Tinto and Odiel basin rivers are strongly affected by acid mine drainage (AMD) showing low pH values and high concentrations of sulfate, iron, aluminum and other metal(loid)s [1].Both schwertmannite and basaluminite are, respectively, Fe and Al poorly-crystalline oxyhydroxysulfates that form precipitates after colloidal aggregation in AMD-affected systems. While much has been reported on the important role of Fe-bearing phases as scavengers of contaminants such as As or Cr [2], less is known about the role of Al-SO4-phases [3]. In the current study, lab-experiments have been performed to determine Al and Fe nanoparticle growth process by dynamic light scattering (DLS) during spontaneous Fe oxidation and alkaline titration, as well as removal capacity of As by sorption-isotherm and structural information by differential pair distribution function (dPDF). Results from the DLS experiment in AMD solutions where all Fe is initially Fe(II) show a continuous growth of iron particlesat a short time whenFe(II) is spontaneously oxidizing to Fe(III) and schwertmannite starts to precipitate at pH around 3. Once the colloid size is bigger than 0.8 µm, schwertmannite decants due to the aggregation process. On the other hand, basaluminite precipitation is induced by alkaline addition of the solution at pH 4.5; therefore, the particle growth is very quick leading to the saturation of the instrumental signal. Ion exchange processes between AsO43- and SO42-were observed during the sorption experiments, where the 50% and 35% of SO4were exchanged by As with aAs/S ratio of 2 and 2.3 in basaluminite and schwertmannite, respectively. Finally, basaluminite showed higher adsorption capacity than schwertmannite, where the bonding mechanics of As in basaluminite were characterized as bidentateinner-sphere complex. In this study the adsorption capacity of As by basaluminite has been quantified. This role has been hitherto masked by previous precipitation of ferric phases in natural conditions; providing a new view in the mobility of toxic elements. [1] Sarmiento et al. (2009) App. Geoch. 24, 697–714. [2] Burton et al. (2009) Env. Sci.Tech. 43, 9202–9207. [3] Carrero et al. (2015) Chem. Geo. DOI: 10.1016/j.chemgeo.2015.10.020.

Role of Fe and Al-nanominerals on the contaminant mobility in Tinto and Odiel rivers

251st National Meeting (2016)

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