Phosphonated cross-linked polyethylenimine for selective removal of uranium ions from aqueous solutions

Among many remediation techniques for metal ion removal, polymeric adsorbents are efficient and widely applied. This has made them comparable with other remediation techniques in terms of technical and economic efficiency, feasibility as well as green technology. This study was dedicated to the development of an insoluble modified chelating polymer for use as an adsorbent for abstraction of uranium from wastewaters. Cross-linked polyethylenimine (CPEI) was phosphonated by phosphorous acid for selective removal of uranium ions. The binding affinity of the phosphonated cross-linked polyethylenimine (PCPEI) to uranium ions was assessed as well as its ability to be regenerated for reuse. It exhibited high removal percentage for uranium ions up to 99% with high selectivity even in the presence of competing ions (Mn, Ni, As). The Freundlich isotherm was found to be the best fit describing the adsorption process of uranyl ions onto the PCPEI. The pseudo-second-order equation was found to better explain the adsorption kinetics, implying chemisorption. The thermodynamic study of the adsorption revealed high activation energies which confirmed the chemisorption as the mechanism of adsorption.     

Removal of Cu(II) ions from aqueous solutions using N-carboxymethyl chitosan

N-carboxymethyl chitosan (NCMC) was synthesized by reacting chitosan with chloroacetic acid in water under triethylamine (Et(3)N) as catalyst. The chemical structures of NCMC were characterized by Fourier transform infrared (FT-IR) and hydrogen-1 nuclear magnetic resonance ((1)H-NMR) spectroscopy and confirmed that carboxymethylation occurred on the amino groups. Samples of NCMC were used for removal of Cu(II) from aqueous solution. The effects of degree of substitution of NCMC, initial pH value and adsorption kinetics on the adsorption were studied. Adsorption experiments showed that NCMC has a high adsorption speed and high adsorption capacity for remove Cu(II) from aqueous solution. The adsorption kinetics data were best fitted with the pseudo-second-order model. The experimental equilibrium data of Cu(II) on the NCMC were both fitted to the Langmuir model and Freundlich model, which revealed that the maximum capacity for monolayer saturation was 147.93 mg/g.     

Imprinted polymers for the removal of heavy metal ions from water

In wastewater treatment, the removal of heavy metals is difficult due to the limited affinity of heavy metal ions to ion exchange resins. Here imprinting polymerization is used to develop resins with high capacity and selectivity for heavy metal ions for water treatment. A random copolymer of methacrylate and methacrylamide was found to be most effective for the removal of hydrophilic metal complexes, like CdCl2, ZnCI2, and the metalloid NaH2AsO4, particularly when the porosity of these resins is increased. For hydrophobic complexes imprinting emulsion polymerization was developed and data for the effective removal of mercury dithizonate will be described. Complete removal for up to 80 ppm of cadmium and mercury with only 200 mg of imprinted resin was obtained; competition and co-imprinting experiments are described as well.     

Simultaneous copper, cobalt and phenol removal from aqueous solutions by alternating biosorption and biodegradation

A strategy for removal of heavy metals and phenol from wastewaters is proposed. It involves consecutive cation biosorption by fungi, phenol biodegradation by the yeast association Candida sp. 2326 + Candida sp. 2327 and regeneration. Copper and cobalt removal from aqueous solutions containing 80-120 mg/L phenol by biosorption, using Rhizopus archizus cells immobilized onto poly (vinyl alcohol), was investigated by conducting a series of batch experiments. The removal efficiencies were 81% for Cu and 5% for Co. The residual concentrations of Cu (1.9 mg/L) and of Co (9.5 mg/L) did not change the biodegradation dynamics of phenol. A quantitative biodegradation of 120 mg/L phenol proceeded within 22 h. After biodegradation of phenol, the removal efficiencies achieved by biosorption after regeneration were 90% for Cu and 44% for Co. It was found that copper and cobalt form positively charged complexes with phenol. This complex formation hinders the retention of Cu and Co by the biosorbent and reduces the uptake of their cations.     

