Papers by ROBERTO LEYVA-RAMOS
Revista Internacional de Contaminación Ambiental, 2005
The ion exchange isotherm data for silver on clinoptilolite were obtained in an experimental batc... more The ion exchange isotherm data for silver on clinoptilolite were obtained in an experimental batch adsorber at different pH values and temperatures. The effect of pH was studied by determining the isotherm at pH of 3, 5 and 7 and it was found that the
exchange capacity of clinoptilolite for Ag(I) was slightly dependent upon the solution
pH. The effect of temperature on the ion exchange isotherm was also investigated and
it was noticed that the exchange capacity did not vary significantly when the temperature
was increased from 25 to 35 °C, but the capacity was increased about 1.5 times when the temperature decreased from 25 to 15 °C. The real exchange capacity is almost half the theoretical exchange capacity and threefold the external cationic exchange
capacity, and represents 70 % of the experimental cationic exchange capacity.
Información Tecnológica Vol. 19(5), 27-36, 2008
The adsorption of Cr(VI) from aqueous solution on an activated carbon fiber of felt type, was stu... more The adsorption of Cr(VI) from aqueous solution on an activated carbon fiber of felt type, was studied. The adsorption equilibrium data of Cr(VI) on the fiber were obtained in a batch adsorber and the concentration of Cr(VI) was determined by a colorimetric method. The Freundlich isotherm fitted reasonably well the experimental data. The Cr(VI) adsorption capacity of the fiber decreased considerably while increasing the solution pH from 4 to 10 but slightly increased as the temperature increased from 15 to 35°C. The effect of the pH was due to the electrostatic interactions between the surface of the fiber and the Cr(VI) anions in solution. The adsorption capacity of the fiber was compared to those of granular activated carbons made from hazelnut shell and from coconut shell. The adsorption capacity of the fiber was twice that of the hazelnut carbon and half of that of the coconut carbon.
Keywords: chromium (VI) adsorption, activated carbon fiber, granular carbon, Freundlich isotherm
Avances en Ingeniería Química 597-610, 1987
Se determinaron experimentalmente las isotermas de adsorci6n de fenol y m-dinitrobenceno en carb... more Se determinaron experimentalmente las isotermas de adsorci6n de fenol y m-dinitrobenceno en carbón activado a 25 °C y 40 °C. Los datos experimentales se correlacionaron por las isotermas de adsorción de Freundlich (F), Potencial de Polanyi (PP) y Prausnitz y Radke (PR). Se encontró que la isoterma de PR correlaciona ligeramente mejor los datos. No se notó ninguna tendencia de los parámetros de la isoterma de PR con respecto a la temperatura. El .calor de adsorción se avaluó por medio da la ecuación da Clausius-Clapeyron. Se observó que el calor da adsorción del
fenol disminuye drásticamente con la cantidad adsorbida mientras que el del m-dinitrobenceno varia muy ligeramente con la cantidad adsorbida.
En “Adsorbentes en la Solución de Algunos Problemas Ambientales.” Editor: Francisco Rodríguez Reinoso, Ediciones CYTED, España, pp. 95-112,, ISBN: 84-96023-20-6, 2004
Algunos metales pesados son elementos sumamente tóxicos aun a
concentraciones muy bajas y su expo... more Algunos metales pesados son elementos sumamente tóxicos aun a
concentraciones muy bajas y su exposición ocasiona un sinnúmero de
enfermedades. La presencia de metales pesados en el medio ambiente se debe a fuentes naturales y antropogénicas. El antimonio, arsénico, berilio, cadmio, cromo, cobre, plomo, mercurio, níquel, selenio, plata, talio y zinc son metales y metaloides considerados contaminantes prioritarios porque se encuentran comúnmente en aguas residuales y representan un serio problema de salud. Diversos métodos se han aplicado exitosamente para remover metales pesados presente en soluciones acuosas ácidas o alcalinas, entre éstos se pueden mencionar a los siguientes: cementación, intercambio iónico, precipitación química y sedimentación, extracción con solvente, deposición electroquímica y adsorción. La precipitación química y sedimentación es el método mas comúnmente utilizado para remover metales en solución acuosa; sin embargo, la efectividad de este proceso depende considerablemente de la composición y naturaleza de los contaminantes presentes en las aguas residuales.
