Chromium stabilization of tannery sludge by co-treatment with ladle furnace slag

Hazardous solid wastes may pose a serious risk to human health and to the environment, if not managed appropriately and disposed of safely. In this study, the effective stabilization of tannery sludge, a toxic industrial solid waste produced from the physico-chemical treatment of tannery wastewaters, was examined by the addition of ladle furnace slag (LFS), another industrial solid waste. Moreover, the simultaneous addition of organoclay (a commercially available chemical additive) and LFS for the stabilization of tannery sludge was also examined. The tannery sludge was mixed with LFS and water, as well as with LFS, organoclay and water at different ratios. The mixtures were left for one week ageing and then subjected to the standard leaching test EN 12457-2. Chromium and dissolved organic carbon (DOC) in tannery sludge (the major control parameters of this waste) were found to exceed the respective non-hazardous and hazardous waste limit concentration values respectively, according to the EU Directive 2003/33/EC. The leachates from the tannery waste stabilized with LFS, presented chromium concentrations below the regulation limit for disposal, even in landfills for non-hazardous wastes; however, DOC cannot meet the respective limit value. On the other hand, the leachates of this waste stabilized with LFS and organoclay, presented both chromium and DOC concentrations below the regulation limits for disposal in landfills for non-hazardous wastes. The ecotoxicity of original, as well as of stabilized waste was also evaluated by applying the standard Microtox procedure.