Calcon-modified silica gel sorbent. Application to preconcentration or elimination of trace metals

Silica gel impregnated with a mixture of Aliquat 336 and Calcon was used as chelating sorbent for preconcentration of metals from dilute aqueous solutions and their separation as well as for additional purification of analytical grade sodium and potassium salts from other metals. The relative capacities of sorbent towards 33 metal ions were determined in the pH range 1-9 as well as the concentrations of hydrochloric and perchloric acid eluting the retained metals. It was found that Calcon was not eluted from sorbent with 5M perchloric and 10M hydrochloric acids. The rate of sorption for Mg, Ca, Cu, Zn, Al, Cr(III) and Fe(III) was also studied and it was found that relatively high flow-rates (up to 5 ml/min) can be used for solutions passed through the column. The sorbent was used for preconcentration of traces of some metals from aqueous solutions before their determination by AAS, for separation of metal ion mixtures by column extraction chromatography and for additional purification of potassium chloride solutions used as supporting electrolyte in determination of some heavy metals by anodic stripping voltammetry.     

Silica gel modified with Eriochrome Blue SE as a sorbent in trace analysis for metal ions

The sorption of 14 metal ions on silica gel impregnated with a mixture of Aliquat 336 and Eriochrome Blue SE was investigated. It was found that the sorption behaviour depends upon the species and the pH of the loading solution. Alkali metal ions were not retained under any of the investigated conditions. The retained metal ions can be eluted with dilute solutions of hydrochloric or perchloric acid without significant elution of the chelating reagent from the sorbent. The sorbent was used for the separation of metal ion mixtures by column — extraction chromatography and for additional purification of some salt solutions from trace amounts of Zn, Cd, Pb and Cu. The effectiveness of purification was confirmed by anodic stripping voltammetry.     

Retention of Some Metal Ions and Their Separation on Silica Gel Modified with Acid Red 88

 Acid Red 88 is strongly extracted by chloroform solutions of Aliquat 336 by an ion exchange mechanism and for its reextraction from the ion pair formed, relatively high concentrations of mineral acids are required. By impregnation of silica with the ion pairs between the cation of Aliquat 336 and the anion of the dye a chelating sorbent for metal ions can be obtained. The sorbent prepared may be successfully used for separation of mixtures of various metal ions by the column extraction chromatography technique, additional purification of sodium and potassium salts from ions of heavy metals and for concentration of trace amounts of ions of various metals from aqueous solutions followed by their quantitative determination. The sorbent can be used repeatedly in the process of sorption and desorption of metal ions (especially those forming less stable complexes with the reagent) after regeneration with solutions of perchloric acid. Received January 28, 1998. Revision March 1, 1999.     

Retention and elution of precious metals on cyano-modified solid phase microparticle sorbent

We report on a study on the retention and elution of ions of the precious metals Au, Ir, Pd, Pt, Rh and Ru, sometimes in the presence of ions of the nonprecious elements Co, Cu, Fe, Ni, Pb and Te. A commercial cyano-modified microparticle-based solid phase was used as a sorbent and hydrochloric acid in various concentrations for sample solution and elution. Only Au and Pd (in the form of their chloro complexes) were retained, and Au is found to have a much higher affinity for the sorbent compared to Pd. In addition to the affinity of the metal towards the functional groups, the retention behavior of the precious metals seems to be mainly influenced by steric factors of their respective chloro complexes. Elution with 7.5 M HCl does not require the addition of organic eluent as required in other cases. The method can separate Au or both Au and Pd, from hydrochloric acid solutions containing ions of other precious metals or nonprecious elements. The sorbent was applied to recover gold from a mineral digest containing large amounts of metals such as Fe, Pb, Te, Cu, Ni and Zn.

Properties and Application of a Chelating Sorbent Prepared by Modification of LiChroprep-NH<Subscript>2</Subscript> with Calcon

A new chelating sorbent for metal ions was prepared by modification of chemically modified silica – LiChroprep-NH₂ with Calcon. The molecular mechanism of binding this reagent to the surface of the applied carrier is presented. The properties of this sorbent were compared to analogous sorbents with a plain silica carrier and chemically modified silicas – LiChroprep-RP containing Calcon. The advantages of the new sorbent compared to the silica and LiChroprep-RP chelating sorbents are demonstrated. The sorbent obtained was applied as stationary phase in solid-phase extraction (SPE) for separations of some chosen mixtures of metal ions and for additional purification of aqueous solutions of salts of alkali metals from trace amounts of heavy metals. The multiple use of the sorbent based on LiChroprep-NH₂ in sorption-desorption processes of metal ions without deterioration of its sorption capacity is demonstrated.     