En “Catalizadores y Adsorbentes Iberoamericanos para la Remoción de Metales Pesados en Efluentes Industriales.” Editores: Gerardo Rodríguez-Fuentes y Pedro Ávila García, Ediciones CYTED, Madrid, pp. 52-61,., 2000
En 1978, la Agencia para la protección Ambiental de los Estados Unidos de América (USEPA) elaboró... more En 1978, la Agencia para la protección Ambiental de los Estados Unidos de América (USEPA) elaboró una lista de 129 contaminantes orgánicos e inorgánicos que se encuentran presentes en aguas residuales y que representan un serio peligro para la salud humana; ésta se conoce como la Lista de Contaminantes Prioritarios, en ella se incluyen los trece metales
siguientes: Antimonio, arsénico, berilio, cadmio, cromo, cobre, plomo, mercurio, níquel, selenio, plata, talio y zinc. A diferencia de los compuestos orgánicos, los metales no pueden ser biodegradados o destruidos y por lo tanto tienen que ser removidos de las aguas residuales. Varios procesos para remover metales pesados de solución acuosa se han desarrollado y
actualmente algunos de ellos se usan en el ámbito industrial. Entre estos procesos destacan el intercambio iónico con resinas poliméricas y zeolitas naturales, la adsorción, la ósmosis inversa, la precipitación química/sedimentación, la filtración, la electrodiálisis y la flotación. El método de remoción que se seleccione depende de las propiedades fisicoquímicas y concentración de los contaminantes en solución acuosa.
Libro: Sólidos Porosos. Preparación, Caracterización y Aplicaciones. Editor: Juan Carlos Moreno-Piraján. Ediciones Uniandes, , 2007
La adsorción es un fenómeno superficial que involucra la acumulación o concentración de sustancia... more La adsorción es un fenómeno superficial que involucra la acumulación o concentración de sustancias en una superficie o interfase. El compuesto que se adsorbe se le llama adsorbato y la fase don-de ocurre la adsorción se le conoce como adsorbente.
Desde un punto de vista comercial, los adsorbentes más usados en orden decreciente son carbón activado, zeolitas, silica gel y alúmina activada. El carbón activado es el adsorbente más usado en el ámbito industrial y se emplea tradicionalmente en la remoción de olor, color y sabor que son causados por contaminantes en niveles traza. En 1794 el carbón activado se aplicó industrialmente por primera vez cuando carbón activado de madera se usó para decolorar jarabes en la industria azucarera en Inglaterra.
El carbón activado se aplica en el tratamiento de muy diversos tipos de efluentes residuales gracias a su gran capacidad de adsorción y versatilidad.
