Cement-waste and clay-waste derived products from metal hydroxides wastes - Environmental characterization

Metal hydroxide sludges from the wastewater treatment of metal finishing ef fluents are complex wastes, mainly inorganic, with a high content of heavy metals and anions. This makes it necessary to employ careful environmental management. In this work, two selected metal hydroxide cakes from the 'on s ite' wastewater treatment of nickel and chromium electroplating activities and the anodizing of aluminium materials were treated with Portland cement and mixed with clay, offering two possibilities of solidification/stabiliza tion prior to landfilling, and reutilization in ceramic products, respectiv ely. The obtained products were characterized by the determination of ecoto xicity values, EC50. Of the TCLP leachates and the chemical characterizatio n of DIN-38414-S4 leachates. The unconfined compressive strength (UCS) was determined in all derived products. Cement formulations show values of EC50 higher than 3000 mg l(-1) and high concentrations of chromium in the DIN 38414-S4 leachates, due to the alkali ne medium resulting from the cement addition. The clay/waste products are n on-hazardous based on the EC50 and the low concentrations of heavy metals i n the leachates. The paper establishes environmental characterization of bo th kind of products, showing that there are environmental benefits of waste dosification in ceramic materials.