Chelating Sorbents Prepared by the Modification of Silica Gel, Lichroprep RP-8 and Lichroprep RP-18 with Calcon and Their Application in the Analysis of Some Metal Ions

 Two new chelating sorbents for metal ions were prepared by the impregnation of chemically modified silicas LiChroprep RP-8 and RP-18 with ion pairs composed of the cation of Aliquat 336 and the anion of Calcon. The sorbents were compared with an analogous sorbent with a plain silica carrier containing the same ion pairs. A hypothesis for binding this ion pair by the surfaces of the applied carriers was presented. A higher stability of the two sorbents in comparison with that of the plain silica chelating sorbent was demonstrated. The sorbents obtained were applied for chromatographic separations of some chosen mixtures of some metal ions and for additional purification of aqueous solutions of alkali metals from trace amounts of heavy metals. The multiple use of the sorbents based on RP-8 and RP-18 in sorption–desorption processes of metal ions without deterioration of their sorption capacities was demonstrated. Received March 8, 2000. Revision March 5, 2001.     

Removal of Cd Ions by Sol-Gel Silica Doped with 1-(2-Pyridylazo)-2-Naphthol

1-(2-Pyridylazo)-2-Naphthol (PAN) doped sol-gel silica has been investigated for removal of metal ions from aqueous media. In the doped sol-gel silica, the large reagent molecules are entrapped inside the pores while small metal ions can diffuse into the pores where they are complexed by the reagent and retained inside the pores. This new solid sorbent was applied for removal of Cd(II) from aqueous solutions. The kinetics, adsorption isotherm, equilibration time and pH effect on the removal were studied to optimize the conditions to be utilized on a large scale. It was observed that a sol gel loaded with 0.09 mmol PAN/g, had a capacity of 0.044 mmol Cd/g. The desorption of metal ions was carried by 1 M HCl and the sol-gel silica sorbent could be regenerated and reused repeatedly.     

Removal of Zinc Ions by Sol-Gel Silica Doped with Cibacron Blue

Chemically doped sol-gel silica has been developed by entrapping organic dye cibacron blue as a complexing reagent in porous silica prepared by the sol-gel method for removal of metal ions from water samples. In the doped sol-gel silica, the large reagent molecules are entrapped inside the pores while small metal ions can diffuse into the pores where they are complexed by the reagent and retained inside the pores. This new solid sorbent was tested for removal of Zn(II) from aqueous solutions. The kinetics, isotherm, and pH effect of the removal were investigated. With a loading of 0.10 mmol cibacron blue/g, the sol-gel silica sorbent had a capacity of 0.09 mmol Zn/g. It was demonstrated that the sol-gel silica sorbent could be regenerated and reused repeatedly.     

Preconcentration of lead, cadmium and zinc on silica gel loaded with diethyldithiocarbamate prior to their determination by flame-atomic absorption spectrometry

A silica gel sorbent loaded with sodium diethyldithiocarbamate has been developed for the preconcentration of lead, cadmium and zinc prior to their determination by flameatomic absorption spectrometry (FAAS). The sorption and desorption of the metal ions was studied under both static and dynamic conditions. The metal ions were quantitatively retained on the silica gel sorbent based on an equilibrium time of less than 1 min. In case of the batch method, the effects of pH, shaking time, amount of sorbent, and desorption time were investigated. Among the desorption agents studied, only EDTA in ammonium chloride/ammonia buffer yielded quantitative recoveries. Freundlich's sorption isotherms determined for each metal show that sufficient sorption ability is obtained. The column method allows the preconcentration of metal ions from large sample volumes (e.g. 200 mL) using a flow rate of 5 mL min^–1. The influence of foreign ions present in natural waters and saline solutions was examined. The reproducibility of the total analytical method, expressed as relative standard deviation (RSD) is 1.8, 0.5 and 0.6%, for lead, cadmium and zinc, respectively.     

