Miranda Vidales J.M.,Institute Metalurgia
Protection of Metals and Physical Chemistry of Surfaces | Year: 2014
One of main disadvantages of using environmentally friendly chemical mixtures for pickling, is stabilization of hydrogen peroxide (H 2O2), due to its decomposition is affected by the presence of metal ions. In previous studies, p-toluenesulfonic acid (C7H 10O4S) was used as a hydrogen peroxide stabilizer; however, benzene rings in its structure have a certain level of toxicity. In this work, ascorbic acid (C6H8O6) was tested as a stabilizer agent for H2O2 in a pickling mixture composed by sulfuric acid (H2SO4) and hydrofluoric acid (HF)-H2O2, this mixture was tested on 316L stainless steel (SS). Decomposition of H2O2 in pickling solution was evaluated for different ferric ions concentration between 0 to 40 g/L and at different temperatures from 25° to 60°C. Pickling rates at 25°C for 316L SS were 26873 mg/dm2 and 27799 mg/dm2 using ascorbic acid and p-toluenesulfonic acid, respectively. Ascorbic acid has a positive influence on stabilization processes of H2O2. © 2014 Pleiades Publishing, Ltd.
Stainless steel pickling using ecologies friendly mixtures composed of H2O2 - H2SO4 - F- ions [Decapado de un acero inoxidable austenítico mediante mezclas ecológicas basadas en H2O2 - H2SO 4 - iones F-]
Miranda J.M.,Institute Metalurgia |
Revista de Metalurgia | Year: 2013
This study reports the pickling of 316L stainless steel using mixtures of hydrogen peroxide (H2O2), sulphuric acid (H 2SO4) and fluoride ions as hydrofluoric acid (HF), sodium fluoride (NaF) and potassium fluoride (KF). The decomposition of H 2O2 in the mixtures was assessed at different temperatures 25°C to 60°C, with ferric ion contents from 0 to 40 g/l. According to the results obtained, were established the optimal condition pickling at 20 g/l of ferric ions, 25°C and p-toluensulphonic acid as stabilizer of H 2O2. The HF pickling mixture was the only capable to remove totally the oxide layer from the 316L stainless steel after 300 s. The fluoride salts pickling mixtures only remove partially the oxide layer (20 to 40 % aprox.) after 300 s. When the pickling time was increased until 1200 s, the removal percentages were around to 80 %.
Figueroa F.,Institute Metalurgia |
Aragon A.,Institute Metalurgia |
Garcia-Meza J.V.,Institute Metalurgia
Environmental Earth Sciences | Year: 2010
The 7-year-old mine tailings pile P2 from Concepción del Oro has been revegetated spontaneously by xerophyte grasses, covering about the 30% of its surface. To elucidate the effect of the grass cover in the geochemical behavior of the sulfide minerals (SM) and metals, the strata of four selected profiles (P2-I, P2-II, P2-III and P2-IV, with high, middle, low, and null grass cover, respectively) were analyzed mineralogically and chemically, using scanner electron microscopy, X-ray diffractometer and performing a six-step sequential extraction method. An older (50-year-old) and uncovered (without grass cover) profile of the tailings pile P3 was also analyzed. In all the profiles from P2, the SM oxidation is not yet an extended process; however, the samples from the uncovered profile P2-IV showed evidences of SM (pyrite and chalcocite) oxidation, as well as the presence of gypsum and Fe oxides, as the major secondary phases resulted from the SM oxidation. Additionally, the carbonate content and pH values in P2-IV were lower than in the covered profiles from P2. The oldest and uncovered P3-I profile showed an extensive oxidation of sulfurs which resulted in the depletion of carbonates and a pH 2. Another distinctive characteristics of the covered profiles was that Pb, Cu, and Zn were mainly associated with the reducible fractions (carbonates and/or amorphous oxides); meanwhile, in the uncovered (P2-IV and P3-I) such metals were mainly associated with the oxidizable fraction (crystalline oxides). The results suggest that the mineralogical transformations control metal stability in plant-covered impoundments (phytostabilization): the occurrence of a thick grass cover, with an efficient water usage and retention, seems to shun both the acidic dissolution of carbonates and the reductive dissociation of the formerly present oxyhydroxides, which is desired for remediation tasks. This is the first report about the effects of grass cover for a carbonaceous and unsaturated mine tailings from a semiarid region, that can help in a better understanding of the scope of phytoremediation in such conditions. © 2009 Springer-Verlag.
