Browsing by Author "Alsina, Marco A."

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    Copper entrapment and immobilization during cement hydration in concrete mixtures containing copper tailings
    (2021) Vargas, Felipe; Alsina, Marco A.; Gaillard, Jean-François; Pasten Gonzalez, Pablo Arturo; López, Mauricio; CEDEUS (Chile)
    The use of copper tailings as supplementary cementitious material can reduce the environmental impacts ofconcrete production and the mining industry. A key concern limiting its application is the potential leaching oftoxic metals from the cementitious matrix, especially copper. To analyze and reduce the risk of leaching, themechanisms by which copper is entrapped in the cementitious matrix were investigated, by combining micro-scopic and spectroscopic approaches. Decreasing the water-to-binder ratio was statistically relevant to reducecopper leaching. Scanning Electron Microscope micrographs allowed to spatially localize enriched copperclusters within the cementitious hydration products. In the early stages of the cementitious hydration (i.e., 24 h),no spatial correlation between copper and hydration products was found; however, after seven days, copper wasspatially associated with calcium silicate hydrates. Cu K-edge X-ray absorption near edge structure spectroscopyprovided insights into the chemical speciation of copper in the cementitious matrix. It showed that copper sulfideand oxide phases persisted, whereas the copper sulfate phases were prone to dissolution and reprecipitation ascupric hydroxides induced by the relatively high pH from calcium hydroxides formed during hydration. Pro-moting the formation of hydration products can further reduce copper leaching from the alkaline cementitiousmatrix. A better understanding of metal entrapment mechanisms could lead to new strategies that reduce themobility of toxic elements when using copper tailings, increasing their use as a replacement of cement. With thisknowledge, it is expected to answer if it is possible to improve the copper entrapment into the cementitiousmatrix and if there is a risk of leaching once is entrapped.
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    Enhanced copper release from pipes by alternating stagnation and flow events
    (AMER CHEMICAL SOC, 2007) Calle, Gustavo R.; Vargas, Ignacio T.; Alsina, Marco A.; Pasten, Pablo A.; Pizarro, Gonzalo E.
    Traditional studies of copper release in plumbing systems assume that the water extracted from a pipefollows a plug-type flow and that the pipe surface does not interact with the bulk water under flow conditions. We characterized actual stagnation-flushing cycles in a household pipe undergoing Corrosion in the presence of a microbial biofilm. The mass of copper released in 10 experiments was on average 8 times the value estimated by using the plug-flow assumption. The experimental copper release pattern was explained by an advection-diffusion model only if a high copper concentration occurs near the pipe surface after stagnation. Microscopic examination of the pipe surface showed a complex assemblage of biotic and abiotic features. X-ray diffraction analyses identified only malachite, while X-ray absorption spectroscopy also revealed cupric hydroxide and cuprite. These results indicate that the surface serves as a storage compartment of labile copper that may be released under flow conditions. Thus, the diffusive transport from the pipe surface to the bulk during stagnation is not the only control of the flux of copper to the tap water when porous reactive microstructures cover the pipe. Our results highlight the need for models that consider the interaction between the hydrodynamics, chemistry, and structure at the solid-water interface to predict the release of corrosion byproducts into drinking water.
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    Influence of solid corrosion by-products on the consumption of dissolved oxygen in copper pipes
    (PERGAMON-ELSEVIER SCIENCE LTD, 2009) Vargas, Ignacio T.; Alsina, Marco A.; Pasten, Pablo A.; Pizarro, Gonzalo E.
    Research on corrosion of copper pipes has given little consideration to the influence of solid corrosion by products on the processes occurring at the metal-liquid interface. Consequently, the effect of such solid phases on the rate of dissolved oxygen (DO) consumption remains poorly understood. In-situ experiments were performed in copper pipes under different carbonate concentrations and ageing times. Our results show that the amount of solid corrosion by-products and concentration of hydrogen ions affect the rate of DO consumption during stagnation. Furthermore, our findings support the existing hypothesis that the available concentration of hydrogen ions, rather than DO, is the limiting factor for copper release into drinking water. (C) 2009 Elsevier Ltd. All rights reserved.