A greenhouse study on phytostabilization of sulfidic mine tailings

The reclamation of sulfidic mine tailings with the potential to release toxic metals into the surrounding environment, has been an urgent, yet difficult, task for a long period. Direct revegetation is a more cost-effective reclamation method than a multilayer covering system on tailings. Phytostabilization can stabilize toxic metals in the rhizosphere, which is an emerging revegetation method in mine reclamation. Since previous research has not looked into the inorganic geochemical processes in the rhizosphere, a greenhouse study was conducted to explore the geochemical processes affecting the mobility of As, Cu, Pb, and Zn through the establishment of phytostabilization on sulfidic mine tailings. The three-month greenhouse experiment selected candidates for phytostabilization from four grass species in North America: wheat, ryegrass, tall fescue, and sheep fescue. The effectiveness of amendments (bauxite residue, lime, and compost), on enhancing plant growth and metal stabilization were analyzed. Total metals in plants, tailings, and substrates after pot experiments were analyzed, the mineralogy of materials before and after experiments were quantified, and drainage from each pot was collected weekly for metal analysis. The results show wheat and ryegrass can stabilize more metals in roots than in aboveground tissues, so they are good candidates for phytostabilization. Three amendments can improve the tailing pH, grass survival, and plant growth, but compost should be carefully considered for the phytostabilization of Zn. During experiments, pH decreased and metal concentrations in the drainage from amended tailings started to increase from the 6th or 7th week, suggesting that sulfide oxidation, organic matter decomposition, and root exudates are three processes of soil acidification. The other geochemical processes affecting metal mobility include neutralization processes at such sequences: (1) dissolution of carbonates, (2) dissolution of Al- and Fe- (oxy)hydroxide, and (3) silicate weathering. The long-term reliability of phytostabilization is likely to be achieved by re-application of amendment to initiate neutralization in the rhizosphere. This research fills a gap of study on the geochemical processes controlling metal mobility during phytostabilization, and provides a reference for land reclamation and remediation practitioners considering the application of phytostabilization of sulfidic mine tailings.Applied Science, Faculty ofMining Engineering, Keevil Institute ofGraduat