Verónica Martínez-Miranda

Evaluation of Natural and Surfactant‐Modified Zeolites in the Removal of Cadmium from Aqueous Solutions

ABSTRACT The present study involves an investigation on the comparison of a Mexican clinoptilolite-heulandite zeolitic mineral and the modified zeolitic material with the surfactant hexadecyltrimethylammonium bromide (HDTMA) for the removal of cadmium from aqueous solutions. The effects of pH and contact lime on the adsorption process were examined. The optimum pH for adsorption was found to be 7. Cadmium retention reached equilibrium in 32 h and the rate of cadmium adsorption by the zeolites was rapid in the first I Oh. Elovich’s model best described the reaction rate. Batch adsorption experiments conducted at room temperature showed that the adsorption pattern followed the Langmuir-Freundlich isotherm model. The cadmium retention capacity decreased very slightly when the zeolite surface was modified with the surfactant HDTMA, and this material has advantages for its use in the removal of some other contaminants, such as anions and nonpolar organic compounds, like phenols. The results showed that natural zeolite and the surfactant modified zeolite could be considered as potential adsorbents for cadmium removal from aqueous solutions.

Comparison of aluminum modified natural materials in the removal of fluoride ions

The removal behaviors of fluoride ions from aqueous solutions and drinking water by aluminum modified hematite, zeolitic tuff and calcite were determined. Drinking water containing naturally 8.29 mg of fluoride ions per liter was characterized. The hematite, zeolitic tuff and calcite were aluminum modified by an electrochemical method. The effects of contact time and the dose of adsorbent were determined. The PZC (point of zero charge) values for aluminum modified hematite, zeolitic tuff and calcite were 6.2, 5.8 and 8.4, respectively. Adsorption kinetic data were best fitted to pseudo-second-order and Elovich models and equilibrium data to Langmuir-Freundlich isotherm model. The highest fluoride sorption capacities (10.25 and 1.16 mg/g for aqueous solutions and drinking water respectively) were obtained for aluminum modified zeolite with an adsorbent dosage of 10 g/L and an initial F(-) concentration of 9 and 8.29 mg/L for aqueous solutions and drinking water respectively (the final concentrations were 0.08 and 0.7 mg/L respectively). The main mechanism involved in the adsorption of fluoride ions is chemisorption on heterogeneous materials according to the results obtained by fitting the data to kinetic and isotherm models respectively. Aluminum modified zeolitic tuff showed the best characteristics for the removal of fluoride ions from water.

Fluoride Ions Behavior in the Presence of Corrosion Products of Iron: Effects of Other Anions

The behavior of fluoride ions in the presence of corrosion products of iron in drinking and water solutions was analyzed and the adsorption capacities of the iron oxides (corrosion products of iron) for fluoride ions were determined. Drinking water containing naturally 2.45 mg of fluoride ions per liter was characterized and the concentrations of other anions were determined. The effect of contact time, the initial concentration of fluoride ions, and the effect of other anions naturally present in the drinking water were considered. The kinetic results could be adjusted to the pseudo-second order model, which indicated that the sorption mechanism was chemisorption and the equilibrium was reached in 24 hours. The presence of bicarbonate and chloride ions diminishes the removal efficiency of the fluoride ions, whereas other anions (sulfate, phosphate, and nitrate) did not show any significant effect. The results reflect that the iron oxides products from the corrosion of a hydraulic infrastructure allow the removal of fluoride ions from water.

Distribution and partitioning of iron, zinc, and arsenic in surface sediments in the Grande River mouth to Cuitzeo Lake, Mexico

Cuitzeo Lake is one of the largest and most important lakes in Mexico. It receives different types of pollutants through its main tributary, the Grande River of Morelia. The aim of this work was to determine if high concentrations of iron, zinc, and arsenic are present in sediments in an area near the river mouth to the lake, as well as to estimate the partitioning of these metals using a sequential extraction procedure in order to obtain information of their potential bioavailability. Sediment samples were collected from three different sites in Cuitzeo Lake and two sites in Grande River in both dry and wet seasons. A sequential extraction procedure was carried out to determine the concentrations of these elements in different geochemical phases of the sediments. Total metal concentrations were evaluated by using the enrichment factor and the geoaccumulation index. A comparison with sediment quality guidelines and shale values has also been made. The results indicate that sediments are considered unpolluted by iron and moderately polluted by zinc and arsenic. However, fractionation studies showed that significant amounts of Zn and As could be released to the lake ecosystem depending on the environmental conditions, representing a medium risk potential of bioavailability to the biota.

Boron-Doped Diamond Electrode Performance in Cr(VI) Reduction Using Synthetic and Plating Wastewater

The goal of this work was to evaluate the effectiveness of iron and boron-doped-diamond (BDD) as cathodic electrodes on the reduction of Cr(VI) in synthetic and wastewater samples. The pH and electrolyte composition were varied, and the effect on the Cr(VI) reduction rate was measured. The optimized conditions from the synthetic water Cr(VI) reduction experimental data, were tasted on electroplating wastewater. The results indicated that both a pH of 2 and the use of NaCl as an electrolyte significantly increase the Cr(VI) reduction rate for all synthetic systems, especially the iron-BDD system. The Cr(VI) reduction rate in Fe-BDD systems was also affected by nitrate and sulfate ions. In the case of electroplating wastewater, Cr(VI) reduction by BDD cathodes was faster than with iron cathodes, achieving a complete reduction of 180 mg Cr(VI)/L in 25 min, with 40% less sludge produced. The elemental composition of sludge was analyzed using SEM/EDS and X-ray spectroscopy to confirm that iron and chromium precipitated out of the solution. The sludge had a chemical composition of (31.9%) Fe2O3, (29.6%) FeOOH, (21%) FeO, and (17.4%) FeSO4. Therefore, BDD as an electrode material effectively reduces Cr(VI) in electroplating wastewater, and can be effectively scaled up to industrial applications.