PubMed | Universidad Juárez del Estado de Durango, CNRS Laboratory of Physical Chemistry and Microbiology for the Environment, Metropolitan Autonomous University, Institute Metalurgia and Autonomous University of Ciudad Juárez
Type: Journal Article | Journal: Environmental science and pollution research international | Year: 2016
Mining activities release arsenopyrite into calcareous soils where it undergoes weathering generating toxic compounds. The research evaluates the environmental impacts of these processes under semi-alkaline carbonated conditions. Electrochemical (cyclic voltammetry, chronoamperometry, EIS), spectroscopic (Raman, XPS), and microscopic (SEM, AFM, TEM) techniques are combined along with chemical analyses of leachates collected from simulated arsenopyrite weathering to comprehensively examine the interfacial mechanisms. Early oxidation stages enhance mineral reactivity through the formation of surface sulfur phases (e.g., S n (2-)/S(0)) with semiconductor properties, leading to oscillatory mineral reactivity. Subsequent steps entail the generation of intermediate siderite (FeCO3)-like, followed by the formation of low-compact mass sub-micro ferric oxyhydroxides (, -FeOOH) with adsorbed arsenic (mainly As(III), and lower amounts of As(V)). In addition, weathering reactions can be influenced by accessible arsenic resulting in the formation of a symplesite (Fe3(AsO4)3)-like compound which is dependent on the amount of accessible arsenic in the system. It is proposed that arsenic release occurs via diffusion across secondary , -FeOOH structures during arsenopyrite weathering. We suggest weathering mechanisms of arsenopyrite in calcareous soil and environmental implications based on experimental data.
Casas-Flores S.,Autonomous University of San Luis Potosi |
Gomez-Rodriguez E.Y.,Autonomous University of San Luis Potosi |
Garcia-Meza J.V.,Institute Metalurgia
AMB Express | Year: 2015
Soluble arsenic (As) in acidic feed solution may inhibit the copper (Cu) bioleaching process within mine heaps. To clarify the effect of soluble arsenic on the live biomass and bioxidative activity in heaps, toxicological assays were performed using a synthetic feed solution given by a mine company. The microorganisms had previously been isolated from two heap samples at up to 66 m depth, and cultured using specific media for chemolithotrophic acidophiles (pH 1–2) and moderate thermophiles (48°C), for arsenic tolerance assay. The four media with the highest biomass were selected to assay As-resistance; one culture (Q63h) was chosen to assay biooxidative activity, using a heap sample that contained chalcopyrite and covellite. We found that 0.5 g/L of As does not affect living biomass or biooxidative activity on Cu sulfides, but it dissolves Cu, while As precipitates as arsenic acid (H3AsO4·½H2O). The arsenic tolerant community, as identified by 16S rDNA gene sequence analysis, was composed of three main metabolic groups: chemolithotrophs (Leptospirillum, Sulfobacillus); chemolithoheterotrophs and organoheterotrophs as Acidovorax temperans, Pseudomonas alcaligenes, P. mendocina and Sphingomonas spp. Leptospirillum spp. and S.thermosulfidooxidans were the dominant taxa in the Q63–66 cultures from the deepest sample of the oldest, highest-temperature heap. The results indicated arsenic resistance in the microbial community, therefore specific primers were used to amplify ars (arsenic resistance system), aio (arsenite oxidase), or arr (arsenate respiratory reduction) genes from total sample DNA. Presence of arsB genes in S. thermosulfidooxidans in the Q63–66 cultures permits H3AsO4-As(V) detoxification and strengthens the community’s response to As. © 2015, Casas-Flore et al.
