María del Rosario Martínez

Arsenic removal by goethite and jarosite in acidic conditions and its environmental implications

Schwertmannite (Fe(8)O(8)(OH)(5.5)(SO(4))(1.25)), jarosite (KFe(3)(SO(4))(2)(OH)(6)) and goethite (FeOOH) control natural attenuation of arsenic in acid mine drainage (AMD) impacted areas. Batch experiments were conducted to examine the sorption capacity of synthetic goethite and synthetic jarosite at highly acidic pH (1.5-2.5), at two ionic strengths (0.02-0.15 mol dm(-3), NaCl) and at sulphate concentrations in the range of 5 x 10(-3) to 2.8 x 10(-1) mol dm(-3). In the absence of competitive effects of other anions, K-jarosite presents better removal efficiency than goethite for As(V). The maximum sorption capacity is estimated to be 1.2 x 10(-4) and 7.0 x 10(-6)mol m(-2) for jarosite and goethite, respectively, under similar experimental conditions. The variation of arsenic sorbed on goethite as a function of the equilibrium arsenic concentration in solution fits a non-competitive Langmuir isotherm. In the case of K-jarosite, sorption data could not fit a Langmuir or Freundlich isotherm since sulphate-arsenate anion exchange is probably the sorption mechanism. Ionic strength and pH have little effect on the sorption capacity of goethite and jarosite in the small range of pH studied. The presence of sulphate, which is the main anion in AMD natural systems, has a negative effect on arsenic removal since sulphate competes with arsenate for surface sorption sites. Moreover, mobilization of arsenic in the transformation of schwertmannite to jarosite or goethite at pH 2-3 is proposed since the sorption capacities of goethite and K-jarosite are considerably lower than those reported for schwertmannite.

Heavy metal uptake from aqueous solution by cork and yohimbe bark wastes

In this work the ability of cork and yohimbe bark wastes to remove Cu(II) and Ni(II) from aqueous solutions has been studied. The influence of pH, sodium chloride and metal concentration on metal uptake was investigated. Metal uptake showed a pH-dependent profile. Maximum sorption for both metals was found to occur at around pH 6–7. In the case of cork an increase of sodium chloride concentration provoked a decrease in metal removal. Adsorption isotherms at the optimum pH were expressed by the non-competitive Langmuir adsorption model, and model parameters were determined. It was seen that the adsorption equilibrium data fitted very well to the model in the concentration range studied. When comparing both biomaterials, yohimbe bark waste was found to be the most efficient adsorbent for both metals studied. © 2000 Society of Chemical Industry

Simultaneous determination of Cr(III), Fe(III), Cu(II) and Pb(II) as UV-absorbing EDTA complexes by capillary zone electrophoresis

Abstract Capillary zone electrophoresis (CZE) with on-column UV detection was used to separate and determine Cr(III), Fe(III), Cu(II) and Pb(II) complexes with EDTA. Distribution species-pH diagrams showed that, under the experimental conditions chosen (pH 5.5), [Me-EDTA] − and [Me-EDTA] 2− species for trivalent and divalent metals, respectively, were present. By adding a cationic surfactant, such as TTAB (tetradecyltrimethylammonium bromide), to the background electrolyte, an improvement in the peak shapes and shorter migration times were achieved. The chelating complexes showed the following order of mobility in electropherograms: [EDTA] 2− > [Cu-EDTA] 2− >[Pb-EDTA] 2− >[Cr-EDTA] − >[Fe-EDTA] − . At 225 nm under a negative applied voltage of 30 kV, using a capillary of 30.5 cm effective length, in 0.1 M acetate buffer and 0.1 m M TTAB as carrier solution, the complexes were determined within 6 min, but the resolution of the Cu(II) and Pb(II) chelates was poor. However, by using a capillary of 60 cm effective length, simultaneous separation of these chelates the EDTA was achieved. Factorial design was used to investigate the effects of chromium,, excess of EDTA and boiling time of the solution on the formation of the [Cr-EDTA] − complex. A fitting model was found in which the EDTA concentration was a significant factor. The detection limits of all chelates were in the range 6–27 μM .

Determination of gold(I) and silver(I) cyanide in ores by capillary zone electrophoresis

Abstract Capillary zone electrophoresis (CZE) with on-column UV detection at 214 nm was used to detect and determine gold(I) and silver(I) cyanide complexes in alkaline cyanide solution. Under an applied voltage of 25 kV, dicyanoaurate(I) and dicyanoargentate(I) were separated in less than 6 min. Carbonate buffer was used and the separation of both anions was achieved using an anodic injection and cathodic detection scheme. The method was applied to the determination of gold and silver cyanide in ore samples. Quantitative analysis was possible and good agreement between CZE and atomic absorption spectrometric results was obtained.

Modelling of the Ni(II) removal from aqueous solutions onto grape stalk wastes in fixed-bed column.

Grape stalk wastes generated in the wine production process were used for the removal of nickel (II) from aqueous solution. The experimental breakthrough curves were obtained in fixed-bed columns. Experiments we carry out in order to evaluate the influence of inlet metal concentration (30 and 70 mg L(-1)) and the regeneration process in a double sorption cycle. The CXTFIT code was used to fit the experimental data and to determine the transport and sorption parameters of the convective-dispersive equation (CDE) and the two-site deterministic non-equilibrium (TSM/CDE) model by adjusting the models to the experimental breakthrough curves (BTC). The results showed that bed capacity as well as transport and sorption parameters were affected by the initial metal concentration, at the highest Ni(II) concentration the grape stalks column saturated quickly leading to earlier breakthrough. The sorption capacity of the sorbent was slightly reduced in a double sorption cycle, while the recovery of the metal in the desorption step was ranging between 80% and 85% in both cycles.

