Kinetic approach for the appropriate selection of indigenous limestones for acid mine drainage treatment with passive systems.

Acid mine drainage treatments using limestones have been widely reported in the literature; however, additional studies are needed to select the most effective limestone type based on an adequate characterization and in consideration of the kinetics of the rock's reaction upon exposure to high iron concentrations. In this study, with the aim to select the most appropriate limestone to use in a passive treatment system, the regular characterization (calcium carbonate analysis, determination of specific superficial area, and porosity) was complemented with a heterogeneous kinetic analysis of limestone dissolution. The physico-chemical conditions of high acidity and a high Fe concentration were similar to those measured in leachates from the "Compañía Minera Zimapán" (CMZ) tailings impoundment located in a historical Mexican mining zone. Column experiments were carried out with the selected limestone to treat leachates from two tailing deposits; one highly weathered and un-active (CMZ) and the other still active (San Miguel Nuevo). Removal efficiencies close to 100% were reached for arsenic, iron, cadmium, and aluminum. There was also a partial removal of zinc and silica, and the pH increased close to neutrality. Electrical conductivity, sulfate levels, and oxidation reduction potential were also measured during the experiments. Concentration profiles for some elements were established. Chemical results, stoichiometric relationships between elements obtained by scanning electron microscopy-energy dispersive spectroscopy, and scanning electron microscopy-wavelength dispersive spectroscopy allowed for determining the chemical associations of the elements at the surface. The results indicated that the methodology for limestone selection to treat AMD from San Miguel Nuevo tailings was adequate; however, additional studies are required to improve the permeability and the lifetime of the system used to treat CMZ leachates.

Galena weathering under simulated calcareous soil conditions.

Exploitation of polymetallic deposits from calcareous mining sites exposes galena and others sulfides to weathering factors. Galena weathering leads to the formation of lead phases (e.g., PbSO(4), PbCO(3)) with a higher bioaccessibility than galena, thus increasing the mobility and toxicity of lead. Despite the environmental impacts of these lead phases, the mechanisms of galena oxidation and the transformation of lead secondary phases, under neutral-alkaline carbonated conditions, have rarely been studied. In this work, an experimental approach, combining electrochemical and spectroscopic techniques, was developed to examine the interfacial processes involved in the galena weathering under simulated calcareous conditions. The results showed an initial oxidation stage with the formation of an anglesite-like phase leading to the partial mineral passivation. Under neutral-alkaline carbonated conditions, the stability of this phase was limited as it transformed into a cerussite-like one. Based on the surface characterization and the formation of secondary species, the weathering mechanisms of galena in calcareous soil and its environmental implications were suggested.

EC treatment for reuse of tissue paper wastewater: aspects that affect energy consumption.

The need for more rational use of water also calls for more efficient usage. An example is the production of tissue paper, where large amounts of water are discharged into the drain because its turbidity does not allow for recirculation. While this is a serious problem, even worse is the fact that the quality of such wastewater makes it difficult not only to recirculate but also to discharge due to environmental law restrictions. In this paper, electrocoagulation is proposed as a suitable technology to meet standards of water discharge, and even better, as a treatment option for removal of turbidity. Since energy consumption has been a drawback for EC applications, relevant aspects that contribute to increase it such as cell voltage and current density have been reviewed. For this purpose a systematic micro-electrolysis study combined with macro-electrolysis experiments have provided evidence that shows it is possible to achieve a turbidity removal of 92% with an energy consumption of 0.68 kWh/m(3). Thus, the results presented in this paper support the use of EC to obtain water of acceptable quality for reuse in the tissue paper industry.