ABSTRACT This work presents a study on the chemical and electrochemical properties of Sm(III) sol... more ABSTRACT This work presents a study on the chemical and electrochemical properties of Sm(III) solutions in two molten chloride mixtures with different acidity properties: (i) the eutectic LiCl–KCl, in the temperature range 673–823 K and (ii) the equimolar CaCl2–NaCl melt at 823 K. In both media and on a W inert electrode, the electro-reduction of Sm(III) takes place via one step Sm(III)/Sm(II). The second system Sm(II)/Sm(0) has not been observed within the electrochemical windows, because of the prior reduction of Li(I) and Na(I) from the solvent, which inhibits the electro-extraction of Sm species from the salts on the inert substrate.On the W electrode, the electro-reduction of Sm(III) to Sm(II) takes place in a quasi-reversible electrochemical mode. Accurate values of the reversible half wave potential, the intrinsic rate constant of charge transfer, k0, and the charge transfer coefficient, α, have been calculated for the first time in both molten chlorides, by simulation of the cyclic voltammograms and logarithmic analysis of the convoluted curves. The diffusion coefficient of Sm(III) has been also calculated by different electrochemical techniques, avoiding the meniscus effect by modification of the immersion dept of the working electrode in stages. The values of the diffusion coefficient indicate that Sm(III) diffuses slower in the equimolar CaCl2–NaCl than in the eutectic LiCl–KCl. This behaviour can be explained by the different viscosities of both media, which significantly reduces the mobility of Sm(III) in the CaCl2–NaCl melt.The identification of the SmO compounds that are stable in the melts as well as the determination of their solubility products were carried out by potentiometric titration using an yttria stabilised zirconia membrane electrode (YSZME). The results indicated that SmOCl is a solid stable compound in the studied melts and that Sm2O3 is a strong oxobase leading to the formation of SmOCl. The best chlorination conditions have been extracted from the comparison of the E-pO2− diagram of samarium and that of some gaseous chlorinating mixtures previously reported.
To investigate the possibility of selective chlorination to separate copper traces from zinc matr... more To investigate the possibility of selective chlorination to separate copper traces from zinc matrixes, we have determined redox and oxoacidobasic properties of the copper in the molten ZnCl2-2NaCl. In this way, the stability of copper chlorides and oxides as well as the electrochemical behaviour of Cu(I) have been studied by using voltammetric, chronopotentiometric, chronoamperometric and potentiometric techniques. The experiments were
A UV photo-oxidation device was constructed for the destruction of dissolved organic matter (DAM)... more A UV photo-oxidation device was constructed for the destruction of dissolved organic matter (DAM) in freshwater samples in order to determine traces of zinc, cadmium, lead and copper bound to D a M as inert species, by anodic stripping voltammetry in the differential pulse mode (DPASV). The photodigestor performance was optimised by means of the Taguchi experimental design. Four control factors (or design parameters) at three levels were explored: exposure-time to the UVirradiation, pH of the sample, hydrogen peroxide concentration and mineral acid added, and assigned to the columns of a L9(3 4) saturated orthogonal array. A noise factor (nitrilotriacetic acid concentration) at three levels was introduced in the experiment to simulate the uncontrollable amount of D a M in water samples. The experiment was conducted with two replications of each trial and an optimum response insensitive to the variations of D a M concentration was found when samples, acidified at pH 2 with sulphuric acid, were irradiated for 30 rain in the presence of 12.3 mmol/L hydrogen peroxide. The proposed procedure is more precise, accurate and fast than the wet digestion method.
Journal of Environmental Science and Health . Part A: Environmental Science and Engineering and Toxicology, 1997
The complexation of the pesticide Metamitron by copper was investigated by polarography, anodic s... more The complexation of the pesticide Metamitron by copper was investigated by polarography, anodic stripping voltammetry and cathodic stripping voltammetry. The influence of the pH on the complexation was determined and a maximum value for the conditional stability constant of the copper‐metamitron complex (log β'=3.8) was obtained at pH 5.6.An investigation into the photochemical degradation of the pesticide demonstrated that copper
A method has been developed for the determination of phosphorus, as phosphate, by means of the ca... more A method has been developed for the determination of phosphorus, as phosphate, by means of the catalytic polarographic wave for the reduction of hydrogen peroxide in the presence of Mo(V1). This reduction is combined with the previous formation and extraction of l2-molybdophosphoric acid. Depending on the extractant chosen, ethyl acetate or methyl isobutyl ketone, the determination limit is 2.3 or 3.1 rig/l.. respectively. The procedure has been applied to certified steel samples with good results.
