Limestone systems are generally used for acid neutralization of mining impacted waters. However they can also be designed to remove heavy metal constituents. The issues surrounding the design of a limestone system for metal removal are different from the issues involved in acid neutralization. Experiments were carried out to explore these issues by evaluating the interaction of CaCO 3 with solutions containing a primary metal (Fe, Al), and a secondary metal (Zn, Ni). The fate of the secondary metals and their removal as a function of pH, alkalinity, and primary metal concentration are reported. Although these parameters by themselves are not necessarily good indicators of secondary metal removal, when coupled with the influent primary:secondary metal ratio, trends become apparent that can be used as design parameters. Zinc and Ni removals appear to be a function of Fe +3 concentrations and removals are shown to be as high as 97% and 87%, respectively, at near neutral pH values. The removal reaches a saturation point at an Fe:Zn ratio of 50:1, and for Ni the saturation ratio is 45:1 Zinc and Ni removals with Al gave ambiguous results.