Zinc and nickel removal in simulated limestone treatment of mining influenced water

Mining influenced water (MIW) is often characterized by low pH (acid mine drainage) and high dissolved metal concentrations. Treatment of MIW is often required to mitigate these two characteristics. One option, which has traditionally been used only for pH neutralization, is limestone based treatment systems. However, there is field evidence that limestone systems are also effective at removing metals such as Zn and Ni. These field systems are often too complex to examine specific removal hypotheses, while certain modes of laboratory examination are too simplistic to be applied to field settings. Instead, the batch reactors used here were intentionally more complex to allow for the examination of how certain variables (pH, alkalinity, and primary metal concentrations) interact to affect Zn and Ni removal. The data herein suggest that one possible removal process for Zn and Ni is through surface interactions on the precipitated primary metals Fe and Al. The specific processes are complex and conditional, and were found to depend on pH, alkalinity, and total amount of primary metal present. Indeed the complex interplay between these variables led to an observed local maximum in Zn removal that would not be predicted from traditional surface complexation theory or observed from simpler experimental systems.