ABSTRACT A procedure for purifying waters polluted with metal ions has been designed. The method ... more ABSTRACT A procedure for purifying waters polluted with metal ions has been designed. The method is based on the precipitation of metals as magnetic ferrite from the alkalinised solution containing iron(II). The working conditions were optimised by using a Taguchi L9(34) experimental design in order to minimise the total residual concentration (TRC) of metal ions in solution. A statistical analysis of the experimental data revealed the most influential factor to be the Fe(II)/metal concentration ratio (F), with a 29.5% contribution, followed by pH (P, 5.2%) and time (H, 2.3%). On the other hand, temperature (T) had little effect on the purification efficiency (1.0%), whereas noise (N, KMnO4) was found to contribute by as much as 22.1%. Maximal purification efficiency (99.99%) is achieved when wastewater samples are treated for 3 h at 50°C and pH 10 in the presence of iron(II) in a ratio Fe(II)/total metal of 15. In these conditions, the process efficiency is also the least influenced by variability in the sample composition, which validates the proposed procedure.
A method for determination of arsenic(V) in the range between 1 x 10(-7) and 1.2 x 10(-6)M has be... more A method for determination of arsenic(V) in the range between 1 x 10(-7) and 1.2 x 10(-6)M has been developed. These levels are reached by means of the multiplication factor yielded by use of 12-molybdoarsenic acid and the great sensitivity of polarographic determination of the Mo(VI) in the heteropoly acid. The procedure has been successfully applied to determination of arsenic in copper alloys, after selective extraction of phosphorus.
The global average effective dose from natural radiation sources is estimated to be 2.4 mSv y(-1)... more The global average effective dose from natural radiation sources is estimated to be 2.4 mSv y(-1). Nevertheless, local variations in the radiation exposure may differ by orders of magnitude. In this paper, we study a rural area in western Salamanca (Spain) where doses are potentially well above the stated average value. Its geology consists mostly of granite and schist, presenting various uranium mineralisations, some of which were exploited in former years. Water samples, both surface and groundwater, were collected in selected villages and measured by liquid-scintillation spectrometry. 222Rn in dwellings was determined in dwellings by means of short-term measurements, using Picorad vials and long-term measurements with CR-39 detectors. The committed effective doses to the inhabitants due to indoor 222Rn and 222Rn and 226Ra in drinking water were assessed using the dose conversion factors proposed in the UNSCEAR 2000 report.
ABSTRACT This work presents a study on the chemical and electrochemical properties of Sm(III) sol... more ABSTRACT This work presents a study on the chemical and electrochemical properties of Sm(III) solutions in two molten chloride mixtures with different acidity properties: (i) the eutectic LiCl–KCl, in the temperature range 673–823 K and (ii) the equimolar CaCl2–NaCl melt at 823 K. In both media and on a W inert electrode, the electro-reduction of Sm(III) takes place via one step Sm(III)/Sm(II). The second system Sm(II)/Sm(0) has not been observed within the electrochemical windows, because of the prior reduction of Li(I) and Na(I) from the solvent, which inhibits the electro-extraction of Sm species from the salts on the inert substrate.On the W electrode, the electro-reduction of Sm(III) to Sm(II) takes place in a quasi-reversible electrochemical mode. Accurate values of the reversible half wave potential, the intrinsic rate constant of charge transfer, k0, and the charge transfer coefficient, α, have been calculated for the first time in both molten chlorides, by simulation of the cyclic voltammograms and logarithmic analysis of the convoluted curves. The diffusion coefficient of Sm(III) has been also calculated by different electrochemical techniques, avoiding the meniscus effect by modification of the immersion dept of the working electrode in stages. The values of the diffusion coefficient indicate that Sm(III) diffuses slower in the equimolar CaCl2–NaCl than in the eutectic LiCl–KCl. This behaviour can be explained by the different viscosities of both media, which significantly reduces the mobility of Sm(III) in the CaCl2–NaCl melt.The identification of the SmO compounds that are stable in the melts as well as the determination of their solubility products were carried out by potentiometric titration using an yttria stabilised zirconia membrane electrode (YSZME). The results indicated that SmOCl is a solid stable compound in the studied melts and that Sm2O3 is a strong oxobase leading to the formation of SmOCl. The best chlorination conditions have been extracted from the comparison of the E-pO2− diagram of samarium and that of some gaseous chlorinating mixtures previously reported.
