Alejandro Carrillo-Chávez

Cd (II) removal from aqueous solution by Eleocharis acicularis biomass, equilibrium and kinetic studies

Batch experiments were carried out to determine the capacity of Eleocharis acicularis biomass to adsorb Cd(2+) ions from contaminated solutions with respect to pH, initial Cd(2+) concentration, contact time, solution ionic strength and biomass dose. The experimental data were modeled by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. Freundlich and D-R models resulted in the best fit of the adsorption data. The maximum adsorption capacity for Cd(2+) was 0.299 mmol g(-1) (33.71 mg g(-1)) with efficiency higher than 80% (pH 6.0 and 5 g L(-1) biomass dose). The mean adsorption free energy value derived from the D-R model (8.058 kJ mol(-1)) indicated that adsorption was governed by an ionic exchange process. The pseudo-first order, pseudo-second order, Elovich kinetic models and the intra-particle diffusion models were used to describe the kinetic data and to evaluate rate constants. The best correlation was provided by the second-order kinetic model, implying that chemical sorption was the rate-limiting step, although intra-particle diffusion could not be ignored. The practical implication of this study is the development of an effective and economic technology for Cd(2+) removal from contaminated waters. The macrophyte biomass used in this study did not undergo any chemical or physical pre-treatment, which added to macrophyte abundance and its low cost makes it a good option for Cd(2+) removal from waste water.

Paleocene adakite Au-Fe bearing rocks, Mezcala, Mexico: evidence from geochemical characteristics

The Au–Fe mineralized granitoids at Mezcala district have a porphyry texture with a quartz+feldspar microcrystalline matrix and phenocrysts of plagioclase, quartz (with reaction rims), hornblende and biotite. The primary minerals are oligoclase–andesine, microcline and h-quartz. The accessory minerals are biotite, hornblende and, in minor amounts, apatite+zircon+sphene+titanomagnetite. Some intrusive rocks present abundant hornblende autoliths. Based on the petrography and bulk geochemistry of these granitoids, they are classified as monzonite, tonalite (the most abundant) and granodiorite with a strong calc-alkaline trend in potassium (K2O=3.8% average). The bulk and trace elements chemistry is SiO2=63.8%, Al2O3=15.83%, Fe2O3+MgO+MnO+TiO=6.52%; V=76.7 ppm, Cr=50.2 ppm, Ni=19.7 ppm, Sr=694 ppm. These granitoids show a strong depletion in heavy rare-earth elements (HREE), with average values of Yb=1 ppm and Y=13 ppm, this being the characteristic geochemical signature for adakite. The trace elements content suggests that the adakite granitoids from Mezcala were formed within a tectonic framework of volcanic arc related to the interaction between the Farallon and North America plates. This interaction occurred during the Paleocene after the Laramide Orogeny (post-collision zone) in a fast convergent thick continental crust (>50 km) subduction regime. The original magma is interpreted as being the product of partial melting of an amphibolite–eclogite transition zone source with little contribution of the mantle wedge. Along with the hydration processes, a metallic fertility also took place in the area. The geochemical signature of the adakites within the

Fluorite deposits at Encantada–Buenavista, Mexico: products of Mississippi Valley type processes

Petroleum and aqueous fluid inclusions from the Encantada–Buenavista fluorite mineralized zone in northern Mexico were analyzed by microthermometry, UV fluorescence, Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR) and Confocal Scanning Laser Microscopy (CSLM) to evaluate the geochemical evolution of the mineralizing fluids. Two-phase (petroleum or brine+vapor) and three-phase (petroleum+brine+vapor) inclusions are described. Aqueous and petroleum-rich inclusions commonly occur in the same plane. Vapor-decrepitated and stretched fluid inclusions are present. A low-salinity methane-saturated fluid and a high salinity-fluid with highly variable methane contents are recognized. H2S is not quantified but is always detected in close association with methane. Petroleum inclusions are of two types: a low methane petroleum fluid (20 mol%) with low Th (60 jC) and a petroleum fluid with a methane of content near 30 mol% and a Th of 90 jC. Pressure and temperature diagrams for the aqueous and petroleum inclusions show three main intersects that allow P–T–X reconstruction of fluid evolution at La Encantada–Buenavista. A CH4- and H2S-rich low-salinity brine was mixed with oil that migrated under hydrostatic conditions with a thermal gradient of 70 jC/km. The arrival and mixing of a high-salinity aqueous fluid produced overpressure to 300 bars. A return to hydrostatic conditions was accompanied by an increase in the thermal gradient. The brine related to the fluorite orebodies appears to have a genetic relationship with the brines reported from the Jurassic petroleum basins located west of the fluorite bodies and similarities with reported fluids from Mississippi Valley type deposits. It is interpreted that the fluorine-rich fluids migrated toward the platform margins during the mid-Tertiary (30 to 32 Ma) using extension zones related to Basin and Range tectonism. Mixing of two different brines was responsible for precipitation and mineralization. Heat from magmas, related to tectonic extension, caused decrepitation and changes in the shape of fluid inclusions near the contact zones. D 2003 Elsevier Science B.V. All rights reserved.

