Evaluation of dispersed alkaline substrate and diffusive exchange system technologies for the passive treatment of copper mining acid drainage

The study evaluates the performance of the novel ADES (alkaline diffusive exchange System), SDES (sulfidogenic diffusive exchange system) and DAS (Dispersed Alkaline Substrate) technologies for the passive treatment of high-strength acid mine drainage (AMD) from copper mining (pH~3, 633 mg Cu L^-1). The chemical DAS and ADES prototypes showed the best performance in the removal of Cu, Al, and Zn (98-100%), while the biochemical SDES reactors achieved a high sulfate removal rate (average of 0.28 mol m^-3 day^-1). Notably, the DES technology was effective in protecting the sulfate-reducing communities from the high toxicity of the AMD, and also in maintaining bed permeability, an aspect that was key in the ADES reactor. The DAS reactor showed the highest reactivity, accumulating the metallic precipitates in a lower reactor volume, allowing to conclude that it requires the lowest hydraulic residence time among all the reactors. However, the concentration of precipitates resulted in the formation of a hardpan, which may trigger the need of removing it to avoid compromising the continuity of the treatment process. This study suggests the development of new treatment alternatives by combining the strengths of each technology in combined or serial treatments.