Revista de la Sociedad Mexicana de Biotecnología y Bioingeniería, 1993
The ·equations required for investigating the existence of multiple steady states in bioparticles... more The ·equations required for investigating the existence of multiple steady states in bioparticles were developed in thls study. It was assumed that the microbial growth kinetics involved two limiting substrates, one expressed as the Haldane-type equation and the other one as the Monod-type. It was found that depending on the concentrations of the two substrates, three steady states can exist in the bioparticle. The sufficient ·and·necessary· conditions • for .the existen of these three steady states were reported.-
Journal of Environmental Engineering Management, Jun 13, 2008
The adsorption of fluoride from a water solution on an activated alumina prepared from
pseudo-bo... more The adsorption of fluoride from a water solution on an activated alumina prepared from
pseudo-boehmite was investigated in this work. The activated alumina was characterized to determine its physicochemical and textural properties. It was found that the fluoride adsorption capacity of the activated alumina was considerably dependent upon the solution pH and diminished considerably with increasing solution pH from 4 to 11. The effect of the pH was attributed to the electrostatic interactions between the surface of the activated alumina and the fluoride in solution. The activated alumina was dissolved at pH lower than 4. It was not possible to ascertain the effect of the temperature on the adsorption of fluoride because the adsorption capacity increased and then decreased while the temperature was augmented from 15 to 25 °C and from 25 to 35 °C, respectively. The adsorption equilibrium was not reversible at pH of 5 but was reversible at pH of 11. The solution pH was a very important factor in desorbing fluoride and more mass of fluoride was desorbed increasing the solution pH. The adsorption of fluoride on activated alumina was mainly due to both electrostatic attraction and chemisorption mechanisms, but not to ion exchange
The adsorption capacity of sepiolite towards the removal of heavy metal ions from aqueous solutio... more The adsorption capacity of sepiolite towards the removal of heavy metal ions from aqueous solution was studied in this work, with adsorption equilibrium data being obtained with a bath adsorber. The sepiolite sample was chemically stable over the pH range 2-12, but dissolved in acidic solutions with pH values less than 2. The Langmuir isotherm gave a better fit of the experimental adsorption equilibrium data, since the average absolute percentage deviation of the Langmuir isotherm was lower than that of the Freundlich isotherm. The adsorption capacity of sepiolite towards metal ions decreased in the following order: Cr(III) > Cd(II) > Cu(II) > Zn(II) > Ni(II) > Ag(I). Increasing the temperature from 15 ЊC to 35 ЊC led to an increase in the adsorption capacity. The capacity of sepiolite towards the adsorption of Cd(II) ions was diminished considerably on reducing the solution pH from 7 to 3. The effect of the solution pH was attributed to electrostatic interaction between the negatively charged sepiolite surface and the positively charged Cd(II) ions in the aqueous solution. The surface charge of sepiolite became less negative when Cd(II) ions were adsorbed onto the sepiolite surface. This result indicates that electrostatic interaction between the sepiolite surface and the Cd(II) ions in the aqueous solution played a very important role in determining the adsorption capacity of sepiolite. The adsorption of Cd(II) ions onto sepiolite at pH 7 was reversible when desorption was undertaken at pH 3, but not when desorption was undertaken at pH 7.
Studies in Surface Science and Catalysis, 2002
The experimental data for the single exchange isotherms for Pb(II) and Cd(II) were
adjusted quit... more The experimental data for the single exchange isotherms for Pb(II) and Cd(II) were
adjusted quite well by the Langmuir isotherm and the exchange capacity for the Pb(II) ion is about 2.3 times that for the Cd(II) ion. The results of the competitive exchange showed that the ion exchange isotherm for Pb(II) was not significantly dependent upon the Cd(II)
concentration, this means that Pb(II) ion was exchanged more selectively than the Cd(II) ion. However, the exchange isotherm for Cd(II) was considerably affected by the presence of Pb(II) ions. The exchange capacity for Cd(II) diminished drastically increasing the concentration of Pb(II) ion. Therefore, both ions compete for the same cationic sites of the zeolite but the zeolite is much more selective for the Pb(II) ion than for the Cd(II) ion.
Influence of industrial emissions on the atmospheric aerosol of San Luis Potosí, México, 2006
ABSTRACT
The city of San Luis Potosí, México, has grown in an area of intense metallurgic
activ... more ABSTRACT
The city of San Luis Potosí, México, has grown in an area of intense metallurgic
activity with more than a century of operations. This metallurgic activity has an impact
on the pollution levels for heavy metals particles resulting in health problems in
the population, that have been attributed exclusively to the copper and zinc refineries
of the city. However, the high industrial development has given place to other important
industries located in an area opposed to the location of the metallurgic zone.
This industrial area has also considerably contributed to the generation of polluting
particles. The measurements of pollution levels of total suspended particles and heavy
elements has provided quantitative global information, nevertheless, these studies do
not generate specific information on the morphology and chemical composition of
the anthropogenic particles, and therefore, it is not possible to associate them to
specific types of polluting sources. The aim of this work is to reveal the morphological
characteristics and chemical composition of the anthropogenic airborne particles,
through electron microscopy techniques, which allow the association with specific
industrial emissions. To compare and confirm the origin of the anthropogenic airborne
particles, the characterization of some industrial emissions with the same
methodology, has also been carried out.
