Résumé - Abstract
Permeable reactive barriers (PRB) are a passive remediation technique that have been installed at mine sites in Canada and around the world. The purpose of this study is to gain an improved understanding of these passive remediation techniques for applications in neutral mine drainage containing nickel and cobalt. Columns were prepared containing mixtures of zero valent iron (ZVI), peat, leaves, and sand. Each of the four columns was filled with a different ratio of organic reactive materials, ZVI, and an inoculum of enrichment culture prepared from mine waste rock. The columns will be pumped continuously for a period of six to eight months with a synthetic medium containing nickel and cobalt. Water sampling will be conducted every second week, from sample ports in the columns. This will allow us to track reactive fronts and concentration gradients of the metals within the materials. At the end of the experiment, we will perform solids analyses on the column solids (e.g., powder X-ray Diffraction (pXRD), X-ray Absorption Near-Edge Spectroscopy (XANES), and X-ray Fluorescence (XRF) mapping) as well as microbiological analyses and sequential extractions to examine nickel and cobalt solid speciation and concentration totals. Our preliminary batch experiments demonstrated that peat and leaves outperform other organic materials for nickel and cobalt sorption, and peat also demonstrated a capacity for buffering increases in pH, which is an important consideration to this project because it may mitigate pH increases in the systems due to ZVI corrosion, and limit carbonate precipitation that may negatively impact the hydrologic properties of the columns. In another batch trial, experiments containing similar volume ratios of peat and ZVI led to a consistently neutral pH over time; in contrast samples containing higher volume proportions of either peat or ZVI developed more acidic and alkaline pH over time, respectively. Our column experiments will test if the use of similar volume ratios of peat and ZVI will also prevent a rise in pH in the system. This research will hopefully give some insight into approaches to extend the longevity of a modular PRB system and its potential efficacy for sequestration of metals from neutral mine drainage.