Applicability of solidified/stabilized dye sludge char as a landfill cover material

The applicability of solidification/stabilization (S/S) to reduce leaching potential of metal(loid)s from dye sludge char (DSC) and the suitability of the treated DSC as a landfill cover material was investigated. The dye sludge charred at 350oC (DSC350) and 550oC (DSC550) was solidified and stabilized by the amendment of cement, lime, ladle slag or hydroxyapatite (HAP). Leaching potential of metal(loid)s from the binder-amended DSC550 was below the Korean Standard Leaching Test (KSLT) and US EPA Toxicity Characterization Leaching Procedure (TCLP) criteria. DSC550 had higher Unconfined Compressive Strength (UCS) than DSC350 due to higher ash content and less volatile matter content. Calcium oxide and silica present in cement, lime or ladle slag enhanced the UCS of DSCs. The dose of 0.05 g cement, 0.075 g lime or 0.075 g ladle slag per g of dry DSC550, respectively was optimum to meet the UCS criteria (350 kPa), but not HAP. After blending with a natural soil, the hydraulic conductivity of the binder-amended DSC550 was higher than that of clayey soil (1 × 10−5 cm/s to 1 × 10−6 cm/s). Further study such as blending with clayey soil is needed to decrease hydraulic conductivity to 10−5 to 10−6 cm/s.