Modeling Pb sorption to microporous amorphous oxides as discrete particles and coatings

Hydrous amorphous Al (HAO), Fe (HFO), and Mn (HMO) oxides are ubiquitous in the subsurface as both discrete particles and coatings and exhibit a high affinity for heavy metal contaminants. To assess risks associated with heavy metals, such as Pb, to the surrounding environment and manage remedial activities requires accurate mechanistic models with well-defined transport parameters that represent sorption processes. Experiments were conducted to evaluate Pb sorption to microporous Al, Fe, and Mn oxides, as well as to montmorillonite and HAO-coated montmorillonite. Intraparticle diffusion, a natural attenuating process, was observed to be the rate-limiting mechanism in the sorption process, where best-fit surface diffusivities ranged from 10(-18) to 10(-15) cm(2) s(-1). Specifically, diffusivities of Pb sorption to discrete aluminum oxide, aluminum oxide-coated montmorillonite, and montmorillonite indicated substrate surface characteristics influence metal mobility where diffusivity increased as affinity decreased. Furthermore, the diffusivity for aluminum oxide-coated montmorillonite was consistent with the concentrations of the individual minerals present and their associated particle size distributions. These results suggest that diffusivities for other coated systems can be predicted, and that oxide coatings and montmorillonite are effective sinks for heavy metal ions.     

The impact of Mn oxide coatings on Zn distribution

Zinc sorption to hydrous manganese oxide (HMO)-coated clay was investigated macroscopically, kinetically, and spectroscopically. Adsorption edges and isotherms revealed that the affinity and capacity of the HMO-coated montmorillonite was greater than that of montmorillonite, and when normalized to the oxide present, the coatings behaved similarly to the discrete Mn oxide. Over two pH conditions, 5 and 6, a linear relationship was observed for the isotherms; further analysis with X-ray absorption spectroscopy (XAS) resulted in one type of sorption configuration as a function of loading and ionic strength at pH 5. However, at a surface loading of 10(-3) mol(Zn) g(HMO-coatedclay)(-1) when the pH increased from 5 to 7, the first shell distance decreased slightly, while the atoms and coordination numbers remained the same; this change may be attributed to an increase in electrostatic interactions. After a contact time of 4 months where an additional 60% of the sites become occupied, the slower sorption process was modeled as intraparticle surface diffusion. Best fit diffusivities ranged from 10(-18) to 10(-17) cm2/s, where a slower process was observed for the coated surface as compared to the discrete oxide. Interestingly, the porosity of the Mn oxide coating appears to be influenced by the substrate during its growth, as its increase and shift to a smaller pore size distribution resulted in a diffusivity between that observed for discrete HMO and montmorillonite.     

Intraparticle surface diffusion of metal contaminants and their attenuation in microporous amorphous Al, Fe, and Mn oxides

Intraparticle surface diffusion is an important and rate-limiting process in the sorption of metal ions to microporous sorbents such as those of hydrous amorphous Al (HAO), Fe (HFO), and Mn (HMO) oxides; these minerals are abundant in the environment, exhibiting a high affinity for metal contaminants. In aquatic systems representative of natural environments, internal micropore surfaces of HAO, HFO, and HMO can account for 40 to 90% of the sorption sites. Surface diffusivities have been observed to range between 10(-16) and 10(-10) cm2 s(-1) for metals including Sr, Cd, Zn, and Ni. The combination of significant microporosity and small diffusivities results in the amorphous oxides acting as natural attenuating sinks.     

Surface complexation of Pb(II) on amorphous iron oxide and manganese oxide: spectroscopic and time studies

Hydrous Fe and Mn oxides (HFO and HMO) are important sinks for heavy metals and Pb(II) is one of the more prevalent metal contaminants in the environment. In this work, Pb(II) sorption to HFO (Fe(2)O(3) x nH(2)O, n=1-3) and HMO (MnO(2)) surfaces has been studied with EXAFS: mononuclear bidentate surface complexes were observed on FeO(6) (MnO(6)) octahedra with PbO distance of 2.25-2.35 Angstrom and PbFe(Mn) distances of 3.29-3.36 (3.65-3.76) Angstrom. These surface complexes were invariant of pH 5 and 6, ionic strength 2.8 x 10(-3) to 1.5 x 10(-2), loading 2.03 x 10(-4) to 9.1 x 10(-3) mol Pb/g, and reaction time up to 21 months. EXAFS data at the Fe K-edge revealed that freshly precipitated HFO exhibits short-range order; the sorbed Pb(II) ions do not substitute for Fe but may inhibit crystallization of HFO. Pb(II) sorbed to HFO through a rapid initial uptake ( approximately 77%) followed by a slow intraparticle diffusion step ( approximately 23%) resulting in a surface diffusivity of 2.5 x 10(-15) cm(2)/s. Results from this study suggest that mechanistic investigations provide a solid basis for successful adsorption modeling and that inclusion of intraparticle surface diffusion may lead to improved geochemical transport depiction.     

