Natural weathering of slags from primary Pb–Zn smelting as evidenced by Raman microspectroscopy

Lead (Pb) and zinc (Zn) smelters produce high amount of granulated slags which are currently stored on unconfined slag heaps and exposed to weathering. The environmental risk related to slags disposals can be estimated through the results of a variety of characterization methods coupled with laboratory leaching experiments and in situ monitoring. The present study is focused on the Raman characterization and distribution at a microscopic scale of secondary products resulting to the alteration of glassy slags exposed to natural weathering for at least ten years. The slag alteration is characterized by the formation of a crack network around iron sulfide inclusions and Pb droplets embedded in the glassy matrix. The Raman images clearly point out the gradually weathering processes. The dissolution of the FeS species lead to the formation of Fe (oxy-hydr)oxide phases. The successive layer formation highlights a probable local pH/Eh changes. The fluids-containing sulfates issued from the alteration of sulfide species are conveyed in the crack network inducing a local alteration of the crack edges together with the formation of (Al,Fe)-hydroxide phases. The fluids-containing sulfates when in contact with Pb droplets induce a progressive dissolution of the droplets from the edge to the core to form Pb sulfate species (mainly basic lead sulfates) and Pb oxides in complex mixture. In a last step, carbonation occurs with local increasing pH due to the presence of CO2 from air or HCO3-/CO32− in fluids originating from glassy matrix alteration

Three-dimensional characterization of a fractured granite and transport properties

International audienceA three-dimensional fracture network in a granite block is reconstructed from a series of experimental serial sections. It is visualized and its most important geometrical characteristics are studied, namely the orientation of the fractures, the connectivity of the fractures, the number of cycles, per unit volume, the distributions of surface areas and of the intersection lengths, and the number of finite solid blocks isolated in the solid matrix by the network. Though the network mostly consists of two families of fractures, it is interesting to note that a simple model of randomly oriented, monodisperse hexagons often yields a good order of magnitude for the various geometrical properties, which have been measured on the real block. The flow properties are then studied; examples of velocity field are provided as well as histograms of velocities; the permeability tensor is determined and is found to be in good agreement with Snow's formula. Finally, dispersion is analyzed by means of a random walk method; histograms of arrival times are provided and interpreted in terms of dispersion tensor