Journal of Chemical Technology & Biotechnology, 2004
This work investigated the ion exchange of ammonia on clinoptilolite obtained from mineral deposi... more This work investigated the ion exchange of ammonia on clinoptilolite obtained from mineral deposits located in San Luis Potosi and Sonora, Mexico. Experimental ion exchange isotherm data were obtained in a batch adsorber. The effects of temperature and solution pH on the ion exchange capacity were studied and it was found that the exchange capacity was slightly increased by augmenting the temperature and by decreasing the pH from 6 to 3. The ion exchange capacity was independent of the diameter of the zeolite particles. The reversibility of ion exchange was analyzed by desorbing the ammonia exchanged on the zeolite. The ion exchange was reversible when 1% NaCl solution was used as the desorbing solution, but more ammonia was desorbed using 1% KCl solution in the desorption step. It was concluded that a considerable amount of ammonia was exchanged on the clinoptilolite and that the exchange capacity was slightly dependent on the temperature and pH.
Journal of Chemical Technology & Biotechnology, 2007
Adsorption of an anionic detergent (sodium dodecyl benzene sulfonate) from aqueous solutions onto... more Adsorption of an anionic detergent (sodium dodecyl benzene sulfonate) from aqueous solutions onto activated carbon is investigated as an alternative for eliminating detergents from wastewaters. The adsorption isotherm was measured experimentally at 25°C, 30°C and 35°C and the experimental data were correlated reasonably well by the adsorption isotherm of Prausnitz-Radke. The adsorption capacity is considerably affected by pH and there exists an optimal pH, near pH = 7, where the maximum adsorption takes place. The adsorption capacity increases with rising temperature, the adsorption is irreversible and the heat of adsorption is lessened with the amount of detergent adsorbed and its order of magnitude corresponds to a chemical reaction. It is concluded that the detergent is chemically adsorbed onto the activated carbon.
Adsorption of trivalent chromium from aqueous solutions onto activated carbon
Journal of Chemical Technology AND Biotechnology, 1995
Centro de Investigacion y Estudios de Posgrado, Facultad de Ciencias Quimicas/UASLP, Av. Dr. Manu... more Centro de Investigacion y Estudios de Posgrado, Facultad de Ciencias Quimicas/UASLP, Av. Dr. Manuel Nava No. 6, San Luis Potosi, SLP 78210, Mexico ... (Received 1 December 1993; revised version received 29 June 1994; accepted 14 July 1994)
Adsorption of Pentachlorophenol from Aqueous Solution onto Activated Carbon Fiber
Industrial & Engineering Chemistry Research, 2006
Experimental data for the equilibrium adsorption of pentachlorophenol (PCP) onto activated carbon... more Experimental data for the equilibrium adsorption of pentachlorophenol (PCP) onto activated carbon fibers (ACFs) in the form of felt (AC-felt) and cloth (AC-cloth) were obtained in a batch adsorber. The effect of pH on the adsorption capacity was investigated by determining the adsorption isotherm in the pH range from 6 to 12. It was found that the adsorption capacity was reduced upon increasing the pH from 6 to 12. The speciation diagram of PCP revealed that PCP was adsorbed on the ACFs as the pentachlorophenolate ion. The adsorption capacity was diminished slightly upon increasing the temperature from 15 to 35 °C. The adsorption of PCP on AC-felt was due to dispersion forces caused by π−π interactions. These interactions explained why the adsorption of PCP on the AC-felt was reversible. Also, the adsorption capacity of the AC-felt was 1.7 times higher than that of the AC-cloth because the AC-felt contained a greater concentration of basic sites that made the π−π interactions stronger. It was concluded th...
