Novel metal-binding hydrogel particles alleviate soil toxicity and facilitate healthy plant establishment of the native metallophyte grass Astrebla lappacea in mine waste rock and tailings

摘要

Soil contaminants are potentially a major threat to human and ecosystem health and sustainable production of food and energy where mineral processing wastes are discharged into the environment. It is rarely possible to totally stabilise, render harmless or remove toxic metals from these wastes. Metallophytes (metal-tolerant plants) have evolved mechanisms to survive on many natural metal-rich soils and mining wastes. However, in extreme conditions, metal concentrations in soils/wastes often exceed even the metal-tolerance thresholds of metallophytes and the sites remain barren with high risks of contaminant leaching and dispersion into the environment via erosion. A novel soil amendment based on micron-size thiol functional cross-linked acrylamide polymer hydrogel particles (X3) binds toxic soluble metals irreversibly and significantly reduces their concentrations in the soil solution to below the phytotoxicity thresholds. X3 thoroughly mixed with the surface soil layer (top 50 mm) of toxic mine waste materials in pots in glasshouse conditions successfully reduced total soluble concentrations of major contaminants in waste rock (aluminium (Al), copper (Cu), zinc (Zn), cobalt (Co) and manganese (Mn)) and tailings (sodium (Na), sulphur (S), Zn, Mn, Co and cadmium (Cd)) by 90.3 to 98.7% in waste rock, and 88.6 to 96.4% in tailings immediately after application. Soil solution pH was significantly increased from 2.5-3.8 and from 7.1-7.7 in X3-amended waste rock and tailings, respectively.