Toxicity leaching of brick making from sludge containing heavy metals

The problems of heavy metal in sludge from sewage treatment plants has attracted much attentions. One proposal to reduce the harm of heavy metals was to make brick which can solidify them during the sintering process. The sewage sludge was mixed with shale according to a certain proportion to prepare brick, then the solidified effect of heavy metals as well as the toxicity extraction were studied to examine the safety of sintered brick. The results showed that the leaching concentrations of Cr, Cu, As, Pb hardly changed with time under neutral and acidic conditions, while that of Zn was relatively high firstly then reduced. Moreover, under alkaline conditions, the leaching concentrations of Cr, Cu, Pb stayed stable, whereas that of Zn, As changed irregularly. Overall, the performance of stabilization/solidification for Cr, Cu, Zn, As, Pb is well-behaved, and the leachate toxicity of sludge bricks is lower than that of the national standard.