Effect of acid buffering capacity on the long-term mobility of heavy metals in clay liner

The pH and Eh effects on the mobility of zinc within landfill clay liner are investigated by modified batch tests on Osaka marine clay with cultivation of native microorganisms in the soil. The long-term mobility of zinc in landfill clay liner is discussed based on the pH buffering capacity of liner soil-leachate system. Tests results show that both pH and Eh conditions control the mobility of zinc in Osaka marine clay. Low redox potentials and neutral to basic pH conditions in landfill sites tend to prompt the insolubilization of zinc in landfill liner, in particular in the case where marine clay is used to serve as a natural liner material at offshore landfill sites. In the long-term perspective, oxygen will intrude finally into the landfill, which switches the anaerobic decomposition into an aerobic one and results a decrease in pH. Titration test results indicate that the newly generated leachate has a higher acid buffering capacity than the aged leachate, while leachates from MSW incineration ash have high hydroxides alkalinity at pH > 8. Test results reveal that both of the wastes and clay liner possess enough acid buffering capacity to consume the protons produced in organic oxidation reactions. Therefore, high levels of remobilization of heavy metals are not expected in the long-term perspective.