Arsenic in iron cements developed within tailings of a former metalliferous mine—Enguialès, Aveyron, France

Arsenopyrite-rich waste from a former metalliferous mine were spread out over the sloping side of a deep valley after processing. Over the past 30 a, they have been subjected to rainfall and acid water originating from the abandoned mine galleries. This intensive leaching has led to the formation of thin layers of As–Fe crusts on the tailings surface acting as a cement. X-ray diffraction and SEM coupled with EDS determined that jarosite was present in all mineral samples and could contain a small amount of As (not, vert, similar5.7 wt.%). In addition EMPA and Raman microspectroscopy characterised the presence of amorphous As(V) Fe hydrates as well as rare arsenate minerals (e.g. scorodite). Raman microspectroscopy in particular identified a preponderance of goethite or hematite within the mineral framework of the tailings materials that is likely to sorb recalcitrant As species. The characterisation of the components of the tailings enable the identification of their evolution, shows the progressive decrease of their As-content and emphasises the consequences of the temporary trapping of As in the very acidic and oxidising conditions prevailing in such environments. Resinous amorphous material was identified as the richest in As with As not, vert, similar17.1 wt.%. This material evolved toward more crystallised phases (e.g. goethite, jarosite) which contained less As (3.2 wt.%