The preparation of geopolymer for solidification/stabilization of heavy metal contaminated soils using industrial solid waste was a sustainable method. In this study, a binary geopolymer curing agent was synthesized from red mud and fly ash for the treatment of copper- and cadmium- contaminated soils. The changes in the properties of the cured soil were investigated by analyzing compressive strength, permeability coefficient, pH value, toxicity leaching, and the chemical forms of heavy metals. These parameters were examined under varying amounts of curing agent and curing time. The solidification mechanism of contaminated soil was revealed by microscopic experiments such as X-ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDS). The results showed that geopolymer could significantly improved the mechanical properties and environmental safety of contaminated soil. Compressive strengths of Cu and Cd contaminated soils after 28d of curing with 30 % geopolymer were 1.27 and 1.44 MPa, the permeability coefficients were 4.2 and 3.8-6cm/s, and toxic leaching amounts of Cu2+ and Cd2+ were 4.8 and 0.21 mg/L, and pH values were 10.9 and 10.6, respectively. Geopolymer gel structures not only filled the voids between soil particles but also physically encapsulated, chemically bonded, precipitated and ion-exchanged to achieve solidification/stabilization of contaminated soils. This research provided a new technology for the management of heavy metal contaminated soil and promoted the sustainable use of industrial solid waste.

In this study, wild barley (Hordeum brevisubulatum) infected (E+) and uninfected (E-) by Epichlo & euml; bromicola were used for hydroponic experiments during the seedling stage. Various attributes, such as the effect of fungal endophyte on the growth and development of wild barley, the absorption of cadmium (Cd) and mineral elements (Ca, Mg, Fe, Mn, Cu, Zn), subcellular distribution, and chemical forms were investigated under CdCl2 stress. The results showed that the fungal endophy significantly reduced the Ca content and percentage of plant roots under Cd stress. The Fe and Mn content of roots, the mineral element content of soluble fractions, and the stems in the pectin acid or protein-chelated state increased significantly in response to fungal endophy. Epichlo & euml; endophyte helped Cd2+ to enter into plants; and reduced the positive correlation of Ca-Fe and Ca-Mn in roots. In addition, it also decreased the correlation of soluble components Cd-Cu, Cd-Ca, Cd-Mg in roots, and the negative correlation between pectin acid or protein-chelated Cd in stems and mineral elements, to increase the absorbance of host for mineral elements. In conclusion, fungal endophy regulated the concentration and distribution of mineral elements, while storing more Cd2+ to resist the damage caused by Cd stress. The study could provide a ground for revealing the Cd tolerance mechanism of endophytic fungal symbionts. NOVELTY STATEMENT The present study is the first to study the effect of fungal endophy on essential mineral elements of plants under heavy metal stress, filling a gap in the existing research. The study could be helpful to reveal the mechanism of endophytic fungi to improve the host's tolerance to heavy metals and provide a foundation for the grass-endophyte symbionts to improve heavy metal-contaminated soils as ecological grasses.