Use of sesame stalk biomass for the removal of Ni(II) and Zn(II) from aqueous solutions

In this study an agricultural residue, sesame stalk, was evaluated for the removal of Ni(II) and Zn(II) metal ions from aqueous solutions. Biosorption studies were carried out at different pH, biosorbent dosage, initial metal ion concentrations, contact time, and solution temperature to determine the optimum conditions. The experimental data were modeled by Langmuir, Freundlich, Dubinin-Radushkevich (D-R) and Temkin isotherm models. Langmuir model resulted in the best fit of the biosorption data. The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetic data and to evaluate rate constants. The best correlation was provided by the second-order kinetic model. The thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated for predicting the nature of adsorption. The experimental results showed that sesame stalk can be used as an effective and low-cost biosorbent precursor for the removal of heavy metal ions from aqueous solutions.     

Potential application of manganese coated sand in the removal of Mn(II) from aqueous solutions.

The aim of this study was to explore the applicability of manganese coated sand (MCS) in the presence and absence of sodium hypochlorite for the removal of Mn(II) (2 mg/L) from aqueous solutions. Sand itself is widely used as a filter media for the treatment of wastewaters and it was reported that during the treatment, Mn(II), which is present in the wastewater, is to be deposited on the surface of sand in the form of manganese dioxide. The present investigation dealt with various MCS samples, prepared in the laboratory by various doses of Mn(II) (i.e. from 0.05 to 0.2 mol/L) and the samples were obtained from the pilot plant and naturally coated in the water treatment plant for the removal of Mn(II) in the batch and column studies. Moreover, it was realised that the role of hypochlorite is multifunctional as it not only enhances the uptake of Mn(II) on the surface of MCS through oxidation of Mn(II) into Mn(IV) and hence the formation of manganese dioxide, but it was also supposed to disinfect the bacteria or harmful pathogens from the waste/surface waters. The results obtained clearly inferred that various MCS samples used for the removal of Mn(II) from aqueous solutions showed comparable removal efficiency. However, the presence of sodium hypochlorite greatly enhanced the removal of Mn(II) as more than 80% Mn(II) was removed in the presence of sodium hypochlorite at around pH 6.5. Similarly, while comparing the column data it was again noted that the breakthrough points occurred after the 4,100 and 6,500 bed volumes, respectively, in the absence and in the presence of sodium hypochlorite (2 mg/L).     

The sorption of lead, cadmium, copper and zinc ions from aqueous solutions on a raw diatomite from Algeria

The adsorption of Cu(2+), Zn(2+), Cd(2+) and Pb(2+) ions from aqueous solution by Algerian raw diatomite was studied. The influences of different sorption parameters such as contact pH solution, contact time and initial metal ions concentration were studied to optimize the reaction conditions. The metals ions adsorption was strictly pH dependent. The maximum adsorption capacities towards Cu(2+), Zn(2+), Cd(2+) and Pb(2+) were 0.319, 0.311, 0.18 and 0.096 mmol g(-1), respectively. The kinetic data were modelled using the pseudo-first-order and pseudo-second-order kinetic equations. Among the kinetic models studied, the pseudo-second-order equation was the best applicable model to describe the sorption process. Equilibrium isotherm data were analysed using the Langmuir and the Freundlich isotherms; the results showed that the adsorption equilibrium was well described by both model isotherms. The negative value of free energy change ΔG indicates feasible and spontaneous adsorption of four metal ions on raw diatomite. According to these results, the high exchange capacities of different metal ions at high and low concentration levels, and given the low cost of the investigated adsorbent in this work, Algerian diatomite was considered to be an excellent adsorbent.     