Solvent extraction of iron (III) by bis (2,4,4-trimethylpentyl) phosphinic acid: experimental equilibrium study

Abstract The extraction of iron(III) from aqueous nitrate solutions by bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272=HA) dissolved in Isopar-H was studied at 25°C and 0.1 ionic strength. The distribution of the metal was measured as a function of pH and metal and extractant concentration. The data have been analyzed both graphically and numerically to determine the stoichiometry of extracted species and their equilibrium constants. It was found that iron (III) was extracted into the organic phase by the formation of the species FeA3, FeA3(HA)3 and Fe(NO3)3(HA)3.

Simultaneous determination of chloride complexes of Pt(IV) and Pd(II) by capillary zone electrophoresis with direct UV absorbance detection

Abstract The chloride ion was found to be a suitable complexing agent for the separation and determination of a Pt(IV)/Pd(II) mixture with by capillary zone electrophoresis, using direct UV absorbance detection at 270 nm. The pH and chloride concentration had a significant effect on the determination for which a carrier solution containing 0.1 M HCl and 0.4 M NaCl was used. The optimum applied voltage was around — 8 kV. The Joule heating effect was not observed, as the electric current and migration times were rather stable and reproducible. The method was validated with respect to its response linearity and reproducibility. The detection limits found were 0.9 and 1.4 μg ml −1 for Pt(IV) and Pd(II), respectively. By use of stacking conditions, the detection limits were improved by a factor of 13. It was demonstrated that at pH 2, two species of platinum were present, one probably having a negative charge, [PtCl 5 H 2 O] − . The method was applied to the determination of Pt in samples of catalytic converters. The same samples were analysed by flame atomic absorption spectrometry.

Determination of chloride complex of Au(III) by capillary zone electrophoresis with direct UV detection

Abstract Capillary zone electroophoresis was used for the determination of gold(III) chloride using direct UV detection at 220 nm. By using a capillary column 70 cm long, the optimum applied voltage was found to be around −7 kV; carrier solution containing 0.1 M HCl and 0.4 M NaCl was used as an additive. At this pH, the electroosmotic flow-rate appears to be almost zero. The effects of chloride concentration and the applied voltage on determination efficiency are discussed. Heat generation appeared negligible as the electric current and migration time were reproducible. The analytical performance is discussed in terms of the detection limit, linearity and reproducibility. A single trial was performed in 18 min. Under these conditions, Pd(II) and Pt(IV) can also be determined; the order of mobility in the electropherogram was as follows: PdCl42− > PtCl62− > AuCl4−. The method was applied to the monitoring of Au concentration during a study of AuCl4− transport through solid-supported liquid membranes.

Grape Stalks Waste as Low Cost Biosorbents: An Alternative for Metal Removal from Aqueous Solutions

Abstract Grape stalks waste generated in the wine production process has been investigated as metal sorbent for Pb(II), Ni(II), Cu(II), and Cd(II) from aqueous solutions. Kinetic studies revealed that the initial uptake was rapid and equilibrium was established in one hour. The results obtained from batch experiments at initial pH 6.0±0.5 were described by the Langmuir isotherm. The highest value of the Langmuir maximum uptake, (q max ), was found for cadmium (0.248 mmol g−1) followed by lead (0.241 mmol g−1), nickel (0.181 mmol g−1), and copper (0.159 mmol g−1). Column experiments were also performed at a constant metal concentration of around 0.250 mmol dm−3 at pH 6.0±0.5 and the results were modelled by means of the reactive transport code RETRASO (REactive TRAnsport of SOlutes) applying a Langmuir sorption mechanism as well. The values obtained from both experimental approaches are found to coincide fairly well. The Langmuir constants (L mol−1) determined are: Copper (1.5 · 103 and 1.0 · 104), Nickel (1.4 · 103 and 2.5 · 103), Lead (8.3 · 104 and 3.5 · 103), and Cadmium (7.0 · 103 and 4.5 · 103), where values in parenthesis correspond to the batch and column determinations, respectively.

Reactive transport of arsenic(III) and arsenic(V) on natural hematite: experimental and modeling.

Natural hematite was used for the removal of arsenic(III) and arsenic(V) from aqueous solution. The experimental breakthrough curves were obtained in fixed-bed columns. The transport of arsenic in a simplified fixed-bed configuration was quantified by using the CXTFIT code, which was used to estimate the transport and sorption parameters of the convective-dispersive equation (CDE) and the two-site deterministic nonequilibrium (TSM/CDE) model by fitting the models to the experimental breakthrough curves (BTC). The prediction of the breakthrough curves performed by the two-site nonequilibrium sorption model resulted in a good fit, indicating that this model can properly describe the transport and sorption processes of arsenic on natural hematite. Additionally the parameters obtained indicate that nonequilibrium sorption governs the As(III) and As(V) uptake onto hematite in a fixed-bed column. No significant differences in the transport and sorption parameters of As(III) and As(V) on natural hematite were obtained; the retardation factor values were in the same order of magnitude for both species.