Chemical Engineering Science, 1985
A general mathematical model for the rates of adsorption of solutes from a liquid by porous solid... more A general mathematical model for the rates of adsorption of solutes from a liquid by porous solids in a batch system has been derived. The model includes external mass transfer, pore volume accumulation and diffusion, adsorption using nonlinear isotherms, and surface diffusion. Numerical solutions and parametric plots were obtained. The presence. of surface diffusion has a large effect on increasing rates of adsorption for slightly and highly adsorbing solutes. External mass transfer controls the rate for small values of the mass transfer coefficient. Appreciable errors can occur if pore diffusion is neglected for the slightly adsorbing case with little error for the highly adsorbing case. Internal concentration profiles show marked differences for slightly and highly adsorbing &lutes.
Carbon, 2007
The adsorption equilibrium data of pentachlorophenol (PCP) onto activated carbon fiber (ACF) in f... more The adsorption equilibrium data of pentachlorophenol (PCP) onto activated carbon fiber (ACF) in felt form were obtained in a batch adsorber at T = 25°C and pH 12 and the Langmuir isotherm fitted reasonably well with the experimental data. The rate of adsorption of PCP on ACF was investigated in this work and the experimental concentration decay data were obtained in a differential column batch adsorber. The overall rate of adsorption of PCP was interpreted by a diffusional model that takes into account the external mass transport and intrafiber diffusion. The experimental concentration decay can be described quite well with the diffusional model if the overall rate of adsorption is mainly controlled by intrafiber diffusion and the external mass transport is not important to the overall rate of adsorption. Moreover, intrafiber diffusion was significantly affected by restricted diffusion since the molecular diameter of the PCP was closed to 55% of the average pore diameter. The effect of restricted diffusion was estimated using correlations reported in the literature. The molecules of PCP adsorbed on the surface of the pore also hindered the diffusion of PCP molecules inside the pores.
The Canadian Journal of Chemical Engineering, 1994
The adsorption isotherms on activated carbon were measured for the following six systems: benzald... more The adsorption isotherms on activated carbon were measured for the following six systems: benzaldehyde, phenol, and potassium chloride in water; benzene, isopropylbenzene, and phenol in cyclohexane. The systems isopropylbenzene and benzene each in cyclohexane and potassium chloride in water proved to be slightly adsorbing systems, whereas the benzaldehyde and phenol each in water were highly adsorbing systems. The rate of diffusion of the slightly adsorbing solutes was interpreted by assuming that the intraparticle diffusion was due to pore volume diffusion. The results indicated that the tortuosity factor for activated carbon is 3.5. The effective pore volume diffusivity and the tortuosity factor were not affected by the concentration of the solute, solute molecular size and the particle diameter. The external mass transfer resistance was negligible when pore volume diffusion was the controlling intraparticle diffusion mechanism. On a mesure les isothermes d'adsorption sur du charbon actif pour les six systkmes suivants: benzaldehyde, phenol et chlorure de potassium dans l'eau; benzkne, isopropylbenzkne et phenol dans le cyclohexane. Les systkmes isopropylbenzbne et benzkne dans du cyclohexane ou du chlorure de potassium dans l'eau se sont r6vClCs ltgbrement adsorbants, tandis que le benzaldehyde et le phenol dans l'eau sont hautement adsorbants. La vitesse de diffusion des solutes ltgbrement adsorbants a 6t6 interpr6ttCe en supposant que la diffusion intraparticulaire est due ? i la diffusion volumique des pores. Les rksultats indiquent que le facteur de tortuositk pour le charbon actif est de 3,5. La diffusivite volumique effective des pores et le facteur de tortuositt ne sont pas influences par la concentration du solute, la taille moltculaire du solutC et le diamktre des particules. La resistance externe au transfert de matiere est negligeable lorsque la diffusion volumique des pores est contrBlCe par le mecanisme de diffusion intraparticulaire.