To investigate the possibility of selective chlorination to separate copper traces from zinc matr... more To investigate the possibility of selective chlorination to separate copper traces from zinc matrixes, we have determined redox and oxoacidobasic properties of the copper in the molten ZnCl2-2NaCl. In this way, the stability of copper chlorides and oxides as well as the electrochemical behaviour of Cu(I) have been studied by using voltammetric, chronopotentiometric, chronoamperometric and potentiometric techniques. The experiments were
A UV photo-oxidation device was constructed for the destruction of dissolved organic matter (DAM)... more A UV photo-oxidation device was constructed for the destruction of dissolved organic matter (DAM) in freshwater samples in order to determine traces of zinc, cadmium, lead and copper bound to D a M as inert species, by anodic stripping voltammetry in the differential pulse mode (DPASV). The photodigestor performance was optimised by means of the Taguchi experimental design. Four control factors (or design parameters) at three levels were explored: exposure-time to the UVirradiation, pH of the sample, hydrogen peroxide concentration and mineral acid added, and assigned to the columns of a L9(3 4) saturated orthogonal array. A noise factor (nitrilotriacetic acid concentration) at three levels was introduced in the experiment to simulate the uncontrollable amount of D a M in water samples. The experiment was conducted with two replications of each trial and an optimum response insensitive to the variations of D a M concentration was found when samples, acidified at pH 2 with sulphuric acid, were irradiated for 30 rain in the presence of 12.3 mmol/L hydrogen peroxide. The proposed procedure is more precise, accurate and fast than the wet digestion method.
Journal of Environmental Science and Health . Part A: Environmental Science and Engineering and Toxicology, 1997
The complexation of the pesticide Metamitron by copper was investigated by polarography, anodic s... more The complexation of the pesticide Metamitron by copper was investigated by polarography, anodic stripping voltammetry and cathodic stripping voltammetry. The influence of the pH on the complexation was determined and a maximum value for the conditional stability constant of the copper‐metamitron complex (log β'=3.8) was obtained at pH 5.6.An investigation into the photochemical degradation of the pesticide demonstrated that copper
A method has been developed for the determination of phosphorus, as phosphate, by means of the ca... more A method has been developed for the determination of phosphorus, as phosphate, by means of the catalytic polarographic wave for the reduction of hydrogen peroxide in the presence of Mo(V1). This reduction is combined with the previous formation and extraction of l2-molybdophosphoric acid. Depending on the extractant chosen, ethyl acetate or methyl isobutyl ketone, the determination limit is 2.3 or 3.1 rig/l.. respectively. The procedure has been applied to certified steel samples with good results.
ABSTRACT A procedure for purifying waters polluted with metal ions has been designed. The method ... more ABSTRACT A procedure for purifying waters polluted with metal ions has been designed. The method is based on the precipitation of metals as magnetic ferrite from the alkalinised solution containing iron(II). The working conditions were optimised by using a Taguchi L9(34) experimental design in order to minimise the total residual concentration (TRC) of metal ions in solution. A statistical analysis of the experimental data revealed the most influential factor to be the Fe(II)/metal concentration ratio (F), with a 29.5% contribution, followed by pH (P, 5.2%) and time (H, 2.3%). On the other hand, temperature (T) had little effect on the purification efficiency (1.0%), whereas noise (N, KMnO4) was found to contribute by as much as 22.1%. Maximal purification efficiency (99.99%) is achieved when wastewater samples are treated for 3 h at 50°C and pH 10 in the presence of iron(II) in a ratio Fe(II)/total metal of 15. In these conditions, the process efficiency is also the least influenced by variability in the sample composition, which validates the proposed procedure.
A method for determination of arsenic(V) in the range between 1 x 10(-7) and 1.2 x 10(-6)M has be... more A method for determination of arsenic(V) in the range between 1 x 10(-7) and 1.2 x 10(-6)M has been developed. These levels are reached by means of the multiplication factor yielded by use of 12-molybdoarsenic acid and the great sensitivity of polarographic determination of the Mo(VI) in the heteropoly acid. The procedure has been successfully applied to determination of arsenic in copper alloys, after selective extraction of phosphorus.
The global average effective dose from natural radiation sources is estimated to be 2.4 mSv y(-1)... more The global average effective dose from natural radiation sources is estimated to be 2.4 mSv y(-1). Nevertheless, local variations in the radiation exposure may differ by orders of magnitude. In this paper, we study a rural area in western Salamanca (Spain) where doses are potentially well above the stated average value. Its geology consists mostly of granite and schist, presenting various uranium mineralisations, some of which were exploited in former years. Water samples, both surface and groundwater, were collected in selected villages and measured by liquid-scintillation spectrometry. 222Rn in dwellings was determined in dwellings by means of short-term measurements, using Picorad vials and long-term measurements with CR-39 detectors. The committed effective doses to the inhabitants due to indoor 222Rn and 222Rn and 226Ra in drinking water were assessed using the dose conversion factors proposed in the UNSCEAR 2000 report.
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Papers by Rafael Pardo