Potential environmental impact of technosols composed of gossan and sulfide-rich wastes from S?o Domingos mine: assay of simulated leaching

摘要

Abstract Purpose The aim of this study was to evaluate (i) the ability of two Technosols, prepared with gossan or sulfide-rich wastes plus mixtures of organic/inorganic amendments, to improve the characteristics of the wastes by the analysis of the variation of elemental concentrations in their simulated leachates, and (ii) the potential environmental risk of these Technosols evaluated through the concentrations of the elements leached from the tailings containing the two wastes, considering their mass in the S?o Domingos mine. Materials and methods Composite samples of two S?o Domingos mining wastes (gossan wastes—GW; sulfide-rich wastes—SW) were collected. Amendment mixtures, containing different organic/inorganic wastes (from green agriculture, distillation of Ceratonia siliqua and Arbutus unedo fruits, and limestone quarry), were applied at 12, 30, and 60?g/kg. Two sets of microcosm assays were performed under controlled conditions in greenhouse and monitored during 7 and 13?months for GW and SW, respectively. Materials from each pot/treatment (5?cm of depth) were collected after 1, 4, 7, and 13?months of incubation and used to obtain simulated leachates (DIN extraction). The analytical parameters evaluated in the leachates were pH, electrical conductivity, and element concentrations using flame atomic absorption spectrometry for cations and graphite furnace atomic absorption spectrometry, ionic chromatography, and UV-VIS for elements that normally occur as anions in aqueous solution. Results and discussion Simulated leachates from SW had lower pH and higher concentrations of potentially hazardous elements than leachates from GW. The concentrations of As in leachates from GW-Technosols were higher than those in leachates from GW-control but 0.6?mg/kg. In GW-Technosols leachates, the pH and the concentrations of some nutrients (e.g., Ca and phosphates) also increased when compared to the control. In the SW-Technosols, the pH of the leachates increased only in the first month as long as limestone was present. In these leachates, a general decrease of the concentrations of some elements was observed (e.g., As, sulfate, Fe, Pb), especially in the first month. A clear influence of the dose and type of amendments was not observed during the experimental time span for both wastes. Conclusions The concentrations of elements like Al, Ca, Fe, and Pb in the leachates are controlled by both the pH of the solutions and the concentrations of phosphates and sulfates. The extensive mass of the studied mine wastes contribute to the release to the neighboring environment of considerable amounts of potentially hazardous elements. The rehabilitation of the mine wastes by the conception of Technosols, especially with sulfide-rich wastes, can reduce significantly their environmental impact. ]]>