Different strategies for recovering metals from CARON process residue

The capacity of Acidithiobacillus thiooxidans DMS 11478 to recover the heavy metals contained in the residue obtained from the CARON process has been evaluated. Different bioreactor configurations were studied: a two-stage batch system and two semi-continuous systems (stirred-tank reactor leaching and column leaching). In the two-stage system, 46.8% Co, 36.0% Mg, 26.3% Mn and 22.3% Ni were solubilised after 6h of contact between the residue and the bacteria-free bioacid. The results obtained with the stirred-tank reactor and the column were similar: 50% of the Mg and Co and 40% of the Mn and Ni were solubilised after thirty one days. The operation in the column reactor allowed the solid-liquid ratio to be increased and the pH to be kept at low values (<1.0). Recirculation of the leachate in the column had a positive effect on metal removal; at sixty five days (optimum time) the solubilisation levels were as follows: 86% Co, 83% Mg, 72% Mn and Ni, 62% Fe and 23% Cr. The results corroborate the feasibility of the systems studied for the leaching of metals from CARON process residue and these methodologies can be considered viable for the recovery of valuable metals.     

In situ degradation of phenol and promotion of plant growth in contaminated environments by a single Pseudomonas aeruginosa strain

For bioremediation of contaminated environments, a bacterial strain, SZH16, was isolated and found to reduce phenol concentration in a selective medium. Using the reaction vessel containing the soil mixed with phenol and bacteria, we found that the single strain degraded efficiently the phenol level in soil samples. The strain was identified as Pseudomonas aeruginosa on the basis of biochemical tests and by comparison of 16S rDNA sequences, and phosphate solubilization and IAA production were not observed in the strain. Simultaneous examination of the role of strain SZH16 in the plant growth and phenol biodegradation was performed. Results showed that inoculation of the single strain in the phenol-spiked soil resulted in corn growth promotion and in situ phenol degradation and the increase in plant biomass correlated with the decrease in phenol content. Colonization experiments showed that the population of the SZH16 strain remained relatively constant. All these findings indicated that the corn growth promotion might be due to reduction in phytotoxicity, a result of phenol biodegradation by the single strain SZH16. Furthermore, the strain was found to stimulate corn growth and reduce phenol concentration simultaneously in phenol-containing water, and even historically contaminated field soils. It is attractive for environment remediation and agronomic applications.     

Use of biogenic and abiotic elemental selenium nanospheres to sequester elemental mercury released from mercury contaminated museum specimens

Mercuric chloride solutions have historically been used as pesticides to prevent bacterial, fungal and insect degradation of herbarium specimens. The University of Manchester museum herbarium contains over a million specimens from numerous collections, many preserved using HgCl(2) and its transformation to Hg(v)(0) represents a health risk to herbarium staff. Elevated mercury concentrations in work areas (～ 1.7 μg m(-3)) are below advised safe levels (<25 μg m(-3)) but up to 90 μg m(-3) mercury vapour was measured in specimen boxes, representing a risk when accessing the samples. Mercury vapour release correlated strongly with temperature. Mercury salts were observed on botanical specimens at concentrations up to 2.85 wt% (bulk); XPS, SEM-EDS and XANES suggest the presence of residual HgCl(2) as well as cubic HgS and HgO. Bacterially derived, amorphous nanospheres of elemental selenium effectively sequestered the mercury vapour in the specimen boxes (up to 19 wt%), and analysis demonstrated that the Hg(v)(0) was oxidised by the selenium to form stable HgSe on the surface of the nanospheres. Biogenic Se(0) can be used to reduce Hg(v)(0) in long term, slow release environments.     

Thorough removal of inorganic and organic mercury from aqueous solutions by adsorption on Lemna minor powder

The adsorption ability of duckweed (Lemna minor) powders for removing inorganic and organic mercury (methyl and ethyl mercury) has been studied using cold vapour atomic absorption spectrometry. The optimal adsorption conditions were: (a) the pH value of the solution 7.0 for inorganic and ethyl mercury, 9.0 for methyl mercury, and (b) equilibrium adsorption time 10, 20, and 40 min for inorganic mercury, methyl mercury, and ethyl mercury, respectively. After adsorption by L. minor powder for 40 min, when the initial concentrations of inorganic and organic mercury were under 12.0 μg L⁻¹ and 50.0 μg L⁻¹, respectively, the residual concentrations of mercury could meet the criterion of drinking water (1.0 μg L⁻¹) and the permitted discharge limit of wastewater (10.0 μg L⁻¹) set by China and USEPA, respectively. Thorough removal of both inorganic and organic mercury from aqueous solutions was reported for the first time. The significant adsorption sites were C–O–P and phosphate groups by the surface electrostatic interactions with aqueous inorganic and organic mercury cations, and then the selective adsorption was resulted from the strong chelating interaction between amine groups and mercury on the surface of L. minor cells.     

