Separation of Cr(III) and Cr(VI) using melamine-formaldehyde resin and determination of both species in water by FAAS

Adsorptive detoxification of Cd2+ and Pb2+ from wastewater using MWCNTs functionalized with -di-(2-ethyl hexyl phosphoric acid) and bis-(2,4,4-trimethyl pentyl) phosphonic acid

Selective and rapid determination of procedure for Cd2+ and Pb2+ samples using MWCNT surfaces can be modified by loading ligands such as D2EHPA and Cyanex 272 which is described. The adsorbent was modified with D2EHPA and Cyanex 272. Effect of pH, amount of adsorbent, contact time for adsorption, and the optimum eluent for the quantitative recovery of Cd2+ and Pb2+ were investigated and the subsequent determination by FAAS. The adsorption was found to be mainly due to the chemical interactions between the metal ions and functional groups -COO- and -OH which were characterized by FT-IR. The adsorption of metal occurs at pH 4.5 with 500 mg of MWCNTs. The enrichment factor was 40 and 30. The detection limit was 0.03 and 0.05 μg L-1. The quantitative recovery of metal ion used 1 mol L-1 HNO3. The thermodynamic parameter of Langmuir and Freundlich adsorption isotherm revealed that the adsorption of free energy (ΔG) was spontaneous and the monolayer adsorption of Cd2+ and Pb2+ was mainly on the surfaces. The adsorbent performance of R2 in the range of 0.93-0.99 and also the identified adsorption efficiency of Cd2+ and Pb2+ are linear or non-linear curves respectively. The proposed method was applied to heavy metals from environmental samples.

A facile route for the synthesis of mesoporous melamine-formaldehyde resins for hexavalent chromium removal

A facile route for the synthesis of mesoporous melamine-formaldehyde resins (MMF) for hexavalent chromium removal.

A novel method for speciation of Cr(III) and Cr(VI) and individual determination using Duolite C20 modified with active hydrazone

Trivalent and hexavalent chromium have been successfully separated and estimated from different solutions using 1-(3,4-dihydroxybenzaldehyde)-2-acetylpyridiniumchloride hydrazone (DAPCH) loaded on Duolite C20 in batch and column modes. The obtained modified resin [DAPCH-Duolite C20] was identified by C, H and N analyses and infrared spectra. The presence of multi-active chelating sites gives the ability for DAPCH to bind more chromium, Cr(III) by forming stable complex and chromate by forming ion pair molecule [H(2)DAPCH-Duolite C20](2+)[Cr(2)O(7)](2-) (H(2)DAPCH-Duolite C20 is the protonated form in acidic medium). The extraction isotherms were measured at different pH. The pH was found to be the backbone for the separation procedure in which the Cr(VI) and Cr(III) ions are sorbed selectively from aqueous solution at pH 2 and 6, respectively. The sorbed ions can be eluted using different concentrations of HCl. The saturation sorption capacity (41.6 and 20.05 mg g(-1)), the preconcentration factor (150 and 200) and the detection limit (13.3 and 10.0 ppb) were calculated for Cr(III) and (VI). The loaded resin can be regenerated for at least 50 cycles. The utility of the modified resin was tested in aqueous samples and shows R.S.D. value of <4% reflecting its accuracy and reproducibility.

A new chelating resin containing azophenolcarboxylate functionality: synthesis, characterization and application to chromium speciation in wastewater

The synthesis of a new stable chelating resin from the polystyrene divinylbenzene copolymer is reported. The polystyrene is first functionalized with a phenolic group and then allowed to couple with diazotized anthranilic acid through the --N==N-- bond. The resulting polymer containing azophenolcarboxylate with an ONO chelating environment has been characterized by elemental analysis, hydrogen ion capacity, and water regain value. Its stability towards thermal and different chemical environments has been evaluated. The sorption capacity of the chelating resin for Cr(III) and Cr(VI) as a function of pH has been studied. The interesting point is that chromium(III) is selectively retained at ca. pH 5.0 and chromium(VI) at ca. pH 2.0. When packed in a column, the new material is able to separate Cr(III) from Cr(VI). Five replicate determinations of 10 microg Cr(III) and 10 microg Cr(VI) present in 100 mL solution gave recoveries of 96.9+/-2.9% (for Cr(III)) and 96.2+/-2.1% (for Cr(VI)) at the 95% confidence level. Calibration graph was linear over the concentration range of 0-250 microg L(-1) of chromium species with correlation coefficient (R) of 0.99994. The detection limits based on 3sigma criterion were determined to be 0.6 microg L(-1) for Cr(III) and 0.9 microg L(-1) for Cr(VI). The developed method was successfully used for the speciation of chromium in wastewater.

Application of pneumatic flow injection-tandem spectrometer system for chromium speciation

In this approach, a pneumatic flow injection-tandem spectrometer system, without a delivery pump, has been developed to study chromium speciation. In this system, suction force of pneumatic nebulizer of a flame atomic absorption spectrometer has been used for solution delivery through the manifold. Cr(VI) and total Cr concentrations were determined using UV-Vis and FAAS spectrometers, respectively. The Cr(III) was determined by difference. The calibration curves were linear up to 10 mug mL-1 and 20 mug mL-1 for Cr(VI) and total Cr with detection limit of 0.12 mug mL-1 and 0.07 mug mL-1 for Cr(VI) and Cr(III), respectively. The midrange precision and accuracy are less than 1.98% and +/- 2.50% for two species, respectively, at a sampling rate of 100 h-1. This system was applied for the determination of the chromium species in spiked and natural waters as well as industrial waters.

Preconcentration and Speciation of Chromium in Water Samples by Atomic Absorption Spectrometry after Cloud-Point Extraction

A rapid, sensitive and accurate atomic absorption method for Cr(III) and Cr(VI) ions was developed based on the cloud-point extraction (CPE) technique. Cr(III) reacts with a new Schiff's base ligand to form the hydrophobic complex, which is subsequently entrapped in the surfactant micelles. The Cr(VI) assay is based on its reduction to Cr(III) by the addition of concentrated H2SO4 and ethanol to the sample solution. The condensed surfactant phase containing the metal chelates is introduced into an atomic absorption spectrometer. The relative standard deviations were 2.1% for both species and the limits of detection were around 0.17 microg l(-1).