Properties and structure of manganese oxide-coated clay

In the environment, heavy metals are important contaminants that sorb to and accumulate in soils and sediments. Dominant minerals in the subsurface are oxides and clay, which occur as discrete particles and heterogeneous systems; these surfaces can significantly impact the mobility and bioavailability of metals through sorption. To better understand heterogeneous systems, amorphous (hydrous manganese oxide (HMO)) and crystalline manganese oxides (birnessite and pyrolusite) were coated on montmorillonite. However, the montmorillonite substrate potentially inhibited crystallization of the pyrolusite coating, and also resulted in a poorly crystalline birnessite. Mineralogy and morphology of the coated systems suggest an amorphous structure for HMO and uniform coverage for HMO and birnessite coatings; the presence of Si and Al indicates uncoated areas along intraplanar surfaces. The coating surface charge behaved similarly to that of discrete oxides and clay where the pH(znpc) of HMO- and birnessite-coated clay were 2.8 and 3.1, respectively. Surface area of the coated systems increased while the pore size distribution decreased as compared to the external surface area and pores of montmorillonite. X-ray absorption spectroscopy (XAS) revealed the local structural environment of Mn in the HMO- and birnessite-coated clay was consistent with the pure phase oxides: for HMO-coated clay 3.1 atoms of oxygen at 1.89 +/- 0.02 A in the first shell and 2.7 atoms of manganese at 2.85 +/- 0.02 in the second shell; and, for birnessite-coated clay 6 atoms of oxygen at 1.91 +/- 0.02 A in the first shell and 6 atoms of manganese at distance 2.99 +/- 0.02 A in the second shell. Overall, the surface properties suggest that the coating behaves like that of discrete oxides, an important sink for metal contaminants.     

Enrichment of Pb(II) ions using phthalic acid functionalized XAD-16 resin as a sorbent

A simple and reliable method has been developed using polymeric material containing phthalic acid as a chelating agent to concentrate ultratrace amounts of lead ions in aqueous solutions. After characterization by CHN, IR, and thermal studies, the static and dynamic sorption behavior of Pb(II) ions onto new synthetic resin has been investigated. The sorption has been optimized with respect to pH, shaking speed, and contact time between the two phases. Maximum sorption is achieved from solution of pH 5-8 after 10 min agitation time. The lowest concentration for quantitative recovery is 5.8 ng cm(-3) with a preconcentration factor of approximately 850. The kinetics of sorption follows the first-order rate equation with the rate constant k=0.58+/-0.04 min(-1). The variation of the equilibrium constant K(c) with temperature between 10 and 50 degrees C yields values of DeltaH, 52.4+/-1.65 kJmol(-1), DeltaS, 186+/-5.21 Jmol(-1)K(-1), and DeltaG(303K), -4.15+/-0.002 kJmol(-1). The sorption data of Pb(II) ions in the concentration range from 2.41x10(-6) to 1.44x10(-4) molL(-1) follows the Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherms at all temperatures investigated. The sorption of Pb(II) ions onto synthesized resin in the presence of common anions and cations has also been measured. The possible sorption mechanism of Pb(II) ions onto phthalic acid modified XAD-16 is also discussed. The sorption procedure is utilized to preconcentrate Pb(II) ions prior to their determination in automobile exhaust particulates by atomic absorption spectrometry using direct and standard addition methods.     

Determination of trace metal ions by AAS in natural water samples after preconcentration of pyrocatechol violet complexes on an activated carbon column

A simple preconcentration method is described for the determination of Cu, Mn, Co, Cd, Pb, Ni and Cr in water samples by flame AAS. Trace metal ions in water were sorbed as pyrocatechol violet complexes on activated carbon column at the pH range of 4–8, then eluted with 1 M HNO₃ in acetone. The effect of major cations and anions of the natural water samples on the sorption of metal ions has been also investigated. The concentration of the metal ions detected after preconcentration was in agreement with the added amount. The present method was found to be applicable to the preconcentration of Cu, Mn, Co, Cd, Pb, Ni and Cr in natural water samples with good results such as R.S.D. from 3 to 8% (N=10) and detection limits under 70 ng l⁻¹.     