Adsorption-regeneration by heterogeneous Fenton process using modified carbon and clay materials for removal of indigo blue

ABSTRACT Indigo blue dye is mainly used in dyeing of denim clothes and its presence in water bodies could have adverse effects on the aquatic system; for this reason, the objective of this study was to promote the removal of indigo blue dye from aqueous solutions by iron and copper electrochemically modified clay and activated carbon and the saturated materials were regenerated by a Fenton-like process. Montmorillonite clay was modified at pH 2 and 7; activated carbon at pH 2 and pH of the system. The elemental X-ray dispersive spectroscopy analysis showed that the optimum pH for modification of montmorillonite with iron and copper was 7 and for activated carbon was 2. The dye used in this work was characterized by infrared. Unmodified and modified clay samples showed the highest removal efficiencies of the dye (90–100%) in the pH interval from 2 to 10 whereas the removal efficiencies decrease as pH increases for samples modified at pH 2. Unmodified clay and copper-modified activated carbon at pH 2 were the most efficient activated materials for the removal of the dye. The adsorption kinetics data of all materials were best adjusted to the pseudo-second-order model, indicating a chemisorption mechanism and the adsorption isotherms data showed that the materials have a heterogeneous surface. The iron-modified clay could be regenerated by a photo-Fenton-like process through four adsorption-regeneration cycles, with 90% removal efficiency.

Comparison of Fe–Al-modified natural materials by an electrochemical method and chemical precipitation for the adsorption of F− and As(V)

ABSTRACT The adsorption of fluoride and arsenic ions by modified natural materials may have an impact on the removal of F− and As(V) from waters. In this work, a zeolitic material and pozzolan (commonly known as pumicite) were modified with aluminium an iron by an electrochemical method and chemical precipitation, respectively. The adsorbents were characterized by X-ray diffraction, scanning electron microscopy with energy X-ray disperse spectroscopy analysis and the point of zero charge (pHzpc). F− and As(V) adsorption properties of both materials were investigated. Adsorption kinetic data were best fitted to pseudo-second-order model and equilibrium data to the Langmuir isotherm model. The highest F− and As(V) sorption capacities were obtained for modified zeolitic (0.866 mg/g) and pozzolan (3.35 mg/g) materials, respectively, with initial F− or As(V) concentrations of 10 mg/L. It was found that the unmodified materials did not show either adsorption of F− ions or As(V), which indicated that Al and Fe in the adsorbents are responsible for the adsorption of these ions. In general, both modified materials show similar capacities for the adsorption of F− and As(V).

Chemical oxygen demand, total organic carbon and colour reduction in slaughterhouse wastewater by unmodified and iron-modified clinoptilolite-rich tuff

In this study, reduction of chemical oxygen demand (COD), colour, and total organic carbon in effluents from a slaughterhouse in central Mexico was performed using clinoptilolite-rich tuff. The experimental parameters considered were initial concentration of the adsorbate, pH, adsorbent dosage, and contact time. Surface morphology of the materials was tested by using scanning electron microscopy. Specific surface area was analysed by using Brunauer–Emmett–Teller (BET) and phase composition was analysed by using X-ray diffraction. The experimental adsorption data were fitted to the first- and pseudo-second-order kinetic models. The highest COD removal was observed in slightly acidic pH conditions. The maximum reduction efficiency of COD was accomplished with unmodified clinoptilolite-rich tuff at a contact time of 1440 min. In these conditions, the adsorbent was efficient for treating wastewater from a slaughterhouse. Moreover, after several regeneration cycles with Fenton reagent or hydrogen peroxide, the regenerated zeolite with H2O2(3%) showed the best reduction efficiencies.

Behavior of Fluoride Ions in the Presence of Lanthanum and Magnesium Modified Corrosion Products

An excess of fluoride ion in drinking water is an important issue worldwide. The present paper shows the effects of lanthanum or magnesium in corrosion products (CP) on the removal of fluoride ions from water using batch experiments. The effects of pH, contact time, fluoride concentration, and the dose of sorbent on the sorption of fluoride ions by the modified corrosion products were considered. Equilibrium was reached in 24 h of contact time and the sorption of fluoride was similar in the equilibrium pH range between 3.0 and 9.0. The pseudo-second-order model described the kinetic sorption process, and this behavior indicated that the sorption mechanism was chemisorption. The study revealed that the presence of lanthanum in the corrosion products significantly improved the F sorption capacity of this material.

Treatment of a Textile Effluent by Electrochemical Oxidation and Coupled System Electooxidation–Salix babylonica

The removal of pollutants from textile wastewater via electrochemical oxidation and a coupled system electrooxidation—Salix babylonica, using boron-doped diamond electrodes was evaluated. Under optimal conditions of pH 5.23 and 3.5 mA·cm−2 of current density, the electrochemical method yields an effective reduction of chemical oxygen demand by 41.95%, biochemical oxygen demand by 83.33%, color by 60.83%, and turbidity by 26.53% at 300 minutes of treatment. The raw and treated wastewater was characterized by infrared spectroscopy to confirm the degradation of pollutants. The wastewater was oxidized at 15-minute intervals for one hour and was placed in contact with willow plants for 15 days. The coupled system yielded a reduction of the chemical oxygen demand by 14%, color by 85%, and turbidity by 93%. The best efficiency for the coupled system was achieved at 60 minutes, at which time the plants achieved more biomass and photosynthetic pigments.