Sorption of benzoic acid from aqueous solution by cetyltrimethylammonium bromide modified birnessite

Layered manganese oxide (birnessite) has been studied for its use as catalytic materials. The research presented in this study investigates the sorption of benzoic acid from water on synthesized cetyltrimethylammonium bromide modified birnessite (CTAB-birnessite). The synthesized CTAB-birnessite was characterized by X-ray powder diffraction (XRD). The experimental results of sorption kinetic were well fitted to the pseudo-second-order equation. The sorption isotherms were linear at different pH values, and it indicates a partition mechanism. Up to about 53% of the dissolved benzoic acid was sorbed by CTAB-birnessite; in contrast, only 16% of the dissolved benzoic acid was sorbed by birnessite. These results indicate that CTAB-birnessite can be a potential sorbent for benzoic acid removal.     

Development of adsorbent for the simultaneous removal of organic and inorganic contaminants from aqueous solution

In this study, a modified adsorbent, alginate complex beads, was prepared and applied to the removal of mixed contaminants from wastewater. The alginate complex beads were generated by the immobilization of powdered activated carbon and synthetic zeolites onto alginate gel beads, which were then dried at 110 °C for 20 h until the diameter had been reduced to 1 mm. This dry technique increased the hardness of the adsorbent to assure its durability and application. The adsorption onto the alginate complex beads of organic and inorganic compounds, as target contaminants, was investigated by performing both equilibrium and kinetic batch experiments. From the adsorption isotherms, according to the Langmuir equation, the alginate complex bead was capable of effectively removing benzene, toluene, zinc and cadmium. From kinetic batch experiments, the removal efficiencies of benzene, toluene, zinc and cadmium were found to be 66.5, 92.4, 74.1 and 76.7%, respectively, for initial solution concentrations of 100 mg L(-1). The results indicated that the adsorbent developed in this study has the potential to be a promising material for the removal of mixed pollutants from industrial wastewater or contaminated groundwater.     

涂铁砂过滤去除水中磷的研究

试验制备一种涂铁砂(IOCS)滤料用于对水中磷的去除,与石英砂相比IOCS表面粗糙,空隙多,比表面积大,且附有α-Fe_2O_3晶体,吸附能力增强。通过过滤试验研究了IOCS滤料在不同的试验条件下(pH、空床接触时间、进水磷浓度、滤床深度等)对水中磷的去除效果。结果表明:中性条件下磷的去除效果最佳,pH太高和太低都不利于磷的去除;中性条件下,当空床接触时间为13min,进水磷浓度为1.0 mg/L,滤床深度为50 cm时,去除效果较好,平均去除率可达82%;空床接触时间、进水磷浓度、滤床深度等是影响过滤运行周期的主要因素。     

Pervaporative removal of acrylonitrile from aqueous streams through polydimethylsiloxane membrane

This study describes the successful separation of acrylonitrile (ACN) from dilute aqueous streams using pervaporation process. The influences of ACN feed concentration, permeate pressure, operating temperature, feed flow rate and membrane thickness on the membrane separation performance were investigated. The results showed that with an increase in ACN concentration in the feed solution, the permeation flux of ACN increased while the enrichment factor decreased. It was also indicated that increasing the permeate pressure reduced the driving force for mass transfer and consequently the permeation flux dropped while the enrichment factor enhanced. Polydimethylsiloxane membranes used in this study showed very good properties in the separation process, leading to enrichment factors in the range of 70-140. Furthermore, the activation energy for pervaporation of both ACN and water calculated from Arrhenius plot indicated that the permeation of water through the membrane was more temperature dependant than ACN.     

Removal of copper(II) and cadmium(II) ions from aqueous solutions by biosorption onto pine cone

In this study, the removal of copper(II) and cadmium(II) ions from aqueous solutions by biosorption onto pine cone was studied. Variables that affect the biosorption process such as pH, biosorbent dosage, initial metal ion concentration, contact time and temperature of solution were optimized. Experimental data were fitted to Langmuir, Freundlich, Dubinin Radushkevich and Temkin isotherm models to investigate the equilibrium isotherms. Pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models were used to determine the biosorption mechanism. The thermodynamics of biosorption were studied for predicting the nature of biosorption. Experimental results showed that pine cone could be evaluated as an alternative precursor for removal of heavy metal ions from aqueous solutions, due to its high biosorption capacity, availability, and low cost.     