Equilibrium and heat of adsorption of diethyl phthalate on heterogeneous adsorbents

The sorption of sodium silicate by synthetic magnetite (Fe3O4) at different pH conditions (pH 7-11) and initial silicate concentrations (1 x 10(-3) and 10 x 10(-3) molL(-1)) was studied using in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The analysis of infrared spectra of sodium silicate in solution as well as adsorbed on magnetite nano-particles clearly showed the evolution of different silicate species depending on pH and silica concentration. The silicate concentration studied (10 x 10(-3) molL(-1)) contained polymeric or condensed silicate species at lower pH as well as monomers at high pH, as evident from infrared spectra. Condensation of monomers resulted in an increased intensity of absorptions in the high frequency part (>1050 cm(-1)) of the spectral region, which contains information about both silicate in solution and sorbed silicate viz. 1300 cm(-1)-850 cm(-1). In the pH range studied, infrared spectra of sorbed silicate and sorbed silicate during desorption both indicated the presence of different types of surface complexes at the magnetite surface. The sorption mechanism proposed is in accordance with a ligand exchange reaction where both monodentate and bidentate complexes could exist at low surface loading level, the relative proportion of the complexes being due to both pH and concentration in solution. Oligomerization occurred on the magnetite surface at higher surface loading.     

A new chelating sorbent for metal ion extraction under high saline conditions

A new chelating polymeric sorbent was developed by functionalizing Amberlite XAD-16 with 1,3-dimethyl-3-aminopropan-1-ol via a simple condensation mechanism. The newly developed chelating matrix offered a high resin capacity and faster sorption kinetics for the metal ions such as Mn(II), Pb(II), Ni(II), Co(II), Cu(II), Cd(II) and Zn(II). Various physio-chemical parameters like pH-effect, kinetics, eluant volume and flow rate, sample breakthrough volume, matrix interference effect on the metal ion sorption have been studied. The optimum pH range for the sorption of the above mentioned metal ions were 6.0–7.5, 6.0–7.0, 8.0–8.5, 7.0–7.5, 6.5–7.5, 7.5–8.5 and 6.5–7.0, respectively. The resin capacities for Mn(II), Pb(II), Ni(II), Co(II), Cu(II), Cd(II) and Zn(II) were found to be 0.62, 0.23, 0.55, 0.27, 0.46, 0.21 and 0.25 mmol g⁻¹ of the resin, respectively. The lower limit of detection was 10 ng ml⁻¹ for Cd(II), 40 ng ml⁻¹ for Mn(II) and Zn(II), 32 ng ml⁻¹ for Ni(II), 25 ng ml⁻¹ for Cu(II) and Co(II) and 20 ng ml⁻¹ for Pb(II). A high preconcentration value of 300 in the case of Mn(II), Co(II), Ni(II), Cu(II),Cd(II) and a value of 500 and 250 for Pb(II) and Zn(II), respectively, were achieved. A recovery of >98% was obtained for all the metal ions with 4 M HCl as eluting agent except in the case of Cu(II) where in 6 M HCl was necessary. The chelating polymer showed low sorption behavior to alkali and alkaline earth metals and also to various inorganic anionic species present in saline matrix. The method was applied for metal ion determination from water samples like seawater, well water and tap water and also from green leafy vegetable, from certified multivitamin tablets and steel samples.     

Separation of antimony(III) with iodide and dithizone by sorption on polyurethane foam from sulphuric acid medium for its spectrophotometric determination in glasses

A method for quantitative separation of antimony(III) by sorption on polyether based polyurethane foam and its spectrophotometric determination has been described. The method involves formation of a pink-red complex of antimony(III) with iodide (0.045M) and dithizone (2.3 x 10(-5)M) in 0.25-0.75M H(2)SO(4) medium, sorption of the complex on polyurethane foam (within 45 min) at room temperature followed by its elution with acidified acetone (acetone containing 0.008% H(2)SO(4)) and spectrophotometric measurement at 507.2 nm ( = 2.56 x 10(4) l mol cm). The method obeys Beer's law from 0.1 to 6.0 mug antimony(III). Tolerance limits of other ions are Co (100 mug), Ni (100 mug), Fe (10 mug), Cu (0.5 mug), Sn (20 mug), Zn (100 mug), As (100 mug), Mn (200 mug), Pb (50 mug), Ti (100 mug), V (50 mug), etc. Interference by iron and copper have been eliminated by treating with KOH prior to the extraction of antimony. The method has been standardized with glass samples spiked with known amounts of antimony and applied to the determination of antimony in various glasses.     