Fluoride removal from aqueous solution by Ca-pretreated macrophyte biomass

Environmental context. Fluoride concentrations in drinking water above 1.5 mg L–1 may be detrimental to human health. Many methods have been developed for removing excessive fluoride from drinking water. The use of an aquatic macrophyte biomass (Eleocharis acicularis) pretreated with Ca2+, a low-cost natural material, could be a technique for rural populations in developing countries that cannot afford treated or bottled water for daily consumption. Abstract. The use of an aquatic macrophyte biomass (Eleocharis acicularis) pretreated with Ca2+ as a low-cost natural material for the removal of fluoride from aqueous solution was studied. Batch experiments were carried out to determine fluoride sorption capacity and the efficiency of the sorption process under different pH, initial F– and macrophyte biomass doses. The experimental data showed good fitting to Langmuir and Freundlich isotherm models. The maximum F adsorption capacity was 0.110 mmol g–1 with an efficiency of 64.5% (pH 6.0; 5.0 g L–1 Ca-pretreated biomass). The binding of Ca2+ to the biomass increased the removal efficiency over 100%. The F– removal kinetics were rapid, less than 30 min, and best described by the pseudo-second order rate model. The rate constant, the initial sorption rate and the equilibrium sorption capacity were determined. These results may be useful for deprived rural population water supply schemes in Mexico and in other developing countries.

Genetic implications of fluid inclusions in skarn chimney ore, Las Animas Zn–Pb–Ag(–F) deposit, Zimapán, Mexico

Three tectonic and physiographic provinces are present in the study area: (1) the Sierra Madre Oriental (SMOR; Suter, 1987; Carrillo-Martinez and Suter, 1982) formed by the succession of anticlines and synclines with a consistent NNW– SSE trend; (2) the Basin and Range (BR), formed by horst and grabens oriented NE–SW and NW– SE; and (3) the Trans-Mexican Volcanic Belt (TMBV; Aranda-Gomez et al., 2000), a continental volcanic arc on the southwest margin of the NorthAmerican plate resulting from the subduction of the Rivera and Cocos plates along the Acapulco trench (Fig. 1). The SMOR hosts a huge variety of ore deposits: Skarn Pb +Zn +Ag+(Hg–Sb) type ore deposits of Paleocene–Eocene age are found mostly at the El Pinon anticline; low sulfidation epithermal Au–Ag

Heavy Metal Distribution in Rocks, Sediments, Mine Tailings, Leaching Experiments, and Groundwater from the Mineral de Pozos Historical Mining Site, North-Central Mexico

Silver and gold mineralization in epithermal veins was discovered during the 1600s in the Mineral de Pozos area, north-central Mexico. The main period of mining was between 1880 and 1926. Exploitation in the district is estimated at 1,200,000 tons of ore, with average grades of 1.35 kg/ton Ag, and 8.5 g/ton Au. Tailings were deposited (less than 1.2 million tons) along the main creek in the area, under semi-desert conditions, and widely dispersed by fluvial water during rainy seasons. Concentrations of Cr, Co, and Ni in rocks, sediments, and tailings are below average concentrations in the Earths crust, but Cu, Zn, As, Cd, and Pb concentrations are above crustal averages. Concentrations of As and Pb in groundwater (As = 0.011 to 0.090 mg/l; and Pb = 0.025 to 0.035 mg/l) generally exceed the World Health Organization (WHO) standards for drinking water. Results from humidity cell and leaching column experiments indicate that the potential for leaching As is relatively low (average <0.050 mg/l); Pb concentrations in the experiments range from 0.001 to 0.180 mg/l (average of 0.010 mg/l), and Zn is relatively concentrated (up to 80 mg/l). These results suggest that, given the relatively small amount of mine tailings, the As and Pb concentrations in groundwater may be mostly derived from natural sources rather than from mine waste. The high concentration of Zn in tailings and leachates (up to 306 mg/kg and 80 mg/l, respectively), suggest that zinc could be leaching from the tailings; however, under geochemical conditions of the shallow aquifer (near neutral pH, oxidizing conditions, high Fe content), Zn in solution is mostly controlled by adsorption onto Fe-oxyhydroxides.

Concentrations of Mercury and Other Inorganic Ions in Wet Precipitation Collected from a Mountain Mining Zone and an Urban Area in Central Mexico

We measured and compared mercury (Hg) and other ions in rainwater collected in San Joaquin (mining zone) and Juriquilla (urban area), central Mexico, from 2009 to 2012. A total of 274 rainwater samples were collected and analyzed for pH, electrical conductivity,

Hydro-geochemical and isotopic fluid evolution of the Los Azufres geothermal field, Central Mexico

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