Metal accumulation potential of wild plants in tannery effluent contaminated soil of Kasur, Pakistan: field trials for toxic metal cleanup using Suaeda fruticosa

The tannery effluent contaminated lands, adjacent to Depalpur Road, Kasur, Pakistan, have been rendered infertile due to long term effluent logging from the leather industry. The area has been colonized by twelve plant species among which Suaeda fruticosa, Salvadora oleoides and Calatropis procera have been found to be the most common and high biomass producing plants. S. fruticosa was subjected to further experimentation because of its high biomass and phytoextraction capabilities for metals. The pot and field experiments were carried out simultaneously. Pot experiments were conducted using the same field soil in column pots with stoppard bottoms to obtain the leachate. EDTA treatment caused a greater solubility of Cr in the soil pore water. In higher doses more amount of the heavy metal was leached. The increase in the amount of EDTA significantly caused a decrease in the biomass of plants without toxicity symptoms. A higher biomass of plants was observed in the field as compared to the pot experiment. The greatest amount of Na was accumulated by leaves of S. fruticosa followed by stem and roots. Similarly, the greatest amount of Cr was bioaccumulated by leaves of S. fruticosa, but followed by roots and then stem. S. fruticosa can be employed in rehabilitation of tannery effluent contaminated soil using small doses of EDTA.     

Promotional effects of carbon nanotubes on V2O5/TiO2 for NOX removal

A series of V₂O₅/TiO₂-carbon nanotube (CNT) catalysts were synthesized by sol-gel method, and their activities for NO_X removal were compared. A catalytic promotional effect was observed by adding CNTs to V₂O₅/TiO₂. The catalyst V₂O₅/TiO₂-CNTs (10 wt.%) showed an NO_X removal efficiency of 89% at 300 °C under a GHSV of 22,500 h⁻¹. Based on X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, NH₃-temperature-programmed desorption, temperature-programmed reduction, Brunauer-Emmett-Teller surface area measurements, differential scanning calorimetry, and thermogravimetric analysis, the increased acidity and reducibility, which could promote NH₃ adsorption and oxidation of NO to NO₂, respectively, contributed to this promotion.     

Biosorption of heavy metals and uranium by starfish and Pseudomonas putida

Biosorption of heavy metals and uranium from contaminated wastewaters may represent an innovative purification process. This study investigates the removal ability of unit mass of Pseudomonas putida and starfish for lead, cadmium, and uranium by quantifying the adsorption capacity. The adsorption of heavy metals and uranium by the samples was influenced by pH, and increased with increasing Pb, Cd, and U concentrations. Dead cells adsorbed the largest quantity of all heavy metals than live cells and starfish. The adsorption capacity followed the order: U(VI)>Pb>Cd. The results also suggest that bacterial membrane cells can be used successfully in the treatment of high strength metal-contaminated wastewaters.     

Potential of Sargassum wightii biomass for copper(II) removal from aqueous solutions: application of different mathematical models to batch and continuous biosorption data

This paper reports biosorption of copper(II) ions onto Sargassum wightii biomass in batch and continuous mode of operation. Batch experiments were fundamentally aimed to determine the favorable pH for copper(II) biosorption. Langmuir model was used to describe the copper(II) biosorption isotherm and maximum uptake of 115 mg/g was obtained at pH 4.5. Continuous experiments in a packed column (2 cm i.d. and 35 cm height) were performed to study the influence of bed height, flow rate and inlet solute concentration on copper(II) biosorption. The highest bed height (25 cm), lowest flow rate (5 ml/min) and highest inlet Cu(II) concentration (100 mg/l) resulted in highest copper(II) uptake of 52.6 mg/g, compared to other conditions examined. Column data obtained at different conditions were described using the Thomas, Yoon-Nelson and modified dose-response models. All three models were able to predict breakthrough curves; in particular, the breakthrough curve prediction by the Thomas and Yoon-Nelson models were found to be very satisfactory. Also, the well-established design model, the Bed depth-service time (BDST) model was used to analyze the experimental data. The BDST model plot at 5 ml/min (flow rate) and 100 mg/l (inlet solute concentration) was used to predict bed depth-service time data at different conditions. The BDST model predicted values always coincide with experimental values with high correlation coefficients.     

