Abstract
The reclamation of tailings, especially sulfidic mine tailings with the potential to release toxic metal(loid)s to the environment, has been an urgent but difficult task for a long period. Phytoremediation has been received great concerns in the area of metal (loid)s removal in recent two decades. For now most successful cases of revegetation are applying several covers on the tailings, including the physical coarse rock cover, chemical amendment cover, the topsoil and the final plants cap. However, these are quite expensive by applying such large volume of materials. The technique of direct revegetation on tailings is cost-effective, which has drawn increasingly concerns by academia andindustry, and the technique of phytostabilization can stabilize the toxic metals in the rhizosphere by special plants species. The plant species need to be not only toxic-tolerate but also can absorb and store the metals in the rhizosphere with zero or small storage in the aboveground tissues.
This research has explored cost-effective amendments for direct revegetation to improve the reclamation results, and also found out two native grass species for phytostabilization. Greenhouse experiments were conducted in UBC Horticulture greenhouse from February 2020 to June 2020. Six substitutes: T(tailings), T+BR(tailings and bauxite residue), T+L(tailings and lime), T+C(tailings and compost), T+BR+C(tailings, bauxite residue and compost), T+L+C(tailings, lime and compost), were set as the pot materials for plant growth. Four grass candidates: wheatgrass, ryegrass, tall fescue and sheep fescue, were selected to be sowed first and then grow in these pots. Plant growth (germination rates and heights) was recorded, and samples of shoots and roots, and pot soils were collected and then analysed for metal(loid)s (As, Cu, Pb, Zn) in the lab.
Results showed that amendments could obviously improve the germination rates and survival rates of all grasses on acid-generating tailings. Specially, tailings amended with pH adjustment and organic matter provider, such as T+BR+C and T+L+C, can more enhance the growth. Sheep fescue and tall fescue are not ideal species for direct revegetation on acid-generating tailings because of their poor growth on all substrates. Wheatgrass and ryegrass can be phytostabilization candidates for stabilizing As, Cu and Pb, and only ryegrass can be able to stabilize Zn for phytostabilization purpose.
This research concluded the strategy of adding pH adjustment (e.g. lime or bauxite residue) and organic matter provider (e.g. compost) into the acid-generating tailings is reliable for direct revegetation on sulfidic mine tailings. Wheatgrass and ryegrass are Canadian native species that can be used in phytostabilization. In the future, geochemical mechanics of stabilization process in the rhizosphere needs to be further researched on to explore better strategies of phytostabilization on sulfidic mine tailings.