Co-stabilization of Pb/Cu/Zn by beneficial utilization of sewage sludge incineration ash: Effects of heavy metal type and content

The release and migration of heavy metals from the industrial sludge has become one of the most serious environmental threats, which is urgently required to be relieved. Heavy metals can be stabilized by using ceramic precursors, via interactions with aluminum (Al), silicon (Si) and iron (Fe) as the major components. The sewage sludge incineration ash (SSA) can be recognized as a type of ceramic raw materials due to the abundant content of Al, Si and Fe, which make it possible to be beneficially used for heavy metal stabilization. This study investigated the stabilization of lead (Pb), zinc (Zn), and copper (Cu) after ceramic sintering with the SSA as ceramic precursors, and further explored the influences of heavy metal types and contents on phase transformation and immobilization effect. Results show that the heavy metals could achieve co-stabilization by the SSA in reaction series with different metal types and contents (Pb-Zn and Pb-Cu). Pb tends to combine with Al, Si and P to form PbAl2Si2O8 and Pb3(PO4)3, while Zn was finally incorporated into a spinel solid solution (ZnFexAl2-xO4). Meanwhile, Cu is more likely to combine with Fe with the generation of CuFe2O4 which will be transformed to CuFeO2 with elevated temperatures. In both Pb-Zn and Pb-Cu series, the Zn and Cu were distributed in crystal grains while Pb was in regions around the grains. Moreover, the leachability of Pb, Zn and Cu can be substantially decreased with the eventual incorporation of the heavy metals into different product phases by the SSA. Therefore, through this study the coimmobilization of heavy metals in the simulated industrial waste can be realized by the utilization of sewage sludge incineration ash as ceramic precursors.
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