Sorption of Copper(II) Ions with Nanosized Magnesium Phosphate

A new approach to the preparation of a nanosized sorbent based on magnesium phosphate has been developed. The patterns of copper(II) ions sorption with nanosized magnesium phosphate from aqueous solutions have been investigated. The sorption parameters have been determined, and the kinetics and mechanism of the processes have been elucidated. The high sorption ability of the nanoscale sorbent has been shown in comparison with existing sorbents based on magnesium phosphate.     

Sorption of noble-metal ions on silica with chemically bonded nitrogen-containing ligands

A study has been made of the sorption of Ir(IV), Rh(III), Pt(IV), Ru(IV), Os(VIII), Pd(II) and Au(III) from aqueous solutions by silica chemically modified with nitrogen-containing organic ligands, as a function of hydrochloric acid concentration, time of contact, concentration of the element and the ionic strength. Sorption of noble-metal ions at pH > 1 on a sorbent containing monoamine groups seems to be due to a complexation mechanism, and to an anion-exchange mechanism at pH < 1. With aminopropyl-silica 1000-fold concentration of Ir(IV) and Rh(III) from their 10(-8)-10(-7)M solutions was achieved and these metals were subsequently determined on the sorbent surface by X-ray fluorescence. Detection limits were 10-20 ng/ml. There was no interference from 1000-fold quantities of non-ferrous metal ions and Fe(III). With the sorbent containing bonded diethylenetriamine groups, 1000-fold concentration of Au(III) was achieved, and it was then determined on the sorbent surface by an atomic-emission method. Conditions for desorption of Au(III) with pyridine and potassium thiocyanate were developed.     

Complexation of transition metal ions on the surface of carboxyethylated aminopolysiloxanes

The effect of the nature of the sorbent matrix and the state of ions of some transition metals in solution on their sorption by carboxyethylated alumino-, zircono-, and titano-aminopolysiloxanes was studied. Modification of the aminopolysiloxane matrix with zirconia, alumina, or titania results in displacement of the optimal sorption ranges for copper(II), nickel(II), and cobalt(II) to alkaline pH. Comparison of the results of structural studies of the complexes of N-aryl-3-aminopropionic acids in solutions and compositions of equilibrium solutions upon sorption of metal ions from ammonia-acetate buffer systems demonstrated that metal ions are simultaneously coordinated by the functional groups of iminodipropionic acid, which are rigidly attached to on the polysiloxane matrix, and by monodentate molecular ligands (ammonia molecules) present in the buffer solution. A competitive influence of copper(II), nickel(II), and cobalt(II) on the sorption from mixed solutions was established.     

Thermodynamics of Pb2+ and Ni2+ adsorption onto natural bentonite from aqueous solutions

Removal of Pb2+ and Ni2+ from aqueous solutions by sorption onto natural bentonite was investigated. Experiments were carried out as a function of particle size, the amount of bentonite, pH, concentration of metals, contact time, and temperature. The adsorption patterns of metal ions onto followed the Langmuir, Freundlich, and Dubinin-Radushkevich isotherms. This included adsorption isotherms of single-metal solutions at 303 K by batch experiments. The thermodynamic parameters (DeltaH,DeltaS,DeltaG) for Pb2+ and Ni2+ sorption onto bentonite were also determined from the temperature dependence. The adsorptions were endothermic reactions. The results suggested that natural bentonite is suitable as a sorbent material for recovery and adsorption of metal ions from aqueous solutions.     

Recovery of heavy metal ions from aqueous solutions using modified organosilicas

Sorption of Cu(II), Pb(II), Cd(II), and Zn(II) from aqueous solutions on two-component organosilicas was studied as influenced by sorbent composition, contact time, ratio of solid and liquid phases, solution pH, nature and concentration of heavy metal ions, and content of modifying agent. The degrees of sorption of these metal ions from aqueous solutions using organosilicas modified with aluminum(III) added into the siloxane matrix or with copper(II) grafted to the sorbent surface layer were compared.     

Adsorption of alkali and alkaline earth radionuclides on zeolite from water solutions

The adsorption of cesium and strontium ions from water solutions on zeolite has been investigated in presence of sodium, potassium, magnesium and calcium ions. Distribution ratios of cesium and strontium on the zeolite were determined in solutions of various compositions and solution volume to sorbent weight ratios (batch factor). Breakthrough curves for zeolite layers are reported.     