Sorption mechanism of Cd(II) from water solution onto chicken eggshell
Applied Surface Science, 2013
ABSTRACT The mechanism and capacity of eggshell for sorbing Cd(II) from aqueous solution was exam... more ABSTRACT The mechanism and capacity of eggshell for sorbing Cd(II) from aqueous solution was examined in detail. The eggshell was characterized by several techniques. The eggshell was mainly composed of Calcite (CaCO3). The surface charge distribution was determined by acid–base titration and the point of zero charge (PZC) of the eggshell was found to be 11.4. The sorption equilibrium data were obtained in a batch adsorber, and the adsorption isotherm of Langmuir fitted the data quite well. The sorption capacity of eggshell increased while raising the pH from 4 to 6, this tendency was attributed to the electrostatic interaction between the Cd2+ in solution and the surface of the eggshell. Furthermore, the sorption capacity was augmented by increasing the temperature from 15 to 35 °C because the sorption was endothermic. The sorption of Cd(II) occurred mainly onto the calcareous layer of the eggshell, but slightly on the membrane layer. It was demonstrated that the sorption of Cd(II) was not reversible, and the main sorption mechanisms were precipitation and ion exchange. The precipitation of (Cd,Ca)CO3 on the surface of the eggshell was corroborated by SEM and XRD analysis.
Applied Clay Science, 2014
The adsorption equilibrium data of Cd(II) on vermiculite was obtained in a batch adsorber. The ad... more The adsorption equilibrium data of Cd(II) on vermiculite was obtained in a batch adsorber. The adsorption data were interpreted with the Langmuir, Freundlich and Prausnitz-Radke (PR) isotherm models, and the PR isotherm best fitted the experimental data. The adsorption capacity of vermiculite towards Cd(II) was increased by raising the solution pH and temperature. The first effect was attributed to electrostatic interactions and competition between the protons and Cd(II) for the cationic sites. The second trend indicated that the adsorption was endothermic. The desorption of Cd(II) adsorbed on vermiculite at pH = 7, was irreversible and reversible when the pH of desorption solution was 7 and 3, respectively. The maximum uptake of Cd(II) on vermiculite was greater than the cationic exchange capacity. This result revealed that the adsorption of Cd(II) on vermiculite occurred by other adsorption mechanisms besides ion exchange. It was demonstrated that the greater the uptake of Cd(II) on vermiculite, the higher the reduction of the negative charge of the surface. Hence, the electrostatic interactions between the Cd 2+ cations in solution and the negative zeta potential of the surface played an important role on the adsorption capacity of vermiculite. Hence, the adsorption of Cd(II) on vermiculite is mainly due to the mechanisms of ion exchange and electrostatic attraction.
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Papers by ROBERTO LEYVA-RAMOS
exchange capacity of clinoptilolite for Ag(I) was slightly dependent upon the solution
pH. The effect of temperature on the ion exchange isotherm was also investigated and
it was noticed that the exchange capacity did not vary significantly when the temperature
was increased from 25 to 35 °C, but the capacity was increased about 1.5 times when the temperature decreased from 25 to 15 °C. The real exchange capacity is almost half the theoretical exchange capacity and threefold the external cationic exchange
capacity, and represents 70 % of the experimental cationic exchange capacity.
Keywords: chromium (VI) adsorption, activated carbon fiber, granular carbon, Freundlich isotherm
fenol disminuye drásticamente con la cantidad adsorbida mientras que el del m-dinitrobenceno varia muy ligeramente con la cantidad adsorbida.
concentraciones muy bajas y su exposición ocasiona un sinnúmero de
enfermedades. La presencia de metales pesados en el medio ambiente se debe a fuentes naturales y antropogénicas. El antimonio, arsénico, berilio, cadmio, cromo, cobre, plomo, mercurio, níquel, selenio, plata, talio y zinc son metales y metaloides considerados contaminantes prioritarios porque se encuentran comúnmente en aguas residuales y representan un serio problema de salud. Diversos métodos se han aplicado exitosamente para remover metales pesados presente en soluciones acuosas ácidas o alcalinas, entre éstos se pueden mencionar a los siguientes: cementación, intercambio iónico, precipitación química y sedimentación, extracción con solvente, deposición electroquímica y adsorción. La precipitación química y sedimentación es el método mas comúnmente utilizado para remover metales en solución acuosa; sin embargo, la efectividad de este proceso depende considerablemente de la composición y naturaleza de los contaminantes presentes en las aguas residuales.
