Characterization of metal finishing sludges: influence of the pH

Metal finishing sludges are classified as metal hydroxide hazardous wastes due to the heavy metal release to the environment. This release, commonly d etermined by compliance lixiviadon tests based on the equilibrium condition s at the end of the leaching experiment, is mainly dependent on the pH of t he solution. In this work, the leaching behaviour of Cd, Cr, Cu, Fe, Ni, Pb and Zn, of the 32 metal finishing sludges coming from 16 European industri al facilities, and using the distilled water compliance test DIN 38414-S4, have been studied. The concentrations of chromium and copper in the leachat es do not follow the solubility evolution of their hydroxide with the pH. T he simple assumption of a heavy metal concentration in the leachate directl y related to the solubility of the hydroxide is not in good agreement with the experimental results of the distilled water leaching test, probably due to the presence of different species, which can contribute to the metal mo bility depending on the sludge composition. An experimental evaluation of t he easily available amount of metals in real wastes seems to be necessary f or disposal assessment. This paper contains valuable information, from orde rly handling metal finishing wastes to the statistical studies of productio n and management of wastes suggested recently by the Commission of the Euro pean Community. (C) 2000 Elsevier Science B.V. All rights reserved.