The addition of marble-cutting sludge to soils and sediments was assessed as a possible way of remediating heavy metal contamination. Two sediments from a site affected by historic mining activities and two sediment samples obtained from a highly industrialized area were used for the study. The samples were mixed with marble-cutting sludge providing four stabilized samples from which forty leachates were studied. The results suggest that the addition of this sludge, consisting mainly of carbonates, to heavy metal polluted sediments, decreases available metal forms. The leached solutions showed a nontoxic effect when they were submitted to the Microtox® bioassay. The carbonate content plays a role in the chemical stabilization of metals and in lowering the toxicity of these types of samples. © 2010 American Institute of Chemical Engineers Environ Prog, 2010.