Development of a modified kinetic test using EDTA and citric acid for the prediction of contaminated neutral drainage

Predicting the quality of mine drainage is a very important step in the management of mine wastes. A variety of useful tools are available for acid mine drainage (AMD), but new tests must be developed to improve the accuracy of predictions for contaminated neutral drainage (CND), or metal leaching. This study was performed using 0.01 M EDTA and citric acid in the leaching solutions of kinetic tests on waste rocks and low-grade ore from the BlackRock project. Results showed an increase in metal (Co, Cu, Mn, Ni, and Zn) concentrations in the leachates, except for Zn with citric acid. Several major cations (Al, Ca and Mg) were also chelated by EDTA, but did not appear to be in competition with metal chelation because the chelating agent was present in excess in the kinetic test leachates. Ca and Mg were also chelated by citric acid, but Al was not. The release rate of iron was compared to the release rate of total sulphur in the leachates. For the waste rock samples, these release rates corresponded to the dissolution of sulphides. For the low-grade ore sample, the release rate of iron was higher and likely associated with the dissolution of iron oxides. Further studies will be needed to explore how the selection and concentration of specific chelating agents for use in modified kinetic tests must be adjusted depending on the mineralogy of the samples.