Abstract
Phytostabilization has been advocated as a promising approach to reduce mine tailings' adverse effects to surrounding environment. With many years of efforts in both laboratory and field trials, organic amendments are found to be essential in tailing revegetation. Yet, the associate geochemical dynamics caused by different amendments has rarely been examined. As reactive minerals are usually rich in tailings, geochemical changes induced by amendments would influence seepage management and revegetation strategies. The present study aimed to investigate geochemical dynamics in Cu-Au tailing leachate, in response to amendments with biochar produced from hardwood timber at high charring temperature or woodchips of mixed native tree species in a column leaching experiment under laboratory conditions. Results showed that the Cu-Au tailings tested in this study were relatively stable after natural weathering, with little resilience of peak salinity, stable pH and low levels of metals in leachate against the six cycles of leaching over 20 weeks. In comparison with the control without any amendments, biochar treatment did not cause any substantial changes in most examined properties of leachate, except for the reduction in dissolved organic C and NO2-. In contrast, woodchip treatment had a reduced leachate pH and a strong resilience in leachate salinity (and thus major saline ions). The geochemical changes in the woodchip treatment may be related to the active decomposition of woodchips, as indicated by the sharp increases in microbial biomass and activity as well as labile organic C at the end of leaching. The present results suggest that dynamic hydrogeochemical changes may be induced by amendment of fresh biomass like woodchips, which can increase the load of salts and metals in tailing pore water. This may affect seepage water quality at least in the short-term and thus plant survival if tailings are immediately revegetated after amendment. In contrast, biochar with highly stable carbon may help alleviate geochemical environment in the tailings.
Highlights
Phytostabilization has been advocated as a promising approach to reduce mine tailings' adverse effects to surrounding environment
Woodchip treatment had a substantial recovery of Electrical conductivity (EC) after each cycle and a lower median pH maintained over the six cycles
The results showed that SOC, microbial biomass C (MBC) and soil basal respiration (SBR) were comparable in the pure tailings and the biochar treatment, while they were relatively high in the woodchip treatment
Summary
Phytostabilization has been advocated as a promising approach to reduce mine tailings' adverse effects to surrounding environment. As reactive minerals are usually rich in tailings, geochemical changes induced by amendments would influence seepage management and revegetation strategies. As tailings are usually rich in reactive minerals, pyrites and carbonates, the lifecycle of organic amendment in tailings will have to be associated with the hydrogeochemical processes driven by active mineral weathering and possibly impact seepage quality [5]. Hydrogeochemical stability is a critical factor affecting the fitness of plants established in tailings for phytostabilization [6]. It is useful to understand what geochemical changes can be induced by different organic matters in mine tailings in the short/medium term. For base metal mines (Pb/Zn/Cu/Ni), tailings are mainly composed of gangue and residue ore minerals normally rich in pyrites. There has been an increasing awareness that such hydrogeochemical instability can be the primary constrain for plants' initial establishment in tailings and merits a systematic assessment for tailing rehabilitation [6], especially when various amendments are used
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
