Use of EDTA in modified kinetic testing for contaminated drainage prediction from waste rocks: case of the Lac Tio mine

The tools developed for acid mine drainage (AMD) prediction were proven unsuccessful to predict the geochemical behavior of mine waste rocks having a significant chemical sorption capacity, which delays the onset of contaminated neutral drainage (CND). The present work was performed in order to test a new approach of water quality prediction, by using a chelating agent solution (0.03 M EDTA) in kinetic testing used for the prediction of the geochemical behavior of geologic material. The hypothesis underlying the proposed approach is that the EDTA solution should chelate the metals as soon as they are released by sulfide oxidation, inhibiting their sorption or secondary precipitation, and therefore reproduce a worst-case scenario where very low metal attenuation mechanisms are present in the drainage waters. Fresh and weathered waste rocks from the Lac Tio mine were submitted to small-scale humidity cells in control tests and using an EDTA solution. Results show that EDTA effectively prevents the metals from being sorbed or precipitated as secondary minerals, enabling to bypass the delay associated with metal sorption in predicting water quality from these materials. This work demonstrates that the use of a chelating agent solution is a promising novel approach for water quality prediction and provides guidelines for future studies, assisting practitioners and regulators in planning more efficient management and disposal strategies for mine wastes.