PubMed | National Autonomous University of Mexico, Servicio Of Epidemiologia Del Hospital Central Dr Ignacio Morones Prieto, Autonomous University of San Luis Potosi and Institute Metalurgia
Type: | Journal: Micron (Oxford, England : 1993) | Year: 2015
To determinate the significance of risk factors with the presence of biofilm on catheters of patients attended at tertiary hospital cares.A total of 126 patients were included, data collection by observing the handling of the CVC, clinical history and microbiological isolation methods of CVCs tips (Roll-plate, sonication and scanning electron microscopy) were evaluated.Certain factors, such as the lack of proper hand washing, the use of primary barriers and preparing medications in the same hospital service, showed an important relationship between biofilm formation in CVCs. The sonication method presented that most of the samples had isolation of multispecies 29 samples (64%); in contrast with the roll-plate method, just one sample (3%) was isolated.The importance of the strict aseptic techniques of insertion and of the handlings of CVC was highlighted, the failure of both techniques was related to the biofilm formation and was evidenced using the scanning electron microscopy. Since this tool is not available in most hospitals, we present the correlation of those evidences with other standard microbiological methods and risk factors, which are necessary for the sensible detection of the different steps of the biofilm formation on CVC and their correct interpretation with clinical evidences.
Alvarado L.,Lakehead University |
Torres I.R.,Institute Metalurgia |
Chen A.,Lakehead University
Separation and Purification Technology | Year: 2013
Mining and electroplating wastewaters contain many harmful ions, which are discharged into waterways and water bodies and cause significant environmental damage. Hexavalent chromium (Cr(VI)) is an ion that is commonly present in these effluents, which has been proven as toxic to humans. In the present work, continuous ion exchange and electrodeionization are proposed as a new hybrid technology for the effective treatment of Cr(VI) wastewater as well as the recovery of chromium ions. We have systemically studied a strong basic macroreticular anion exchange resin (Amberlite® IRA900) for the removal of Cr(VI). The ion exchange isotherm and kinetics of the resin were determined, showing that the IRA900 anionic ion exchange resin has a high capacity for ion exchange with hexavalent chromium (116 mg Cr(VI) per gram of resin). When the anionic resin was combined with a strong acidic macroreticular cation exchange resin (Amberlite® 200C) and employed in continuous electrodeionization, over 98.5% of Cr(VI) was continuously removed from the dilute compartment with an energy consumption of less than 0.07 kW h/m3, while Cr(VI) was recovered in the concentrate compartment. © 2012 Elsevier B.V. All rights reserved.
Garcia-Meza J.V.,Institute Metalurgia |
Fernandez J.J.,Institute Metalurgia |
Lara R.H.,National Autonomous University of Mexico |
Gonzalez I.,Metropolitan Autonomous University
Applied Microbiology and Biotechnology | Year: 2013
Biofilms of Acidithiobacillus thiooxidans were grown on the surface of massive chalcopyrite electrodes (MCE) where different secondary sulfur phases were previously formed by potentiostatic oxidation of MCE at 0.780 ≤ E an ≤ 0.965 V (electrooxidized MCE, eMCE). The formation of mainly S0 and minor amounts of CuS and S n 2- were detected on eMCEs. The eMCEs were incubated with A. thiooxidans cells for 1, 12, 24, 48, and 120 h in order to temporally monitor changes in eMCE's secondary phases, biofilm structure, and extracellular polymeric substance (EPS) composition (lipids, proteins, and polysaccharides) using microscopic, spectroscopic, electrochemical, and biochemical techniques. The results show significant cell attachments with stratified biofilm structure since the first hour of incubation and EPS composition changes, the most important being production after 48-120 h when the highest amount of lipids and proteins were registered. During 120 h, periodic oxidation/formation of S0/S n 2- was recorded on biooxidized eMCEs, until a stable CuS composition was formed. In contrast, no evidence of CuS formation was observed on the eMCEs of the abiotic control, confirming that CuS formation results from microbial activity. The surface transformation of eMCE induces a structural transformation of the biofilm, evolving directly to a multilayered biofilm with more hydrophobic EPS and proteins after 120 h. Our results suggest that A. thiooxidans responded to the spatial and temporal distribution and chemical reactivity of the S n 2-/S0/CuS phases throughout 120 h. These results suggested a strong correlation between surface speciation, hydrophobic domains in EPS, and biofilm organization during chalcopyrite biooxidation by A. thiooxidans. © 2012 Springer-Verlag Berlin Heidelberg.
