Stability prediction of the xanthate-stabilized Zn(OH)₂ and Cu(OH)₂ sludge in simulated landfill environment

In this work, the long-term stability of the xanthate-stabilized Zn(OH)₂ sludge (ZnBX matrices) and Cu(OH)₂ sludge (CuBX matrices) under simulated acidic landfill environment was studied. The semi-dynamic leaching test (SDLT) using 1N acetic acid solution as leachant was performed to simulate the landfill age as one SDLT leaching cycle provided the equivalent acidity of a 5-yr landfill period. The SDLT had been performed 10 weeks totally (i.e., 10 leaching cycles), which gives the simulation of the time period for 50 years of landfill age. The leaching and stabilizing characteristics of the ZnBX and CuBX matrices through the SDLT were characterized using pH meter, ORP meter, A.A., UV-vis, XRD and EA techniques. The result of SDLT after 10 weeks of extractions showed that the leached species were reducing and alkaline materials, and both the metal released rate in ZnBX and CuBX matrices gradually decreased with the increase of extraction time. The cumulative fraction of zinc released was 71.9 %, whereas the copper was 2.6 %. The xanthate treatment was suitable for copper-bearing sludges than zinc-bearing sludges when choosing landfill as final disposal. The rate of containment leaching was controlled by dissolution (diffusion) and surface wash-off. The UV-vis spectra of leaching solutions indicated that the xanthate species were decomposed in the acidic solution. The XRD patterns showed the Cu(BX)₂ and ZnS to be the residual phase of the ZnBX and CuBX matrices after SDLT. The long-term stability of the CuBX matrices might be attributed to the formation of Cu(BX)₂ complexes.