Influence of steel slag content on the mechanical and hydraulic properties of compacted silt-bentonite mixtures.

The reuse of by-products has become increasingly important as a means of minimising the consumption of natural resources and reducing waste disposal. This study examines the potential reuse of steel slag for soil stabilisation, with benefits such as conserving natural resources and mitigating the greenhouse gas emissions associated with the production of conventional stabilising agents. It focuses on evaluating the effect of pozzolanic reactions on the strength and stiffness of both loess silt and silt-bentonite mixtures. The experimental tests included the physical characterisation of granular materials, reactivity tests of the pozzolanicity of soil mixtures, compaction tests, unconfined compression tests, and hydraulic conductivity tests. The impact of the curing period was also analysed to quantify the effects of natural cementation and the development of hydrogels within soil pores on the compacted soil properties. The findings suggest that adding steel slag can significantly increase the strength and the stiffness of compacted loess silts by over 300% and 500%, respectively, after 56 days of curing, substantially reducing the hydraulic conductivity of granular materials, such as the tested silt, as hydrogels partially occupy the pores available for liquid flow. It should be noted that the chemical reactions during hydrogel formation may hinder the free expansion of clay mixtures and release Ca2+ ions, thereby counteracting the expected reduction in hydraulic conductivity when bentonite is added to compacted earthen barriers.

Environmental application of basic oxygen furnace slag for the removal of heavy metals from leachates.

Industrial waste is a major environmental concern nowadays, stimulating the thorough study of the minimization and recycling of solid wastes and of the containment and treatment of liquid contaminants. Basic oxygen furnace (BOF) slag, a solid waste from the steel industry, has been found to be effective in the removal of heavy metals. However, this has not been applied so far in low permeability barriers, such as those used as bottom liners in landfills. This work studies the performance of BOF slag in both containment and treatment technologies for toxic leachates. Flow models are developed to assess the transport of metal ions through a permeable reactive barrier and a composite clay barrier. Reactive transport through the slag barrier and adsorption in the clay barrier are coupled for different conditions to find the residence time, the barrier life span and the optimum operative conditions. The results show that the use of BOF slag increases the breakthrough time of the contaminants, enabling improve design of low and high conductivity reactive barriers, and expands the life cycle of the material.

Digital analysis technique for uncertainty reduction in colorimetric arsenic detection method.

This article proposes an alternative to increase the reliability and reproducibility of a colorimetric method to measure arsenic (As) concentrations. The method of analysis developed incorporates a digital analysis technique to eliminate the operator dependence of results, and As concentrations are quantitatively determined from digital levels computed from photographs of the colorimetric reaction that emerges during the test. This technique allows the sensitivity of the detection to be increased at low concentration ranges, which is of fundamental importance for the detection of As given the current acceptable limit for drinking water. The results obtained show a very good correlation between As concentrations determined by means of analytical laboratory techniques and the method proposed in this research.

Assessment of natural arsenic in groundwater in Cordoba Province, Argentina.

Groundwater in the central part of Argentina contains arsenic concentrations that, in most cases, exceed the value suggested by international regulations. In this region, Quaternary loessical sediments with a very high volcanic glass fraction lixiviate arsenic and fluoride after weathering. The objectives of this study are to analyze the spatial distribution of arsenic in different hydrogeological regions, to define the naturally expected concentration in an aquifer by means of hydrogeochemistry studies, and to identify emergent health evidences related to cancer mortality in the study area. The correlation between arsenic and fluoride concentrations in groundwater is analyzed at each county in the Cordoba Province. Two dimensionless geoindicators are proposed to identify risk zones and to rapidly visualize the groundwater quality related to the presence of arsenic and fluoride. A surface-mapping system is used to identify the spatial variability of concentrations and for suggesting geoindicators. The results show that the Chaco-Pampean plain hydrogeologic region is the most affected area, with arsenic and fluoride concentrations in groundwater being generally higher than the values suggested by the World Health Organization (WHO) for drinking water. Mortality related to kidney, lung, liver, and skin cancer in this area could be associated to the ingestion of arsenic-contaminated water. Generated maps provide a base for the assessment of the risk associated to the natural occurrence of arsenic and fluoride in the region.

Análisis de tuberías enterradas en suelos loéssicos : Efecto de la saturación del suelo

El cálculo y diseño de tuberías enterradas se realiza normalmente mediante fórmulas aproximadas o métodos semiempíricos. A pesar de su amplia difusión, estas teorías no permiten explicar las fallas observadas en numerosas tuberías. Tampoco es posible tener en cuenta el efecto de la pérdida de confinamiento lateral que ocurre cuando se satura o inunda el terreno natural. Este problema es de fundamental importancia en los limos loéssicos del centro de Argentina, y se ha convertido en una de las principales causas de rotura de tuberías. En este trabajo se desarrolló un modelo bidimensional en elementos finitos para analizar el comportamiento de tuberías enterradas en suelos loéssicos. Los resultados obtenidos permitieron determinar la influencia de la rigidez de la tubería y de la saturación del suelo en las deflexiones de la misma. Se analizó el efecto de las interfases suelo-caño, la influencia del comportamiento no-elástico del suelo, la necesidad de considerar pequeñas y grandes deformaciones en el cálculo, y la contribución del ancho de la trinchera y del módulo de deformación del relleno en las deflexiones de las tuberías. Se concluye en este trabajo, que el método de elementos finitos permite modelar en forma efectiva el comportamiento de las tuberías enterradas en suelos loéssicos. Se demostró que los métodos tradicionales de cálculo tienden a predecir deflexiones y esfuerzos no conservadores, lo cual permite apreciar la importancia de utilizar métodos numéricos en el análisis de tuberías enterradas.(AU)