Sorption/desorption of radionickel on/from Na-montmorillonite: kinetic and thermodynamic studies

In this work, Na-montmorillonite was used as a novel adsorbent for the sorption of Ni(II) from aqueous solutions. The sorption and desorption of Ni(II) on Na-montmorillonite was investigated as the function of pH, ionic strength, Ni(II) concentrations and temperature. The results indicated that the sorption of Ni(II) on Na-montmorillonite was strongly dependent on pH, ionic strength and temperature. The sorption of Ni(II) increases slowly from 22.1 to 51.4% at pH range 2–6.5, abruptly at pH 6.5–9, and at last maintains high level with increasing pH at pH > 9 in 0.1 mol/L NaNO₃ solutions. The Ni(II) kinetic sorption on Na-montmorillonite was fitted by the pseudo-second-order model better than by the pseudo-first-order model and the experimental data implies that Ni(II) sorption on montmorillonite were mainly controlled by the film diffusion mechanism. The Langmuir, Freundlich and D–R models were used to simulate the sorption data at three different temperatures (298.15, 318.15 and 338.15 K) and the results indicated that Langmuir model simulates the experimental data better than Freundlich and D–R models. The sorption–desorption isotherm of Ni(II) on montmorillonite suggested that the sorption is irreversible. The irreversible sorption of Ni(II) on montmorillonite indicates that montmorillonite can be used to pre-concentration and solidification of Ni(II) from large volumes of solution and to storage Ni(II) ions stably.     

Spectral characterization of a newly synthesized fluorescent semicarbazone derivative and its usage as a selective fiber optic sensor for copper(II)

In this work photoluminescent properties of highly Cu(2+) selective organic fluoroionophore, semicarbazone derivative; bis(naphtho[2,1-b]furan-2-yl)methanone semicarbazone (BNF) was investigated in different solvents (dichloromethane, tetrahydrofuran, toluene and ethanol) and in polymer matrices of polyvinylchloride (PVC) and ethyl cellulose (EC) by absorption and emission spectrometry. The BNF derivative displayed enhanced fluorescence emission quantum yield, Q(f)=6.1 x 10(-2) and molar extinction coefficient, epsilon=29,000+/-65 cm(-1)M(-1) in immobilized PVC matrix, compared to 2.6 x 10(-3) and 24,573+/-115 in ethanol solution. The offered sensor exhibited remarkable fluorescence intensity quenching upon exposure to Cu(2+) ions at pH 4.0 in the concentration range of 1.0 x 10(-9) to 3.0 x 10(-4)M [Cu(2+)] while the effects of the responding ions (Ca(2+), Hg(+), Pb(2+), Al(3+), Cr(3+), Mn(2+), Mg(2+), Sn(2+), Cd(2+), Co(2+) and Ni(2+)) were less pronounced.     

Ni(II) complexation to amorphous hydrous ferric oxide: an X-ray absorption spectroscopy study

Ni(II) sorption onto iron oxides and in particular hydrous ferric oxide (HFO) is among the important processes impacting its distribution, mobility, and bioavailability in environment. To develop mechanistic models for Ni, extended X-ray absorption fine structure (EXAFS) analysis has been conducted on Ni(II) sorbed to HFO. Coprecipitation revealed the formation of the metastable alpha-Ni(OH)(2) at a Ni(II) loading of 3.5 x 10(-3) molg(-1). On the other hand, Ni(II) formed inner-sphere mononuclear bidentate complexes along edges of FeO(6) octahedra when sorbed to HFO surfaces with Ni-O distances of 2.05-2.07 A and Ni-Fe distances of 3.07-3.11 A. This surface complex was observed by EXAFS study over 2.8 x 10(-3) to 10(-1) ionic strength, pH from 6 to 7, a Ni(II) loading of 8 x 10(-4) to 8.1 x 10(-3) molg(-1) HFO, and reaction times from 4 hours to 8 months. The short- and long-range structure analyses suggest that the presence of Ni(II) inhibited transformation of the amorphous iron oxide into a more crystalline form. However, Ni(2+) was not observed to substitute for Fe(3+) in the oxide structure. This study systematically addresses Ni(II) adsorption mechanisms to amorphous iron oxide. The experimentally defined surface complexes can be used to constrain surface complexation modeling for improved prediction of metal distribution at the iron oxide/aqueous interface.     