Removal of ammonium from aqueous solutions using the residue obtained from struvite pyrogenation

This paper reports the results of laboratory studies on the removal of ammonium from aqueous solutions using struvite pyrogenation residues. A series of experiments were conducted to examine the effects of the pyrogenation temperature (90-210 °C) and time (0.5-4 h) on the ammonium release of struvite. In addition, the pyrolysate of struvite produced at different pyrogenation temperatures and times was recycled for ammonium removal from aqueous solutions. The experimental results indicated that the ammonium release ratio of struvite increased with an increase in the pyrogenation temperature and time, and the struvite pyrolysate used as magnesium and phosphate source for ammonium removal was produced at the optimal condition of pyrogenation temperature of 150 °C for 1 h. Furthermore, experimental results showed that the optimum pH and pyrolysate dosage for ammonium removal from 100 ml synthetic wastewater (1,350 mg ammonium/L) were at pH 9 and 2.4 g of struvite pyrolysate, respectively, and initial ammonium concentration played a significant role in the ammonium removal by the struvite pyrolysate. In order to further reduce the cost of struvite precipitation, the struvite pyrolysate was repeatedly used for four cycles. The results of economic analysis showed that recycling struvite for three process cycles should be reasonable for ammonium removal, with ammonium removal efficiencies of over 50% and a reduction of 40% in the removal cost per kg NH(4)(+).     

Layered double hydroxide (LDH)-coated attapulgite for phosphate removal from aqueous solution

In this study, a composite adsorbent, layered double hydroxide (LDH)-coated attapulgite (LDH-AP), was synthesized and characterized. Its potential application for LDH stabilizer and phosphate (P) removal from aqueous solution was evaluated using the batch mode and continuous mode in a packed bed column. The batch experiments revealed that the data of P adsorption onto LDH-AP could be well described by the Freundlich equation, and the maximum adsorption capacity was estimated to be 6.9 mg/g. The column experiments were conducted in the tap water and the results indicated that the competing anions could slightly decrease phosphate removal. The saturated column was regenerated by 0.2 mol/L of NaOH and the regenerated column was examined for its reuse in phosphate removal. The results of this study suggested that attapulgite could be used as an applicable stabilizer of LDH and LDH-AP could be potentially used as a promising filtration medium for phosphate removal.     

Sorption of Cr(III) ion from aqueous solution by two kinds of modified diatomite

Raw diatomite modified by microemulsion (DMM) and manganese oxide (MnD) were used for the removal of Cr(III) ions from aqueous solution. The characteristics and performance of these two types of modified diatomite on Cr(III) ion adsorption were compared. The results indicate that the Cr(III) ion adsorption capacities of diatomite were considerably improved after modifications by manganese oxide (MnO) and microemulsion. The surface area of MnD was increased because of the formation of MnO on the diatomite surface, and that of DMM was promoted owing to the existence of the hydrolyzed aromatic acid. Because of the stronger surface ionized function, the adsorption performance of Cr(III) ions in DMM was better than that in MnD. Within the experimental range of pH (i.e. 2.2-6.3), the Cr(III) ion removal of DMM (35-70%) was higher than that of MnD (33-59%) owing to the different electrostatic forces between the Cr(III) ion and the surface of the modified diatomite. The Cr(III) ion removal in MnD and DMM was improved with the increase of synthetic solution concentration in volumes from 0 to 2,500 mL.     

Electrocoagulative treatment of mercury containing aqueous solutions

In recent years, electrocoagulation has been successfully used for wastewater treatment and is efficient in heavy metal ions removal. In the present work, electrocoagulation has been used for the removal of Hg(II) from synthetic wastewaters containing up to 20 mg/L of mercury. The electrode materials used are stainless steel (SS) and aluminum (Al). The effects of operating parameters, viz., current density, time of electrocoagulation, distance between electrodes, initial pH of the solution, presence of electrolyte in the solution and temperature have been studied. It was observed that more than 99% Hg(II) removal can be achieved by keeping the distance between SS and Al electrodes from 2 to 6 cm and initial pH range from 3 to 7. The results show that the pseudo second-order kinetics fits the data well. Also, preliminary cost estimation was reported.     