Villavelazquez-Mendoza C.I.,University of Colima |
Rodriguez-Mendoza J.L.,University of Colima |
Hodgkins R.P.,University of Colima |
Ibarra-Galvan V.,University of Colima |
And 3 more authors.
Materials Letters | Year: 2014
Sea-urchin-like rutile (su-TiO2) microstructures were successfully synthesized by thermal decomposition and oxidation of a solid precursor, K2TiF6. During the synthesis, precursor temperature (640 C), N2-flow (15 cm3/min) and inner pressure (90 mbar above the atmospheric pressure) remained constant. In order to evaluate the effect of time on the morphology of su-TiO2, five levels (0.5, 1, 1.5, 2, and 2.5 h) were considered. The thermal decomposition an oxidation of the K2TiF6 precursor was studied by thermal analyses. It was found that TiO2 was segregated from the matrix, leading to the formation of su-TiO2 during processing. At 640 C, the precursor underwent thermal decomposition and oxidation that produced three different products: K3TiOF5(s), TiO2(s), and F2(g). The su-TiO2 is synthesized only at t=2 h and t=2.5 h, presenting defined spikes at the former (100 μm×100 nm) and rougher structures at the latter (50 μm×10 μm). © 2014 Elsevier B.V.
PubMed | Institute Metalurgia
Type: Journal Article | Journal: Applied microbiology and biotechnology | Year: 2013
Biofilms of Acidithiobacillus thiooxidans were grown on the surface of massive chalcopyrite electrodes (MCE) where different secondary sulfur phases were previously formed by potentiostatic oxidation of MCE at 0.780Ean0.965 V (electrooxidized MCE, eMCE). The formation of mainly S and minor amounts of CuS and Sn were detected on eMCEs. The eMCEs were incubated with A. thiooxidans cells for 1, 12, 24, 48, and 120 h in order to temporally monitor changes in eMCEs secondary phases, biofilm structure, and extracellular polymeric substance (EPS) composition (lipids, proteins, and polysaccharides) using microscopic, spectroscopic, electrochemical, and biochemical techniques. The results show significant cell attachments with stratified biofilm structure since the first hour of incubation and EPS composition changes, the most important being production after 48-120 h when the highest amount of lipids and proteins were registered. During 120 h, periodic oxidation/formation of S/Sn was recorded on biooxidized eMCEs, until a stable CuS composition was formed. In contrast, no evidence of CuS formation was observed on the eMCEs of the abiotic control, confirming that CuS formation results from microbial activity. The surface transformation of eMCE induces a structural transformation of the biofilm, evolving directly to a multilayered biofilm with more hydrophobic EPS and proteins after 120 h. Our results suggest that A. thiooxidans responded to the spatial and temporal distribution and chemical reactivity of the Sn/S/CuS phases throughout 120 h. These results suggested a strong correlation between surface speciation, hydrophobic domains in EPS, and biofilm organization during chalcopyrite biooxidation by A. thiooxidans.