Preconcentration/separation of lead at trace level from water samples by mixed micelle cloud point extraction

Investigation of the Conditions for Preconcentration of Cadmium Ions by Solid Phase Extraction Method Using Modified Juglans regia L. Shells

BACKGROUND

Juglans regia L. shells as agricultural waste can be considered as alternative sorbents to minimize the problems associated with heavy metal pollution.

OBJECTIVE

In this study, J. regia shells (JRS) and JRS modified with hydrazine hydrate (JRS-HH) were used as sorbents and compared for the preconcentration of Cd(II) ions from aqueous solution.

METHODS

For the characterization of sorbents, scanning electron microscopy and energy dispersive X-ray (SEM/EDX) analysis and Fourier transform infrared (FTIR) spectroscopy were used. For preconcentration, the solid phase extraction (SPE) technique was used. Preconcentration studies were performed by column method and pH, eluent type and concentration, sample volume, flow rate, and interfering ions effect were studied to determine the optimum column parameters.

RESULTS

The limit of detection (LOD) of the sorbents (JRS and JRS-HH) are 0.31 and 0.18 µg/L, respectively. According to the Langmuir isotherm model for both sorbents, for JRS KL = 0.030 L/mg, R2 = 0.992, 0.016 L/mg, and for JRS-HH KL = 0.016 L/mg, R2 = 0.998 and maximum adsorption capacities of the sorbents were found to be as 29.6 and 65.7 mg/g, respectively. The mean recoveries and RSD values at a 95% confidence level (N = 6) for Cd(II) were 100.9% and 3.42, and 100.6% and 3.79, for the JRS and JRS-HH sorbents, respectively.

CONCLUSIONS

Using this method good results were obtained when compared with those in the literature and the proposed method was successfully applied to the analysis of the certificated reference material (NIST 1640).

HIGHLIGHTS

JRS are an effective and inexpensive sorbent for the preconcentration of metal ions when modified. Thus, low-cost agricultural wastes are both recovered and have an economic value.

Feasibility of calcium alginate beads to preconcentrate lead in river water samples prior to determination by flame atomic absorption spectrometry

Lead (Pb) is a potentially toxic element with significant environmental interest. Simple and sensitive analytical methods are necessary to allow determination of this element at trace levels using sample preparation procedures related to green chemistry. For this, calcium alginate beads (CA-beads), a low-cost and environmentally friendly biopolymer, have been proposed for extraction and preconcentration of Pb²⁺ in river water samples and determination by flame atomic absorption spectrometry (FAAS). CA-beads were prepared and applied to extract and preconcentrate Pb²⁺ in river water samples, providing an enrichment factor (EF) of 50, enhancement factor (E) of 54, a detection limit of 2 μg L^-1, and a relative standard deviation < 5%. The extraction of Pb²⁺ in CA-beads achieved good selectivity, with recoveries from 94.8 to 100.2% in real samples, demonstrating the good accuracy of the proposed method. The results were also compared to those obtained by ICP-MS. The reuse of CA-beads was evaluated for six cycles, and under these conditions, the extraction and preconcentration efficiency of Pb²⁺ were not significantly affected. The developed methodology was applied to determine Pb²⁺ in water samples from rivers that are part of the hydrographic areas of Tibagi and Pitangui Rivers, in which the Pb²⁺ concentration was less than 2 μg L^-1, a concentration lower than that established by Brazilian legislation for class I and II rivers.

Removal of Lead(II) from Aqueous Solution Using Triton X-114 in the Presence of Alanine or Phenylalanine as Biodegradable System

The Cloud Point Extraction (CPE) of Pb(II) ion, using Triton X-114/ alanine and Triton X-114/phenyalanine as biodegradable systems, was carried out. The experimental results are expressed by four responses to surfactant concentration, amino acid concentration and temperature variations: extent of solute extraction (E), remaining solute (Xm,w) and surfactant (Xt,w) concentrations in dilute phase and volume fraction of coacervate (}C) at equilibrium. An empirical smoothing method was used, where the results were represented on three dimensional plots using the Box-Behnken design (BBD) and the response surface methodology (RSM). High extraction efficiencies (94% with alanine and 98% with phenylalanine) are reached in optimal conditions. Thereby, solute concentration reduction in the dilute phase is about 4 and 12 times with alanine and phenylalanine, respectively. The pH effect is also studied. Finally, the possibility of recycling the surfactant/amino acid system by pH change is proved.

