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 determined by compliance lixiviadon tests based on the equilibrium conditions at the end of the leaching experiment, is mainly dependent on the pH of the 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 industrial facilities, and using the distilled water compliance test DIN 38414-S4, have been studied. The concentrations of chromium and copper in the leachates do not follow the solubility evolution of their hydroxide with the pH. The simple assumption of a heavy metal concentration in the leachate directly 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 mobility depending on the sludge composition. An experimental evaluation of the easily available amount of metals in real wastes seems to be necessary for disposal assessment. This paper contains valuable information, from orderly handling metal finishing wastes to the statistical studies of production and management of wastes suggested recently by the Commission of the European Community. (C) 2000 Elsevier Science B.V. All rights reserved.