Study of the effect of oxidative-bisulfite modification of the cotton cellulose on its ion exchange properties

The effect of chemical modification on the sorption properties of cotton cellulose toward Cu(II) and Ni(II) ions was studied. The modification was carried out in two stages: oxidation of cellulose with the formation of dialdehydocellulose, followed by its sulfonation. The optimal conditions for modifying the cellulose to produce a sorbent capable to remove effectively the heavy metal ions from aqueous solutions of corresponding salts were elucidated. The modified sorbent exceeds the native cellulose in the sorption capacity (in terms of sorption maximum) about 3 times, therewith the time of extraction of heavy metal ions is reduced from 45 to 8 min. The high sorption properties are defined by the formation of new sorption sites -SO₃Na along with initially formed -COOH groups on the sorbent surface.     

Sorption isotherms of Nickel(II), Cobalt(II), Mercury(II), and Lead(II) ions on a phosphorus-containing polymeric sorbent

The influence of the concentration of a complexing ion on the sorption recovery of nickel, cobalt, mercury, and lead ions from aqueous solutions by a phosphorus-containing polymeric polybutadiene-based sorbent was studied. Sorption isotherms of the studied metal ions were processed by the Langmuir and Freindlich models. The affinity of metal ions to the functional groups of a sorbent and the stability of complexes were established to decrease in the order Hg(II) > Pb(II) > Co(II) > Ni(II).     

Effect of oxidation of activated carbon on its enrichment efficiency of metal ions: comparison with oxidized and non-oxidized multi-walled carbon nanotubes

The effect of oxidation of activated carbon (AC) with various oxidizing agents (nitric acid, hydrogen peroxide, ammonium persulfate) on preconcentration of metal ions (Cr3+, Mn2+, Pb2+, Cu2+, Cd2+ and Zn2+) from environmental waters prior to their flame atomic absorption spectroscopic analysis was investigated. The highest recoveries and adsorption capacities towards metal ions were achieved when using nitric acid-oxidized AC (sorbent AC-NA) as preconcentrating sorbent at pH 9. A preconcentration procedure was optimized using AC-NA as sorbent, which was then compared with non-oxidized AC in terms of analytical performance of the preconcentration method. Higher sensitivity, lower detection limits and wider linear ranges were achieved when AC-NA was used. The analytical performance of the method using AC-NA as preconcentrating sorbent was also compared with nitric acid-oxidized multi-walled carbon nanotubes (sorbent MWCNT-NA) and non-oxidized multi-walled carbon nanotubes (sorbent MWCNT). The analytical performance of the preconcentration method using AC-NA was close to MWCNT-NA, but AC-NA was better than non-oxidized MWCNT. Application of the optimized preconcentration method (using AC-NA sorbent) to environmental waters (tap water, reservoir water, stream water) gave spike recoveries of the metals in the range 63-104%.     

Preconcentration of Some Trace Metal Ions from Drinking and Tap Water Samples by Sorption on Amberlite XAD‐4 after Complexation with Di‐2‐Pyridyl Ketone Thiosemicarbazone

Abstract

A method was established for enrichment of trace levels of Co(II), Ni(II), Fe(II), and Cu(II) ions in aqueous solutions. These metals were quantitatively retained on an Amberlite XAD‐4 column, after complexation with di‐2‐pyridyl ketone thiosemicarbazone (DPKT). After elution with 1 M HNO₃ in acetone, concentration of metals were measured by atomic absorption spectrometry. The effect of major cations of drinking and tap water samples on the sorption of metal ions also were investigated. The amount of the analyte metal ions determined after preconcentration was basically in agreement with the added amount.

The developed method was used for the determination of trace amounts of metal ions in drinking and tap water samples with good results, such as relative standart deviations below 2% (N=6) and recoveries greater than >95%.     

Sorption and preconcentration of copper and cadmium on silica gel modified with 3-aminopropyltriethoxysilane

3-Aminopropyltriethoxysilane, (C₂H₅O)₃ Si(CH₂)₃NH₂, loaded on silica gel was used as a pre-concentration sorbent for copper and cadmium prior to their determination by flame atomic absorption spectrometry (FAAS). Both batch and column methods were used for the separation of the above metals. The analytes are quantitatively retained on the proposed adsorbent at pH 6.5. The complexation capacity of the collector is 0.032 mmol Cu/g silica. In the batch method, the effects of shaking time and the ratio of metal/silica on the retention by the asorbent were investigated. Columns filled with the collector provided quantitative recovery of the above metals from standardized samples as well as from sodium chloride solutions.