Solid Phase Extraction of Trace Metals in Seawater Using Morpholine Dithiocarbamate‐Loaded Amberlite XAD‐4 and Determination by ICP‐AES

Abstract

Application of morpholine dithiocarbamate (MDTC) coated Amberlite XAD‐4, for preconcentration of Cu(II), Cd(II), Zn(II), Pb(II), Ni(II) and Mn(II) by solid phase extraction and determination by inductively coupled plasma (ICP) atomic emission spectrometry (AES) was studied. The optimum pH values for quantitative sorption of Cu(II), Cd(II), Zn(II), Pb(II), Ni(II), and Mn(II) were 6.5–8.0, 7.0–8.5, 6.0–8.5, 6.5–8.5, 7.5–9.0, and 8.0–8.5, respectively. The metals were desorbed with 2 mol L^?1. The t_1/2 values for sorption of metal ions were 2.6, 2.9, 2.5, 2.6, 3.0, and 3.8 min respectively for Cu(II), Cd(II), Zn(II), Pb(II), Ni(II) and Mn(II). The effect of diverse ions on the determination of the previously named metals was studied. Simultaneous enrichment of the six metals was accomplished, and the method was applied for use in the determination of trace metal ions in seawater samples.     

A multi-scale assessment of Pb(II) sorption on dolomite

Macroscopic sorption studies indicated that Pb sorption capacity was independent of pH over the pH range 5-7, while sorption as a function of reaction time up to two weeks for systems with no bulk precipitate phases showed continuous Pb uptake on dolomite. This could be due to diffusion of Pb into the micropores of dolomite as well as an increase in surface sites caused by particle size reduction during suspension mixing. Normalized XANES spectra for systems undersaturated with respect to Pb carbonate precipitates resembled the spectrum of Pb4(OH)4(4+), suggesting that Pb is mainly coordinated to dolomite as an inner-sphere surface complex. On the other hand, the XANES spectrum for 10(-3) M Pb at 1 atm CO2(g) in a 2 M Mg(NO3)2 background electrolyte solution resembled that of cerussite, while a sample at 5 x 10(-4) M Pb in equilibrium with air and 2 M Mg(NO3)2 resembled that of hydrocerussite. EXAFS analyses of sorption samples in chloride solutions showed that there were only first-shell contributions under 1 atm CO2(g), while higher shell contributions from Ca/Mg were seen at 10(-3.42) atm CO2(g). On the other hand, EXAFS samples prepared in nitrate solutions showed noticeable differences in speciation under different reaction conditions-from outer-sphere surface complexes at low Pb concentrations and pH, to inner-sphere surface complexes at moderate Pb concentrations and neutral pH, to the formation of Pb carbonate precipitates at the highest Pb loadings.     

On-column complexation of metal ions using 2,6-pyridinedicarboxylic acid and separation of their anionic complexes by capillary electrophoresis with direct UV detection

On-column complexation of metal ions with 2,6-pyridinedicarboxylate (2,6-PDC) to form anionic complexes enabled their separation by capillary zone electrophoresis with direct UV detection at 214 nm. Nine metal ions, Cu2+, Zn2+, Ni2+, Cd2+ Mn2+, Pb2+, Fe3+, Al3+ and Ca2+, were determined in less than 7 min using 10 mM 2.6-PDC solution containing 0.75 mM tetradecyltrimethylammonium bromide at pH 4.0. Satisfactory working ranges (20-300 microM), detection limits (3-10 microM) and good repeatability of the peak areas (RSD 2.1-4.2%, n=5) were obtained using hydrodynamic injection (30 s). The proposed method was used successfully for the determination of Mn2+, Fe3+, Al3+ and Ca2+ in groundwaters.     

