Abstract
Contaminated neutral drainage (CND) is challenging to predict using methods designed to predict acid rock drainage (ARD). Efforts have been made to adapt tools used to predict ARD but a systematic approach needs to be defined to assess the risk of CND generation that would apply to all materials, similarly to what is available for ARD. An approach was suggested earlier using chelating agents in modified kinetic experiments to prevent immobilization mechanisms that hinder the release of contaminants, such as sorption and secondary precipitation, that often control the water quality during a limited time in CND-generating materials. In this study, sorption experiments were used to estimate the extent at which the materials can retain the potential contaminants identified through geochemical characterizations and modified kinetic testing. An approach was developed to combine the results of kinetic tests with those of sorption experiments and geochemical characterizations to assess the risk of CND generation. Mine waste samples from different mines were used to develop and validate the method. One of the samples is known to generate Ni-CND and was used to benchmark the method. Since the development of this novel approach mainly focused on the potential release of metal cations thus far, a known As-CND generating sample was used to assess whether the method is also relevant for dissolved oxyanions like arsenate. Submitting these different materials to the novel approach developed helped to refine its methodology and appreciate its limits, as well as to identify potential improvements to address in the future.