A scheme for solving strongly coupled chemical reaction equations appearing in the removal of SO2 and NOx from flue gases

The removal of NO_x from mixtures of NO-NO₂-N₂ and NO-NO₂-O₂-H₂O is discussed theoretically in this study, and the removal of ₂SO and xNO is further discussed when a gas system of NO_x-N₂-O₂-H₂O contains CO₂ and SO₂. The involved chemical reaction rate equations in the process of SO₂/NO_x removal are solved numerically using Treanor's method, in which a scheme separating chemical reactions into fast and slow groups has been proposed for improving the numerical stability. Numerical results show that the contribution of ion reactions to xNO removal is negligible, and that high temperature is not beneficial for the NO oxidation. However, high concentration of O₂ is conducive to the NO oxidation. Addition of water facilitates the NO_x removal, and increasing water vapor concentration enhances the NO_x removal efficiency; inclusion of CO₂ and SO₂ into the system favors the NO removal.     

A novel biosorbent for dye removal: extracellular polymeric substance (EPS) of Proteus mirabilis TJ-1

This paper deals with the extracellular polymeric substance (EPS) of Proteus mirabilis TJ-1 used as a novel biosorbent to remove dye from aqueous solution in batch systems. As a widely used and hazardous dye, basic blue 54 (BB54) was chosen as the model dye to examine the adsorption performance of the EPS. The effects of pH, initial dye concentration, contact time and temperature on the sorption of BB54 to the EPS were examined. At various initial dye concentrations (50-400 mg/L), the batch sorption equilibrium can be obtained in only 5 min. Kinetic studies suggested that the sorption followed the internal transport mechanism. According to the Langmuir model, the maximum BB54 uptake of 2.005 g/g was obtained. Chemical analysis of the EPS indicated the presence of protein (30.9%, w/w) and acid polysaccharide (63.1%, w/w). Scanning electron microscopy (SEM) images showed that the EPS with a crystal-linear structure was whole enwrapped by adsorbed dye molecules. FTIR spectrum result revealed the presence of adsorbing groups such as carboxyl, hydroxyl and amino groups in the EPS. High-molecular weight of the EPS with more binding-sites and stronger van der Waals forces together with its specific construct leads to the excellent performance of dye adsorption. The EPS shows potential board application as a biosorbent for both environmental protection and dye recovery.     

The use of protonated Sargassum muticum as biosorbent for cadmium removal in a fixed-bed column

The protonated Sargassum muticum seaweed was studied as a possible biosorbent for cadmium removal in a fixed-bed column. The experiments were conducted in order to determine the effect of flow rate (0.42, 5, 10 and 20 mL min(-1)) and bed height (0.6 and 15.3 cm for the lowest flow rate or 7.4, 13 and 16.6 cm for the others) on breakthrough curves behaviour. The determined breakthrough and exhaustion times increased with the diminution in flow rate and with the increase in bed height. The maximum cadmium uptake capacity, obtained from the area below adsorbed cadmium concentration versus time curves, was found to remain practically constant with bed depth and flow rate. The bed depth service time (BDST) model was applied to analyse experimental data, determining the characteristic process parameters. The optimal lowest sorbent usage rate was evaluated at 2 min contact time and the minimum bed height values necessary to prevent the effluent solution concentration from exceeding 0.02 mg L(-1) at zero time were 5.3, 6.9 and 7.5 cm for flow rates of 5, 10 and 20 mL min(-1), respectively. Several empirical models proposed in the literature (Bohart-Adams, Yan, Belter and Chu models) were investigated in order to obtain the best fit of column data, describing in a simple manner the breakthrough curves. A correlation between model parameters and the variables implied in the process was attempted.     

