Browsing by Author "Castillo, Daniela"

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    A simple low-cost approach for transport parameter determination in mountain rivers
    (2021) Castillo, Daniela; Runkel, Robert L.; Duhalde, Denisse; Pasten Gonzalez, Pablo Arturo; Arumí, José L.; Oyarzún, Jorge; Núñez, Jorge; Maturana, Hugo; Oyarzún, Ricardo; CEDEUS (Chile)
    A simplified low-cost approach to experimentally determine transport parameters inmountain rivers is described,with an emphasis on the longitudinal dispersion coefficient(DL). The approach is based on a slug injectionof table salt (NaCl) as a tracer and specificconductance readings at different locations downstream of the injection spot. Observedspecific conductance readings are fit using the advection-dispersion equation withOTIS-P, yielding estimates of cross-sectional area and longitudinal dispersion coefficientfor various stream reaches. Estimates of theDLare used to assess the accuracy of sev-eral empirical equations reported in the literature. This allowed the determination ofcomplementary transport parameters related to transient storage zones. The empiricalequations yielded rather highDLvalues, with some reaching up an order of magnitudehigher to those obtained from tracer additions and OTIS-P. Overall, the proposedapproach seems reliable and pertinent for river reaches of ca. 150 m in length.
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    Assessment of a conservative mixing model for the evaluation of constituent behavior below river confluences, Elqui River Basin, Chile
    (2021) Rossi, Catalina; Oyarzún, Jorge; Pasten Gonzalez, Pablo Arturo; Runkel, Robert L.; Núñez, Jorge; Duhalde, Denisse; Maturana, Hugo; Rojas, Eduardo; Arumí, José L.; Castillo, Daniela; Oyarzún, Ricardo
    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.