A Geomicrobiological Study of the Rabbit Lake In-Pit Tailings Management Facility

Abstract

Microorganisms can strongly influence geochemical conditions and element mobility, which is an important consideration in planning for long-term stability of mine waste. In this study, I have characterized microbial communities in a uranium mine waste facility, the Rabbit Lake In-Pit Tailings Management Facility (RLITMF) in Northern Saskatchewan, Canada. The tailings have an alkaline pH (median 8.8), high Eh (median 210 mV), and low temperatures (median 2 ºC). They also contain abundant Fe(III)-oxides which control the mobility of elements such as arsenic. I am particularly interested in the potential interactions between microorganisms and arsenic and iron, which may influence arsenic mobility. Microbial diversity was investigated by analyzing high-throughput amplicon sequencing (bacterial and archaeal 16S rRNA gene, V4 region, analyzed using mothur). Geochemical data (ICP-MS analyses) and core log data were provided by the tailings facility operator, Cameco Corporation. Our results show the presence of populations related to microorganisms typically involved in iron, sulfur, and arsenic cycling. We were able to culture sulfate-reducing bacteria (SRB) from tailings samples at neutral pH; this suggests the relatives of sulfate-reducing bacteria identified in sequencing are viable. The current pH, Eh, and temperature conditions in the RMITMF are not ideal for microbial growth but if the pH and Eh decreased or the temperature increased this could promote microbial growth. Thus, this study provides evidence to support tailings management decisions that prevent microbially-driven processes from occurring in the future i.e. maintaining high pH and Eh conditions in the tailings to maintain iron oxide stability through time.