Zn2+ adsorption from wastewater using a chitosan/β-cyclodextrin-based composite membrane

In this study, a β-cyclodextrin polymer (β-CDP) was synthesized by pretreating β-cyclodextrin (β-CD) with citric acid (CA), and then, chitosan (CTS) and β-CDP were cross-linked to prepare a biomass-based (CTS/β-CDP) composite membrane. The effects of the preparation conditions in sodium hydroxide on the adsorption amount and adsorption rate of zinc ions (Zn²⁺ ) from simulated wastewater were investigated. The results showed that a maximum adsorption amount 123.7 μg/g and adsorption rate 94.14% of Zn²⁺ were obtained when the reaction between CTS and β-CDP was performed at 50°C, the concentration of acetic acid was 2%, dissolving β-CDP water dosage was 30 ml, and the soaking time in sodium hydroxide was 1 hr. Comparative studies on the adsorption of CTS membranes, β-CD, β-CDP, and CTS/β-CDP composite membrane showed that the CTS/β-CDP composite membrane had the highest Zn²⁺ adsorption efficiency. The CTS/β-CDP composite membrane was characterized by FTIR, SEM, and XRD. Characteristic absorption peaks of CTS and β-CDP appeared in the FTIR spectra of the CTS/β-CDP composite membrane, confirming its synthesis. The SEM images showed that the surface of the composite membrane was rougher than the porous CTS membrane, which increased the number of adsorption sites and the adsorption efficiency. XRD patterns showed that the CTS/β-CDP composite membrane was amorphous, indicating that β-CDP changed the crystal structure of the CTS. The swelling degree and transmittance of the CTS/β-CDP composite membrane were lower than the CTS membrane, which should be conducive to recycling after wastewater treatment. PRACTICAL APPLICATIONS: Industrial wastewater often contains heavy metal ions such as Zn²⁺ , which are difficult to degrade and are highly toxic, and direct wastewater discharge can greatly harm the ecosystems and humans. In this study, CTS and β-CD were cross-linked to synthesize a biomass membrane for adsorbing Zn²⁺ to reduce the Zn²⁺ content in wastewater via adsorption.The results show that the CTS/β-CDP composite membrane can be applied to small-scale wastewater treatment fields such as food and chemical industry. After the Zn²⁺ -containing wastewater underwent pretreatment, the composite membrane was placed into the wastewater for effective adsorption, which could achieve high adsorption efficiency. The process played a major role in effectively treating Zn²⁺ and other difficult to degrade heavy metal ions; thereby, simplifying Zn²⁺ -containing wastewater. The treatment process reduces the investment and operating costs of sewage treatment, and at the same time, has a significant removal effect, and hence, can meet the requirements of environmental protection discharge.

Composite nanofibers membranes of poly(vinyl alcohol)/chitosan for selective lead(II) and cadmium(II) ions removal from wastewater

The nanofibers membranes were fabricated by poly(vinyl alcohol)/chitosan (PVA/Chi) using an electro-spun technique for selective and high adsorption of lead (Pb(II)) and cadmium (Cd(II)) ions based on the solution acidity. The PVA/Chi NFs membranes were characterized systematically using several instrumentations. In addition, several experimental parameters such as initial metal ions concentration, interaction time, adsorbent dosage, solution pH and the effects of competing ions on Pb(II) and Cd(II) adsorption were evaluated. The adsorption data were also clarified that the PVA/Chi NFs membranes were exhibited high kinetic performances towards the both toxic ions at the optimum conditions. The adsorption data were manipulated using different kinetics models, and it was confirmed that only pseudo-second-order model obeyed the adsorption kinetics for Pb(II) and Cd(II) ions. Similarly, the equilibrium data were well fitted with the Langmuir adsorption isotherms model, and the maximum adsorption capacity was 266.12 and 148.79 mg/g for Pb(II) and Cd(II) ions, respectively. The Pb(II) and Cd(II) ions adsorptions were also measured to know the selectivity with simulated environmental solution, and the data were confirmed the high selectivity to Pb(II) and Cd(II) ions at the optimum condition and the nanofibers membrane shown the potentiality for possible use in efficient removal of the selected toxic ions from waste samples. Thus, the PVA/Chi NFs are considered to be effective and promising materials for Pb(II) and Cd(II) ions from wastewaters with high efficiency.

Formulation of chelating agent with surfactant in cloud point extraction of methylphenol in water

Cloud point extraction (CPE) is a separation and preconcentration of non-ionic surfactant from one liquid phase to another. In this study, Sylgard 309 and three different types of additives for CPE, namely CPE-Sylgard, CPE-Sylgard-BMIMBr and CPE-Sylgard-GLDA, are investigated to extract methylphenol from water samples. The methylphenols are well separated by reversed-phase high-performance liquid chromatography (HPLC) with isocratic elution of acetonitrile : water; 60 : 40 (v/v) and detection at 260 nm. The optimized parameters for the effect of salt, surfactant, temperature, time of extraction, pH, interference study and the performance of different additives on methylphenol extraction are investigated. CPE-Sylgard-GLDA is chosen because it gives us a high peak and good peak area compared with CPE-Sylgard and CPE-Sylgard-BMIMBr. The recovery extractions of CPE-Sylgard-GLDA are obtained in the range of 80-99% as the percentage of relative standard deviation (RSD) is less than 10. The LOD and LOQ are 0.05 ppm and 0.18 ppm, respectively. The method developed for CPE-Sylgard-GLDA coupled with HPLC is feasible for the determination of methylphenol because it is simple, effective, cheap, and produces a high percentage of recovery.