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Water balance was measured for five field experimental cells with an oxygen-barrier type of reclamation cover combined with elevated water table including a control cell with functional layer of desulfurized tailings over a reactive tailings layer, and 4 other cells with additional layers and different vegetation. Hydrogeological (moisture content and suction in layers, water table positions in cells), and precipitation data collected throughout three successive growing seasons after revegetation were compared to investigate the effects of different material layering and vegetation scenarios on the water balance. Above- and below-ground vegetation developments were also monitored. Results showed that for all tested scenarios the main water balance component remained the evapotranspiration (79-98% of the total precipitated water). Herbaceous vegetation was found to provide much safer support for the cover performance than woody vegetation, keeping the reactive tailings more saturated during the whole study period (mean Sr>90.77%). In presence of woody plants, however, the Sr in the reactive tailings could reach a value as low as ~32%. Increasing the thickness of the additional layer over 30 cm above the functional layer with fine-grained HDS sludge could also pose a threat against its functionality by stimulating willow growth, lowering the water table position as well as the Sr in the reactive tailings. Finally, adding a coarse-grained capillary break layer impeded the willow root colonization of the functional layer in the short term but increased percolation and should be coupled to water conservation strategies in the overall system to maintain the elevated water table.

An organic–inorganic composite of chitosan, nanoclay, and biochar (named as MTCB) was chosen to develop a bionanocomposite to simultaneously immobilize Cu, Pb, and Zn metal ions within the contaminated soil and water environments. The composite material was structurally and chemically characterized with the XRD, TEM, SEM, BET, and FT-IR techniques. XRD and TEM results revealed that a mixed exfoliated/intercalated morphology was formed upon addition of small amounts of nanoclay (5% by weight). Batch adsorption experiments showed that the adsorption capacity of MTCB for Cu2+, Pb2+, and Zn2+ were much higher than that of the pristine biochar sample (121.5, 336, and 134.6 mg g−1 for Cu2+, Pb2+, and Zn2+, respectively). The adsorption isotherm for Cu2+ and Zn2+ fitted satisfactorily to a Freundlich model while the isotherm of Pb2+ was best represented by a Temkin model. That the adsorption capacity increased with increasing temperature is indicative of the endothermic nature of the adsorption process. According to the FTIR analysis, the main mechanism involved in immobilization of metals is binding with –NH2 groups. Results from this study indicated that modification of biochar by chitosan/clay nanocomposite enhances its potential capacity for immobilization of heavy metals, rendering the bionanocomposite into an efficient heavy metal sorbent in mine-impacted acidic waters and soils.