Desarrollo y estudio comparativo de nuevos métodos automáticos de extracción dinámica para la determinación de elementos traza en muestras sólidas medioambientales

Abstract

The limitations of batchwise extraction and fractionation methods based on extraction equilibrium between the target solid and chemical extractant for the analyte have been widely recognized and discussed in the literature, as is the potential bias of the analytical results. To this end, novel automatic flow-through dynamic extraction systems have been developed and critically compared for the evaluation of mobility and thus bioaccessibility of trace elements (TE) in environmental solid samples. The present PhD thesis is divided into five chapters. The first three chapters are focused on the development of new analytical methodologies to solve current environmental demands, while the two remaining chapters have addressed the potential harmonization and set quality control tools for flow-through dynamic extraction methods. Firstly, a novel automated flow-through microcolumn extraction system was devised as screening tool to evaluate the influence of weathering of bottom ash from incineration of solid wastes on the immobilization of potentially hazardous TE (Pb, Zn, Cd, Cu and Cr), so as to discern and recommend the best timing for bottom ash reuse. Further, the proposed system facilitated the investigation of the kinetics of the leaching processes, the association of TE within the solid matrix and the effect of the dissolved organic carbon on the adsorption of TE. Secondly, a flow-through extraction method incorporating a dedicated column of large volume capacity was developed for highly heterogeneous municipal solid waste incinerator bottom ash fractionation. The effects of fluidization, solid to extractant volume ratio and extraction flow rate onto TE (Cd, Cr, Cu, Pb and Zn) leachability were assessed via a full factorial design. The novel flow based method capitalized on fluidized bed extraction was compared with batchwise extraction and earlier dynamic fractionation microcolumn based tests in terms of trueness, reproducibility and operational time. Thirdly, a highly integrated and portable flow assembly, based on automated dynamic microcolumn extraction and exploiting carbon nanoparticle-based solid-phase extraction was developed for automated leaching, preconcentration, speciation and quantification of readily bioaccessible chromium (VI) in soils, without interconversion of Cr(VI) to Cr(III) as described in conventional extraction protocols in soils and sediments. In this work, the trueness of the analytical results was evaluated via analysis of a standard reference soil material contaminated with hexavalent chromium (SRM 2701), as well as by resorting to doped environmental soils. . Fourthly, two novel dynamic fractionation methodologies for TE: the so-called rotating coiled column extraction and sequential injection microcolumn extraction, were critically compared for bioaccessibility tests. The pros and cons of each individual approach were comprehensively pinpointed in terms of TE extractabilities (Zn, Cu and Pb). Experimental results demonstrated that both techniques are strongly dependent on the physicochemical properties of targeted solid substrates. Finally, the sequential injection microcolumn extraction and sequential injection stirred flow-chamber extraction techniques were critically appraised for fly ash fractionation of TE by resorting to the European BCR fractionation test (now termed SM&T). The extractability of a suite of TE (Cr, Cu, Ni, Pb and Zn) in both approaches was investigated in detail by means of a full factorial design to ascertain the effect of the extractant flow-rate and the solid to extractant volume ratio on TE leachability. The last two works were aimed at setting the basis for harmonization of dynamic bioaccessibility tests of TE.