The application of fluidized fly ash in underground mining excavations is limited due to its significant content of free calcium and calcium sulfate. In order to increase the amount of utilized fly ash from fluidized beds, it should be converted to a product with properties that meet the requirements for mining applications. This research presents the results of an attempt to adapt fluidized fly ashes for use in underground mining techniques, by means of carbonation and granulation. Carbonation was performed with the use of technical carbon dioxide and resulted in the reduction of free calcium content to a value below 1%. Granulation on the other hand, resulted in obtaining a product with good physical and mechanical parameters. The performed mineralogical and chemical studies indicate that trace amounts of “binding” phases, such as basanite and/or gypsum are present in the carbonized ash. The addition of water, during the granulation of carbonized fluidized fly ash, resulted in changes in the mineral phases leading to the formation of ettringite and gypsum as well as the recrystallization of the amorphous substance. It was confirmed that the carbonization and granulation of flying fluidized ashes positively affects the possibility of using these ashes in underground mining excavations.

Nine phyto-ashes from the biomass combustion of birch (Betula), oak (Quercus), red oak (Quercus rubra), horbeam (Carpinus), pine (Pinus sylvestris), poplar (Populus), maple (Acer), oilseed rape straw (Brassica napus) and wheat straw (Triticum aestivum) were blended with a biogas digestate at 1:1 mass ratio to give nine organic-mineral soil improvers. The concept of the research was to outline an eco-friendly and low cost soil improver for remediating degraded lands. These (i.e. phyto-ashes, improvers and the biogas digestate) were applied (0, 5, 10, 20, 40 t·ha^-1) to a soil metallurgically contaminated with Cu, Zn, Pb and Cd. Of several tested parameters, pH changes revealed that organic-mineral soil improvers may efficiently replace (linear R²>0.90****, P<0.001) phyto-ashes in soil remedial goals. Buffering properties expressed by the cation exchange capacity (CEC) improved progressively: 29, 52, 71, 100% (phyto-ash treatments) and: 18, 37, 44, 73% (improvers treatments) for the rates 5, 10, 20, 40 t·ha^-1, respectively as referred to the control CEC. The Dynamic Remediation Efficiency (DRE) indices for Cu, Zn, Pb, Cd revealed metal-specific geochemical reactions initiated by phyto-ashes, improvers and biogas digestate. The rates 5.0–10.0 t·ha^-1 for phyto-ashes and about 20 t·ha^-1 for improvers [1:1, i.e. Phyto-ash:Biogas digestate] are recommended. For biogas digestate, the rates 10–20 t·ha^-1 were found more efficient.