Ni(II) removal from aqueous solutions using cone biomass of Thuja orientalis

The biomass of terrestrial-plant materials has high removal capacities for a number of heavy metal ions. The Ni(II) biosorption capacity of the cone biomass of Thuja orientalis was studied in the batch mode. The biosorption equilibrium level was determined as a function of contact time, pH, temperature, agitation speed at several initial metal ion and adsorbent concentrations. The removal of Ni(II) from aqueous solutions increased with adsorbent concentration, temperature and agitation speed of the solution were increased. The biosorption process was very fast; 90% of biosorption occurred within 3 min and equilibrium was reached at around 7 min. It is found that the biosorption of Ni(II) on the cone biomass was correlated well (R2 > 0.99) with the Langmuir equation as compared to Freundlich, BET Temkin and D-R isotherm equation under the concentration range studied. According to Langmuir isotherm, the monolayer saturation capacity (Q(o)) is 12.42 mg g(-1). The pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models were applied to test the experimental data for initial Ni(II) and cone biomass concentrations. The pseudo-second-order kinetic model provided the best correlation of the used experimental data compared to the pseudo-first-order and intraparticle diffusion kinetic models. The activation energy of biosorption (E(a)) was determined as 36.85 kJ mol(-1) using the Arrhenius equation. This study indicated that the cone biomass of T. orientalis can be used as an effective and environmentally friendly adsorbent for the treatment of Ni(II) containing aqueous solutions.     

Screening for novel antibacterial agents based on the activities of compounds on metabolism of Escherichia coli: a microcalorimetric study

The emergence and prevalence of resistance to antibacterial agents is a pressing threaten for human health. Screening for novel antibacterial agents targeting not only multiplying but also non-multiplying bacteria using appropriate approach is in great demand. In this study, the microcalorimetric method was used to measure the metabolic curves of E. coli growth affected by chenodeoxycholic acid (CDCA) and ursodeoxycholic acid (UDCA). By analyzing the metabolic curves and thermo- kinetic/dynamic parameters, the antibacterial activities of CDCA and UDCA on multiplying and non-multiplying bacteria of Escherichia coli (E. coli) were evaluated. The results illustrated that, for the multiplying metabolism of E. coli, the two compounds controlled the anaerobic fermentative, with IC(50(1)) (half-inhibitory concentration) of 566.2 μg/mL for CDCA and 573.6 μg/mL for UDCA, respectively, but had no effective action on aerobic metabolism of the bacteria. The action of the two compounds on the non-multiplying metabolism was studied by taking the heat output of E. coli in the stationary phase as the additive guideline of the activity. The values of IC(50(2)) were 543.4 and 547.5 μg/mL, and MSC(50) (minimum stationary-cidal concentration 50) were 532.6 and 537.3 μg/mL for CDCA and UDCA, respectively. So, CDCA had more powerful antibacterial activity on E. coli than UDCA either for multiplying bacteria or non-multiplying metabolism, and they both showed stronger activities on non-multiplying metabolism than on multiplying metabolism of the bacteria. The microcalorimetric method should be strongly suggested in screening novel antibacterial agents for fighting against multidrug-resistant bacteria.     

Efficacy of modified distillation sludge of rose (Rosa centifolia) petals for lead(II) and zinc(II) removal from aqueous solutions

Removal of lead(II) and zinc(II) from aqueous solutions was studied using chemically modified distillation sludge of rose (Rosa centifolia) petals by pretreatment with NaOH, Ca(OH)(2), Al(OH)(3), C(6)H(6), C(6)H(5)CHO and HgCl(2). The adsorption capacity of biomass was found to be significantly improved. NaOH pretreated biomass showed remarkable increase in sorption capacity. Maximum adsorption of both metal ions was observed at pH 5. When Freundlich and Langmuir isotherms were tested, the latter had a better fit with the experimental data. The overall adsorption process was best described by pseudo second order kinetics. The thermodynamic assessment of the metal ion-Rosa centifolia biomass system indicated the feasibility and spontaneous nature of the process and DeltaG degrees was evaluated as ranging from -26.9501 to -31.652 KJmol(-1) and -24.1905 to -29.8923KJmol(-1) for lead(II) and zinc(II) sorption, respectively, in the concentration range 10-640mgL(-1). Distribution coefficient (D) showed that the concentration of metal ions at the sorbent-water interface is higher than the concentration in the continuous aqueous phase. Maximum adsorption capacity of biomass tends to be in the order Pb(II) (87.74mgg(-1))>Zn(II) (73.8mgg(-1)) by NaOH pretreated biomass.     

