Juan M. Menéndez-Aguado

Analysis of soil washing effectiveness to remediate a brownfield polluted with pyrite ashes.

Soil in a brownfield contaminated by pyrite ashes showed remarkably high concentrations of several toxic elements (Hg, Pb, Zn, Cu, Cd, and As). Initially, we assessed various physical, chemical and mineralogical properties of this soil. The data obtained, and particularly multivariate statistics of geochemical results, were useful to establish the predominant role of the soil organic matter fraction (6%) and iron oxyhydroxides in the binding of heavy metals and arsenic. In addition, we studied the viability of soil washing techniques to reduce the volume of contaminated soil. Therefore, to concentrate most of the contaminants in a smaller volume of soil, the grain-size fraction below 125 microm was treated by hydrocycloning techniques. The operational parameters were optimized by means of a factorial design, and the results were evaluated by attributive analysis. This novel approach is practical for the global simultaneous evaluation of washing effectiveness for several contaminants. A concentration factor higher than 2.2 was achieved in a separated fraction that contained less than 20% of the initial weight. These good yields were obtained for all the contaminants and with only one cycle of hydrocycloning. Hence full-scale soil washing is a plausible remediation technique for the study site.

Comprehensive waste characterization and organic pollution co-occurrence in a Hg and As mining and metallurgy brownfield.

The abandonment of Hg-As mining and metallurgy sites, together with long-term weathering, can dramatically degrade the environment. In this work it is exemplified the complex legacy of contamination that afflicts Hg-As brownfields through the detailed study of a paradigmatic site. Firstly, an in-depth study of the former industrial process was performed to identify sources of different types of waste. Subsequently, the composition and reactivity of As- and Hg-rich wastes (calcines, As-rich soot, stupp, and flue dust) was analyzed by means of multielemental analysis, mineralogical characterization (X-ray diffraction, electronic, and optical microscopy, microbrobe), chemical speciation, and sequential extractions. As-rich soot in the form of arsenolite, a relatively mobile by-product of the pyrometallurgical process, and stupp, a residue originated in the former condensing system, were determined to be the main risk at the site. In addition, the screening of organic pollution was also aimed, as shown by the outcome of benzo(a) pyrene and other PAHs, and by the identification of unexpected Hg organo-compounds (phenylmercury propionate). The approach followed unravels evidence from waste from the mining and metallurgy industry that may be present in other similar sites, and identifies unexpected contaminants overlooked by conventional analyses.

Nanoscale zero-valent iron-assisted soil washing for the removal of potentially toxic elements

The present study focuses on soil washing enhancement via soil pretreatment with nanoscale zero-valent iron (nZVI) for the remediation of potentially toxic elements. To this end, soil polluted with As, Cu, Hg, Pb and Sb was partitioned into various grain sizes (500-2000, 125-500 and <125 μm). The fractions were pretreated with nZVI and subsequently subjected, according to grain size, to Wet-High Intensity Magnetic Separation (WHIMS) or hydrocycloning. The results were compared with those obtained in the absence of nanoparticles. An exhaustive characterization of the magnetic signal of the nanoparticles was done. This provided valuable information regarding potentially toxic elements (PTEs) fate, and allowed a metallurgical accounting correction considering the dilution effects caused by nanoparticle addition. As a result, remarkable recovery yields were obtained for Cu, Pb and Sb, which concentrated with the nZVI in the magnetically separated fraction (WHIMS tests) and underflow (hydrocyclone tests). In contrast, Hg, concentrated in the non-magnetic fraction and overflow respectively, while the behavior of As was unaltered by the nZVI pretreatment. All things considered, the addition of nZVI enhanced the efficiency of soil washing, particularly for larger fractions (125-2000 μm). The proposed methodology lays the foundations for nanoparticle utilization in soil washing operations.

Particle size distribution fitting of surface detrital sediment using the Swrebec function

PurposeThe development of mathematical models to accurately represent the particle size distribution (PSD) of sediment has been addressed by different authors. Here, we introduce the three-parameter Swrebec function as a tool to fit the PSD of sediments. Moreover, we also assess the physical meaning of the undulation parameter (b) in the function.Materials and methodsWe performed PSD by means of laser diffraction spectroscopy. Then, sediments were classified and the statistical parameters (mean, skewness, sorting and kurtosis) calculated using GRADISTAT software, according to the Folk and Ward’s method. Subsequently, the Swrebec function (programmed in Matlab) was applied to the data and its goodness-of-fit were evaluated by means of the adjusted coefficient of determination (R2-Adj) and the root mean squared error (RMSE). The results obtained by Swrebec were also compared with other functions using the Ezyfit toolbox.Results and discussionThe Swrebec model provided excellent correlations and low RMSE when fitting all grain size data. Furthermore, a correlation between b and both the skewness and RMSE was established. This indicates that the greater the asymmetry of the function, and therefore the larger the presence of coarse-grained particles, the lower the performance of the function. It was also observed that a change in the behaviour of all trends seems to occur at a b value of ~4.5.ConclusionsResults suggest that the studied function could be a simple approach for modelling PSD, with potential applications in soil and sediment science, geochemistry, sedimentology and coastal research modelling.

Environmental engineering in mining engineering education

In this paper, the current profile of the environmental engineer and the programming of the subject “Environmental Engineering and Technology” corresponding to the studies of Mining Engineering at the University of Oviedo in Spain, is discussed. Professional profile, student knowledge prior to and following instruction as well as available teaching time, are taken into account in order to define the subject objectives. These objectives were the starting point for the design of the program. Information regarding the student perspective is gathered by means of anonymous surveys at the beginning and end of the teaching period. Some of the results are collected in this paper.