Trace metal ion partitioning at polymer film-metal oxide interfaces: long-period X-ray standing wave study

The distributions of Pb(II) and As(V)O4(3-) ions in the interfacial region between thin poly(acrylic acid) (PAA) coatings and aalpha-A12O3(0001), alpha-Al2O3(1-102), and alpha-Fe2O3(0001) single-crystal substrates were studied using long-period X-ray standing wave fluorescent yield (XSW-FY) and X-ray reflectivity techniques. The PAA film serves as a simplified analogue of natural organic matter (NOM) coatings on mineral surfaces. Such coatings are often assumed to play an important role in the partitioning and speciation of trace heavy metals in soils and aquatic systems. On the alpha-Al2O3(1-102) surface, Pb(II) ions were found to preferentially bind to the PAA coating, even at sub-micromolar Pb(II) concentrations, and to partition increasingly onto the metal oxide surface as the Pb(II) concentration was increased ([Pb(II)] = 5 x 10(-8) to 2 x 10(-5) M, pH = 4.5; 0.01 M NaCl background electrolyte). This observation suggests that the binding sites in the PAA coating outcompete those on the alpha-Al2O3(1-102) surface for Pb(II) under these conditions. The As(V)O4(3-) oxoanion partitions preferentially to the L-Al2O3(1-102) surface for the As(V)O4(3-) concentrations examined (1 x 10(-7) to 5 x 10(-7) M, pH = 4.5; 0.01 M NaCl background electrolyte). Partitioning of Pb(II) (at 1 x 10(-7) M and pH 4.5) was also examined at PAA/alpha-Al2O3(0001), and PAA/alpha-Fe2O3(0001) interfaces using XSW-FY measurements. Our results show that the PAA coating was the dominant sink for Pb(II) in all three samples; however, the relative order of reactivity of these metal oxide surfaces with respect to Pb(II) sorption is alpha-Fe2O3(0001) > alpha-Al2O3(1-102) > alpha-Al2O3(0001). This order is consistent with that found in previous studies of the PAA-free surfaces. These XSW results strongly suggest that the characteristics of the organic film (i.e., binding affinity, type, and density of binding sites) as well as metal oxide substrate reactivity are key factors determining the distribution and speciation of Pb(II) and As(V)O4(3-) at organic film/metal oxide interfaces.     

Atomic absorption spectrometric determination of Cd(II), Mn(II), Ni(II), Pb(II) and Zn(II) ions in water,fertilizer and tea samples after preconcentration on Amberlite XAD-1180 resin loaded with l-(2-pyridylazo)-2-naphthol

A new chelating resin, 1-(2-pyridylazo)-2-naphthol (PAN) coated Amberlite XAD-1180 (AXAD-1180), was prepared and used for the preconcentration of Cd(II), Mn(II), Ni(II), Pb(II) and Zn(II) ions prior to their determination by flame atomic absorption spectrometry (FAAS). The optimum pH for simultaneous retention of the elements and the best elution means for their simultaneous elution were pH 9.5 and 3 M HNO₃, respectively. The sorption capacity of the resin was found to be 5.3 mg/g for Cd and 3.7 mg/g for Ni. The detection limits for Cd(II), Mn(II), Ni(II), Pb(II) and Zn(II) were 0.7, 10, 3.1, 29 and 0.8 μg/L, respectively. The effects of interfering ions for quantitative sorption of the metal ions were investigated. The preconcentration factors of the method were in the range of 10–30. The recoveries obtained were quantitative (≥95%). The standard reference material (GBW07605 Tea sample) was analysed for accuracy of the described method. The proposed method was successfully applied to the analysis of various water, urea fertilizer and tea samples. The article is published in the original.     

Sorption of trace metals on human hair and application for cadmium and lead pre-concentration with flame atomic absorption determination

Human hair shavings were characterized as a sorbent for trace metals. At pH 7.0 metal sorption follows the order Pb(II)>Cd(II)>Cr(VI)>Fe(III)>Cu(II)>Ni(II)>Mn(VI). Metal recovery is quantitative for Pb and Cd after 30 min of equilibration. Recovery of other metals is less quantitative and varies with pH. For example, while Cu is best recovered at pH 5, Ni and Mn are sorbed optimally in the basic pH region. Sorbed metals can be washed off the sorbent with 0.5 mol L(-1) strong mineral acids or more completely with 0.1 mol L(-1) ethylenediaminetetraacetic acid (EDTA). Typical sorption isotherms were obtained for Cd and Pb with sorption capacities of 39 and 26 micromol g(-1), respectively.Hair sorbent was used for 40-fold pre-concentration of Cd and Pb from treated wastewater samples followed by flame atomic absorption spectroscopic (FAAS) determination. Comparison of the data obtained for lead and cadmium by the proposed pre-concentration method with that by graphite furnace atomic absorption spectroscopy (GFAAS) showed 79 to 86% recovery and comparable analytical precision. Common cations and anions at the levels normally present in natural water do not interfere in the proposed pre-concentration-FAAS method.