Mg/Al layered double hydroxide for bacteriophage removal in aqueous solution

The objective of this study was to investigate the removal of bacteriophages in Mg/Al layered double hydroxide (LDH). Batch experiments were performed with bacteriophage MS2 in a powder form of Mg/Al LDH under various LDH doses. Column experiments were also performed under flow-through condition with bacteriophages MS2 and phiX174 in Mg/Al LDH immobilized on sand surfaces. Batch tests demonstrated that the powder form of Mg/Al LDH was effective in removing MS2 with the removal capacity of 2.2 × 10(8) plaque forming unit (pfu)/g under the given experimental conditions (LDH dose = 2 g/L; initial MS2 concentration = 4.61 × 10(5) pfu/mL). Column experiments showed that the log removal of phiX174 was 4.40 in columns containing 100% Mg/Al LDH-coated sand while it was 0.05 in 100% quartz sand. These findings indicated that Mg/Al LDH-coated sand was effective in removing bacteriophages compared with sand. A more than 4 log removal (=5.44) of MS2 was achieved in 100% Mg/Al LDH-coated sand. This study demonstrates the potential application of Mg/Al LDH for virus removal in water treatment.     

Biosorption of As(V) from aqueous solutions by living cells of Bacillus cereus

In this work, the biosorption of As(V) from aqueous solutions by living cells of Bacillus cereus has been reported. The batch biosorption experiments were conducted with respect to biosorbent dosage 0.5 to 15 g/L, pH 2 to 9, contact time 5 to 90 min, initial concentration 1 to 10 mg/L and temperature 10 to 40 °C. The maximum biosorption capacity of B. cereus for As(V) was found to be 30.04 at pH 7.0, at optimum conditions of contact time of 30 min, biomass dosage of 6 g/L, and temperature of 30 ± 2 °C. Biosorption data were fitted to linearly transformed Langmuir isotherms with R(2) (correlation coefficient) >0.99. Bacillus cereus cell surface was characterized using AFM and FTIR. The metal ions were desorbed from B. cereus using both 1 M HCl and 1 M HNO(3). The pseudo-second-order model was successfully applied to predict the rate constant of biosorption.     

Camellia oleifera Abel shells as a new biosorbent to remove methylene blue from aqueous solutions

This study aimed at investigating the feasibility of using Camellia oleifera Abel shell (COAS), an agriculture product in middle-west region in China, for the adsorption of methylene blue (MB), a cationic dye. Batch adsorption experiments were carried out to evaluate the effects of contact time, pH, adsorbent dosage, temperature and initial concentration on the adsorption of MB. Adsorption equilibrium studies showed that MB adsorption followed Langmuir model with a maximum adsorption capacity of 454.54 mg/g. The results demonstrated that the COAS is a promising adsorbent in the removal of MB from aqueous solutions.     

Modification of granular activated carbon using low molecular weight polymer for enhanced removal of Cu(2+) from aqueous solution.

Palm shell activated carbon was modified via surface impregnation with polyethyleneimine (PEI) to enhance removal of Cu(2+) from aqueous solution in this study. The effect of PEI modification on batch adsorption of Cu(2+) as well as the equilibrium behavior of adsorption of metal ions on activated carbon were investigated. PEI modification clearly increased the Cu(2+) adsorption capacities by 68% and 75.86% for initial solution pH of 3 and 5 respectively. The adsorption data of Cu(2+) on both virgin and PEI-modified AC for both initial solution pH of 3 and 5 fitted the Langmuir and Redlich-Peterson isotherms considerably better than the Freundlich isotherm.