacity after five adsorption-desorption cycles remains 90% that of the first time, and the separation factors of ATR for binary metal ion solutions are larger than 995, indicating that ATR is of good regeneration property and selectivity. XPS results show that the functional atoms of ATR supply electrons for Au and coordinate with Au during the adsorption.     

Microwave-assisted extraction of polysaccharides from solanum nigrum

The microwave-assisted method was used to extract polysaccharides from solanum nigrum. The optimum experimental parameters, mechanism of the extraction and the effect of microwave-assisted extraction process on the structures of polysaccharides were investigated. The extract was analyzed by the modified phenol-sulfuric acid method at 490 nm. The optimum experimental parameters were obtained by orthogonal experiments as follows： extraction time 15 min, microwave radiation power 455 W and the process ratio of materials mass to solvent volume 1 ： 20. The results show that compared with the conventional reflux extraction, the microwave-assisted extraction has a higher yield in shorter time, with no effect on the finally obtained polysaccharides as seen from the FT-IR spectra. The scanning electron microscopy images reveal that the mechanism of the extraction is related to the structural changes of the plant cells in different extracting conditions.