Studying effect of cell wall's carboxyl-carboxylate ratio change of Lemna minor to remove heavy metals from aqueous solution

The pre-treated Lemna minor can remove Hg(II), Cr(III), Cr(VI) and Cu(II) from the aqueous solution. The concentration determination of carboxyl and carboxylate groups and its rule to change the metal ions uptake was done by the curves of the potentiometric titration. It was shown that the removal percent of the heavy metal ions (Co=1.00 mM) increased 25.1, 26.0, 17.2 and 24.1% for these ions, respectively, with increasing the carboxylate from 0.92 to 2.42 mmol/g L. minor and then activating by the activator chloride salts. The removal percent of these ions was decreased 33.1, 27.5, 20.7 and 15.01%, respectively, with increasing the carboxyl from 1.50 to 2.41 mmol/g L. minor, inspite of activating by the chloride salts. The enthalpy change (DeltaH) was -27.43, -25.94, -28.12 and -22.27 kJ/mol and the entropy change (DeltaS) was 81.3, 79.9, 86.1 and 67.7 J/mol K, by activated biomass, respectively. L. minor removed these heavy metals corresponding to pseudo-second-order kinetic model that the activation energy (E(a)) was obtained 18.59, 15.93, 20.36 and 21.12 kJ/mol by the activated and 23.02, 22.27, 23.98 and 24.46 kJ/mol by the reference biomass to uptake Hg(II), Cr(III), Cr(VI) and Cu(II), respectively.     

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.     

A sensitivity-based parameterization concept for the automated design and placement of reinforcement doublers

This paper presents a sensitivity-based approach for an automated generation of laminated composite structures with local reinforcement doublers. The method is demonstrated on the problem of finding structural design solutions with maximal frequency-to-mass ratios but can be extended to optimization of different objectives. Eigenvalue sensitivities on finite element level with respect to the thickness of laminate layers are derived analytically and provide the basis for the generation of laminate doublers. Sensitivities can also be evaluated for non-existent layers, namely Ghost Layers. Predefined material properties and orientations are assigned to them but their thickness is specified to zero by a thickness control factor. Assigning a real thickness to parts of these layers, which is controlled by sensitivity information, creates local reinforcement doublers. The locally reinforced solutions are superior to solutions with fully covered layers in terms of eigenfrequency-to-mass ratio. Due to the choice of the parameterization and the iterative thickening process, solutions can be manufactured without significant modifications. The efficiency as well as the solution quality is demonstrated with a numerical experiment.     

Synthesis and application of Poly(acrylamide-itaconic Acid)/Zirconium tungstate composite material for cesium removal from different solutions

This study is conducted to find the conditions required to synthesize composite material for cesium (¹³⁴Cs⁺) removal from the generated liquid waste associated with nuclear, medical, industrial, and/or research activities. The study shows that the optimum conditions required for synthesizing “Poly [acrylamide (AM)-itaconic acid (IA)]/N,N′-methylenediacrylamide (DAM)/Zirconium tungstate (ZrW)” or “Poly(AM-IA)/DAM/ZrW” are 0.01 g DAM dose as a cross-linker, a co-monomer concentration of 20%, a co-monomer composition (AM-IA) (12:88), and 0.03 g (melted at 450 °C–500 °C) ZrW with gamma irradiation dose of 30 kGy. The composite material was characterized by Fourier infrared (FTIR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscope (SEM), and Brunauer-Emmett-Teller (BET) surface area measurements. The adsorption performance of the composite was investigated. The maximum removal efficiency of ¹³⁴Cs⁺ ions was found to be 93% in moderate alkaline solutions at pH 8 ± 0.2 after 90 min. Kinetic studies indicated that the adsorption process is controlled by the pseudo-second-order kinetic model as a chemisorption process. Fitting of the adsorption data has pointed out that the adsorption process follows the Freundlich isotherm model as heterogeneous process. The maximum adsorption capacity (q_max) is 5.298 mmol Cs⁺ g^?1 adsorbent. Applicability of the synthesized composite material was also examined to remove ¹³⁴Cs⁺ ions in different aqueous solutions.