Chemical and mineralogical characterization of blast-furnace sludge from an abandoned landfill.

Blast-furnace sludge is generated during the production of pig iron and is disposed of in the environment in large surface landfills. We investigated blast-furnace sludge samples of an abandoned landfill in order to determine its chemical and mineralogical nature and to evaluate some environmental hazards that may arise from this industrial waste. The mineralogical inventory, which was quantified by Rietveld refinement of XRD analyses using the fundamental-parameter approach, revealed that blast-furnace sludge is dominated by X-ray amorphous substances (with a mean of 590 g kg(-1)) including coke and (hydr)oxides of Fe, Si, Al, Zn, and Pb. Calcite (CaCO3) (136 g kg(-1)), dolomite (Ca,Mg[CO3]2) (14 g kg(-1)), quartz (SiO2) (55 g kg(-1)), kaolinite (Al2[OH]4Si2O5) (40 g kg(-1)), graphite (C) (27 g kg(-1)), and chemically not specified layered double hydroxides (28 g kg(-1)) were identified in almost all samples. Iron is present as magnetite (Fe3O4) (34 g kg(-1)), hematite (Fe2O3) (38 g kg(-1)), wuestite (FeO) (20 g kg(-1)) and alpha-iron (Fe0) (6 g kg(-1)). Chemically, blast-furnace sludge is dominated by C (190 g kg(-1)) and Fe (158 g kg(-1)) reflecting the process of pig-iron production. On the basis of total contents, environmentally problematic metals (including As) are Zn (32.6 g kg(-1)), Pb (10.3 g kg(-1)), Cd (81 mg kg(-1)), and As (129 mg kg(-1)). As the forested landfill is used by residents for leisure activities, the exposure assessment by pathway oral uptake of blast-furnace sludge particles by humans has to be critically evaluated, particularly as significant proportions of metals are acid-soluble. However, under the prevailing slightly alkaline pH values of the sludge (pH 7.6-9.2), the solubility of the metals is very low as indicated by low pore water concentrations. Currently, groundwater monitoring should be focused mainly on F- since the F- concentrations in the pore water of blast-furnace sludge are at high level (2.65-24.1 mg of F- L(-1)).