siguientes: Antimonio, arsénico, berilio, cadmio, cromo, cobre, plomo, mercurio, níquel, selenio, plata, talio y zinc. A diferencia de los compuestos orgánicos, los metales no pueden ser biodegradados o destruidos y por lo tanto tienen que ser removidos de las aguas residuales. Varios procesos para remover metales pesados de solución acuosa se han desarrollado y
actualmente algunos de ellos se usan en el ámbito industrial. Entre estos procesos destacan el intercambio iónico con resinas poliméricas y zeolitas naturales, la adsorción, la ósmosis inversa, la precipitación química/sedimentación, la filtración, la electrodiálisis y la flotación. El método de remoción que se seleccione depende de las propiedades fisicoquímicas y concentración de los contaminantes en solución acuosa.
Desde un punto de vista comercial, los adsorbentes más usados en orden decreciente son carbón activado, zeolitas, silica gel y alúmina activada. El carbón activado es el adsorbente más usado en el ámbito industrial y se emplea tradicionalmente en la remoción de olor, color y sabor que son causados por contaminantes en niveles traza. En 1794 el carbón activado se aplicó industrialmente por primera vez cuando carbón activado de madera se usó para decolorar jarabes en la industria azucarera en Inglaterra.
El carbón activado se aplica en el tratamiento de muy diversos tipos de efluentes residuales gracias a su gran capacidad de adsorción y versatilidad.
pseudo-boehmite was investigated in this work. The activated alumina was characterized to determine its physicochemical and textural properties. It was found that the fluoride adsorption capacity of the activated alumina was considerably dependent upon the solution pH and diminished considerably with increasing solution pH from 4 to 11. The effect of the pH was attributed to the electrostatic interactions between the surface of the activated alumina and the fluoride in solution. The activated alumina was dissolved at pH lower than 4. It was not possible to ascertain the effect of the temperature on the adsorption of fluoride because the adsorption capacity increased and then decreased while the temperature was augmented from 15 to 25 °C and from 25 to 35 °C, respectively. The adsorption equilibrium was not reversible at pH of 5 but was reversible at pH of 11. The solution pH was a very important factor in desorbing fluoride and more mass of fluoride was desorbed increasing the solution pH. The adsorption of fluoride on activated alumina was mainly due to both electrostatic attraction and chemisorption mechanisms, but not to ion exchange
adjusted quite well by the Langmuir isotherm and the exchange capacity for the Pb(II) ion is about 2.3 times that for the Cd(II) ion. The results of the competitive exchange showed that the ion exchange isotherm for Pb(II) was not significantly dependent upon the Cd(II)
concentration, this means that Pb(II) ion was exchanged more selectively than the Cd(II) ion. However, the exchange isotherm for Cd(II) was considerably affected by the presence of Pb(II) ions. The exchange capacity for Cd(II) diminished drastically increasing the concentration of Pb(II) ion. Therefore, both ions compete for the same cationic sites of the zeolite but the zeolite is much more selective for the Pb(II) ion than for the Cd(II) ion.
The city of San Luis Potosí, México, has grown in an area of intense metallurgic
activity with more than a century of operations. This metallurgic activity has an impact
on the pollution levels for heavy metals particles resulting in health problems in
the population, that have been attributed exclusively to the copper and zinc refineries
of the city. However, the high industrial development has given place to other important
industries located in an area opposed to the location of the metallurgic zone.
This industrial area has also considerably contributed to the generation of polluting
particles. The measurements of pollution levels of total suspended particles and heavy
elements has provided quantitative global information, nevertheless, these studies do
not generate specific information on the morphology and chemical composition of
the anthropogenic particles, and therefore, it is not possible to associate them to
specific types of polluting sources. The aim of this work is to reveal the morphological
characteristics and chemical composition of the anthropogenic airborne particles,
through electron microscopy techniques, which allow the association with specific
industrial emissions. To compare and confirm the origin of the anthropogenic airborne
particles, the characterization of some industrial emissions with the same
methodology, has also been carried out.